Module 4 Limbs and Back

Question 1

Describe the generic structure of a synovial joint and the function of each of its features​

Answer 1

Articular Cartilage (hyaline) on bone surfaces

Articular Capsule
Inner synovial membrane
Outer fibrous membrane

Synovial fluid-filled Joint Cavity

Question 2

What are Bursae?

Answer 2

Bursae - Synovial membrane-lined ‘sacs’ or ‘cushions’ which are normally ‘collapsed’

Vary in size depending on the individual and the location in the body, usually really thin

Located at points of friction between bone and surrounding soft tissue, such as skin, muscles, ligaments and tendons

Some bursae are just beneath the skin’s surface while others are deep below muscles and other soft tissue

adventitious bursae may develop as a result of repeated stress

Question 3

tendon sheath

Answer 3

This is a delicate synovial structure (like the finest ‘silk’) called tenosynovium (also known as a tendon sheath), which can be found lining some tendons in specific parts of the body.

Question 4

Tenosynovitis

Answer 4

Inflammation of the tendon sheath

Question 5

Articular discs & menisci

Answer 5

Fibrocartilage (type I collagen fibres)
Between poorly congruent articular surfaces
If crescent shaped: ‘menisci’ (sing. meniscus)
If complete: ‘articular discs’

Improvement of fit between articulating surfaces
Deployment of weight over larger surface areas
Shock absorption
Limitation and facilitation of automatic movements
Protection of articular margins

Question 6

Structural Classification of Joints

Answer 6

SOLID JOINTS
(Joints without a joint cavity)

Fibrous (synarthrotic) joints: bones held together by dense fibrous connective tissue. Very little or no movement.

Cartilaginous (amphiarthrotic) joints: bones are held together by either fibrocartilage (symphysis joints) or hyaline cartilage (synchondrosis joints). Moderate but limited movement.

SYNOVIAL (DIARTHROTIC) JOINTS

Bones are connected by a joint capsule composed of two layers (fibrous+synovial) enclosing a joint cavity. Freely moveable.

Question 7

Examples of fibrous joints

Answer 7

Sutures between flat bones e.g. skull
Gomphosis - peridontal ligament e.g. teeth
Syndesmosis - interosseous membrane

Question 8

Examples of cartilaginous joints

Answer 8

Synchrondrosis - cartialge betwwen head and shaft of long bone
Symphysis - intervertebral discs and pubic symphysis

Question 9

Hinge joint

Answer 9

Uniaxial
Flexion/extension
Elbow Joint

Question 10

Pivot joint

Answer 10

Uniaxial
Rotation
Atlantoaxial joint - first and second cervical vertebrae

Question 11

Plane/gliding joint

Answer 11

Gliding in multiple directions
Slide/glide
Intertarsal; intercarpal joints

Question 12

Condyloid (ellipsoid)

Answer 12

Biaxial
Flexion/extension, adduction/abduction
The atlantooccipital joint - synovial articulation between the occipital bone and the first cervical vertebra (atlas).

Question 13

Ball and socket

Answer 13

tri-axial
Flexion/extension, adduction/abduction, rotation/ circumduction
Pelvic and Pectoral girdle

Question 14

Saddle

Answer 14

Biaxial
Flexion/extension, adduction/abduction
Carpometacarpal of the thumb

Question 15

Three major factors that determine the balance of mobility and stability of a joint:

Answer 15

The shape of the bones of the joint

The musculature of the joint

The ligament/joint capsule complex of the joint

Question 16

Ligaments (in the MSK system):

Answer 16

Bone to bone

Dense fibrous connective tissue

Different proportion of collagen/elastin fibres

contain great amount of collagen fibres -> strength to withstand pulling forces

poorly vascularised -> do not heal quickly after injury

Question 17

Tendons:

Answer 17

Muscle to bone

Dense fibrous connective tissue

Few elastin fibres

contain great amount of collagen fibres -> strength to withstand pulling forces

poorly vascularised -> do not heal quickly after injury

Question 18

Arthritides symptoms

Answer 18

Joint pain, tenderness and stiffness

Joint Inflammation

Warm, red skin over affected joint(s)

Question 19

Osteoarthritis

Answer 19

Disease involving inflammation of the bone and joint cartilage

Not life threatening, but it can cause severe pain and loss of mobility and independence.

Question 20

Typical radiographic changes in osteoarthiritis: LOSS

Answer 20

Loss of cartilage
Osteophytes
Sclerosis and eburnation of the subchondral bone
Subchondral cysts (geodes)

Question 21

osteoarthritic joint changes

Answer 21

Inflammation of the joint cartilage and bone
loss of articular cartilage - usually maintained by chondrocytes
Bone hypertrophy - Subchondral sclerosis and osteophyte formation
Narrowing of the joint space
Synovial membrane hyperplasia

Question 22

Two types of cell within the synovium

Answer 22

Type A synovocytes - macrophages
Type B synovocytes - Fibroblasts; produce fluid

Question 23

Gout characteristics

Answer 23

Hyperuricaemia (abnormally high level of uric acid in the blood)

Deposition of urate crystals within synovial joints causing attacks of acute inflammatory arthritis

Tophi (deposits of uric acid crystals) in soft tissues after 10+ years

Possible joint destruction

Renal disease and uric acid urolithiasis

Question 24

Gout: Pathophysiology

Answer 24

Humans unable to degrade uric acid to a more soluble compound due to lack of the enzyme uricase

Within the joint, urate crystals interact with undifferentiated phagocytes which results in the release of TNF-alpha and interleukin (IL)-8, and other chemokines
An acute inflammatory responseis triggered

Cardinal signs of inflammation
(Usually) spontaneous resolution of an acute gout attack as urate crystals are gradually cleared

Question 25

Gout: Signs and symptoms

Answer 25

A painful, red, hot, swollen joint, usually at the big toe metatarsophalangeal joint (MTPJ) in the first attack (‘Podagra’) is the typical presentation - but it can affect any joint. Additional signs and symptoms: Tophi Firm, white, translucent nodules NB: it usually takes at least 10 years after the first attack of acute gout for tophi to develop

Question 26

Most common cause of acute monoarthritis in the elderly

Answer 26

Pseudogout

Question 27

Pseudogout

Answer 27

Most common cause of acute monoarthritis in the elderly Most cases idiopathic Caused by deposition of calcium pyrophosphate crystals Also known as Calcium pyrophosphate dihydrate deposition (CPPD) disease Most commonly involves the knee and the upper limb. Knee most affected joint but shoulders, wrists and metacarpophalangeal joints can be too

Question 28

Pseudogout S + S

Answer 28

Severe pain, stiffness, swelling, overlying erythema. Tenderness over the joint Fever

Question 29

Psuedogout vs gout differentiation

Answer 29

Pseudogout: Calcium pyrophosphate dihydrate crystals extracted from the synovial fluid of a patient with pseudogout viewed under polarised light – crystals are rhomboid-shaped Gout: Monosodium urate monohydrate crystals from a gouty tophus viewed under polarised light – crystals are needle-shaped

Question 30

Septic Arthritis

Answer 30

Destructive arthropathy caused by an intra-articular infection. Infection caused by micro-organisms via either direct inoculation or haematogenous spread Large joints with abundant blood supply (i.e. shoulder, hip, knee). Can lead to permanent joint damage and even death. Requires prompt treatment. Fever Purulent synovial fluid Hot, swollen, acutely painful joint with restriction of movement

Question 31

How should this presentation be treated until proven otherwise? Fever Purulent synovial fluid Hot, swollen, acutely painful joint with restriction of movement

Answer 31

Septic Arthritis

Question 32

A hot, swollen, acutely painful, stiff joint is a .... until proven otherwise!

Answer 32

Septic arthiritis

Question 33

Diagnosing septic arthritis

Answer 33

Arthrocentesis of affected joint for white blood cell (WBC) count, Gram stain and culture. Cloudy, yellowish appearance of synovial fluid Raised WBC count, but not 100% sensitive or specific and can be raised in other arthropathies Identification of causative bacterium via culture (but negative culture does not exclude diagnosis) Blood samples for cultures: Full blood count: WBC count raised in 50% of cases (not 100% sensitive or specific) Blood culture: should always be taken (but negative result does not exclude diagnosis) Arthrocentesis and blood samples before starting antibiotic therapy unless more urgent treatment is indicated. Imaging: Usually adjunct to arthrocentesis

Question 34

Anatomy of muscle compartments: upper limb

Answer 34

Arm Anterior compartment: arm flexion; forearm flexion and supination Posterior compartment: forearm extension Forearm Anterior compartment: hand, thumb and digits flexion; forearm pronation Posterior compartment: hand, thumb and digits extension; forearm supination

Question 35

Anatomy of muscle compartments: lower limb

Answer 35

Thigh: Anterior compartment: leg extension Medial compartment: thigh adduction Posterior compartment: thigh extension and leg flexion Leg: Anterior compartment: foot dorsiflexion and digits extension Lateral compartment: predominantly foot eversion Posterior compartment: foot plantarflexion and digits flexion

Question 36

What define the muscular compartments?

Answer 36

Deep fascia: tough and inelastic Inward projections called intermuscular septa Septa define muscular compartments in limbs Compartments contain muscles sharing neurovascular supply and fulfilling similar functions

Question 37

compartment syndrome

Answer 37

Swelling/bleeding in a muscular compartment Increased compartmental pressure Ischaemia of muscles and nerves Tissue necrosis

Question 38

How is compartment syndrome relieved?

Answer 38

Urgent fasciotomy required to relieve the compartmental pressures and ‘save’ the muscle and nerve tissue

Question 39

Fibroblast: Chondrocyte: Osteoblast: Myofibroblast: Adipocyte:

Answer 39

Fibroblast: secretes ECM for most tissues: collagen and elastin Chondrocyte: secretes ECM for cartilage: collagen II Osteoblast: secretes ECM of bone: collagen I Myofibroblast: secrete ECM and have contractile function Adipocyte: storage and metabolism of fat

Question 40

Connective tissue makeup

Answer 40

Characterised by abundance of extracellular matrix (ECM, 95%) with few cells (5%) when mature Cells depend on function/location ECM is composed of fibres (collagen and elastin) and ground substance

Question 41

Cartilage cells and matrix

Answer 41

Specialised connective tissue with a support function (often the shock absorbers of the body, can be tough or flexible depending on composition of matrix) Cells: chondrocytes Matrix: Type II collagen and proteoglycans + others depending on type of cartilage

Question 42

Cartilage cells

Answer 42

Embryonic mesenchymal cells (spindle) become clusters of chondroblasts (rounded) Surrounded by a layer of perichondrium (mesenchyme derived fibroblastic cells and collagen) Growth of cartilage is by interstitial (limited division of chondroblasts in ECM) and appositional growth (new chondroblasts from perichondrium). After matrix deposition cells become less active and become maintaining cells (chondrocytes)

Question 43

Cartilage ECM

Answer 43

ECM = 70% water + Collagen II + ground substance Proteoglycan - numerous glycosaminoglycans (GAGs) attached to a core protein (bottle-brush structure- negatively charged chains) Hyaluronic acid – also a GAG Aggrecan – cartilage specific proteoglycan arrangement Hydrophilic - provides compressive strength: flexible cushioned surface Woven with collagen to form an elastic and compressible structure

Question 44

Hyaline cartilage at joints

Answer 44

Resist compression: elasticity and stiffness of proteoglycans Tensile strength: collagen and hydrogel ground substance Limited repair and regeneration capacity Most is avascular: nutrition is by diffusion-limits thickness Articular surfaces of joints has no perichondrium-no source of new chondroblasts Cartilage atrophy is reversible after immobilisation – no impact exercise - gradual

Question 45

Bone matrix

Answer 45

Organic: osteoid Collagen I (90% of organic matrix) Non-collagenous proteins Osteocalcin: binds calcium ( local conc.) Osteonectin: binds calcium to collagen Inorganic: calcium salt-hydroxyapatite: 66% of dry weight of bone Calcium phosphate (with some carbonate and fluoride) Deposited in collagen hole zones

Question 46

Bone organisation

Answer 46

Periosteum Fibrous CT layer limiting bone Carries blood supply and osteoprogenitor cells Not present at the joint ends of long bones Endosteum Lines the interior of bones Dense outer shell: compact bone arranged in osteons (parallel to long axis) Inner cancellous bone arranged in interconnecting trabeculae with spaces for bone marrow

Question 47

2 Types of bone structure

Answer 47

Woven Bone: immature, haphazard fibre arrangement, mechanically weak – foetal development/fracture repair (rapid osteoid formation) Lamellar Bone: remodelled woven bone –regular parallel collagen, strong: all adult bone

Question 48

Bone cells

Answer 48

Derived from mesenchymal stem cells Differentiate into osteoprogenitor cells or chondroblasts Osteoprogenitor cells differentiate into osteoblasts (periosteum) Specialises to become osteoblast (ECM & collagen I secretion) Osteoblasts becomes osteocyte when surrounded by mineralised bone Osteoclasts from monocyte-macrophage lineage

Question 49

Osteoblasts

Answer 49

Bone building cell – lines bone surfaces Cuboidal cell with numerous RER and Golgi Secretes organic bone matrix - osteoid (collagen and non-collagenous proteins) Mediates mineralisation of osteoid (deposition of inorganic salts into the osteoid)

Question 50

Mineralisation of bone tissue

Answer 50

Osteoblasts secrete collagen and matrix vesicles Matrix vesicles contain calcium phosphatase. Calcium released from osteocalcin, which enters the vessel to produce hydroxyapatite crystals.

Question 51

Canals connecting osteon channels

Answer 51

Haversian canal - middle of osteon channel Volkmanns channel - connect haversian channels

Question 52

Osteocytes

Answer 52

Mature osteoblasts - surrounded by mineralised matrix Long cytoplasmic processes connecting to each other and osteoblasts (gap junctions) In lacunae surrounded by extracellular bone fluid that allows nutrient diffusion through the bony channels (canaliculi) Maintain matrix -no osteocytes: matrix is resorbed Stress information: respond to tiny currents generated when bone is deformed Mediates short term release of calcium from bone

Question 53

Osteoclasts

Answer 53

Bone resorbing cell Phagocytic cell from monocyte-macrophage cell line Multinucleate mobile cell which attaches to bone surface and resorbs bone leaving a pit behind (Howships lacuna) Work with osteoblast to regulate bone turnover and remodelling

Question 54

Osteoclasts action

Answer 54

Actin clear zone and ruffled border Mineral is dissolved by acids lysosomal enzymes resorb organic matrix Number and function affected by parathyroid hormone (PTH) and calcitonin Oestrogen also reduces activity - menopause

Question 55

Wolff’s Law

Answer 55

Bone is constantly remodelled through the coordinated actions of bone cells, to adjust to stresses and strains. Affects density, orientation and responds to micro fractures and wear & tear

Question 56

In adults bone turnover is slower than in children, but can increase due to:

Answer 56

Change in function (onset of walking) New demands (running, tennis, jumping) Repair of fractures Disease (e.g. Paget’s disease)

Question 57

Bone growth

Answer 57

In long bones: bone grows in length via the epiphyseal growth plate This fuses in adulthood Other bones grow by coordinated appositional growth at periosteum and resorption at inner surface (long bones gain in circumference by this method also)

Question 58

Intramembranous bone development

Answer 58

Sheets of mesenchymal cells Differentiation to osteoblasts in centres of ossification- these merge to form trabecular bone that is remodelled (bone template) Remaining mesenchyme makes bone marrow and periosteum Flat bones of skull, maxilla and mandible In the adult to increase the width of long bones

Question 59

Endochondral bone development

Answer 59

Cartilage template Blood supply to shaft of bone causes osteoblast differentiation: primary centre of ossification At birth blood supply to the epiphyses instigate secondary centres of ossification Cartilage growth plate remains to allow the bone to lengthen Long bones

Question 60

Growth plate of bone development

Answer 60

Epiphyseal end: Proliferation Diaphyseal end: chondrocytes mature and die and are replaced by bone

Question 61

What is autoimmunity?

Answer 61

Loss of self-tolerance and the production of antibodies (typically) against self proteins within cells or tissues which results in a hypersensitivity reaction or autoimmune disease.

Question 62

How does self tolerance come about?

Answer 62

During lymphocyte maturation, clonal selection/de-selection prevents production of cells that recognise self-proteins and these are eliminated via apoptosis. Remaining circulatory pool of mature B and T cells are non-responsive, that is tolerant to the normal components of the body. But deselection not 100% effective, everyone has potentially autoreactive cells.

Question 63

Peripheral tolerance

Answer 63

Can encounter antigens that are not exposed to lymphocytes or are present at such low amounts that they do not activate lymphocytes. Peripheral tolerance can arise from lack of co-stimulatory signals to autoreactive cells. Peripheral tolerance can arise from inhibition of autoreactive T-cells by Treg cells.

Question 64

Autoimmune classifactions

Answer 64

antibodies to specific proteins (autoantibodies) (Type II). formation of soluble immune complexes (Type III). activation of T-cells (Type IV).

Question 65

Organ specific autoimmune diseases and antigens examples

Answer 65

Graves disease - thyroid stimulating hormone receptor Type I diabetes - islet cells

Question 66

systemic autoimmune diseases and antigens examples

Answer 66

RA - IgG Lupus - ds DNA

Question 67

Examples of Type II autoimmune diseases

Answer 67

haemolytic anaemia - Rh blood antigen pempigus vulgaris - epidermal cadherin

Question 68

Examples of Type III autoimmune diseases

Answer 68

RA - Rh factor IgG complexes Lupus - DNA

Question 69

Examples of Type IV autoimmune diseases

Answer 69

RA Type I diabetes

Question 70

Autoimmune susceptibility: genetic influences

Answer 70

Human leukocyte antigen (HLA) houses a super locus with contains many genes that reside together on chromosome 6. Allelic variation within these genes is linked to risk of autoimmune disease.

Question 71

Rheumatoid Arthritis pathophysiology

Answer 71

abnormally produced antibody generally of IgM class specific for the Fc region of IgG. IgM RF can indicate poor prognosis if at high titre. Termed rheumatoid factor present in ~85% of RA patients so reasonably sensitive marker but also detected in other autoimmune diseases such as SLE. Anti-citrullinated protein antigen (ACPA) antibodies present in ~85% of RA patients so quite sensitive for RA and not often observed in other diseases. Citrulline formed from de-imination of arginine residues in proteins Citrullinted proteins detected in synovial membranes of affected joints in RA. ACPA prognostic for more aggressive version of RA. Presence of ACPA in undifferentiated arthritis indicates probably progression to RA.

Question 72

Risk factors for RA

Answer 72

Shared HLA epitopes - favours autoantigenic presentation PTPN22 - less clonal deletion Smoking - induces citrullination of lung proteins

Question 73

Other information that can differentiate between inflammatory (RA) and non-inflammatory (osteo) arthritis ?

Answer 73

Extra-articular features  Synovial fluid examination ESR, CRP

Question 74

Inflammatory joint features of RA

Answer 74

Morning stiffness (longer than 30 minutes) Joint swelling Symmetry  No DIP joints involvement Deformed joints (if untreated, long-standing disease)

Question 75

Visual signs of rheumatoid arthritis

Answer 75

Metacarpophalangeal joint, proximal interphalangeal joint inflammation symmetrical 30 minutes of pain in the morning but gets better as day goes on Boutonniere deformity of the thumb (bent upwards) Ulnar deviation at MCP Swan necking of the fingers Hammer toe

Question 76

What can form within a joint after a period of RA

Answer 76

Pannus - a type of extra growth in your joints that can cause pain, swelling, and damage to your bones, cartilage, and other tissue.

Question 77

Investigations of RA

Answer 77

Regular blood tests: FBC, U&E, LFT, ESR, CRP Immunological : RF, Anti CCP Blood tests to exclude other diseases Radiology

Question 78

Radiographic features of RA

Answer 78

Peri-articular osteopenia Bony erosions Joint space narrowing Joint subluxations

Question 79

Features of RA associated with poor prognosis

Answer 79

Presence of (and titre) of rheumatoid factor Presence of (and titre) of anti-CCP antibodies Presence of erosive disease at presentation Disease activity at presentation Number of swollen joints Levels of acute phase reactants (CRP/ESR) Presence of extra-articular features nodules vasculitis

Question 80

Treatment of RA

Answer 80

NSAIDs Nonsteroidal anti-inflammatory drugs (NSAIDs) can relieve pain and reduce inflammation. Over-the-counter NSAIDs include ibuprofen and naproxen  Steroids Corticosteroid medications, such as prednisone, depomedrone  Conventional DMARDs (Disease modifying anti rheumatic drugs) These drugs can slow the progression of rheumatoid arthritis and save the joints and other tissues from permanent damage. Common DMARDs include methotrexate leflunomide, hydroxychloroquine and sulfasalazine  Biologic DMARDs (biology therapy) Various classes

Question 81

Timeline of RA treatment

Answer 81

Early initiation of DMARD and escalation of treatment reduces risk of disease progression and co-morbidities

Question 82

UK, WHO, UK EQUALITY ACT 2010 definition of long-term illness

Answer 82

Long-term conditions or chronic diseases are conditions for which there is currently no cure, and which are managed with drugs and other treatment, for example: diabetes, chronic obstructive pulmonary disease, arthritis and hypertension. Disabilities is an umbrella term, covering impairments, activity limitations, and participation restrictions. An impairment is a problem in body function or structure; an activity limitation is a difficulty encountered by an individual in executing a task or action; while a participation restriction is a problem experienced by an individual in involvement in life situations a physical or mental impairment that has a ‘substantial’ and ‘long-term’ negative effect on your ability to do normal daily activities. Substantial = impacts daily tasks Long-term = 12 months or more

Question 83

International Classification of Functioning, Disability & Health

Answer 83

Principles: universality – applicable to all irrespective of health condition or physical, social and cultural context parity and aetiological neutrality – focuses on functioning, does not distinguish between ‘mental’ and ‘physical neutrality – captures positive & negative aspects of disability recognises environmental influence (e.g. climate, building design, attitudes, laws) as ‘an essential aspect of the scientific understanding of functioning and disability’ Dimensions: (i) body functions and structures e.g. mobility at purely bodily level – can’t raise arm above head (ii) activities (individual level) e.g. mobility at home – needs stairlift to access bedroom (iii) participation (social level) e.g. mobility in performing social role – unable to walk unaided to work a mile away (iv) environmental factors (whether as facilitators or barriers) e.g. mobility in wider social context – bus route to work exists but this bus doesn’t have wheelchair access

Question 84

QALYs and DALYs

Answer 84

QALYs are years of healthy life lived; DALYs are years of healthy life lost

Question 85

Kubler-Ross’s five stages of grief

Answer 85

Denial Anger Bargaining Depression Acceptance

Question 86

Shontz adjustment theory

Answer 86

Shock Realisation Defensive retreat Acknowledgment Adjustment

Question 87

Transactional model of stress & coping (Lazarus & Folkman)

Answer 87

Primary appraisal – benign or stressful Secondary appraisal – challenge or threat Coping – emotion based vs. problem based

Question 88

Moo’ and Schafer’s crisis model

Answer 88

Desire of psychological homeostasis Seven challenges Coping shaped by: event-related factors, environmental factors, personal factors, and cognitive & coping styles

Question 89

Frank’s 3 types of illness narratives

Answer 89

Restitution narrative Chaos narrative Quest Narrative

Question 90

Social model of disability

Answer 90

Social model of disability

Question 91

Impairment vs disability

Answer 91

Impairment = physical and/or cognitive limitation a person has e.g. the inability to walk because of a spinal cord injury Disability = the barriers to living a full life a person with an impairment experiences b/c of the way society is organised e.g. Cannot eat out because restaurants are not wheelchair accessible

Question 92

Vertebral Column levels

Answer 92

7 cervical vertebrae 12 thoracic vertebrae 5 lumbar vertebrae 5 fused sacral vertebrae 3-4 fused coccygeal vertebrae

Question 93

A Typical Vertebra

Answer 93

Body Pedicles Vertebral (neural) Arch Transverse processes Laminae Spinous process Superior and inferior articular facets Intervertebral notch* Spinal canal

Question 94

Typical Cervical Vertebrae

Answer 94

Saddle-shaped body Uncinate process Transverse foramina Triangular spinal canal Bifid spinous process Parallel articular facets (cup-shaped or planar)

Question 95

Atypical Cervical Vertebrae: C1

Answer 95

No vertebral body or spinous process Kidney shaped articular facets Anterior and posterior arch and tubercues

Question 96

Atypical Cervical Vertebrae: C2

Answer 96

Dens/Odontoid process Facies articularis posterior - attaches transverse ligament Facies articularis anterior - articulates with C1

Question 97

Atypical Cervical Vertebrae: C7

Answer 97

Long spinous process - vertebral prominens attaches ligmentum nuchae

Question 98

Typical Thoracic Vertebrae

Answer 98

Heart-shaped body Demifacets for ribs Round spinal canal Long spinous process Articulating facets on transverse processes Planar articular facets Superior: face posteriorly Inferior: face anteriorly

Question 99

Atypical Thoracic Vertebrae: T1, T10 - T12

Answer 99

T1 - complete superior costal facet T10 - complete superior costal facet T11 - No transverse articular facet T12- Lumbar like pattern of inferior facet

Question 100

Lumbar Vertebrae

Answer 100

Large vertebral body Very small arch Blunt, hatchet-shaped spinous process Comparatively small transverse processes Articular facets Superior: face posteromedially, have mammillary bodies Inferior: face anterolaterally

Question 101

Lumbosacral transitional vertebrae

Answer 101

Lumbarisation of S1 Sacralisation of L5

Question 102

Vertebral Column: Curvatures

Answer 102

Cervical Lordosis Thoracic Kyphosis Lumbar Lordosis

Question 103

What is between adjacent vertebral bodies

Answer 103

Intervertebral (IV) discs

Question 104

IV Disk

Answer 104

Inner nucleus polposus Outer annulus fibrosis

Question 105

IV discs degeneration with age

Answer 105

The nucleus pulposus gradually becomes less hydrated and increasingly fibrous with age The discs become stiffer and more liable to injury

Question 106

Joints of the vertebral bodies: Ligaments

Answer 106

Anterior Longitudinal Ligament Posterior longitudinal Ligament

Question 107

In which direction to slipped discs protrude

Answer 107

Lateral to posterior longitudinal ligament Towards rami

Question 108

Joints between inferior and superior articular facets

Answer 108

Zygapophyseal joints

Question 109

Joints of the vertebral arches: Accessory ligaments

Answer 109

Ligamentum Flavum - connects adjacent lamina Interspinous Ligament - between spinous processes Supraspinous Ligament - connects tips of the spinous processes Intertransverse Ligament - connects transverse processes Ligamentum Nuchae - occipital to cervical

Question 110

Atlanto-occipital joint

Answer 110

superior facet of the atlas - condyloid joint - condoyle of occiput

Question 111

Atlanto-axial joint

Answer 111

1 median joint - pivot - anterior arch of the atlas and the Dens 2 lateral joints - plane/gliding - Z joint

Question 112

Ligaments of the occipito-atlantoaxial region

Answer 112

Nuchal ligament Posterior atlanto-occipital membrane - continuation of the flavum Cruciate ligament of the dens - body of axis -> clivus Alar ligaments of the dens - oblique direction dens -> clivus Apical odontoid ligament - dens -> clivus Tectorial membrane - continuation of the posterior longitudinal ligament

Question 113

Muscles of the Back

Answer 113

(Extrinisic -> intrinsic) Trapezius Latissimus dorsi Levator scapulae Rhomboid minor Rhomboid major Serratus posterior superior Serratus posterior inferior Splenius capitis Splenius cervicis Erector Spinae group - Iliocostalis, longissimus, spinalis Transversospinalis group - rotatores, semispinalis, multifidus.

Question 114

Postural muscles

Answer 114

Psoas major – attaches to all the lumbar vertebrae and discs It is a primary hip flexor but also helps to stabilize the spine Quadratus lumborum – attaches to the lumbar vertebrae and pelvis and helps to maintain posture

Question 115

The muscles of the back consist of:

Answer 115

Extrinsic back muscles – superficial and intermediate muscles, innervated by anterior rami of spinal nerves Intrinsic (‘true’) back muscles – deep muscles, innervated by posterior rami of spinal nerves Extrinsic muscles are responsible for producing movements of the ribs and upper limbs Intrinsic muscles maintain posture and move the vertebral column (and head) Gross spinal movements are a result of the sum of many small movements occurring at each vertebral level

Question 116

Spinal cord origin and terminus

Answer 116

Spinal cord continuous cranially with the medulla oblongata and terminates caudally as the conus medullaris around L1/L2 vertebral level

Question 117

Spinal nerve rootlets and roots

Answer 117

Ventral (anterior) rootlets and ventral root contain axons of somatic motor neurons and sympathetic neurons (for T1 – L1/L2 spinal nerves) Dorsal (posterior) rootlets and dorsal root contain the central processes of pseudo-unipolar somatic sensory neurons and visceral afferent (sensory) neurons Neuronal cell bodies in dorsal root ganglion Ventral and dorsal roots join to form a spinal nerve

Question 118

diseases that can affect the intervertebral foramen

Answer 118

Some disease processes that can affect this opening and compress the spinal nerve: Osteoarthritis Injury affecting the facet joints or the pedicles Intervertebral disc herniation Vertebral body fracture/dislocation Injury to spinal ligaments

Question 119

Ventral and dorsal rami

Answer 119

Ventral rami Larger, supply the limbs and the anterolateral aspects of the trunk Unite to form major nerve plexuses, e.g. the brachial plexus Dorsal rami Smaller and supply intrinsic back muscles, facet joints and a narrow strip of skin on the back

Question 120

Cauda equina

Answer 120

Made up of spinal nerve rootlets from L3 – Co segments of the spinal cord Innervate lower limbs + pelvic region Rootlets of the sacral spinal nerves (S1-5) exit the spinal cord at vertebral level T12/L1 – the sacral spinal cord These rootlets then run all the way down in the vertebral canal to exit the IV foramina of the sacrum The actual spinal nerves for these rootlets are formed just prior to entering the intervertebral foramen

Question 121

Cauda equina syndrome (spinal stenosis)

Answer 121

Sciatica Loss of bladder and bowel control Flaccid paralysis of the lower limbs ‘Saddle area’ (perineal) sensory loss

Question 122

Spinal cord meninges - coverings

Answer 122

Dura mater Extends from the foramen magnum to the coccyx Continuous with cranial dura (around the brain) Merges with epineurium of spinal nerves Arachnoid mater Surrounds the brain and extends down to S2 vertebral level Has fine strands of connective tissue crossing subarachnoid space - trabeculae Pia mater Firmly adhered to the brain and spinal cord Forms flat denticulate ligaments Continuous with filum terminale

Question 123

Spinal cord meninges - spaces

Answer 123

Epidural space (extradural space) Between the dura mater and the vertebral column Contains fat (adipose) and internal vertebral venous plexus Local anaesthetics can be injected into this space Subdural space Potential space between dura and arachnoid mater Only obvious when it fills with blood, CSF or pus Subarachnoid space Between arachnoid and pia mater Extends further (S2) than the spinal cord (L1/2) Contains cerebrospinal fluid (CSF) and vessels Local anaesthetics can be injected into this space CSF can be drawn from this space: lumbar puncture

Question 124

Lumbar puncture (spinal tap) procedure

Answer 124

Needle inserted in adults between L3/L4 vertebrae or L4/L5 vertebrae Avoids spinal cord (L1/L2 vertebral level) Different in children: between L4/L5 recommended as spinal cord may extend more inferiorly e.g. L3 vertebral level Contraindications Raised intracranial pressure, local skin infections, coagulopathy

Question 125

What happens to the spinal meninges when spinal nerves merge off

Answer 125

The dura mater of the spinal cord covers the rootlets and merges with the epineurium. The arachnoid mater and pia mater merge with the perineurium of the spinal nerve, sealing the subarachnoid space

Question 126

The spinal cord and its roots and nerves are supplied with blood via:

Answer 126

Longitudinal branches from the vertebral arteries One anterior spinal artery Two posterior spinal arteries Segmental arteries – help to provide additional blood to supplement the anterior + posterior spinal arteries

Question 127

Segmental arteries

Answer 127

Vertebral and deep cervical arteries (cervical region) Intercostal arteries (thoracic region) Lumbar arteries (lumbar region) The largest segmental artery is the great radicular artery (artery of Adamkiewicz): reinforces blood supply to lower spinal cord

Question 128

How do segmental arteries join the longitudinal arteries?

Answer 128

Segmental arteries enter the vertebral canal through the intervertebral foramina and anastomose with branches of the longitudinal spinal arteries to form a pial plexus

Question 129

What supplies each section of the spinal cord

Answer 129

Anterior spinal artery = anterior 2/3rds of the spinal cord Posterior spinal artery supplies the posterior 1/3rd of the spinal cord

Question 130

Spinal cord: venous drainage

Answer 130

Veins from within the spinal cord drain into the venous plexus of the pia mater The veins of the internal vertebral venous plexus (Batson’s plexus) lie in the epidural space Veins draining the spinal cord and vertebral column eventually drain into the major veins of the body: Azygos Hemiazygos Right highest intercostal veins And eventually into the Superior vena cava (and back to the heart) Internal vertebral plexus veins are valveless Drainage flow dependent on posture and respiration

Question 131

What about venous drainage of the spinal cord is problematic?

Answer 131

This venous plexus is continuous with the veins draining the prostate prostate cancer may metastasise via the internal vertebral venous plexus to the CNS

Question 132

Structure of a spinal nerve layers

Answer 132

epineurium: dense layer of fibrous tissue; external coat of nerve perineurium: several layers of flattened cells separated by layers of collagen, surrounding a bundle (fascicle) of nerve fibres. Cells that form the inner surface are joined by tight junctions endoneurium: thin layer of tissue surrounding individual axons and myelin sheath

Question 133

Characteristics of muscle types

Answer 133

Skeletal muscle: striated capable of rapid, strong contractions attached to the skeleton (hence its name), so it moves bones under voluntary nervous control (usually) multi-unit muscle (see later) Cardiac muscle, confined to the heart: striated contracts rhythmically involuntary, innervated by autonomic neurones single-unit muscle (functional syncytium) Non-striated or smooth muscle: so-called because no striations visible contracts in a slow and sustained manner involuntary, innervated by autonomic neurones can be single-unit OR multi-unit, depending on location or circumstances

Question 134

Skeletal muscle organization

Answer 134

Myofibers (muscle cells) - formed from myofibrils Elongate cells Arranged parallel to one another and bundled by connective tissue into fascicles Sarcolemma – cell membrane Striated (banded)

Question 135

myofibrils

Answer 135

Myofibrils: long bundles of protein Made up of thick (myosin) and thin (actin) protein filaments Myofilaments arranged in sarcomeres Repeated units i.e. a polymer From one Z-disc to the next, thick filaments are at center, thin filaments at either end attached to the Z-discs I-band near either end – only thin myofilaments A-band at midsection – thick filaments H-zone at center – only thick filaments (no overlap with thin)

Question 136

Two types of muscle fibre arrangments

Answer 136

Parellel-fibred muscles have longer fibres (more sarcomeres in series) than pennate-fibred muscles, thus they are capable of a greater shortening velocity Pennate-fibres muscles have more fibres but of shorter length. Hence pennate muscles are stronger but slower contracting than parallel-fibred muscles

Question 137

Motor units

Answer 137

an alpha motor neurone in the spinal cord and all of the muscle fibres it innervates

Question 138

Muscles; HENNEMAN’S SIZE PRINCIPLE:

Answer 138

SMALLEST MOTOR UNITS RECRUITED FIRST

Question 139

Types of Skeletal Muscle Fibres

Answer 139

Type I (slow twitch, red) fibers Slow contraction speeds Adapted for aerobic respiration Large blood supply High myoglobin content (O2 storing pigment) High mitochondrial densities Type II (fast twitch, white) fibers Fast contraction speeds Adapted for anaerobic respiration (fermentation) Less blood, myoglobin, and mitochondria High content of glycogen and glycolytic enzymes - Two types Fast glycolytic fibers (rely mainly on glycolysis) Fast oxidative fibers (more capacity for aerobic respiration)

Question 140

Nerve endings are referred to as sensory receptors. Functionally, there are 3 types of receptors:

Answer 140

Interoceptors. Occur in viscera and respond principally to mechanical and chemical stimuli Exteroceptors. Lie superficially in the skin and respond to different sensory modalities i.e. painful, temperature and touch stimuli, Proprioceptors. Occur in muscles, joints, and tendons and provide awareness of posture and movement (kinaesthesia)

Question 141

Structurally, Sensory receptors may be:

Answer 141

Encapsulated – surrounded by a structural specialisation of non-neural tissue (often called a corpuscle) Unencapsulated – terminal branch of sensory nerve fibre lying freely in the innervated tissue

Question 142

Properties of cutaneous sensory receptors

Answer 142

Receptor type - Function - Threshold - Adaptation Thermoreceptor (Free nerve ending) Temperature Varies Rapid Nociceptor (Free nerve ending) Pain High Slow Mechanoreceptor (Meissner corpuscle) Touch (dynamic deformation) Low Rapid Mechanoreceptor (Merkel cell/disks) Touch (indentation) Low Slow Mechanoreceptor (Ruffini corpuscle) Touch (stretch) Low Slow Mechanoreceptor (Pacinian corpuscle) Touch (vibration) Low Very rapid

Question 143

Properties of nerve fibres

Answer 143

Fibre type -Function - Diameter (µm) - Conduction velocity (m/s) Aa (fast!) Motor 12-20 (big!) 70-90 Ab Touch, pressure 5-12 30-70 Ag Muscle spindle motor 3-6 15-30 Ad Pain, T, touch 2-5 12-30 B Preganglionic autonomic <3 3-15 C (slow!) Pain, reflex, postganglionic sympathetic 0.3-1.3 (small!) 0.5-2.3

Question 144

Muscle spindles detect changes in :

Answer 144

Muscle spindles (stretch receptors) detect changes in length of a muscle.

Question 145

Muscle spindle structure function

Answer 145

Small muscle fibres inside are known as intrafusal fibres The main muscle fibres outside are known as extrafusal fibres Type I(a) Annulospiral fibres sense muscle length and rate of change in length Type II Flower-spray fibres only really sense muscle length

Question 146

(Golgi) Tendon Organs sense:

Answer 146

(Golgi) Tendon Organs sense tension in muscle (or force of contraction)

Question 147

Golgi tendon structure function

Answer 147

Located at the junction of the muscle & the tendon Active contraction of the muscle activates the Golgi tendon organ (it is compressed by collagen and fires action potentials) Sensitive to increases in muscle tension caused by muscle contraction It’s normal function is to regulate muscle tension within an optimal range (may also prevent muscle overload). Golgi sensory neurone: 1b afferent fibre

Question 148

Stretch reflex (or myotatic reflex)

Answer 148

Anatomically, one of the simplest reflexes Mediated by just two neurones – one afferent and one efferent This is a monosynaptic reflex Afferent neurones convey impulses from intrafusal muscle stretch receptors to the CNS Motor neurones convey impulses back to the extrafusal muscle Reciprocal innervation: The inhibitory input to the hamstrings involves inhibitory interneurones and is polysynaptic.

Question 149

Gamma motor neurones adjust:

Answer 149

Gamma motor neurones adjust the sensitivity of muscle spindles

Question 150

Gamma motor neurones structure function

Answer 150

Innervate intrafusal muscle at two ends of muscle spindle They stretch muscle spindles & lower the threshold of stretch receptors to externally applied stretch (increases sensitivity of stretch reflex) Increases likelihood of discharge of 1a afferents This is a mechanism for maintaining sensitivity of the spindle over a wide range of muscle lengths

Question 151

AP Refractory period

Answer 151

When Na+ channels are closed and inactivated, no new action potential (AP) can be initiated – this is termed the absolute refractory period When the membrane potential is returning to its resting level, some Na+ channels are in the resting state and a new AP can be initiated if the stimulus is strong enough – this is the relative refractory period These mechanisms help to: Limit the rate of firing of neurone Prevent antidromic conduction

Question 152

ACh release at the NMJ AP

Answer 152

Release of a single vesicle of ACh (at rest) results in a so-called miniature end-plate potential, whereas release of several (when the motor neurone is activated) causes an end-plate potential or EPP

Question 153

Links to excitation-contraction coupling in skeletal muscle…

Answer 153

Action potential propagates down the sarcolemma Transverse tubules conduct AP into the cell’s interior Ca2+ release channels open in sarcoplasmic Reticulum

Question 154

What’s the relationship between T tubules and the SR?

Answer 154

The T tubules are deep invaginations of the muscle cell membrane and are placed at the junction of the A bands and the I bands They provide a mechanism for changes in membrane potential to be communicated right to the inners of the muscle fibre In striated muscle, each T tubule comes into close apposition with SR at several different levels When the membrane on the T tubule is depolarised, this triggers release of calcium from the SR Thus, the T tubules and SR allow calcium concentration in the sarcoplasm to rise in the area where they are needed

Question 155

Non-depolarising neuromuscular blocking drugs.

Answer 155

Competitive antagonists at nicotinic acetylcholine receptor on skeletal muscle Derived from curare and tubocurarine (no longer used) Tubocurarine – slow to recover, has adverse effects. Superseded by… Atracurium Short-acting (15-30 min) Can be given by infusion for longer term effects Pancuronium Longer duration (60-120 min) Used for longer term action in intensive care Rocuronium Faster onset (within 2 min) Intermediate duration (30-40min)

Question 156

Acetylcholinesterase inhibitors

Answer 156

Neostigmine, pyridostigmine Increase concentration of acetylcholine in synapse increased receptor activation – both nicotinic and muscarinic => depolarising block + PS effects

Question 157

Depolarising block drugs

Answer 157

Suxamethonium, fast onset and short duration Nicotinic acetylcholine receptors are ligand-gated ion channels. Activation of neuron  influx of sodium ions through nicotinic receptor and sodium channels  depolarisation (increase in membrane potential) Muscle contraction Continued activation  block

Question 158

Myasthenia Gravis + diagnosis + treatment

Answer 158

Most people with myasthenia gravis have weakness in the muscles of the eyes, eyelids and face. Autoimmune – antibodies against nicotinic acetylcholine receptors  reduced muscle control Diagnosis – use short-acting acetylcholinesterase inhibitor – edrophonium Treatment – use medium-duration acetylcholinesterase inhibitor e.g. pyridostigmine

Question 159

Osteological landmarks of the clavicle:

Answer 159

Shaft (body) Sternal end  Sternal facet  Acromial end  Acromial facet 

Question 160

Osteological landmarks of the scapula:

Answer 160

Inferior angle Medial border  Lateral border  Supraspinous fossa  Infraspinous fossa  Spine of the scapula Acromion  Clavicular facet  Glenoid fossa  Supraglenoid and infraglenoid tubercles  Coracoid process  Subscapular fossa

Question 161

Osteological landmarks of the proximal humerus:

Answer 161

Head Anatomical neck  Surgical neck Lesser tubercle and crest  Greater tubercle and crest  Intertubercular (bicipital) groove (sulcus) Deltoid tuberosity  Radial (spiral) groove

Question 162

Structures stabilising the sternoclavicular Joint:

Answer 162

Synovial saddle joint: elevation/depression; protraction/retraction Anterior and posterior sternoclavicular joint ligaments  Interclavicular ligament  Costoclavicular ligament  Articular disc  Sternocleidomastoid, sternothyroid, sternohyoid, and subclavius muscles

Question 163

acromioclavicular joint

Answer 163

Between acromion and clavicle Plane/gliding synovial joint: gliding movements in elevation/depression; protraction/retraction Incomplete articular disc (when present) Periarticular structures reinforcing joint Dislocations common due to loose fibrous capsule

Question 164

Structures stabilising the acromioclavicular joint:

Answer 164

Acromioclavicular joint ligaments  Deltoid and upper trapezius Coracoclavicular ligament  Articular disc (when present) 

Question 165

scapulothoracic joint

Answer 165

The scapulothoracic ‘joint’ is a muscular articulation between the scapula and the rib cage. Enables the scapula to slide and glide over the ribs

Question 166

glenohumeral joint

Answer 166

Between humeral head and glenoid fossa Ball and socket joint, multiaxial Very mobile, very unstable Active and passive stabilisers Dislocations more common antero-inferiorly

Question 167

Stabilisers of the GH joint:

Answer 167

Joint capsule and associated GH capsular ligaments  Coracohumeral ligament  Rotator cuff muscles Tendon of long head of the biceps brachii & transverse humeral ligament Glenoid labrum Vacuum effect (negative intracapsular pressure)

Question 168

Condition affecting Glenohumeral joint capsule

Answer 168

adhesive capsulitis - frozen shoulder

Question 169

The subacromial space

Answer 169

Inferior to coraco-acromial arch Subacromial bursa Supraspinatus muscle & tendon Inflammation of bursa or tendon  swelling and pain in flexion and abduction

Question 170

Osteological landmarks of the distal humerus

Answer 170

Trochlea Coronoid fossa Capitulum Radial fossa Medial and lateral epicondyles Olecranon fossa Groove for ulnar nerve

Question 171

Osteological landmarks of the proximal ulna

Answer 171

Olecranon process Coronoid process Trochlear notch Radial notch Ulnar tuberosity

Question 172

Osteological landmarks of the proximal radius

Answer 172

Articular facet head of the radius Head of radius Neck of radius Radial tuberosity

Question 173

Radial head subluxation (‘Nursemaid’s elbow’)

Answer 173

Elbow dislocations: most common type in children Bones and periarticular tissues still developing Little force  ‘pulled elbow’ Reduction by gently moving bones back into position Likelihood of recurrence Prevention: educating parents and caregivers

Question 174

Muscles stabilising the pectoral girdle and nerve supply

Answer 174

Trapezius: supplied by a cranial nerve (Accessory CN XI) Rhomboids: dorsal scapular nerve (C5) Levator scapulae: dorsal scapular nerve (C5) Serratus anterior: long thoracic nerve (C5-7)

Question 175

Rotation of the scapula in flexion and abduction

Answer 175

Trapezius and serratus anterior muscles laterally rotate the scapula during upper limb elevation If the scapula can’t rotate, the humeral head ‘hits’ the acromion at about 90˚ of elevation  further flexion or abduction is impossible

Question 176

Anterior axio-appendicular muscles

Answer 176

Deltoid, pec major

Question 177

Pectoral girdle muscles origin and insertion

Answer 177

Rhomboids - spine => medial scapula Levator scapulae - C vertebrae => superior angle of scapula Serratus anterior - ribs => medial border of scapula Pectoralis major - clavicle/sternum => greater tubercle of humerus Deltoid - clavicle and scapula => deltoid tuberosity of humerus Rotator cuff muscles - scapula => proximal humerus

Question 178

An unstable ‘winging’ scapula

Answer 178

Loss of the strength in stabilising muscles = loss of some stability of the whole of the upper limb If you can’t place the hand where it needs to be for prehension (ie gripping activities), then major functional problems result

Question 179

The rotator cuff muscles

Answer 179

Originate from the scapula Insert into proximal humerus C5-6 nerve supply Movement Stability

Question 180

The rotator cuff muscles (SITS) - function

Answer 180

Supraspinatus - initiates abduction Infraspinatus - external rotation Teres minor - external rotation Subscapularis - internal rotation

Question 181

Muscles controlling the elbow joint

Answer 181

Anterior: Flexors (and supinator) Musculocutaneous nerve Biceps brachii reflex Posterior: Extensor Radial nerve Triceps reflex

Question 182

The axilla: contents

Answer 182

AXillary artery and vein Infraclavicular part of brachial plexus Lymph Nodes (5 groups) Long thoracic nerve and intercostal nerves Axillary fat tissue

Question 183

5 groups of axillary lymph nodes:

Answer 183

Apical: medial to axillary vein, superior to pectoralis minor Central: near the floor, easiest to palpate Pectoral (anterior): along lower border pectoralis minor Subscapular (posterior): anterior to subscapularis Humeral (lateral): behind axillary vein, drain the upper limb

Question 184

upper limb arterial and venous supply

Answer 184

Subclavian > axillary > Anterior and posterior humeral circumflex arteries – GHJ, humeral head, muscles > Profunda brachii artery – posterior compartment of arm > radial and ulna The cephalic vein usually forms over the anatomical snuff-box on the radial side of the wrist from the radial end of the dorsal venous plexus > The basilic vein arises medially in the dorsal venous network of the hand The median cubital vein runs medially to join the basilic vein Deep veins accompany the radial and ulnar arteries They unite near the elbow as paired, deep brachial veins Brachial veins drain into Axillary vein Axillary vein  Subclavian vein Subclavian vein + internal jugular vein = brachiocephalic vein L+R brachiocephalic veins drain into SVC

Question 185

Function of The arterial anastomoses around the scapula

Answer 185

anastomotic network provides alternative route for arterial blood in the event of occlusion

Question 186

Topography of brachial plexus

Answer 186

Emerges from the posterior triangle of the neck Passes deep to the clavicle Passes through the axilla

Question 187

posterior triangle of the neck

Answer 187

Boundaries of posterior triangle: Middle third of the clavicle inferiorly  Trapezius muscle posteriorly  Posterior border of the sternocleidomastoid muscle anteriorly Contents of posterior triangle: Accessory nerve (CN XI) Phrenic nerve Lymph nodes Subclavian artery Roots of the brachial plexus

Question 188

Roots of the brachial plexus emerge from

Answer 188

Roots of the brachial plexus emerge between anterior scalene and middle scalene muscles

Question 189

Route of the Autonomic fibres of the brachial plexus

Answer 189

Exit the spinal cord segment of T1 travelling in anterior rootlets/root Enter the spinal nerve Exit via the white ramus communicans to enter the sympathetic chain Use the sympathetic chain to travel up to join cervical spinal nerves (via grey ramus communicans)

Question 190

Which spinal nerves form the brachial plexus?

Answer 190

C5-8 and T1 Only part of T1 contributes to brachial plexus There is some variation (as is usual in anatomy!!) – C4 and T2 may be involved

Question 191

Which rami of these spinal nerves form the brachial plexus?

Answer 191

Ventral (anterior) rami Remember that this is the larger of the two rami that spinal nerves divide into (the smaller one is the dorsal or posterior ramus)

Question 192

What are the brachial plexus root short branches and their clinical relavance

Answer 192

Dorsal scapular n from C5 Long thoracic n. from C5,6,7 Nerve lesion: muscle paralysis and unstable scapula with ‘winging’

Question 193

What are the brachial plexus trunk short branches and their clinical relavance

Answer 193

Suprascapular n. from superior trunk lesions > muscle wasting to supraspinatus muscle

Question 194

What are the brachial plexus cords short branches and their clinical relevance

Answer 194

Sup. subscapular n. from C5,6 Thoracodorsal n. from C6,7,8 Inf. subscapular n. from C5,6 All from the posterior cord

Question 195

Axillary Nerve

Answer 195

Axillary Nerve (C5-6) Motor function: Deltoid and teres minor Sensory function: Skin over upper lateral arm (Sergeant’s patch) Clinical significance: Numbness Sergeant’s patch & weak arm abduction (15-90°)

Question 196

Radial Nerve

Answer 196

Radial Nerve (C5-8; T1) Motor function: All muscles of posterior compartments of arm and forearm Sensory function: Skin posterior aspect of arm and forearm, lower lateral surface of the arm, dorsal lateral surface of the hand Clinical significance: Numbness rn distribution & weak extension @ elbow, wrist, fingers; ‘wrist drop’ deformity

Question 197

Musculocutaneous Nerve

Answer 197

Musculocutaneous Nerve (C5-7) Motor function: All muscles of anterior compartment of the arm Sensory function: Skin lateral aspect of forearm Clinical significance: Weak supination & flexion of the forearm

Question 198

Median Nerve

Answer 198

Median Nerve (C5; C6-T1) Motor function: All muscles anterior compartment forearm, except flexor carpi ulnaris and medial ½ of flexor digitorum profundus Thenar muscles and 2 lateral lumbricals (hand) Sensory function: Palmar aspect of lateral 3 and ½ digits Lateral side of palm Middle of wrist Clinical significance: Carpal tunnel syndrome  wasting thenar muscles, numbness, weak grip

Question 199

Ulnar nerve

Answer 199

Ulnar Nerve (C7; C8-T1) Motor function: Flexor carpi ulnaris and medial ½ flexor digitorum profundus (forearm) All intrinsic muscles hand, except thenar muscles and 2 lateral lumbricals Sensory function: Palmar aspect of medial 1 and ½ digits & associated palm and wrist Dorsal aspect of medial 1 and ½ digits Clinical significance: wasting hypothenar muscles, numbness

Question 200

3 Types of nerve lesion

Answer 200

Avulsion: most severe, nerve root pulled out of the spinal cord Stretch (neuropraxia): nerve fibres are stretched Rupture: partial or full tear of the spinal nerve

Question 201

Brachial plexus Lesions usually affect either upper or lower brachial plexus, how?

Answer 201

Upper plexus (C5-C7): Angle between the shoulder and the neck forcibly widens Proximal musculature is involved Lower plexus (C8-T1): Angle between the shoulder and the trunk forcibly widens Distal musculature is involved

Question 202

Upper brachial plexus lesions: causes

Answer 202

Motorcycle accidents: shoulder hits a fixed vertical structure (A) or the ground (B) Large falling objects (C): result in brachial plexus injuries with shoulder fractures Falls from a height (D): resulting in a side flexion stretch of the neck Delivery: brachial plexus is stretched due to traction

Question 203

Upper brachial plexus lesions: clinical signs

Answer 203

‘Erb’s palsy’ or ‘waiter’s tip’ deformity: Adducted and internally rotated gleno-humeral joint Loss of deltoid muscle (C5/6) Loss of supra- and infraspinatus muscles (C5/6) Pronated forearm and extended elbow joint Loss of elbow flexor muscles (C5-7) Sensory changes: lateral surface of arm & forearm; ‘sergeant’s patch’ Absent biceps reflex

Question 204

Lower brachial plexus lesions: causes

Answer 204

Upper extremity hyper – abduction Traction injury in difficult childbirth

Question 205

Lower brachial plexus lesions: presentation

Answer 205

Klumpke's palsy: Claw hand: Loss of intrinsic muscles of the hand (C8/T1) Inability to grip Loss of wrist and finger flexors (C6-T1) Sensory changes: Medial hand and forearm (C8/T1)

Question 206

Pancoast tumour pathophysiology

Answer 206

Tumour in the apex of the lung can result in compression of: Inferior trunk (C8,T1) of the brachial plexus Sympathetic chain The patient will present with: Klumpke’s palsy Horner’s syndrome (due to damage to T1) Ptosis (a drooping upper eyelid) Miosis (constricted pupil) Anhidrosis (loss of sweating of the face)

Question 207

Calcium Physiological Functions

Answer 207

Mechanical role in bone Excitation – contraction coupling ↑ cytosolic Ca 2+ signals several cell processes Cell shape change & motility (e.g. cilia action) Secretion (e.g. exocytosis) Mitosis Second messenger system Cofactor in the clotting cascade and the complement cascade

Question 208

Effect of pH on calcium levels

Answer 208

pH affects free ionized calcium Acidosis increases proportion Alkalosis decreases proportion Example: Hyperventilation Respiratory alkalosis (raised pH) Increased calcium-albumin binding Signs and symptoms of hypocalcaemia Total calcium remains the same

Question 209

homeostasis of calcium level control - quick and slow

Answer 209

Long term regulation Slow changes in intestinal absorption & renal excretion maintain total body Ca 2+ Short term regulation Rapid, adjustments between bone & plasma maintains constant free Ca 2+

Question 210

Vitamin D metabolism

Answer 210

7-dehydrocholesterol -> D3 via UV-B in skin / via diet then to liver to become calcifediol Then to kidney to become calcitriol (active)

Question 211

Vitamin D (calcitriol)

Answer 211

Synthesis stimulated by PTH acting on kidney Feedback loop - calcitriol increases calcium concentration & directly acts on parathyroid gland Acts at kidneys to increase calcium reabsorption Increases activity and production of calcium transport proteins

Question 212

(Hormone) Regulation of Calcium

Answer 212

Calcitonin from C cells in thyroid parafollicular cells: Released in response to high plasma Ca2+ Inhibits osteoclast activity – slows release Stimulates excretion from kidneys PTH from parathyroid chief cells: Released in response to low plasma Ca2+ Increases release from bone by affecting osteoblast and osteoclast activity – RANKL Increases resorption from kidneys Stimulates formation and secretion of calcitriol by kidneys

Question 213

Relationship between osteoblasts and osteoclasts and effect of PTH

Answer 213

Osteoclast precursors have RANK (Receptor Activator of Nuclear factor Kappa B) receptors on their cell membranes Osteoblasts have the ligand for this receptor on their cell membranes: RANKL Osteoblasts also produce osteoprotegrin which prevents resorption by binding to RANKL The ratio of RANKL:osteoprotegrin determines bone resorption PTH upregulates RANKL which binds to RANK and stimulates the differentiation of osteoclasts

Question 214

Other influential hormones on calcium levels

Answer 214

Oestrogen – increases osteoblast production and release of OPG Corticosteroids – reduce gut absorption and increase renal excretion of Ca2+ Growth hormone – favours Ca2+ absorption Also linked with serum phosphate levels (calcitriol, PTH, FGF23)

Question 215

Hyperalcaemia signs and symptoms

Answer 215

Decreased nerve & muscle excitability - can give cardiac arrythmia Signs and symptoms Bone softening & fractures Renal stones Headaches Decreased muscle tone Polyuria, polydipsia, renal colic, lethargy, dyspepsia ….. Bones, Stones, Groans, Moans

Question 216

Hypocalcaemia signs and symptoms

Answer 216

Increased nerve & muscle excitability - Low Ca 2+ increases Na+ permeability so threshold is reached quicker Signs and symptoms Neuromuscular irritability Muscle twitching Muscle spasm & cramp (asphyxia!) Increased nerve excitability, psychosis, glottis spasm, convulsions….. Tetany, Convulsions, Systolic arrest

Question 217

Tumour peptide PTH-related protein

Answer 217

Peptide that shares structural homology with PTH Expressed in squamous cell carcinomas lung, breast, kidney, lymphoid tumours Not under feedback regulation by plasma calcium Activates PTH receptor on osteoblasts (PTHR1) and mimics its biological effects (paraneoplastic) Stimulates osteoclastic bone resorption Malignancy associated hypercalcaemia

Question 218

Explain the process of fracture repair in bone

Answer 218

Periosteum is breached, haematoma, blood clot forms Replaced by vascular collagenous tissue (granulation tissue) New osteoprogenitor cells arise from mesenchymal cells Neutrophils and macrophages phagocytose the heamatoma and necrotic debris External callus – bridges fracture on the outside, uses cartilage Internal callus – bridges fracture in the cavity, woven bone Well established by 3rd week after fracture Remodelling of callus takes many months Osteoclasts remove woven bone and osteoblasts replace this with lamellar bone Full replacement with lamellar bone Orientation of trabecular bone determined by stresses applied when mobile Some residual fibrosis, irregular cortical bone and muscle scarring

Question 219

Brittle Bone Disease

Answer 219

Osteogenesis Imperfecta, OI Group of hereditary disorders Defective synthesis of collagen I – quantity or quality (disrupts structure of triple helix) Fragile skeleton – too little bone Extra-skeletal manifestations: skin, joints, eyes: blue sclera Many types with a range of clinical outcomes – Type I increased childhood fractures (pre-puberty), normal stature Type II fatal in utero or perinatal Type III progressive and deforming, short stature Type IV increased childhood fractures, short stature

Question 220

Achondroplasia

Answer 220

Most common form of dwarfism Caused by mutation on the fibroblast growth factor receptor 3 resulting in activation (autosomal dominant and heterozygous) FGFR3 activation inhibits chondrocyte proliferation: affects growth plates Growth plates are disorganised and hypoplastic All bones that develop by endochondral ossification are affected Short stature with stunted extremities (esp. proximal), bowed legs, frontal bossing, pronounced lordosis/kyphosis

Question 221

Osteopetrosis

Answer 221

Rare group of inherited conditions Characterised by high bone mass Due to interference with osteoclast formation and differentiation & directly affecting their action Leads to defective bone remodelling e.g. osteoclasts can not excrete H+ ions to dissolve bone mineral (needs H+ for the acidic environment) Dense 'stone bone' but brittle and easily fractured Deposited bone is not remodelled and remain as woven bone Clinical effects: fractures, spinal nerve compression (excess bone) and recurrent infection (reduced bone marrow cavity). Hepatosplenomegaly due to haematopoiesis outside the bone Bone marrow transplant to provide healthy osteoclast precursors can be effective

Question 222

Osteoporosis

Answer 222

Loss of bone mass - mineralisation of bone is normal Trabeculae are thinned and eventually cortex is thinned also. Affects areas with lots of trabecular bone (vertebrae, wrists, neck of femur) Due to: Old age Post menopausal decrease in oestrogen Disuse and reduced activity Prolonged steroid use (especially in RA) Some endocrine disease e.g. Cushings Daiagnosis:Asymptomatic pre fracture, Serum ALP, Ca and Pi levels are unreliable, 30-40% reduction in bone mass needed to be seen radiologically. No marked numbers of osteoclasts on histology: Need sensitive DEXA Clinical outcomes: Pathological fractures due to falls in the elderly Back pain and kyphosis due to compression fractures Hip replacements-fractured neck of femur Treatment: prevention (diet and exercise), Bisphosphonates, oestrogen receptor agonists, PTH

Question 223

Osteomalacia & Rickets

Answer 223

In mature bones: osteomalacia, growing bones: rickets Vitamin D deficiency or abnormal metabolism Dietary/sunlight/malabsorption (intestinal disease)/renal disease (conversion of vitamin D impaired in chronic renal failure) Normal osteoid and architecture of bone but failure of correct mineralisation of osteoid leading to soft bones (cortical and trabecular) Symptoms are bone pain (pelvis, back, legs), and if untreated structural abnormalities such as bowing of the legs In children early signs can be swelling of the epiphyses of bones (wrist) and along the costochondral cartilage of ribs. Diagnosis: X ray and labs show low serum vitamin D Treatment is by supplementation and advice on prevention

Question 224

Hyperparathyroidism

Answer 224

Calcium metabolism: Increased PTH secretion Osteoclasts stimulated to resorb bone Calcium is released into plasma Feedback to reduce PTH secretion Failure of this feedback is responsible for hyperparathyroidism: unchecked PTH secretion and osteoclast resorption More susceptible to fractures, bone deformation & joint issues Reduction PTH levels can reverse bone changes Types: Primary: Tumour - elevated serum calcium + focal osteolytic lesions Secondary: low serum calcium caused by renal disease (excessive loss via abnormal kidneys) causes hyperplasia of parathyroid glands (kidney disease causes osteomalacia

Question 225

Paget’s disease

Answer 225

Affects up to 2.5% of population In Europe and US-mostly mild cases. Excessive bone resorption by osteoclasts followed by haphazard bone formation; not related to stresses –poor architecturally Net gain in bone mass, but it is structurally weak - immature woven bone – prone to fractures Metabolic demand is high due to excessive bone turnover Bone pain (80% in axial skeleton/proximal femur), consequences of nerve impingement (headaches, back pain) Viral infection of osteoclasts (paramyxovirus) or hypersensitivity of osteoclasts?

Question 226

Osteomyelitis

Answer 226

Inflammation of the bone and marrow cavity Most common in children under 12 Almost always due to infection Staphylococcus aureus (>80%) Mycobacterium tuberculosis Escherichia Coli (particularly elderly & infants) Salmonella (sickle cell disease) Gains access by 3 main routes: Open wound Haematogenous spread Extension from an adjacent site Present with severe bone pain at sight of infection + fever & malaise Acute inflammation causes cell death - organisms move throughout the Haversian system and reach the periosteum: abscess formation (subperiosteal and in adjacent soft tissues) and impaired blood supply Can progress to chronic condition: limb deformity, fracture, increased cancer risk, spread of infection etc. TB causes caseating granulomatous inflammation in joints and vertebral bodies (Pott's disease)

Question 227

Osteonecrosis

Answer 227

Interruption of blood vascular supply leading to ischaemic necrosis and infarction due to: Fractures Steroid use Alcohol use Vessel disease (vasculitis) Haematological diseases Symptoms depend on size and location of injury Sub-chondral infarcts – present with pain during physical activity that becomes more persistent with time. Often collapse and may lead to osteoarthritis Medullary infarcts – stable and silent unless large Dead bone with empty lacunae, interspersed with fat necrosis and insoluble calcium soaps Rarely in cortical bone unaffected due to collateral supply Overlying articular cartilage remains viable due to synovial fluid (subchondral) Common locations: Femoral neck Scaphoid Talus

Question 228

Primary benign bone tumours

Answer 228

bone forming (osteoma, osteoid osteoma, osteoblastoma, osteochondroma), osteolytic (Giant cell tumour) or fibrous tumours Benign are more common than malignant, malignant are more common over age 40 Diagnosed by biopsy and histology Evaluated by radiology Location and age can give insights May present as fracture Associated with some genetic syndromes, Paget’s disease, infarction, osteomyelitis, radiation and metal orthopaedic implants though this is rare and usually the cause is unknown

Question 229

Primary malignant bone tumours

Answer 229

Osteosarcoma, Ewing sarcoma High-grade bone-forming malignant tumour of osteoblasts 20% of primary bone cancers (2nd most common) Men x1.6 compared to women Affects 2 distinct age groups. 10-25 years old – majority of cases Tumour usually arises near the end of a limb long bone (particularly around the knee) Over 60 years old 50% associated with Paget’s disease. Long bones, pelvis and vertebrae most effected Symptoms: gradually increasing bone pain as the tumour grows. Soft tissue mass if tumour extends beyond bony cortex and periosteum Radiological features: Mass with indistinct, infiltrating margins. Mix of sclerotic and lytic activity Histological features: poorly differentiated most common variety is medullary. Essential to see mineralised bone/osteoid production by malignant cells. Many mitoses Prognosis: aggressive and metastatic (haematogenous to lungs). 5 year survival 60%

Question 230

Metastatic bone tumours

Answer 230

Most metastatic bone tumours are osteolytic – erosion of bone Promotion of osteoclast activity e.g. PTH-rP Prostatic carcinoma is osteosclerotic – new bone formation Clinical features: Bone pain Pathological fracture Leucoerythroblastic anaemia Symptoms of hypercalcaemia

Question 231

Osteology: mid-distal ulna

Answer 231

Supinator fossa Head of ulna: Articular circumference of head of ulna Articular facet of head of ulna Ulnar styloid process

Question 232

Osteology: mid-distal radius

Answer 232

Radial styloid process Ulnar notch Dorsal radial tubercle Scaphoid articular facet of radius Lunate articular facet of radius

Question 233

Colles’ Fracture:

Answer 233

Dorsal displacement distal radius, ‘dinner-fork deformity’ Fall on outstretched hand (FOOSH)

Question 234

Smith’s Fracture:

Answer 234

Volar (= ventral) displacement distal radius Fall on dorsum of hand with flexed wrist

Question 235

Monteggia fracture-dislocation.

Answer 235

Ulna fracture, radial head dislocation proximally

Question 236

Galeazzi fracture-dislocation

Answer 236

Radial fracture, distal radioulnar joint dislocation

Question 237

Essex-Lopresti type injury

Answer 237

interosseus membrane rupture

Question 238

Osteology of the wrist: carpal bones

Answer 238

L->M Scaphoid, lunate, triquetrum, pisiform M->L Hamate, capitus, trapezoid, trapezium

Question 239

Radio-carpal (wrist) joint articulation and reinforcement

Answer 239

Articulation between: Distal radius, scaphoid and lunate  Radiocarpal joint Intervening articular disc between ulna and triquetrum Synovial ellipsoid joint Reinforced by: Palmar and dorsal radiocarpal ligaments Palmar and dorsal ulnocarpal ligaments Lateral (radial) collateral ligament Medial (ulnar) collateral ligament

Question 240

Intercarpal joints articulation and reinforcements

Answer 240

Synovial plane joints Contribute towards wrist movements Reinforced by: Palmar and dorsal intercarpal ligaments Ulnar and radial collateral ligaments

Question 241

carpometacarpal (CMC) joints articulation and reinforcement

Answer 241

CMC joints: Between distal row of carpal bones and metacarpal bones Synovial saddle joint for the thumb Synovial plane joints for digits 2-5 Reinforced by: articular capsules and by dorsal, palmar and interosseous ligaments

Question 242

metacarpo-phalangeal (MP) joints articulation and reinforcement

Answer 242

Articulation between: metacarpal bones and proximal row of phalanges Synovial ellipsoid joints Allow flexion/extension; adduction/abduction Reinforced by: articular capsules and by palmar ligament and collateral ligaments

Question 243

inter-phalangeal (IP) joints

Answer 243

Synovial hinge joints  flexion/extension Proximal and distal IP joints in digits 2-5 1 IP joint in the thumb Reinforced by: articular capsules and by dorsal, palmar and collateral ligaments

Question 244

Anterior forearm muscles

Answer 244

Superficial group (L->M): pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris. Intermediate: flexor digitorum superficialis deep group: flexor digitorum profundus, flexor pollicis longus and pronator quadratus

Question 245

Posterior compartment of the forearm muscles

Answer 245

Superficial: Brachioradialis Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris Deep: Supinator Abductor pollicus longus Extensor pollicus longus Extensor pollicus brevis Extensor indicis

Question 246

Nerve supply of the forearm muscles

Answer 246

All except for two muscles of the flexor/anterior compartment are innervated by the median nerve The flexor carpi ulnaris and ulnar half of flexor digitorum profundus are innervated by the ulnar nerve The radial nerve supplies all muscles of the extensor/posterior compartment

Question 247

medial and lateral epicondylitis

Answer 247

Golfers elbow - M Tennis elbow - L

Question 248

Flexor Retinaculum

Answer 248

Thick ligament Further reinforces carpal system Prevents bowstringing of tendons across wrist joint Roof of the carpal tunnel Attachments: (medial): pisiform+ hamate (lateral): scaphoid and trapezium

Question 249

Extensor Retinaculum

Answer 249

Strong, obliquely oriented ligament Prevents bowstringing of tendons across wrist joint Gives off septa  6 extensor compartments Attachments: (medial): pisiform and triquetrum (lateral): distal radius, near styloid process

Question 250

Palmar Aponeurosis

Answer 250

Anterior antebrachial fascia  palmar aponeurosis Firmly attached to palmar skin It forms fibrous digital sheaths for flexor muscles It forms deep palmar spaces Palmar aponeurosis + fascial projections  compartments of the hand

Question 251

Dupuytren’s contracture

Answer 251

Benign fibromatosis of unknown aetiology Characterised by: Finger flexion contractures Contracture of palmar aponeurosis Thickened bands of palmar/digital fascia Formation of nodules Pain, decreased range of motion (ROM) Hand function compromised Risk Factors: Northern European origin Family history of Dupuytren’s Diabetes mellitus Smoking Alcoholism Vascular disorders

Question 252

Muscles of the medial compartment of hand, nerve supply and movements

Answer 252

Palmaris brevis Abductor digiti minimi Flexor digiti minimi brevis Opponens digiti minimi Nerve supply: (branches of) ulnar nerve Movements: act on 5th digit, except for palmaris brevis

Question 253

Muscles of the central compartment of hand, nerve supply and movements

Answer 253

Adductor pollicis Origin: MCs & capitate Insertion: PP and extensor expansion of thumb Nerve supply: (deep branch of) ulnar nerve Movements: Adducts thumb Palmar and dorsal interossei Origin: MCs Insertion: PP and extensor expansion of digits Nerve supply: (deep branch of) ulnar nerve Movements: PAD and DAB Palmar interossei ADduct Dorsal interossei ABduct Lumbricals Origin: tendons of flexor digitorum profundus Insertion: extensor expansion of digits 2-5 Nerve supply: Lumbricals 1 and 2: median nerve Lumbricals 3 and 4: (deep branch of) ulnar nerve Movements: Flex digits @ metacarpophalangeal joints Extend digits @ interphalangeal joints

Question 254

Extensor expansions of hands

Answer 254

Triangular aponeuroses Tendons of extensor digitorum flatten and wrap around metacarpals and proximal phalanges Spread out distally: Central band - attaching to middle phalanx Lateral bands - attaching to distal phalanx

Question 255

Muscles of the lateral compartment of hand

Answer 255

Opponens pollicis Flexor pollicis brevis Abductor pollicis brevis Nerve supply: (branches of) median nerve Movements: act on the thumb

Question 256

The radial nerve pathway:

Answer 256

Passes anterior to the elbow joint Both the motor and sensory branches wind round to the posterior forearm

Question 257

The median nerve pathway:

Answer 257

Passes under the bicipital aponeurosis at the cubital fossa Travels down the anterior forearm Passes under the flexor retinaculum and through the carpal tunnel to enter the hand

Question 258

The ulnar nerve pathway:

Answer 258

Passes posterior to the medial epicondyle in the cubital tunnel at the elbow Re-enters the anterior compartment of the forearm Travels down the medial border of the forearm Enters the hand

Question 259

Cubital fossa boundaries and content

Answer 259

Triangular space anterior to the elbow Boundaries: Base: line drawn between epicondyles Medial border: pronator teres Lateral border: brachioradialis Floor: brachialis & supinator Roof: fascia + bicipital aponeurosis Contents: Median nerve Brachial artery Biceps Tendon Superior to roof: venous drainage and cutaneous nerves

Question 260

Hand blood supply

Answer 260

radial artery -> thumb and 1/2 of digit 2 Ulnar -> rest of digits Radial gives off deep palmar arch Ulnar gives off superficial palamr arch Both anastomose; tested by alans test

Question 261

Carpal tunnel

Answer 261

Boundaries: Floor: carpal arch Roof: flexor retinaculum Contents: Flexor digitorum profundus tendons Flexor digitorum superficialis tendons Flexor pollicis longus tendon Median nerve

Question 262

carpal tunnel syndrome

Answer 262

Idiopathic in most cases Associated with: Repetitive strain or job-related mechanical overuse Mass occupying lesions or as a result of trauma Risk factors: Diabetes Obesity female sex Age Pregnancy Hypothyroidism Rheumatologic & autoimmune disorders

Question 263

Anatomical Snuffbox

Answer 263

Boundaries: Base: wrist Medial border: tendon extensor pollicis longus Lateral border: tendon extensor pollicis brevis Floor: scaphoid & trapezium; tendons of extensor carpi radialis longus and brevis Contains radial artery Cephalic vein travels superior to it Tenderness  scaphoid fracture

Question 264

What are the thick and thin filaments made of?

Answer 264

Thick filaments Myosin Head - interacts with the thin filaments Tail - several of these come together in the centre of the sarcomere (arranged like two bunches of golf clubs, held together at the grip end) to form what we see as the M line Thin filaments Actin arranged like a twisted string of beads Tropomyosin – filamentous protein that sits in the ‘groove’ of the actin polymer and can prevent the myosin head binding to the actin Troponin complex composed of troponins C [calcium binding], T and I – regulate the position of the tropomyosin filament on the actin polymer

Question 265

muscle contraction at filament level

Answer 265

Action potentials induce the release of Ca2+ into the sarcoplasm When Ca2+ binds to troponin on the thin filament, troponin changes Shifts tropomyosin off myosin binding sites Enables myosin to bind to actin Myosin head binds to actin (ADP+Pi) Globular head bends toward center of sarcomere (ADP) thin filaments pulled toward center of sarcomere (nothing) Cross bridge link broken and head ‘unbends’ (ATP) Myosin binds to next actin molecule on the thin filament (ADP+Pi)

Question 266

Properties of slow and fast motor units

Answer 266

Slow motor units contain slow fibers: Myosin with long cycle time and therefore uses ATP at a slow rate. Many mitochondria, so large capacity to replenish ATP. Economical maintenance of force during isometric contractions and efficient performance of repetitive slow isotonic contractions. Fast motor units contain fast fibers: Myosin with rapid cycling rates. For higher power or when isometric force produced by slow motor units is insufficient. Type 2A fibers are fast and adapted for producing sustained power. Type 2X fibers are faster, but non-oxidative and fatigue rapidly.

Question 267

Visible fibre differences in muscle

Answer 267

Slow = red / high myoglobin content Fast = white / low myoglobin content

Question 268

What determines the speed of contraction/relaxation and fatigue?

Answer 268

Activation rate of Ca2+ release from SR Cross-bridge kinetics myosin ATPase, myosin HC isoform Relaxation rate Rate of removal of Ca2+ (rate of pumping back to SR) Oxidative/ gycolytic potential Mitochondrial density (capacity for O2 extraction/ use) Glycolytic capacity (anaerobic enzymes)

Question 269

What can increase force in muscle contraction

Answer 269

The force generated by a contracting muscle can be increased by: Recruiting additional MUs Increasing the firing frequency of MUs

Question 270

How can muscle activity be assesed

Answer 270

EMG = muscle activity assessed by surface or needle electrodes

Question 271

Osteology of the pelvic girdle

Answer 271

A: Obturator foramen Pubic tubercles Pubic symphysis Superior and inferior pubic rami Anterior superior iliac spine (ASIS) Anterior inferior iliac spine (AIIS) Iliac crest P: Posterior superior iliac spine Posterior inferior iliac spine Ischial spine Ischial tuberosity Sacrum & coccyx

Question 272

Sacro-iliac (SI) joints and ligaments

Answer 272

Synovial joints, become fibrous with age  ossify Irregular, interlocking joint surfaces for very little movement Weight bearing & transmission of forces Ligaments of the SI Joint: Anterior sacro-iliac ligament Interosseous sacro-iliac ligament (the strongest!) Posterior sacro-iliac ligament

Question 273

Other important ligaments of the pelvic girdle

Answer 273

Ligaments of the SI Joint: Anterior sacro-iliac ligament Interosseous sacro-iliac ligament (the strongest!) Posterior sacro-iliac ligament + Iliolumbar ligament Sacrospinous ligament  greater sciatic foramen Sacrotuberous ligament  lesser sciatic foramen

Question 274

Pubic symphysis anatomy

Answer 274

Solid, fibrocartilaginous (symphysis) Contains inter-pubic disc Ligaments reinforcing the joint: Superior pubic ligament Inferior pubic ligament

Question 275

Pubic symphysis diastasis examples

Answer 275

Pregnancy & childbirth Trauma Osteogenesis imperfecta Bladder exstrophy Hypothyroidism

Question 276

Gateways to the lower limb

Answer 276

Anterior aspect: Obturator canal: abdominopelvic region with the medial compartment of thigh.  Gap between the inguinal ligament and superior pubic ramus— abdominopelvic region with the anterior compartment of thigh.  Posterior aspect: Greater sciatic foramen  —between the pelvis and the gluteal region of the lower limb. Lesser sciatic foramen  — inferior to the greater sciatic foramen. Between gluteal region and perineum

Question 277

Osteology of the Femur

Answer 277

Head Neck Greater trochanter Lesser trochanter Shaft Distal portion Fovea capitis Intertrochanteric line Intertrochanteric crest Gluteal tuberosity Linea aspera

Question 278

The Acetabulo-femoral (hip) joint and stabilisers

Answer 278

Between femoral head and lunate surface of acetabulum Ball and socket joint, multiaxial Very stable, not quite mobile Active and passive stabilisers Very hard to dislocate Stabilisers of the acetabulo-femoral joint: (intracapsular) Ligament of the head of the femur Transverse acetabular ligament Acetabular labrum Vacuum effect Strong joint capsule & ligaments: Iliofemoral Pubofemoral Ischiofemoral

Question 279

Fasciae of the Lower Limb

Answer 279

Superficial, subcutaneous fascia In the thigh: continuous with abdominal fascia In the gluteal region: continuous with fascia of the back Deep fascia: Fascia lata Encloses tensor fasciae latae muscle Iliotibial band (tract)

Question 280

Gluteal muscles and movements

Answer 280

Gluteus maximus: Power extensor of the thigh Assists in external rotation Gluteus medius: Abduction of the thigh Medial rotation of the thigh Assists in extension of the thigh Gluteus minimus: Abduction of the thigh Medial rotation of the thigh

Question 281

Lateral rotators of the thigh

Answer 281

Piriformis: External rotation of the thigh Assists in abduction of the thigh Supplied by S1-S2 Gemellus superior Gemellus inferior Obturator internus Quadratus femoris

Question 282

Quadriceps femoris - muscles, nerve supply, attachment, movement

Answer 282

Muscles: Rectus femoris Vastus medialis Vastus lateralis Vastus intermedius (deep to rectus femoris) Nerve supply: femoral nerve (L2, L3, L4) Distal attachment: quadriceps femoris tendon Movement: leg extension at the knee

Question 283

Sartorius movements

Answer 283

Flexion, abduction, external rotation of the thigh Flexion of the leg

Question 284

Tensor fasciae latae movement

Answer 284

Abduction & flexion of thigh

Question 285

iliopsoas group

Answer 285

Power flexor of the thigh Iliacus supplied by femoral nerve Psoas supplied by L1-L3 They form a common tendon (iliopsoas muscle tendon) which inserts onto the lesser trochanter

Question 286

Medial compartment movements: Gracilis Pectineus Obturator externus

Answer 286

Movements: Adduction of the thigh: Gracilis, Pectineus Lateral rotation the thigh: Obturator externus Flexion of the leg: Gracilis

Question 287

Adductors group

Answer 287

Adductor longus Adductor brevis Adductor magnus Movements: Adduction of the thigh Medial rotation of the thigh

Question 288

Hamstrings

Answer 288

Muscles: Biceps femoris Semitendinosus Semimembranosus Movements: Extension of the thigh Flexion of the leg Medial rotation of the thigh & leg: Semitendinosus Semimembranosus Lateral rotation of the thigh & leg: Biceps femoris

Question 289

The femoral triangle

Answer 289

Boundaries: Base: inguinal ligament Medial border: adductor longus Lateral border: sartorius Floor: adductor longus, pectineus, iliopsoas Apex: opens inferiorly to continue with the adductor canal which passes through the adductor hiatus

Question 290

Main blood supply to the tissues of the thigh

Answer 290

Profunda femoris - Main supply to the tissues of the thigh (anterior and posterior compartments) Gives off: Medial and lateral circumflex arteries Penetrating branches

Question 291

Blood supply to femoral head comes from...

Answer 291

Blood supply to femoral head comes from the medial and lateral circumflex arteries They anastomose to form a ring around the neck of the femur.  small arteries perfuse the femoral head Negligible contribution from artery of the ligament of the head of the femur Fractures of the neck of femur and dislocations of the hip joint can result in avascular necrosis (osteonecrosis) of the femoral head

Question 292

Femoral fractures types

Answer 292

Due to simple falls (older patients) or high impact trauma (young patients) Fractures of the proximal femur can be intracapsular (hip fractures) or extracapsular Intracapsular fractures threaten blood supply to femoral head

Question 293

How does a femoral fractures present?

Answer 293

externally rotated and shortened right leg

Question 294

The gluteal arteries

Answer 294

Direct or indirect branches of internal iliac artery Anastomose with branches of profunda femoris around gluteal region Anastomoses may provide collateral circulation is one of the vessels is interrupted

Question 295

The obturator artery

Answer 295

Branch of the internal iliac artery Travels through the obturator canal Enters medial compartment of thigh

Question 296

The femoral artery

Answer 296

Major artery of the lower limb Continuation of the external iliac artery Travels in the femoral triangle

Question 297

lumbo-sacral plexus

Answer 297

Anterior rami of lumbar spinal nerves (L1-L4) -> lumbar plexus Anterior rami of sacral spinal nerves (L4-L5, S1-S4) -> sacral plexus L4 shared -> lumbo-sacral trunk

Question 298

Important nerves of the lower limb:

Answer 298

Femoral nerve (L2-L4) Obturator nerve (L2-L4) Sciatic nerve (L4-S3) Superior and inferior gluteal nerves

Question 299

The Femoral Nerve

Answer 299

The Femoral Nerve (L2-L4) Pathway: Passes through psoas major Leaves the abdomen beneath inguinal ligament Enters the femoral triangle Branches: Muscular: anterior compartment thigh (& pectineus) Cutaneous: anteromedial thigh & leg

Question 300

The Obturator Nerve

Answer 300

The Obturator Nerve (L2-L4) Pathway: Emerges from medial aspect of psoas major In the abdomen is deep to internal iliac vessels Enters the obturator canal Branches: Muscular: medial compartment thigh Cutaneous: medial thigh

Question 301

The Sciatic Nerve

Answer 301

The Sciatic Nerve (L4-S3) Pathway: Emerges from greater sciatic foramen Exits the pelvis inferior to piriformis Travels distally deep to the hamstrings It splits into 2 divisions above the popliteal fossa Branches: Muscular: hamstrings & posterior portion adductor magnus; all muscles leg & foot Cutaneous: posterior thigh, lateral leg and sole of foot

Question 302

The Gluteal Nerves

Answer 302

Superior Gluteal Nerve (L4-S1) Leaves the pelvis via greater sciatic foramen superior to piriformis Motor supply: gluteus medius and minimus, tensor fasciae latae Inferior Gluteal Nerve (L5-S2) Leaves the pelvis via greater sciatic foramen inferior to piriformis Motor supply: gluteus maximus

Question 303

safe injection site in gluteal region

Answer 303

The upper lateral quadrant is the ‘safe zone’ for intramuscular gluteal injections – you’re unlikely to hit the sciatic and gluteal nerves up here!

Question 304

Primary Survey of a trauma patient

Answer 304

Primary Survey ABCDE C Catastrophic Haemorrhage Control A Airway and C-spine management B Breathing C Circulation and Haemorrhage Control D Disability E Exposure

Question 305

Classes of shock types

Answer 305

Hypovolaemic, Obstructive, cardiogenic, distributive

Question 306

Shock definition

Answer 306

Abnormality of the circulatory system that results in inadequate organ perfusion and tissue oxygenation

Question 307

Statistical tests for two groups of data

Answer 307

Unpaired (independent) t-test - Samples that are not related to each other (i.e. comparisons are made between values that are recorded from different individuals) Paired t-test - Samples that are related to each other (i.e. comparisons are made between values recorded from the same individual) The non-parametric version of an unpaired t-test is the Mann-Whitney U test The non-parametric version of a paired t-test is the Wilcoxen signed-ranks test

Question 308

Statistical tests for more than one set of data

Answer 308

A one-way ANOVA tests the difference in means of two or more unmatched groups. The non-parametric version of a one-way ANOVA is the Kruskal-Wallis test Two-way ANOVAs are used when two experimental factors are being manipulated. Repeated measures one-way ANOVA - The difference between an ordinary and repeated measures ANOVA is similar to the difference between unpaired and paired t-tests. The term repeated measures means that you give treatments repeatedly to each subject.

Question 309

Femur osteological landmarks

Answer 309

Medial and lateral condyles Articular surfaces of the condyles Intercondylar fossa Medial and lateral epicondyles Adductor tubercle Patellar surface

Question 310

Tibia osteological landmarks

Answer 310

Tibia: Tibial plateau Medial and lateral condyles Intercondylar eminence Tibial tuberosity Articular facet for the fibula Medial malleolus Articular surface for the talus

Question 311

Fibula osteological landmarks

Answer 311

Head Facet for articulation with the tibia Neck Shaft Lateral malleolus Articular surface for the talus

Question 312

Clinical applications of anatomy: Genu varum & genu valgum

Answer 312

Genu varum = knees spread apart genu valgum = knock knee

Question 313

The knee joint: Intra- articular stabilisers

Answer 313

Medial & lateral menisci Anterior & posterior cruciate ligaments Transverse ligament Coronary (menisco-tibial) ligament

Question 314

Meniscal pathology and s $ s

Answer 314

Acute tears can occur in young sports people Degenerative tears occur in older people Signs and symptoms: Swelling, pain, tenderness, crepitus Sensation of instability or buckling/’locking’ of the knee Meniscectomy  secondary osteoarthritis

Question 315

Intra-articular structures of the knee: Cruciate ligaments

Answer 315

Resistance to displacement of the tibia relative to the femur: Anterior cruciate ligament (ACL) – restraint to anterior displacement Posterior cruciate ligament (PCL) – restraint to posterior displacement Provide some mediolateral stability too

Question 316

How is ACL most commonly damaged?

Answer 316

Deceleration injuries are the most common mechanism of injury

Question 317

The knee joint: Extra-articular stabilisers

Answer 317

Joint capsule merging with tendinous expansions Patellar ligament Oblique and arcuate popliteal ligaments Ilio-tibial band Tibial (medial) and fibular (lateral) collateral ligaments

Question 318

The Knee joint: Collateral ligaments stability

Answer 318

The collateral ligaments of the knee provide passive stability to the joint especially to varus and valgus stresses Collateral ligaments, cruciate ligaments & popliteal ligaments pulled taut in extension  knee is more stable in full extension (close packed position)

Question 319

Where is arthrocentesis performed for inflammatory arthirits

Answer 319

arthrocentesis of the suprapatellar bursa of the knee joint in a patient with inflammatory arthritis.

Question 320

Tibiofibular Joint types

Answer 320

Proximal tibio-fibular joint: Synovial plane Interosseous membrane Distal tibiofibular joint: Syndesmosis but slight rotation to accompany movements of the ankle

Question 321

tarsal bones

Answer 321

Proximal group: Talus & calcaneus Intermediate bone: Navicular Distal group (lateral to medial): Cuboid; lateral, intermediate & medial cuneiforms

Question 322

Ankle joint structure and stabilisers

Answer 322

Between distal tibia and fibula & talus Synovial hinge joint with a ‘mortice & tenon’ or ‘nut & wrench’ configuration Plantarflexion and dorsiflexion Deltoid (or medial collateral): Tibionavicular, tibiocalcaneal, and posterior tibiotalar Anterior tibiotalar ligament Lateral ligaments: Anterior talofibular ligament Posterior talofibular ligament Calcaneofibular ligament

Question 323

The subtalar and transverse tarsal joints and related ligaments

Answer 323

Subtalar joint: Between talus and calcaneus Synovial plane joint Midtarsal joints: Functional unit formed by: Talocalcaneonavicular joint, Calcaneocuboid joint Ligaments: Plantar calcaneonavicular (spring) Plantar and dorsal calcaneocuboid Long plantar ligament Bifurcate ligament

Question 324

Joints of the foot and type

Answer 324

Tarsometatarsal (TMT) joints: Synovial plane joints Intermetatarsal joints: Synovial plane joints Metatarsophalangeal (MTP) joints: Synovial condyloid joints Interphalangeal (IP) joints: Synovial hinge joints

Question 325

Clinical applications of anatomy: Osteoarthritis of the hand and foot

Answer 325

Whereas the CMCJ of the thumb is a common site for osteoarthritis and deformity, the MTPJ of the great toe (hallux) is a common site for degenerative processes which result in a valgus deformity (hallux valgus or a ‘bunion’)

Question 326

Muscle compartments of the leg, main action and innervation

Answer 326

Anterior compartment: Dorsiflexion of the foot Extension of toes Supplied by deep fibular (peroneal) nerve Lateral compartment: Eversion of foot Supplied by superficial fibular (peroneal) nerve Posterior compartment: Superficial group: Plantarflexion of foot Deep group: Plantarflexion & inversion of foot Flexion of toes Supplied by tibial nerve

Question 327

Anterior compartment of the leg - muscles, innervation, movements

Answer 327

Muscles: Tibialis anterior Extensor hallucis longus Extensor digitorum longus Fibularis (peroneus) tertius Nerve supply: Deep fibular (peroneal) nerve Movements: All: Dorsiflexion of the foot Extensor digitorum & hallucis longus: extension toes & hallux Tibialis anterior: inversion of the foot & dynamic support arches of the foot Fibularis tertius: eversion of the foot

Question 328

Lateral compartment of the leg - muscles, innervation, movements

Answer 328

Muscles: Fibularis (peroneus) longus Fibularis (peroneus) brevis Nerve supply: Superficial fibular (peroneal) nerve Movements: All: Eversion of the foot Fibularis (peroneus) longus: plantarflexion of foot & support for arches of foot

Question 329

Posterior compartment of the leg - muscles, innervation, movements

Answer 329

Muscles of the superficial layer: Gastrocnemius Plantaris Soleus All attach to calcaneus via calcaneal (Achille’s) tendon Nerve supply: Tibial nerve Movements: All: Plantarflexion of the foot Gastrocnemius & plantaris: Flexion of the leg @ the knee Muscles of the deep layer: Tibialis posterior Flexor hallucis longus Flexor digitorum longus Popliteus Nerve supply: Tibial nerve All (except popliteus): Plantarflexion of the foot Flexor digitorum & hallucis longus: Flexion toes & hallux Tibialis posterior: Inversion of the foot & dynamic support medial arch Popliteus: Acts on the knee joint

Question 330

Spinal segments innervating leg muscles

Answer 330

Anterior: All these muscles are supplied by the spinal segments L5-S1, except tibialis anterior (L4, L5) Lateral: All these muscles are supplied by the spinal segments L5, S1, S2 Posterior superficial : All these muscles are supplied by the tibial nerve, spinal segments S1, S2 Posterior Deep: Flexor digitorum and hallucis longus supplied by S2,S3; tibialis posterior by L4, L5; popliteus by L4, L5, S1

Question 331

Locking/unlocking mechanism of the knee, by which muscle

Answer 331

Popliteus rotates femur over the tibia Origin: lateral femoral condyle Insertion: posterior surface proximal tibia Functions: Stabilises knee joint Unlocks knee joint (laterally rotates femur on tibia)

Question 332

The arches of the foot

Answer 332

Longitudinal arches Calcaneus -> head of metatarsals Lateral and medial Transverse arch On the coronal plane; Highest proximally (near the talus) Active support: Extrinsic and intrinsic muscles Weakness of these muscle groups will result in pes planus (flat feet) Passive support: Bones, joints and ligaments

Question 333

The popliteal fossa

Answer 333

Superomedial border: semitendinosus & semimembranosus Superolateral border: biceps femoris Inferomedial border: medial head gastrocnemius Inferolateral border: lateral head gastrocnemius Floor: knee joint capsule + popliteus inferiorly Roof: deep fascia Contents: Common fibular nerve Tibial nerve Popliteal artery Popliteal vein

Question 334

The tarsal tunnel

Answer 334

Formed by: Depression found between: Medial malleolus Posteromedial surfaces of the talus Medial surface of calcaneus Overlying flexor retinaculum Contents (A->P): Tibialis Posterior tendon Flexor Digitorum longus tendon Posterior tibial Artery Tibial Vein Tibial Nerve Flexor Hallucis longus tendon

Question 335

Blood supply of leg

Answer 335

Femoral -> popliteal -> anterior tibial artery -> dorsal pedis -> posterior tibial artery -> fibular artery

Question 336

Venous drainage of the lower limb

Answer 336

Deep veins follow the arteries Superficial venous system: Dorsal venous arch of the foot Great saphenous vein (medial)  drains into femoral vein Small saphenous vein (lateral)  drains into popliteal vein Popliteal vein receives blood from tibial veins Popliteal vein becomes femoral vein Femoral vein  external iliac vein External iliac vein  common iliac vein Common iliac vein  IVC

Question 337

The sciatic nerve (L4-S3) and its branches

Answer 337

The sciatic nerve enters the posterior compartment of the thigh where it divides into the tibial (L4-S3) and common fibular (L4-S2) nerves The tibial nerve enters the leg through the popliteal fossa and gives off a cutaneous branch (sural nerve) – the tibial nerve enters the sole of the foot through the tarsal tunnel (behind the medial malleolus) The common fibular nerve enters the leg through the popliteal fossa and then winds round the neck of the fibula to enter the lateral compartment of the leg It divides into the superficial and deep fibular branches The superficial fibular nerve continues in the lateral compartment of the leg and supplies the muscles here The deep fibular nerve enters the anterior compartment of the leg and supplies the muscles found here

Question 338

Clinical applications of anatomy: Sciatic, tibial, common fibular Nerve lesions & resultant muscle weakness

Answer 338

Sciatic nerve May be damaged by posterior dislocations of the hip joint Results in weakness of posterior thigh muscle group (hamstrings) and weakness of all leg and foot muscles Tibial nerve Vulnerable to compression in the tarsal tunnel Results in weakness of foot muscles Common fibular nerve Is easily compressed at the neck of the fibula e.g. by plaster casts or sitting crossed legged Results in foot drop/loss of dorsiflexion due to weakness of anterior and lateral leg muscles

Question 339

Embryology; Week 1: Fertilisation to Implantation

Answer 339

Fertilisation and Cleavage The early rapid, multiple rounds of cell division which occur in the first few days after fertilization Morula Development Means ‘mulberry’ – when the fertilized cell has divided into a solid mass of cells (12-16 cells) Occurs by the 3rd day following fertilization Blastocyst Development and Implantation The name for the hollow cellular mass that forms after the morula and about 4-5 days after fertilization The process of attachment and invasion of the uterus endometrium by the blastocyst (conceptus)

Question 340

Embyology; Week 2 and 3: Bilaminar and Trilaminar Disc Development

Answer 340

Bilaminar Disc Formation Cells of the inner cell mass or embryoblast differentiate into the hypoblast layer (yellow) and epiblast layer (blue) Gastrulation (Trilaminar Disc Formation) Gastrulation begins with formation of the primitive streak on the surface of the epiblast layer Cells of the epiblast layer migrate toward the primitive streak and then slip underneath it (invaginate) Once the cells have invaginated, some displace the hypoblast, creating the embryonic endoderm Other cells come to lie between the epiblast and newly-created endoderm to form mesoderm Cells that do not migrate through the streak but remain in the epiblast form ectoderm

Question 341

Embyology; Week 3: Notochord Formation

Answer 341

Notochordal Plate The notochordal plate forms in the midline during the development of the trilaminar embryonic disc Notochord The definitive notochord develops from cells of the notochordal plate, which proliferate and detach to form this solid cord of mesodermal cells The notochord lies in the midline, under the neural tube It is a signalling centre for inducing the axial skeleton – it will eventually disappear but does form the nucleus pulposus of the intervertebral discs

Question 342

Neurulation

Answer 342

Neural Plate Development The appearance of the notochord induces the overlying ectoderm to thicken and form the neural plate (start of the 3rd week) This begins the process of neurulation Neurulation Neurulation is the process whereby the neural plate forms the neural tube The neural plate lengthens and as it does so its lateral edges elevate to form neural folds with the neural groove lying in the middle Gradually, the neural folds approach each other in the midline, where they fuse together This forms the neural tube

Question 343

Development of spinal nerves

Answer 343

A 25-day (3.5 week) embryo showing the structure of the neural tube wall and central lumen The cells of the wall of the neural tube are called neuroepithelial cells and they form the neuroepithelium The neuroepithelial cells give rise to neuroblast cells (primitive neurons) Neuroblast cells form the mantle layer (yellow in images below) The mantle layer goes on to form the alar plate and basal plate thickenings in the primitive spinal cord alar plate forms the sensory dorsal horn of the spinal cord The basal plate contains the cell bodies of motor nerve cells and forms the ventral motor horn

Question 344

How do motor neurons develop?

Answer 344

Motor axons from primitive nerve cells (neuroblasts) grow out from the basal plate (ventral horn) of the developing spinal cord They will form the ventral (motor) rootlets of the spinal nerves

Question 345

How do sensory neurons develop?

Answer 345

Neural crest cells form spinal sensory ganglia: Neural crest cells, which are ectodermal in origin, (light blue in image A and B) will migrate from the edges of the neural folds to form (amongst other things) spinal sensory ganglia - eg the dorsal root ganglion During further development, the neuroblasts (ie primitive neurons) in the sensory ganglia form two processes (remember that sensory neurons are pseudo-unipolar neurons) The central process: the centrally growing processes grow towards to the neural tube and penetrate the dorsal portion of the neural tube and terminate in the dorsal horn (alar plate area) – these central processes form the dorsal (sensory) rootlets of the spinal nerve The peripheral process: the peripherally growing processes join with fibres of the ventral motor roots to form the (mixed ie sensory and motor) spinal nerve – eventually these peripheral processes will grow outwards and terminate in the relevant sensory receptor organ (eg a temperature receptor in the index finger)

Question 346

How do sympathetic neurons develop?

Answer 346

The cell bodies of pre-ganglionic sympathetic neurons lie in the gray matter of the intermediate horn of the developing spinal cord – this area of the gray matter only exists at thoracic (T1–T12) and upper lumbar levels (L1 or L2) of the spinal cord! Post-ganglionic sympathetic neurons and the associated sympathetic ganglia (eg in the sympathetic chain) develop from neural crest cells, which migrate to their relevant location in the body

Question 347

Embryology Week 3-8: Development of the Somites – review of mesoderm

Answer 347

By approximately the 17th day (image B), mesoderm cells of the trilaminar disc close to the midline proliferate and form a thickened plate of tissue known as paraxial mesoderm By the start of week 3 the paraxial mesoderm has begun to organize itself into segments, called somites By the end of week 5 there are 42-44 pairs of somites in the embryo

Question 348

Embrology; Week 4: Somite Differentiation

Answer 348

With further development, some of the cells of the somite will come to surround the neural tube to form the sclerotome (image C) This collection of cells will differentiate into the vertebrae and ribs Some of the cells of the somite form the myotome These cells will form the muscles of the back, body wall and limbs Some of the cells of the somite gather together to form the dermatome These cells will form the dermis in the back, body wall and limbs

Question 349

Sclerotome

Answer 349

At the end of the fourth week, sclerotome cells (of the somite) form loosely organized tissue, called mesenchyme or embryonic connective tissue (blue structure in image above) Mesenchymal cells can become fibroblasts, chondroblasts or osteoblasts and will go on to form The vertebrae (eg the neural arch, vertebral canal, vertebral body and transverse and spinous processes) The annulus fibrosus of the intervertebral disc The ribs

Question 350

Embyrology; limb development

Answer 350

At the end of the 4th week of development, visible out-pocketings from the ventrolateral body wall can be seen (NB the upper limb develops before the lower limb) At the end of the 5th week of development, limb buds become visible In the 6th week the terminal portion of the limb buds become flattened to form the handplates and footplates Fingers and toes are then formed as a result of cell death (apoptosis) In the 7th week, the limbs rotate in different directions The upper limb rotates 90° laterally The extensor muscles then lie on the lateral and posterior surface The thumbs lie laterally The lower limb rotates approximately 90° medially The extensor muscles then lie on the anterior surface The big toe lies medially By the 10th week, the shafts of the limb bones are partly ossified (brown), although much of the skeleton and especially the distal bones (e.g. the carpal bones) remain cartilaginous (blue) at birth

Question 351

Carpal ossification

Answer 351

At birth, there is no calcification in the carpal bones The capitate ossifies between 1-3 months after birth The hamate ossifies between 2-4 months after birth The whole carpus is not ossified until a child is 8-12 years of age!

Question 352

Limb and digital defects: Amelia, meromelia, Brachydactyly, Syndactyly (fused digits), Polydactyly, Cleft foot

Answer 352

Unilateral complete absence (amelia) of the an upper limb meromelia (partial absence) called phocomelia - the long bones are absent, and rudimentary hands and feet are attached to the trunk by small, irregularly shaped bones A: Brachydactyly (short digits) B: Syndactyly (fused digits)   C: Polydactyly (extra digits)   D: Cleft foot – an abnormal cleft between the 2nd and 4th MT/MC

Question 353

skeletal muscle development

Answer 353

Skeletal muscle is derived from paraxial mesoderm (which forms the somites) and lateral plate mesoderm Cells of the paraxial mesoderm which stay close to the neural tube will form the epiaxial muscles (i.e. the muscles of the back) Epiaxial muscles (from paraxial mesoderm) – form the muscles of the back (e.g. erector spinae) They are supplied by the dorsal rami of spinal nerves Some paraxial mesoderm cells will migrate to the lateral plate parietal layer of mesoderm to form the hypaxial muscles (i.e. the muscles of the body wall and limbs) Hypaxial muscles (from lateral plate mesoderm) – form the muscles of the body wall and limbs As muscle cells move into the limb, they split into dorsal (extensor) and ventral (flexor) muscle compartments They are supplied by the ventral rami of spinal nerves