Week 1 Flashcards

Question

What are some of the important differences between skeletal and cardiac muscle?

Answer 1

Initation of propagation of contraction * skeletal is neurogenic, NMJs are present and there are no gap junctions i.e. excitation cannot spread from cell to cell * cardiac is cardiogenic (contraction is initiated by pacemaker cells, there are no NMJs but gap junctions are present Excitation contraction coupling * skeletal - Ca2+ comes **entirely from the sarcoplasmic reticulum** * cardiac - Ca2+ comes from both the **ECF** and **the sarcoplasmic reticulum** (calcium-induced calcium release)

Answer 2

A **single** alpha motor neurone, along with **all** the muscle fibres it innervates The number of motor units determines the function of the muscle... * few motor units = precision * many motor units = power generation

Answer 3

**Whole muscle** is made up of... * **Muscle fibre** (one cell) contains many... * **Myofibril** (specialised intracellular structure * **Sarcomere** (functional unit) * Myocin (thick, darker filaments) * Actin (thin, lighter filaments

Answer 4

Sarcomeres, made up of overlapping actin (thin filaments) and myocin (thick filaments)

Answer 5

**A-band -** made up of thick filaments with overlapping portions of thin filaments at both ends **H-zone -** lighter area within the middle of the A-band where thin filaments don't reach **M-line -** extends vertically down the middle of A-band within the centre of H-zone **I-band -** consists of the remaining portion of thin filaments that do not project into A-band **Z-lines -** border of the sarcomere, connect the thin filaments of 2 adjoining sarcomeres

Answer 6

Asynchronous motor unit recruitment during submaximal contractions helps to prevent muscle fatigue

Answer 7

Frequency of stimulation and summation of contractions Length of muscle fibre at the onset of contraction Thickness of the musce fibre

Answer 8

Duration of action potential is much shorter than that of twitch, meaning that repetitive action potentials can bring about a stronger contraction via a summation of twitches. The tension developed by skeletal muscle increases with increasing frequency of stimulation. If a muscle fibre is stimulated so rapidly that it doesn't have an opportunity to relax, a maximal sustained contraction known as a **tetanus** occurs.

Answer 9

**Isotonic contraction** (muscle tension remains constant as the muscle length changes) - used for... * body movements * moving objects **Isometric contraction** (muscle tension develops at constant muscle length - used for * supporting objects in a fixed position * maintaining body posture

Answer 10

Suspect - history, examination etc. Sample - gold standard is bone biopsy, also use cross-sectional imaging Treat - wait until the results of biopsy, unless patient is septic/acutely unwell

Answer 11

Debrided bone takes approx 6 weeks to be covered by vascularised soft tissue, and must be protected during this time

Answer 12

If the patient is septic, has acute illness or is unstable then empirical broad-spectrum antibiotics can be used.

Answer 13

Streptococcus Alpha haemolytic - pneumoniae, viridans Beta haemolytic - Groups A, B and C Strep Gamma haemolytic - enterococcus spp

Answer 14

Staphylococcus Coagulase +ve - Staph. aureus Coagulase -ve - Staph epidermidis Some strains produce toxins e.g. enterotoxin, SSSST, PVL Treatment of choice is **FLUCLOXACILLIN**, alternatively Vancomycin if patient is \*properly\* allergic

Answer 15

Early management is key - aggressive debridement, fixation and soft tissue cover Treat for Staph aureus (Flucloxacillin) and aerobic gram negative bacteria (Gentamicin)

Answer 16

Often polymicrobial i.e. often anaerobes and gram -ves, as well as Staph. Probe to bone, and upon receiving results treat with debridement and antimicrobials Staph - fluclox gram -ves - gentamicin anaerobes - metronidazole

Answer 17

Imaging studies - **MRI scan**

Answer 18

Staphylococcus, typically Streptococci More unusual pathogens - pseudomonas, candida, mycobacterium TB

Answer 19

The addition of Rifampicin - allows penetration of the sessile biofilm of bacteria lining the prosthesis. NEVER give Rifampicin by itself to treat Staph infections however, give alongside fluclox. to prevent the development of resistance

Answer 20

Bones - 6 weeks Joints - 4 weeks

Answer 21

Staphylococcus aureus Streptococci Coag -ve staphylococci if prosthetic joints are present Possible Neisseria gonorrhoea if patient is sexually active

Answer 22

Gout, need to exclude crystal formation High doses of Flucloxacillin to cover presumptive Staph aureus, if the patient is less than 5 years old then add Ceftriaxone to cover Haemophilus influenzae

Answer 23

Debridement is paramount, followed by antibiotic therapy - antibiotics cannot penetrate necrotic/pus-covered tissues. Important to bear in mind that the presenting symptom from the patient may just be very localised severe pain.

Answer 24

**Toxin-mediated** infection - *Clostridium tetani* Gram +ve strictly anaerobic rods (loves dead tissue). The neurotoxin causes spastic paralysis by binding to inhibitory neurones and preventing the release of neurotransmitters. Important to remember that the bacteria itself is not invasive, and the damage is done purely by the toxin

Answer 25

Cardiac - centred nucleus Skeletal - nuclei are moved to the edge of the elongated syncitium (many cells fused together)

Answer 26

Fascicles Epimysium Perimysium Endomysium

Answer 27

Sarcomere Myofibril

Answer 28

Type I * relatively slowly contracting fibres that depend on **oxidative metabolism** * abundant mitochondria and myoglobin * resistant to fatigue and produce less force * 'red' in colour Type IIA * intermediate between I and IIB * relatively fast contracting but also reasonably resistant to fatigue * relatively uncommon Type IIB * fast contracting fibres that depend of **anaerobic metabolism** * Few mitochondria and less myoglobin * Fatigue relatively easily but produce greater force * 'White' in colour

Answer 29

Cartilage * semi-rigid, deformable * permeable * avascular * cells nourished via diffusion through the ECM Bone * rigid * non-permeable * cells within bone must be nourished by blood vessels that pervade the tissue

Answer 30

Found in the cartilage (chondroblasts when immature) Live within a space in the ECM known as the **lacuna** Both excrete and maintain the ECM that surrounds them.

Answer 31

75% water 25% organic material * 60% is type II collagen (forms a 3D meshwork rather than linear bundles like type I) * 40% proteoglycan aggregates (made up of GAGs - most commonly keratin sulfate and chondroitin sulfate)

Answer 32

**Hyaline cartilage** - most common type **Elastic cartilage** - elastic fibres make it quite flexible **Fibrocartilage** - hybdrin between tendon and hyaline. has bands of densely packed type I collagen interleaved with rows of chondrocytes, surrounded by small amounts of cartilagenous ECM.

Answer 33

Articular surfaces Tracheal rings Costal cartilage Epiphyseal growth plates

Answer 34

Protection of vital organs Support of structure Calcium store - 95% of all calcium is stored in bone, constant exchange between bone and blood Haemopoiesis - mostly in utero, and by early twenties typically only the axial and limb girdle are still involved in blood production

Answer 35

cortical bone, diaphysis cancellous/trabecular bone, epiphysis

Answer 36

Osteon - layers of collagen are in alternating directions, giving bone a great deal of strength (similar to plywood) Haversian's canal runs vertically through the centre of the osteon. Volkmann's canal runs horizontally through the osteon, connecting neighbouring Haversian canals.

Answer 37

Bone cells of the matrix are similar, but trabecular bone also has numerous spaces throughout the matrix (marrow cavities)

Answer 38

As bone is a living tissue it needs a nutrient supply. This is in the form of small canals running through the bone that contain blood vessels, nerves and osteocytes. Trabecular bone typically lacks Haversian canals

Answer 39

* located on bone surface, serve as a pool of reserve oseoblasts * bone-forming cells found on the surface of developing bones, plentiful RER and mitochondria * bone cell trapped within the bone matrix * "bone destroyer", large multinucleated cells thought to be due to fusion of multiple macrophages. Found on bone surface and responsible for bone resorption

Answer 40

Organic components (collagen, GAGs, proteoglycans etc.) secreted by osteoblasts. Becomes mineralised over time in the ECM to become bone.

Answer 41

Fibrous - e.g. elbow, knee Synovial - e.g. fusion of skull bones Cartilagenous - e.g. intervertebral discs, pubic symphsis

Answer 42

* bones are separated by a **cavity** containing **synovial fluid** and lined by a **fibrous capsule** * Inner aspect of capsule is lined with a **synovial membrane** which contains synovial cells (SCs, fibroblasts). These cells secrete **synovial fluid** * Surfaces of the bones are lined with **articular hyaline cartilage** * Can be classified as either **simple** or **compound**, depending on how many bones/articular surfaces are involved

Answer 43

Tendons Ligaments Bursae

Answer 44

Cartilage interstitial fluid Synovium-derived hyaluronic acid (**mucin**) Synovium-derived **lubricin** - glycoprotein

Answer 45

Lubricates joint, facilitates joint movements and reduces wear and tear Aids in the nutrition of articular cartilage by supplying chondrocytes with O₂ and nutrients, and removing CO₂ and waste products

Answer 46

* Continuously reabsorbed and replenished by the synovial membrane * High viscosity due to the presence of mucin * Normally contains few cells (mainly mononuclear lymphocytes) Movement * Rapid movement is associated with decreased viscosity and increased elasticity, and vice versa in stasis Disease * Inflammation - low viscosity, straw colour, increase in total white cell count from less than 200 to 2,000 - 75,000 * Sepsis - Variable viscosity and colour, extremely high WBC count (\>100,000)

Answer 47

Superficial zone (10-20%) Middle zone (40-60%) Deep zone (30%) Calcified zone Zones differ in organisation of collagen fibres and relative content of cartilage components

Answer 48

Made predominantly of water (70%) - unevenly distributed with more towards the articular surface and % decreases with age 20% collagen (mainly type II) - contributes to the elastic behavior of cartilage and provides tensile strength. Decreases with age 10% proteoglycans - mostly present in the middle and deep zones and confers compressive properties used in load bearing. Composed mainly of GAGs e.g. chondroitin sulphate, which decreases with age

Answer 49

98% ECM 2% chondrocytes - synthesises, organises and degrades ECM. Receives nutrients and O2 via synovial fluid (as articular cartilage is avascular)

Answer 50

* Changes in the relative amounts of the 3 major components that make up cartilage * Water * Collagen * Proteoglycans * If the rate of ECM degradation exceeds the rate at which it is synthesised and replaced

Answer 51

**Catabolic** * Stimulate proteolytic enzymes and **inhibit proteoglycan synthesis** * TNF-alpha * IL-1 **Anabolic** * **Stimulates proteoglycan synthesis** and counteract the effects of IL-1 * TGF-beta * Insulin-like growth factor (IGF)-1

Answer 52

**Serum and synovial** **keratin sulphate** (mainly found in proteoglycans) - increased levels = cartilage breakdown, levels increase with age and in patients with osteoarthritis **Type II collagen in synovial fluid** - increased levels = cartilage breakdown. Useful in evaluating cartilage breakdown

Answer 53

Myelinated axons and cell bodies while travelling down the spinal cord. The axon then divides into unmyelinated branches near the surface of the muscle, with each branch innervating a separate skeletal muscle fibre. This is known as a **motor unit.** Each of these branches further subdivides into multiple fine branches that end in a terminal bouton and form a chemical synapse with the NMJ on the muscle membrane. **ACh** is the neurotransmitter involved and acts on nicotinic ACh receptors

Answer 54

* terminal bouton (and surrounding Schwann cell) * synaptic vesciles containing ACh that release upon AP causing depolarisation * synaptic clefts in the muscle cell containing nicotinic ACh receptors * the end plate region of the muscle cell membrane (**sarcolemma**)

Answer 55

* **Synthesis** of ACh from choline and acetyl CoA by choline acetyltransferase * **Storage** in vesicles * **Release** upon the entering of Ca2+ into pre-synaptic terminal * **Receptor activation** on the post-synaptic end-plate, allowing Na+ to flow into the muscle cell and cause a contraction * **Neurotransmitter deactivation** via acetylecholinesterase, which hydrolyses ACh into choline and acetate. Choline is taken back into the pre-synapse via a **choline-sodium symporter**

Answer 56

* Nicotinic ACh receptors are arranged in a pentamer of glycoprotein subunits (2 alpha, 1 beta, 1 delta and 1 epsilon) that surround a central **cation-selective pore** * Binding of ACh causes a conformational change, which allows each subunit to rotate and move their amino-acid side chain from blocking the pore. * This allows Na+ to flow into the cell, and K+ to flow out of the cell. The permeability for these two ions is roughly similar, however because the **driving force for Na+ is greater than that of K+**, influx of Na+ is greater than efflux of K+. * This generates a depolarisation known as the **end plate potential (e.p.p.)**

Answer 57

A quantum is fairly fixed size of vesicle that contains numerous ACh molecules. The electronic response to the release of a single quantum is known as the miniature end plate potential. Many m.e.p.p.s summate to produce an e.p.p. and, if this exceeds the threshold, an 'all or nothing' response is achieved that generates a contraction **Note - it is NOT the e.p.p. that generates the contraction, but rather the AP that the e.p.p. elicits**

Answer 58

The presence of voltage-activated Na+ channels along the muscle fibre, allows the propagation of action potentials along the muscle fibre and the generation of a contraction

Answer 59

AP enters the **transverse tubules** (invaginations of the sarcolemma that travel deep down into the muscle cell), which are located closely to the **sarcoplasmic reticulum** (Ca2+ store) When the AP reaches the transverse tubules, this causes a release of Ca2+ from the SR which in turn causes contraction by interacting with troponin associated with myofibrils

Answer 60

* Nociceptive - adaptive * Inflammatory - adaptive * Pathological - maladaptive

Answer 61

**Glutamate** - fast **Peptide** - slower Both of these are transmitted to secondary receptors in the spinal cord. Nociceptors are **1st (order) degree neurones**

Answer 62

Adaptive - serves a biological purpose High threshold - only provoked by intense stimuli that activate nociceptors Nociceptive pain overrides most ongoing activities in the nervous system, prompting an autonomic response and withdrawal relfex. It also engages an emotional response and inscribes preventative memories.

Answer 63

Adaptive and protective, inolves activation of the immune system and assists in healing of a damaged body part. Although adaptive, does require suppression of ongoing inflammatory response. Hypersensitivity - heightened response to minor stimuli Allodynia - previously innocuous stimuli elicit severe pain

Answer 64

Maladaptive - abnormal nervous system function that serves no process. **Neuropathic** - e.g. damage to peripheral nerves, neural lesions resulting in faulty nervous system activity etc. Associated with both hypersensitivity/allodynia and desensitisation Dysfunctional - no apparent cause, only associated with positive symptoms i.e. no desensitisation.

Answer 65

Muscle fibres are bound into **fascicles** Within the fascicle, the connective tissue covering the muscle fibres is the **endomysium**

Answer 66

The **perimysium**

Answer 67

Actin are **thin, lighter-coloured** filaments Myocin are **thick, darker-coloured** filaments A sarcomere is the unit of muscle contraction, and comprises the area between **two Z-discs**

Week 1 Flashcards

(93 cards)