Nerve supply of the limbs

Question 1

Cross sectional structure of the spinal cord

Answer 1

• central region of grey matter surrounded by white matter

Question 2

Function of white matter

Answer 2

arranged in columns containing the nerves containing the brain and spinal cord

Question 3

Structure of grey matter

Answer 3

• H shape around a central canal

- grey matter broadly divided into two dorsal horns and two ventral horns (posterior and anterior respectively)

Question 4

What are the dorsal and ventral roots?

Answer 4

Pairs of spinal nerves each formed by the fusion of nerve segments knows as the ventral and dorsal roots

Question 5

What are the rami?

Answer 5

The dorsal root, containing sensory information and the ventral root containing motor, join together and then branch off to form the ventral and dorsal rami, each with a mixture of nerves

Question 6

The posterior (dorsal) ramus structure and function

Answer 6

Supplies muscles and sensation to the back- extensors of spine and overlying skin

The dorsal ramus of each spinal nerve travels backward, apart from C1, L4,L5 and coccygeal

Each posterior ramus innervates a narrow strip of skin and muscle along the back, more or less at the level at which it leaves the spinal nerve

Question 7

The anterior (ventral) ramus structure and function

Answer 7

• supply anterograde-lateral parts of the trunk and the limbs
• anger than dorsal rami
• in thoracic region, each ventral ramus supplies a narrow strip of muscle and skin along the sides, chests, ribs and abdominal wall- refereed to as intercostal nerves
• in regions other than thoracic, the nerves from different rami combine to form plexuses

Question 8

What are plexuses?

Answer 8

A network of tangled nerves from different ventral rami, thus containing several spina; nerves

Question 9

What is the benefit of nerve plexuses?

Answer 9

Fibres from each ventral ramus travels along different routes so that each limb muscle receives innervation from several spinal nerves, thus there is a back up plan in case of injury

Question 10

What is the brachial plexus?

Answer 10

Group of nerve fibres that gets its contribution from the transitional area from neck into axilla, between C5-T1

Question 11

Brachial plexus function

Answer 11

Provides almost all the innervation of the upper limb, including the back and scapular muscles that control the limb

Question 12

5 stages in a plexus

Answer 12

root-trunk-division-cord-terminal

Question 13

5 major nerves in the arm + their roots

Answer 13

Musculocutaneous- C5- C7

Axillary- C5-C6

Radial- C5-T1

Median- C5-T1

Ulnar- C8, T1

Question 14

Lumbosacral plexus function and roots

Answer 14

L1-L4 is lumbar plexus and sacral is L4-S5

Lumbar innervates the anterior thigh, abnormal wall and iliopsoas muscle

Sacral innervates buttocks, pelvis, perineum and lower limb, apart from anterior and medial thigh

Question 15

5 major nerves in the leg + their roots

Answer 15

Obturator L2-L4

femoral- L2-L4

sciatic- L4-S3

tibial- L4-S3

common fibular- L4-S2

Question 16

How are sensory nerves organised?

Answer 16

Afferent nerve fibres from a single dorsal root of spinal nerve innervate a specific area of skin called the dermatome

Question 17

Dermatome structure

Answer 17

Like stacks of discs forming a human

each supplied by a different spinal nerve

dermatomes run longitudinally along the limbs

Slight overlap between dermatomes

Question 18

Function of dermatome + clinical significance

Answer 18

sensory region- allow for cutaneous innervation

If a symptom appears to follow the dermatome, such as a rash, there may indicate a pathology that involves the related nerve root

Question 19

How are the spinal nerves distributed in the dermatome?

Answer 19

Ventral ramus supplies anterior aspect whereas dorsal ramus supplies posterior

Question 20

What damage could occur to a dermatome?

Answer 20

entrapment or damage of a spinal nerve of spinal cord segment

e.g unilateral pain in an S1 dermatome may occur due to the compression of the S1 nerve as a result of disc herniation

Question 21

Myotome definition

Answer 21

Unilateral portion of skeletal muscle receiving innervation from a single spinal nerve

Question 22

Explain how a myotome is defined

Answer 22

Each region of muscle often receives innervation from many spinal nerves, thus each muscle is organised using different myotomes.

Question 23

Clinical importance of a myotome

Answer 23

muscle weakness in a specific myotome territory indicates a lesion at that spinal segment or to that spinal nerve

Question 24

Do dermatomes and myotomes occupy the same region?

Answer 24

No, dermatomes and myotomes of the same segmental level do not necessarily overlap spatially

Question 25

myotatic reflex definition

Answer 25

A muscle contractual in response to stretching within a muscle

Question 26

Monosynaptic reflex

Answer 26

a stretch reflex that provides automatic regulation of a skeletal muscle length, whereby a signal entering the spinal cord arises from a change in muscle length or velocity

Question 27

How does a myotatic reflex work?

Answer 27

Muscle spindle structures, whose extrafusal muscle fibres lie parallel to the muscle, sense changes in length and velocity. Eventually causes an action potential in the alpha motor neurone causing the fibres to contract and thus resist the stretching

Question 28

Explain anatomical basis of biceps reflex

Answer 28

Examines the function of the C5/C6 reflex arc Tendon hammer used to knock the cubital fossa in which the biceps brachii tendon resides Depresses the muscle spindle, mainly associated with C5 than C6, due to the roots of the musculocutaneous nerve

Question 29

Biceps reflex process

Answer 29

Arm is extended, tendon hammer used to strike the examiner's fingers placed on the biceps tendon

Question 30

Biceps Reflex types and clinical relevance

Answer 30

Strong contraction- brisk reflex, weak or absent- diminished

Question 31

Knee jerk reflex process

Answer 31

Muscle in neutral position, patellar tendon struck with reflex hammer just bellow the patella Stretches the muscle spindle of the quadriceps muscle- causes leg to kick

Question 32

Explain anatomical basis of knee jerk

Answer 32

Examines the function of the L3 spinal nerve- femoral nerve

Question 33

Clinical relevance

Answer 33

Absence or decrease- Westphal's sign Multiple oscillations (pendular reflex) - cerebellar disease exaggerated deep tendon reflexes- hyperthyroidism

Question 34

What are both these an example of ? + stages

Answer 34

Reflex arc 1. Spindle muscles sense changes in length and velocity 2. impulse carried by afferent sensory neurone from the muscle to the spinal cord 3. action potential carried to the dorsal root ganglion 4. action potential carried by efferent motor neurones from the ventral root of the spinal cord to the muscle does the alpha motor neurone 5. synapses on the extrafusal muscle spindle fibres, causing contraction

Question 35

Two types of plexus + what they innervate

Answer 35

autonomic- thorax, abdomen and pelvis- blood vessels and viscera somatic- limbs- skin, muscle, bone

Question 36

Where are the trunks of the brachial plexus found?

Answer 36

between the scalene muscle and clavicle

Question 37

Different trunks and their roots

Answer 37

Upper- C5,C6 Median- C7 Lower- C8, T1

Question 38

How does each trunk divide + what they innervate?

Answer 38

Each trunk forms an anterior and posterior division anterior divisions will supply anterior flexor compartments of the rubber limb posterior divisions will innervate the posterior compartments of the upper limn

Question 39

What do the divisions form?

Answer 39

Cords

Question 40

How are they named?

Answer 40

Named relative to the axillary artery- li with the axillary arteries and vein surrounded by the axillary sheath

Question 41

3 cords + divisions + trunks

Answer 41

posterior- all posterior divisions of all trunks lateral cord- anterior division of upper and middle trunks medial cord- anterior division of lower trunk

Question 42

What are the branches?

Answer 42

major nerves supplying the upper limb

Question 43

Musculocutaneous nerve origin, location and function

Answer 43

- C5,C6- upper trunk- terminal branches of lateral and medial cord Passes anteriorly to supple the anterior muscle compartment of the arm supplies the coracobrachialis, biceps brachii and brachialis muscles Elbow and shoulder flexion, forearm supination sensory nerve which supplies skin of the lateral forearm

Question 44

median nerve origin, location and function

Answer 44

C5-T1 - at cubital fossa, nerve lies medial to brachial artery - passes into the forearm and at the wrist passes through the carpal tunnel and enters the palm of the hand - anterior compartment of the forearm and hand and skin over the lateral aspect of hand - innervates wrist, finger, thumb flexion - thenar muscle group- abduction, flexion and opposition of thumb

Question 45

Ulnar nerve origin, location and function

Answer 45

C8- T1 - lies medial to brachial artery, passes between medial epicondyle of the humorous in the cubital tunnel - motor to muscle of anteromedial aspect of the forearm and hand

Question 46

Radial, nerve origin, location and function

Answer 46

C5-T1 - posterior, extensor, compartments of the arm and forearm - supplies no muscle in the hand but does innervate the skin of the dorsum of the hand - elbow extension due to the triceps brachii, wrist extension

Question 47

Axillary nerve, origin, location and function

Answer 47

C5-C6 - Innervates deltoid and teres minor muscles, shoulder joint and skin overlying deltoid muscle - regimental badge

Question 48

Lumbar plexus roots

Answer 48

L1-part of L4

Question 49

Where is the lumbar plexus located?

Answer 49

Deep two psoas major muscle

Question 50

lumbar sacral trunk roots

Answer 50

L4, ventral ramus L5

Question 51

Sacral plexus roots

Answer 51

S1,S2,S3

Question 52

Sacral plexus location

Answer 52

anterior to piriformis muscle

Question 53

Where do the branches pass?

Answer 53

greater sciatic foramen to the gluteal region and lower limb

Question 54

Femoral nerve, origin, location and function

Answer 54

-L2,L3,L4 innervates muscles of the anterior compartment of the thigh- quadriceps femurs group, sartorius and the skin overlying he anterior thigh - carries sensory information from the knee and hip joint - lateral to psoas major, enters thigh behind inguinal ligament - lies lateral to femoral blood vessels - in the femoral triangle

Question 55

Obturator nerve, origin, location and function

Answer 55

L2, L3, L4 - emerges from medial border of psoas major muscle - follows the curve of lateral pelvic wall - passes through the obturator foramen of the pelvis t -enter the medial compartment of the thigh where it supplies adductor muscles and skin overlying the medial aspect of the thigh

Question 56

Sciatic nerve, origin, location and function

Answer 56

L4-S3 - emerges from pelvis via the greater sciatic foramen and passes midway between the greater tech-anger and ischial tuberosity - supplies all leg and foot muscles

Question 57

What does the sciatic nerve divide into + where?

Answer 57

Common perineal and tibial nerve at about the mid-thigh level, above the popliteal fossa

Question 58

Tibial nerve, origin, location and function

Answer 58

L4-S3 - passes into leg to run deep to the soleus muscle - innervates muscles in posterior compartment of the leg - responsible for plantar flexion and inversion - enters sole of foot behind medial mallows

Question 59

What does the tibial nerve divide into + where?

Answer 59

medial and lateral plantar nerves

Question 60

Common perineal nerve, origin, location and function

Answer 60

L4-S2 - curves posteriorly around the neck of the fibula - supply anterior and lateral compartment of the leg

Question 61

What does the common perineal nerve divide into + where?

Answer 61

Superficial peroneal nerve- supplies muscles in lateral compartment, and anterolateral distal 1/3 of the leg and dorsal surface of foot deep perineal nerve- anterior compartment

Question 62

Different ways in which a nerve is damaged explained

Answer 62

neurapraxia- nerve is bruised or squashed but the outer layer and inner fibres are still in tact- works properly again after a few weeks axonotmesis- nerve is crushed, inner nerve fibres damaged but outer layer in tact neurotmesis- both layers are cut

Question 63

Main effects of damage

Answer 63

loss of sensation, loss of dexterity or paralysis

Question 64

Examples of common nerve injuries, explained

Answer 64

Erb palsy- upper trunk of brachial plexus caused by excessive lateral flexion of the neck- causes weak biceps etc axillary nerve injury- anterior shoulder isolation- paralysis of deleted muscle- impaired arm abduction carpal tunnel syndrome- median nerve trapped as it travels through the wrist at the carpal tunnel - causes pain, numbness and tingling