Limb Innervation

Question 1

How many cervical, thoracic, lumbar and sacral vertebrae are there?

Answer 1

7 cervical, 12 thoracic, 5 lumbar and 5 fused sacral

Question 2

How many cervical, thoracic, lumbar and sacral nerves are there and where are they located?

Answer 2

8 cervical, with C1-C7 arising above the cervical vertebrae and C8 arising below the 7th cervical vertebra, then 12 thoracic, 5 lumbar and 5 sacral, all arising below the vertebrae

Question 3

Between which two spinal nerves does the spinal cord end and why?

Answer 3

L1-L2, because during development the vertebral column and the spinal cord are the same length but with growth the vertebral column elongates so that by adulthood the spinal cord ends before the vertebral column.

Question 4

The spinal nerves are described as mixed… why?

Answer 4

Because they contain somatic (m+s) and sympathetic nerves

Question 5

What is the first division of the mixed spinal nerves? Describe their general innervation.

Answer 5

Posterior primary ramus: innervates extensor muscles of vertebral column and the skin of the back
Anterior primary ramus: innervates limbs and ventral trunk

Question 6

Diagram of the brachial plexus

Answer 6

https://geekymedics.com/brachial-plexus/

Question 7

General innervation of the two divisions in the brachial plexus?

Answer 7

Posterior innervates extensor muscles and overlying skin, anterior innervates flexor muscles and overlying skin

Question 8

What is a dermatome and why are axial lines clinically relevant?

Answer 8

A dermatome is an area of skin innervated by a sensory nerve, and axial lines are the lines that separate two adjacent dermatomes innervated by two spinal nerves that are not located at immediately adjacent spinal levels, so are more useful locations for clinicians to compare sensory loss.

Question 9

Label dermatome test sheet on Notability

Answer 9

https://www.physio-pedia.com/images/9/97/Asia_exam_worksheet.jpg

Question 10

What embryonic structure is the spinal cord derived from, and how does it come to form from which embryonic layer?

Answer 10

Spinal cord derived from neural tube. Neural tube is an infolding of the ectoderm-derived neural plate, which is induced by the notochord, a collection of mesoderm cells in the midline axis below the ectoderm which secrete transcription factors such as sonic hedgehog.

Question 11

What structure forms on each side of the dorsal aspect of the neural tube, and what type of neurons arise from it?

Answer 11

Neural crest, from whence arise sensory neurons

Question 12

What is a myotome?

Answer 12

A set of muscles innervated by a specific single spinal nerve

Question 13

Which myotome?

1. Abduction of shoulder
2. Adduction of shoulder
3. Flexion of elbow
4. Extension of elbow
5. Supination of forearm
6. Pronation of forearm
7. Plantar and dorsiflexion of wrist
8. Flexion and Extension of IP joints

Answer 13

1. C5
2. C6, C7, C8
3. C5, C6
4. C7, C8
5. C5, C6
6. C7, C8
7. C6, C7
8. C7, C8

Question 14

Which spinal nerves form the lumbro-sacral plexus? Differentiate between the lumbar and sacral plexi after.

Answer 14

Anterior primary rami of L2-S3
Lumbar plexus is L2-L4 (also T12 and L1)
Sacral Plexus is L5-S3

Question 15

Which nerves are formed by the posterior and anterior divisions of the the lumbar plexus, and what muscles do they generally supply?

Answer 15

Femoral nerve arises from the posterior divisions of L2-L4, supplying knee extensors, most hip flexors and their cutaneous covering
Obturator nerve arises from anterior divisions of L2-L4, supplying hip adductors and their cutaneous covering

Question 16

Which muscle is innervated directly by nerves of the lumbar plexus, and which nerves?

Answer 16

Psoas major, by L1-L3

Question 17

Which nerves innervate which gluteal muscles, and from which nerve roots?

Answer 17

Superior gluteal nerve (L4-S1) innervates gluteus medius, minimus and tensor fasciae latae
Inferior gluteal nerve (L5-S2) innervates gluteus maximus

Question 18

Which compartments are supplied by the 5 branches of the Brachial Plexus?

Answer 18

MC = flexors of shoulder joint and elbow joint
M = most plantarflexors and muscles of thumb and lateral 3.5 fingers of palmar surface
U = two plantar flexors and intrinsic muscles of hand, as well as 1.5 fingers of medial palmar surface
R = extensors of shoulder joint, elbow joint, dorsiflexion of hand and dorsal hand
A = deltoid and teres minor

Question 19

List direct branches of sacral plexus to lateral rotators of the hip and their innervations

Answer 19

piriformis nerve to piriformis - S1, S2
obturator internus nerve to obturator internus and superior gemellus - L5, S1, S2
quadratus femoris nerve to quad. fem. and inferior gemellus - L4, L5, S1

Question 20

What is the main nerve arising from the sacral plexus? What are its anterior and posterior divisions called, and what movements do they cause?

Answer 20

Sciatic nerve, anterior branch becomes tibial nerve (causing flexion of knee joint, plantarflexion of foot, flexion of toes and sensation to sole of foot and posterior lower leg) and posterior branch becomes common peroneal nerve (causing dorsiflexion of foot, extension of toes and cutaneous innervation of anterior surface of lower leg and dorsum of foot)

Question 21

Which nerves supply the extensors and flexors of the knee joint?

Answer 21

Femoral nerve and tibial nerve respectively

Question 22

Which nerves supply plantarflexors and dorsiflexors of ankle joint?

Answer 22

Tibial nerve and common peroneal nerve respectively

Question 23

Which nerves supply toe flexors and extensors?

Answer 23

Tibial nerve and common peroneal nerve respectively

Question 24

Which nerves supply the evertors and invertors of the subtalar joint?

Answer 24

Common peroneal nerve and tibial/common peroneal nerve respectively

Question 25

As well as the anterior aspect of the thigh, the femoral nerve provides sensation to what are of the body and through what branch? Where does this branching occur?

Answer 25

Saphenous nerve, arising just as femoral nerve enters the thigh, supplying skin of the medial side of the calf and foot down to the MCP joint

Question 26

The common peroneal nerve splits into two branches. What are their names and what do they innervate?

Answer 26

Superficial peroneal nerve innervates anterior surface of lower leg and dorsum of foot
Deep peroneal nerve innervates dorsiflexors of ankle and extensors of toes

Question 27

From which nerve roots does the sciatic nerve originate?

Answer 27

L4-S3

Question 28

Why do peripheral nerves have a segmental organisation?

Answer 28

Because the caudal half of each sclerotome (which become vertebrae) releases inhibitory molecules to prevent nerve fibre outgrowth from neural tube through them

Question 29

Which nerve passes through the quadrangular space?

Answer 29

Axillary nerve

Question 30

Which tendons are involved in the forearm jerk and knee jerk reactions?

Answer 30

Biceps tendon and the patellar tendon respectively

Question 31

Describe the forearm jerk reaction, mentioning attachment of tendon involved, instrument used, and what the result of no contraction and delayed contraction would imply

Answer 31

Clinician uses tendon hammer to tap biceps brachii tendon, which attaches to the radial tuberosity. No contraction would suggest damage to C5-C6 roots of the musculocutaneous nerve. Delayed reflex would imply lost myelination or initial signs of nerve damage

Question 32

Describe the knee jerk reaction, mentioning attachment of tendon involved, instrument used, and what the result of no contraction and delayed contraction would imply

Answer 32

Clinician uses tendon hammer to tap patellar tendon, which attaches to patellar and is the distal portion of quadriceps femoris. No contraction would suggest damage to nerve roots L2-L4, delay could imply demyelination or early signs of nerve damage.

Question 33

From which cords arise which branches of the brachial plexus?

Answer 33

MC = lateral cord
A = posterior cord
R = posterior cord
M = lateral and medial cord
U = medial cord

Question 34

Draw any minor branches of brachial plexus onto a simple diagram of the brachial plexus

Answer 34

Dorsal scapular nerve: C5 root
First intercostal nerve: T1 root
Long thoracic nerve: C5, C6 and C7 roots
Suprascapular nerve: Superior trunk (C5, C6)
Subclavius nerve: Superior trunk (C5, C6)
Lateral pectoral nerve: Lateral cord (C5, C6, C7)
Upper subscapular nerve: Posterior cord (C5, C6)
Thoracodorsal nerve: Posterior cord (C6, C7, C8)
Lower subscapular nerve: Posterior cord (C5, C6)
Medial pectoral nerve: Medial cord (C8, T1)
Medial cutaneous nerve of arm: Medial cord (T1)
Medial cutaneous nerve of forearm: Medial cord (C8)