Peripheral Neuroanatomy

Question 1

What are dermatomes?

Answer 1

An area of the skin that is innervated by the sensory fibers that stem from a specific nerve root is called a dermatome.

Question 2

What are myotomes?

Answer 2

A group of muscles that is innervated by the motor fibers that stem from a specific nerve root is called a myotome

Question 3

What innervates the arm?

Answer 3

Cervial C5- T1 (thoracic)

Question 4

What muscle does C5 innvervate?

Answer 4

Elbow flexors

Question 5

What muscle does C6 innvervate?

Answer 5

Wrist extensors

Question 6

What muscle does C7 innvervate?

Answer 6

Elbow extensors

Question 7

What muscle does C8 innvervate?

Answer 7

Finger flexors

Question 8

What muscle does T1 innvervate?

Answer 8

Finger adductors

Question 9

What is the dorsal ramus and what does it innervate?

Answer 9

Formed from the dorsal root nerve–> It’s a dorsal branch of the spinal nerve that contains nerves that serve the dorsal portions of the trunk

Innervates skin (of the back) and paraspinal muscles

Question 10

What is the ventral ramus?

Answer 10

It contains nerves that serve the ventral parts of the trunk and upper limbs

It innervates the skin and muscle of the anterior part of the trunk

Question 11

What area of skin does nerve root C5 innervate?

Answer 11

Deltoid (rounded shoulder muscle)

Question 12

What area of skin does nerve root C6 innervate?

Answer 12

Index finger

Question 13

What area of skin does nerve root C7 innervate?

Answer 13

Middle finger

Question 14

What area of skin does nerve root C8 innervate?

Answer 14

Little finger

Question 15

What area of skin does nerve root T1 innervate?

Answer 15

Inner arm

Question 16

What nerve roots form the brachial plexus?

Answer 16

C5 C6 C7 C8 T1

Question 17

The lateral cord gives rise to which two nerves?

Answer 17

Musculocutaneous nerve
Lateral root of the median nerve

Question 18

The posterior cord gives rise to which two nerves?

Answer 18

Axillary nerve
Radial nerve

Question 19

The medial cord gives rise to which two nerves?

Answer 19

Medial root of the median nerve
Ulnar nerve

Question 20

What is the origin of the musculocutaneous nerve?

Answer 20

Lateral cord of brachial plexus, formed from anterior divisions of superior and middle trunks

Question 21

What is the sensory and motor supply of the musculocutaneous nerve?

Answer 21

Sensory:
Skin of the lateral forearm

Motor:
It innervates the anterior compartment of arm (BBC):

Biceps: flexes elbow, supinates forearm
Brachialis: flexes elbow
Coracobrachialis: flexes and adducts the arm at the glenohumeral joint

Question 22

What are the clinical features of musculocutaneous nerve palsy?

Answer 22

Sensory loss:
numbness over lateral forearm

Motor deficit:
Paralysis of anterior compartment of arm
Weak elbow flexion
Weak forearm supination
Absent biceps reflex

Question 23

What is the origin of the axillary nerve?

Answer 23

The posterior cord of brachial plexus formed from posterior division of upper trunk

Question 24

What is the sensory and motor supply of the axillary nerve?

Answer 24

Sensory:
skin over the lower part of deltoid muscle

Motor:
It innervates two shoulder muscles:
1. Deltoid: abducts, flexes and extends shoulder
2. Teres minor: externally rotates shoulder, stabilises shoulder joint

Question 25

What are the clinical features of axillary nerve palsy?

Answer 25

Sensory loss: numbness over “sergeant’s patch”- skin over lower part of deltoid Motor deficit: paralysis of deltoid leading to very weak shoulder abduction from 15-90°- weak shoulder flexion and extension. Paralysis of teres minor leading to weak shoulder external rotation. Deformity: Bones of the shoulder joint very prominent and obvious Shoulder may appear adducted and internally rotated.

Question 26

What is the origin of the radial nerve?

Answer 26

The radial nerve originates from the posterior cord formed from posterior divisions of all three trunks.

Question 27

What is the sensory and motor supply of the radial nerve?

Answer 27

Sensory: Posterior arm and forearm Lateral ⅔ of dorsum of hand Proximal dorsal aspect of lateral 3½ fingers- thumb, index, middle and half of ring finger Motor: The radial nerve innervates muscles in the posterior compartment of the forearm: Brachioradialis: flexes elbow Anconeus: extends elbow, stabilises elbow joint Supinator: supinates forearm Extensor carpi radialis longus and brevis: extend and abduct wrist Extensor carpi ulnaris: extends and adducts wrist Extensor digitorum, extensor pollicis longus and brevis, extensor indicis and extensor digiti minimi Abductor pollicis longus: abducts thumb

Question 28

What are the clinical features of radial nerve palsy?

Answer 28

Sensory loss: numbness of skin over posterior arm, posterior forearm and radial distribution of dorsum of hand Motor deficit: weak elbow extension weak wrist extension weak thumb extension and finger MCPJ extension Absent triceps and supinator reflexes Deformity: “Wrist drop” deformity at rest and on attempted wrist extension Cannot extend wrist/fingers, resulting in unopposed wrist flexion. Forearm is pronated, the fingers are flexed, and the thumb adducted.

Question 29

What is the origin of the median nerve?

Answer 29

The lateral and medial cords of the brachial plexus. The lateral root arises from anterior divisions of superior and middle trunks. The medial root arises from anterior division of inferior trunk.

Question 30

What is the sensory and motor supply of the median nerve?

Answer 30

Sensory: the hand Skin over thenar eminence Lateral ⅔ palm of hand Palmar aspect of lateral 3½ fingers Dorsal fingertips of lateral 3½ fingers (thumb, index, middle and half of ring finger) Motor: All muscles of anterior compartment of forearm except flexor carpi ulnaris and the medial two parts of flexor digitorum profundus: Pronator teres and pronator quadratus: pronate forearm Flexor carpi radialis: flexes and adducts wrist Palmaris longus: flexes wrist and tenses palmar aponeurosis Flexor digitorum superficialis: flexes fingers at PIPJs Lateral two parts of flexor digitorum profundus: flex index and middle fingers at DIPJs Flexor pollicis longus: flexes thumb at IPJ The median nerve also supplies the intrinsic muscles of hand (LOAF muscles): Lateral two lumbricals: flex MCPJs and extend IPJs of index and middle finger Opponens pollicis: opposes thumb Adductor pollicis brevis: adducts thumb Flexor pollicis brevis: flexes thumb at MCPJ

Question 31

What are the clinical features of median nerve palsy?

Answer 31

Sensory loss: numbness of skin over thenar eminence and median distribution of hand. Motor deficit: Weak forearm pronation, wrist flexion and abduction, Weak finger flexion with preservation of DIPJ flexion at ring and little fingers. Paralysis of thenar eminence: weak pincer grip and overall grip strength, weak thumb opposition. Deformity: “Hand of benediction” deformity on attempted finger flexion, cannot flex index or middle fingers- cannot make a fist with all of their fingers. Wasting of anterior compartment of forearm and thenar eminence

Question 32

What is the origin of the ulnar nerve?

Answer 32

The medial cord of brachial plexus, formed from anterior division of inferior trunk

Question 33

What is the sensory and motor supply of the ulnar nerve?

Answer 33

Sensory: hand Skin over hypothenar eminence Medial ⅓ palm of hand Palmar aspect of the medial 1½ fingers Medial ⅓ dorsum of hand Dorsal aspect of medial 1½ fingers (little finger and half of ring finger) Motor: The ulnar nerve innervates two muscles in the anterior compartment of the forearm: Flexor carpi ulnaris: flexes and adducts wrist Medial two parts of flexor digitorum profundus: flex ring and little fingers at DIPJs The ulnar nerve innervates most of the intrinsic muscles of the hand (HILA muscles): Hypothenar eminence: opponens digiti minimi, flexor digiti minimi brevis and abductor digiti minimi: oppose, flex and abduct little finger Interossei: palmar interossei adduct, dorsal interossei abduct Medial two lumbricals: flex MCPJs and extend IPJs of ring and little finger Adductor pollicis: adducts thumb.

Question 34

What are the clinical features of ulnar nerve palsy?

Answer 34

Sensory loss: numbness over hypothenar eminence and ulnar distribution of hand Motor deficit: Weak wrist flexion and adduction Weak flexion of ring and little finger DIPJs Weak MCPJ flexion and IPJ extension of ring and little fingers Loss of finger abduction and adduction Loss of opposition of little finger Deformity: “Claw hand” deformity at rest and on attempted finger extension: cannot extend the IPJs of ring or little fingers, resulting in fixed flexion of the IPJs and hyperextension of the MCPJs of these two fingers

Question 35

What myotome (movements of which muscle) tests the C5 spinal nerve?

Answer 35

Elbow flexion Biceps reflex

Question 36

What myotome (movements of which muscle) tests the C6 spinal nerve?

Answer 36

Wrist extension Biceps reflex Supinator reflex

Question 37

What myotome (movements of which muscle) tests the C7 spinal nerve?

Answer 37

Elbow extension Triceps reflex

Question 38

What myotome (movements of which muscle) tests the C8 spinal nerve?

Answer 38

Middle finger flexion

Question 39

What myotome (movements of which muscle) tests the T1 spinal nerve?

Answer 39

Little finger abduction

Question 40

What is the dermatome testing point for the C5 spinal nerve?

Answer 40

Lateral antecubital fossa (next to elbow joint)

Question 41

What is the dermatome testing point for the C6 spinal nerve?

Answer 41

Dorsal proximal phalanx of thumb

Question 42

What is the dermatome testing point for the C7 spinal nerve?

Answer 42

Dorsal proximal phalanx of middle finger

Question 43

What is the dermatome testing point for the C8 spinal nerve?

Answer 43

Dorsal proximal phalanx of little finger

Question 44

What is the dermatome testing point for the T1 spinal nerve?

Answer 44

Medial antecubital fossa (next to elbow joint)

Question 45

What is winging scapula?

Answer 45

shoulder blade protrudes from a person's back in an abnormal position

Question 46

What lesions cause winged scapula?

Answer 46

Long thoracic n. (most common) Serratus anterior muscle Accessory n. (less common) Trapezius muscle Dorsal scapular n. (extremely rare) Rhomboid muscle

Question 47

Name the median nerve innervated hand muscles

Answer 47

Lateral 2 lumbricals Opponens pollicis Abductor pollicis brevis Flexor pollicis brevis LOAF

Question 48

Name muscles that abduct the shoulder

Answer 48

Supraspinatus, deltoid Trapezius Serratus anterior

Question 49

Name muscles that flex the elbow

Answer 49

Biceps brachii Brachialis Brachioradialisspi