Peripheral Neuroanatomy Flashcards
What are dermatomes?
An area of the skin that is innervated by the sensory fibers that stem from a specific nerve root is called a dermatome.
What are myotomes?
A group of muscles that is innervated by the motor fibers that stem from a specific nerve root is called a myotome
What innervates the arm?
Cervial C5- T1 (thoracic)
What muscle does C5 innvervate?
Elbow flexors
What muscle does C6 innvervate?
Wrist extensors
What muscle does C7 innvervate?
Elbow extensors
What muscle does C8 innvervate?
Finger flexors
What muscle does T1 innvervate?
Finger adductors
What is the dorsal ramus and what does it innervate?
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
What is the ventral ramus?
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
What area of skin does nerve root C5 innervate?
Deltoid (rounded shoulder muscle)
What area of skin does nerve root C6 innervate?
Index finger
What area of skin does nerve root C7 innervate?
Middle finger
What area of skin does nerve root C8 innervate?
Little finger
What area of skin does nerve root T1 innervate?
Inner arm
What nerve roots form the brachial plexus?
C5 C6 C7 C8 T1
The lateral cord gives rise to which two nerves?
Musculocutaneous nerve
Lateral root of the median nerve
The posterior cord gives rise to which two nerves?
Axillary nerve
Radial nerve
The medial cord gives rise to which two nerves?
Medial root of the median nerve
Ulnar nerve
What is the origin of the musculocutaneous nerve?
Lateral cord of brachial plexus, formed from anterior divisions of superior and middle trunks
What is the sensory and motor supply of the musculocutaneous nerve?
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
What are the clinical features of musculocutaneous nerve palsy?
Sensory loss:
numbness over lateral forearm
Motor deficit:
Paralysis of anterior compartment of arm
Weak elbow flexion
Weak forearm supination
Absent biceps reflex
What is the origin of the axillary nerve?
The posterior cord of brachial plexus formed from posterior division of upper trunk
What is the sensory and motor supply of the axillary nerve?
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
What are the clinical features of axillary nerve palsy?
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.
What is the origin of the radial nerve?
The radial nerve originates from the posterior cord formed from posterior divisions of all three trunks.
What is the sensory and motor supply of the radial nerve?
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
What are the clinical features of radial nerve palsy?
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.
What is the origin of the median nerve?
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.
What is the sensory and motor supply of the median nerve?
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
What are the clinical features of median nerve palsy?
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
What is the origin of the ulnar nerve?
The medial cord of brachial plexus, formed from anterior division of inferior trunk
What is the sensory and motor supply of the ulnar nerve?
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.
What are the clinical features of ulnar nerve palsy?
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
What myotome (movements of which muscle) tests the C5 spinal nerve?
Elbow flexion
Biceps reflex
What myotome (movements of which muscle) tests the C6 spinal nerve?
Wrist extension
Biceps reflex
Supinator reflex
What myotome (movements of which muscle) tests the C7 spinal nerve?
Elbow extension
Triceps reflex
What myotome (movements of which muscle) tests the C8 spinal nerve?
Middle finger flexion
What myotome (movements of which muscle) tests the T1 spinal nerve?
Little finger abduction
What is the dermatome testing point for the C5 spinal nerve?
Lateral antecubital fossa (next to elbow joint)
What is the dermatome testing point for the C6 spinal nerve?
Dorsal proximal phalanx of thumb
What is the dermatome testing point for the C7 spinal nerve?
Dorsal proximal phalanx of middle finger
What is the dermatome testing point for the C8 spinal nerve?
Dorsal proximal phalanx of little finger
What is the dermatome testing point for the T1 spinal nerve?
Medial antecubital fossa (next to elbow joint)
What is winging scapula?
shoulder blade protrudes from a person’s back in an abnormal position
What lesions cause winged scapula?
Long thoracic n. (most common)
Serratus anterior muscle
Accessory n. (less common)
Trapezius muscle
Dorsal scapular n. (extremely rare)
Rhomboid muscle
Name the median nerve innervated hand muscles
Lateral 2 lumbricals
Opponens pollicis
Abductor pollicis brevis
Flexor pollicis brevis
LOAF
Name muscles that abduct the shoulder
Supraspinatus, deltoid
Trapezius
Serratus anterior
Name muscles that flex the elbow
Biceps brachii
Brachialis
Brachioradialisspi
