Anatomy Week 11 - Nerves of the upper limb - terminal nerves

Question 1

List the terminal nerves of the brachial plexus.

Answer 1

1. Musculocutaneous nerve
2. Axillary nerve
3. Radial nerve
4. Median nerve
5. Ulnar nerve

Question 2

Where does the Musculocutaneous nerve originate from and list its motor and sensory innervations.

Answer 2

Origin: Lateral cord (C5 - C7)

Motor innervations: Muscles in the anterior part of the arm (Biceps brachii, Brachialis, Coracobrachialis).

Sensory innervations: Skin on the lateral forearm.

Question 3

Where does the Axillary nerve originate from and list its motor and sensory innervations.

Answer 3

Origin: Posterior cord (C5 - C6)

Muscular innervation: Deltoid and teres minor.

Sensory innervation: Gives rise to the upper lateral cutaneous nerve of the arm, which innervates the skin over the lower deltoid.

Question 4

Where does the Radial nerve originate from and list its motor and sensory innervations.

Answer 4

Origin: Posterior cord (C5 – C8, T1).

Muscle innervation: Posterior muscles of the arm and forearm (Triceps brachii, Brachioradialis, Anconeus, Supinator, extensor carpi radialis longus and brevis, extensor carpi ulnaris) and muscles extending the fingers.

Sensory innervation: Skin of posterolateral surface of the arm.

Question 5

Where does the Median nerve originate from and list its motor and sensory innervations.

Answer 5

Origin: Two branches
- Lateral cord (C5 - C7)
- Medial cord (C8 -T1)

Muscle innervation: Innervates the flexor muscles of the forearm and pronator muscles. Median nerve innervates muscles of the lateral palm.

Sensory innervation: Skin of lateral two thirds of hand, dorsum of fingers 2 and 3.

Question 6

Where does the Ulnar nerve originate from and list its motor and sensory innervations.

Answer 6

Origin: Medial cord (C8 - T1).

Muscle innervation: Flexor muscles of anterior forearm and intrinsic muscles of the hand.

Sensory innervation: Skin of medial third of the hand.
Via 3 branches
- Palmar cutaneous branch – innervates the medial half of the palm.
- Dorsal cutaneous branch – innervates the dorsal surface of the medial 1 and ½ fingers, and the
associated dorsal hand area.
- Superficial branch – innervates the palmar surface of the medial one and a half fingers.

Question 7

Describe Long Thoracic Nerve (LTN) injury, including causes and signs/symptoms.

Answer 7

Causes: traction, compression, and
neuralgic amyotrophy.

Signs and symptoms:
- Pain around the base of the neck, deltoid, and scapula.
- Limitation of forward flexion and abduction of the shoulder.
- Winging scapula

Question 8

Describe Radial nerve injury in the arm, including causes and signs/symptoms.

Answer 8

Causes: If the humerus is fractured, the radial nerve may become stretched or transected, leading to permanent damage and loss of function.

Symptoms:
- Wrist drop (due to denervation of the extensor muscles).
- Sensory changes over the dorsum of the hand.

Question 9

Describe Carpal tunnel syndrome in the arm, including causes and signs/symptoms.

Answer 9

Causes:
* Overuse.
* Swelling of the tendons and tendon sheaths (e.g. rheumatoid arthritis).
* Cysts arising from the carpal joints.

Signs/symptoms:
* Pain and pins-and-needles sensations in the distribution of the median nerve.
* Weakness and atrophy of the thenar muscles.
* Gently tapping over the median nerve readily produces these symptoms (Tinel’s sign).