Brachial Plexus Overview

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Questions and Answers

Which nerve roots are involved in innervating the ulnar nerve?

C8 and T1 (correct)

C6 and T2

C5 and C7

C3 and C4

What is the primary sensory function of the ulnar nerve?

Innervates the lateral aspect of the hand

Innervates the thumb and index finger

Innervates the posterior arm

Innervates the medial one and a half fingers (correct)

Which muscles are affected in an upper brachial plexus injury like Erb's Palsy?

Flexor carpi radialis and extensor digitorum

Pectoralis major and latissimus dorsi

Deltoid and teres minor (correct)

Triceps and anconeus

Which position of the upper limb is typical for a patient with an upper brachial plexus injury?

Arm hangs limply, medially rotated Signup and view all the answers

Which nerves are primarily affected in an upper brachial plexus injury?

Musculocutaneous and axillary nerves Signup and view all the answers

What indicates an upper brachial plexus injury during assessment?

Loss of supination of the forearm Signup and view all the answers

What structure should be observed during a dissection of the brachial plexus for orientation?

An ‘M’ shape Signup and view all the answers

What motor functions are significantly affected by an upper brachial plexus injury?

Shoulder abduction and lateral rotation Signup and view all the answers

What structure is formed by the anterior divisions of the superior and middle trunks in the brachial plexus?

Lateral cord Signup and view all the answers

Which nerve innervates the biceps brachii muscle?

Musculocutaneous nerve Signup and view all the answers

The posterior cord of the brachial plexus is formed by the posterior divisions of which trunks?

Superior, middle Signup and view all the answers

What is the function of the axillary nerve?

Innervates the deltoid and teres minor Signup and view all the answers

Which major branch of the brachial plexus derives from roots C6 to T1?

Radial nerve Signup and view all the answers

What sensory function does the median nerve perform?

Innervates the lateral part of the palm Signup and view all the answers

Which muscle is NOT innervated by the musculocutaneous nerve?

Teres major Signup and view all the answers

To which region does the lateral cutaneous branch of the forearm provide sensory innervation?

Lateral half of the anterior forearm Signup and view all the answers

What spinal nerves contribute to the formation of the brachial plexus?

C5, C6, C7, C8, T1 Signup and view all the answers

Which part of the brachial plexus is formed by the convergence of roots?

Trunks Signup and view all the answers

What is the role of the anterior rami of the spinal nerves in the brachial plexus?

They form the roots of the brachial plexus. Signup and view all the answers

Which structure is NOT innervated by the brachial plexus?

Trapezius Signup and view all the answers

How many trunks does the brachial plexus form?

Three Signup and view all the answers

What part of the brachial plexus does each trunk divide into?

Divisions Signup and view all the answers

Which spinal roots combine to form the superior trunk of the brachial plexus?

C5 and C6 Signup and view all the answers

What is the primary function of the brachial plexus?

Motor innervation of the upper extremity Signup and view all the answers

Signup and view all the answers

Study Notes

Brachial Plexus

The brachial plexus is a network of nerves formed by the anterior rami of the lower four cervical nerves (C5, C6, C7, C8) and the first thoracic nerve (T1).
This network extends from the spinal cord through the cervicoaxillary canal in the neck, over the first rib, and into the armpit.
It supplies the skin and muscles of the upper limb.

Parts of the Brachial Plexus

Roots: The anterior rami of the spinal nerves that comprise the plexus. These are C5, C6, C7, C8, and T1.
Trunks: At the base of the neck, the roots converge to form three trunks: superior (combination of C5 and C6 roots), middle (continuation of C7), and inferior (combination of C8 and T1 roots). They traverse laterally, crossing the posterior triangle of the neck.
Divisions: Each trunk divides into anterior and posterior divisions within the posterior triangle of the neck.
Cords: The anterior and posterior divisions enter the axilla and combine to form three cords (lateral, posterior, and medial) identified by their position relative to the axillary artery.
- The lateral cord is formed by the anterior division of the superior trunk and anterior division of the middle trunk.
- The posterior cord is formed by the posterior divisions of the superior, middle, and inferior trunks.
- The medial cord is formed by the anterior division of the inferior trunk.
Branches: The cords give rise to the major branches of the brachial plexus.

Major Branches

Musculocutaneous Nerve: Innervates the brachialis, biceps brachii, and coracobrachialis muscles. Sensory to the lateral half of the anterior forearm and a small portion of the posterior forearm. (Roots: C5, C6, C7)
Axillary Nerve: Innervates the teres minor and deltoid muscles. Sensory to the inferior region of the deltoid. (Roots: C5 and C6)
Median Nerve: Innervates most flexor muscles in the forearm, thenar muscles, and two lateral lumbricals. Sensory to the lateral part of the palm and the lateral three and a half fingers. (Roots: C6 - T1)
Radial Nerve: Innervates the triceps brachii, and the posterior compartment muscles of the forearm (primarily wrist and finger extensors). Sensory to the posterior aspect of the arm and forearm, and the posterolateral aspect of the hand. (Roots: C5 - T1)
Ulnar Nerve: Innervates muscles of the hand (excluding thenar and two lateral lumbricals), flexor carpi ulnaris, and medial part of flexor digitorum profundus. Sensory to the anterior and posterior surfaces of the medial one and a half fingers, and the associated palm area. (Roots: C8 and T1)

Clinical Significance

Brachial Plexus Injuries: Two main types: upper (Erb's palsy, commonly affecting C5 and C6 roots, often due to birth trauma or shoulder trauma; leading to weakened arm abduction) and lower (Klumpke's palsy, affecting lower roots, notably T1, often from excessive arm abduction, causing a "claw hand")
Practical Relevance: The brachial plexus can sometimes be challenging to dissect, but recognizing the "M" shape formed by the musculocutaneous, median, and ulnar nerves can be helpful.

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Description

This quiz covers the anatomy and functions of the brachial plexus, focusing on its formation from cervical and thoracic nerves. You'll explore the various parts, including roots, trunks, divisions, and cords that are essential for upper limb function. Test your knowledge on this crucial network of nerves!