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?

<p>Arm hangs limply, medially rotated (D)</p> Signup and view all the answers

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

<p>Musculocutaneous and axillary nerves (D)</p> Signup and view all the answers

What indicates an upper brachial plexus injury during assessment?

<p>Loss of supination of the forearm (D)</p> Signup and view all the answers

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

<p>An ‘M’ shape (A)</p> Signup and view all the answers

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

<p>Shoulder abduction and lateral rotation (B)</p> Signup and view all the answers

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

<p>Lateral cord (D)</p> Signup and view all the answers

Which nerve innervates the biceps brachii muscle?

<p>Musculocutaneous nerve (C)</p> Signup and view all the answers

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

<p>Superior, middle (D)</p> Signup and view all the answers

What is the function of the axillary nerve?

<p>Innervates the deltoid and teres minor (C)</p> Signup and view all the answers

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

<p>Radial nerve (C)</p> Signup and view all the answers

What sensory function does the median nerve perform?

<p>Innervates the lateral part of the palm (C)</p> Signup and view all the answers

Which muscle is NOT innervated by the musculocutaneous nerve?

<p>Teres major (C)</p> Signup and view all the answers

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

<p>Lateral half of the anterior forearm (B)</p> Signup and view all the answers

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

<p>C5, C6, C7, C8, T1 (D)</p> Signup and view all the answers

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

<p>Trunks (A)</p> Signup and view all the answers

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

<p>They form the roots of the brachial plexus. (C)</p> Signup and view all the answers

Which structure is NOT innervated by the brachial plexus?

<p>Trapezius (A), Levator scapula (C)</p> Signup and view all the answers

How many trunks does the brachial plexus form?

<p>Three (C)</p> Signup and view all the answers

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

<p>Divisions (A)</p> Signup and view all the answers

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

<p>C5 and C6 (D)</p> Signup and view all the answers

What is the primary function of the brachial plexus?

<p>Motor innervation of the upper extremity (D)</p> Signup and view all the answers

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Flashcards

What is the brachial plexus?

A network of nerves formed by the anterior rami of the lower four cervical nerves and the first thoracic nerve (C5, C6, C7, C8, and T1). It extends from the spinal cord into the armpit, supplying the upper limb.

What muscles does the brachial plexus innervate?

The brachial plexus is responsible for providing motor innervation to all muscles of the upper limb except the trapezius and levator scapulae.

How is the brachial plexus organized?

The brachial plexus is divided into five parts, or levels: Roots, Trunks, Divisions, Cords, and Branches.

What makes up the roots of the brachial plexus?

The anterior rami of spinal nerves C5, C6, C7, C8, and T1 form the roots of the brachial plexus.

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How are the trunks of the brachial plexus formed?

The three trunks are formed at the base of the neck by the convergence of the roots. These are named according to their position - Superior, Middle, and Inferior.

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What are the divisions of the brachial plexus?

Each trunk divides into two branches within the neck, forming the divisions. These are named Anterior and Posterior.

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How are the cords of the brachial plexus formed?

The cords are formed by the merging of divisions. They are named according to their position relative to the axillary artery: Lateral, Posterior, and Medial.

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What are the branches of the brachial plexus?

The branches of the brachial plexus are the final nerves that supply the specific muscles, tendons, and skin of the upper limb.

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Ulnar nerve: Sensory function

The ulnar nerve provides sensory innervation to the back of the hand, except the thumb and index finger.

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Ulnar nerve: Motor function

The ulnar nerve provides motor innervation to hand muscles (except for the thenar and two lateral lumbricals) and some forearm muscles.

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Median nerve: Sensory function

The median nerve provides sensory innervation to the anterior and posterior surfaces of the medial one and a half fingers, and the associated palm area.

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Median nerve: Motor function

The median nerve innervates a cluster of muscles in the thumb region, some forearm muscles, and a portion of the hand muscles.

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Brachial Plexus

The brachial plexus is a complex network of nerves responsible for controlling the movement and sensation of the upper limb.

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Anatomic landmark: Brachial Plexus 'M'

When dissecting the brachial plexus, look for an 'M' shape formed by the musculocutaneous, median, and ulnar nerves. This shape helps identify the different components of the brachial plexus.

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Upper Brachial Plexus Injury: Erb's Palsy

An injury to the upper brachial plexus affects the superior roots (C5, C6), leading to Erb's palsy.

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Lower Brachial Plexus Injury

An injury to the lower brachial plexus affects the inferior roots, resulting in a decreased ability to move and feel the hand.

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Brachial Plexus: Trunks

The first stage of brachial plexus formation, where nerve roots from the spinal cord join together to form trunks. These trunks are named superior, middle, and inferior based on their position.

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Brachial Plexus: Divisions

The second stage of brachial plexus formation, where the trunks further split into anterior and posterior divisions. These divisions are named based on their relative position: front (anterior) or back (posterior).

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Brachial Plexus: Cords

The final stage of brachial plexus formation, where the anterior and posterior divisions merge to form three cords: lateral, posterior, and medial. These cords are named based on their location relative to the axillary artery in the arm.

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Brachial Plexus: Major Branches

The main branches of the brachial plexus that innervate muscles and skin in the upper limb. These branches ultimately provide motor function (movement) and sensory function (feeling).

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Musculocutaneous Nerve

A branch of the brachial plexus that innervates the muscles responsible for flexing the elbow (biceps brachii, brachialis, and coracobrachialis). It also provides sensory input to the lateral part of the forearm.

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Axillary Nerve

A branch of the brachial plexus that innervates the muscles responsible for shoulder movement (teres minor and deltoid) and provides sensory input to the inferior region of the deltoid muscle.

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Median Nerve

A branch of the brachial plexus that innervates most of the flexor muscles in the forearm, including the thumb muscles (thenar) and some finger muscles (lumbricals). It also provides sensory input to the lateral part of the palm and the lateral three and a half fingers on the palm.

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Radial Nerve

A branch of the brachial plexus that innervates the muscles responsible for extending the elbow (triceps brachii) and the muscles in the back of the forearm which extend wrist and fingers. It also provides sensory input to the posterior side of the arm and forearm.

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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!

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