Ulnar Nerve | Anatomy2Medicine
Ulnar Nerve

Ulnar Nerve

 

  • Cutaneous nerves of the upper limb

 

      • Supraclavicular Nerve
        • arises from the cervical plexus (C3, C4)
        • innervates the skin over the upper pectoral, deltoid, and outer trapezius areas.
      • Medial Brachial Cutaneous Nerve
        • Arises from the medial cord of the brachial plexus

 

  • innervates the medial side of the arm.

 

      • Medial Antebrachial Cutaneous Nerve
        • Arises from the medial cord of the brachial plexus
        • innervates the medial side of the forearm.
      • Lateral Brachial Cutaneous Nerve
        • Arises from the axillary nerve
        • innervates the lateral side of the arm
      • Lateral Antebrachial Cutaneous Nerve
        • Arises from the musculocutaneous nerve
        • innervates the lateral side of the forearm.
      • Posterior Brachial and Antebrachial Cutaneous Nerves
        • Arise from the radial nerve
        • innervate the posterior sides of the arm and forearm, respectively.
      • Intercostobrachial Nerve
        • Is the lateral cutaneous branch of the second intercostal nerve

 

  • emerge from the second intercostal space
  • communicate with the medial brachial cutaneous nerve

 

  • Brachial plexus
    • Is formed by the ventral primary rami of the lower four cervical nerves and the first thoracic nerve (C5–T1).
    • Has roots that pass between the scalenus anterior and medius muscles.
    • Is enclosed with the axillary artery and vein in the axillary sheath, which is formed by a prolongation of the prevertebral fascia.
    • Branches From the Roots
    • Dorsal Scapular Nerve (C5)
      • Pierces the scalenus medius muscle to reach the posterior cervical triangle
      • Innervates the rhomboids and frequently the levator scapulae muscles
    • Long Thoracic Nerve (C5–C7)
    • Supplies  serratus anterior muscle
    • Injury to the long thoracic nerve is caused by a stab wound or during radical mastectomy or thoracic surgery.
    • It results in paralysis of the serratus anterior muscle and inability to elevate the arm above the horizontal.
    • It produces a winged scapula in which the vertebral (medial) border of the scapula protrudes away from the thorax
    • Branches From the Upper Trunk

 

  • Suprascapular Nerve (C5–C6)

 

      • Runs laterally across the posterior cervical triangle.
      • Passes through the scapular notch under the superior transverse scapular ligament, whereas the suprascapular artery passes over the ligament.
      • (Mnenonic : the army [artery] runs over the bridge [ligament], and the navy [nerve] runs under the bridge.)
      • Supplies

 

  • supraspinatus muscle
  • shoulder joint
  • infraspinatus muscle.

 

    • Nerve to Subclavius (C5)
      • innervates

 

  • subclavius muscle.

 

        • sternoclavicular joint.

 

  • Usually branches to the accessory phrenic nerve (C5), which enters the thorax to join the phrenic nerve.
  • Branches From the Lateral Cord
  • Lateral Pectoral Nerve (C5–C7)

 

      • Innervates the pectoralis major muscle primarily
      • also supplies the pectoralis minor muscle by way of a nerve loop to the medial pectoral nerve
      • Pierces the costocoracoid membrane of the clavipectoral fascia.
      • Is accompanied by the pectoral branch of the thoracoacromial artery.

 

  • Musculocutaneous Nerve (C5–C7)

 

      • Pierces the coracobrachialis muscle
      • innervates three muscles.

 

  • coracobrachialis muscle
  • biceps brachii
  • brachialis muscles

 

  • Branches From the Medial Cord

 

  • Medial Pectoral Nerve (C8–T1)

 

      • supplies the pectoralis minor muscle

 

  • Medial Brachial Cutaneous Nerve (C8–T1)

 

      • Innervates the skin on the medial side of the arm.

 

  • Medial Antebrachial Cutaneous Nerve (C8–T1)

 

      • Innervates the skin on the medial side of the forearm

 

  • Ulnar Nerve (C7–T1)

 

  • Branches From the Medial and Lateral Cords:
  • Median Nerve (C5–T1) is formed by heads from both the medial and lateral cords.
  • Branches From the Posterior Cord

 

  • Upper Subscapular Nerve (C5–C6)

 

      • Innervates the upper portion of the subscapularis muscle

 

  • Thoracodorsal Nerve (C7–C8)

 

      • Innervates the latissimus dorsi muscle.

 

  • Lower Subscapular Nerve (C5–C6)

 

      • Innervates the lower part of the subscapularis and teres major muscles.

 

  • Axillary Nerve (C5–C6)

 

      • Innervates the deltoid and teres minor muscles

 

  • gives rise to the lateral brachial cutaneous nerve.

 

      • Passes posteriorly through the quadrangular space accompanied by the posterior circumflex humeral artery
      • winds around the surgical neck of the humerus (may be injured when this part of the bone is fractured).
      • Injury to the axillary nerve
        • caused by a fracture of the surgical neck of the humerus or inferior dislocation of the humerus.

 

  • It results in weakness of

 

        • lateral rotation
        • abduction of the arm

 

  • the supraspinatus can abduct the arm but not to a horizontal level
  • Radial Nerve (C5–T1)

 

      • largest branch of the brachial plexus

 

  • occupies the musculospiral groove on the back of the humerus with the profunda brachii artery.

 

      • Injury to the radial nerve
        • caused by a fracture of the midshaft of the humerus.
        • It results in
          • loss of function in the extensors of the forearm, hand, metacarpals, and phalanges.
          • loss of wrist extension, leading to wrist drop
          • weakness of abduction and adduction of the hand.

 

  • Crutch palsy
  • Injury to the posterior cord
  • It results in loss in function of the extensors of the arm, forearm, and hand

 

    • It produces a wrist drop

Nerves of the arm, forearm, and hand

 

  • Musculocutaneous Nerve (C5–C7)

 

      • Pierces the coracobrachialis muscle
      • descends between the biceps and brachialis muscles.
      • Innervates all of the flexor muscles in the anterior compartment of the arm, such as the coracobrachialis, biceps, and brachialis muscles.
      • Continues into the forearm as the lateral antebrachial cutaneous nerve.
      • Injury to the musculocutaneous nerve results in
        • weakness of supination (biceps)
        • weakness of flexion (biceps and brachialis) of forearm
        • loss of sensation on the lateral side of forearm.
    • Radial Nerve (C5–T1)
      • Arises from the posterior cord
      • largest branch of the brachial plexus.
      • Descends posteriorly between the long and medial heads of the triceps, after which it passes inferolaterally with the profunda brachii artery in the spiral (radial) groove on the back of the humerus
      • Passes between the medial and lateral heads of the triceps.
      • Gives rise to muscular branches which supply

 

  • Brachioradialis
  • extensor carpi radialis longus
  • extensor carpi radialis brevis
  • supinator muscles

 

        • extensor muscles of the forearm.

 

  • Sensory supply
  • articular branches

 

        • posterior brachial and posterior antebrachial cutaneous branches.
        • innervate the skin of the radial side of the hand and the radial two and one-half digits over the proximal phalanx
        • This nerve does not supply the skin of the distal phalanges.
    • Ulnar Nerve (C7–T1
      • Arises from the medial cord of the brachial plexus,
      • runs down the medial aspect of the arm,
      • Descends behind the medial epicondyle in a groove or tunnel (cubital tunnel)
      • it is readily palpated
      • most commonly injured.
      • It may be damaged by a fracture of the medial epicondyle
      • Enters the forearm and innervates

 

  • flexor carpi ulnaris

 

        • flexor digitorum profundus muscles
      • Enters the hand superficial to the flexor retinaculum and lateral to the pisiform bone, where it is vulnerable to damage from cuts or stab wounds
      • Terminates by dividing into superficial and deep branches at the root of the hypothenar eminence.

 

  • Superficial Branc

 

          • Innervates the palmaris brevis
          • Innervates skin over the palmar and dorsal surfaces of the medial one-third of the hand, including the hypothenar eminence
          • Terminates in the palm by dividing into three palmar digital branches, which supply
            • the skin of the little finger
            • the medial side of the ring finger.

 

  • Deep Branc

 

        • Arises at and travels through the Guyon’s canal
        • passes between the pisiform and the hook of the hamate
        • Innervates the

 

  • hypothenar muscles
  • medial two lumbricals
  • all interossei
  • adductor pollicis
  • deep head of the flexor pollicis brevis
  • Injury to the ulnar nerve

 

        • caused by a fracture of the medial epicondyle
        • results in a claw hand,
          • ring and little fingers are hyperextended at the metacarpophalangeal joints and flexed at the interphalangeal joints.

 

  • It results in loss of abduction and adduction of the fingers and flexion of the metacarpophalangeal joints because of the paralysis of the palmar and dorsal interossei muscles and the medial two lumbricals.

 

      • It also produces a wasted hypothenar eminence and palm
      • It leads to loss of adduction of the thumb because of the paralysis of the adductor pollicis muscle.