Logan Steele
The muscles of the thumb are innervated by a variety of nerves, including the median nerve, the ulnar nerve, and the radial nerve. The median nerve is one of the five main nerves originating from the brachial plexus and is the only nerve that passes through the carpal tunnel. The ulnar nerve, on the other hand, has a deep branch that innervates the deep head of the flexor pollicis brevis muscle. Meanwhile, the radial nerve innervates the abductor pollicis longus muscle. The intrinsic muscles of the thumb can be divided into two groups: the thenar eminence and other muscles. The thenar eminence refers to the group of muscles on the palm at the base of the thumb, including the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis muscles.
| Characteristics | Values |
|---|---|
| Innervation | Ulnar nerve, Median nerve, Deep branch of the radial nerve, Anterior interosseus branch of the median nerve |
| Muscles | Thenar, Hypothenar, Adductor Pollicis, Flexor Pollicis Longus, Abductor Pollicis Longus, Extensor Pollicis Longus, Extensor Pollicis Brevis, Flexor Pollicis Brevis, Opponens Pollicis, Abductor Pollicis Brevis |
| Actions | Flexes the metacarpophalangeal joint of the thumb, Adduction of the digits, Assists in flexion at the metacarpophalangeal joints, Extension at the interphalangeal joints, Adduction of the thumb, Abduction, Extension, Lateral rotation of the thumb at CMC joint, Flexes proximal phalanx of the thumb at MCP joint, Abducts thumb at CMC and MCP joints, Pulls and rotates MC1 across the palm |
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Median nerve
The median nerve is a major peripheral nerve in the upper limb of humans and other animals. It is one of the five main nerves originating from the brachial plexus, specifically from the lateral and medial cords of the plexus. The nerve contains fibres from roots C6-T1, and in some cases, fibres from C5.
The median nerve provides sensory innervation to the dorsal aspect (nail bed) of the distal first two digits of the hand, the palmar aspect of the thumb, index, middle, and half of the ring finger, the palm, and the medial aspect of the forearm. It also provides sympathetic innervation to the brachial artery and its distal branches, the radial and ulnar arteries.
The nerve enters the anterior compartment of the forearm via the cubital fossa, travelling between the two heads of the pronator teres muscle. It then descends in a plane between the flexor digitorum profundus and flexor digitorum superficialis muscles. The median nerve gives rise to two major branches in the forearm: the anterior interosseous nerve and the palmar cutaneous nerve.
The anterior interosseous nerve supplies the deep muscles in the anterior forearm, while the palmar cutaneous nerve innervates the skin of the lateral palm. The median nerve then enters the hand through the carpal tunnel, where it divides into two branches: the recurrent branch and the palmar digital nerves.
The recurrent branch innervates the thenar muscles, including the flexor pollicis brevis, abductor pollicis brevis, and opponens pollicis. The palmar digital nerves innervate the palmar surface and fingertips of the lateral three and a half digits. The median nerve is the only nerve that passes through the carpal tunnel, and compression of the nerve within the tunnel can result in carpal tunnel syndrome (CTS).
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Ulnar nerve
The ulnar nerve is one of the five terminal branches of the brachial plexus, which originates from the C8-T1 nerve roots. It is the largest nerve in the human body that is unprotected by muscle or bone. This nerve stimulates muscles in the forearm, hand, and fingers, and controls movement and feeling in the hand, ring finger, and little finger. It also helps with fine motor skills, such as writing.
The ulnar nerve runs near the ulna, one of the two long bones in the forearm. It is directly connected to the little finger and the adjacent half of the ring finger, innervating the palmar aspect of these fingers. The nerve enters the palm of the hand via Guyon's canal, a fibro-osseous tunnel formed by the pisiform and hook of the hamate.
In the forearm, the ulnar nerve gives off several branches, including the muscular branches, the palmar branch, and the dorsal branch. The muscular branches supply the flexor carpi ulnaris and the medial half of the flexor digitorum profundus. The palmar branch arises from the middle part of the forearm and supplies the skin over the hypothenar eminence. The dorsal branch arises from 7.5 cm above the wrist and supplies the skin of the proximal part of the ulnar and the adjoining area between the fingers.
The ulnar nerve innervates the flexor muscles of the forearm, including the flexor carpi ulnaris and flexor digitorum profundus. It also innervates the intrinsic muscles of the hand, including the thenar muscles, the hypothenar muscles, and the interossei muscles. The deep branch of the ulnar nerve passes between the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi, supplying all three muscles. It then turns laterally, supplying the third and fourth lumbricals and all the palmar interossei muscles and dorsal interossei of the hand.
The ulnar nerve is commonly known as the "funny bone" because bumping the elbow against a hard surface can cause a tingling, funny-feeling sensation. Pressure on the ulnar nerve can lead to health issues that cause pain, numbness, and weakness in the hand, arm, and elbow, affecting grip and sensation.
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Radial nerve
The radial nerve is a major peripheral nerve of the upper limb that takes a winding path from the lower armpit to some of the fingers. It is one of five nerve branches that extend from the brachial plexus. The brachial plexus nerves start from nerves that extend from the spinal cord (nerve roots) in the lower neck (cervical spine) and upper chest (thoracic spine). They travel underneath the collarbone (clavicle) and through the armpit. The radial nerve starts at the lower armpit and wraps around the humerus—the long upper arm bone that runs from the shoulder to the elbow.
The radial nerve provides movement (motor) and sensory information between the brain and parts of the arm, wrist, and hand. The motor branch of the radial nerve stimulates the triceps muscles on the back of the upper arm to straighten the elbow. It also stimulates muscles in the outer part of the forearm that rotate the forearm and straighten (extend) the wrist and fingers. The sensory branch of the radial nerve provides touch, pain, and temperature sensations for the skin on the inner upper arm, outer forearm, and the back part of the wrist and hand that is closest to the thumb.
The radial nerve divides into a deep branch, which becomes the posterior interosseous nerve, and a superficial branch, which goes on to innervate the dorsum (back) of the hand. The deep branch of the radial nerve pierces the supinator muscle, winds around the radius under the cover of the supinator, and reaches the posterior of the forearm, where it is known as the posterior interosseous nerve. The superficial branch of the radial nerve is widely separated from the radial artery in the upper third of the forearm. It is closely related to the radial artery in the middle third of the forearm and descends in the lower third under the tendon of the brachioradialis.
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Abductor pollicis brevis
The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb. It is a flat, thin muscle located just under the skin. It is a thenar muscle, contributing to the bulk of the palm's thenar eminence. The thenar eminence refers to the group of muscles on the palm at the base of the thumb. The three muscles that make up the thenar eminence are the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.
The abductor pollicis brevis has several points of origin. Most of the muscle fibres originate from the flexor retinaculum, with two smaller origins located on carpal bones: the tubercle of the scaphoid and the tubercle of the trapezium. From these origins, the muscle fibres form a single muscle belly that runs towards the thumb. The muscle ends in a flat tendon that inserts into the lateral side of the base of the first phalanx of the thumb and the capsule of the metacarpophalangeal joint.
The abductor pollicis brevis is innervated by the recurrent (thenar) branch of the median nerve (root value C8 and T1). The superficial palmar branch of the radial artery runs across the superficial aspect of the abductor pollicis brevis, which is vascularized by the superficial palmar branch that arises from the radial artery.
The main function of the abductor pollicis brevis is the abduction of the thumb at the carpometacarpal and metacarpophalangeal joints. This movement involves the thumb moving anteriorly, perpendicular to the palm. The abductor pollicis brevis works in synergy with the abductor pollicis longus muscle to facilitate the movement of the thumb towards the fingertips in the carpometacarpal joint (opposition) and flexion in the metacarpophalangeal joint.
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Opponens pollicis
The main function of opponens pollicis is to produce an opposition of the thumb, which is a complex movement that combines flexion, adduction, and medial rotation at the first carpometacarpal joint. This movement allows the tip of the thumb to touch the tips of the other fingers, enabling precise and efficient movements such as grasping round objects or fine gripping of a pencil.
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Frequently asked questions
The muscles in the thumb include the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, abductor pollicis longus, and adductor pollicis.
The abductor pollicis brevis is innervated by the median nerve.
The superficial head of the flexor pollicis brevis is innervated by the median nerve, while the deep head is innervated by the ulnar nerve.
The opponens pollicis is innervated by the median nerve.
The abductor pollicis longus is innervated by the radial nerve.
