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The median nerve is a sensory and motor nerve that plays a crucial role in the functionality of the hand and upper limb. It arises from the brachial plexus and travels through the forearm and wrist, providing signals to and from the brain and spinal cord. The nerve is responsible for the innervation of several muscles in the anterior forearm and hand, including the flexor digitorum superficialis, pronator teres, and flexor carpi radialis. It also gives rise to branches that innervate specific muscles, such as the anterior interosseous nerve supplying the deep muscles in the anterior forearm. The median nerve is particularly vulnerable to injury at the wrist, which can lead to conditions like carpal tunnel syndrome.
| Characteristics | Values |
|---|---|
| Type | Sensory and motor nerve |
| Location | Upper limb, arising from the brachial plexus |
| Innervation | Flexor and pronator muscles in the anterior compartment of the forearm, except the flexor carpi ulnaris and part of the flexor digitorum profundus |
| Sensory Innervation | Thenar eminence of the palm, central palm, dorsal aspect of the distal first two digits of the hand, palmar aspect of the thumb, index, middle, and half of the ring finger, medial aspect of the forearm |
| Branches | Palmar cutaneous branch, articular branch, recurrent branch, anterior interosseous nerve, digital cutaneous branch, radial and ulnar divisions, common palmar digital branches |
| Injuries | Carpal tunnel syndrome, proximal injury, distal injury, anterior interosseous syndrome, pronator teres syndrome |
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What You'll Learn
Median nerve injury
The median nerve is one of the major nerves of the upper limb, originating from the brachial plexus and extending into the hand. It is the only nerve that passes through the carpal tunnel, a passageway that connects the hand to the forearm. The median nerve controls movement and feeling in the forearm, wrist, hand, thumb, and fingers. It also sends touch, pain, and temperature sensations from the lower arm and hand to the brain.
Median nerve injuries can occur through multiple mechanisms and at different sites along the upper limb. The nerve is particularly vulnerable to injury at the wrist, where it moves numerous times during various activities. Common injuries to the median nerve include anterior shoulder dislocation, elbow dislocation, humerus fracture, midshaft radius fractures, stab wounds, and repeated use of crutches. These injuries are rarely in isolation and are often associated with radial or ulnar nerve neuropathies.
The nerve can also become damaged during multiple-cause degenerative processes and neuropathies. The median nerve can become compressed under the fascial sheath of the flexor retinaculum, causing burning pain, numbness, and tingling (neuropathic pain). This condition is known as entrapment syndrome or carpal tunnel syndrome. Carpal tunnel syndrome can cause wrist pain and problems grasping and holding items. It is treated with carpal tunnel surgery, which releases space in the carpal tunnel for the median nerve.
Another condition related to median nerve damage is anterior interosseous nerve syndrome, which can cause weakness or paralysis in the thumb and fingers. Compression on the nerve can cause pain, tingling, numbness, and weakness in the hand. If the nerve has been severely damaged, this can lead to muscle wastage.
The median nerve innervates the majority of the muscles in the anterior forearm and some intrinsic hand muscles. In the forearm, the nerve directly innervates muscles in the superficial and intermediate layers, including the pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis. The median nerve also gives rise to the anterior interosseous nerve, which supplies the deep flexors, including the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus.
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Carpal tunnel syndrome
When the median nerve is compressed or irritated, it can send incorrect signals to the hand and wrist, resulting in symptoms such as pain, numbness, tingling, and weakness. These symptoms typically manifest at night, disturbing sleep, and can progress to affect daytime activities, particularly those involving repetitive motions like typing or writing. The pain associated with carpal tunnel syndrome is often described as a sharp, burning sensation or a constant ache, and it tends to feel like it originates from inside the hand or wrist rather than the surface of the skin.
The syndrome can be diagnosed through a clinical examination, and in some cases, a nerve conduction study may be recommended for further evaluation. Treatment options include non-invasive methods such as splinting, hand therapy, and anti-inflammatory medications, as well as surgical procedures to alleviate nerve compression. Carpal tunnel syndrome usually responds well to treatment, but if left untreated, it can lead to permanent damage to the median nerve.
In terms of the muscles innervated by the median nerve, it directly innervates muscles in the superficial and intermediate layers of the forearm. In the superficial layer, it innervates the pronator teres, flexor carpi radialis, and palmaris longus muscles. In the intermediate layer, it innervates the flexor digitorum superficialis. Additionally, the median nerve gives rise to the anterior interosseous nerve, which supplies the deep flexors in the deep layer, including the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus. The median nerve also has two terminal branches, the common palmar digital nerves, which innervate the thenar muscles and the lateral two lumbricals.
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Forearm muscles innervated
The median nerve is a sensory and motor nerve of the upper limb, arising from the brachial plexus. It is the only nerve that passes through the carpal tunnel, a narrow passageway in the palm-side of the wrist. The median nerve innervates the muscles of the hand and forearm, providing signals to and from the brain and spinal cord.
The median nerve innervates the majority of the muscles in the anterior forearm, and some intrinsic hand muscles. In the forearm, the median nerve directly innervates muscles in three layers: the superficial, intermediate, and deep layers. The superficial layer includes the pronator teres, flexor carpi radialis, and palmaris longus muscles. The intermediate layer includes the flexor digitorum superficialis muscle. The deep layer includes the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus (the medial half of the muscle is innervated by the ulnar nerve).
The median nerve also gives rise to the anterior interosseous nerve, which supplies the deep flexors. The anterior interosseous nerve passes deeper than the median nerve, just anterior to the interosseous membrane. The median nerve and its branches innervate all of the flexor muscles of the forearm except for the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus. These two muscles are supplied by the ulnar nerve.
The median nerve also innervates the skin of the palmar (or volar) side of the hand, including the thumb, index finger, middle finger, and half of the ring finger, as well as the nail bed. This sensory innervation is provided by the palmar cutaneous branch of the median nerve, which arises in the forearm and travels into the hand. The palmar cutaneous branch innervates the lateral aspect of the palm and the palmar surface of the fingertips of the lateral three and a half digits.
The median nerve is susceptible to injury at the wrist, most commonly due to carpal tunnel syndrome (CTS) caused by a pinched nerve in the carpal tunnel. This can result in pain, tingling, and numbness in the hand and arm, as well as atrophy of the muscles in the thenar eminence due to a lack of stimulation from the median nerve. Proximal injuries to the median nerve can occur at the elbow, often due to a fracture of the humerus bone of the upper arm, and can result in an inability to make a complete fist.
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Hand muscles innervated
The median nerve is a sensory and motor nerve of the arm that provides innervation to various muscles in the hand and forearm. It arises from the lateral and medial cords of the brachial plexus and travels through the anterior forearm, passing through the carpal tunnel, a narrow passageway in the wrist.
In the forearm, the median nerve directly innervates muscles in the superficial and intermediate layers. The superficial layer includes the pronator teres, flexor carpi radialis, and palmaris longus. The intermediate layer comprises the flexor digitorum superficialis, which is involved in flexing the wrist and digits of the hand. The median nerve also innervates some deep flexor muscles in the forearm, including the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus. The medial half of the flexor digitorum profundus is innervated by the ulnar nerve.
The median nerve also innervates some intrinsic hand muscles, including the thenar muscles, which are responsible for movements of the thumb, such as opposition, abduction, and adduction. The thenar recurrent motor branch of the median nerve supplies the flexor pollicis brevis, abductor pollicis brevis, and opponens pollicis. Additionally, the median nerve provides sensory innervation to the palmar surface and fingertips of the lateral three and a half digits, including the thumb, index, middle, and half of the ring finger.
The median nerve is susceptible to injury, particularly at the wrist, where carpal tunnel syndrome (CTS) can occur due to compression within the carpal tunnel. CTS can cause pain, tingling, and numbness in the hand and arm, and may result in atrophy of the thenar eminence muscles due to a lack of stimulation from the median nerve.
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Median nerve functions
The median nerve is a major peripheral nerve of the upper limb, arising from the brachial plexus. It is a mixed nerve that plays a crucial role in hand functionality. It innervates the muscles in the anterior forearm and some intrinsic hand muscles.
In the forearm, the nerve travels between the two heads of the pronator teres, then descends 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 former supplies the deep muscles in the anterior forearm, while the latter innervates the skin of the lateral palm.
The median nerve then enters the hand via the carpal tunnel, where it divides into two branches: the recurrent branch and the palmar digital nerves. The recurrent branch innervates the thenar muscles, which are associated with thumb movements. The thenar muscles enable thumb opposition, abduction, and adduction. The palmar digital nerves innervate the palmar surface and fingertips of the lateral three and a half digits, providing sensitivity to the palmar side of the thumb, index, middle, and radial side of the ring finger.
The median nerve also provides sensory innervation to the dorsal skin of the last two phalanges of the index and middle fingers, as well as the lateral half of the ring finger past the proximal interphalangeal joint. It further extends to the dorsal aspect of the distal first two digits of the hand.
The median nerve is vulnerable to injury, particularly at the wrist, due to its proximity to the wrist bones and tendons. Compression of the nerve can occur due to overuse, oedema, or inflammation, resulting in carpal tunnel syndrome. This can lead to pain, numbness, and muscle wasting in the thenar eminence, potentially causing a condition called ape hand, characterised by severely limited thumb movement.
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Frequently asked questions
The median nerve is a sensory and motor nerve of the arm or upper limb. It is one of the major peripheral nerves of the upper limb.
The median nerve originates from the brachial plexus, which forms in the cervical area of the spinal cord.
The median nerve innervates the muscles in the superficial and intermediate layers of the anterior forearm. This includes the pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis. In the hand, the median nerve innervates the thenar muscles, which are associated with movements of the thumb.
The median nerve has 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.
Injury to the median nerve can result in carpal tunnel syndrome, characterised by pain, numbness, and weakness in the hand and wrist. Proximal injury to the median nerve at the elbow can lead to a condition known as "ape hand," where the individual loses the ability to oppose the thumb due to atrophy of the thenar muscles.
