In human anatomy, the ulnar nerve is a

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

that runs near the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

bone. The

ulnar collateral ligament of elbow joint The ulnar collateral ligament (UCL) or internal lateral ligament is a thick triangular ligament at the medial aspect of the elbow uniting the distal aspect of the humerus to the proximal aspect of the ulna. Structure It consists of two portio ...

is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is common. This nerve is directly connected to the

little finger The little finger, or pinkie, also known as the baby finger, fifth digit, or pinky finger, is the most ulnar and smallest digit of the human hand, and next to the ring finger. Etymology The word "pinkie" is derived from the Dutch word ''p ...

, and the adjacent half of the

ring finger The ring finger, third finger, fourth finger, leech finger, or annulary is the fourth digit of the human hand, located between the middle finger and the little finger. Sometimes the term ring finger only refers to the fourth digit of a left-han ...

, innervating the palmar aspect of these fingers, including both front and back of the tips, perhaps as far back as the fingernail beds. This nerve can cause an electric shock-like sensation by striking the

medial epicondyle of the humerus The medial epicondyle of the humerus is an epicondyle of the humerus bone of the upper arm in humans. It is larger and more prominent than the lateral epicondyle and is directed slightly more posteriorly in the anatomical position. In birds, whe ...

posteriorly, or inferiorly with the elbow flexed. The ulnar nerve is trapped between the bone and the overlying skin at this point. This is commonly referred to as bumping one's "funny bone". This name is thought to be a

pun A pun, also known as paronomasia, is a form of word play that exploits multiple meanings of a term, or of similar-sounding words, for an intended humorous or rhetorical effect. These ambiguities can arise from the intentional use of homophoni ...

, based on the sound resemblance between the name of the bone of the upper arm, the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

, and the word "

humorous Humour (Commonwealth English) or humor (American English) is the tendency of experiences to provoke laughter and provide amusement. The term derives from the humoral medicine of the ancient Greeks, which taught that the balance of fluids in th ...

". Alternatively, according to the

Oxford English Dictionary The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a com ...

, it may refer to "the peculiar sensation experienced when it is struck".

Structure

Arm

The ulnar nerve originates from the C8- T1 nerve roots (and occasionally carries C7 fibers which arise from the

lateral cord The lateral cord is the part of the brachial plexus formed by the anterior divisions of the upper (C5-C6) and middle trunks (C7). Its name comes from it being lateral to the axillary artery as it passes through the axilla. The other cords of the br ...

), which then form part of the medial cord of the

brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in t ...

, and descends medial to the

brachial artery The brachial artery is the major blood vessel of the (upper) arm. It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa ...

, up until the insertion point of

coracobrachialis muscle The coracobrachialis muscle is the smallest of the three muscles that attach to the coracoid process of the scapula. (The other two muscles are pectoralis minor and the short head of the biceps brachii.) It is situated at the upper and medial part ...

(middle 5 cm over the medial border of the humerus). Then, it pierces the medial intermuscular septum and enters the posterior compartment of the arm, accompanied by superior ulnar collateral vessels. It runs at the posteromedial aspects of the humerus, passing behind the medial epicondyle (in the

cubital tunnel The cubital tunnel is a space of the dorsal medial elbow which allows passage of the ulnar nerve around the elbow. It is bordered medially by the medial epicondyle of the humerus, laterally by the olecranon process of the ulna and the tendinous arc ...

) at the elbow, where it can be palpated by hand.

Forearm

The ulnar nerve is not a content of the cubital fossa. It enters the anterior (flexor) compartment of the forearm between the two heads of

flexor carpi ulnaris The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. Structure Origin The flexor carpi ulnaris has two heads; a humeral head and ulnar head. The humeral head originates from the medial epicondyle of ...

, and lies along the lateral border of the flexor carpi ulnaris. The ulnar nerve runs between the

flexor digitorum superficialis Flexor digitorum superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest pa ...

(laterally) and

flexor digitorum profundus The flexor digitorum profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. Together ...

medially. Near the wrist, it courses superficial to the flexor retinaculum of hand, but covered by volar carpal ligament to enter the hand. In the forearm it gives off the following branches: * Muscular branches of ulnar nerve - supplies one and a half muscles (flexor carpi ulnaris and the medial half of

) *

Palmar branch of ulnar nerve The palmar branch of the ulnar nerve arises about five cm proximal to the wrist from where the ulnar nerve splits into palmar and dorsal branches. It supplies sensory innervation to a small area in the palmar surface of the wrist. The palmar bran ...

- arises from the middle part of the forearm and supplies the skin over the hypothenar eminence. *

Dorsal branch of ulnar nerve The dorsal branch of ulnar nerve arises about 5 cm. proximal to the wrist; it passes backward beneath the Flexor carpi ulnaris, perforates the deep fascia, and, running along the ulnar side of the back of the wrist and hand, divides into two d ...

- arises from 7.5 cm above the wrist, winds backwards to supply the skin of the proximal part of the ulnar one and half fingers and the adjoining area between the fingers. * Articular branches are given off to the elbow joint.

Hand

Ulnar nerve enters the palm of the hand via the

Guyon's canal The ulnar canal or ulnar tunnel (also known as Guyon's canal or tunnel) is a semi-rigid longitudinal canal in the wrist that allows passage of the ulnar artery and ulnar nerve into the hand. The roof of the canal is made up of the superficial pa ...

, superficial to the flexor retinaculum and lateral to the

pisiform bone The pisiform bone ( or ), also spelled pisiforme (from the Latin ''pisifomis'', pea-shaped), is a small knobbly, sesamoid bone that is found in the wrist. It forms the ulnar border of the carpal tunnel. Structure The pisiform is a sesamoid bone, ...

. Here it gives off the following branches: * Superficial branch of ulnar nerve - supplies the

palmaris brevis Palmaris brevis muscle is a thin, quadrilateral muscle, placed beneath the integument of the ulnar side of the hand. It acts to fold the skin of the hypothenar eminence transversally. Structure Origin and insertion Palmaris brevis muscle is l ...

and gives digital branches to the medial one and a half fingers. *

Deep branch of ulnar nerve Deep or The Deep may refer to: Places United States * Deep Creek (Appomattox River tributary), Virginia * Deep Creek (Great Salt Lake), Idaho and Utah * Deep Creek (Mahantango Creek tributary), Pennsylvania * Deep Creek (Mojave River tributary), ...

- It accompanies the deep branch of the ulnar artery. It passes backwards between the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi, supplying all the three muscles, and lying on the hook of

hamate bone The hamate bone (from Latin hamatus, "hooked"), or unciform bone (from Latin ''uncus'', "hook"), Latin os hamatum and occasionally abbreviated as just hamatum, is a bone in the human wrist readily distinguishable by its wedge shape and a hook-l ...

. It then turns laterally, supplying the 3rd and 4th lumbricals and all the

palmar interossei muscles In human anatomy, the palmar or volar interossei (interossei volares in older literature) are three small, unipennate muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are sm ...

and

dorsal interossei of the hand In human anatomy, the dorsal interossei (DI) are four muscles in the back of the hand that act to abduct (spread) the index, middle, and ring fingers away from hand's midline (ray of middle finger) and assist in flexion at the metacarpophalange ...

. It terminates by supplying the

adductor pollicis In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment benea ...

. * Articular branches to the wrist.

Function

Ulnar nerve is also known as "musician's nerve" as it controls the fine movements of the fingers.

Sensory

The ulnar nerve also provides

sensory innervation Cutaneous innervation refers to the area of the skin which is supplied by a specific cutaneous nerve. Dermatomes are similar; however, a dermatome only specifies the area served by a spinal nerve. In some cases, the dermatome is less specific (wh ...

to the fifth digit and the medial half of the fourth digit, and the corresponding part of the palm: *

- supplies cutaneous innervation to the anterior skin and nails *

Dorsal cutaneous branch of ulnar nerve Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal ...

- supplies cutaneous innervation to the dorsal medial hand and the dorsum of the medial 1.5 fingers

Motor

The ulnar nerve and its branches innervate the following muscles in the forearm and hand: *An articular branch that passes to the elbow joint while the ulnar nerve is passing between the olecranon and medial epicondyle of the humerus *In the

forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in ...

, via the muscular branches of ulnar nerve: **

Flexor carpi ulnaris The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. Structure Origin The flexor carpi ulnaris has two heads; a humeral head and ulnar head. The humeral head originates from the medial epicondyle of ...

Flexor digitorum profundus The flexor digitorum profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. Together ...

(medial half) *In the

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...

, via the

deep branch of ulnar nerve Deep or The Deep may refer to: Places United States * Deep Creek (Appomattox River tributary), Virginia * Deep Creek (Great Salt Lake), Idaho and Utah * Deep Creek (Mahantango Creek tributary), Pennsylvania * Deep Creek (Mojave River tributary), ...

: **

Hypothenar The hypothenar muscles are a group of three muscles of the palm that control the motion of the little finger. The three muscles are: * Abductor digiti minimi * Flexor digiti minimi brevis * Opponens digiti minimi Structure The muscles of hypot ...

muscles ***

Opponens digiti minimi The opponens digiti minimi (opponens digiti quinti in older texts) is a muscle in the hand. It is of a triangular form, and placed immediately beneath the palmaris brevis, abductor digiti minimi and flexor digiti minimi brevis. It is one of t ...

*** Abductor digiti minimi *** Flexor digiti minimi brevis **The third and fourth lumbrical muscles ** Dorsal interossei **

Palmar interossei In human anatomy, the palmar or volar interossei (interossei volares in older literature) are three small, unipennate muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are sm ...

Adductor Pollicis In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment benea ...

Flexor pollicis brevis The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part. Origin and insertion The muscle's superficial head arises from the distal edge of the f ...

(deep head) *In the hand, via the superficial branch of ulnar nerve: **

Palmaris brevis Palmaris brevis muscle is a thin, quadrilateral muscle, placed beneath the integument of the ulnar side of the hand. It acts to fold the skin of the hypothenar eminence transversally. Structure Origin and insertion Palmaris brevis muscle is l ...

Clinical significance

The ulnar nerve can suffer injury anywhere between its proximal origin of the brachial plexus all the way to its distal branches in the hand. It is the most commonly injured nerve around the elbow. Although it can be damaged under various circumstances, it is commonly injured by local trauma or physical impingement ("pinched nerve"). Injury of the ulnar nerve at different levels causes specific motor and sensory deficits. At the elbow * ''Common mechanisms of injury'':

Cubital tunnel syndrome Ulnar nerve entrapment is a condition where the ulnar nerve becomes physically trapped or pinched, resulting in pain, numbness, or weakness, primarily affecting the little finger and ring finger of the hand. Entrapment may occur at any point from ...

, fracture of the medial epicondyle of the humerus (causing direct ulnar nerve injury), fracture of the lateral epicondyle of the humerus (causing

cubitus valgus Cubitus valgus is a medical deformity in which the forearm is angled away from the body to a greater degree than normal when fully extended. A small degree of cubitus valgus (known as the carrying angle) is acceptable and occurs in the general ...

with tardy ulnar nerve palsy), Driver's Elbow * ''Motor deficit'': ** Weakness in flexion of the hand at the wrist, loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand. (Note: Motor deficit is absent or very minor in

cubital tunnel syndrome Ulnar nerve entrapment is a condition where the ulnar nerve becomes physically trapped or pinched, resulting in pain, numbness, or weakness, primarily affecting the little finger and ring finger of the hand. Entrapment may occur at any point from ...

as the ulnar nerve is compressed in the cubital tunnel, rather than transected.) ** Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the

metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cav ...

s, and flexion at the

interphalangeal joints Interphalangeal joint may refer to: *Interphalangeal articulations of hand The interphalangeal joints of the hand are the hinge joints between the phalanges of the fingers that provide flexion towards the palm of the hand. There are two sets in ...

. ** Weakness of adduction of the thumb, which may be assessed by the presence of

Froment's sign Froment's sign is a special test of the wrist for palsy of the ulnar nerve, specifically, the action of adductor pollicis. Froment's maneuver can also refer to the cogwheel effect from contralateral arm movements seen in Parkinson's disease. __ ...

. * ''Sensory deficit'': Loss of sensation or

paresthesia Paresthesia is an abnormal sensation of the skin (tingling, pricking, chilling, burning, numbness) with no apparent physical cause. Paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes. Paresthesias ar ...

e in ulnar half of the palm and dorsum of hand, and the medial 1½ digits on both palmar and dorsal aspects of the hand At the wrist * ''Common mechanism'': penetrating wounds, Guyon canal cyst (and other lesions) * ''Motor deficit'': ** Loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand. ** Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the

s, and flexion at the

. ** The claw hand deformity is more prominent with injury at the wrist as opposed to a lesion higher up in the arm, for instance, at the elbow, as the ulnar half of the

is not affected. This pulls the distal interphalangeal joints of the 4th and 5th digit into a more flexed position, producing a more deformed 'claw'. This is known as the ulnar paradox. ** Weakness of adduction of the thumb, which may be assessed by the presence of

. * ''Sensory deficit'': Loss of sensation or

e in ulnar half of the palm, and the medial 1½ digits on the palmar aspect of the hand, with dorsal sparing. The dorsal aspect of the hand is unaffected as the posterior cutaneous branch of the ulnar nerve is given off higher up in the forearm and does not reach the wrist. In severe cases, surgery may be performed to relocate or "release" the nerve to prevent further injury.

Additional images

Image:Brachial_plexus_color.svg, Brachial plexus with courses of spinal nerves shown Image:Gray413.png, Cross-section through the middle of upper arm. Image:Gray417.png, Cross-section through the middle of the forearm. Image:Gray421.png, Transverse section across distal ends of radius and ulna. Image:Gray422.png, Transverse section across the wrist and digits. Image:Gray528.png, Ulnar and radial arteries. Deep view. Image:Gray809.png, The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front. Image:Gray1235.png, Front of right upper extremity, showing surface markings for bones, arteries, and nerves. Image:Gray1236.png, Back of right upper extremity, showing surface markings for bones and nerves. File:Slide4t.JPG, Ulnar nerve File:Slide4zzz.JPG, Brachial plexus with characteristic M, ulnar nerve labeled. File:Slide3bbbb.JPG, Ulnar nerve File:Slide2hhhh.JPG, Ulnar nerve File:Slide10WWW.JPG, Ulnar nerve File:Slide1ecc.JPG, Brachial plexus.Deep dissection. Anterolateral view

References

External links

Cubital Tunnel Support Forums
* - "The major subdivisions and terminal nerves of the

." * - "Anterior view of the nerves, vessels, and superficial tendons that cross the left

wrist In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...

." * - "Transverse section through the

carpal tunnel In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the hand. The tunnel is bounded by the bones of the wrist and flexor retinaculum from connective tissue. Norma ...

and distal row of the

carpal The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, the ...

bones." * * * - "Axilla, dissection, anterior view"
Overview at neuro.wustl.edu

Shoulder Ulnar Nerve Entrapment
* {{Authority control Nerves of the upper limb