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The thenar muscles are a group of three or four short muscles located at the base of the thumb. They are considered part of the thenar eminence, which is the mound formed at the base of the thumb on the palm of the hand. The thenar muscles are responsible for the fine movements of the thumb, including abduction, flexion, and opposition of the thumb. These muscles work together with the adductor pollicis muscle to produce a combination of flexion, adduction, and medial rotation, allowing for precision pinching and power gripping. The thenar muscles are innervated by the median nerve, with the exception of the deep head of flexor pollicis brevis, which receives innervation from the ulnar nerve.
| Characteristics | Values |
|---|---|
| Number of thenar muscles | 3 or 4 |
| Muscle names | Abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and possibly adductor pollicis |
| Muscle function | Fine movements of the thumb, including abduction, flexion, and opposition |
| Innervation | Median nerve (T1) and ulnar nerve (C8, T1) |
| Blood supply to abductor pollicis brevis | Superficial palmar branch of the radial artery |
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What You'll Learn
Thenar muscles are three short muscles at the base of the thumb
The thenar muscles are three short muscles located at the base of the thumb. They form a fleshy bulge, known as the thenar eminence, on the radial side of the palm of the hand. The thenar eminence is made up of the following three muscles: abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. A fourth muscle, the adductor pollicis, is also located in this region but is not part of the thenar muscle group. It is classified on its own as the muscle of the adductor compartment of the hand.
The thenar muscles are responsible for the fine movements of the thumb, including abduction and flexion at the metacarpophalangeal (MCP) and carpometacarpal (CMC) joints. The abductor pollicis brevis abducts the thumb, while the flexor pollicis brevis lies next to the abductor and flexes the thumb, curling it up in the palm. The opponens pollicis is the largest of the thenar muscles and lies underneath the other two. It opposes the thumb by medially rotating and flexing the metacarpal on the trapezium.
The thenar muscles are innervated by the median nerve (T1), with the exception of the deep head of flexor pollicis brevis, which, together with the adductor pollicis muscle, receives innervation via the ulnar nerve (C8, T1). The ulnar nerve is exclusively responsible for the innervations of the hypothenar eminence, which is a muscular protrusion on the medial side of the palm, at the base of the little finger. The hypothenar eminence is made up of four muscles that contract to manifest motion through the little finger.
The thenar muscles are intrinsic muscles of the hand, located within the hand itself. They are responsible for the fine motor functions of the hand, which include precision pinching and power gripping. The complex integrity of the human hand is one of the factors that set humans apart from other primates and animals. The movement of opposition, made possible by the thenar muscles, played an important role in human evolution.
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They are responsible for fine movements of the thumb
The thenar muscles are an intrinsic group of muscles of the thumb that are responsible for its fine movements. They are three short muscles—abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis—located at the base of the thumb, producing a bulge known as the thenar eminence. The opponens pollicis is the largest of the thenar muscles and lies underneath the other two. The abductor pollicis brevis is the most superficial muscle of the thenar group, abducting the thumb, while the flexor pollicis brevis, lying next to the abductor, flexes the thumb, curling it up in the palm.
The thenar muscles are innervated by the median nerve, except for the deep head of flexor pollicis brevis, which, along with the adductor pollicis muscle, is innervated by the ulnar nerve. The adductor pollicis is a large triangular muscle with two heads, which, together with the thenar muscles, forms the short muscles of the thumb. The radial artery passes anteriorly through the space between the two heads, forming the deep palmar arch. The nerves that reach the thenar muscles arise from the C8 and T1 roots, passing through the lower trunk of the brachial plexus and the medial cord of the plexus.
The thenar muscles are involved in the abduction and flexion of the thumb at the metacarpophalangeal (MCP) and carpometacarpal (CMC) joints. Their combined actions with the adductor pollicis muscle can produce the opposition of the thumb, which is the combination of flexion, adduction, and medial rotation. This opposition movement played an important role in human evolution, contributing to our unique dexterity.
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The median nerve innervates all thenar muscles
The thenar muscles are three short muscles located at the base of the thumb. The muscles produce a bulge, known as the thenar eminence. They are responsible for the fine movements of the thumb, including opposition, abduction, and adduction. The median nerve innervates all the thenar muscles. This innervation allows for two-way communication between the brain and spinal cord, and the muscles and overlying skin. The brain and spinal cord can send signals through the median nerve to the muscles, instructing them on when to contract and complete specific actions.
The median nerve is a sensory and motor nerve of the arm. It arises from the lateral and medial cords of the brachial plexus and enters the arm at the axilla (armpit). It then travels with the brachial artery down the shaft of the humerus bone and into the cubital fossa, which is on the surface of the elbow joint. The median nerve innervates some of the major muscles of the forearm and hand.
The median nerve enters the hand via the carpal tunnel, where it divides into two branches: the recurrent branch and the palmar digital nerve. The recurrent branch innervates the thenar muscles, while the palmar digital nerve innervates the palmar surface and fingertips of the lateral three and a half digits. The median nerve also gives rise to the anterior interosseous nerve, which supplies the deep muscles in the anterior forearm.
The thenar eminence contains the palm muscles at the base of the thumb. The three muscles of the thenar eminence are the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. The abductor pollicis brevis abducts the thumb and is the most superficial of the thenar group. The flexor pollicis brevis lies next to the abductor and flexes the thumb, curling it up in the palm. The opponens pollicis is the largest of the thenar muscles and lies underneath the other two. It opposes the thumb by medially rotating and flexing the metacarpal on the trapezium.
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The opponens pollicis is the largest thenar muscle
The thenar muscles are three short muscles located at the base of the thumb. They are responsible for the fine movements of the thumb. The thenar eminence is the mound formed at the base of the thumb on the palm of the hand by the intrinsic group of muscles of the thumb. The word thenar comes from the Ancient Greek 'θέναρ' (thenar) meaning 'palm of the hand'.
The opponens pollicis is the largest of the thenar muscles. It lies underneath the other two muscles, the abductor pollicis brevis and the flexor pollicis brevis. The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It originates from the flexor retinaculum of the hand and the tubercle of the trapezium, and it inserts onto the lateral margin of the first metacarpal. The median nerve innervates the muscle, although in 20% of people, it is innervated by the ulnar nerve.
The opponens pollicis is one of the three muscles that form the thenar eminence, along with the abductor pollicis brevis and the flexor pollicis brevis. The abductor pollicis brevis abducts the thumb, while the flexor pollicis brevis lies next to the abductor and flexes the thumb, curling it up in the palm. The opponens pollicis lies deep to the abductor pollicis brevis and, as its name suggests, opposes the thumb, bringing it against the fingers. This opposition of the thumb is a combination of actions that allows the tip of the thumb to touch the tips of the other fingers.
The two opponens muscles, the opponens pollicis and the opponens digiti minimi, are named so because they oppose each other, but their actions appose the bones. The part of apposition that the opponens pollicis is responsible for is the flexion of the thumb's metacarpal at the first carpometacarpal joint. This specific action cups the palm.
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Thenar muscles can show wasting in Carpel Tunnel Syndrome
The thenar muscles are three short muscles located at the base of the thumb. They are responsible for the fine movements of the thumb. The median nerve innervates all the thenar muscles, except for the flexor pollicis brevis, which is innervated by the ulnar nerve.
The thenar eminence is the mound formed at the base of the thumb due to the thenar muscles. The three muscles of the thenar eminence are:
- Abductor pollicis brevis: This muscle abducts the thumb and is the most superficial of the thenar group.
- Flexor pollicis brevis: This muscle lies next to the abductor and flexes the thumb, curling it up in the palm.
- Opponens pollicis: This muscle lies deep to the abductor pollicis brevis and opposes the thumb, bringing it against the fingers.
Carpal tunnel syndrome (CTS) is a condition that causes numbness, nocturnal paresthesia, and hypoesthesia in the skin innervated by the median nerve. It is caused by compression of the median nerve within the carpal tunnel. CTS is often associated with thenar atrophy, which is the wasting or shrinking of the thenar muscles. Thenar atrophy is a specific symptom of CTS, with a specificity of 90-99%, although its sensitivity is low at only 12.6%. Patients with CTS and thenar atrophy may experience grip and pinch strength deficits, which can be improved through surgical treatment.
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Frequently asked questions
The thenar muscles are three short muscles located at the base of the thumb. They are responsible for the thumb's fine movements.
The thenar muscles are responsible for the abduction and flexion of the thumb at the metacarpophalangeal (MCP) and carpometacarpal (CMC) joints. They also contribute to the medial rotation of the thumb.
The thenar muscles originate from different carpal bones and insert distally onto the thumb.
There are three thenar muscles: abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. A fourth muscle, the adductor pollicis, is located in the same region but is not part of the thenar muscle group.
The thenar and hypothenar muscles are both intrinsic muscles of the hand. The thenar muscles are located at the base of the thumb, while the hypothenar muscles are located at the base of the little finger.
