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The human hand is a complex network of bones, muscles, nerves, connective tissue, and blood vessels. There are 34 muscles in each hand, which can be divided into intrinsic and extrinsic groups. Intrinsic muscles are located within the hand itself and are responsible for fine motor functions. Extrinsic muscles are located near the outside of the hand and in the forearm, providing strength. The muscles of the hand are innervated by the radial, median, and ulnar nerves. The fingers have two long flexors, which allow for the bending of the fingers, and extensors, which straighten the digits. The thumb has its own set of muscles that allow it to move in opposition to the fingers, making grasping possible.
| Characteristics | Values |
|---|---|
| Number of muscles in each hand | 34 |
| Muscle groups | Thenar, Hypothenar, Interossei, Lumbrical, Flexor, Extensor |
| Intrinsic muscles | Located within the hand itself and responsible for fine motor functions |
| Extrinsic muscles | Located near the outside of the hand and forearm, providing strength |
| Flexion | Moves the wrist down, towards the palm |
| Extension | Pulls the wrist up |
| Adduction | Bends the wrist in, towards the center of the body |
| Abduction | Bends the wrist out, away from the center of the body |
| Innervation | Radial, Median, and Ulnar nerves |
| Interossei muscles | Between the metacarpal bones in the palm, helping fingers move side-to-side |
| Lumbrical muscles | At the base of the four non-thumb fingers, helping finger flexion |
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What You'll Learn
Interossei muscles: help fingers move side-to-side
The interossei muscles are located between the metacarpal bones in the palm of the hand. They are intrinsic muscles, meaning they are located within the hand itself. They are responsible for fine motor functions and assist in moving the fingers side-to-side.
The interossei muscles can be divided into two groups: the dorsal interossei and the palmar interossei. There are four dorsal interossei muscles and three or four palmar interossei muscles. The first palmar interosseous muscle is often considered rudimentary and part of either the adductor pollicis or the flexor pollicis brevis.
The dorsal interossei muscles abduct the fingers, moving them away from each other. The dorsal interossei 1-2 pull the digits 2-3 laterally, while the dorsal interossei 3-4 move the digits 3-4 medially. The third digit can be abducted both medially and laterally, depending on which dorsal interosseous muscle contracts. The dorsal interossei muscles also assist in flexion at the metacarpophalangeal (MCP) joints and extension at the interphalangeal (IP) joints.
The palmar interossei muscles, on the other hand, adduct the fingers, pulling them together. They also contribute to flexion at the MCP joints and extension at the IP joints.
The interossei muscles work together with the lumbrical muscles, which are crucial for finger movement. The lumbricals link the extensor tendons to the flexor tendons, allowing for flexion at the MCP joint and extension at the IP joints.
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Lumbrical muscles: help flex fingers
The human hand is a complex network of bones, muscles, nerves, connective tissue, and blood vessels. There are 34 muscles in each hand, which work together to help you move your fingers and control objects.
The lumbrical muscles are a group of four intrinsic muscles in each hand that help flex the fingers. They are located at the base of the four non-thumb fingers. They are small, worm-like muscles that do not attach to bones. Instead, they attach proximally to the tendons of the flexor digitorum profundus and distally to the extensor expansions.
The lumbricals are crucial for finger movement, linking the extensor tendons to the flexor tendons. They allow for flexion at the metacarpophalangeal (MCP) joints and extension at the interphalangeal (IP) joints. This enables complex movements of the hand, such as holding a pen, and contributes to the hand's dexterity.
The lumbricals are innervated by the median and ulnar nerves. The lateral two lumbricals, controlling the index and middle fingers, are innervated by the median nerve. The medial two lumbricals, controlling the little and ring fingers, are innervated by the ulnar nerve.
Injuries to the lumbrical muscles can result in adhesions between the lumbrical and the interosseous muscle, causing pain when making a fist. A condition known as lumbrical-plus finger can occur when the tendons of the flexor digitorum profundus detach distal to the origin points of the lumbricals. This results in the paradoxical extension of the fingers when attempting to close the fist.
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Flexion and extension: muscles that move the wrist up and down
The human hand and wrist are complex parts of the body that enable us to interact with the world around us. The wrist acts as a pivot point, allowing the hand to move in almost any direction. The hand and wrist are made up of a complicated network of bones, muscles, nerves, connective tissue, and blood vessels.
Flexion and extension are two types of movements that allow the wrist to move up and down. Flexion is the movement of the wrist down toward the palm. Muscles that enable flexion include the flexor carpi ulnaris, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis. The flexor carpi radialis is an elbow muscle that crosses the elbow and wrist and attaches to the base of the second hand bone. It can also help move the wrist toward the thumb. The palmaris longus muscle, on the other hand, travels down the forearm to the centre of the wrist and palm, where it attaches to the palmar aponeurosis. It functions as a flexor of the wrist.
Extension is the movement of the wrist up and away from the palm. Muscles that enable extension include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, and extensor digitorum. The extensor carpi radialis longus and brevis work together to straighten and stabilize the wrist. The extensor carpi ulnaris also functions to straighten and stabilize the wrist, providing the ability to move the wrist away from the thumb.
The radiocarpal joint is the intersection of the distal end of the radius and the proximal row of carpals. This joint allows the hand and wrist to move down (palmar flexion) and up (extension or dorsiflexion). It is a true synovial joint, containing lubricating fluid within a joint capsule. The radiocarpal joint is commonly hypermobile in gymnasts, acrobats, and yogis due to the demands of their sports, which can make it susceptible to injury.
In summary, the flexion and extension movements of the wrist are enabled by a complex interplay of muscles, tendons, and joints. These movements allow us to perform various tasks and motions in our daily lives.
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Thenar muscles: control the thumb
The human hand is a complex network of bones, muscles, nerves, connective tissue, and blood vessels. The muscles in the hand work together with the muscles in the forearm to give the hand its strength and dexterity. There are 34 muscles in each hand, which can be categorised into different groups. One such group is the thenar muscles, which control 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 thenar eminence is made up of three separate muscles that work to control the thumb's fine motions, including grabbing, gripping, and pinching. The three muscles are:
- Opponens pollicis: This is the largest of the muscles found in the thenar eminence. Its function is very important to what makes human thumbs opposable. The opponens pollicis works to move the thumb away from the other fingers of the hand. During this motion, the thumb rotates so that it opposes, or is across from, the other four fingers of the hand. This motion is very important for tasks such as gripping and grasping objects.
- Abductor pollicis brevis: This muscle is located above the opponens pollicis along the outside of the thumb. Its function is to help move the thumb away from the index finger. It is the most superficial of the thenar group.
- Flexor pollicis brevis: This muscle lies next to the abductor pollicis brevis and will flex the thumb, curling it up in the palm.
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Hypothenar muscles: control the area opposite the thumb
The hypothenar muscles are a group of three or four muscles in the palm that control the motion of the little finger, or the area opposite the thumb. They form the hypothenar eminence, a "fleshy" mound on the medial side of the palm, at the base of the little finger. The hypothenar muscles are similar to the thenar muscles in both name and organisation. The thenar muscles are three short muscles located at the base of the thumb, which control the thumb's movements.
The hypothenar eminence is innervated by the ulnar nerve. If the ulnar nerve is damaged, hypothenar atrophy can occur, along with a loss of sensory and motor function in the region. This is known as Guyon's canal syndrome, similar to carpal tunnel syndrome, but involving the ulnar nerve. Arterial injury to the ulnar artery can also affect the hypothenar eminence, leading to a condition called hypothenar hammer syndrome.
The opponens digiti minimi lies deep to the other hypothenar muscles. It originates from the hook of hamate and associated flexor retinaculum, inserting into the medial margin of metacarpal V. It rotates the metacarpal of the little finger towards the palm, producing opposition.
The palmaris brevis is a small, thin muscle found in the subcutaneous tissue of the hypothenar eminence. It originates from the palmar aponeurosis and flexor retinaculum, attaching to the dermis of the skin on the medial margin of the hand. When it contracts, it wrinkles the skin of the hypothenar eminence and deepens the curvature of the hand, improving grip.
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Frequently asked questions
The muscles that move the wrist include the flexor carpi radialis, which bends the wrist, and the extensor carpi radialis longus, which straightens and stabilises the wrist.
The muscles that move the fingers include the interossei muscles, which help the fingers move side-to-side, and the lumbrical muscles, which help flex the fingers.
The muscles that move the thumb are the thenar muscles.
The two types of grip are power grip and precision grip. Power grip is where your grip strength comes from, for example, when picking up a heavy box. Precision grip is using your hand and fingers to move or touch a smaller object, for example, picking up a pen off your desk.
