Logan Steele
The human hand is a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. There are no muscles in the fingers themselves; instead, the muscles that control finger movement are located in the forearm and hand. The muscles of the hand can be divided into two groups: extrinsic and intrinsic. The extrinsic muscles are the long flexors and extensors, while the intrinsic muscles are the smaller muscles located within the hand itself. The muscles that bend the fingers include the flexor digitorum superficialis, flexor digitorum profundus, and the flexor pollicis longus.
| Characteristics | Values |
|---|---|
| Muscles that bend fingers | Flexor digitorum profundus, flexor digitorum superficialis, flexor pollicis longus, flexor pollicis brevis, flexor carpi radialis, flexor carpi ulnaris, palmaris longus, extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, extensor pollicis brevis, extensor pollicis longus, extensor indicis, extensor digitorum, extensor digiti minimi, abductor pollicis longus, abductor digiti minimi, opponens digiti minimi, abductor pollicis brevis, adductor pollicis, opponens pollicis |
| Muscle groups | Extrinsic and intrinsic |
| Intrinsic muscle groups | Thenar (thumb), hypothenar (little finger), intermediate (middle of the hand), interossei (four dorsally and three volarly), lumbrical |
| Muscle belly | Located on the forearm |
| Muscle belly divisions | Four tendons |
| Tendon function | Connect muscle to bone |
| Ligaments | Collateral, volar plate, ulnocarpal, radiocarpal, volar carpal, dorsal radiocarpal |
| Repetitive strain injuries | Trigger finger, trigger thumb, Dupuytren contracture |
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What You'll Learn
Flexor tendons help bend the fingers
The human hand is a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. Tendons are fibrous cords, similar to ropes, and are made of collagen. They connect muscles to bones and help the joints move smoothly.
Flexor tendons are tendons that help bend the fingers, hand, and wrist. They are also called FDP tendons. When muscles contract, their tendon pulls through the attachments to the bone and causes a joint to move. The flexor tendons are under tension as they connect the muscle to the bone. The muscles that move the fingers and thumb are located in the forearm and hand. Long tendons run from the end of the muscles through small tunnels in the wrist and hand to attach to the small bones (phalanges) of the fingers and thumb. These tunnels are called tendon sheaths. The tendon sheaths keep the tendons close to the bones and joints and also provide lubrication to the tendons to help them glide freely.
The flexor digitorum profundus (FDP) tendon helps bend the index, middle, ring, and small fingers at the fingertip joint. The muscle that moves these tendons is a common muscle belly shared by all the fingers. The muscle belly divides into four tendons that run down the forearm and within the carpal tunnel. The four tendons glide in sheaths along the hand and fingers and insert into the fingertip bone. These tendons run closer to the bone compared to the rest of the flexors in the hand and fingers.
The FCU tendon is one of two tendons that bend the wrist. Its muscle belly is in the forearm. The tendon travels along the inside of the forearm on the side of the small finger and crosses the wrist. It attaches to the wrist bone and the fifth hand bone. The flexor pollicis longus (FPL) tendon bends the thumb. The FPL tendon is the ninth tendon to pass through the carpal tunnel on its way to the thumb.
Injuries to flexor tendons can cause serious issues. A cut or ruptured tendon in the forearm, at the wrist, in the palm, or along the finger will make it difficult or maybe impossible to bend one or more joints in a finger. It is recommended that flexor tendon injuries should be repaired within 7 to 10 days of the injury. A flexor tendon takes approximately 3 to 4 months to heal before the hand is strong enough to use without restrictions.
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Extensor tendons straighten the fingers
The human hand is a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. Tendons are fibrous cords, similar to ropes, and are made of collagen. They have blood vessels and cells to maintain tendon health and repair injured tendons. Tendons are attached to muscles and bones. As the muscle contracts, it pulls on the tendon, and the tendon moves the bone to which it is attached, as well as any joints it crosses.
Extensor tendons are one of the two groups of tendons in the hand and wrist, the other being flexor tendons. Extensor tendons help extend and straighten the fingers, hand, and wrist. When you bend or straighten your finger, the extensor tendons slide through snug tunnels called tendon sheaths, which keep the tendons in place next to the bones. On the bottom of the hand, this system of pulleys improves mechanical efficiency.
The EIP tendon, for example, straightens the index finger. It works with the extensor digitorum communis to the index finger. It has its own muscle belly in the forearm, and as it becomes a tendon, it travels through a tough band or retinaculum in the wrist. The band of tissue, or retinaculum, holds the tendons in place but allows them to slide up and down the arm. It travels down the hand and attaches to the back of the index finger to straighten the three index finger joints.
The EPL tendon straightens the most distal (farthest from the body) joint of the thumb. Its muscle belly is in the forearm, and the tendon travels along the wrist and enters the third compartment of the band that holds the tendons in position at the wrist. It then travels around a prominent part of the radius bone that acts like a pulley, called Lister's tubercle. The tendon then attaches to the most distal bone in the thumb.
Extensor tendon injuries often require surgery. A torn or cut tendon in the forearm, at the wrist, in the palm, or along the finger will make it impossible to extend one or more joints of the finger or wrist. Because extensor tendons are close to the surface of the skin, a deep cut will most likely hit an extensor tendon.
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Thenar muscles control the thumb
The thenar eminence is a group of muscles that form a mound at the base of the thumb on the palm of the hand. The word "thenar" comes from the Ancient Greek "θέναρ" (thenar), meaning "palm of the hand". The thenar eminence is made up of three muscles that work together to control the fine movements of the thumb, allowing humans to carefully handle and manipulate items and objects.
The three muscles that form the thenar eminence are the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. The abductor pollicis brevis pulls the thumb away from the index finger. This muscle is the most superficial of the thenar group. The flexor pollicis brevis lies next to the abductor and bends the thumb towards the small finger, curling it up in the palm. The opponens pollicis is the largest of the muscles found in the thenar eminence and is located beneath the abductor pollicis brevis. It performs one of the most important functions of the human hand: opposability, or the ability to bring the thumb away from the fingers so that we can grasp objects. The opponens pollicis pulls the thumb away from the index finger, rotating it so that the tip of the thumb is opposite, or "opposes", the tips of the other fingers.
The thenar eminence is innervated by the median nerve and the ulnar nerve. 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 muscle group is formed by three muscles: the abductor digiti minimi, the flexor digiti minimi, and the opponens digiti minimi. The median nerve runs along the inside of the arm, supplying nerves to the muscles of the forearm, wrist, and hand. A small portion of the flexor pollicis brevis, referred to as the deep head, is supplied with nerves by the ulnar nerve. Additionally, the opponens pollicis is supplied with nerves by the ulnar nerve in about 20% of people.
The thenar eminence is susceptible to various conditions that can affect its function or lead to atrophy of the muscles. For example, basal thumb arthritis is caused by the breakdown of cartilage around the lower thumb joint, resulting in a loss of motion or weakness of the thumb. Trauma to the forearm, wrist, or thumb can also lead to nervous or arthritic conditions that affect the thenar eminence. Repetitive strain injuries can occur from overuse of the hand and wrist, and it is important to rest and recover after intense activity.
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Hypothenar muscles control the little finger
The hand and wrist are a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. The intrinsic muscles of the hand are located within the hand itself and are responsible for fine motor functions. The hypothenar muscles are a group of three muscles of the palm that control the motion of the little finger. The three muscles are the abductor digiti minimi, the flexor digiti minimi, and the opponens digiti minimi.
The abductor digiti minimi allows the little finger to pull away from the ring finger. The flexor digiti minimi allows the little finger to bend at the MCP joint. The opponens digiti minimi allows us to cup our hands, bringing the little finger towards the thumb. The opponens digiti minimi, along with the largest of the thenar muscles, the opponens pollicis, leads to opposition between the little finger and the thumb.
The hypothenar muscles are innervated by the ulnar nerve. Hypothenar atrophy is associated with lesions of the ulnar nerve, which can lead to a loss of sensory and motor function in the region. Ulnar nerve repair requires knowledge of its course in the Guyon's canal, as compression or injury can result in atrophy of the hypothenar eminence.
The lumbrical muscles are crucial to finger movement, linking the extensor tendons to the flexor tendons. The medial two lumbricals, associated with the little and ring fingers, are innervated by the ulnar nerve. Denervation of these muscles can result in the ulnar claw and hand of benediction.
The hand and wrist are susceptible to various injuries and conditions due to their complexity and frequent use. Common issues include tendonitis, carpal tunnel syndrome, and repetitive strain injuries. It is important to take preventive measures, such as wearing protective equipment, stretching, and allowing for rest and recovery, to maintain hand and wrist health.
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Lumbrical muscles help bend the MCP joints
The human hand and wrist are a complex network of bones, muscles, nerves, tendons, and ligaments. The main role of the lumbrical muscles is to allow the fingers to straighten, but they can also help bend the MCP joints, which are at the knuckle. The name of this muscle is derived from the Greek word for earthworm.
The lumbrical muscles of the hand flex the fingers at the MCP joints and extend them at the interphalangeal (IP) joints. These actions are important for many functions of the hand, such as gripping movements. The lumbricals of the foot have a similar action on the toes. The lumbrical muscles of the hand are numbered 1-4 from the most radial/lateral to the most ulnar/medial. Each lumbrical muscle originates from one or two adjacent tendons of the flexor digitorum profundus muscle. Lumbricals 1-2 are usually unipennate, meaning their fibres arise obliquely from one tendon, while lumbricals 3-4 are bipennate, arising from two adjacent tendons. The first lumbrical arises from the radial side and palmar surface of the tendon of the index finger. The fourth lumbrical arises from the ulnar side of the ring finger tendon and the radial side of the little finger tendon.
The fact that the lumbrical muscles of the hand originate from tendons and insert into the extensor expansions, instead of bony structures, makes both of their attachment points quite mobile. This means the muscles are capable of two different actions: flexion at the MCP joints and extension in both the proximal (PIP) and distal interphalangeal joints (DIP). The reason for the opposite actions is that the tendons cross the MCP on the palmar side but distally insert at the dorsal side of the finger. These combined movements play a role in the complex movement of the hand, such as holding a pen, and contribute to the general dexterity of the hand.
The interossei muscles also bend the MCP joints. While the dorsal interossei allow us to spread our fingers away from each other, the palmar interossei pull our fingers together. The first dorsal interosseous muscle is the largest and originates from the 1st and 2nd hand bones. It forms the contour between the thumb and index finger when looking at the top of the hand. The flexor digitorum profundus muscle also plays a role in bending the fingers. Four tendons emerge from this muscle that pass through the carpal tunnel and insert into the tips of the index, middle, ring, and small fingers.
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Frequently asked questions
The muscles that control finger motion are located in the hand and forearm. The muscles that bend the fingers are the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus. The flexor digitorum profundus arises from the ulna and interosseous membrane. Four tendons emerge from the flexor digitorum profundus muscle, which bend the index, middle, ring, and small fingers.
Flexor tendons help you flex and curl your fingers, hand, and wrist. Extensor tendons help you extend and straighten your fingers, hand, and wrist.
Intrinsic muscles are smaller muscles located within the hand itself. Extrinsic muscles are long flexors and extensors with the muscle belly located on the forearm.
There are four dorsal and three palmar interossei muscles. The dorsal interossei allow us to spread our fingers apart, while the palmar interossei pull our fingers together.
The thenar muscle group is found at the base of the thumb and is comprised of three muscles: the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis.
