Maximus Gage
The muscles in our hands and wrists are part of a complicated network of bones, nerves, tendons, ligaments, and blood vessels. The muscles in our hands can be divided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors, which are located in the forearm. The intrinsic group is made up of smaller muscles found within the hand itself. The muscles in our hands and wrists allow us to perform a wide range of motions, such as bending our fingers. The flexor digitorum profundus, for example, is a muscle that arises from the ulna and interosseous membrane in the forearm. Four tendons emerge from this muscle, which pass through the carpal tunnel and insert into the tips of the index, middle, ring, and small fingers, allowing them to bend.
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What You'll Learn
The flexor digitorum profundus muscle bends the index, middle, ring, and small fingers
The flexor digitorum profundus is a muscle in the forearm that bends the index, middle, ring, and small fingers. It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. The flexor digitorum profundus arises from the ulna and interosseous membrane in the mid-forearm and fans out into four tendons that pass through the carpal tunnel and insert into the tips of the index, middle, ring, and small fingers.
The primary action of the flexor digitorum profundus is to bend these fingers, and due to its insertion past the last joint of the finger, it can bend all three finger joints. The flexor digitorum profundus is the only muscle that can bend the distal interphalangeal (DIP) joint of the second to the fifth digits. It also acts as a flexor of the midcarpal (wrist), metacarpophalangeal, and proximal interphalangeal (PIP) joints of the same fingers. The flexor digitorum profundus is the main gripping muscle and functions optimally when the wrist is extended.
The flexor digitorum profundus is a hybrid muscle supplied by two different nerves. The medial half, which flexes the ring and little fingers, is supplied by the ulnar nerve. The lateral half, which flexes the middle and index fingers, is supplied by the anterior interosseous nerve, a motor branch of the median nerve.
The flexor digitorum profundus also aids the lumbrical muscles, which originate on the palmar side of the hand and attach on the dorsal aponeurosis, in their role as extensors of the interphalangeal joints. By transferring power from the flexor digitorum profundus, the lumbrical muscles are able to fully extend the fingers as well as flex the metacarpophalangeal joints.
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The flexor pollicis longus muscle bends the thumb
The flexor pollicis longus muscle is a muscle in the forearm and hand that bends the thumb. It is one of three deep flexor muscles found in the volar compartment of the forearm, with its muscle belly located on the forearm. It is the ninth tendon to pass through the carpal tunnel on its way to the thumb.
The flexor pollicis longus muscle is unique to humans, being either rudimentary or absent in other primates. However, in orangutans, there is a tendon similar in insertion and function to the FPL in humans, but with an intrinsic origin on the oblique head of the adductor pollicis. Lesser apes, such as gibbons, and Old World monkeys, like baboons, share an extrinsic FPL muscle tendon with humans.
The primary function of the flexor pollicis longus muscle is to flex the thumb, making it crucial for grip strength. It provides flexion at both the metacarpophalangeal and interphalangeal joints, allowing the thumb to bend inwards towards the palm of the hand. This muscle also assists in weak flexion of the wrist joint when the thumb is fixed.
To strengthen the flexor pollicis longus muscle, a simple exercise can be performed. Sit in a comfortable chair with your hand and palm facing you. Place a band around your thumb, and then move your thumb towards your little finger. Touch your thumb to each of your fingers in turn, focusing on the flexion of your thumb. Be sure to fully extend your fingers and thumb between each finger touch. Repeat this exercise ten times and then switch to your other hand.
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The lumbrical muscles help bend the MCP joints
The lumbrical muscles are a group of four muscles in the hand. They are special because they have no bony origin, instead arising from the deep flexor and inserting into the extensor hood mechanism. The name 'lumbrical' comes from the Greek word for earthworm.
The primary function of the lumbrical muscles is to allow the fingers to straighten. However, they can also help bend the MCP joints, which are at the knuckle. The lumbricals arise from the flexor digitorum profundus tendons and insert into the dorsal extensor expansions of the proximal phalanges. This means they are capable of flexion at the MCP joints and extension in the proximal (PIP) and distal interphalangeal joints (DIP).
The lumbricals' ability to perform opposite actions is due to the tendons crossing the MCP on the palmar side, but distally inserting at the dorsal side of the finger. These combined movements contribute to the complex movement and dexterity of the hand. For example, the lumbricals are involved when holding a pen.
The lumbricals are also involved in a clinical phenomenon known as the lumbrical-plus finger. This occurs when there is an injury or amputation of the flexor digitorum profundus tendon distal to the lumbrical origin. The intended fist closure paradoxically leads to an extension of the fingers.
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The thenar muscle group is found at the base of the thumb
The muscles of the hand can be divided into two groups: the extrinsic and intrinsic muscle groups. The intrinsic muscles of the hand are located within the hand itself and are responsible for the fine motor functions of the hand. The thenar muscle group is found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. It is made up of three muscles: the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. The abductor pollicis brevis pulls the thumb away from the index finger, and the flexor pollicis brevis bends the thumb towards the small finger. The opponens pollicis is responsible for one of the human hand's most important functions: the ability to bring the thumb away from the fingers so that we can grasp objects. It helps pull the thumb away from the index finger, rotating it so that the thumb tip is opposite or "opposes" the tips of the other fingers.
The adductor pollicis is another muscle that controls the movement of the thumb, allowing for rotation and opposition. Despite its name, the adductor pollicis is not part of the thenar group of muscles and is supplied by the ulnar nerve. The opponens pollicis and abductor pollicis brevis are typically innervated by the recurrent branch of the median nerve. The flexor pollicis brevis has two heads: a superficial and a deep head. The superficial head is usually innervated by the recurrent branch of the median nerve, while the deep head is innervated by the deep branch of the ulnar nerve (C8 and T1 roots). The abductor pollicis brevis is the most superficial muscle of the thenar group.
The thenar muscles consist of three short muscles located on the lateral (radial) aspect of the hand. These muscles originate from different carpal bones and distally attach to the thumb. The majority of the thenar muscles are innervated by the median nerve (T1). An exception is the deep head of flexor pollicis brevis, which, along with the adductor pollicis muscle, is innervated by the ulnar nerve (C8 and T1). The prime function of the flexor pollicis brevis muscle is to produce flexion of the thumb at the metacarpophalangeal and carpometacarpal joints, as well as contributing to the medial rotation of the thumb.
The interossei muscles, consisting of four dorsal and three palmar interossei muscles, also play a role in finger movement. While all interossei muscles bend the MCP joints, the dorsal interossei allow us to spread our fingers apart, and the palmar interossei pull our fingers together. The first dorsal interosseous muscle is the largest and is responsible for pulling the index finger away from the middle finger and the thumb towards the index finger. This action provides strength and stability when pinching.
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The hypothenar muscle group is formed by three muscles
The human hand is made up of extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors, while the intrinsic groups are the smaller muscles located within the hand itself. The intrinsic muscle groups include the thenar (thumb) and hypothenar (little finger) muscles.
The flexor digiti minimi allows the little finger to bend at the MCP joint. The flexor digitorum profundus arises from the ulna and interosseous membrane. Four tendons emerge from the muscle, which pass through the carpal tunnel and insert into the tips of the index, middle, ring, and little fingers. Its primary action is to bend these fingers. The opponens digiti minimi is the deepest of the hypothenar muscles. It originates from the hook of hamate and associated flexor retinaculum and inserts into the medial margin of metacarpal V. The opponens muscle allows us to cup our hands, bringing the little finger towards the thumb.
The hypothenar muscles are innervated by the ulnar nerve, except for the palmaris brevis, which is innervated by the superficial branch of the ulnar nerve. The ulnar nerve supplies the three hypothenar muscles, and its lesion is associated with hypothenar atrophy. The ulnar nerve also innervates the flexor digitorum profundus, which is the chief gripping muscle.
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Frequently asked questions
The muscles that bend the fingers are the flexor muscles. These include the flexor digitorum superficialis and the flexor digitorum profundus, which extend from the forearm into the hand via tendons. The flexor digitorum profundus is the chief gripping muscle.
The flexor pollicis longus and flexor pollicis brevis are the muscles that bend the thumb. The flexor pollicis longus is a flexor muscle that arises from the mid-forearm and allows us to bend the tip of our thumb. The flexor pollicis brevis is part of the thenar muscle group, which forms the muscle bulk on the thumb side of the hand.
The flexor digiti minimi is the muscle that bends the little finger. It is part of the hypothenar muscle group, which forms the muscle bulk on the little finger side of the hand.
The extensors are the muscles that help to straighten the fingers. There are nine extensor muscles found in the forearm that work against the flexor muscles to extend the hand and fingers.
Flexor muscles are responsible for flexing and curling movements of the fingers, hand, and wrist. Extensor muscles, on the other hand, help to extend and straighten the digits. Both types of muscles work together to provide a wide range of motion to the hand and fingers.
