Home > For Consumers > How does the hand work?

PubMed Health. A service of the National Library of Medicine, National Institutes of Health.

Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-.

Informed Health Online [Internet].

How does the hand work?

Last Update: December 23, 2016; Next update: 2019.

The hand has a very delicate and complex structure. This allows muscles and joints in the hand a great range of movement and precision. The different forces are also distributed in the hand in the best possible way. But the hand is also quite vulnerable: tendons, nerve fibers, blood vessels and very thin bones are all positioned right under the skin and are only protected by a thin layer of muscle and fat. Only the palm is protected by a strong pad of tendons (aponeurosis) for a powerful grip. Our hands are put through quite a lot day in and day out, and are often within range of dangerous tools. This makes hand injuries and problems due to wear and tear very common.

The right and left hand are each controlled by the opposite hemisphere of the brain. Usually one hand is preferred for fine and complex motion, leading us to speak of someone as being either right- or left-handed.

Bones and joints

The human hand has a complex structure made up of a total of 27 individual bones: 8 carpal bones, 5 metacarpal bones and 14 finger bones (also called phalanges) are connected by joints and ligaments. About one fourth of all our body’s bones are found in our hands. The hand can be viewed in three sections by joint function:

Illustration: The human hand has a complex structure made up of a total of 27 individual bones

The human hand has a complex structure made up of a total of 27 individual bones.

Wrist

The wrist is made up of two parts working together as one functional unit. It allows us to flex or extend the hand. The hand can also be tilted in the direction of the little finger or the thumb.

Carpus

The carpal bones are held together tightly by ligaments, and are more or less fixed in relation to one another. They form two rows: four carpal bones are in the first row closer to the forearm. Two of these, together with the radius form the inferior radioulnar joint, which is very important for the movement of the hand. The ulna is separated from the carpal bones by a cartilage disc. The other joint is located between the two rows of carpal bones.

Metacarpus

The metacarpus extends from the second row of the carpal bones. It has five elongated metacarpal bones. You can feel them quite well through the skin on the back of your hand. One of the metacarpal bones together with the thumb’s proximal phalanx makes up the carpometacarpal joint of the thumb, giving the thumb better freedom of movement compared with the other fingers.

Fingers

The five fingers make up the freely moveable part of the hand. Each has three individual bones – except for the thumb, which has only two. In each of these four fingers there are three joints, which can only be moved in one way (extension and flexion). The thumb, however, can also rotate owing to the carpometacarpal joint so that it can also be positioned opposite the other four fingers.

Muscles

The hand and forearm, connected by the wrist, make up a functional unit. There are over 30 muscles here, working together in a highly complex way.

Long forearm muscles

Movements of the hand are mostly started by muscles in the forearm. Only the thin tendons of these muscles are directly a part of the hand: the extensor tendons used for extending the hand run through the back of the hand to the tips of the fingers, and the flexor tendons run through the palms to the fingers.

Short hand muscles

The short muscles of the hand lie between the individual metacarpal bones. They allow us to spread our fingers (abduction) and then press them back together (adduction). They also help us to flex the metacarpophalangeal joints and extend our fingers.

The thenar eminence and the hypothenar eminence muscles

Two groups of more powerful muscles in the hand itself make up the thenar eminence (at the base of the thumb) and the hypothenar eminence (controlling the little finger). The thenar eminence helps the thumb to move. This includes the essential movement of opposition, allowing the thumb and the tips of the remaining four fingers to touch. A separate muscle for flexing (adductor) can help move the thumb towards the palm. The muscles of the hypothenar eminence are mainly used for extending and bending the little finger, as well as for tightening the skin that covers the hypothenar eminence.

Lumbricals

The lumbricals of the hand are four thin, worm-shaped muscles that help bend the metacarpophalangeal joints and extend the fingers.

Connective tissue and tendons

The long flexor and extensor tendons of the forearm muscles are partially surrounded by protective layers, called tendon sheaths. They produce a fluid that acts as a joint lubricant to lessen any friction caused by movement. The tendon sheaths can become inflamed, which may be caused by injuries or by overuse resulting from repetitive uniform motions.

Muscle tendons, nerves and blood vessels run from the forearm to the hand through a passageway, which is level with the wrist on the inside of the hand. This passageway is called the carpal tunnel and is made up of connective tissue and carpal bones. If the tissue around the carpal tunnel swells up as a result of an inflammation or an injury, the nerves may be compressed, causing pain and distortions in sensation.

Illustration: The carpal tunnel: Passageway leading from the forearm to the hand

The carpal tunnel: Passageway leading from the forearm to the hand

Function of the muscles: Power, touch and precision

 To grasp and move objects, the hand has two different ways of gripping things:

The technique used depends on whether the object is very large and very heavy, and what sort of shape it has and how easy it is to handle. The power grip is better suited for large, heavy objects, and the precision grip is used for small, lighter objects.

Power grip

The power grip is used for carrying heavy bags or for holding on to a handle, for example. In the power grip, the object is held in the palm of the hand, the long flexor tendons pull the fingers and the thumb so that they can tightly close around the object. This grip is made possible by the four other fingers flexing and, more importantly, the ability of the thumb to be positioned opposite the fingers. With the hand in this position, larger objects such as a stone or a heavy bottle can be held and moved in a controlled way. The greater the weight and the smoother the surface is, the more strength is needed for holding and moving the object.

Precision grip

The precision grip is important for delicately handling and moving an object, for example when writing, sewing or drawing. When using the precision grip, the thumb and the index finger work like a forceps: The thumb is opposite one or more fingertips, allowing the hand a controlled grip of even very small objects like a pencil or fine instruments. Depending on the weight of the object and the direction and speed of the movement, the brain directs the use of force and coordinates the muscles of the hand.

Blood supply

The hand is supplied with blood through two main arteries: one on the same side as the thumb, and one on the little finger side. These two arteries each curve where the palm is, so that the hand is supplied with oxygen-rich blood through a double-loop. These loops have branches leading off into the individual fingers. Each artery is accompanied by veins and nerves; in total, each finger is supplied by four bundles of nerves and blood vessels

Illustration: Course of the most important nerves and blood vessels in the hand

Course of the most important nerves and blood vessels in the hand

Nerves

The hand’s muscles and skin are supplied by three nerves:

The ulnar nerve moves the muscles of the hypothenar eminence, the muscles between the bones of the metacarpus (interossei), the muscle that pulls the thumb inwards (adductor) and two of the lumbricals. The nerve also carries sensations from the region below the little finger and the near side of the ring finger.

The median nerve is responsible for the movement of the thenar eminence muscles and the rest of the lumbricals. It also is used to sense stimuli to the skin on the palm, thumb, index finger, and middle finger, as well as to the skin on the side of the ring finger that touches the middle finger.

The radial nerve controls several muscles, including the ones that extend the fingers and those that extend the wrist. This nerve also carries sensations of touch from the skin on the back of the hand and the back of the thumb on to the brain.

The sense of touch

The hand must deal with all kinds of challenges every day. The fingers on one hand will be flexed and extended about 25 million times over the course of one lifetime. And the hand also has very sensitive “antennae” for receiving stimuli from the environment: There are a total of 17,000 touch receptors and free nerve endings in the palm for passing on sensations of pressure, movement and vibration, so it is with good reason that the sense of touch is associated so strongly with the hand. The skin on your fingertips is especially sensitive to touch.

Sources

  • Menche N. (ed.) Biologie Anatomie Physiologie. Munich: Urban & Fischer/ Elsevier; 2012.
  • Pschyrembel W. Klinisches Wörterbuch. Berlin: De Gruyter; 2014.
  • Schmidt R, Lang F, Heckmann M. Physiologie des Menschen: mit Pathophysiologie. Heidelberg: Springer; 2011.
  • IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

© IQWiG (Institute for Quality and Efficiency in Health Care)

Download

IQWiG (Institute for Quality and Efficiency in Health Care)

PubMed Health Blog...

read all...

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...