Finger

Most people have five fingers on each hand.

One is the thumb. The others are the index, middle, ring, and pinkie.

Inside your hands, you have small bones. These bones help you move. They work with muscles in your arm.

Your fingers help you feel the world. They can feel if things are hot or cold. They can even feel tiny bumps.

When you stay in water, your skin wrinkles. This might help you grip wet things.

Fingers are very useful tools for your body.

Most people have five digits on each hand. These are called fingers.

Your fingers are made of many small bones. We call these bones phalanges. The thumb has two phalanges. The other four fingers have three each. These bones meet at joints. Joints let your fingers bend and move.

Fingers do not have muscles inside them. Instead, muscles in your arm and palm move them. These muscles use long cords called tendons. Tendons pull on the bones to make them move. Some muscles help you bend your fingers. Other muscles help you straighten them out.

Your fingertips are very sensitive. They have many parts that feel touch. You can feel heat, cold, and texture. You can even feel tiny wrinkles on a surface.

When you stay in water, your skin wrinkles. This happens because blood vessels shrink. Some think this helps you grip wet things.

Sometimes, people are born with extra fingers. This is called polydactyly. Some people may also be born with fewer fingers.

{ "text": "Fingers are the digits found on the forelimbs of many animals. Most land animals have five digits, which is a pattern called pentadactyly.

In humans and primates, these digits are often used for grasping objects. We call the longer digits fingers and the shorter ones toes. Fingers are very important because they help us feel the world. They allow for fine movements and great dexterity. This helps us pick up small things with ease.\n\nInside your hand, fingers are moved by a clever system. Fingers do not actually contain muscles themselves. Instead, muscles in your forearm and palm move them using long cords called tendons.

There are two main types of muscles used for this. Extrinsic muscles are in the forearm and help with large movements. Intrinsic muscles are located within the hand itself. These muscles work together to let you bend or straighten your digits.\n\nYour fingers are built from many small bones called phalanges.

The thumb is unique because it only has two phalanges. The other four fingers each have three phalanges. These bones are connected by joints that allow for bending. There is a joint at the base, one in the middle, and one near the tip. You also have metacarpal bones in your palm that connect to your fingers. Small bones called sesamoid bones can also sit in the tendons to help

A finger is a prominent digit located on the forelimbs of most tetrapod vertebrates. In many species, especially primates, these digits are prehensile, meaning they are capable of grasping. Most tetrapods follow a pattern known as pentadactyly, which means they possess five digits.

While shorter digits on the hindlimbs are typically called toes, the elongated digits on the forelimbs are referred to as fingers. In humans, fingers are essential for tactile sensation and the fine motor movements required for dexterity.

The internal structure of a human finger is composed of bones called phalanges. Each hand contains fourteen phalanges in total. The thumb is unique because it contains only two phalanges: a proximal and a distal phalanx. The other four fingers each contain three phalanges: the proximal, middle, and distal phalanx. These bones are connected to the metacarpal bones in the palm.

Joints form wherever these bones meet, allowing for movement. There are three main joints in each finger: the metacarpophalangeal joint at the base, the proximal interphalangeal joint in the middle, and the distal interphalangeal joint near the tip. Small ossified nodes called sesamoid bones may also be embedded in the tendons to provide leverage.

Fingers do not contain muscles themselves, with the exception of the arrector pili. Instead, movement is controlled by muscles located in the palm and the forearm. These muscles connect to the finger bones via long tendons. Muscles are categorized as either extrinsic or intrinsic. Extrinsic muscles have their muscle belly in the forearm. The long flexors allow the fingers to bend, while the extensors, located on the back of the forearm, allow the digits to straighten.

Intrinsic muscles, such as the thenar and hypothenar groups, are located within the hand itself. The thenar muscles specifically allow the thumb to move in opposition, which is vital for grasping.

Movement in the fingers is a complex coordination of flexion, extension, abduction, and adduction. Flexion, or bending, is the strongest movement. While fingers appear to move independently, they actually experience finger interdependence, also known as finger enslaving. This means moving one finger often causes slight movements in the others. The precision of these movements is clearly visible in skilled tasks, such as a pianist playing a musical piece.

This high level of control is managed by the direct corticomotoneuronal pathway in the brain.

The fingertips are among the most sensitive parts of the human body. They contain the highest concentration of touch receptors and thermoreceptors in the skin. This allows humans to sense pressure, vibration, texture, moisture, and temperature. A 2013 study even suggested that fingers can detect nano-scale wrinkles on smooth surfaces. Interestingly, fingertips wrinkle when immersed in water. This is not caused by swelling, but by the sympathetic nervous system signaling blood vessels to constrict. Some scientists propose the "rain tread" hypothesis, suggesting these wrinkles help grip wet objects.

Human fingers can also undergo remarkable biological processes, such as regeneration. In children, if a fingertip is torn off, it can regrow in less than eight weeks. This happens because the distal phalanges are regenerative in youth, and stem cells in the nails create new tissue. However, this regrowth only occurs if the injury is above the nail. There are also various clinical anomalies. Polydactyly is a condition where an individual is born with more than five digits, affecting about 1 in 500 humans.

Another condition, syndactyly, involves webbed or fused fingers. This can even affect the brain, as the somatosensory cortex maps for fused fingers appear fused as well.

Fingers serve as a vital connection between the biological body and the physical environment. They act as sensory probes that allow us to ascertain the properties of the world. Beyond simple touch, the ratio of finger lengths, such as the index and ring fingers, has been linked to different biological and behavioral traits. From the evolutionary perspective of terrestrial vertebrates, the finger structure is a highly modified version of the pectoral fins found in lobe-finned fish. This evolutionary history explains why the basic pentadactyl plan is so widely shared across different species.