Evolution and Anatomy of Fingers
- Land vertebrate fingers
- Fingers of tree frogs, red-eyed crocodile skinks, red squirrels, and bats
- Terrestrial vertebrates' forelimbs evolved from lobe-finned fish
- Variation in the basic pentadactyl plan and the metacarpals and phalanges
- Different fingers of terrestrial vertebrates are homologous
- Primates, like chimpanzees, have specialized lower limbs for manipulation and fingers on their lower limbs
- Human fingers
- Humans typically have five digits on each hand
- Some people have more or fewer than five due to congenital disorders or amputations
- Definitions of finger vary, with some including the thumb and others not
- English dictionaries describe finger as one of the five digits or one of the four digits excluding the thumb
- Thumb can be called a finger, depending on the definition
- Skeleton of the hand includes the thumb, palm, metacarpal bones, and phalanges
- Each finger has three joints: metacarpophalangeal, proximal interphalangeal, and distal interphalangeal
- Sesamoid bones provide extra leverage and reduce pressure
- Articulations include interphalangeal articulations and metacarpophalangeal joints
- Muscles in the palm and forearm control finger movements
Muscles and Movements of Fingers
- Each finger can flex, extend, abduct, adduct, and circumduct
- Flexion is the strongest movement, produced by large muscles and augmented by additional muscles
- Finger movements are not completely independent due to finger interdependence
- Finger joints are moved by muscles in the palm and forearm
- Muscles of the fingers can be divided into extrinsic and intrinsic muscles
Sensory Capabilities of Fingers
- Fingertips have the highest concentration of touch and thermoreceptors
- Fingers are extremely sensitive to temperature, pressure, vibration, texture, and moisture
- Fingers can feel nano-scale wrinkles on seemingly smooth surfaces
- Fingers are commonly used as sensory probes to ascertain properties of objects
- Fingertip wrinkling in water is caused by blood vessel constriction in response to water exposure
- Anatomy and Function of Fingers
- Fingertips provide better handling of wet objects but no advantage for handling dry objects.
- A 2014 study failed to demonstrate any improvement in handling wet objects with wrinkled fingertips.
- Fingertips can regrow in less than 8 weeks if torn off, although they may not look the same as before.
- Healing does not occur if the tear happens below the nail.
- Distal phalanges are regenerative in youth, and stem cells in the nails create new tissue for fingertip regrowth.
Brain Representation and Clinical Significance of Fingers
- Brain Representation of Fingers
- Each finger has an orderly somatotopic representation in the cerebral cortex.
- The somatosensory cortex area 3b and part of area 1 are involved in finger representation.
- Supplementary motor area and primary motor area also have distributed, overlapping representations of fingers.
- In syndactyly, where fingers are fused, the cortical maps of individual fingers also form a club hand.
- Surgical division of fused fingers can separate the cortical maps and improve hand function.
- Clinical Significance of Fingers
- Anomalies such as polydactyly (extra fingers) and symbrachydactyly (underdeveloped fingers) can occur.
- Phalanges are commonly fractured, and damaged tendons can cause loss of fine motor control.
- Fingers can be affected by diseases like rheumatoid arthritis, gout, and neurovascular disorders.
- The ratio of lengths between index and ring fingers has been linked to various physical and behavioral traits.
- Fingers are used by diabetics for blood sugar testing, and they can be affected by conditions like Raynaud's phenomenon.
Cultural and Linguistic Aspects of Fingers
- Cultural and Linguistic Aspects of Fingers
- The name 'pinkie' derives from the Dutch word 'pinkje'.
- In some languages, the translated version of 'fingers' can refer to both hand and foot digits.
- English distinguishes between fingers and toes for foot digits.
- Finger snapping is a cultural gesture associated with making a sharp sound by pressing the fingers together and then releasing them.
- The term 'digit' is used in scientific and medical contexts to refer to both fingers and toes.
Finger Data Sources