Head (anatomy)

The body region at the front or upper end of many animals, containing the brain and major sensory organs. Its structures vary widely across animal groups.

Brain: The central nervous system organ that processes information and coordinates many body functions. It is the head’s principal neural structure in animals with a centralized brain.
Vision: The sensory process by which organisms detect and interpret light. Eyes in the head provide a major route for gathering information about the surroundings.
Headless animal: An animal that lacks a distinct head region with concentrated sensory organs and nervous tissue. It shows that complex animals can function without the anatomy typical of a head.
Cambrian explosion: A period of rapid diversification of animal forms beginning about 539 million years ago. Early fossils from this interval document major changes in animal body plans and sensory structures.
Head injury: Physical trauma to the scalp, skull, or contents of the skull. The head’s exposed position and enclosed brain make trauma clinically significant.
Cranium: The skull portion that encloses and protects the brain. In vertebrates, it forms the bony enclosure around the brain.
Hearing: The sensory process of detecting sound vibrations and interpreting them. Head-located auditory organs channel sound into neural signals.
Radial symmetry: A body organization in which parts are arranged around a central axis rather than a distinct front and back. Radially organized animals often lack the front-to-back layout associated with a head.
Hox gene: A developmental gene that helps specify the identities of regions along an animal’s body axis. Hox genes contribute to regional patterning that distinguishes anterior structures from the trunk.
Concussion: A traumatic brain injury that temporarily disrupts normal brain function, usually after a blow or jolt. It is a common brain injury associated with impacts to the head.

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