Aistielimet

Aistielimet (sense organs; Finnish for sense organs) are specialized structures that detect stimuli and convert them into neural signals interpreted by the brain. They form the peripheral part of the nervous system and mediate perception of the external environment and the body's internal state. They are commonly grouped into exteroceptors (external stimuli), interoceptors (internal state), and proprioceptors (position and movement). Traditional classification recognizes five classical senses—vision, hearing, taste, smell, and touch—along with additional modalities such as temperature, pain, and proprioception.

Vision: The eye houses photoreceptors in the retina. Light is converted into electrical signals that travel via the optic nerve to the thalamus and visual cortex, enabling sight. Accessory structures (cornea, lens) focus light to form images.

Hearing and balance: The ear converts sound vibrations into neural signals through hair cells in the cochlea; the vestibular apparatus detects head movement and orientation, contributing to balance.

Taste and smell: Taste buds detect soluble chemicals; olfactory receptors in the nasal cavity respond to airborne compounds. Signals are relayed to dedicated cortical areas for gustation and olfaction.

Touch and other somatic senses: The skin contains mechanoreceptors, thermoreceptors, and nociceptors that detect pressure, temperature, and pain. Proprioceptors in muscles and joints report limb position and movement.

Transduction and pathways: Receptors generate action potentials that travel along cranial or spinal nerves to brain regions responsible for perception; some reflexes occur without conscious processing.

Clinical notes: Aistielimet can be affected by congenital or acquired conditions such as visual or hearing impairment, anosmia, ageusia, and neuropathic pain, underscoring their role in daily functioning.