The Somatic Nervous System

Sensory Receptors

Cells that detect different types of stimuli and convert them into neural signals.

Classifications of Receptor Cells

Receptor cells can be classified based on cell type, position, function, and transduction of stimuli.

Free Nerve Ending

A neuron with dendrites embedded in tissue that receives sensations such as pain and temperature.

Encapsulated Ending

A neuron in which the sensory nerve endings are encapsulated in connective tissue, enhancing their sensitivity.

Special Receptor Cell

A receptor with distinct structural components that interpret a specific type of stimulus.

Exteroceptor

Receptor located near a stimulus in the external environment.

Interoceptor

Receptor that interprets stimuli from internal organs and tissues.

Proprioceptor

Receptor located near moving parts of the body that interprets tissue positions.

Chemoreceptor

Receptor that interprets chemical stimuli, such as taste or smell.

Osmoreceptor

Receptor that responds to solute concentrations of body fluids.

Thermoreceptor

Receptor sensitive to temperature changes, either heat or cold.

General Sense

A sense that is distributed throughout the body, involving touch, proprioception, and visceral sense.

Special Sense

A sense that has a specific organ devoted to it, such as the eye or ear.

Sensory Modality

The way that information is encoded by the senses.

Papillae

Raised bumps on the tongue that contain structures for gustatory transduction.

Olfactory Epithelium

Tissue in the nasal cavity where olfactory receptor neurons are located.

Auricle

The large fleshy structure on the lateral aspect of the head, part of the external ear.

Tympanic Membrane

Also known as the eardrum, it vibrates when struck by sound waves.

Ossicles

Three small bones in the middle ear that transmit sound vibrations.

Cochlea

A spiral-shaped organ in the inner ear responsible for hearing.

Stereocilia

Hair-like structures on hair cells in the cochlea that help transduce sound waves.

Utricle

A structure in the inner ear that senses head position.

Saccule

A structure in the inner ear that works with the utricle to maintain balance.

Macula

Tissue in the utricle and saccule involved in sensing balance.

Palpebral Conjunctiva

Thin membrane on the inner surface of each eyelid.

Lacrimal Gland

Gland that produces tears, located superior and lateral to the eyeball.

Extraocular Muscles

Muscles that control eye movements.

Photon

A unit of light described as a packet of energy with particle and wave properties.

Photoisomerization

The process where photons cause molecules to switch from cis to trans conformation.