Chapter 16: Sense Organs

Sensory receptor

A structure specialized to detect a stimulus and convert its energy into a nerve signal (transduction).

Receptive field

The area in which a sensory neuron detects stimuli; smaller fields (like in fingertips) allow for fine two-point touch discrimination.

Thermoreceptors

Sensory receptors that respond to temperature changes.

Photoreceptors

Sensory receptors that respond to light.

Nociceptors

Sensory receptors that respond to tissue damage and pain.

Chemoreceptors

Sensory receptors that respond to chemical changes, such as taste, smell, and blood chemistry.

Mechanoreceptors

Sensory receptors that respond to physical deformation, pressure, touch, vibration, hearing, and proprioception.

Referred pain

Pain originating in viscera that is mistakenly perceived to come from the skin or a superficial site due to the convergence of neural pathways in the CNS.

Outer ear

Consists of the auricle (pinna) and auditory canal, which conduct sound vibrations to the tympanic membrane.

Tympanic membrane

The eardrum that separates the outer ear from the middle ear and vibrates freely in response to sound waves.

Auditory ossicles

The three small bones of the middle ear: malleus, incus, and stapes.

Auditory (Eustachian) tube

Connects the middle ear to the nasopharynx to equalize air pressure on both sides of the tympanic membrane.

Cochlea

The snail-shaped organ of hearing located in the inner ear, containing fluid-filled chambers and the spiral organ (organ of Corti).

Scala vestibuli

The superior fluid-filled chamber of the cochlea beginning at the oval window.

Scala tympani

The inferior fluid-filled chamber of the cochlea ending at the round window.

Cochlear duct (scala media)

The middle chamber of the cochlea containing endolymph and the spiral organ.

Spiral organ (organ of Corti)

The organ containing hair cells that convert mechanical fluid vibrations into nerve impulses for hearing.

Static equilibrium

The perception of the orientation of the head when the body is stationary (detected by the maculae in the saccule and utricle).

Dynamic equilibrium

The perception of motion or acceleration, including linear and angular acceleration.

Semicircular ducts

Inner ear structures housed in bony canals that detect angular acceleration and rotational movements.

Crista ampullaris

A mound of hair cells in the ampulla of each semicircular duct covered by a gelatinous cupula.

Sclera

The dense, white outer fibrous layer of the eye.

Cornea

The transparent anterior cover of the eye that admits and refracts light.

Choroid

The highly vascular, deeply pigmented middle layer of the eye behind the retina.

Iris

The colored muscular diaphragm of the eye that controls the size of the pupil.

Aqueous humor

A clear serous fluid filling the anterior cavity of the eye, secreted by the ciliary body.

Vitreous body (humor)

The jelly-like substance filling the space between the lens and retina.

Fovea centralis

A pit in the center of the macula lutea of the retina that provides the highest visual acuity (clearest vision).

Optic disc

The blind spot where the optic nerve exits the retina and no photoreceptors are present.

Emmetropia

The relaxed state of the eye when focused on objects more than 20 feet away.

Accommodation

The change in the curvature of the lens that enables the eye to focus on nearby objects.

Myopia

Nearsightedness caused by an eyeball that is too long, corrected with a concave lens.

Hyperopia

Farsightedness caused by an eyeball that is too short, corrected with a convex lens.

Presbyopia

The age-related loss of lens accommodation and elasticity, causing difficulty focusing up close.

Astigmatism

An irregular curvature of the cornea or lens that refracts light differently across different planes.

Rods

Photoreceptors in the retina specialized for low-light and night vision, containing the visual pigment rhodopsin and seeing only in shades of gray.

Cones

Photoreceptors in the retina specialized for color vision and bright light, containing photopsin.