Term | Definition |
Receptors | Specialized nerve cells or nerve endings that detect physical or chemical events outside the cell membrane |
Receptive field | The certain area in which each sensory neuron responds to stimuli |
Sensory projection | When a particular neuron carries a stimulus to the brain and the brain knows where the stimulus originated |
Adaptation | When a stimulus is continuous, the firing frequency of the nerve begins to slow, causing the sensation to diminish |
Proprioceptor | Provides information about body movement, muscle stretch, and the general orientation of the body |
Chemoreceptors | React to various chemicals, including odors and tastes, as well as the concentration of various chemicals |
Mechanoreceptors | Respond to factors, such as pressure, stretch, or vibration, that change the position of a receptor |
Thermoreceptors | Activated by a change in temperature |
Nociceptors | Pain receptors that respond to tissue damage from trauma as well as from heat, chemicals, pressure, or lack of oxygen |
Photoreceptors | Found only in the eyes; respond to light |
Fast pain fibers | Abundant in the skin and mucous membranes; produce a sharp, localized, stabbing-like pain at the time of injury |
Slow pain fibers | Congregated on deep body organs and structures; produce a dull, aching pain |
Referred pain | Pain originating in a deep organ may be sensed as if it's originating from the body's surface |
Analgesics | Drugs used to relieve pain |
Gustation | Sense of taste |
Papillae | Protrusion on the tongue containing most of the taste buds |
Olfaction | Sense of smell |
Auricle | Pinna; visible part of the ear; funnels sound into the auditory canal |
Auditory canal | Has glands that produce secretions that mix with dead skin cells to form cerumen; leads through the temporal bone to the eardrum |
Auditory ossicles | 3 smallest bones in the body; connect the eardrum to the inner ear; malleus (hammer), incus (anvil), and stapes (stirrup) |
Tympanic membrane | Eardrum; separates the outer ear from the middle ear; vibrates freely in response to sound waves |
Eustachian tube | Passageway from the middle ear to the nasopharynx; equalizes pressure on both sides of the tympanic membrane |
Bony labyrinth | A complicated system of passageways within the temporal bone that contains the inner ear |
Membranous labyrinth | Lines the inside of the bony labyrinth; filled with endolymph |
Semicircular canals | Crucial for the maintenance of equilibrium and balance; fluid filled canals that lie at right angles to one another |
Vestibule | Marks the entrance to the labyrinths; contains the utricle and saccule, necessary for the sense of balance |
Cochlea | Snail-like structure that contains the structures for hearing |
Organ of Corti | Resting on the basilar membrane of the cochlear duct; hearing sense organ |
Eyebrow | Enhance facial expressions, help keep perspiration out of the eye, and shield the eye from glare |
Eyelids | Palpebrae; protect the eye from foreign bodies and block light when closed to allow for sleeping; helps moisten the eye and wash out debris |
Eyelashes | Hairs along the edges of the eyelids that help keep debris out |
Palpebral fissure | The opening between the lids |
Conjunctiva | Transparent mucous membrane that lines the surface of the eyelid and covers the anterior surface of the eyeball; creates a thin mucous |
Tarsal glands | Lie along the tarsal plate; secrete oil to slow the evaporation of tears; form a barrier seal when the eyes are closed |
Lacrimal punctum | Tiny pore through which tears drain into the lacrimal canal and the nasolacrimal duct |
Lacrimal gland | Small gland that secretes tears |
Tears | Clean and moisten the eye's surface; deliver oxygen and nutrients to the conjunctiva; contain lysozyme that helps prevent infection |
Nasolacrimal duct | Carries tears into the nasal cavity |
Extrinsic muscles | 6 muscles that reside outside the eyeball and attach to the bony walls of the orbit and to the surface of the eyeball |
Intrinsic muscles | Arise from within the eyeball; regulate the size of the pupil and the shape of the lens |
Sclera | Formed from dense connective tisse; outermost layer of the eye; forms the "white of the eye" |
Cornea | Transparent extension of the sclera; sits over the iris and admits light into the eye |
Iris | Ring of colored muscle; works to adjust the diameter of the pupil to control the amount of light entering the eye |
Ciliary body | Thickened extension of the choroid that forms a collar around the lens; secretes aqueous humor |
Choroid | Highly vascular layer of tissue that supplies oxygen and nutrients to the retina and sclera |
Retina | Lines the posterior 2/3 of the eye; thin layer of light-sensitive cells |
Optic nerve | Cranial nerve II; exits from the posterior portion of the eyeball; transmits signals to the brain |
Macula lutea | Patch of cells that are the centerpoint of the retina, as seen through an ophthalmoscope |
Fovea centralis | Depression inside the macula lutea; most of the cones are concentrated here; produces the sharpest vision |
Optic disc | Medial to the macula lutea; where nerve fibers leave the retina and converge to become the optic nerve; where blood vessels enter and leave the eye |
Blind spot | A spot in the visual field of each eye that contains no photorecetors |
Anterior cavity | Space between the lens and the cornea; divided into the anterior and posterior chambers; filled with aqueous humor |
Posterior cavity | Larger cavity lying posterior to the lens; filled with vitreous humor |
Vitreous humor | Jelly-like substance that fills the posterior cavity of the eye; helps keep the eyeball from collapsing |
Lens | Transparent disc of tissue just behind the pupil; changes shape for near and far vision |
Canal of Schlemm | Blood vessel where aqueous humor drains |
Refraction | Bending of light rays |
Convergence | Lines up the visual axis of each eye toward the object so that the light rays fall on the corresponding spots on each retina |
Diplopia | Double vision; failure of the eyes to converge |
Emmetropia | Normal vision |
Myopia | Nearsightedness; light rays focus in front of the retina; most common refractive vision defect |
Hyperopia | Farsightedness; light rays focus at a point behind the retina; occurs if the eyeball is too short or the cornea is flatter than normal |
Astigmatism | Uneven or asymmetrical curvature of the cornea; light is focused unevenly; often accompanies myopia or hyperopia |
Presbyopia | Loss of flexibility of the lens with age; focusing muscles in the eyes weaken; begins between the ages of 40 & 50 |
Visual acuity | Sharpness of visual perception |
Pupillary constrictor | Muscle that encircles the pupil; stimulated by the parasympathetic nervous system; narrows the pupil to admit less light |
Pupillary dilator | Stimulated by the sympathetic nervous system; pulls the edges of the iris outward to admit more light |
Photopupillary reflex | Pupils constrict automatically when exposed to bright light |
Accommodation | The curvature of the lens changes to allow the eye to focus on a near object |
Rods | Located at the periphery of the retina; active in dim light; responsible for night vision; cannot distinguish colors from each other |
Cones | Concentrated in the center of the retina; active in bright light; primarily responsible for sharp vision; responsible for color vision |
Optic chiasm | Where fibers from the nasal side cross over to the other side; located just anterior to the pituitary gland |