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Sense Organs

Chapter 11 definitions

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
Created by: cbooher16



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