Slide 0 Copyright © Mosby Inc. All Rights Reserved. Chapter 9 The Senses

Slide 1 Copyright © Mosby Inc. All Rights Reserved. Classification of the Sense Organs General sense organs  Often exist as individual cells or receptor units  Widely distributed throughout the body Special sense organs  Large and complex organs  Localized grouping of specialized receptors (Cont’d…)

Slide 2 Copyright © Mosby Inc. All Rights Reserved. Classification of the Sense Organs Classification by presence or absence of covering capsule  Encapsulated  Unencapsulated (“free” or “naked”) (Cont’d…)

Slide 3 Copyright © Mosby Inc. All Rights Reserved. Classification by type of stimuli required to activate receptors (6)  Photoreceptors (light)  Chemoreceptors (chemicals)  Pain receptors (injury)  Thermoreceptors (temperature changes)  Mechanoreceptors (movement or deforming of capsule)  Proprioceptors (position of body parts or changes in muscle length or tension) Classification of the Sense Organs

Slide 4 Copyright © Mosby Inc. All Rights Reserved. Converting a Stimulus into a Sensation All sense organs have common functional characteristics  All are able to detect a particular stimulus  A stimulus is converted into a nerve impulse  A nerve is perceived as a sensation in the CNS

Slide 5 Copyright © Mosby Inc. All Rights Reserved. General Sense Organs Distribution is widespread; single-cell receptors are common Examples  Free nerve endings—pain and crude touch  Meissner’s corpuscles—fine touch and vibration  Ruffini’s corpuscles—pressure and vibration  Krause’s end-bulbs—touch  Golgi tendon receptors—proprioception  Muscle spindles—proprioception

Slide 6 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs The eyeball  Layers of the eyeball  Sclera—tough outer coat; “white” of eye; the cornea is transparent part of the sclera over the iris  Choroid—pigmented vascular layer prevents scattering of light; from part of this layer made of ciliary muscle and iris; the colored part of the eye; the pupil is the hole in the center of the iris; contraction of iris muscle dilates or constricts pupil  Retina—innermost layer of the eye; contains rods (receptors for night vision) and cones (receptors for day vision and color vision) (Cont’d…)

Slide 7 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs (…Cont’d)  Conjunctiva—mucous membrane covering the front surface of the sclera and lining the eyelid  Lens—transparent body behind the pupil; focuses light rays on the retina  Eye fluids  Aqueous humor—in the anterior chamber in front of the lens  Vitreous humor—in the posterior chamber behind the lens (Cont’d…)

Slide 8 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs  Visual pathway  Innermost layer of retina contains rods and cones  Impulse travel from the rods and cones through the bipolar and ganglionic layers of retina  Nerve impulse leaves the eye through the optic nerve; the point of exit is free of receptors and is therefore called a blind spot  Visual interpretation occurs in the visual cortex of the cerebrum

Slide 9 Copyright © Mosby Inc. All Rights Reserved.

Slide 10 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs The ear  The ear functions in hearing and in equilibrium and balance  Receptors for hearing and equilibrium are mechanoreceptors

Slide 11 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs  Divisions of the ear  External ear o Auricle (pinna) o External auditory canal Curving canal 2.5 cm (1 inch) in length Contains ceruminous glands Ends at the tympanic membrane

Slide 12 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs  Middle ear o Houses ear ossicles—malleus, incus, and stapes o Ends in the oval window o The auditory (eustachian) tube connects the middle ear to the throat o Inflammation called otitis media

Slide 13 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs  Inner ear o Bony labyrinth filled with perilymph o Subdivided into the vestibule, semicircular canals, and cochlea o Membranous labyrinth filled with endolymph o The receptors for balance in the semicircular canals are called cristae ampullaris o Specialized hair cells on the organ of Corti respond when bent by the movement of surrounding endolymph set in motion by sound waves

Slide 14 Copyright © Mosby Inc. All Rights Reserved. Divisions of the Ear (F 8-4)

Slide 15 Copyright © Mosby Inc. All Rights Reserved.

Slide 16 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs The taste receptors  Receptors are chemoreceptors called taste buds  Cranial nerves VII and IX carry gustatory impulses  Six kinds of “primary” taste sensations—sweet, sour, bitter, salty, metallic, and umami  Gustatory and olfactory sense work together

Slide 17 Copyright © Mosby Inc. All Rights Reserved. Special Sense Organs The smell receptors  Receptors for fibers of olfactory or cranial nerve I lie in olfactory mucosa of nasal cavity  Olfactory receptors are extremely sensitive but easily fatigued  Odor-causing chemicals initiate a nervous signal that is interpreted as a specific odor by the brain