slide 0 copyright © 2004. mosby inc. all rights reserved. chapter 9 the senses

Copyright © 2004. Mosby Inc. All Rights Reserved.

Chapter 9Chapter 9

The Senses


Classification of the Sense OrgansClassification 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…)



• Classification by presence or absence of covering capsule Encapsulated Unencapsulated (“free” or “naked”)

(Cont’d…)


• 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)



Converting a Stimulus into a SensationConverting 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


General Sense OrgansGeneral 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


Special Sense OrgansSpecial 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…)


Special Sense OrgansSpecial 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…)



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



The ear The ear functions in hearing and in equilibrium and balance Receptors for hearing and equilibrium are mechanoreceptors



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



Middle earo Houses ear ossicles—malleus, incus, and stapes

o Ends in the oval windowo The auditory (eustachian) tube connects the middle ear to the throat

o Inflammation called otitis media



Inner earo Bony labyrinth filled with perilympho Subdivided into the vestibule, semicircular canals, and cochlea

o Membranous labyrinth filled with endolympho 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


Divisions of the Ear (F 8-4)



• 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



• 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

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