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The General & Special Senses

Chapter 17

Introduction

•  Senses – our perception of what is “out there”

•  2 groups – General senses – Special senses

General Senses

•  Includes senses that are skin or kinesthetic – Temperature, pressure, touch, pain, vibration,

proprioception •  Pass information along the spinal nerves

and pathways to the somatosensory cortex

Special Senses

•  Olfaction, gustation, equilibrium, hearing, & vision

•  Found within complex sense organs •  Pass information along the cranial nerves to

specific areas of the cerebral cortex.

Receptors

•  Sensory receptors are transducers – Change stimuli into electro-chemical impulses – Specific receptors can transduce only certain

types of stimuli •  Two general types

– Exteroceptors –  Interoceptors

Interpretation of Sensory Information

•  Occurs in cerebral cortex •  Depends on the area of the cerebral cortex

that receives the information •  Also depends on the sequence of neurons

carrying the information

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Central Processing and Adaptation

•  Adaptation – the loss of sensitivity after continuous stimulation – Tonic receptors are always active – Phasic receptors only relay changes in the

conditions they are monitoring •  Role – prevents brain from being

overloaded with unimportant information

Receptors of the General Senses

Nociceptors

•  Detect pain – Referred pain – Phantom pain

Mechanoreceptors

•  Respond to pressure & touch – Tactile receptors – Baroreceptors – Proprioreceptors – Thermoreceptors

Tactile Receptors •  Found in the dermis

Baroreceptors •  Monitor changes in pressure

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Chemoreceptors •  Detect chemicals in solution

–  Blood composition

The Special Senses

Olfaction (the nose) •  Olfactory receptors

–  Can detect at least 50 different primary smells –  Located in the epithelium of roof of nasal cavity

Olfactory Receptors

•  Molecules dissolve in the mucus or lipids of the epithelium

•  Olfactory neurons pass through the cribiform plate and synapse in the olfactory bulb

•  Olfactory tracts go directly to the cerebral cortex

Gustation (the tongue)

•  Taste receptors are in the taste buds

•  4 primary tastes –  Sweet, sour, salty,

bitter •  Located in papillae on

the surface of the tongue

•  Contain the gustatory receptors –  Molecules dissolve in

saliva

Pathway of Gustatory Sense

•  3 cranial nerves relay sensory impulses to the cerebral cortex –  Facial,

glossopharyngeal, vagus

–  All pass through the medulla & thalamus

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Equilibrium & Hearing (the ear) •  External ear

– The auricle directs sound waves into the external auditory meatus to the tympanic membrane

The Middle Ear •  Located in the temporal bone •  Contains the auditory ossicles

–  Malleus –  Incus –  stapes

•  Connected to throat by the eustachian tube

The Inner Ear •  Located in the temporal bone •  Separated from the middle ear by the oval window

The Inner Ear

•  Consists of a series of canals called the bony labyrinth –  Lined by a

membranous labyrinth filled with endolymph

–  Perilymph flows between the bony and membranous labyrinth

The Inner Ear

•  The bony labyrinth is divided into 3 areas –  Vestibule contains

•  Saccule & utricle –  Semicircular canals

•  Each has an ampulla

–  Cochlea contains •  Organ of Corti

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The Utricle & Saccule

•  Detects static position •  Hair cells are

embedded in a gelatinous material

Otoliths at Work •  Otoliths are

balanced on top of gelatinous material –  Slide when head

tips –  Bend hairs –  Generates nerve

impulse

The Semicircular Canals •  Detect dynamic

balance •  Arranged at right

angles to each other •  In the ampula, hair

cells are embedded in gelatinous material (cupula) with fluid over it

•  Movement of head –  Bends the hairs –  Creates nerve

impulses

Semicircular Canals at Work

The Cochlea

•  Divided into 3 tunnels by the vestibular and basilar membranes –  Scala vestibuli ends

in the oval window –  Cochlear duct

contains the organ of Corti

–  Scala tympani ends in the round window

Cochlear Chambers

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The Organ of Corti •  Consists of hair cells

on the basilar membrane

•  Tips of hairs touch the tectorial membrane

•  Basement membrane vibrates –  Hair cells bend –  Sends a nerve

impulse

Pathway of Auditory Sense

Summary of Hearing

•  Sound waves enter the external auditory meatus •  Tympanic membrane vibrates •  Auditory ossicles vibrate •  Oval window vibrates •  Perilymph in scala vestibuli & scala tympani

moves •  Basilar membrane moves •  Hairs rub against the tectorial membrane •  Nerve impulse is sent along the vestibulocochlear

nerve to the brain

Vision (the eye) – Accessory Structures •  Eyelids protect the eye

–  Conjunctiva lines the eyelid

•  Lacrimal apparatus –  Lacrimal gland

produces tears –  Lacrimal canals

drain tears into lacrimal sacs

–  Nasolacrimal duct drains into the nasal cavity

•  Extrinsic muscles move the eyeball

Structure of the Eye – 3 Tunics

•  Fibrous tunic –  Includes cornea &

sclera •  Vascular tunic

–  Includes choroid coat, ciliary body, lens, iris & pupil

•  Neural tunic (retina) –  Contains

photoreceptors •  Rods & cones

–  Includes optic disc, macula lutea & fovea centralis

Human Anatomy, 3rd editionPrentice Hall, © 2001

Figure 18-22c

Photo of Posterior Eye

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The Cavities of the Eye

•  The lens separates the interior of the eye into 2 cavities –  Anterior cavity

•  Contains aqueous humor

•  Glaucoma

–  Posterior cavity

•  Contains vitreous humor

The Vascular Tunic

•  Contains many blood vessels & nerves

•  The iris controls the size of the pupil

•  Suspensory ligaments attach the lens to the ciliary body –  Controls the shape

of the lens

The Retina •  Cones allow for sharp

color vision in bright light –  Contain pigments –  Macula lutea –  Fovea centralis

•  Rods provide for vision in dim light –  Contain the pigment

rhodopsin –  Most dense at

periphery of retina

Pathway of Vision Sense

Summary of Vision

•  Light rays enters through the pupil •  Light rays cross in the lens •  Retina receives reversed & upside down

image •  Rods & cones are stimulated •  Optic nerve carries impulse to the brain

Abnormal Vision

•  Myopia •  Hyperopia •  Presbyopia •  Astigmatism