2009 the mcgraw-hill companies, inc. all rights reserved special senses chapter 12

© 2009 The McGraw-Hill Companies, Inc. All rights reserved

Special Senses

Chapter 12Chapter 12


Introduction Special senses

Sensory receptors located in head Nose – smell Tongue – taste Eyes – vision Ears – hearing

and equilibrium Touch is a

generalized sense


35-3


How do senses work? Receptors collect information Stimulate neurons Information is sent to the brain The cerebral cortex integrates the

information with that from other senses Forms a perception (a person’s

particular view of the stimulus)


Receptor Structure Receptors are structured in two

basic ways: Nerve endings Cells which are associated with

nerve endings When these are stimulated, they

produce graded potentials. If they hit threshold, nerve fires.


The Ear


The Ear and the Senses of Hearing and Equilibrium:

StructuresExternal Ear

Auricle (pinna) Collects sound waves

External auditory canal Guides sound wave to

tympanic membrane

Ear



Structures (cont.)

Tympanic membrane Concave shaped

membrane Separates external

canal and middle ear Vibrates when sound

hits it Ear ossicles

Malleus, Incus, Stapes Ossicles vibrate in

response to vibration of tympanic membrane

Tympanic Cavity Surrounds ossicles

Eustachian tube Connects middle ear

to throat Equalizes pressure on

eardrum Oval window

Separates middle ear from inner ear

The Middle Ear

Ear


Middle Ear Diagram



Structures (cont.)Inner Ear

Labyrinth of communicating chambers

Semicircular canals (3): detect balance of the body

Vestibule: central part of labyrinth; equilibrium

Cochlea: coiled canal ofdense bone tissue of the skull; shaped like a snail; Filled with two fluids

(endolymph and perilymph). The Organ of Corti is the

sensory receptor inside the cochlea which holds the hair cells, the nerve receptors for hearing.

Ear


Ear Wax Cerumen; naturally produced by your

body Produced in sebaceous and modified

apocrine glands of the ear Coats the ear canal to moisturize it, fight

off infection, keep dust, dirt, and other debris from getting inside ear

20 to 50 percent fat


The Ear and the Senses of Hearing and Equilibrium: Hearing Process

Sound waves collected through external ear canal

Waves cause tympanic membrane to vibrate

Ossicles amplify vibrations The mechanical energy from movement of the middle

ear bones pushes in a membrane (the oval window) in the cochlea.

This force moves the cochlea's fluids that, in turn, stimulate tiny hair cells.

Movement of hairs lining cochlea are converted into nerve impulses

Impulses are transmitted by auditory nerve to the brain for interpretation

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The Ear and the Senses of Hearing and Equilibrium: Hearing Process (cont.)

Bone conduction Alternative pathway Bypasses external

and middle ear directly to inner

Useful in determining cause of hearing problem

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Equilibrium Position of Body/Movement

Above the cochlea are two interconnecting chambers filled with endolymph, the sacculus and utriculus.

On their inner surface are patches of hair cells to which are attached thousands of tiny spheres of calcium carbonate (CaCO3).

Gravity pulls these downward. As the head is oriented in different directions, these ear stones (otoliths) shift their position. Impulses initiated in the hair cells are sent back to the brain.

Motion of the body is detected in the semicircular canals Whenever the head is moved, the fluid within the canals lags; this

stimulates the hair cells to send impulses back to the brain. When the hair cells send messages that are incongruent with what

the eyes are seeing and our body is feeling, as may occur in a boat or aircraft during rough weather, motion sickness can result.

Some people also suffer severe dizziness because otoliths have become dislodged from their utriculus (following a blow to the head) and settled in a semicircular canal.

35-15


How to Recognize Hearing Problems in Children

Guidelines Infants to 4 months

Startled by loud noises Recognize mother’s voice

4 to 8 months Regularly follow sounds Babble at people

8 to 12 months Respond to the sound their

name Respond to “no”

35-16


The Aging EarThe Aging Ear External ear larger / earlobe

longer Cerumen dryer and prone to

impaction Ear canal narrower Eardrum shrinks and appears dull

and gray Ossicles do not move as freely Semicircular canals less

sensitive to changes in position – affects balance


Hearing Loss

Interruption in transmission to inner ear

Causes Obstruction of ear

canal Infection of middle ear Reduced movement of

stirrup

Sound waves not perceived by brain as sound

Causes Hereditary Repeated exposure to

loud noises / viral infections

Side effect of medication

Conductive hearing loss Sensorineural hearing loss

Symptom of a disease, not a normal part of aging


Hearing and Diagnostic Tests

Hearing tests Tuning forks – differentiate between types of

loss Audiometer – measures hearing acuity

Diagnostic testing Tympanometry

Measures the ability of the eardrums to move

Detects diseases and abnormalities of the middle ear


“Cauliflower Ear” Cauliflower ear is medically known as

an auricular hematoma. The external ear is made of cartilage

and it is the shape of the cartilage that gives the ear its distinctive shell-like shape. The cartilage is lined by perichondrium, a tight layer of connective tissue.

Auricular hematoma occurs when the ear cartilage is injured

Trauma results in fluid or blood collecting between the perichondrium and the cartilage. This blood or fluid can become permanent and scarred, resulting in the appearance of cauliflower ear.


Olfaction – Sense of Smell

Olfactory epithelium in roof of nasal cavity Pseudostratified columnar

epithelium Has millions of bipolar neurons

= olfactory receptor cells Only neurons undergoing replacement

throughout adult life Olfactory cilia bind odor

molecules Mucus captures & dissolves

odor molecules Each receptor cell has an

axon – the cells are bundled into “filaments” of olfactory nerve Penetrate plate of ethmoid

bone & enter olfactory bulb


Olfaction!35-22


Olfaction Olfactory receptors

Chemoreceptors – respond to changes in chemical concentrations Chemicals must be dissolved in mucus

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Day 2 - Taste

Chapter 12 – Special Senses


Olfaction

Smell sensation

that send the information along olfactory bulbs and tracts

to different areas of the cerebrum;

cerebrum interprets the information as a particular type of smell

Activation of smell receptors information sent to olfactory nerves


Nose and Sense of Smell (cont.)

Sensory Adaptation Chemical(s) can stimulate receptors for

limited amounts of time Chemoreceptors fatigue and stop

responding to chemical Result = no longer smell odor

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The Tongue… The tongue is a muscular organ in the

mouth. Covered with moist, pink tissue called

mucosa. Tiny bumps called papillae give the

tongue its rough texture. Thousands of taste buds (receptor

cells) cover the surfaces of the papillae. Taste buds are collections of nerve-like cells that connect to nerves running into the brain.

The tongue is anchored to the mouth by webs of tough tissue and mucosa. The tether holding down the front of the

tongue is called the frenum. In the back of the mouth, the tongue is

anchored into the hyoid bone. The tongue is vital for chewing and

swallowing food, as well as for speech.


Tongue and Sense of Taste

Taste buds: detect chemicals dissolved in saliva from food in the mouth and throat (chemoreceptors) Taste buds send their sensory information

through neurons to the gustatory center of the brain.

The average person has around 10,000 taste buds in their mouth and throat, although the number of taste buds peaks in early childhood and declines throughout our lives.

Location Papillae of the tongue Roof of mouth Walls of throat

Tongue

} fewer than on tongue


Papillae Types Foliate papillae: these are

ridges and grooves towards the posterior part of the tongue found at the lateral borders.

Fungiform papillae: small, on entire surface of tongue Vallate papillae: inverted “V” near back of tongue Filiform papillae: these are thin, long papillae "V“shaped cones that don't contain taste buds but are the most numerous. These papillae are mechanical and not involved in gustation

35-29


Taste Buds


Tongue Maps… 35-31


Tongue and Sense of Taste (cont.)

Taste sensation 4 primary

Sweet Sour Salty Bitter

Umami 5th basic taste Glutamic acid

Spicy foods Activate pain

receptors Interpreted by

brain as “spicy”Tongue


Tongue and Sense of Taste (cont.)

Taste sensation

Activation of taste cells

Cranial nerves

Gustatory cortex of cerebruminterprets information

2009 the mcgraw-hill companies, inc. all rights reserved special senses chapter 12

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