Lecture Human anatomy and physiology - Chapter 15: The special senses (part d)

After completing this unit, you should be able to: Describe the structure and general function of the outer, middle, and internal ears; describe the sound conduction pathway to the fluids of the internal ear, and follow the auditory pathway from the spiral organ (of Corti) to the temporal cortex; explain how one is able to differentiate pitch and loudness, and localize the source of sounds;...

Trang 1

PowerPoint ® Lecture Slides

prepared by Janice Meeking, Mount Royal College

C H A P T E R

15

The Special Senses:

Part D

Trang 2

Properties of Sound

high and low pressure) produced by a vibrating object

wave

Trang 3

Area of high pressure (compressed molecules)

Crest Trough

Area of low pressure (rarefaction)

A struck tuning fork alternately compresses and rarefies the air molecules around it, creating alternate zones of high and low pressure.

(b) Sound waves radiate outward

Trang 4

Properties of Sound Waves

Trang 5

Properties of Sound

Trang 6

Time (s) (a) Frequency is perceived as pitch.

High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch

High amplitude = loud Low amplitude = soft

Trang 7

Transmission of Sound to the Internal Ear

the oval window

the scala vestibuli

Trang 8

Transmission of Sound to the Internal Ear

of hearing travel through the helicotrema and scali tympani to the round window

cochlear duct, vibrating the basilar membrane

at a specific location, according to the

frequency of the sound

Trang 9

Scala tympani Cochlear duct Basilar

membrane

1

Sound waves vibrate

the tympanic membrane

Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells.

Sounds in the hearing range

go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells.

Malleus Incus

Auditory ossicles

Stapes

Oval window

Scala vestibuli Helicotrema Cochlear nerve

3 2

1

Round window

Tympanic membrane

(a) Route of sound waves through the ear

Trang 10

Resonance of the Basilar Membrane

membrane are short and stiff near oval

window, and resonate in response to frequency pressure waves

lower-frequency pressure waves

Trang 11

Fibers of basilar membrane

(b) Different sound frequencies cross the

basilar membrane at different locations.

Medium-frequency sounds displace the basilar membrane near the middle.

Low-frequency sounds displace the basilar membrane near the apex.

Base

(short, stiff fibers)

Frequency (Hz)

Apex

(long, floppy fibers)

Basilar membrane

High-frequency sounds displace the basilar membrane near the base.

Trang 12

Excitation of Hair Cells in the Spiral Organ

the bases of hair cells

Trang 13

(c)

Tectorial membrane Inner hair cell

Outer hair cells

fibers

Basilar membrane

Fibers of cochlear nerve Supporting cells

Trang 14

Excitation of Hair Cells in the Spiral Organ

• The stereocilia

• Protrude into the endolymph

• Enmeshed in the gel-like tectorial membrane

• Bending stereocilia

• Opens mechanically gated ion channels

• Inward K + and Ca 2+ current causes a graded potential and the release of neurotransmitter glutamate

• Cochlear fibers transmit impulses to the brain

Trang 15

Auditory Pathways to the Brain

• Impulses from the cochlea pass via the spiral

ganglion to the cochlear nuclei of the medulla

• From there, impulses are sent to the

• Superior olivary nucleus

• Inferior colliculus (auditory reflex center)

• From there, impulses pass to the auditory cortex via the thalamus

• Auditory pathways decussate so that both cortices receive input from both ears

Trang 16

Vibrations

Trang 17

Auditory Processing

interpreted as specific pitches

of action potentials that result when the hair cells experience larger deflections

intensity and relative timing of sound waves reaching both ears

Trang 18

Homeostatic Imbalances of Hearing

internal ear

eardrum, or otosclerosis of the ossicles

from the cochlear hair cells to the auditory cortical cells

Trang 19

Homeostatic Imbalances of Hearing

in the absence of auditory stimuli

inflammation of middle or internal ears, side effects of aspirin

affects the cochlea and the semicircular

canals

Trang 20

Equilibrium and Orientation

equilibrium receptors in the semicircular

canals and vestibule

equilibrium

Trang 21

Maculae

• Sensory receptors for static equilibrium

• One in each saccule wall and one in each utricle wall

• Monitor the position of the head in space, necessary for control of posture

• Respond to linear acceleration forces, but not

rotation

• Contain supporting cells and hair cells

• Stereocilia and kinocilia are embedded in the otolithic membrane studded with otoliths (tiny CaCO3 stones)

Trang 22

Macula of saccule

Otoliths

Hair bundle

Kinocilium Stereocilia

Otolithic membrane

Hair cells Supporting Macula of

utricle

Trang 23

Maculae

movements and tilting the head side to side

movements

Trang 24

Activating Maculae Receptors

kinocilia

release and increases the frequency of action potentials generated in the vestibular nerve

Trang 25

Activating Maculae Receptors

position of the head

Trang 26

Otolithic membrane Kinocilium

Stereocilia

Receptor potential Nerve impulses generated in vestibular fiber

When hairs bend toward the kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials.

When hairs bend away from the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing the action potential frequency.

Depolarization

Hyperpolarization

Trang 27

Crista Ampullaris (Crista)

that extend into a gel-like mass called the

cupula

the base of the hair cells

Trang 28

Fibers of vestibular nerve

Hair bundle (kinocilium plus stereocilia)

Hair cell

Supporting cell

Membranous labyrinth

Crista

ampullaris

Crista ampullaris

Trang 29

Activating Crista Ampullaris Receptors

rotatory movements of the head

brain at a faster rate

Trang 30

Activating Crista Ampullaris Receptors

causes

the brain

movements of the head

Trang 31

Fibers of vestibular nerve

At rest, the cupula stands

During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind due to inertia).

Endolymph flow bends the cupula and excites the hair cells.

As rotational movement slows, endolymph keeps moving in the direction

of the rotation, bending the cupula in the

opposite direction from acceleration and

inhibiting the hair cells.

Trang 32

Equilibrium Pathway to the Brain

• Pathways are complex and poorly traced

• Impulses travel to the vestibular nuclei in the brain stem or the cerebellum, both of which receive other input

• Three modes of input for balance and orientation

• Vestibular receptors

• Visual receptors

• Somatic receptors

Trang 33

Cerebellum

Oculomotor control (cranial nerve nuclei

III, IV, VI) (eye movements)

Spinal motor control (cranial nerve XI nuclei and vestibulospinal tracts) (neck movements)

Visual receptors

Somatic receptors (from skin, muscle and joints)

Vestibular nuclei

(in brain stem)

Input: Information about the body’s position in space comes from three main sources and is fed into two major processing areas in the central nervous system.

Output: Fast reflexive control of the muscles serving the eye and neck, limb, and trunk are provided by the outputs of the central nervous system.

Vestibular receptors

Central nervous system processing

Trang 34

Developmental Aspects

• All special senses are functional at birth

• Chemical senses—few problems occur until the

fourth decade, when these senses begin to decline

• Vision—optic vesicles protrude from the

diencephalon during the fourth week of development

• Vesicles indent to form optic cups; their stalks form optic nerves

• Later, the lens forms from ectoderm

Trang 35

• Vision is not fully functional at birth

• Babies are hyperopic, see only gray tones, and eye movements are uncoordinated

• Depth perception and color vision is well developed

Trang 36

• Ear development begins in the three-week embryo

• Inner ears develop from otic placodes, which

invaginate into the otic pit and otic vesicle

• The otic vesicle becomes the membranous labyrinth, and the surrounding mesenchyme becomes the bony labyrinth

• Middle ear structures develop from the pharyngeal pouches

• The branchial groove develops into outer ear

structures

Trang 37

Human Eye: Study Guide

Định dạng
Số trang	37
Dung lượng	1,33 MB