Transcript The Special Senses

Essentials of Anatomy & Physiology, 4th Edition
Martini / Bartholomew
9
The General and
Special Senses
PowerPoint® Lecture Outlines
prepared by Alan Magid, Duke University
Slides 1 to 106
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Sensory Basics
• Sensory receptors—Specialized
cells or cell processes that monitor
external or internal conditions.
Simplest are free nerve endings.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
More Sensory Basics
• Receptive field—The area monitored
by a single receptor cell
• Adaptation—Reduction in sensitivity
at a receptor or along a sensory
pathway in the presence of a
constant stimulus.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Receptors and Receptive Fields
Figure 9-1
The General Senses
General versus Special Senses
• General senses—Temperature, pain,
touch, pressure, vibration, and
proprioception. Receptors throughout the
body
• Special senses—Smell, taste, vision,
balance, and hearing. Receptors located
in sense organs (e.g., ear, eye).
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Key Note
Stimulation of a receptor produces
action potentials that propagate along
the axon of a sensory neuron. The
frequency or pattern of action potentials
contains information about the stimulus.
A person’s perception of the nature of
that stimulus depends on the path it
takes inside the CNS.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Pain Definitions
• Nociceptors—Receptors for tissue damage
to lead to the sensation of pain
• Referred pain—Perception of pain in a part
of the body not actually stimulated
• Fast (prickling) pain—Localized pain carried
quickly to the CNS on myelinated axons
• Slow (burning) pain—Generalized pain
carried on slow unmyelinated axons
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Referred Pain
Figure 9-2
The General Senses
Temperature
• Thermoreceptors detect temperature
change
• Free nerve endings
• Found in dermis, skeletal muscle, liver,
hypothalamus
• Fast adapting
• Cold receptors greatly outnumber warm
receptors
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Touch, Pressure, and Position
• Mechanoreceptors—Receptors that respond
to physical distortion of their cell
membranes.
• Tactile receptors—Sense touch, pressure, or
vibration
• Baroreceptors—Sense pressure changes in
walls of blood vessels, digestive organs,
bladder, lungs
• Proprioceptors—Respond to positions of
joints and muscle
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Tactile Receptors
• Fine touch or pressure receptors
• Highly detailed information about a stimulus
• Crude touch or pressure receptors
• Poorly localized information about a
stimulus
• Important types: root hair plexus, tactile disks,
tactile corpuscles, lamellated corpuscles,
Ruffini corpuscles
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Tactile Receptors in the Skin
Figure 9-3
The General Senses
Baroreceptors
• Provide pressure information essential
for autonomic regulation
• Arterial blood pressure
• Lung inflation
• Digestive coordination
• Bladder fullness
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Baroreceptors and the Regulation of
Autonomic Functions
Figure 9-4
The General Senses
Proprioceptors
• Monitor joint angle, tension in
tendons and ligaments, state of
muscular contraction
• Include:
• Muscle spindles
• Golgi tendon organs
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Chemical Detection
• Chemoreceptors respond to chemicals
dissolved in body fluids that surround
them and monitor the chemical
composition of blood and tissues
• Chemicals that can be sensed include:
• Carbon dioxide
• Oxygen
• Hydrogen ion
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The General Senses
Locations and Functions of Chemoreceptors
Figure 9-5
The Special Senses—Smell
Olfactory Organs
• Olfactory epithelium
• Olfactory receptor cells
• Neurons sensitive to odorants
• Supporting cells
• Basal (stem) cells
• Olfactory glands
• Mucus-secreting cells
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Smell
The Olfactory
Organs
Figure 9-6(a)
The Special Senses—Smell
The Olfactory
Organs
Figure 9-6(b)
The Special Senses—Smell
The Olfactory Pathways
• Axons from olfactory receptors
penetrate cribriform plate of ethmoid
bone
• Synapse in olfactory bulb
• Olfactory tract projects to:
• Olfactory cerebral cortex
• Hypothalamus
• Limbic System
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Taste
Taste (Gustatory) Receptors
• Taste buds
• Found within papillae on tongue,
pharynx, larynx
• Contain gustatory cells, supportive
cells
• Taste hairs (cilia) extend into taste
pores
• Sense salt, sweet, sour, bitter
• Also sense umami, water
• Synapse in medulla oblongata
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Taste
Gustatory Receptors
Figure 9-7(a)
The Special Senses—Taste
Gustatory
Receptors
Figure 9-7(b)
The Special Senses—Taste
Gustatory Receptors
Figure 9-7(c)
The Special Senses
Key Note
Olfactory information is routed directly
to the cerebrum, and olfactory stimuli
have powerful effects on mood and
behavior. Gustatory sensations are
strongest and clearest when integrated
with olfactory sensations.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Accessory Structures of the Eye
• Eyelids (palpebra) and glands
• Superficial epithelium of eye
• Conjunctiva
• Lacrimal apparatus
• Tear production and removal
• Extrinsic eye muscles
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The
Accessory
Structures
of the Eye
Figure 9-8(a)
The Special Senses—Vision
The Lacrimal Apparatus
• Lacrimal gland produce tears
• Bathe conjunctiva
• Contain lysozyme to attack bacteria
• Tears drain into nasal cavity
• Pass through lacrimal canals,
lacrimal sac, nasolacrimal duct
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The Lacrimal Apparatus of the Eye
Figure 9-8(b)
The Special Senses—Vision
The Sectional
Anatomy of the
Eye
Figure 9-10(a)
The Special Senses—Vision
Extrinsic Eye Muscles
• Move the eye
• Six muscles cooperate to
control gaze
• Superior and inferior rectus
• Lateral and medial rectus
• Superior and inferior oblique
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The Extrinsic
Eye Muscles
Figure 9-9(a)
The Special Senses—Vision
The Extrinsic
Eye Muscles
Figure 9-9(b)
The Special Senses—Vision
Layers (Tunics) of
the Eye
• Fibrous tunic
• Outermost layer
• Vascular tunic
• Intermediate layer
• Neural tunic
• Innermost layer
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The Sectional Anatomy of the Eye
Figure 9-10(b)
The Special Senses—Vision
Layers of the Eye
• Fibrous tunic
• Sclera
• Dense fibrous connective
tissue
• “White of the eye”
• Cornea
• Transparent
• Light entrance
PLAY
The Eye: Light Path
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Layers of the Eye
• Vascular tunic
• Iris
• Boundary between anterior and
posterior chambers
• Ciliary body
• Ciliary muscle and ciliary process
• Attachment of suspensory ligaments
• Choroid
• Highly vascular
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Functions of the Vascular Tunic
• Provide a route for blood vessels
• Control amount of light entering eye
• Adjust diameter of pupil
• Secrete and absorb aqueous humor
• Adjust lens shape for focusing
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The Pupillary Muscles
Figure 9-11
The Special Senses—Vision
The Sectional Anatomy of the Eye
Figure 9-10 (c)
The Special Senses—Vision
Layers of the Eye
• Neural tunic (Retina)
• Outer pigmented part
• Absorbs stray light
• Inner neural part
• Detects light
• Processes image
• Communicates with brain
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Organization of the Retina
• Photoreceptor layer
• Bipolar cells
• Amacrine, horizontal cells
modify signals
• Ganglion cells
• Optic nerve (II)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Retinal Organization
Figure 9-12(a)
The Special Senses—Vision
Retinal
Organization
Figure 9-12(b)
The Special Senses—Vision
Retinal
Organization
Figure 9-12(c)
The Special Senses - Vision
The Special Senses—Vision
Chambers of the Eye
• Two cavities (Anterior & Posterior)
• Ciliary body, lens between the two
• Anterior cavity
• Anterior compartment
Between cornea and iris
Aqueous humor
• Posterior compartment
Between iris and lens
• Posterior cavity
• Vitreous body
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The Aqueous Humor
• Secreted by ciliary processes into
posterior chamber
• Flows into anterior chamber
• Maintains eye shape
• Carries nutrients and wastes
• Reabsorbed into circulation
• Leaves at canal of Schlemm
• Excess humor leads to glaucoma
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Eye Chambers and the Circulation of
Aqueous Humor
Figure 9-14
The Special Senses—Vision
The Lens
• Supported by suspensory
ligaments
• Built from transparent cells
• Surrounded by elastic capsule
• Lens and cornea focus light on
retina
• Bend light (refraction)
• Accommodation changes lens
shape (curvature)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses - Vision
Focal Point: The point on the lens where
nearly parallel lines of light pass through
Focal Distance: how strongly light
diverges or converges
Visual Accomodation: measure of lens
curvature
The Special Senses—Vision
Focal Point, Focal
Distance, and Visual
Accommodation
Figure 9-15(d)
The Special Senses—Vision
Focal Point, Focal
Distance, and Visual
Accommodation
Figure 9-15(e)
The Special Senses—Vision
Image Formation
Figure 9-16(a)
The Special Senses—Vision
Image Formation
Figure 9-16(b)
The Special Senses—Vision
Visual Abnormalities
Figure 9-17(a)
The Special Senses—Vision
Visual Abnormalities
Figure 9-17(b)
Myopia
The Special Senses—Vision
Visual Abnormalities
Figure 9-17(c)
The Special Senses—Vision
Visual Abnormalities
Figure 9-17(d)
Hyperopia
The Special Senses—Vision
Visual Abnormalities
Figure 9-17(e)
The Special Senses—Vision
Key Note
Light passes through the cornea, crosses
the anterior cavity to the lens, moves
through the lens, crosses the posterior
chamber, and then penetrates the retina
to stimulate the photoreceptors. Cones,
most abundant at the fovea and macula
lutea, provide detailed color vision in
bright light. Rods, dominant in the
peripheral retina, provide coarse colorfree vision in dim light.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Visual Physiology
• Photoreceptors—Cells specialized to
respond to photons, packets of light energy
• Two types of photoreceptors
• Rods
• Highly sensitive, non-color vision
• In peripheral retina
• Cones
• Less sensitive, color vision
• Mostly in fovea, center of macula lutea
Site of sharpest vision
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
Photoreceptor Anatomy
• Outer segment
• Discs with visual pigments
• Light absorption by rhodopsin
• Opsin + retinal
• Inner segment
• Synapse with bipolar cell
• Control of neurotransmitter release
• Effect on bipolar cells
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Photon
Retinal changes shape
Retinal and
opsin are
reassembled
to form
rhodopsin
Regeneration
Retinal
restored
enzyme
ADP
Opsin
Bleaching
(separation)
ATP
Opsin
Opsin
inactivated
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-20
1 of 7
Retinal and
opsin are
reassembled
to form
rhodopsin
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-20
2 of 7
Photon
Retinal and
opsin are
reassembled
to form
rhodopsin
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-20
3 of 7
Photon
Retinal changes shape
Retinal and
opsin are
reassembled
to form
rhodopsin
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-20
4 of 7
Photon
Retinal changes shape
Retinal and
opsin are
reassembled
to form
rhodopsin
enzyme
Retinal
restored
ADP
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Bleaching
(separation)
ATP
Figure 9-20
5 of 7
Photon
Retinal changes shape
Retinal and
opsin are
reassembled
to form
rhodopsin
enzyme
Retinal
restored
ADP
Opsin
Bleaching
(separation)
ATP
Opsin
Opsin
inactivated
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-20
6 of 7
Photon
Retinal changes shape
Retinal and
opsin are
reassembled
to form
rhodopsin
Regeneration
Retinal
restored
enzyme
ADP
Opsin
Bleaching
(separation)
ATP
Opsin
Opsin
inactivated
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-20
7 of 7
The Special Senses—Vision
The Visual Pathway
•
•
•
•
Ganglion cells axon converge at optic disc
Axons leave as optic nerve (II)
Some axons cross at optic chiasm
Synapse in thalamus bilaterally
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The Visual Pathway
• Thalamic neurons project to visual cortex
• Located in occipital lobes
• Contains map of visual field
• Visual inputs to hypothalamus and pineal
gland establish daily circadian rhythms
• Affecting metabolic rate, endocrine
function, blood pressure, digestive
activities, awake-sleep cycle and other
processes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Special Senses—Vision
The Visual Pathway
Figure 9-21
Color Vision
The colors of the rainbow
as viewed by a person
with no color vision
deficiencies.
The colors of the rainbow as viewed
by a person with protanopia –
affects red receptors
The colors of the rainbow as viewed
by a person with tritanopia – affects
blue- yellow receptors
The colors of the rainbow as viewed by
a person with deuteranopia – affects
green receptors
Figure 9.18
Essentials of Anatomy & Physiology, 4th Edition
Martini / Bartholomew
9
The General and
Special Senses
PowerPoint® Lecture Outlines
prepared by Alan Magid, Duke University
Equilibrium and Hearing
Overview of the Ear
• Chambers, canals filled with fluid
endolymph
• Bony labyrinth
• Surrounds membranous labyrinth
• Surrounded by fluid perilymph
• Consists of vestibule, semicircular canals,
cochlea
• External, middle ear feed sound to cochlea
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
The Anatomy of the Ear
Figure 9-22
Equilibrium and Hearing
Anatomy of the Ear
• External ear
• Pinna (auricle)
• External acoustic canal
• Tympanic membrane (eardrum)
• Middle ear
• Auditory ossicles
• Connect tympanic membrane to inner ear
• Auditory tube
• Connection to nasopharynx
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
The Structure of the Middle Ear
Figure 9-23
Equilibrium and Hearing
Anatomy of the Inner Ear
• Vestibule
• Membranous sacs
• Utricle
• Saccule
• Receptors for linear acceleration,
gravity
• Semicircular canal with ducts
• Receptors for rotation
• Cochlea with cochlear duct
• Receptors for sound
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
Sensory Functions of the Inner Ear
• Dynamic equilibrium
• Static equilibrium
• Hearing
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
Receptors of the Inner Ear
• Hair cells
• Mechanoreceptors
• Stereocilia on cell surface
• Bending excites/inhibits hair cell
• Information on direction and strength
of mechanical stimuli (sound)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
The Anatomy of the Ear
Figure 9-24(a,b)
Equilibrium and Hearing
The Anatomy
of the Ear
Figure 9-24(c)
PLAY
The Ear: Ear Anatomy
Equilibrium and Hearing
Equilibrium
• Semicircular ducts
• Connect to utricle
• Contains ampulla with hair cells
• Stereocilia contact cupola
• Gelatinous mass distorted by fluid
movement
• Detects rotation of head in three planes
• Anterior, posterior, lateral ducts
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
Equilibrium (continued)
• Saccule and utricle
• Hair cells cluster in maculae
• Stereocilia contact otoliths
(heavy mineral crystals)
• Gravity pulls otoliths
• Detect tilt of head
• Sensory axons in vestibular
branch of CN VIII
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
The Vestibular Complex
Figure 9-25(a-c)
Equilibrium and Hearing
The Vestibular Complex
Figure 9-25(a, d)
Head in horizontal position
Gravity
Head tilted posteriorly
Gravity
Receptor
output increases
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Otolith
moves
“downhill,”
distorting
hair cell
processes
Figure 9-25(e)
1 of 4
Head in horizontal position
Gravity
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-25(e)
2 of 4
Head in horizontal position
Gravity
Head tilted posteriorly
Gravity
Otolith
moves
“downhill,”
distorting
hair cell
processes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-25(e)
3 of 4
Head in horizontal position
Gravity
Head tilted posteriorly
Gravity
Receptor
output increases
PLAY
The Ear: Balance
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Otolith
moves
“downhill,”
distorting
hair cell
processes
Figure 9-25(e)
4 of 4
Equilibrium and Hearing
Overview of Hearing
• Sound waves vibrate tympanic membrane
• Ossicles transfer vibration to oval window
• Oval window presses on perilymph in
vestibular duct
• Pressure wave distorts basilar membrane
• Hair cells of organ of Corti press on
tectorial membrane
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
The Cochlea and the Organ of Corti
Figure 9-26(a)
Equilibrium and Hearing
The Cochlea and the Organ of Corti
Figure 9-26(b)
External
acoustic
Incus
Oval
canal
Malleus Stapes window
Cochlear branch of
cranial nerve VIII
Vestibular duct
(perilymph)
Movement
of sound
waves
Vestibular membrane
Cochlear duct
(endolymph)
Basilar membrane
Tympanic duct
(perilymph)
Tympanic
membrane
Sound waves
arrive at tympanic
membrane.
Movement of
tympanic membrane
causes displacement
of the auditory
ossicles.
Round
window
Movement of the
stapes at the oval
window establishes
pressure waves in
the perilymph of
the vestibular duct.
The pressure waves
distort the basilar
membrane on their
way to the round
window of the
tympanic duct.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Vibrations of the
basilar membrane
causes vibration of
hair cells against
the tectorial
membrane.
Information about the
region and the intensity
of stimulation is
relayed to the CNS over
the cochlear branch of
cranial nerve VIII.
Figure 9-27
1 of 7
External
acoustic
canal
Movement
of sound
waves
Tympanic
membrane
Sound waves
arrive at tympanic
membrane.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-27
2 of 7
External
acoustic
Incus
canal
Malleus Stapes
Movement
of sound
waves
Tympanic
membrane
Sound waves
arrive at tympanic
membrane.
Movement of
tympanic membrane
causes displacement
of the auditory
ossicles.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-27
3 of 7
External
acoustic
Incus
Oval
canal
Malleus Stapes window
Movement
of sound
waves
Tympanic
membrane
Sound waves
arrive at tympanic
membrane.
Movement of
tympanic membrane
causes displacement
of the auditory
ossicles.
Movement of the
stapes at the oval
window establishes
pressure waves in
the perilymph of
the vestibular duct.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-27
4 of 7
External
acoustic
Incus
Oval
canal
Malleus Stapes window
Movement
of sound
waves
Tympanic
membrane
Sound waves
arrive at tympanic
membrane.
Movement of
tympanic membrane
causes displacement
of the auditory
ossicles.
Round
window
Movement of the
stapes at the oval
window establishes
pressure waves in
the perilymph of
the vestibular duct.
The pressure waves
distort the basilar
membrane on their
way to the round
window of the
tympanic duct.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 9-27
5 of 7
External
acoustic
Incus
Oval
canal
Malleus Stapes window
Vestibular duct
(perilymph)
Movement
of sound
waves
Vestibular membrane
Cochlear duct
(endolymph)
Basilar membrane
Tympanic duct
(perilymph)
Tympanic
membrane
Sound waves
arrive at tympanic
membrane.
Movement of
tympanic membrane
causes displacement
of the auditory
ossicles.
Round
window
Movement of the
stapes at the oval
window establishes
pressure waves in
the perilymph of
the vestibular duct.
The pressure waves
distort the basilar
membrane on their
way to the round
window of the
tympanic duct.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Vibrations of the
basilar membrane
causes vibration of
hair cells against
the tectorial
membrane.
Figure 9-27
6 of 7
External
acoustic
Incus
Oval
canal
Malleus Stapes window
Cochlear branch of
cranial nerve VIII
Vestibular duct
(perilymph)
Movement
of sound
waves
Vestibular membrane
Cochlear duct
(endolymph)
Basilar membrane
Tympanic duct
(perilymph)
Tympanic
membrane
Sound waves
arrive at tympanic
membrane.
PLAY
Movement of
tympanic membrane
causes displacement
of the auditory
ossicles.
Round
window
Movement of the
stapes at the oval
window establishes
pressure waves in
the perilymph of
the vestibular duct.
The pressure waves
distort the basilar
membrane on their
way to the round
window of the
tympanic duct.
The Ear: Receptor Complexes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Vibrations of the
basilar membrane
causes vibration of
hair cells against
the tectorial
membrane.
Information about the
region and the intensity
of stimulation is
relayed to the CNS over
the cochlear branch of
cranial nerve VIII.
Figure 9-27
7 of 7
Equilibrium and Hearing
Auditory Pathways
• Hair cells excite sensory neurons
• Sensory neurons located in spiral
ganglion
• Afferent axons form cochlear branch of
vestibulocochlear nerve (CN VIII)
• Synapses in cochlear nucleus in medulla
• Neurons relay to midbrain
• Midbrain relays to thalamus
• Thalamus relays to auditory cortex
(temporal lobe) in a frequency map
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Equilibrium and Hearing
Pathways for
Auditory
Sensations
Figure 9-28
Equilibrium and Hearing
Key Note
Balance and hearing both rely on hair
cells. Which stimulus excites a particular
group depends on the structure of the
associated sense organ. In the
semicircular ducts, fluid movement due to
head rotation is sensed. In the utricle and
saccule, shifts in the position of otoliths
by gravity is sensed. In the cochlea,
sound pressure waves distort the basilar
membrane.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Aging and the Senses
Impact of Aging on Sensory Ability
• Gradual reduction in smell and taste
sensitivity as receptors are lost
• Lens changes lead to presbyopia
(loss of near vision)
• Chance of cataract increases
• Progressive loss of hearing
sensitivity as receptors are lost
(presbycusis)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings