18 Lecture Presentation

8/9/2019 18 Lecture Presentation

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© 2012 Pearson Education, Inc.

18The Nervous System:General and SpecialSenses

PowerPoint ® Lecture Presentations prepared by

Steven Bassett

Southeast Community College

L incoln, Nebraska


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Introduction

•Sensory information arrives at the CNS• Information is “picked up” by sensory

receptors

•

Sensory receptors are the interface betweenthe nervous system and the internal and

external environment

• General senses

• Refers to temperature, pain, touch, pressure,vibration, and proprioception

• Special senses

• Refers to smell, taste, balance, hearing, and vision


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Receptors

•Receptors and Receptive Fields• Free nerve endings are the simplest receptors

• These respond to a variety of stimuli

•

Receptors of the retina (for example) are veryspecific and only respond to light

• Receptive fields

• Large receptive fields have receptors spread far

apart, which makes it difficult to localize a stimulus• Small receptive fields have receptors close

together, which makes it easy to localize a stimulus.


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Figure 18.1 Receptors and Receptive Fields

Receptive fields

Receptive

field 1

Receptive

field 2


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Receptors

•Interpretation of Sensory Information• Information is relayed from the receptor to

a specific neuron in the CNS

• The connection between a receptor and a neuron is

called a labeled line

• Each labeled line transmits its own specific

sensation


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Interpretation of Sensory Information

•Classification of Receptors• Tonic receptors

• Always active

• Photoreceptors of the eye constantly monitor body

position

• Phasic receptors

• Normally inactive but become active when

necessary (for short periods of time)• Touch and pressure receptors of the skin (for

example)


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Receptors

•Central Processing and Adaptation• Adaptation

• Reduction in sensitivity due to a constant stimulus

•

Peripheral adaptation• Receptors respond strongly at first and then decline

• Central adaptation

• Adaptation within the CNS

• Consciously aware of a stimulus, which quicklydisappears



The General Senses

•Classification of the General Senses• One classification scheme:

• Exteroceptors: provide information about the

external environment

• Proprioceptors: provide information about the

position of the body

• Interoceptors: provide information about the inside

of the body



The General Senses

•Classification of the General Senses• Another classification scheme:

• Nociceptors: respond to the sensation of pain

• Thermoreceptors: respond to changes in

temperature

• Mechanoreceptors: activated by physical

distortion of cell membranes

• Chemoreceptors: monitor the chemical

composition of body fluids



The General Senses

•Nociceptors• Known as pain receptors

• Associated with free nerve endings and large

receptor fields. This makes it difficult to

“pinpoint” the location of the origin of the pain

• Three types

• Receptors sensitive to extreme temperatures

• Receptors sensitive to mechanical damage

• Receptors sensitive to chemicals



The General Senses

•Nociceptors• Fast pain:

• Sensations reach the CNS fast

• Associated with pricking pain or cuts

• Slow pain:

• Sensations reach the CNS slowly

• Associated with burns or aching pains

• Referred pain:• Sensations reach the spinal cord via the dorsal roots

• Some visceral organ pain sensations may reach the

spinal cord via the same dorsal root



Figure 18.2 Referred Pain

Heart

Liver and

gallbladder

Stomach

Small

intestine

Appendix

Colon

Ureters



The General Senses

•

Thermoreceptors• Found in the dermis, skeletal muscles, liver,

and hypothalamus

• Cold receptors are more numerous than hot

receptors

• Exist as free nerve endings

• These are phasic receptors

• Information is transmitted along the same

pathway as pain information



The General Senses

•

Mechanoreceptors• Receptors that are sensitive to stretch,

compression, twisting, or distortion of the

plasmalemmae

• There are three types

• Tactile receptors

• Baroreceptors

•Proprioceptors



The General Senses

•

Mechanoreceptors• Tactile receptors

• Provide sensations of touch, pressure, and

vibrations

• Unencapsulated tactile receptors: free nerve

endings, tactile disc, and root hair plexus

• Encapsulated tactile receptors: tactile corpuscle,

Ruffini corpuscle, and lamellated corpuscle



The General Senses

•

Mechanoreceptors• Unencapsulated tactile receptors

• Free nerve endings are common in the dermis

• Tactile discs are in the stratum basale layer

• Root hair plexus monitors distortions and

movements of the body surface

Fi 18 3 T til R t i th Ski



Figure 18.3a Tactile Receptors in the Skin

Free nerve endings

Hair

Root hair plexus

Lamellated corpuscle

Ruffini corpuscle

Merkel cells and

tactile discsTactile

corpuscle

Free nerve

ending

Sensory

nerves


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Figure 18 3c Tactile Receptors in the Skin


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Figure 18.3c Tactile Receptors in the Skin

Hair

Root hair plexus


Ruffini corpuscle

Merkel cells and

tactile discs

Tactile

corpuscle

Free nerve

ending

Sensory

nerves

Free nerve endings

of root hair plexus


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The General Senses

•

Mechanoreceptors• Encapsulated tactile receptors

• Tactile corpuscle: common on eyelids, lips,

fingertips, nipples, and genitalia

• Ruffini corpuscle: in the dermis, sensitive to

pressure and distortion

• Lamellated corpuscle: consists of concentric

cellular layers / sensitive to vibrations

Figure 18 3d Tactile Receptors in the Skin


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Figure 18.3d Tactile Receptors in the Skin

Tactile corpuscle; the capsule

boundary in the micrograph is

indicated by a dashed line.

Tactile

corpuscle Epidermis

Dermis

Tactile corpuscle LM 550

Capsule

Accessory

cells

Dendrites

Sensory

nerve fiber

Hair

Root hair plexus


Ruffini corpuscle

Merkel cells and

tactile discs

Tactile

corpuscleFree nerve

ending

Sensory

nerves

Figure 18 3e Tactile Receptors in the Skin


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Figure 18.3e Tactile Receptors in the Skin

Capsule

Dendrites

Ruffini corpuscle

Sensory

nerve fiber

Collagen

fibers

Hair

Root hair plexus


Ruffini corpuscle

Merkel cells and

tactile discs

Tactile

corpuscle

Free nerve

ending

Sensory

nerves

Figure 18 3f Tactile Rece

ptors in the Skin


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Figure 18.3f Tactile Receptors in the Skin


Dendritic

process

Concentric layers (lamellae)

of collagen fibers

separated by fluid

Concentric layers (lamellae)

of collagen fibers

separated by fluid

Accessory cells(specialized fibrocytes)

Dendritic process

Dermis

LM 125Lamellated corpuscle

Hair

Root hair plexus


Ruffini corpuscle

Merkel cells and

tactile discs

Tactile

corpuscle

Free nerve

ending

Sensory

nerves


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The General Senses

•

Mechanoreceptors• Baroreceptors

• Stretch receptors that monitor changes in the

stretch of organs

• Found in the stomach, small intestine, urinarybladder, carotid artery, lungs, and large intestine

Figure 18.4 Baroreceptors and the Regulation of Autonomic Functions


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Figure 18.4 Baroreceptors and the Regulation of Autonomic Functions

Provide information on volume of

tract segments, trigger reflex

movement of materials along tract

Provide information on volume of

urinary bladder, trigger urinary reflex

Baroreceptors of BladderWall

Baroreceptors of DigestiveTract

Baroreceptors of CarotidSinus and Aortic Sinus

Baroreceptors of Lung

Baroreceptors of Colon

Provide information on blood

pressure to cardiovascular and

respiratory control centers

Provide information on lung

stretching to respiratory

rhythmicity centers for

control of respiratory rate

Provide information on volume

of fecal material in colon,

trigger defecation reflex


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The General Senses

•

Mechanoreceptors• Proprioceptors

• Monitor the position of joints, tension in the tendons

and ligaments, and the length of muscle fibers upon

contraction• Muscle spindles are receptors in the muscles

• Golgi tendon organs are the receptors in the

tendons


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The General Senses

•

Chemoreceptors• Detect small changes in the concentration of

chemicals

• Respond to water-soluble or lipid-soluble

compounds

• Found in respiratory centers of the medulla

oblongata, carotid arteries, and aortic arch

Figure 18.5 Chemoreceptors


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g p

Carotid body LM 1500

Blood vessel

Chemoreceptive

neuronsTrigger reflexive

adjustments indepth and rate of

respiration

Trigger reflexive

adjustments inrespiratory and

cardiovascular

activity

Via cranialnerve IX

Via cranial

nerve X

Sensitive to changes in pH

and PCO2 in cerebrospinal

fluid

Sensitive to changes in pH,

PCO2, and PO2 in blood

Sensitive to changes in

pH, PCO2, and PO2 in blood

Chemoreceptors in andnear Respiratory Centersof Medulla Oblongata

Chemoreceptors

of Carotid Bodies

Chemoreceptorsof Aortic Bodies


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The Special Senses

•

The special senses include:• Olfaction (smell)

• Gustation (taste)

•

Equilibrium• Hearing

• Vision


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Olfaction (Smell)

•

Olfactory Pathways• Axons leave the olfactory epithelium

• Pass through the cribriform foramina

•

Synapse on neurons in the olfactory bulbs• Impulses travel to the brain via CN I

• Arrive at the cerebral cortex, hypothalamus,

and limbic system

Figure 18.6a The Olfactory Organs


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The distribution of the olfactory receptors

on the left side of the nasal septum is

shown by the shading.

Olfactory

bulb

Olfactory nerve

fibers (N I)

Olfactorytract

Cribr i form plate

of ethmoid

Olfactory

epithelium

Figure 18.6b The Olfactor

y Organs


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© 2012 Pearson Education, Inc.A detailed view of the olfactory epithelium

Substance being smelled

Olfactory

epithelium

Lamina

propria

Cribr i form

plate

Knob

Olfactory cilia:

surfaces contain

receptor proteins

Mucous layer

Supporting cell

Olfactory

receptor cell

Developing olfactory

receptor cell

Olfactory

nerve fibers

To olfactory

bulb

Olfactory

(Bowman’s)

gland

Regenerative basal cell:

divides to replace worn-out

olfactory receptor cells


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Olfaction (Smell)

•

Olfactory Discrimination• The epithelial receptors have different

sensitivities and we therefore “detect” different

smells

• Olfactory receptors can be replaced

• The replacement activity declines with age


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Gustation (Taste)

•Gustation• The tongue consists of papillae

• Papillae consist of taste buds

•

Taste buds consist of gustatory cells• Each gustatory cell has a slender microvilli

that extends through the taste pore into the

surrounding fluid


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Gustation (Taste)

•

Gustation Pathways• Dissolved chemicals contact the taste hairs

(microvilli)

• Impulses go from the gustatory cell through

CN VII, IX, and X

• Synapse in the nucleus solitarius of the

medulla oblongata

• The impulses eventually arrive at the cerebralcortex

Figure 18.8 Gustatory Pathways


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Gustatory

cortex

Thalamic

nucleus

Medial

lemniscus

Nucleus

solitarius

Vagus nerve

(N X)

Facial nerve(N VII)

Glossopharyngeal

nerve (N IX)


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Gustation (Taste)

•

Gustation Discrimination• We begin life with more than 10,000 taste

buds

• The number declines rapidly by age 50

• Threshold level is low for gustatory cells

responsible for unpleasant stimuli

• Threshold level is high for gustatory cells

responsible for pleasant stimuli


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Equilibrium and Hearing

•

Equilibrium and Hearing• Structures of the ear are involved in balance

and hearing

• The ear is subdivided into three regions

• External ear

• Middle ear

• Inner ear

ANIMATION The Ear: Ear Anatomy

http://localhost/var/www/apps/conversion/tmp/scratch_7/ear_anatomy.mpg


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•

The External Ear• Consists of:

• Auricle

• External acoustic meatus

• Tympanic membrane

• Ceruminous glands

Figure 18.9 Anatomy of the Ear


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EXTERNAL EAR MIDDLE EAR INNER EAR

Auricle

Auditory ossicles Semicircularcanals

Petrous partof temporal

bone

Facial nerve(N VII)

Externalacousticmeatus

Elasticcartilage

Tympanicmembrane

Tympaniccavity

Oval window

Round window

Vestibule

Auditory tube

Cochlea

Tonasopharynx

Bony labyrinthof inner ear

Vestibulocochlearnerve (N VIII)

E ilib i d H i


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•

The Middle Ear• Consists of:

• Tympanic cavity

• Auditory ossicles

• Malleus, incus, and stapes

• Auditory tube (pharyngotympanic tube)



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Auricle



bone

Facial nerve(N VII)


Elasticcartilage

Tympanicmembrane

Tympaniccavity

Oval window

Round window

Vestibule

Auditory tube

Cochlea

Tonasopharynx



Figure 18.10a The Middle Ear


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Inferior view of the right temporal

bone drawn, as if transparent, to

show the location of the middle

and inner ear

Inner ear

Tympanic cavity

(middle ear)

External acoustic

meatus

Tympanic membrane

Auditory ossicles

Auditory tube

Figure 18.10b The Middle Ear


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© 2012 Pearson Education, Inc.Structures within the middle ear cavity

Temporal bone

(petrous part)

Stabilizing

ligament

Chorda tympani

nerve (cut), a

branch of N VII

External acoustic

meatus

Tympanic cavity

(middle ear)

Tympanic membrane

(tympanum)

Malleus

Incus

Base of stapes

at oval window

Tensor tympani

muscle

StapesRound window

Stapedius

muscle

Auditory tube

Figure 18.10c The Middle Ear


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The isolated auditory ossicles

Malleus

Incus

Points ofattachment

to tympanic

membrane

Stapes

Base

of stapes

Figure 18.10d The Middle Ear


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The tympanic membrane and auditory ossicles

as seen through a fiber-optic tube inserted along

the auditory canal and into the middle ear cavity

Incus

Base ofstapes atoval window

Stapes

Stapediusmuscle

Malleus

Tendon of tensortympani muscle

Malleus attachedto tympanic

membraneInner surface

of tympanicmembrane

E ilib i d H i


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•

The Inner Ear• Consists of:

• Receptors

• Membranous labyrinth (within the bony

labyrinth)

• Bony labyrinth

• Vestibule

• Semicircular canals

• Cochlea

• Utricle

• Saccule



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Auricle



bone

Facial nerve(N VII)


Elasticcartilage

Tympanicmembrane

Tympaniccavity

Oval window

Round window

Vestibule

Auditory tube

Cochlea

Tonasopharynx



Figure 18.12a Semicircular Canals and Ducts


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Anterior view of the bony

labyrinth cut away to show the

semicircular canals and the

enclosed semicircular ducts of

the membranous labyrinth

Cochlear duct

Vestibular duct

Saccule

Utricle

Tympanic

duct

Organ of

Corti

Cochlea

Endolymphatic sac

Maculae

Cristae within ampullae

Bony labyrinth

Membranous

labyrinth

KEY

Vestibule

Anterior

LateralPosterior

Semicircular

canal

Semicircularducts

Figure 18.12b Semicircular Canals and Ducts


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Cross section of a semicircular canal toshow the orientation of the bony

labyrinth, perilymph, membranous

labyrinth, and endolymph

Perilymph

Bony labyrinth

Endolymph

Membranouslabyrinth



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•

The Inner Ear• The vestibular complex and equilibrium

• Part of inner ear that provides equilibrium

sensations by detecting rotation, gravity,

and acceleration

• Consists of:

• Semicircular canals

• Utricle• Saccule



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•

The Vestibular Complex and Equilibrium• The semicircular canals

• Each semicircular canal encases a duct

• The beginning of each duct is the ampulla

• Within each ampulla is a cristae with hair cells

• Each hair cell contains a kinocilium and stereocilia

• These are embedded in gelatinous material called

the cupula

• The movement of the body causes movement of

fluid in the canal, which in turn causes movement of

the cupula and hair cells, which the brain detects



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•

The Vestibular Complex and Equilibrium• The utricle and saccule

• The utricle and saccule are connected to the ampulla

and to each other and to the fluid within the cochlea

• Hair cells of the utricle and saccule are in clusterscalled maculae

• Hair cells are embedded in gelatinous material

consisting of statoconia (calcium carbonate crystals)

• Gelatinous material and statoconia collectively arecalled an otolith

ANIMATION The Ear: Ear Balance


http://localhost/var/www/apps/conversion/tmp/scratch_7/ear_balance.mpg


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•

Equilibrium Process• When you rotate your head:

• The endolymph in the semicircular canals begins to move

• This causes the bending of the kinocilium and stereocilia

• This bending causes depolarization of the associatedsensory nerve

• When you rotate your head to the right, the hair cells are

bending to the left (due to movement of the endolymph)

•

When you move in a circle and then stop abruptly, theendolymph moves back and forth causing the hair cells to

bend back and forth resulting in confusing signals, thus

dizziness

Figure 18.13 The Function of the Semicircular Ducts, Part I

Vestibular branch (N VIII)


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Anterior view of

the maculae and

semicircular ducts

of the right side

A section through the ampulla of a

semicircular duct

Endolymph movement along the

length of the duct moves the cupula

and stimulates the hair cells.

Structure of a typical hair cell showing details

revealed by electron microscopy. Bending the

stereocilia toward the kinocilium depolarizes the cell

and stimulates the sensory neuron. Displacement in

the opposite direction inhibits the sensory neuron.

Supporting cell

Sensory nerve

ending

Hair cell

StereociliaKinocilium

Displacement in

this directioninhibits hair cell

Displacement in

this directionstimulates hair cell

At rest

AmpullaSemicircular duct

Direction of

duct rotation

Direction of relative

endolymph movement

Direction of

duct rotation

Crista

Hair cells

Ampulla

filled with

endolymphCupula

Supporting cells

Sensory nerve

Saccule Maculae

Utricle

AmpullaAnterior

Posterior

Lateral

Semicircularducts

Vestibular branch (N VIII)

Cochlea

Endolymphatic sac

Endolymphatic duct


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•

Equilibrium Process (cont.)• When you move up or down (elevator

movement):

• Otoliths rest on top of the maculae

• When moving upward, the otoliths press down onthe macular surface

• When moving downward, the otoliths lift off the

macular surface

• When you tilt side to side:

• When tilting to one side, the otoliths shift to one

side of the macular surface

Figure 18.15ab The Maculae of the Vestibule


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A scanning electron micrograph

showing the crystalline structure of

otoliths

Detailed structure of a sensory macula

Otolith

Gelatinous

materialStatoconia

Hair cells

Nerve fibers

Statoconia

Otolith

Figure 18.15c The Maculae of the Vestibule


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Diagrammatic view of changes in otolith position during tilting of the head

Head in Neutral Position Head Tilted Posteriorly

GravityGravity

Receptor

output

increases

Otolith moves

―downhill,‖

distorting hair

cell processes

Figure 18.16 Neural Pathways for Equilibrium Sensations


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Semicircular

canals

Vestibular

ganglion

Vestibular

branch

Vestibule

Cochlear

branch

Vestibulocochlear nerve

(N VIII)

Vestibulospinal

tracts

To

cerebellum

Vestibular nucleus

To superior colliculus and

relay to cerebral cortex

Red nucleus

N III

N IV

N VI

N XI



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•

The Cochlea• Consists of “snail-shaped” spirals

• Spirals coil around a central area called the

modiolus

• Within the modiolus are sensory neurons

• The sensory neurons are associated with CN

VIII

• Organ of Corti


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•

The Cochlea (cont.)• Each spiral consists of three layers

• Scala vestibuli (vestibular duct): consists of perilymph

• Scala tympani (tympanic duct): consists of perilymph

•

Scala media (cochlear duct): consists of endolymph /this layer is between the scala vestibuli and scalatympani

• There is a basilar membrane between each layer

•

The scala vestibuli and scala tympani areconnected at the apical end of the cochlea

• Sense organs rest on the basilar membranewithin the scala media



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•

The Cochlea• The Organ of Corti

• Also known as the spiral organ

• Rests on the basilar membrane between the scala

media and the scala tympani• Hair cells are in contact with an overlying tectorial

membrane

• This membrane is attached to the lining of the

scala media• Sound waves ultimately cause a distortion of the

tectorial membrane, thus stimulating the organ

of Corti



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•

Auditory Pathways• Sound waves enter the external acoustic

meatus

• The tympanic membrane vibrates

• Causes the vibration of the ossicles

• The stapes vibrates against the oval window of

the scala tympani

• Perilymph begins to move



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Auricle



bone

Facial nerve(N VII)


Elastic

cartilage

Tympanicmembrane

Tympaniccavity

Oval window

Round window

Vestibule

Auditory tube

Cochlea

Tonasopharynx



Figure 18.17a –c The Cochlea and Organ of Corti Round window

Stapes at

oval window


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Structure of the cochlea within the temporal

bone showing the turns of the vestibular duct,

cochlear duct, and tympanic duct

Structure of the cochlea in partialsection

Histology of the cochlea showing many of the structures

in part (b)

KEY

From tip of spiralto round window

From oval windowto tip of spiral

Semicircular

canals

Vestibulocochlear

nerve (VIII)

Cochlear

branch

Vestibular

branch

Tympanic duct

Vestibular duct

Cochlear duct

Apical turn

Spiral ganglion

Modiolus

Vestibular membrane

Tectorial membrane

Basilar membrane

Middle turn

Vestibular duct (scala

vestibuli—contains perilymph)

Organ of Corti

Cochlear duct (scala

media—contains endolymph)

Tympanic duct (scala

tympani—contains perilymph)

Basal turn

Temporal bone (petrous part)

Cochlear nerve

Vestibulocochlear nerve (VIII)From oval

window

To round

window

Vestibular duct

(from oval window)

Vestibular membrane

Organ of Corti

Basal turn

Basilar membrane

Tympanic duct

(to round window)

Sectional view of cochlear spiral LM 60

Apical turn

Middle turn

Vestibular duct

(scala vestibuli)

Cochlear duct(scala media)

Tympanic duct

(scala tympani)

Cochlear branch

Spiral ganglion

Figure 18.17d –f The Cochlea and Organ of Corti


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A color-enhanced SEM

showing a portion of thereceptor surface of the

organ of Corti

Diagrammatic and histological sections through thereceptor hair cell complex of the organ of Corti

Three-dimensional section

showing the detail of the cochlear

chambers, tectorial membrane,and organ of Corti

Bony cochlear wall

Vestibular duct

Vestibular membrane

Cochlear duct

Tectorial membrane

Basilar membrane

Tympanic duct

Organ of Corti

Spiral

ganglion

Cochlear branch

of N VIII

Cochlear duct (scala media)

Vestibular membrane

Tectorial membrane

Organ of Corti LM 125

Tympanic duct

(scala tympani)

Basilar

membrane

Hair cells

of organ

of Corti

Spiral ganglion

cells of

cochlear nerve

Tectorial membrane

Outer

hair cell

Basilar membrane Inner hair cell Nerve fibers

Stereocilia of inner hair cells

Stereocilia of

outer hair cells

Surface of the organ of Corti SEM 1320



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•

Auditory Pathways (continued)• As the perilymph moves:

• Pressure is put on the scala media

• This pressure distorts the hair cells of the organ of

Corti• This distortion depolarizes the neurons

• Nerve signals are sent to the brain via CN VIII

ANIMATION The Ear: Receptor Complexes

Figure 18.17de The Cochlea and Organ of Corti

http://localhost/var/www/apps/conversion/tmp/scratch_7/ear_recept.mpg


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Diagrammatic and histological sections through the

receptor hair cell complex of the organ of Corti

Three-dimensional section

showing the detail of the cochlear

chambers, tectorial membrane,

and organ of Corti

Bony cochlear wall

Vestibular duct

Vestibular membraneCochlear duct

Tectorial membrane

Basilar membrane

Tympanic duct

Organ of Corti

Spiral

ganglion

Cochlear branchof N VIII

Cochlear duct (scala media)

Vestibular membrane

Tectorial membrane

Organ of Corti LM 125

Tympanic duct

(scala tympani)

Basilar

membrane

Hair cells

of organ

of Corti

Spiral ganglion

cells of

cochlear nerve

Tectorial membrane

Outer

hair cell

Basilar membrane Inner hair cell Nerve fibers

Fi

gure 18.18 Pathways for Auditory Sensations


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KEY

First-order neuron

Second-order neuronThird-order neuron

Fourth-order neuron

High-frequency

sounds

Low-frequency

sounds

Cochlea

Cochlear branch

Vestibulocochlear

nerve (N VIII)

Cochlear nuclei

Vestibular

branch

To ipsilateral

auditory cortex

Superior olivary nucleus

Motor output to spinal

cord through the

tectospinal tracts

Motor output

to cranial

nerve nuclei

Inferior colliculus

(mesencephalon)

Medial geniculate

nucleus (thalamus)

Low-frequency

sounds

Auditory cortex

(temporal lobe)High-frequency

sounds

Thalamus

Vision


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Vision

•

Vision• Accessory structures of the eye

• Palpebrae (eyelids)

• Medial and lateral canthus (connect the eyelids at

the corners of the eye)• Palpebral fissure (area between the eyelids)

• Eyelashes (contain root hair plexus, which triggers

the blinking reflex)

• Conjunctiva (epithelial lining of the eyelids)

• Glands: glands of Zeis, tarsal glands, lacrimal

gland, lacrimal caruncle

Figure 18.19a Accessory Structures of the Eye, Part I


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Superficial anatomy of the right eye and its

accessory structures

Pupil

Corneallimbus

Lateralcanthus

Sclera

Eyelashes

Palpebra

Palpebral

fissureMedialcanthus

Lacrimalcaruncle

Figure 18.19c Accessory Structures of the Eye, Part I

S i


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Diagrammatic representation of a deeper dissection

of the right eye showing its position within the orbit

and its relationship to accessory structures,

especially the lacrimal apparatus

Opening ofnasolacrimal duct

Infer ior nasal

concha

Nasolacrimal ductLacrimal sac

Inferior lacrimalcanaliculus

Medial canthus

Superior lacrimalcanaliculus

Lacrimal punctum

Tendon o f super ior

obl iqu e mu scle

Infer ior

obl iqu e mu scle

Infer iorrectus muscle

Super ior

rectus muscle

Lacrimalgland ducts

Lower eyelid

Lateral canthus

Lacrimal gland

Vision


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•

Accessory Structures of the Eye• Conjunctiva

• Covers the inside lining of the

eyelids and the outside lining of the eye

• Fluid production helps prevent these layers frombecoming dry

• Palpebral conjunctiva

• Inner lining of the eyelids

• Ocular conjunctiva• Outer lining of the eye

Vision


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•

Accessory Structures• Glands

• All of the glands are for protection or lubrication

• Glands of Zeis: sebaceous glands / associated with

eyelashes• Tarsal glands: secrete a lipid-rich product / keeps the

eyelids from sticking together / located along the inner

margin of the eyelids

• Lacrimal glands: produce tears / located at thesuperior, lateral portion of the eye

• Lacrimal caruncle glands: produce thick secretions /

located within the canthus areas

Vision


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•

Accessory Structures• Glands

• An infection of the tarsal gland may result in a cyst

• An infection of any of the other glands may result in

a sty

Vision


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•

Accessory Structures• Lacrimal glands

• Part of the lacrimal apparatus

• The lacrimal apparatus consists of:

• Lacrimal glands (produce tears)

• Lacrimal canaliculi

• Lacrimal sac

• Nasolacrimal duct

Vision


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•

Accessory Structures• Lacrimal glands (continued)

• Tears are produced by the lacrimal glands

• Flow over the ocular surface

• Flow into the nasolacrimal canal (foramen)• This foramen enters into the nasal cavity

• Therefore, when you sob heavily, tears flow

across your eye and down your face and also

through the nasolacrimal canal into your noseand out, resulting in a “runny” nose

ANIMATION The Eye: Accessory Structures

Vision

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• The Eyes• Consist of:

• Sclera

• Cornea

• Pupil

• Iris

• Lens

• Anterior cavity

• Posterior cavity

• Three tunics: • (1) fibrous tunic, (2) vascular tunic, and (3) neural

tunic

• Retina

Figure 18.21b Sectional Anatomy of the Eye

Ora serrata


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Major anatomical landmarks and features

in a diagrammatic view of the left eye

Central retinal

artery and vein

Optic nerve

Optic disc

Fovea

Retina

Choroid

Sclera

Posterior cavity

(Vitreous chamber filled

with the vitreous body)

Ora serrata Fornix

Palpebral conjunctiva

Ocular conjunctiva

Ciliary body

Anterior chamber

(filled with aqueous

humor)

Lens

PupilCornea

Iris

Posterior chamber


humor)

Corneal limbus

Suspensoryligaments

Vision


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•

The Eyes• The Fibrous Tunic (outer layer)

• Makes up the sclera and cornea

• Provides some degree of protection

• Provides attachment sites for extra-ocular muscles

• The cornea is modified sclera

Vision


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•

The Eyes• The Vascular Tunic (middle layer)

• Consists of blood vessels, lymphatics, and intrinsic

eye muscles

• Regulates the amount of light entering the eye• Secretes and reabsorbs aqueous fluid (aqueous

humor)

• Controls the shape of the lens

• Includes the iris, ciliary body, and the choroid

ANIMATION The Eye: Uvea Parts

Vision

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•

The Vascular Tunic• The iris

• Consists of blood vessels, pigment, and smooth

muscles

• The pigment creates the color of the eye• The smooth muscles contract to change the

diameter of the pupil

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• The Vascular Tunic

• The ciliary body

• The ciliary bodies consist of ciliary muscles

connected to suspensory ligaments, which are

connected to the lens• The choroid

• Highly vascularized

• The innermost portion of the choroid attaches to the

outermost portion of the retina

ANIMATION The Eye: Ciliary Muscles

Vision

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• The Eyes

• The Neural Tunic (inner layer)

• Also called the retina

• Made of two layers: (pigmented layer – outer layer)

/ (neural layer – inner layer)• Retina cells: rods (night vision) and cones (color

vision)

Figure 18.22a The Lens and Chambers of the Eye


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The lens is suspended between the posterior cavityand the posterior chamber of the anterior cavity.

Pigmented part

Neural partNeural

tunic

(retina)

Posterior

cavity

Choroid

Ciliary body

Iris

Vascular

tunic

(uvea)

Anterior

cavity

Cornea

ScleraFibrous

tunic

Figure 18.21ab Sectional Anatomy of the Eye


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The three layers, ortunics, of the eye

Fibrous

tunic

(sclera)

Vascular

tunic

(choroid)

Neural

tunic(retina)

Major anatomical landmarks and features

in a diagrammatic view of the left eye

Central retinal

artery and vein

Optic nerve

Optic disc

Fovea

Retina

Choroid

Sclera

Posterior cavity

(Vitreous chamber filled

with the vitreous body)

Ora serrataFornix

Palpebral conjunctiva

Ocular conjunctiva

Ciliary body

Anterior chamber


humor)

Lens

Pupil

Cornea

Iris

Posterior chamber


humor)

Corneal limbus

Suspensoryligaments

Figure 18.23a Retinal Organization


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Histological organization of the retina. Note that the

photoreceptors are located closest to the choroidrather than near the vitreous chamber.

LIGHT

Amacrine cell

Horizontal cell Cone Rod

Choroid

Pigmentedpart of retina

Rods andcones

Bipolar cells

Ganglion cells

Nuclei ofganglion cells

Nuclei of rodsand cones

Nuclei ofbipolar cells

The retina LM 70

Vision


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• Cavities and Chambers of the Eye

• Anterior cavity

• Anterior chamber

• Posterior chamber

• Filled with fluid called aqueous fluid

• Posterior cavity

• Vitreous chamber

• Filled with fluid called vitreous fluid

ANIMATION The Eye: Posterior Cavity

Vision

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• Aqueous fluid

• Sometimes called aqueous humor

• Secreted by cells at the ciliary body area

• Enters the posterior chamber (posterior of the iris)

• Flows through the pupil area

• Enters the anterior chamber

• Flows through the canal of Schlemm

• Enters into venous circulation

Figure 18.24

Pupil


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Pigmentedepithelium

Suspensoryligaments

Posteriorcavity

(vitreouschamber)

Lens

Ciliaryprocess

Choroid

Retina

Sclera

Conjunctiva

Ciliary body

Body of iris

Canal ofSchlemm

Posteriorchamber

Anteriorchamber

Anteriorcavity

Cornea

Pupil

Vision


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• Vitreous fluid

• Gelatinous material in the posterior chamber

• Sometimes called vitreous humor

• Supports the shape of the eye• Supports the position of the lens

• Supports the position of the retina

• Aqueous humor can flow across the vitreous fluid

and over the retina

Figure 18.21d Sectional Anatomy of the EyeDura

mater Retina Choroid ScleraOptic nerve

(N II)


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Sagittal section through the eye

Ora serrata

Conjunctiva

Cornea

Lens

Anterior chamber

Iris

Posterior chamber

Suspensory

ligaments

Ciliary body

Posterior

cavity

(vitreous

chamber)

Vision


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• Aqueous fluid

• If this fluid cannot drain through the canal of

Schlemm, pressure builds up

• This is glaucoma

• Vitreous fluid

• If this fluid is not of the right consistency, the

pressure is reduced against the retina

• The retina may detach from the posterior wall(detached retina)

Vision


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• Visual Pathways

• Light waves pass through the cornea

• Pass through the anterior chamber

• Pass through the pupil

• Pass through the posterior chamber• Pass through the lens

• The lens focuses the image on some part of theretina• This creates a depolarization of the neural cells

• Signal is transmitted to the brain via CN II

ANIMATION The Eye: Interior Parts of the Eye

Figure 18.21e Sectional Anatomy of the EyeVisual

axis

Cornea

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Sagittal section through the eye

Orbital fatCentral artery

and vein

Medial rectus

musc le

Ethmoidal

labyr in th

Optic nerve

Optic disc

Fovea

Ora serrata

Ciliary body

LensCiliary

processes

Medial canthus

Lacrimal caruncle

Lacrimal punctum

Nose

Anterior cavity

Posterior

chamber

Anterior

chamber

Edge of

pupil

Cornea

Iris

Suspensory ligament of lens

Corneal limbus

Conjunctiva

Lower eyelid

Lateral canthus

Sclera

Choroid

Retina

Posterior cavity

Lateral rectus mu scle

Figure 18.26 Anatomy of the Visual Pathways, Part II LEFT SIDE RIGHT SIDE


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Left eye

onlyRight eye

only

Binocular vision

Optic nerve (N II)

Optic chiasm

Optic tractOther hypothalamic

nuclei, pineal gland,

and reticular

formation

Suprachiasmatic

nucleus

Superior

colliculus

Lateral

geniculate

nucleus

Projection

fibers (optic

radiation)

Lateral

geniculate

nucleus

RIGHT CEREBRAL

HEMISPHERE

LEFT CEREBRAL

HEMISPHERE

Visual cortex of

cerebral hemispheres

Vision


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• Visual Pathways

• The retina

• There are rods and cones all over the retina

• 100% cones in the fovea centralis area

• The best color vision is when an object isfocused on the fovea centralis

• 0% rods or cones in the optic disc area

• If an object is focused on this area, vision does

not occur• Also known as the “blind spot”

ANIMATION The Eye: Blind Spot

Vision

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• Visual Pathways

• The retina (cont.)• The cones require light to be stimulated (that’s why

we see color)

• At night (still has to be at least a small amount oflight), the cones deactivate and the rods begin to beactivated (that’s why we can see at night but we can’t determine color at night)

ANIMATION The Eye: Light Path

ANIMATION The Eye: Lens and Retina
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18 Lecture Presentation