ch 18_lecture_presentation

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18The Nervous System: General and Special Senses

PowerPoint® Lecture Presentations prepared bySteven BassettSoutheast Community College Lincoln, Nebraska


Introduction

• Stimulation of the receptor directly or indirectly alters the production of action potentials in a sensory neuron.

• The sensory information arriving at the CNS is called a sensation.

• A perception is a conscious awareness of a sensation.

• Sensory receptors are the interface between the nervous system and the internal and external environment


Receptors

• General senses• Refers to temperature, pain, touch, pressure, vibration,

and proprioception• Receptors throughout the body• These sensations arrive at the primary sensory cortex, or

somatosensory cortex• Special senses • Sensations of smell (olfaction), taste (gustation), balance

(equilibrium), hearing, and vision• Specialized receptor cells that are structurally more

complex than those of the general senses


Figure 18.1 Receptors and Receptive Fields

Receptive fields

Receptivefield 1

Receptivefield 2


Receptors

• Receptor specificity — each receptor responds to one type of stimulus

• Receptive field — the area that a receptor monitors• Tonic receptors — always send signals, thus information

is based on the frequency of the action potentials• Phasic receptors — send action potentials only

if stimulated• Peripheral adaptation — receptors may stop

sending AP even if the stimulus is still present• Central adaptation — CNS ignoring a AP from

a receptor


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

• Sensory Limitations• Humans do not have receptors for every

possible stimulus.• Our receptors have characteristic ranges of

sensitivity.• A stimulus must be interpreted by the CNS.

Our perception of a particular stimulus is an interpretation and not always a reality.


The General Senses

• Receptors for general senses classified by location:• Exteroceptors provide information about the external

environment.• Proprioceptors monitor body position.• Interoceptors monitor conditions inside the body.• Receptors for general senses classified by type

of stimulus:• Nociceptors = tissue damage• Thermoreceptors = change in temperature• Mechanoreceptors = physical distortion, contact, or

pressure • Chemoreceptors = chemical composition of body fluids


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 18.3e Tactile Receptors in the Skin

Capsule

Dendrites

Ruffini corpuscle

Sensorynerve fiber

Collagenfibers

Hair

Root hair plexus

Lamellated corpuscle

Ruffini corpuscle

Merkel cells andtactile discs

Tactilecorpuscle

Free nerveending

Sensorynerves


Figure 18.3f Tactile Receptors in the Skin


Dendriticprocess

Concentric layers (lamellae)of collagen fibersseparated by fluid

Concentric layers (lamellae)of collagen fibersseparated by fluid

Accessory cells(specialized fibrocytes)

Dendritic process

Dermis

LM 125Lamellated corpuscle

Hair

Root hair plexus


Ruffini corpuscle

Merkel cells andtactile discs

Tactilecorpuscle

Free nerveending

Sensorynerves


Figure 18.4 Baroreceptors and the Regulation of Autonomic Functions

Provide information on volume oftract segments, trigger reflexmovement of materials along tract

Provide information on volume ofurinary 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 bloodpressure to cardiovascular andrespiratory control centers

Provide information on lungstretching to respiratoryrhythmicity centers forcontrol of respiratory rate

Provide information on volume of fecal material in colon, trigger defecation reflex


Figure 18.5 Chemoreceptors

Carotid body LM 1500

Blood vesselChemoreceptive

neuronsTrigger reflexiveadjustments in

depth and rate ofrespiration

Trigger reflexiveadjustments inrespiratory andcardiovascular

activity

Via cranialnerve IX

Via cranialnerve X

Sensitive to changes in pHand 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

Chemoreceptors of Aortic Bodies


The Special Senses

• The special senses include:• Olfaction (smell)• Gustation (taste)• Equilibrium • Hearing• Vision


Olfaction (Smell)

• Olfaction• Olfactory organs• Nasal cavity

• Olfactory epithelium• Bipolar olfactory receptors (N I)• Supporting cells• Basal cells (stem cells)• Lamina propria

• Olfactory glands (Bowman’s glands)• Blood vessels• Nerves (axons of N I)


Figure 18.6a The Olfactory Organs

The distribution of the olfactory receptorson the left side of the nasal septum isshown by the shading.

Olfactorybulb

Olfactory nervefibers (N I)

Olfactorytract

Cribriform plateof ethmoid

Olfactoryepithelium


Figure 18.6b The Olfactory Organs

A detailed view of the olfactory epithelium

Substance being smelled

Olfactoryepithelium

Laminapropria

Cribriformplate

Knob

Olfactory cilia:surfaces containreceptor proteins

Mucous layer

Supporting cell

Olfactoryreceptor cell

Developing olfactoryreceptor cell

Olfactorynerve fibers

To olfactorybulb

Olfactory(Bowman’s)

gland

Regenerative basal cell:divides to replace worn-out

olfactory receptor cells


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


Gustation (Taste)

• Gustation Pathways• Dissolved chemicals contact the taste hairs

(microvilli)• Impulses go from the gustatory cell through

CN VII, IX, and X• The impulses eventually arrive at the cerebral

cortex


Figure 18.8 Gustatory Pathways

Gustatorycortex

ThalamicnucleusMediallemniscus

Nucleussolitarius

Vagus nerve(N X)

Facial nerve(N VII)

Glossopharyngealnerve (N IX)


Gustation (Taste)

Gustatory receptors are clustered in taste buds, which contain gustatory cells that extend taste hairs through a taste pore.Three types of papillae (epithelial projections) on human tongue:

Filiform Fungiform Circumvallate

Four primary tastes: Salty Bitter Sweet Sour

Also water and umami (characteristic of broth)


Equilibrium and Hearing

The Ear External ear Middle ear

Auditory ossicles Auditory tube

Inner ear Vestible and semicircular canals

Equilibrium Cochlea

Hearing

ANIMATION The Ear: Ear Anatomy


Figure 18.9 Anatomy of the Ear

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)


Figure 18.12a Semicircular Canals and Ducts

Anterior view of the bonylabyrinth cut away to show thesemicircular canals and theenclosed semicircular ducts ofthe membranous labyrinth

Cochlear duct

Vestibular duct

Saccule

Utricle

Tympanicduct

Organ ofCorti

Cochlea

Endolymphatic sacMaculae

Cristae within ampullae

Bony labyrinth

Membranouslabyrinth

KEY

Vestibule

Anterior

Lateral

Posterior

Semicircularcanal

Semicircularducts


Figure 18.13 The Function of the Semicircular Ducts, Part I

Anterior view ofthe maculae andsemicircular ductsof the right side

A section through the ampulla of asemicircular duct

Endolymph movement along thelength of the duct moves the cupulaand stimulates the hair cells.

Structure of a typical hair cell showing detailsrevealed by electron microscopy. Bending thestereocilia toward the kinocilium depolarizes the celland stimulates the sensory neuron. Displacement inthe opposite direction inhibits the sensory neuron.

Supporting cell

Sensory nerveending

Hair cell

StereociliaKinocilium

Displacement inthis direction inhibits hair cell

Displacement inthis direction

stimulates hair cell

At rest

AmpullaSemicircular duct

Direction ofduct rotation

Direction of relativeendolymph movement

Direction ofduct rotation

Crista

Hair cells

Ampullafilled with

endolymphCupula

Supporting cells

Sensory nerve

Saccule Maculae

Utricle

AmpullaAnteriorPosterior

Lateral

Semicircularducts

Vestibular branch (N VIII)

Cochlea

Endolymphatic sac

Endolymphatic duct


Figure 18.15ab The Maculae of the Vestibule

A scanning electron micrograph showing the crystalline structure of otoliths

Detailed structure of a sensory macula

Otolith

Gelatinousmaterial

Statoconia

Hair cells

Nerve fibers

Statoconia

Otolith


Figure 18.16 Neural Pathways for Equilibrium Sensations

Semicircularcanals

Vestibularganglion

Vestibularbranch

Vestibule

Cochlearbranch

Vestibulocochlear nerve(N VIII)

Vestibulospinaltracts

Tocerebellum

Vestibular nucleus

To superior colliculus andrelay to cerebral cortex

Red nucleus

N III

N IV

N VI

N XI


Equilibrium and Hearing

• 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


Figure 18.17ab The Cochlea and Organ of Corti

Structure of the cochlea within the temporalbone showing the turns of the vestibular duct,cochlear duct, and tympanic duct

Structure of the cochlea in partialsection

KEY

From tip of spiralto round window

From oval windowto tip of spiral

Round window

Stapes atoval window

Semicircularcanals

Vestibulocochlearnerve (VIII)

Cochlearbranch

Vestibularbranch

Tympanic duct

Vestibular duct

Cochlear duct

Apical turn

Spiral ganglion

Modiolus

Vestibular membrane

Tectorial membrane

Basilar membrane

Middle turn

Vestibular duct (scalavestibuli—contains perilymph)

Organ of Corti

Cochlear duct (scalamedia—contains endolymph)

Tympanic duct (scalatympani—contains perilymph)

Basal turn

Temporal bone (petrous part)

Cochlear nerve

Vestibulocochlear nerve (VIII)From ovalwindow

To roundwindow


Figure 18.17d–f The Cochlea and Organ of Corti

A color-enhanced SEMshowing a portion of thereceptor surface of theorgan of Corti

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

Three-dimensional sectionshowing the detail of the cochlearchambers, tectorial membrane,and organ of Corti

Bony cochlear wall

Vestibular duct

Vestibular membrane

Cochlear duct

Tectorial membrane

Basilar membrane

Tympanic duct

Organ of Corti

Spiralganglion

Cochlear branchof N VIII

Cochlear duct (scala media)

Vestibular membrane

Tectorial membrane

Organ of Corti LM 125

Tympanic duct(scala tympani)

Basilarmembrane

Hair cellsof organof Corti

Spiral ganglioncells of

cochlear nerve

Tectorial membrane

Outerhair 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


Figure 18.17de The Cochlea and Organ of Corti

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

Three-dimensional sectionshowing the detail of the cochlearchambers, tectorial membrane,and organ of Corti

Bony cochlear wall

Vestibular duct

Vestibular membrane

Cochlear duct

Tectorial membrane

Basilar membrane

Tympanic duct

Organ of Corti

Spiralganglion

Cochlear branchof N VIII

Cochlear duct (scala media)

Vestibular membrane

Tectorial membrane

Organ of Corti LM 125

Tympanic duct(scala tympani)

Basilarmembrane

Hair cellsof organof Corti

Spiral ganglioncells of

cochlear nerve

Tectorial membrane

Outerhair cell

Basilar membrane Inner hair cell Nerve fibers


Figure 18.18 Pathways for Auditory Sensations

KEYFirst-order neuronSecond-order neuronThird-order neuronFourth-order neuron

High-frequencysounds

Low-frequencysounds

Cochlea

Cochlear branch

Vestibulocochlearnerve (N VIII)

Cochlear nuclei

Vestibularbranch

To ipsilateralauditory cortex

Superior olivary nucleus

Motor output to spinalcord through thetectospinal tracts

Motor outputto cranial

nerve nuclei

Inferior colliculus(mesencephalon)

Medial geniculatenucleus (thalamus)

Low-frequencysounds

Auditory cortex(temporal lobe) High-

frequencysounds

Thalamus


Vision

Accessory Structures Eyelids Lacrimal apparatus

Eye Fibrous tunic Vascular tunic Neural tunic Chambers of the eye

Visual pathways


Figure 18.19a Accessory Structures of the Eye, Part I

Superficial anatomy of the right eye and its accessory structures

Pupil

Corneallimbus

Lateralcanthus

Sclera

Eyelashes

Palpebra

Palpebralfissure

MedialcanthusLacrimalcaruncle


Figure 18.19c Accessory Structures of the Eye, Part I

Diagrammatic representation of a deeper dissectionof the right eye showing its position within the orbitand its relationship to accessory structures,especially the lacrimal apparatus

Opening of nasolacrimal duct

Inferior nasalconcha

Nasolacrimal duct

Lacrimal sac

Inferior lacrimalcanaliculus

Medial canthus

Superior lacrimalcanaliculus

Lacrimal punctum

Tendon of superioroblique muscle

Inferioroblique muscle

Inferiorrectus muscle

Superiorrectus muscle

Lacrimalgland ducts

Lower eyelid

Lateral canthus

Lacrimal gland


Figure 18.21ab Sectional Anatomy of the Eye

The three layers, ortunics, of the eye

Fibroustunic

(sclera)

Vasculartunic

(choroid)

Neuraltunic

(retina)

Major anatomical landmarks and featuresin a diagrammatic view of the left eye

Central retinalartery and vein

Optic nerve

Optic disc

Fovea

Retina

Choroid

Sclera

Posterior cavity(Vitreous chamber filledwith the vitreous body)

Ora serrata Fornix

Palpebral conjunctiva

Ocular conjunctiva

Ciliary body

Anterior chamber(filled with aqueoushumor)

Lens

Pupil

Cornea

Iris

Posterior chamber(filled with aqueoushumor)

Corneal limbus

Suspensoryligaments


Figure 18.23a Retinal Organization

Histological organization of the retina. Note that thephotoreceptors are located closest to the choroid rather 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


Figure 18.24

Pigmentedepithelium

Suspensoryligaments

Posteriorcavity

(vitreouschamber)

Lens

Ciliaryprocess

Choroid

Retina

Sclera

Conjunctiva

Ciliary body

Body of iris

Canal ofSchlemm

Posteriorchamber

Anteriorchamber

Anteriorcavity

Cornea

Pupil


Figure 18.21d Sectional Anatomy of the Eye

Sagittal section through the eye

Ora serrata

Conjunctiva

Cornea

Lens

Anterior chamber

Iris

Posterior chamber

Suspensoryligaments

Ciliary body

Posteriorcavity

(vitreouschamber)

Duramater Retina Choroid Sclera

Optic nerve(N II)


Figure 18.21e Sectional Anatomy of the Eye

Sagittal section through the eye

Orbital fatCentral arteryand vein

Medial rectusmuscle

Ethmoidallabyrinth

Optic nerve

Optic disc

Fovea

Ora serrata

Ciliary body

LensCiliaryprocesses

Medial canthus

Lacrimal caruncle

Lacrimal punctum

Nose

Anterior cavity

Posteriorchamber

Anteriorchamber

Edge ofpupil

Visualaxis

Cornea

Iris

Suspensory ligament of lens

Corneal limbus

Conjunctiva

Lower eyelid

Lateral canthus

Sclera

Choroid

Retina

Posterior cavity

Lateral rectus muscle


Figure 18.26 Anatomy of the Visual Pathways, Part IILEFT SIDE RIGHT SIDE

Left eyeonly

Right eyeonly

Binocular vision

Optic nerve (N II)

Optic chiasm

Optic tractOther hypothalamicnuclei, pineal gland,

and reticularformation

Suprachiasmaticnucleus

Superiorcolliculus

Lateralgeniculatenucleus

Projectionfibers (opticradiation)

Lateralgeniculate

nucleus

RIGHT CEREBRALHEMISPHERE

LEFT CEREBRALHEMISPHERE

Visual cortex ofcerebral hemispheres

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