163 ch 09_lecture_presentation

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PowerPoint® Lecture Slidesprepared byMeg FlemmingAustin Community College

C H A P T E R 9

The General and Special Senses


Chapter 9 Learning Outcomes

• 9-1 • Explain how the organization of receptors for the general senses

and the special senses affects their sensitivity.• 9-2

• Identify the receptors for the general senses, and describe how they function.

• 9-3• Describe the sensory organs of smell, and discuss the processes

involved in olfaction.• 9-4

• Describe the sensory organs of taste, and discuss the processes involved in gustation.


Chapter 9 Learning Outcomes

• 9-5• Identify the internal and accessory structures of the eye, and

explain their functions. • 9-6

• Explain how we form visual images and distinguish colors, and discuss how the central nervous system processes visual information.

• 9-7• Describe the parts of the external, middle, and internal ear, and the

receptors they contain, and discuss the processes involved in the senses of equilibrium and hearing.

• 9-8• Describe the effects of aging on smell, taste, vision, and hearing.


Sensory Receptors (9-1)

• Can be special cell processes

• Or separate cells

• Monitor conditions both inside and outside the

body


Free Nerve Endings (9-1)

• The simplest receptors

• Are modified dendritic endings

• Examples:

• Touch receptors

• Pain receptors

• Heat receptors

• Taste receptors


Separate Receptor Cells (9-1)

• Complex structures

• Associated with supportive cells

• Examples:

• Visual receptors in the eyes

• Auditory receptors in the ears


The Receptive Field (9-1)

• The area monitored by a single receptor

• The smaller the field, the more precise the sensory

information


Sensation and Perception (9-1)

• Sensation

• Occurs in the brain

• The action potential from the afferent pathway arrives in

sensory cortex

• Perception

• Awareness and interpretation of sensory input by the

integration areas of cerebral cortex


Adaptation (9-1)

• A reduction in sensitivity due to a constant

stimulus

• Some sensory receptors adapt quickly (e.g.,

jumping into a cold lake)

• Some are slow to adapt or do not adapt at all, like

pain receptors


General Senses (9-1)

• Temperature

• Pain

• Touch

• Pressure

• Vibration

• Proprioception (body position)

• Occur throughout the body


Special Senses (9-1)

• Olfaction (smell)

• Gustation (taste)

• Vision

• Equilibrium (balance)

• Hearing

• Concentrated in the sense organs and located in

the head


Figure 9-1 Receptors and Receptive Fields.

Receptivefield 1

Receptivefield 2


Checkpoint (9-1)

1. What is adaptation?

2. Receptor A has a circular receptive field with a

diameter of 2.5 cm. Receptor B has a circular

receptive field 7.0 cm in diameter. Which receptor

provides more precise sensory information?

3. List the five special senses.


Classes of General Sensory Receptors (9-2)

• Classified by type of stimulus that activates them

• Nociceptors respond to pain

• Thermoreceptors respond to temperature

• Mechanoreceptors respond to touch, pressure, and

body position

• Chemoreceptors respond to chemical stimuli


Nociceptors (9-2)

• Free nerve endings that adapt very slowly

• Can respond to extremes of temperature,

mechanical damage, dissolved chemicals

• Fast pain transmitted to CNS through myelinated axons

• Slow pain transmitted by unmyelinated axons and is

burning or aching

• Referred pain is perception of pain in an unrelated area

of the body


Liver andgallbladder

Heart

Stomach

Smallintestine

Appendix

Colon

Ureters

Figure 9-2 Referred Pain.


Thermoreceptors (9-2)

• Free nerve endings

• In dermis, skeletal muscles, liver, and hypothalamus

• Cold receptors

• More numerous than warm receptors, although there is

no known difference in structure

• They use the same pathway as pain receptors, but

thermoreceptors are adaptive


Three Classes of Mechanoreceptors

1. Tactile receptors

• Touch

2. Baroreceptors

• Pressure

3. Proprioceptors

• Position


Tactile Receptors (9-2)

• Include fine touch and pressure receptors and crude

touch and pressure receptors

• Six types of tactile receptors in the skin

1. Free nerve endings responding to temperature and pain

2. Root hair plexus

3. Tactile (Merkel) disc

4. Tactile (Meissner) corpuscle

5. Lamellated (pacinian) corpuscle

6. Ruffini corpuscle


Free nerve endings

Root hairplexus

Tactile discs innervatingMerkel cells

Tactile disc

Merkel cells

Tactile corpuscle

Dermis

Dendrites

Lamellated corpuscle

Dermis

Dendrite

Ruffini corpuscle

Sensorynerve fiber

DendritesFreenerve

ending

Tactilecorpuscle

Tactile disc(innervatingMerkel cell)

Hair

Root hairplexus

Lamellatedcorpuscle

Ruffinicorpuscle

Sensorynerves

Figure 9-3 Tactile Receptors in the Skin.


Baroreceptors (9-2)

• Monitor changes in pressure in the viscera

• Adapt readily

• Found in the major blood vessels, lungs, digestive,

and urinary tracts


Figure 9-4 Baroreceptors and the Regulation of Autonomic Functions.

Baroreceptors of CarotidSinus and Aortic Sinus

Baroreceptors of Lung

Baroreceptors of Colon

Baroreceptors ofDigestive Tract

Baroreceptors ofBladder Wall


Proprioceptors (9-2)

• Monitor position, tension in tendons and

ligaments, state of muscle contraction

• Nonadaptive and include:

• Free nerve endings that monitor joint capsule pressure,

tension, and movement

• Golgi tendon organs that monitor strain on tendons

• Muscle spindles that monitor the length of a muscle


Chemoreceptors (9-2)

• Respond to chemicals in solution in body fluids

• Include CNS receptors that monitor CSF, plasma

concentrations of carbon dioxide, and pH

• Key peripheral chemoreceptors for plasma carbon

dioxide and pH are in the carotid bodies and

aortic bodies


Figure 9-5 Locations and Functions of Chemoreceptors.

Chemoreceptors in and near Respiratory Centers of Medulla Oblongata

Trigger reflexiveadjustments in

depth and rate ofrespiration

Chemoreceptorsof Carotid Bodies

Chemoreceptorsof Aortic Bodies

Trigger reflexiveadjustments inrespiratory andcardiovascular

activity

Cranialnerve IX

Cranialnerve X


Checkpoint (9-2)

4. List the four types of general sensory receptors,

and identify the nature of the stimulus that excites

each type.

5. Identify the three classes of mechanoreceptors.

6. What would happen if information from

proprioceptors in your legs were blocked from

reaching the CNS?


Special Sense of Olfaction (9-3)

• Olfactory organs found in the nasal cavity

• Olfactory epithelium, containing olfactory

receptor cells, supporting cells, and stem cells,

lines the nasal cavity

• Olfactory glands, which are deeper, secrete

mucus

• Air is warmed and moisturized as it is inhaled


Special Sense of Olfaction (9-3)

• Olfactory receptor cells

• Modified neurons with chemical receptors called

odorant-binding proteins on the cilia

• Odorants are chemicals in the air that bind to the

proteins

• Respond to over 1000 unique smells


Olfactory Pathways (9-3)

• Axons projecting from the olfactory epithelium

• Bundled and pass through the cribriform plate of the

ethmoid bone and into olfactory bulb

• Olfactory tracts extend back to the olfactory cortex of

the cerebrum, the hypothalamus, and the limbic system

• Olfaction is the only sense that is NOT routed

through the thalamus


Figure 9-6a The Olfactory Organs.

Olfactory Pathway to the CerebrumOlfactoryepithe-lium

OlfactorynerveFibers(N I)

Olfactorytract

Centralnervoussystem

Cribriformplate

Superiornasal

concha

The olfactory organ on the rightside of the nasal septum.

Olfactorybulb


Figure 9-6b The Olfactory Organs.

Basal cell:divides to

replaceworn-outolfactoryreceptor

cellsOlfactory

gland

Toolfactory

bulb

Cribriformplate

Areolartissue

Olfactoryepithelium

Substance being smelled

Olfactorynerve fibers

Developingolfactoryreceptor cell

Olfactoryreceptor cell

Supporting cellMucous layer

Olfactory cilia:surfaces containreceptor proteins

An olfactory receptor is a modified neuronwith multiple cilia extending from its freesurface.


Checkpoint (9-3)

7. Define olfaction.

8. How does repeated sniffing help to identify faint

odors?


Special Sense of Gustation (9-4)

• Gustatory receptors

• Found in the gustatory cells of the taste buds, which

are found on the sides of the papillae

• Circumvallate papillae most numerous and on the front

2/3 of the tongue

• Gustatory cells have microvilli (taste hairs) that

extend out through the taste pore


Special Sense of Gustation (9-4)

• Taste hairs respond to chemicals in solution

• Trigger a change in the membrane potential of the

taste cells

• Primary taste sensations

• Sweet, sour, bitter, salty, and umami

• Also receptors in the pharynx for water


The Taste Pathway (9-4)

• Extends from the taste cell axons found in:

• Facial nerve (N VII)

• Glossopharyngeal (N IX)

• Vagus (N X)

• Fibers synapse in the medulla oblongata

• Those neurons extend into the thalamus

• Neurons project to the primary sensory cortex


Water receptors(pharynx) Umami

Tastebuds

TastebudsSour

BitterSaltySweet

Circumvallate papilla

Taste buds LM x 280

Supportingcell

Gustatorycell

Taste hairs(microvilli)

Tastepore

Tastes are detected by gustatory receptors within taste buds, which form pockets along the sides of epithelial projections called papillae.

A diagrammatic view of the structure of a taste bud, showing gustatory receptor cells and supporting cells.

Figure 9-7 Gustatory Receptors.


Checkpoint (9-4)

9. Define gustation.

10. If you completely dry the surface of your tongue

and then place salt or sugar crystals on it, you

cannot taste them. Why not?


The Accessory Structures of the Eye (9-5)

1. Eyelids and associated exocrine glands

2. The superficial epithelium of the eye

3. Structures associated with the production,

secretion, and removal of tears

4. The extrinsic eye muscles


The Eyelids (9-5)

• Also called palpebrae

• Upper and lower eyelids join at the medial canthus and

lateral canthus

• At the medial canthus, glands that secrete gritty "sleep"

are found in the lacrimal caruncle

• Have sebaceous glands that can become infected,

known as a sty


Conjunctiva (9-5)

• Inner surface of the eyelids

• And the outer, white surface of the eye, up to the

edge of the cornea

• Irritation or damage to the conjunctiva is called

conjunctivitis, or pinkeye


The Lacrimal Apparatus (9-5)

• Produces essential tears, distributes them across

the eye, and removes them

• The lacrimal gland secretes the tears and is

superior and lateral to the eyeball

• Tears drain through two pores at the medial

canthus called the lacrimal canals and into the

nasolacrimal duct

PLAYPLAY ANIMATION The Eye: Accessory Structures


Figure 9-8a The Accessory Structures of the Eye.

Lateralcanthus

Sclera

Eyelashes

PupilPalpebra(eyelid)IrisMedialcanthus Lacrimal caruncle

Gross and superficial anatomy of the accessory structures


Figure 9-8b The Accessory Structures of the Eye.

Lacrimal pores

Superior lacrimal canalLacrimal sacInferior lacrimal canal

Nasolacrimal duct

Opening of duct into nasal cavity

The organization of the lacrimal apparatus

Lacrimal gland Lacrimal gland ducts


The Extrinsic Eye Muscles (9-5)

• Control the position of the eye and include:

• Inferior rectus

• Medial rectus

• Superior rectus

• Lateral rectus

• Inferior oblique

• Superior oblique


Frontalbone

Superioroblique

TrochleaSuperiorrectus

Opticnerve

Lateralrectus

Inferiorrectus Maxilla Inferior oblique

Lateral surface, right eye

Superiorrectus

Lateralrectus

Inferior oblique

Anterior view, right eye

Inferiorrectus

Medialrectus

Superioroblique

Trochlea

Figure 9-9 The Extrinsic Eye Muscles.


Table 9-1 The Extrinsic Eye Muscles


The Eye (9-5)

• Found in the orbit with the:

• Lacrimal glands

• Extrinsic eye muscles

• Cranial nerves

• Blood vessels

• Orbital fat cushions the eye


The Eyeball (9-5)

• The eyeball is hollow and divided into two

cavities

1. Posterior cavity

• Filled with jellylike vitreous body

2. Anterior cavity has two subdivisions

• The anterior and posterior chambers

• Filled with aqueous humor


The Fibrous Layer of the Eyeball (9-5)

• The sclera

• The white of the eye

• Supportive dense connective tissue

• The cornea

• Transparent

• Allows light to enter the eye


The Vascular Layer of the Eyeball (9-5)

• Contains blood and lymphatic vessels, and the

intrinsic eye muscles

• Functions

1. Providing a route for vessels supplying the tissue

2. Adjusting the amount of light entering the eye

3. Providing a route for secreting and reabsorbing

aqueous humor

4. Controlling the shape of the lens


The Vascular Layer of the Eyeball (9-5)

• Structures

• The iris, with pupillary muscles that change the size of

the pupil, the "window" into the eye

• The ciliary body, which contains the ciliary muscle and

ciliary processes, and the suspensory ligaments,

which adjust the shape of the lens for focusing

• The choroid, a highly vascular tissue

PLAYPLAY ANIMATION The Eye: Cilliary Muscles


Figure 9-10a The Sectional Anatomy of the Eye.

Optic nerveEyelashConjunctiva

Cornea

Pupil

Iris

Lens

Fovea

Sagittal section of left eye


Figure 9-10b The Sectional Anatomy of the Eye.

Posteriorcavity

Anteriorcavity

Horizontal section of right eye

Sclera

Cornea

Fibrouslayer

Choroid

Iris

Ciliary body

Vascular layer

Neural part

Inner layer(retina)

Pigmented part


Figure 9-10c The Sectional Anatomy of the Eye.

CorneaIris

Suspensory ligament oflensConjunctiva

Lower eyelid

Sclera

Choroid

Retina

Posteriorcavity

Lateral rectusmuscle

Fovea

Orbital fat

Lens

Edge ofpupil

Anterior cavityPosteriorchamber

Anteriorchamber

Nose

Lacrimal pore

Ciliarymuscle

Ciliary body

Medial rectusmuscle

Optic disc

Optic nerveCentral artery

and vein

Lacrimal sac

Horizontal dissection of right eye

Visual axis


Figure 9-11 The Pupillary Muscles.

The pupillary constrictor muscles form a series ofconcentric circles around the pupil. When these sphincter muscles contract, the diameter of the pupil decreases.

The pupillary dilator muscles extend radially away from the edge of the pupil. Contraction of these muscles enlarges the pupil.

.

Pupillary constrictor(sphincter)

Decreased light intensityIncreased sympathetic stimulation

Increased light intensityIncreased parasympathetic stimulation

Pupil

Pupillary dilator(radial)


The Inner Layer (9-5)

• Also called the retina

• The inner layer includes:

• A pigmented part, which absorbs light

• A neural part that contains the photoreceptors

• Supportive cells and neurons

• Blood vessels


Photoreceptors (9-5)

• Rods

• Used in dim light

• Found on the periphery of retinal surface

• Cones

• Used in bright light and detect color

• Found in the macula, the center of which is the fovea,

or fovea centralis


The Inner Layer (9-5)

• Rods and cones synapse with bipolar cells,

which synapse with ganglion cells

• Ganglion cells

• These axons leave the back of the eye through the

optic disc, the origin of the optic nerve

• The blind spot is where there are no photoreceptors on

the retina

PLAYPLAY ANIMATION The Eye: The Retina


Figure 9-12a Retinal Organization.

Nuclei ofganglion cells

Nuclei of rodsand cones

Nuclei ofbipolar cells

Retina LM x 350

ChoroidPigmented

part of retinaRods and

cones

Bipolarcells

Ganglioncells

LIGHT

Amacrinecell

Horizontal cell Cone Rod

The cellular organization of the retina. The photoreceptors are closest tothe choroid, rather than near the posterior cavity (vitreous chamber).


Figure 9-12b Retinal Organization.

Pigmentedpart of retina

Neural partof retina

Centralretinal vein

Centralretinal artery

ScleraChoroid

Optic nerve

The optic disc in diagrammatic sagittal section.

Opticdisc


Figure 9-12c Retinal Organization.

FoveaOptic disc

(blind spot)

MaculaCentral retinal artery and vein

emerging from center of optic discA photograph of the retina as seen through the pupil.


Figure 9-13 A Demonstration of the Presence of a Blind Spot.


The Chambers of the Eye (9-5)

• Anterior cavity

• Anterior chamber extends from the cornea to the iris

• Posterior chamber between the iris and the lens

• Filled with aqueous humor produced by the ciliary

processes

• Maintains pressure in eye

• Drains out through the scleral venous sinus


The Chambers of the Eye (9-5)

• Problems with fluid and pressure is a condition

called glaucoma

• Posterior cavity

• Filled with the vitreous body

• Holds the retina in place


Figure 9-14 The Circulation of Aqueous Humor.

Posterior cavity(vitreous chamber)

Scleral venoussinusBody of iris

ConjunctivaCiliarybodySclera

Choroid

Retina

Cornea

Pupil

Ciliaryprocess

Suspensoryligaments

Pigmentedepithelium

Anterior cavity

Anterior chamberPosterior chamber

Lens


The Lens (9-5)

• Posterior to cornea

• Held in place by suspensory ligaments

• Cells

• Are wrapped in concentric circle

• Elastic fibers make lens spherical

• Changes shape to accommodate for focus


Light Refraction and Accommodation (9-5)

• Light is bent or refracted as it enters the cornea

and lens

• Light rays converge on retina at focal point

• Focal distance is between lens and focal point

• For far-away objects, the ciliary muscles relax, flattening

the lens

• For close objects, the lens accommodates by rounding

when the ciliary muscles contract

PLAYPLAY ANIMATION The Eye: Light Path


Figure 9-15a-c Focal Point, Focal Distance, and Visual Accommodation.

Focal distance

Lightfrom

distantsource(object)

Closesource

Focalpoint

Focal distance Focal distance

Lens

The closer the light source,the longer the focal distance

The rounder the lens,the shorter the focal distance


Figure 9-15d-e Focal Point, Focal Distance, and Visual Accommodation.

Focal point on fovea

Lens rounded Lens flattened

Ciliary musclecontracted

Ciliary musclerelaxed

For Close Vision: Ciliary Muscle Contracted, Lens Rounded

For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened


Light rays projected from a vertical object show why the image arrives upside down. (Note that the image is also reversed.)

Light rays projected from a horizontal object show why the image arrives with a left and right reversal. The image also arrives upside down. (As noted in the text, these representations are not drawn to scale.)

Figure 9-16 Image Formation.


Figure 9-17 Accommodation Problems (1 of 3)

The eye has a fixed focal distance and

focuses by varying the shape of the lens.

A camera focuses an image by moving the lens toward or away from the film. This method cannot work in our eyes, because the distance from the lens to the macula cannot change. We focus images on the retina by changing the shape of the lens to keep the focal distance constant, a process called accommodation.

A camera lens has a fixed size and shape and

focuses by varying the distance to the film or semiconductor device.



Emmetropia (normal vision)

In the healthy eye, when the ciliary muscle is relaxed and the lens is flattened, a distant image will be focused on the retina’s surface. Thiscondition is calledemmetropia (emmetro-, proper + opia, vision).



Myopia (nearsightedness)

If the eyeball is too deep or the rest-ing curvature of the lens is too great, the image of a distant object isprojected in front of the retina. The person will see distant objects as blurry and out of focus. Vision at close range will be normal because the lens is able to round as needed to focus the image on the retina.

Hyperopia (farsightedness)

If the eyeball is too shallow or the lens is too flat, hyperopia results. Theciliary muscle must contract to focus even a distant object on the retina. And at close range the lens cannot provide enough refraction to focus an image on the retina. Older people become farsighted as their lenses lose elasticity, a form of hyperopia called presbyopia (presbys, old man).

Myopia corrected with a diverging, con-cavelens

Hyperopia corrected with a converging, convex lens

Diverginglens

Converginglens


Checkpoint (9-5)

11. Which layer of the eye would be the first to be

affected by inadequate tear production?

12. When the lens is more rounded, are you looking

at an object that is close to you or far from you?

13. As Malia enters a dimly lit room, most of the

available light becomes focused on the fovea of

her eye. Will she be able to see very clearly?


Photoreceptors Respond to Photons (9-6)

• Photons are units of visible light

• Red, orange, yellow, green, blue, indigo, violet

• Color determined by wavelength

• Photons of red have longest wavelength, least energy

• Photons of violet have shortest wavelength, most

energy


Photoreceptors in the Eye (9-6)

• Rods

• Respond to presence or absence of photons regardless of

wavelength

• Very sensitive, therefore effective in dim light

• Cones

• Three different types

• Blue cones, green cones, red cones

• Contain pigments sensitive to blue, green, or red

wavelengths of light

• Less sensitive, therefore function only in bright light


Color Blindness (9-6)

• Occurs when one or more types of cone is not functioning

or is missing

• Most common is red-green color blindness where red

cones are missing

• More common in males (10 percent) than females

(0.67 percent)

• Total color blindness is extremely rare (1 person in

300,000)


Figure 9-18 A Standard Test for Color Vision.


The Structure of Photoreceptors (9-6)

• Outer segment contains hundreds to thousands of

flattened discs

• Contain visual pigments that absorb photons and initiate

photoreception

• Made of compound rhodopsin that contains opsin and

retinal (derived from vitamin A)

• Retinal is the same in rods and cones, opsin is different

• Inner segment contains organelles, synapses with bipolar

cells


Figure 9-19a The Structure of Rods and Cones.

Discs

Connectingstalks

Golgiapparatus

Cone Rods

LIGHT

Bipolar cell

Mitochondria

PigmentEpithelium

Absorbs photons not absorbed by visual pigments.

Melaningranules

Outer SegmentVisual pigments are contained in membrane discs.

Inner Segment

Site of major organelles and cell functions other than photoreception.It also releases neurotransmitters.

Each photoreceptorsynapses with abipolar cell.

Nuclei


Figure 9-19b The Structure of Rods and Cones.

Retinal

Rhodopsinmolecule

Opsin

Structure of rhodopsinmolecule


Photoreception (9-6)

• Photon strikes rhodopsin

• Retinal and opsin break apart, referred to as

bleaching

• Alters rate of neurotransmitter release into

synapse with bipolar cell

• For rod or cone to be able to respond to light

again, the opsin and retinal must recombine


Retinal andopsin are

reassembledto form

rhodopsin

Photon

Retinal changes shape

Regenerationenzyme

Bleaching(separation)

Retinal restored

Opsin

Opsininactivated

Opsin

Figure 9-20 Bleaching and Regeneration of Visual Pigments.


The Visual Pathways (9-6)

• Photoreceptor bipolar cell ganglion cell

• Axons from optic nerves (N II) optic chiasm

• Medial fibers cross, lateral fibers do not cross

• Optic tracts thalamic nuclei

• Superior colliculi of midbrain controls eye reflexes

• Thalamic axons visual cortex of cerebrum


Combined Visual FieldLeft side Right side

Binocular vision

Righteyeonly

The VisualPathway

Photoreceptorsin retina

Optic nerve(N II)

Optic chiasm

Optic tract

Thalamicnucleus

Projection fibers

Visual cortex of cerebral

hemispheres

RetinaOptic disc

Hypothalamus,pineal gland,and reticular

formation

Superiorcolliculus

Left cerebralhemisphere

Right cerebralhemisphere

Lefteyeonly

The Visual Pathways (9-6)


Checkpoint (9-6)

14. Are individuals born without cone cells able to see?

Explain.

15. How would a diet deficient in vitamin A affect vision?


Anatomy of the Ear (9-7)

• External ear

• Visible portion, collects sound waves

• Middle ear

• Chamber with structures that amplify sound waves

• Internal ear

• Contains sensory organs for hearing and equilibrium

PLAYPLAY ANIMATION The Ear: Ear Anatomy


External Ear Middle Ear Internal EarElastic cartilages Auditory ossicles

Auricle

Ovalwindow

Semicircular canals

Temporal bone

Facial nerve(N VII)

Vestibulocochl-ear nerve (N VIII)

Bony labyrinthof internal ear

Cochlea

Auditory tubeTonasopharynx

VestibuleRoundwindow

Tympanicmembrane

External acousticmeatus

Figure 9-22 The Anatomy of the Ear.


The External Ear (9-7)

• Auricle or pinna is fleshy "cup" directing sound

into ear

• External acoustic meatus or auditory canal

• Contains ceruminous glands, secreting earwax

• Tympanic membrane or eardrum

• Thin sheet that vibrates when sound waves strike it


The Middle Ear (9-7)

• Also called the tympanic cavity

• Air-filled chamber

• Auditory tube

• Also called pharyngotympanic or Eustachian tube

• Leads to the pharynx, making a path for microorganisms

to trigger otitis media, an infection

• Allows for pressure equalization on either side of

eardrum


The Auditory Ossicles (9-7)

• Three small bones in middle ear that connect

tympanic membrane to internal ear

1. Malleus attaches to eardrum

2. Incus attaches malleus to innermost bone

3. Stapes has a base that nearly fills the oval window into

the internal ear


Temporal bone

Connections tomastoid air cells

Stabilizingligament

Branch of facial nerve VII (cut)

External acoustic meatus

Tympanicmembrane

Auditory Ossicles

Malleus Incus Stapes

Ovalwindow Muscles of

the Middle Ear

Tensor tympanimuscle

Stapedius muscle

Round window

Auditory tube

Figure 9-23 The Middle Ear.


The Internal Ear (9-7)

• Sensory structures protected by bony labyrinth

• Contains fluid perilymph between bony and

membranous labyrinths

• Inside bony labyrinth is membranous labyrinth

• Tubes that follow contours of bony labyrinth

• Filled with fluid endolymph


Three Parts of the Bony Labyrinth (9-7)

1. Vestibule

• Contains membranous saccule and utricle with

receptors for gravity and linear acceleration

2. Semicircular canals

• Contain membranous semicircular ducts with

receptors for rotational acceleration

3. Vestibular complex is the combination of the

first two, providing sense of balance


Three Parts of the Bony Labyrinth (9-7)

3. Cochlea

• Contains the membranous cochlear duct

• Sensory receptors for hearing

• Oval window is covered with thin membrane

separating perilymph in cochlea from air in middle ear

• Round window is opening in the bone of the cochlea


Hair Cells (9-7)

• Sensory receptors in internal ear

• Surrounded by supporting cells

• Synapse with dendrites of sensory neurons

• Free surface covered with stereocilia

• Movement of stereocilia alters neurotransmitter release

• Bending stereocilia in one direction triggers

depolarization; in the other direction, hyperpolarization


Figure 9-24a The Internal Ear and a Hair Cell.

PerilymphBony labyrinth

EndolymphMembranous

labyrinth

A section through one of the semicir-cular canals, showing the relationship between the bony and membranous labyrinths, and the locations of peri-lymph and endolymph.

KEYMembranous labyrinthBony labyrinth


Figure 9-24b The Internal Ear and a Hair Cell.

SemicircularDucts

Anterior

PosteriorVestibuleCrista ampullarisMaculaeEndolymphatic sac

UtricleSaccule

Cochlear duct

Semicircular canal

Scala tympani Spiral organ

Scala vestibuli

Lateral

The bony and membranous labyrinths. Areas of the membranous labyrinth containing sensory receptors (cristae, maculae, and spiral organ) are shown in purple.

KEYMembranous labyrinthBony labyrinth

Cochlea


Figure 9-24c The Internal Ear and a Hair Cell.

Displacement in thisdirection inhibits hair cell

Stereocilia

Hair cell

SensoryneuronSupportingcell

A representative hair cell (receptor) from the vestibular complex. Bending the stereocilia in one direction depolarizes the cell and stimulates the sensory neuron. Displacement in the opposite direction inhibits the sensory neuron.

Displacement in thisdirection stimulates

hair cell


• Dynamic equilibrium

• Maintaining balance while in motion

• Monitored by semicircular ducts

• Static equilibrium

• Maintaining balance and posture while motionless

• Monitored by saccule and utricle

Equilibrium (9-7)


The Semicircular Ducts (9-7)

• Three ducts

1. Anterior

2. Posterior

3. Lateral

• Organized in three planes

1. Transverse

2. Frontal

3. Sagittal


The Semicircular Ducts (9-7)

• Each contains the ampulla, which contains the

sensory receptors

• The crista ampullaris contains hair cells that are

embedded in gelatinous structure called the

cupula

• When head rotates, endolymph pushes against

the cristae and activates hair cells


The Vestibule (9-7)

• Saccule receptors

• Respond to gravity and linear acceleration

• Utricle receptors

• Respond to horizontal acceleration

• Hair cells clustered in maculae

• Project into gelatinous membrane with otoliths

• Gravity pulls on otoliths, pulling on hair cells


The locations ofequilibrium receptors, a crista ampullarisand a macula.

Figure 9-25a The Vestibular Complex.


Figure 9-25b The Vestibular Complex.

Ampullafilled with

endolymph

Hair cells

Cristaampullaris

Cupula

Supporting cells

Sensory nerveA cross section through the ampulla of asemicircular duct showing the crista ampullaris.


Figure 9-25c The Vestibular Complex.

Direction ofrotation

Direction ofendolymph movement

Direction ofrotation

Semicircular ductCupula

At restEndolymph movement along the axis of thesemicircular duct moves the cupula andstimulates the hair cells.


Figure 9-25d The Vestibular Complex.

Gelatinous layerforming otolithic

membrane

Otoliths

Hair cells

Nervefibers

The structure of an individual macula.


Figure 9-25e The Vestibular Complex.

Head in normal, uprightposition

Gravity

Head tilted posteriorlyGravity

Receptoroutput

increases

Otolith moves

“downhill,”distorting haircell processes

A diagrammatic view of macular functionwhen the head is held horizontally and then tilted back .


Pathways for Equilibrium Sensations (9-7)

• Hair cells of vestibule and semicircular ducts

• Synapse with neurons of vestibular branch of N VIII

• These synapse with neurons in the vestibular nuclei of

the pons and medulla oblongata

• Information is relayed to:

• Cerebellum

• Cerebral cortex

• Motor nuclei in brain stem and spinal cord

PLAYPLAY ANIMATION The Ear: Balance


Hearing (9-7)

• Vibrations of sound waves determine stimulus

• Tympanic membrane vibrates the ossicles

• Pressure pulses travel through perilymph of cochlea

• Pitch (frequency) determined by which part of cochlear

duct is stimulated

• Volume (intensity) determined by how many hair cells

are activated at that site


The Cochlear Duct (9-7)

• Sectional view shows three chambers

1. Scala vestibuli (the vestibular duct)

2. Scala media (the cochlear duct)

3. Scala tympani (the tympanic duct)

• Scala vestibuli and scala tympani are filled with

perilymph and are a continuous chamber


The Spiral Organ of Corti (9-7)

• Located in cochlear duct on basilar membrane

• Hair cell stereocilia project into tectorial

membrane, attached to wall of cochlear duct

• Waves strike basilar membrane, moving it up and

down

• Hair cells are pushed against tectorial membrane,

bending stereocilia


Figure 9-26a The Cochlea and Spiral Organ.

Bony cochlear wall

Scala vestibuli

Vestibular membrane

Tectorial membrane

Basilar membrane

Scala tympani

Spiral organ

Spiralganglion

Cochlear branchof N VIII

Cochlear duct

A three-dimensional section of thecochlea, showing the compartments,tectorial membrane, and spiral organ


Figure 9-26b The Cochlea and Spiral Organ.

Tectorial membrane

Outerhair cell

Basilar membrane Inner hair cell Nerve fibers

Cochlear duct (scala media)

Vestibular membrane

Tectorial membrane

Scalatympani

Basilarmembrane

Hair cellsof spiral

organ

Spiral ganglioncells of

cochlear nerve

Spiral organ

Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ

LM x125


Six Steps of Hearing (9-7)

1. Sound waves strike tympanic membrane

2. Tympanic membrane vibrates auditory ossicles

3. Vibration of stapes applies pressure to perilymph

4. Pressure distorts basilar membrane

5. Movement of basilar membrane distorts hair cells

against tectorial membrane, altering neurotransmitter

release

6. Impulses travel to CNS through N VIII


Figure 9-27 Sound and Hearing.

Externalacousticmeatus

Malleus Incus Stapes Oval windowCochlear branchof cranial nerveVIII

Scala vestibuli(contains perilymph)

Vestibular membrane

Cochlear duct(contains endolymph)Basilar membrane

Scala tympani(contains perilymph)

Tympanicmembrane

Roundwindow

Soundwavesarrive attympanicmembrane.

Movementof thetympanicmembranecausesdisplacem-ent of theauditoryossicles.

Movementof the stapesat the ovalwindowestablishespressurewavesin theperilymphof the scalavestibuli.

Thepressurewaves distortthe basilarmembraneon their wayto theroundwindowof the scalatympani.

Vibration ofthe basilarmembranecausesvibrationof hair cellsagainst thetectorialmembrane.

Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve VIII.

Movementof sound

waves


Auditory Pathways (9-7)

• Cochlear branch of vestibulocochlear nerve

(N VIII) axons arise from spiral ganglion

• To cochlear nuclei of medulla oblongata

• To inferior colliculi of midbrain

• To nuclei in thalamus

• To auditory cortex of temporal lobes


Figure 9-28 Pathways for Auditory Sensations.

Stimulation of hair cells at a specific location along the basilarmembrane activates sensory neurons.

Projection fibers then deliver the information to specific locations within the auditory cortex of the temporal lobe.

High-frequency

soundsThalamus

Cochlea

Low-frequencysounds

High-frequencysounds

Vestibularbranch

Sensory neurons carry the sound information in the cochlear branch of the vestibulocochlear nerve (VIII) to the cochlear nucleus on that side.

Low-frequencysounds

Ascending acoustic information synapes at a nucleus of thethalamus.

The inferior colliculi direct a variety of unconscious motor responses to sounds.

Information ascends from each cochlear nucleus to the inferior colliculi of the midbrain.

Motor output to spinal cord

Vestibulocochlearnerve (VIII)

KEY

Primary pathwaySecondary pathwayMotor output


Checkpoint (9-7)

16. If the round window were not able to bulge out

with increased pressure in the perilymph, how

would sound perception be affected?

17. How would the loss of stereocilia from the hair

cells of the spiral organ affect hearing?


Aging and the Special Senses (9-8)

• Olfaction and gustation decrease with decrease in

number and sensitivity of receptors

• Hearing decreases with age due to loss of

elasticity of tympanic membrane


Checkpoint (9-8)

18. How can a given food be both too spicy for a

child and too bland for an elderly individual?

19. Explain why we have an increasingly difficult

time seeing close-up objects as we age.

163 ch 09_lecture_presentation

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