lecture material is adapted from © 2013 pearson …...–irritation of olfactory pathway • taste...

THE SPECIAL SENSES

Lecture Material is adapted from © 2013 Pearson Education, Inc. Human

Anatomy and Physiology

Dr. Henrik Pallos

Mt. Aspiring Textbook Challenge

https://give.everydayhero.com/au/aspiring-textbook-challenge

Physical Preparation

15kg

3kg







© 2013 Pearson Education, Inc.

Visual pathway to the brain and visual fields, inferior view.

Both eyes

Fixation point

Right eye

Supra- chiasmatic nucleus

Pretectal

nucleus

Lateral

geniculate

nucleus of

thalamus

Superior

colliculus

The visual fields of the two eyes overlap considerably.

Note that fibers from the lateral portion of each retinal field do not cross at the optic chiasma.

Occipital lobe (primary visual

cortex)

Left eye

Optic nerve

Optic chiasma

Optic tract

Lateral

geniculate

nucleus

Superior colliculus (sectioned)

Uncrossed (ipsilateral) fiber

Crossed

(contralateral) fiber

Optic

radiation

Corpus callosum

Photograph of human brain, with the right side

dissected to reveal internal structures.

Optic tract:

Fibers from lateral same side eye &

Fibers from medial opposite eye

Carries all the information from the

same half of the visual field


Visual Pathway To The Brain

1. Axons of retinal ganglion cells form optic nerve

2. Medial fibers of optic nerve decussate at optic

chiasma

3. Most fibers of optic tracts continue to lateral

geniculate body of thalamus

4. Fibers from thalamic neurons form optic

radiation and project to primary visual cortex in

occipital lobes


Visual Pathway

• Fibers from thalamic neurons form optic radiation

• Optic radiation fibers connect to primary visual cortex

in occipital lobes

• Other optic tract fibers send branches to midbrain,

ending in superior colliculi (initiating visual reflexes)


Visual Pathway

• A small subset of ganglion cells in retina

contain melanopsin (circadian pigment)

• Respond directly to light stimuli and their fibers

project to:

– Pretectal nuclei (involved with pupillary light

reflexes)

– Suprachiasmatic nucleus of hypothalamus, timer

for daily biorhythms


Depth Perception

• Both eyes view same image from slightly

different angles

• Depth perception (three-dimensional vision)

results from cortical fusion of slightly different

images

• Requires input

from both eyes

Visual Cliff


Visual Processing

1. Retinal cells split input into channels

• Color, brightness, angle, direction, speed of movement of

edges (sudden changes of brightness or color)

2. Lateral geniculate nuclei of thalamus processes

• Depth perception, cone input emphasized, contrast

sharpened

3. Primary visual cortex (striate cortex) raw vision

• Topographic representation of retina

• Neurons respond to dark and bright edges, and object

orientation

• Provide form, color, motion inputs to visual association

areas (prestriate cortices)

http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/V1/lgn-V1.html


Cortical Processing

4. Occipital lobe centers (visual association areas,

anterior prestriate cortices) continue processing of

form, color, and movement

5. Complex visual processing extends to other regions

– "What" processing identifies objects in visual field

• Ventral temporal lobe

– "Where" processing assesses spatial location of objects

• Parietal cortex to postcentral gyrus

– Output from both passes to frontal cortex

• Can directs movements based on visual input


Developmental Aspects

• Vision not fully functional at birth

• Babies hyperopic (farsighted)

– eyeball is shorter

– only gray tones

– eye movements uncoordinated, often one eye at a time

– tearless for 2 weeks

• By 5th months: can follow moving objects, visual acuity

is still poor

• By 3rd year: depth perception, color vision well

developed

• By 6th year: emmetropic eyes developed

• By 8-9th year: eye reaches its adult size



• With age:

– lens loses clarity and discolors

– dilator muscles less efficient: pupils stay partly constricted

• As a result visual acuity drastically decreased by age 70

• Lacrimal glands less active so eyes dry, more prone to

infection

• Elderly are also risk for conditions that cause

blindness

– Macular degeneration (progressive deterioration of macula

lutea)

– glaucoma, cataracts, atherosclerosis, diabetes mellitus

Are the dots in between the squares

white, black or grey?

Are the lines paralell or crooked?

Is this picture still or moving?

Focus on the 4 dots in the middle of the picture for 30 seconds.

Then look at a blank wall and see what you see or more

importantly - who do you see? Maybe blink your eyes a few

times to find out.

Chemical senses

1. Smell: Olfaction

2. Taste: Gustation

• Chemoreceptors respond to chemicals in

aqueous solution

– Smell receptors: airborne chemicals dissolved in

fluids coating nasal membranes

– Taste receptors: food chemicals dissolved in saliva



Olfactory receptors.

Olfactory epithelium

Olfactory tract

Olfactory bulb

Nasal conchae

Route of inhaled air


Olfactory receptors.

Olfactory tract

Olfactory gland

Olfactory epithelium

Mucus

Mitral cell (output cell, 2nd order)

Olfactory bulb

Cribriform plate of ethmoid bone

Filaments of olfactory nerve Lamina propria connective tissue

Olfactory stem cell

Olfactory sensory Neuron (1st order)

Dendrite

Olfactory cilia

Route of inhaled air containing odor molecules

Glomeruli

Olfactory axon

Supporting cell


Specificity of Olfactory Receptors

• Humans can distinguish ~10,000 odors

• ~400 "smell" genes active only in nose

1. Each encodes unique receptor protein

• Protein responds to one or more odors

2. Each odor binds to several different receptors

3. Each receptor has one type of receptor protein

• Pain and temperature receptors also in nasal

cavities


Physiology of Smell

• Gaseous/volatile odorant must enter nasal

cavity

• Odorant must dissolve in fluid of olfactory

epithelium

• Activation of olfactory sensory neurons

– Dissolved odorants bind to receptor proteins in

olfactory cilium membranes


Smell Transduction

• Odorant binds to receptor activates G protein – G protein activation cAMP (second messenger)

synthesis

• cAMP Na+ and Ca2+ channels opening

• Na+ influx depolarization and impulse transmission

• Ca2+ influx olfactory adaptation

– Decreased response to sustained stimulus


Olfactory transduction process. Slide 6

cAMP opens a cation channel, allowing Na+ and Ca2+ influx and causing depolarization.

Adenylate cyclase converts ATP to cAMP.

G protein activates adenylate cyclase.

Receptor activates G protein (Golf).

Odorant

G protein (Golf)

Adenylate cyclase

cAMP cAMP

Open cAMP-gated cation channel

GDP

Odorant binds to its receptor.

2

1

3 4 5

Receptor


Olfactory Pathway

• Olfactory receptor cells synapse with mitral cells in

glomeruli of olfactory bulbs

• Axons from neurons with same receptor type

converge on given type of glomerulus

– Glomerulus: single aspect of odor

– Each odor activates a unique set of glomeruli

• Mitral cells amplify, refine, and relay signals

• Olfactory bulb:

Amacrine granule cells

release GABA to inhibit mitral

cells

• Only highly excitatory

impulses transmitted


The Olfactory Pathway

• Impulses from activated mitral cells travel via

olfactory tracts to piriform lobe of olfactory cortex

• Some information to frontal lobe

– Smell consciously interpreted and identified

• Some information to hypothalamus, amygdala, and

other regions of limbic system

– Emotional responses to odor elicited

– Sympathetic response: danger

– Parasympathetic response: digestion

– Protective reflexes: sneezing, choking

McGraw Hill Anatomy and Physiology

Human Pheromones

• No clear evidence that human body odors

affect sexual behaviour.

• Evidence: sweat and vaginal secretion affect

other’s sexual physiology

– Woman’s apocrine sweat influence other

women’s menstrual cycle

• “Dormitory effect”: absence of men, synchronized

menstrual cycle

– Presence of men: ovulating (close to it) woman

vaginal secretion contains “ copulin” pheromones

• Can raise testosterone level in males

Noma

http://noma.dk/food-and-wine/


Taste Buds and the Sense of Taste

• Receptor organs are taste buds

– Most of 10,000 taste buds on tongue papillae

• On tops of fungiform papillae

• On side walls of foliate and vallate papillae

– Few on soft palate, cheeks, pharynx, epiglottis


Structure of a Taste Bud

• 50–100 flask-shaped epithelial cells of 2

types

– Gustatory epithelial cells—taste cells

• Microvilli (gustatory hairs) are receptors

• Three types of gustatory epithelial cells

– One releases serotonin; others lack synaptic vesicles but

one releases ATP as neurotransmitter

– Basal epithelial cells—dynamic stem cells that

divide every 7-10 days


Basic Taste Sensations

• There are five basic taste sensations

1. Sweet—sugars, saccharin, alcohol, some amino

acids, some lead salts

2. Sour—hydrogen ions in solution

3. Salty—metal ions (inorganic salts)

4. Bitter—alkaloids such as quinine and nicotine;

aspirin

5. Umami—amino acids glutamate and aspartate

Prof. Kikunae Ikeda

1864-1936

1908

http://chemse.oxfordjournals.org/content/early/2015/07/02/chemse.bjv036.short?rss=1

http://chemse.oxfordjournals.org/content/early/2015/07/02/chemse.bjv036.full.pdf+html


• Possible 6th taste (“oleogustus”)

– Growing evidence humans can taste long-chain

fatty acids from lipids

– Perhaps explain liking of fatty foods









• Taste likes/dislikes have homeostatic value

– Guide intake of beneficial and potentially harmful

substances

– Umami: protein intake

– Sweet: carbohydrate intake

– Salty: minerals

– Sour: Vitamin-C or spoiled food (protective)

– Bitter: many natural poison is alkaloids, protective


Physiology of Taste

• To taste, chemicals must

– Be dissolved in saliva

– Diffuse into taste pore

– Contact gustatory hairs


Activation of Taste Receptors

• Binding of food chemical (tastant) depolarizes taste cell membrane neurotransmitter release

– Initiates a generator potential that elicits an action potential

• Different thresholds for activation

– Bitter receptors most sensitive

• All adapt in 3-5 seconds; complete adaptation in 1-5 minutes


Taste Transduction

• Gustatory epithelial cell depolarization caused by

– Salty taste due to Na+ influx (directly causes depolarization)

– Sour taste due to H+ (by opening cation channels)

– Unique receptors for sweet, bitter, and umami coupled to G protein gustducin

• Stored Ca2+ release opens cation channels depolarization neurotransmitter ATP release


Gustatory Pathway

• Cranial nerves VII and IX carry impulses from taste buds to solitary nucleus of medulla

• Impulses then travel to thalamus and from there fibers branch to

– Gustatory cortex in the insula

– Hypothalamus and limbic system (appreciation of taste)

• Vagus nerve transmits from epiglottis and lower pharynx


The gustatory pathway.

Gustatory cortex (in insula)

Thalamic nucleus (ventral posteromedial nucleus) Pons

Facial nerve (VII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Solitary nucleus in medulla oblongata


Role Of Taste

1. Triggers reflexes involved in digestion

2. Increase secretion of saliva into mouth

3. Increase secretion of gastric juice into stomach

4. May initiate protective reactions

– Gagging

– Reflexive vomiting


Influence of other Sensations on Taste

• Taste is 80% smell

• Thermoreceptors, mechanoreceptors,

nociceptors in mouth also influence tastes

– Temperature and texture enhance or detract from

taste

– VISUAL!


Homeostatic Imbalances of the Chemical

Senses

• Anosmias (olfactory disorders) – no smell

• Most result of head injuries and neurological disorders

(Parkinson's disease)

• Uncinate fits – olfactory hallucinations – Olfactory auras prior to epileptic fits

– Irritation of olfactory pathway

• Taste disorders less common – Receptors are served by 3 nerves

– Infections, head injuries, chemicals, medications, radiation for

CA of head/neck

• Chemical senses—few problems occur until fourth

decade, when these senses begin to decline – Odor and taste detection poor after 65


The Ear: Hearing and Balance

• Three major areas of ear

1. External (outer) ear – hearing only

2. Middle ear (tympanic cavity) – hearing only

3. Internal (inner) ear – hearing and equilibrium

• Receptors for hearing and balance respond to

separate stimuli

• Are activated independently


Structure of the ear.

External

ear

Middle

ear

Internal ear

(labyrinth)

Auricle (pinna)

Helix

Lobule

External acoustic meatus

Tympanic membrane

Pharyngotympanic (auditory) tube

The three regions of the ear


External Ear

• Auricle (pinna) composed of

– Helix (rim); Lobule (earlobe)

– Funnels sound waves into auditory canal

• External acoustic meatus (auditory canal)

– Short, curved tube lined with skin bearing hairs,

sebaceous glands, and ceruminous glands

– Transmits sound

waves to eardrum


External Ear

• Tympanic membrane (eardrum)

– Boundary between external and middle ears

– Connective tissue membrane that vibrates in

response to sound

– Transfers sound energy to bones of middle ear


Middle Ear (Tympanic Cavity)

• A small, air-filled, mucosa-lined cavity in

temporal bone

– Flanked laterally by eardrum

– Flanked medially by bony wall

containing:

• oval (vestibular) window

• round (cochlear) window


Middle Ear

• Epitympanic recess—superior portion of middle ear

• Mastoid antrum

• Canal for communication with mastoid air cells

• Pharyngotympanic (auditory) tube—connects

middle ear to nasopharynx

• Equalizes pressure in middle ear cavity with external air

pressure


Structure of the ear.

Oval window (deep to stapes)

Semicircular canals

Vestibule

Vestibular nerve

Cochlear nerve

Cochlea

Pharyngotympanic (auditory) tube

Entrance to mastoid antrum in the epitympanic recess

Auditory ossicles

Tympanic membrane

Round window

Stapes (stirrup)

Incus (anvil)

Malleus (hammer)

Middle and internal ear


Otitis Media

• Middle ear inflammation

– Result of sore throat

– Especially in children

• Shorter, more horizontal pharyngotympanic tubes

• Most frequent cause of hearing loss in children

– Most treated with antibiotics

– Myringotomy to relieve pressure if severe


Ear Ossicles

• Three small bones in tympanic cavity:

1. Malleus

2. Incus

3. Stapes

– Suspended by ligaments and joined by synovial joints

– Transmit vibratory motion of eardrum to oval window

– Tensor tympani and stapedius muscles contract

reflexively in response to loud sounds to prevent

damage to hearing receptors


The three auditory ossicles and associated skeletal muscles.

View

Superior

Anterior

Lateral

Incus Malleus Epitympanic recess

Pharyngotym-

panic tube

Tensor tympani muscle

Tympanic membrane (medial view)

Stapes Stapedius muscle

Break

Figure 6: Different diameters and slopes of cochlear turns to illustrate individual variations of the human

cochlea (with permission of Helge Rask-Andersen, Uppsala, Sweden).

http://openi.nlm.nih.gov/detailedresult.php?img=3200995_CTO-04-04-g-006&req=4

http://irp.nih.gov/our-research/research-in-action/high-fidelity-stereocilia/slideshow

Auditory transduction

http://youtu.be/PeTriGTENoc

Organ of Corti

http://youtu.be/1JE8WduJKV4


























Two Major Divisions of Internal Ear

1. Bony labyrinth

– Tortuous channels in temporal bone

– Three regions:

1. Vestibule

2. Semicircular canals

3. Cochlea

– Filled with perilymph – similar to CSF

2. Membranous labyrinth

– Series of membranous sacs and ducts

– Filled with potassium-rich endolymph


Membranous labyrinth of the internal ear.

Temporal bone

Facial nerve

Vestibular nerve

Superior vestibular ganglion

Inferior vestibular ganglion Cochlear nerve

Maculae Spiral organ

Cochlear duct

in cochlea

Round window Stapes in oval window

Saccule in

vestibule

Utricle in

vestibule

Cristae ampullares in the membranous ampullae

Lateral Posterior Anterior

Semicircular ducts

in semicircular

canals


Vestibule

• Central egg-shaped cavity of bony labyrinth

• Contains two membranous sacs

1. Saccule is continuous with cochlear duct

2. Utricle is continuous with semicircular canals

• These sacs

– House equilibrium receptor regions (maculae)

– Respond to gravity and changes in position of head


Semicircular Canals

• Three canals (anterior, lateral, and posterior) that each define ⅔ circle

– Lie in three planes of space

– Membranous semicircular ducts line each canal and communicate with utricle

• Ampulla of each canal houses equilibrium receptor region called the crista ampullaris

– Receptors respond to angular (rotational) movements of the head


Membranous labyrinth of the internal ear.

Temporal bone

Facial nerve

Vestibular nerve

Superior vestibular ganglion

Inferior vestibular ganglion Cochlear nerve

Maculae Spiral organ

Cochlear duct

in cochlea

Round window Stapes in oval window

Saccule in

vestibule

Utricle in

vestibule

Cristae ampullares in the membranous ampullae

Lateral Posterior Anterior

Semicircular ducts

in semicircular

canals


The Cochlea

• A spiral, conical, bony chamber

– Size of split pea

– Extends from vestibule

– Coils around bony pillar (modiolus)

– Contains cochlear duct, which houses spiral

organ (organ of Corti) and ends at cochlear apex


Anatomy of the cochlea.

Helicotrema at apex

Modiolus

Cochlear nerve, division of the vestibulocochlear nerve (VIII)

Spiral ganglion

Osseous spiral lamina

Vestibular membrane

Cochlear duct (scala media)


The Cochlea

• Cavity of cochlea divided into three chambers

1. Scala vestibuli abuts oval window, contains perilymph

2. Scala media (cochlear duct)-membranous labyrinth contains endolymph

3. Scala tympani terminates at round window; contains perilymph

• Scalae tympani and vestibuli are continuous with each other at helicotrema (apex)


The Cochlea

• The "roof" of cochlear duct is vestibular membrane

• External wall is stria vascularis – secretes endolymph

• "Floor" of cochlear duct composed of

– Bony spiral lamina

– Basilar membrane, which supports spiral organ

• The cochlear branch of nerve VIII runs from spiral organ to brain



Vestibular membrane

Tectorial membrane

Cochlear duct

(scala media;

contains

endolymph)

Stria vascularis

Spiral organ

(Corti)

Basilar

membrane

Scala

vestibuli

(contains

perilymph)

Scala

tympani

(contains perilymph)

Osseous spiral lamina

Spiral ganglion


Tectorial membrane

Hairs (stereocilia)

Outer hair cells

Supporting cells

Inner hair cell

Afferent nerve

fibers

Fibers of cochlear nerve

Basilar

membrane



Properties of Sound

• Sound is

– Pressure disturbance (alternating areas of high

and low pressure) produced by vibrating object

• Sound wave

– Moves outward in all directions

– Illustrated as an S-shaped curve or sine wave


Sound: Source and propagation.

Area of high pressure (compressed molecules)

Area of low pressure (rarefaction) Wavelength

Crest

Trough

Amplitude Distance

Air p

re

ssu

re

A struck tuning fork alternately compresses

and rarefies the air molecules around it, creating

alternate zones of high and low pressure.

Sound waves radiate

outward in all

directions.


Properties of Sound Waves

– Frequency

• Number of waves that pass given point in given time

• Pure tone has repeating crests and troughs

– Wavelength

• Distance between two consecutive crests

• Shorter wavelength = higher frequency of sound


Properties of Sound

1. Pitch

– Perception of different frequencies

– Normal range 20–20,000 hertz (Hz)

– Most sensitive 1500-4000 Hz

– Higher frequency = higher pitch

2. Quality

– Tone- single frequency: pure but bland

– Most sounds mixtures of different frequencies

– Richness and complexity of sounds (music)


Properties of Sound

3. Amplitude

– Height of crests

• Amplitude perceived as loudness

– Subjective interpretation of sound intensity

– Normal range is 0–120 decibels (dB)

– Severe hearing loss with prolonged exposure

above 90 dB

• Amplified rock music is 120 dB or more

• Gunshot 140dB, single energy, more dangerous


Frequency and amplitude of sound waves.

High frequency (short wavelength) = high pitch

Low frequency (long wavelength) = low pitch

Pre

ssu

re

0.01 0.02 0.03 Time (s)

Frequency is perceived as pitch.

High amplitude = loud

0.01 0.02 0.03 Time (s)

Low amplitude = soft

Amplitude (size or intensity) is perceived as loudness.

Pre

ssu

re


Transmission of Sound to the Internal Ear

1. Sound waves vibrate tympanic membrane

2. Ossicles vibrate and amplify pressure at

oval window

3. Cochlear fluid set into wave motion

4. Pressure waves move through perilymph of

scala vestibuli

Auditory transduction




Transmission of Sound to the Internal Ear

1. Waves with frequencies:

• below threshold of hearing travel through

helicotrema and scali tympani to round window

2. Sounds in hearing range:

• go through cochlear duct

• vibrating basilar membrane at specific location,

according to frequency of sound


Pathway of sound waves and resonance of the basilar membrane. Slide 6

Tympanic membrane

Round window

Auditory ossicles

Oval window

Cochlear nerve

Scala vestibuli

Route of sound waves through the ear

Malleus Incus Stapes

Helicotrema

3

4a

4b

Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli.

Sound waves

vibrate the tympanic

membrane.

Auditory ossicles

vibrate. Pressure is

amplified.

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

4a

4b 3 2 1

1

2

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

Scala tympani

Cochlear duct

Basilar membrane


Resonance of the Basilar Membrane

1. Fibers near oval window short and stiff

– Resonate with high-frequency pressure waves

2. Fibers near cochlear apex longer, more floppy

– Resonate with lower-frequency pressure waves

• This mechanically processes sound before

signals reach receptors


Pathway of sound waves and resonance of the basilar membrane.

Basilar membrane

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

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

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

Different sound frequencies cross the basilar membrane at

different locations.

Apex

(long, floppy fibers)

Fibers of basilar membrane

Base (short, stiff fibers)

20 20,000 Frequency (Hz)

2000 200


Excitation of Hair Cells in the Spiral Organ

• Cells of spiral organ

– Supporting cells

– Cochlear hair cells

• One row of inner hair cells: auditory message

• Three rows of outer hair cells: increase responsiveness of

the inner hair cells by contracting/stretching & protecting

inner hair cells from damage

• Have many stereocilia and one kinocilium

• Afferent fibers of cochlear nerve coil about

bases of hair cells



Tectorial membrane

Hairs (stereocilia)

Outer hair cells

Supporting cells

Inner hair cell

Afferent nerve

fibers

Fibers of cochlear nerve

Basilar

membrane

Organ of Corti




Excitation of Hair Cells in the Spiral Organ

• Stereocilia

– Protrude into endolymph

– Longest enmeshed in gel-like tectorial membrane

• Sound bending these toward kinocilium

– Opens mechanically gated ion channels

– Inward K+ and Ca2+ current causes graded potential and

release of neurotransmitter glutamate

– Cochlear fibers transmit impulses to brain


Auditory Pathways to the Brain

• Impulses from cochlea pass

1. via spiral ganglion

2. to cochlear nuclei of medulla

• From there, impulses sent

3. To superior olivary nucleus

• Via lateral lemniscus to

4. Inferior colliculus (auditory reflex center)

• From there, impulses pass

5. to medial geniculate nucleus of thalamus, then

6. to primary auditory cortex

• Auditory pathways partially decussate so that both

cortices receive input from both ears


The auditory pathway.

Medial geniculate nucleus of thalamus

Primary auditory cortex in temporal lobe

Inferior colliculus

Lateral lemniscus

Superior olivary nucleus (pons- medulla junction)

Cochlear nuclei

Midbrain

Medulla

Vestibulocochlear nerve

Spiral ganglion of cochlear nerve

Bipolar cell

Spiral organ

Vibrations

Vibrations


Auditory Processing

• Pitch:

perceived by impulses from specific hair cells in

different positions along basilar membrane

• Loudness:

detected by increased numbers of action potentials

that result when hair cells experience larger

deflections

• Localization of sound depends on relative intensity

and relative timing of sound waves reaching both

ears


Homeostatic Imbalances of Hearing

1. Conduction deafness

– Blocked sound conduction to fluids of internal ear

• Impacted earwax, perforated eardrum, otitis media,

otosclerosis of the ossicles

2. Sensorineural deafness

– Damage to neural structures at any point from

cochlear hair cells to auditory cortical cells

– Typically from gradual hair cell loss

• Single explosively loud sound

• Prolonged exposure to high intensity sounds

– (headset, earphones on maximum volume)


Treating Deafness

• Cochlear implants for congenital or age/noise

cochlear damage

– Convert sound energy into electrical signals

– Inserted into drilled recess in temporal bone

– So effective that deaf children can learn to speak


Homeostatic Imbalances of Hearing

• Tinnitus

– Ringing or clicking sound in ears in absence of

auditory stimuli

• Usually a symptom, not a disease

– Due to cochlear nerve degeneration, inflammation

of middle or internal ears, side effects of aspirin

Symphony No. 5

“Fate knocks at the door!"

https://upload.wikimedia.org/wikipedia/commons/e/ee/Beet5mov1bars1to5.ogg







Equilibrium and Orientation

• Vestibular apparatus

– Equilibrium receptors in

semicircular canals and

vestibule

1. Vestibular receptors:

monitor static equilibrium

2. Semicircular canal receptors:

monitor dynamic equilibrium


Maculae

• Sensory receptors for static equilibrium

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

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

• Respond to linear acceleration forces – NOT rotation

• Contain supporting cells and hair cells

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


Maculae

1. Maculae in utricle:

respond to horizontal

movements and tilting

head side to side

2. Maculae in saccule:

respond to vertical

movements

• Hair cells synapse with

vestibular nerve fibers


Activating Maculae Receptors

• Hair cells release

neurotransmitter

continuously

– Movement modifies

amount they release

• Bending of hairs in

direction of kinocilia

– Depolarizes hair cells

– Increases amount of

neurotransmitter release

– More impulses travel up

vestibular nerve to brain


Activating Maculae Receptors

• Bending away from

kinocilium

– Hyperpolarizes receptors

– Less neurotransmitter

released

– Reduces rate of impulse

generation

• Thus brain informed of

changing position of head


The effect of gravitational pull on a macula receptor cell in the utricle.

Otolith membrane

Kinocilium

Stereocilia

Receptor potential Depolarization Hyperpolarization

Nerve impulses generated in vestibular fiber

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

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

Linear acceleration


The Crista Ampullares (Crista)

• Sensory receptor for rotational acceleration

– One in ampulla of each semicircular canal

– Major stimuli are rotational movements

• Each crista has supporting cells and hair cells

that extend into gel-like mass called ampullary

cupula

• Dendrites of vestibular nerve fibers encircle base

of hair cells


Location, structure, and function of a crista ampullaris in the internal ear.

Crista ampullaris

Membranous

labyrinth

Crista ampullaris

Fibers of vestibular nerve

Hair bundle (kinocilium plus stereocilia)

Hair cell

Supporting cell

Endolymph

Ampullary cupula

Anatomy of a crista ampullaris in a semicircular canal Scanning electron micrograph

of a crista ampullaris (200x)

Section of ampulla, filled with endolymph

Cupula Fibers of vestibular

nerve

Flow of endolymph

At rest, the cupula stands upright. During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind due to inertia). Endolymph flow bends the cupula and excites the hair cells.

As rotational movement slows, endolymph keeps moving in the direction of rotation. Endolymph flow bends the cupula in the opposite direction from acceleration and inhibits the hair cells.

Movement of the ampullary cupula during rotational acceleration and deceleration


Activating Crista Ampullaris Receptors

• Cristae respond to changes in velocity of rotational

movements of the head

1. Bending of hairs in cristae causes

• Depolarizations, and rapid impulses reach brain at faster

rate

2. Bending of hairs in the opposite direction causes

• Hyperpolarizations, and fewer impulses reach the brain

• Axes of complementary semicircular ducts are

opposite, one ampulla depolarize, one hyperpolarize

• Thus brain informed of rotational movements of head


Location, structure, and function of a crista ampullaris in the internal ear.

Section of ampulla, filled with endolymph

Cupula Fibers of vestibular

nerve

Flow of endolymph

At rest, the cupula stands upright. During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind due to inertia). Endolymph flow bends the cupula and excites the hair cells.

As rotational movement slows, endolymph keeps moving in the direction of rotation. Endolymph flow bends the cupula in the opposite direction from acceleration and inhibits the hair cells.

Movement of the ampullary cupula during rotational acceleration and deceleration


Vestibular Nystagmus

• Strange eye movements during and immediately after rotation

• Often accompanied by vertigo

• As rotation begins eyes drift in direction opposite to rotation, then CNS compensation causes rapid jump toward direction of rotation

• As rotation ends eyes continue in direction of spin then jerk rapidly in opposite direction


Equilibrium Pathway to the Brain

• Equilibrium information goes to reflex centers in brain

stem

– Allows fast, reflexive responses to imbalance

• Impulses travel to vestibular nuclei in brain stem or

cerebellum, both of which receive other input

• Three modes of input for balance and orientation:

1. Vestibular receptors

2. Visual receptors

3. Somatic receptors


Neural pathways of the balance and orientation system.

Input: Information about the body’s position in space comes from

three main sources and is fed into two major processing areas in the

central nervous system.

Vestibular receptors

Visual receptors

Somatic receptors (skin, muscle

and joints)

Cerebellum Vestibular

nuclei (brain stem)

Central nervous

system processing

Oculomotor control (cranial nerve nuclei

III, IV, VI)

(eye movements)

Spinal motor control (cranial nerve XI nuclei

and vestibulospinal tracts)

(neck, limb, and trunk movements)

Output: Responses by the central nervous system provide fast

reflexive control of the muscles serving the eyes, neck, limbs, and

trunk.


Motion Sickness

• Sensory input mismatches

– Visual input differs from equilibrium input

– Conflicting information causes motion sickness

• Warning signs are excess salivation, pallor, rapid deep breathing, profuse sweating

• Treatment with antimotion drugs that depress vestibular input


Homeostatic Imbalances

• Ménière's syndrome: labyrinth disorder that

affects cochlea and semicircular canals

– Repeated attacks of vertigo, nausea, and

vomiting

– Standing is difficult

• Maybe due to excessive endolymph production

• Maybe membrane rupture that allows mixing of

endolymph and perilymph

• Antimotion drugs, low-salt diet, diuretics

• Removal of labyrinth when complete hearing loss



• Newborns can hear but early responses

reflexive

• Language skills tied to ability to hear well

• Congenital abnormalities common

– Missing pinnae, closed or absent external acoustic

meatuses

– Maternal rubella causes sensorineural deafness



• Few ear problems until 60s when deterioration

of spiral organ noticeable

• Hair cell numbers decline with age

– Loud noise, disease, drugs

– Presbycusis occurs first

• Loss of high pitch perception

• Type of sensorineural deafness

• It is becoming more common in younger people!!

THE END

Luis Pasteur (1822-1895)

“ Chance favors the prepared mind. ”

Vaccines for rabies, anthrax

Pasteurization

Fermentation

Are Anatomy and Physiology tests fair?

“Well, tests ain't fair.

Those that study have an unfair advantage.

It's always been that way.”

― Allan Dare Pearce, Paris in April

Thank you all for the fun!

SAYONARA! cu@s12016

lecture material is adapted from © 2013 pearson …...–irritation of olfactory pathway • taste...

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