THE SPECIAL SENSES

THE SPECIAL SENSES

CHEMICAL SENSES: Smell and Taste

THE EAR: Hearing and Balance

THE EYE : Vision

OLFACTION: SENSE OF SMELL

Chemical sense

olfactory receptors are found in the roof of

the nasal cavity

sniffing intensifies the sense of smell

olfactory epithelium consists of:

olfactory receptors

supporting cells

basal stem cells

Anatomy of Olfaction

Olfactory receptors

first order neurons

bipolar neurons ( exposed tips are knobbed

dendrites)

site of olfactory transduction: olfactory

hairs

Supporting Cells

columnar epithelial cells

provides physical support, nourishment

& electrical stimulation for

olfactory receptors

help destroy chemicals

Basal Stem Cell

lie between bases of supporting cells

continuously undergo cell division

Olfactoy mucosa. Note the

thick layer of epithelium.

The underlying lamina

propria possesses many

glands

Olfactory system. 1. Olfactory bulb. 2. nasal cavity. 3.

Brain. 4. Olfactory epithelium 5. Vomeronasal organ. 6.

Ions. 7 Glomeruli. *. Axon. 9. To olfactory cortex

Physiology of Olfaction

1.odorants bind olfactory receptors that are

linked to G proteins

2.activation of the enzyme adenylate cyclase

3.Na+ channels open

4.inflow of Na+ ions

5.depolarization

6.generation and propagation of action

potential

7.nerve impulse

Odor Thresholds and Adaptation

low threshold

decreasing sensitivity

Olfactory Pathway

Olfactory Nerve (CN I)

Olfactory Bulbs

Olfactory Tract ( Brain)

Anosmias

NASAL POLYP

NASAL POLYP

Gustation : Sense of Taste

Chemical sense

4 classes of stimuli

sweet salty

sour bitter

gustation is thousands of times less

sensitive than olfaction

colds block olfaction not gustation

Anatomy of Gustation

Receptors for gustation are located in taste

buds

10,000 receptors are distributed in the

tongue, soft palate, pharynx & larynx

number of taste buds decline with age

The tongue is covered with dozens of pimple-like

projections called papillae. These grip and move food

when you chew. Around the sides of the papillae are about

10,000 microscopic taste buds. Different parts of the

tongue are sensitive to different flavours: sweet, salt, sour

and bitter

Taste buds consist of 3 kinds of cells:

• supporting cells

• 50 gustatory cells

• basal cells

gustatory hair

gustatory receptor

cell

supporting cell

fibers of CNs basal cell

Taste buds

Papillae

• circumvallate

• fungiform

• filiform - no taste buds

Tongue-tie is a condition caused by a short lingual

frenulum that prevents the tongue from

protruding. Occasionally, it could interfere with

breast feeding

The horizontally incised frenulum is now pulled

vertically, allowing the release of the tongue. The

incision is sutured vertically with absorbable

stitches.

Post-operative appearance of the tongue that

can now protrude down to the chin.

Physiology of Gustation

1. chemicals are dissolved in saliva

2. Contact with plasma membrane of

gustatory hair

3. receptor potential stimulates exocytosis of

neurotransmittercontaining synaptic

vesicles

4. Nerve impulse arise in the 1st order

neurons that synapse with gustatory

receptor cells

Taste Threshold and Adaptations

Bitter: lowest

sour: higher than that of bitter

sweet about the same but higher

salty than sour & bitter

complete adaptation occurs in 1-5 minutes

of continuous stimulation

First order gustatory fibers include 3

cranial nerves:

• Facial nerve: anterior 2/3 of tongue

• glossopharyngeal nerve: posterior 1/3 of

tongue

• vagus: throat & epiglottis

Gustatory Pathway

from taste buds, impulses propagate to

medulla oblongata

taste fibers

thalamus, hypothalamus, limbic system

parietal lobe of cerebral cortex

TASTE

The Eye and Vision

Accessory structures of the eye:

• eyelids

• eyelashes

• eyebrows

• lacrimal apparatus

• extrinsic eye muscles

Anatomy of the Eyeball

Eyelids

• palpebrae

• palpebral fissure

• medial commissure

• lateral commissure

• lacrimal caruncle

• meibomian glands

• conjunctiva

Eyelashes and Eyebrows

• ciliary glands

• sty

Ciliary Body

Lacrimal apparatus

• lacrimal gland

• excretory lacrimal

ducts

• lacrimal puncta

• nasolacrimal duct

Extrinsic Eye Muscles

• superior rectus

• inferior rectus

• lateral rectus

• medial rectus

• superior oblique

• inferior oblique

Entrapment of the Inferior Rectus Muscle

of the Eye

in a Blow-out Fracture of the Orbit

Blunt trauma to the right eye, resulting in diplopia.

The right inferior rectus was caught between the

fragments of a blow-out fracture of the floor of the

orbit. This child was unable to move his right eyeball

up on upward gaze.

Tunics of the eye;

• Fibrous tunic; sclera

• Vascular tunic: choroid

• Retina: rods and cones

Uvea

• choroid

• ciliary body: ciliary body and ciliary muscles

• iris: colored portion of eyeball

• pupil: hole at the center of iris

Retina

• photoreceptors: rods and cones

• macula lutea

• fovea centralis

• blind spot

Fovea

Lens

cataract

Chambers of the eye

• anterior chamber: aqueous humor

• posterior chamber: vitreous humor

Intraocular pressure

Glaucoma

Refraction of Light Rays

Images on retina

• inverted

• right to left reversal

• brain coordinates visual images and

orientation of objects

Accomodation

Near point of Vision

Presbyopia

Light enters the front of the eye through the pupil and is

focused by the lens onto the retina. Rod cells on the retina

respond to the light and send a message through the optic

nerve fiber to the brain.

Emmetropia: Normal Vision

Refraction Abnormalities

Myopia: Near sightedness

Hyperopia: Farsightedness

Astigmatism

Nyctalopia

Binocular vision

Photopupillary reflex

Accomodation pupillary reflex

Physiology of Vision

Photopigments:

• rhodopsin (rods)

• opsin

• retinal

1. Light causes

4. cis-retinal isomerization of

binds to photopigments

opsin

trans

retinal

3. retinal isomerase

converts trans to

cis 2. Trans-retinal

separates from opsin

The Cyclic Bleaching & Regeneration of

Photopigments

Light Adaptation

• emerging from a darkened room, visual system

decreases its sensitivity

Dark Adaptation

• entering a darkened room, visual system

increases its sensitivity

The Visual Pathway

Cornea

pupil

iris

photoreceptors

ganglion cells

bipolar cells

thalamus

visual cortex ( occipital lobe)

Keratitis

Mydriasis

Nystagmus

Strabismus

The EAR : Hearing & Equilibrium

3 Principal Regions of the Ear:

• external ear

• middle ear

• internal ear

External Ear

auricle

pinna

external auditory canal

eardrum

Middle Ear

malleus

incus

stapes

oval window

round window

tensor tympani

muscles

stapedius

Eustachian tube

Inner Ear

2 main divisions

• bony labyrinth

– semicircular canal contain

(crista ampullaris & cupula) receptors for

– vestibule equilibrium

– cochlea: receptors for hearing

• membranous labyrinth

– K+

– utricle and saccule

Cochlea

– snail-shaped

spiral organ of Corti

– coiled sheet of epithelial cells

– 16,000 hair cells ( receptors for hearing)

The Nature of Sound Waves

sound waves

pitch

decibels

conduction deafness

sensorineural deafness

The Physiology of Hearing

Auricle

External auditory canal

Malleus

Incus

Stapes

Oval window

Scala vestibuli

Scala tympani

Round window

vestibular membrane

endolymph in cochlea

basilar membrane

stereocilia

generation of action

potential

Auditory Pathway

External auditory canal

tympanic membrane

auditory ossicles

oval window

cochlea

organ of Corti

Mechanisms of Equilibrium

Vestibular Apparatus

• arm for static equilibrium

• arm for dynamic equilibrium

utricle, saccule, and the three semicircular canals.

The saclike utricle and saccule sense the body's

relationship to gravity, or its static equilibrium.

A person knows that the body is right side up because

these structures relay messages about the body's position

to the brain. Both sacs are hollow. Hairlike nerve endings

are anchored into the inner surface of each structure. The

free ends of the nerve endings project into the hollow

space.

Tiny particles of limestone, known as otoliths, rest against

the bottom of each sac.

If the head moves, the otoliths change position. In shifting,

they pass over sensitive nerve endings. These send

immediate impulses to the brain. Notified of a change in

body position, the brain triggers the reflex mechanisms to

correct the position of the body .

Disorders of the Ear

Meniere’s disease

• due to increased amount of endolymph

• fluctuating hearing loss

• roaring tinnitus

• spinning or whirling vertigo

Otitis media

• acute infection of middle ear

PICTURE OF TYMPANIC MEMBRANE

PERFORATION

AURICLE KELOID

AURICULAR ABSCESS

Auricle Perichondritis

Static and Dynamic Equilibrium

vestibular apparatus –• functional components of the

membranous labyrinth involved in

the sensations of static and dynamic

equilibrium are a system of thin-

walled intercommunicating tubes

and ducts situated within the petrous

part of the temporal bone at the

base of the skull;

• there are five vestibular structures,

each containing a specialized

mechanoreceptor, a maculae, within

the utricle and saccule, and a cristae

within the ampullae of the superior,

horizontal, and posterior

semicircular canals.

vestibule –

The central cavity of the bony

labyrinth of the ear containing the

functional components of the

membranous labyrinth involved in

the sensations of static

equilibrium which are two

vestibular structures, each

containing a specialized

mechanoreceptor, a maculae,

within the utricle and saccule.

saccule - The smaller of the two

membranous sacs in the vestibule

of the inner ear; it contains a

specialized mechanoreceptor, a

maculae, for the detection of static

equilibrium.

.

utricle - The larger of the two

membranous sacs in the vestibule

of the inner ear; it contains a

specialized mechanoreceptor, a

maculae, for the detection of static

equilibrium.

static equilibrium - The special sense

which interprets the position of the

head permitting the CNS to maintain

stability and posture when the head

and body are not moving; it is detected

by mechanoreceptors in the vestibule

of the inner ear, the utricle and

saccule, which each contain a macula

with the receptors for static

equilibrium; when the head moves with

reference to gravity, the otolithic

membrane shifts and the

mechanoreceptors (hair cells) in the

macula detect this movement and send

the information along the vestibular

nerve to the brain for interpretation

("which way is up").

maculae - The specialized

mechanoreceptors within the

utricle and saccule for the

detection of static

equilibrium; they make use

of hair cells to detect

movements of the otolithic

membrane; the nerve

impulses thus generated are

transmitted along the

vestibular branch of cranial

nerve VIII to the CNS.

otolithic membrane - The gelatinous covering of macula of the utricle

and saccule of the vestibular apparatus which has many crystals of

calcium carbonate (otoconia or otoliths); their movements in response to

changes in the position of the head with reference to gravity stimulate the

hair cells to send nerve impulses to the CNS which are interpreted as

information about static equilibrium.

Dynamic Equilibrium

dynamic equilibrium –

The special sense which interprets balance when one is moving,

or at least the head is moving;

the semicircular canals contain the receptors for dynamic

equilibrium; within each semicircular canal is a complex

mechanoreceptor called a crista ampullaris which contains the

mechanoreceptors (Hair cells) for dynamic equilibrium;

when the perilymph in one of the semicircular canals moves, the

hair cells in the crista ampullaris are stimulated to send nerve

impulses to the brain;

this advises the brain of whether or not a person has their

balance during body movements or if their body is in motion,

e.g, riding in a car or turning one's head from side to side.

semicircular canals - The functional components of the membranous labyrinth, a series of three

interconnected perilymph-filled tubes with enlarged ends, involved in the sensations of dynamic

equilibrium; the contain the cristae ampullaris which detect acceleration in the three

perpendicular planes (superior, horizontal, and posterior); these accelerometers make use of hair

cells similar to those on the organ of Corti, but these hair cells detect movements of the fluid in the

canals caused by angular acceleration about an axis perpendicular to the plane of the canal; tiny

floating particles aid the process of stimulating the hair cells as they move with the fluid; the nerve

impulses thus generated are transmitted along the vestibular branch of cranial nerve eight to the

CNS.

ampulla - The dilation or expanded

end of each of the semicircular

canals of the vestibular apparatus

which contains the specialized

mechanoreceptor structure, the

crista, which detect acceleration in

the planes of the canal; these

accelerometers make use of hair

cells to detect movements of the

fluid in the canals caused by

angular acceleration about an axis

perpendicular to the plane of the

canal; the nerve impulses thus

generated are transmitted along the

vestibular branch of cranial nerve

eight to the CNS.

crista ampullaris - Within the

ampulla of each semicircular canal

is a complex mechanoreceptor

structure, the crista ampullaris; the

ampulla has a ridge covered by

neuroepithelium consisting of

sensory hair cells and supporting

cells; the hair cells attached to a

gelatinous mass, the cupula, which

rests on top of the crista ampularis;

when the perilymph in one of the

semicircular canals moves, the hair

cells in the crista ampullaris are

stimulated to send nerve impulses

to the brain; this advises the brain of

whether or not a person has their

balance during body movements or

if their body is in motion, e.g, riding

in a car.

vestibular nerve - The division of

the vestibulocochlear (eighth)

cranial nerve which conducts

sensory information regarding static

and dynamic equilibrium from the

vetibular apparatus of the inner ear

to the various centers of the CNS

which process and integrate that

information with visual and

proprioception.

THE SENSE OF TOUCH

The sense of touch is the name given to a network of nerve endings that reach just about every part of our body. These sensory nerve endings are located just below the skin and register light and heavy pressure on the skin and also differences in temperature. These nerve endings gather information and send it to the brain