Special Senses AQ

St. Clair College Continuing Education

Abdul Qadeer MBBS, DTM, MPH,CPHI(C), CIC

Special Senses

ESSENTIALS

OF HUMAN

ANATOMY&

PHYSIOLOGY


The Senses

General senses

Mixture of touch senses

Temperature

Pressure

Pain


The Senses

Special senses

Smell

Taste

Sight

Hearing

Equilibrium


The Eye and Vision

70% of all sensory receptors are in the eyes

Each eye has over a million nerve fibers

Protection for the eye

Most of the eye is enclosed in a bony orbit

A cushion of fat surrounds most of the eye


Accessory Structures of the Eye

Eyelids and eyelashes

Conjunctiva

Lacrimal apparatus

Extrinsic eye muscles



Figure 8.1



Eyelids and eyelashes

Tarsal glands lubricate the eye and located

with in the eyelid edges

modified sebaceous glands

Ciliary glands are located between the

eyelashes

modified sweat glands

Both protect the eye



Conjunctiva

Membrane that lines the eyelids

Connects to the surface of the eye

Secretes mucus to lubricate the eye

Conjunctivitis and Pink eye is bacterial or viral

inflammation of the conjunctiva



Lacrimal apparatus

Lacrimal gland—produces lacrimal fluid

Lacrimal canals—drain lacrimal fluid from eyes

Lacrimal sac—provides passage of lacrimal fluid

towards nasal cavity

Nasolacrimal duct—empties lacrimal fluid into

the nasal cavity



Figure 8.2a



Figure 8.2b



Function of the lacrimal apparatus

Protects, moistens, and lubricates the eye

Empties into the nasal cavity

Blockage of the lacrimal apparatus

Inflamation of nasal mucosa result in swelling

of lacrimal duct and impair drainage of

lacrimal fluid causing watery eyes



Properties of lacrimal fluid

Dilute salt solution (tears)

Contains antibodies

Contains lysozyme

bactericidal



Extrinsic eye muscles

Six muscles attach to the outer surface of the

eye

Produce eye movements



Figure 8.3a–b



Figure 8.3c


Question

What is the role of the eyelid?

Which structure of the eye form tears?

What are tears?

What is the visual role of the external eye muscle?


Structure of the Eye

Layers forming the wall of the eyeball

Fibrous layer

Outside layer

Vascular layer

Middle layer

Sensory layer

Inside layer



Figure 8.4a



Figure 8.4b

Photograph


Structure of the Eye: The Fibrous Layer

Sclera

White connective tissue layer

Seen anteriorly as the “white of the eye”

Cornea

Transparent, central anterior portion

Allows for light to pass through

Repairs itself easily

The only human tissue that can be

transplanted without fear of rejection


Structure of the Eye: Vascular Layer

Choroid is a blood-rich nutritive layer in the

posterior of the eye

Pigment prevents light from scattering

Modified anteriorly into two structures

Ciliary body—smooth muscle attached to

lens

Iris—regulates amount of light entering eye

Pigmented layer that gives eye color

Pupil—rounded opening in the iris


Structure of the Eye: Sensory Layer

Retina contains two layers

Outer pigmented layer

Inner neural layer

Contains receptor cells that respond to

light (photoreceptors)

Rods

Cones



Signals pass from photoreceptors via a two-

neuron chain

Bipolar neurons

Ganglion cells

Signals leave the retina toward the brain through

the optic nerve

Optic disc (blind spot) is where the optic nerve

leaves the eyeball

Cannot see images focused on the optic disc

b/c photoreceptors are absent in the optic

disc



Figure 8.5a



Figure 8.5b



Neurons of the retina and vision

Rods

Most are found towards the edges of the retina

Allow dim light vision and peripheral vision

All perception is in gray tones

Interferences with rod function result in night blindness

Vit. A deficiency

Almost exclusively in males



Neurons of the retina and vision

Cones

Allow for detailed color vision

Densest in the center of the retina

Fovea centralis—area of the retina with

ONLY cones

No photoreceptor cells are at the optic disc, or

blind spot



Cone sensitivity

Three types of cones

Different cones are sensitive to different

wavelengths of visible light

1st blue, 2nd green and 3rd range from

green & red

Color blindness is the result of the lack of one

cone type


Sensitivities of Cones to Different Wavelengths

Figure 8.6


Lens

Biconvex crystal-like structure

Held in place by a suspensory ligament attached

to the ciliary body


Lens

Figure 8.4a


Lens

Lense is Transparent in youth

Cataracts result when the lens becomes hard

and opaque with age

Vision becomes hazy and distorted

Eventually causes blindness in affected eye

Surgical removal of the affected lens and

implant of new lens


Lens

Figure 8.7


Two Segments, or Chambers, of the Eye

Anterior (aqueous) segment

Anterior to the lens

Contains aqueous humor

Posterior (vitreous) segment

Posterior to the lens

Contains vitreous humor


Anterior Segment

Aqueous humor

Watery fluid found between lens and cornea

Similar to blood plasma

Helps maintain intraocular pressure

Provides nutrients for the lens and cornea

Reabsorbed into venous blood through the

scleral venous sinus, or canal of Schlemm

Glaucoma result from blockage of aqueous

humor drainage


Posterior Segment

Vitreous humor

Gel-like substance posterior to the lens

Prevents the eye from collapsing inward by

reinforcing internally

Helps maintain intraocular pressure


Ophthalmoscope

Instrument used to illuminate the interior of the

eyeball and fundus (posterior wall)

Can detect by examination

diabetes

arteriosclerosis

degeneration of the optic nerve and retina


Posterior Wall of Retina (Fundus) as Seen with

Ophthalmoscope

Figure 8.8


Question

What is the meaning of the term blind spot in

relation to the eye?

What function does the choroid of the vascular

layer have in common with the pigmented layer of

the retina?

How do the rods and cones differ from each other?


Pathway of Light Through the Eye

Light must be focused to a point on the retina for optimal

vision

Passes through the lens and refracted

The eye is set for distance vision

(over 20 feet away)

Rays are paralell

Lens does not change shape

Accommodation—the lens must change shape to focus on

closer objects (less than 20 feet away)

Rays are scattered

Lens change shape (more convexity), become thick



Figure 8.9



Image formed on the retina is a real image

Real images are

Reversed from left to right

Upside down

Smaller than the object

Farther away the object, smaller the image


Images Formed on the Retina

Figure 8.10


Visual Fields and Visual Pathways

Optic chiasma

Location where the optic nerves cross

Fibers from the medial side of each eye cross

over to the opposite side of the brain

Optic tracts

Contain fibers from the lateral side of the eye

on the same side and the medial side of the

opposite eye


Figure 8.11

Visual Fields and Visual Pathways


Eye Reflexes

Internal muscles are controlled by the autonomic

nervous system

Bright light causes pupils to constrict through

action of radial, circular, and ciliary muscles

Photopupillary reflex

Viewing close objects causes accommodation

Accommodation pupillary reflex

External muscles control eye movement to follow

objects

Viewing close objects causes convergence (eyes

moving medially)


A Closer Look

Emmetropia—eye focuses images correctly on

the retina

Myopia (nearsighted)

Distant objects appear blurry

Light from those objects fails to reach the

retina and are focused in front of it

Results from an eyeball that is too long


A Closer Look

Hyperopia (farsighted)

Near objects are blurry while distant objects

are clear

Distant objects are focused behind the retina

Results from an eyeball that is too short or

from a “lazy lens”


A Closer Look


A Closer Look

Astigmatism

Images are blurry

Results from light focusing as lines, not

points, on the retina due to unequal

curvatures of the cornea or lens


Homeostatic Imbalances of the Eyes

Night blindness —inhibited rod function that

hinders the ability to see at night

Color blindness —genetic conditions that

result in the inability to see certain colors

Due to the lack of one type of cone (partial

color blindness)

Cataracts —when lens becomes hard and

opaque, our vision becomes hazy and distorted


Homeostatic Imbalances of the Eyes

Glaucoma —can cause blindness due to

increasing pressure within the eye

Hemianopia —loss of the same side of the

visual field of both eyes; results from damage to

the visual cortex on one side only


Question

What are the refractory media of the eye?

What name is given to the ability of the eye to focus

on close objects?

What is difference between the optic nerve and

optic tract?

In what way does the photopupillary reflex protect

the eye?


The Ear

Houses two senses

Hearing

Equilibrium (balance)

Receptors are mechanoreceptors

Physical forces required to stimulate

Different organs house receptors for each sense

and are activated independently of one another


Anatomy of the Ear

The ear is divided into three areas

External (outer) ear

Middle ear (tympanic cavity)

Inner ear (bony labyrinth)


Anatomy of the Ear

Figure 8.12


The External Ear

Involved in hearing only

Structures of the external ear

Auricle (pinna)

External acoustic meatus (auditory canal)

Narrow chamber in the temporal bone

Lined with skin and ceruminous (wax)

glands

Ends at the tympanic membrane


The Middle Ear (Tympanic Cavity)

Air-filled cavity within the temporal bone

Only involved in the sense of hearing


The Middle Ear (Tympanic Cavity)

Two tubes are associated with the inner ear

The opening from the auditory canal is

covered by the tympanic membrane

The auditory tube connecting the middle ear

with the throat

Allows for equalizing pressure during

yawning or swallowing

This tube is otherwise collapsed

Otitis media


Bones of the Middle Ear (Tympanic Cavity)

Three bones (ossicles) span the cavity

Malleus (hammer)

Incus (anvil)

Stapes (stirrip)

Function

Vibrations from eardrum move the malleus

anvil stirrup inner ear


Anatomy of the Ear

Figure 8.12


Inner Ear or Bony Labyrinth

Includes sense organs for hearing and balance

Filled with perilymph (plasma like fluid)

A maze of bony chambers within the temporal

bone

Cochlea

Vestibule

Semicircular canals


Anatomy of the Ear

Figure 8.12


Organs of Equilibrium

Equilibrium receptors of the inner ear are called

the vestibular apparatus

Vestibular apparatus has two functional parts

To monitor

Static equilibrium

Dynamic equilibrium


Organs of Equilibrium

Figure 8.14a–b

Vestibular apparatus


Static Equilibrium

Maculae—receptors in the vestibule

Report on the position of the head at rest

Provide information about up or down

Send information via the vestibular nerve

Anatomy of the maculae

Each macula is a patch of receptor (Hair) cells that are embedded in the otolithic hair membrane

Otoliths (tiny calcium salt stones) float in a gel around the hair cells

Movements cause otoliths to bend the hair cells


Structure and Function of Maculae

Figure 8.13a


Structure and Function of Maculae

Figure 8.13b


Dynamic Equilibrium

Crista ampullaris (with in ampula)—receptor

region in the semicircular canal that respond to

angular or rotatory movement of the head

Consist of

Tuft of hair cells

Cupula (gelatinous cap) covers the hair

cells


Dynamic Equilibrium

Figure 8.14c


Dynamic Equilibrium

Action of angular head movements

The cupula stimulates the hair cells

An impulse is sent via the vestibular nerve to

the cerebellum

Bending the cupula in the opposite direction

reduces impulse generation

Signals from receptors stop during movement

at constant rate, until speed or direction of the

movement changes


Question

What senses do the vestibule and semicircular

canals serve?

Which equilibrium receptors are operating

furiously during a rough voyage?

What are otoliths, and what is their role in

equilibrium?


Organs of Hearing

Organ of Corti

Located within the cochlea

Receptors = hair cells on the basilar membrane

Gel-like tectorial membrane is capable of

bending hair cells

Cochlear nerve attached to hair cells transmits

nerve impulses to auditory cortex on temporal

lobe

Scalae = chamber above and below the

cochlear duct contain perilymph


Organs of Hearing

Figure 8.15a


Organs of Hearing

Figure 8.15b


Mechanism of Hearing

Vibrations from sound waves move tectorial

membrane

Hair cells are bent by the membrane

An action potential starts in the cochlear nerve

Continued stimulation can lead to adaptation

Sounds that reach the auditory receptors tend

to adapt or stop responding and we are no

longer aware of them



Figure 8.16a



Figure 8.16b–c


Homeostatic Imbalance of Hearing & Equilibrium

Deafness—hearing loss of any degree, from a

slight loss to a total inability to hear sound

Conduction deafness—due to interference with

the conduction of sound vibration to the fluid of

inner ear

Temporary – wax

Permanent – otosclerosis (fusion of ossicles)

Sensorineural deafness—due to damage to the

receptor cells in the organ of corti, cochlear

vnerve, or neuron of the auditory cortex

Extended listening to loud sound


Homeostatic Imbalance of Hearing & Equilibrium

Meniere’s syndrome—progressive deafness

Arteriosclerosis

Degeneration of cranial verve VIII

Increased pressure of the inner ear fluid

Vertigo—sensation of spinning


Quection

From the air outside the body, through what

substance do sound waves travel to excite the

receptor cells of the cochlea?

Which nerve transmits impulses from the spiral

organ of the corti to the brain?

Do high pitched sounds peak close to or far from

the oval window?

How do conduction deafness differ from the

sensorineural deafness?


Olfaction—The Sense of Smell

Olfactory receptors are in the roof of the nasal

cavity

Neurons with long cilia—olfactory hair cells

Chemicals must be dissolved in mucus for

detection

Impulses are transmitted via the olfactory nerve

(cranial nerve I)

Interpretation of smells is made in the cortex

Anosmias—loss of smell


Olfactory Epithelium

Figure 8.17


The Sense of Taste

Taste buds house the receptor organs

Location of taste buds

Most are on the tongue

Soft palate

Cheeks


Taste Buds

Figure 8.18


The Tongue and Taste

The tongue is covered with projections called

papillae

Fungifiorm papillae—rounded with taste buds

Circumvallate papillae—large papillae with

taste buds

Taste buds are found on the sides of papillae


Structure of Taste Buds

Gustatory cells are the receptors

Have gustatory hairs (long microvilli)

Hairs are stimulated by chemicals dissolved in

saliva


Structure of Taste Buds

Impulses are carried to the gustatory complex by

several cranial nerves because taste buds are

found in different areas

Facial nerve

Glossopharyngeal nerve

Vagus nerve


Taste Sensations

Sweet receptors

Sugars &Saccharine

Some amino acids

Sour receptors

Acids

Bitter receptors

Alkaloids

Salty receptors

Metal ions


Question

What name is used to describe both taste and

smell receptors? Why?

Where, relative to specific structures, are most

taste buds located?

Why does it help to sniff substances you are

smelling?


Developmental Aspects of the Special Senses

Formed early in embryonic development

Eyes are outgrowths of the brain

All special senses are functional at birth


Chemical Senses: Taste and Smell

Both senses use chemoreceptors

Stimulated by chemicals in solution

Taste has five types of receptors

Smell can differentiate a large range of

chemicals

Both senses complement each other and respond

to many of the same stimuli



Eye problems

Strabismus—“crossed eyes” results from

unequal pulls by the external eye muscles in

babies

Ophthalmia neonatorum—conjunctivitis

resulting from mother having gonorrhea.

Baby’s eyelids are swollen and pus is

produced



Eye problems

Presbyopia—“old vision” results from

decreasing lens elasticity that accompanies

aging



Ear problems

Presbycusis —type of sensorineural

deafness

Otosclerosis—ear ossicles fuse


Question

Which of the following is the blind spot, or

point where the optic nerve leaves the

back of the eyeball?

Optic foramina

Maculae

Optic disc

Sclera

The optic disc is the blind spot, or point where the optic nerve

leaves the back of the eyeball. The sclera is the tough, outer layer

of the eyeball.


Question

What is the condition in which the light rays entering the eyeball focus correctly on the retina?

Glaucoma

Myopia

Astigmatism

Emmetropia

Emmetropia is the condition in which the light rays entering the eyeball focus exactly on the retina. It means “harmonious vision.” Myopia is nearsightedness, and astigmatism is faulty vision due to imperfect curvature of the cornea.


Question

Which of the following is an enzyme

associated with the eye that destroys

bacteria?

Lysozyme

Sclerase

Gamma globulin

Interleukin

Lysozymeis an enzyme that destroys bacteria. This enzyme is

present in tears, sweat, and nasal secretions.


Question

Which of the following is the point of

sharpest vision?

Retina

Optic disc

Maculae

Fovea centralis

The point of sharpest vision is the fovea centralis. Anything

we wish to view critically is focused here.


Question

A modification of this vitamin is important to the formation of the pigment rhodopsin.

A

B

C

K

The protein opsin, and retinal, a product of vitamin A, are combined to form the purple pigment rhodopsin.


Question

Which of the following is a term used to

describe loss of the same side of the

visual field in both eyes which occurs in

some CVAs?

Glaucoma

Astigmatism

Hemianopia

Hyperopia

Hemianopia results in a person not being able to see past the

middle of his or her visual field on the side associated with the site

of the CVA.


Question

Which of the following is the covering of the eye?

a. canthus

b. conjunctiva

c. choroid

d. lacrimal canaliculus


Question

Which of the following are receptor cells in the

eye that sense color?

a. lateral rectus

b. ciliary zonule

c. rods

d. cones


Question

Nearsightedness is:

a. astigmatism

b. myopia

c. hyperopia

d. glaucoma


Question

Wax glands of the ear are called:

a. myobian

b. sebaceous

c. ceruminous

d. lacrimal


Question

Our sense of static equilibrium is dependent on

the

a. vestibular apparatus.

b. maculae.

c. semicircular canals.

d. crista ampullaris.


Question

In the eye, the decreasing lens elasticity that

comes with old age is called

a. astigmatism.

b. myopia.

c. strabismus.

d. presbyopia.

Special Senses AQ

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