special senses

special senses

“traditional” senses—

smell, taste, sight, and

hearing

Conduction Deafness:

Occurs when sound wave

transmission through the outer or

middle ear is hindered.

Causes: Impacted cerumen,

otosclerosis (fusion of ossicles),

perforated eardrum, otitis media.

Sensorineural Deafness

Results from damage to neural

structures anywhere from the

cochlear hair cells to the auditory

cortex.

Causes: Extended exposure to

loud sounds, presbycusis (agerelated hair cell degeneration),

ototoxic medications (e.g.,

aminoglycoside antibiotics, highdose furosemide).

vertigo

A sensation of spinning

caused by vestibular system

impairment

Ménière's Syndrome

Chronic

inner ear disorder characterized

by progressive deafness, tinnitus

(ringing), and severe vertigo due

to excess endolymph

accumulation.

Sweet

Carbohydrates, simple

sugars

Signals calorie-rich energy sources

Sour

Acidic compounds (𝐻+)

Warns against spoilage/unripe

food; regulates pH balance

salty

Sodium chloride (𝑁𝑎

+

)

Ensures essential

electrolyte/osmotic balance

bitter

Alkaloids, nitrogenous

compounds

Natural defense mechanism

against toxic or poisonous plants

umami

Glutamate, protein

hydrolysates

Drives intake of essential dietary

proteins

Sound Collection

Outer Ear

Pinna funnels sound waves into the external acoustic meatus.

Tympanic

Vibration

Eardrum

Sound waves strike the tympanic membrane, setting it into

vibration.

Ossicular

Conduction

Middle Ear

Malleus → Incus → Stapes amplify and transmit vibrations to the

oval window.

Fluid Wave

Generation

Inner Ear

Stapes pushes the oval window, generating pressure waves in the

perilymph and endolymph.

Organ of Corti

Activation

Cochlea

Fluid waves push the basilar membrane, pressing hair cell cilia

against the tectorial membrane.

Signal

Transmission

Brain

Bending of hair cells fires action potentials along the cochlear

nerve (CN VIII)to the primary auditory cortex in the temporal lobe

Dynamic Equilibrium

Receptor Organ: Crista

Ampullaris located in the

swollen base (ampulla) of

each semicircular canal.

• Function: Responds to

angular or rotational

movements of the head

(e.g., spinning, turning,

tumbling).

refraction

Cornea ⟶ Aqueous Humor ⟶ Pupil / Lens ⟶ Vitreous Humor ⟶

Retina

• Accommodation: Ciliary muscle

contraction relaxes suspensory

ligaments, allowing the flexible lens to

bulge for near-object focusing (< 20 feet).

• Retinal Image Formation: The image

formed on the retina is a Real Image—

inverted (upside-down), reversed left-toright, and smaller than actual size.

Photopupillary Reflex

Bright light

triggers parasympathetic

constriction of pupils via CN III to

protect photoreceptors.

Photopupillary Reflex

Bright light

triggers parasympathetic

constriction of pupils via CN III to

protect photoreceptors.

• Accommodation Pupillary

Reflex

Pupils constrict when

shifting focus from distant to near

targets to sharpen visual focus.

Convergence Reflex

Medial

rotation of both eyeballs via extrinsic

muscles to keep close targets

centered on both foveae.

special sense receptors

are either

large, complex sensory organs (eyes and ears) or

localized clusters of receptors (taste buds and

olfactory epithelium).

Static Equilibrium

Organ: Maculae located within

the saclike membrane structures

of the vestibule (utricle and

saccule).

• Function: Evaluates the position

of the head in space relative to

gravity when the body is not

moving (linear

acceleration/deceleratio

Mechanism of Action:

• Hair cells embedded in a jellylike otolithic membrane.

• The membrane is studded with tiny

calcium carbonate crystals

called otoliths ("ear stones").

• When the head tilts, gravity pulls the

heavy otoliths, causing the otolithic

membrane to slide over the hair cells.

• Bending of the hair cell cilia triggers

nerve impulses sent via the vestibular

division of CN VIII to the cerebellum

eyelids

movable folds of skin that protect the eye.

Conjunctiva

a thin membrane that lines the eyelids and covers part of the eyeball.

Lacrimal apparatus

structures that produce and drain tears.

Medial commissure

the inner corner where the eyelids meet.

Lateral commissure

the outer corner where the eyelids meet.

extrinsic

eye muscles, eyelids, conjunctiva, and lacrimal

apparatus

accessory structures of the eye

eyelashes

hairs at the edge of the eyelids that help protect the eye

tarsal glands

modified sebaceous glands in the eyelids that secrete oily fluid.

Ciliary glands

modified sweat glands near the eyelashes.

eyeball

is a hollow

sphere (Figure 8.4, p. 308). Its wall is composed

of three tunics, or layers, and its interior is filled

with fluids called humors that help to maintain its

shape.

Fibrous layer

the outer layer of the eyeball.

Sclera

the thick white connective tissue seen as the “white of the eye.”

Cornea

the transparent front part of the eye where light enters.

Vascular layer

the middle layer of the eyeball.

Choroid

the blood-rich, pigmented part of the vascular layer.

Ciliary body

smooth muscle structure in the vascular layer that helps support the lens.

Ciliary zonule

another name for the suspensory ligament.

Iris

the colored part of the eye that controls light entry.

Pupil

the opening in the iris through which light passes.

sensory layer

the innermost layer of the eyeball.

retina

the delicate inner layer of the eye that contains light-sensitive cells.

Pigmented cells

cells in the outer retina that absorb light.

neural layer

transparent inner of retina that contains receptor cells

cones and rods

photoreceptors

bipolar cells

neurons that pass signals from photoreceptors to ganglion cells.

Ganglion cells

neurons that carry signals out of the retina.

Optic nerve

the nerve that carries visual signals from the retina to the brain.

Optic disc

the point where the optic nerve leaves the eyeball; it has no photoreceptors.

Blind spot

the area with no visual detection because the optic disc lacks photoreceptors.

refracted

When light passes from one substance to another

substance that has a different density, its speed

changes and its rays are bent,

accomodation

ability of the eye to focus specifically for close objects (those less than 20 feet

away)

real image

The image

formed on the retina as a result of the light-bending

activity of the lens

Lateral rectus

Moves eye laterally, VI (abducens)

Medial rectus

Moves eye medially, III (oculomotor)

Superior rectus

Elevates eye and turns it medially, III (oculomotor)

Inferior rectus

Depresses eye and turns it medially, III (oculomotor)

Inferior oblique

Elevates eye and turns it laterally,

III (oculomotor)

Superior oblique

Depresses eye and turns it laterally,

IV (trochlear)

optic chiasma

the fibers from the medial side of each eye cross

over to the opposite side of the brain.

optic tract

bundles of nerve fibers that carry visual information from the optic chiasm to the lateral geniculate nucleus of the thalamus. They are part of the visual pathway.

Optic radiation

the bundle of nerve fibers that carries visual information from the lateral geniculate nucleus to the primary visual cortex in the occipital lobe. It is also called the geniculocalcarine tract.

convergence

which is the reflexive movement

of the eyes medially when we view close objects.

When ______ occurs, both eyes are aimed

toward the near object being viewed

photopupillary reflex

When the eyes are suddenly exposed to bright

light, the pupils immediately constrict; this is the

________. This protective reflex prevents excessively bright light from damaging the

delicate photoreceptors.

accommodation pupillary

pupils also constrict

reflexively when we view close objects; this

______ reflex provides more

acute vision

mechanoreceptors

Receptors that

respond to such physical forces are

the machinery for hearing and

balance

External ear / outer ear

the part of the ear made up of the auricle and external acoustic meatus.

auricle

the visible shell-shaped part of the ear; also called the pinna.

External acoustic meatus

another name for the auditory canal; conducts sound inward.

Ceruminous glands

produce earwax.

Tympanic membrane

vibrates when sound waves strike it. eardrum

Middle ear cavity

transmits sound vibrations from the eardrum to the inner ear. tympanic cavity

Oval window

receives vibrations from the stapes and passes them into the inner ear.

Round window

helps relieve pressure in the inner ear fluids.

Pharyngotympanic tube

equalizes air pressure between the middle ear and throat. Auditory tube

Ossicles

transmit and amplify sound vibrations.

Malleus

passes vibration from the eardrum to the incus.

Incus

passes vibration from the malleus to the stapes.

Stapes

transfers vibrations to the oval window.

internal ear / inner ear

contains hearing and balance organs.

Cochlea

contains hearing receptors and converts vibrations into nerve signals.

Vestibule

helps with balance and connects cochlea to semicircular canals.

Semicircular canals

detect head movement and help maintain balance.detect head movement and help maintain balance.

Perilymph

fluid that surrounds the membranous labyrinth and helps transmit movement.

Membranous labyrinth

contains the sensory structures for hearing and balance.

Endolymph

fluid inside the membranous labyrinth that helps sensory function.

Equilibrium

helps the body maintain balance and sense head movement.

Vestibular apparatus

the inner ear system that detects equilibrium.

Maculae

receptor areas that detect changes in head position and gravity.

Otolithic membrane

the gelatinous layer that holds the hair cell hairs and otoliths.

Vestibular nerve

carries balance information from the inner ear to the brain.

dynamic equilibrium

receptors, found in

the semicircular canals, respond to angular or

rotational movements of the head rather than to

straight-line movements. When you twirl on the

dance floor or suffer through a spinning carnival

ride, these receptors are working overtime

Crista ampullaris

receptor region that senses dynamic equilibrium.

Cupula

gelatinous cap over the crista ampullaris that bends with fluid movement

cochlear duct

contains the organ of Corti and endolymph.

Spiral organ of Corti

the main hearing receptor organ in the cochlea.