special senses

special senses

“traditional” senses—

smell, taste, sight, and

hearing

special sense receptors

are either

large, complex sensory organs (eyes and ears) or

localized clusters of receptors (taste buds and

olfactory epithelium).

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.

Basilar membrane

vibrates in response to sound and stimulates hair cells.

Tectorial membrane

lies over the hair cells; bending against it helps stimulate them.

Cochlear nerve

carries hearing impulses to the brain.

Chemoreceptors

receptors that respond to chemicals in solution.

Olfactory receptors

smell receptors in the roof of the nasal cavity.

Olfactory hairs

cilia on olfactory receptor cells that detect odor chemicals.

Olfactory filaments

bundles of axons that carry smell impulses

olfactory nerve

carries smell signals to the brain.

Taste buds

receptors for taste

Papillae

tongue projections that contain taste buds

vallate papillae

large round papillae near the back of the tongue.

Fungiform papillae

mushroom-shaped papillae on the tongue.

Foliate papillae

leaf-shaped folds on the sides of the tongue.

Gustatory cells

taste receptor cells.

Gustatory hairs

the microvilli of gustatory cells.

Taste pore

the small opening where chemicals enter a taste bud.

Facial nerve

cranial nerve VII; carries taste from the front part of the tongue.

Glossopharyngeal nerve

cranial nerve IX; carries taste from part of the tongue and throat.

Vagus nerve

cranial nerve X; carries taste from areas in the throat.

basal cells

cells that replace old taste bud cells.

presbyopia

ults from decreasing lens elasticity that

accompanies aging. This condition makes it difficult to focus for close vision; it is basically farsightedness. Your grandmother holding a magazine at

arm’s length to read it provides a familiar example

of this developmental change in vision.

presbycusis

, is a type of sensorineural deafness. I