Special Senses

Special senses

Taste, smell, sight, hearing

Touch is a

general sense

Taste

Testing the enviornment, ability to respond to dissolved molecules & ions

Taste Buds: form of chemoreceptor

respond to chemicals in aqueous solution (or liquid form)

Gustation (Sense of taste)

stimulated by soluble chemicals

Pathway from taste buds (Gustation)

cranial nerves to medulla to thalamus to gustatory center of parietal lobe (Cerebral Cortex

Papillae

small, round or cone-shaped protuberances on top of tongue that contain taste buds

taste buds are found in

pits around papilla of tongue

fungiform papilla (most common)

scattered throughout tongue; taste buds found mostly on top

foliate papilla on sides

taste buds on side of papilla

circumvallate (vallate) papilla

Few but large & round; taste buds in side walls

. Basic Taste Perceptions

Sweet, salt, sour, bitter and umami

spicy "hot" foods actually trigger

Pain receptors

taste triggers

salivation and gastric juice in the stomach

80% of taste perception involves

Smell

Olfaction

sense of smell

Olfactory Membrane (chemoreceptors)

in epithelium of nasal mucosa

olfactory receptor cells

dendrite endings called olfactory cilia increase surface area and distribute molecules

olfactory bulb →olfactory tracts

course posteriorly under the frontal lobes → then two primary pathways

From olfactory tract to

primary olfactory cortex of the temporal lobe for interpretation

odors must be in gaseous state, make it to

olfactory membrane & then dissolve in mucus layer to be detected

anosmia

complete loss of smell; may be due to a head injury or a lack of zinc

Vision

70% of all sensory receptors in the body are in the eyes!

conjunctiva

thin mucous membrane lining covers inside of eyelids; also on white of eye - lubricates, moistens surface

eyebrows

shade eyes from sunlight & protect from perspiration

eyelids

protection & some light screening

meibomian gland (tarsal glands)

releases sebum at edge of lids (sebaceous gland)

lacrimal caruncle

“fleshy elevation” that produces white, oily secretion, “sand” when dry

eyelashes

protect eyes from debris

conjunctivitis

infection of the conjunctiva; causes inflammation or \n pinkeye, highly contagious

Lacrimal apparatus

produces tears; lacrimal gland -above eye; ducts drain tears into nasal cavity

tears

water, salts, mucin - lubricates lysozyme - kills bacteria

Extrinsic eye muscles

for fine motor control

rectus muscles

superior, inferior, lateral and medial

oblique muscles

superior and inferior

diplopia

double vision from paralysis or weakness of muscles; also - alcohol

strabismus

cross-eyed from weak eye muscles, repairable until around age 6

fibrous tunic

outermost layer, avascular

sclera

posterior, white, dense connective tissue

cornea

anterior, transparent layer, allows light in

vascular tunic (uvea)

network of blood vessels -supplies blood & nutrients to eye \n tissue

vascular tunic (uvea) consists of

choroid, iris, & ciliary body

choroid area of network

posterior, dark (helps absorb light), rich in blood vessels

iris (rainbow)

anterior, thin smooth muscular diaphragm; colored part of the eye

pupil

opening in center, regulates light coming in

circular muscles: constrict pupil

a consensual, contralateral reflex of parasympathetic nervous system

radial muscles: dilate pupil

controlled by sympathetic nervous system – not consensual

pupillary reflex

pupil constricts in bright light, dilates - dim

ciliary body

produces aqueous humor (thin, watery solution in anterior chamber of eye – between cornea & iris)

nervous tunic

very important inner layer of photoreceptor cells called the "retina."

Retina (neural tunic)

inner layer of eye

outer dark pigmented layer

melanin reduces reflection, stores vitamin A

inner neural layer

transduces light impulses into neural signals for vision

Rods

sensitive in dim light, black and white, detect movement

Rhodopsin

pigment of retina and rods

Cones

Color, less sensitive to light

macula

highly pigmented area of retina

color vision

detect red, green, blue

Photoreceptors detect

light energy

rods use up to 100 bipolar cells to feed into

one ganglion cell to improve night vision

cones are 100X less sensitive to light, because

only 1-3 bipolar cells have their own straight-through connection to a ganglion; resulting in clearer focus

color blindness

deficiency or absence of pigments needed for functional cones, more in males

XY

always shows up in males

XX

females may be carriers if 1 X is okay

night blindness

lack of vitamin A for photoreceptors

retinitis pigmentosa

inherited, visual receptors deteriorate, results in blindness

retinal detachment

pigmented and nervous layers separate, blindness

wet” macular degeneration

abnormal blood vessels grow under macular retina; leak fluids and cause scarring in central retina

Chambers of eye

divided by lens and its suspensory ligaments into anterior/posterior cavities

anterior cavity

contains aqueous humor - clear fluid that supplies oxygen & nutrients to lens and cornea; maintains pressure

Anterior cavity divided into

Anterior and posterior chambers

anterior chamber

in front of iris (between cornea & iris)

posterior chamber

in back of iris (between iris & lens)

posterior cavity

contains transparent vitreous humor (clear gel which binds water) \n a. transmits light \n b. supports lens; holds retina in place \n c. maintains intraocular pressure of eyeball

Glaucoma

abnormal elevation of intraocular pressure – may crush retina & optic nerve

Lens

biconvex, transparent, elastic structure \n a. eyes set for distance vision: far point of vision usually 20 ft. \n b. accommodation: adjustments made to lens to allow for \n focusing for near point of vision (lens thicker – more refraction)

cataracts

cloudiness of lens as fibers of lens accumulate

myopia (nearsightedness)

light rays focus in front of retina, corrected by concave lenses corrected

hyperopia (farsightedness)

focus is behind retina, corrected by convex lenses

astigmatism

unequal curvature of lens or cornea; blurry areas

presbyopia

lens of eye becomes more rigid with aging (40+?) - near point of vision goes further out

optic disc (blind spot)

found where optic nerve & blood vessels leave eye

optic chiasma

ganglion axons cross over

External ear

auricle (pinna), external auditory canal (meatus), tympanic membrane (eardrum):

auricle (pinna)

directs sound waves

external auditory canal (meatus)

hairs & cerumen (wax) protect/ keep canal clean

tympanic membrane (eardrum):

vibrates with sound waves

Middle Ear bordered by tympanic membrane

air-filled, mucous lined chamber (tympanic cavity) in \n temporal bone and houses auditory ossicles (malleus, incus, stapes, hammer, anvil, stirrup)

Ossicles

(malleus, incus, stapes) transmit & amplify vibrations

pharyngotympanic tube

regulates pressure on either side of eardrum and connects middle ear to pharynx

otitis media

middle ear infections, may insert tube to drain fluid where bacteria thrive

Inner Ear

made up of membranous labyrinth inside an osseous labyrinth

perilymph

between two labyrinths (osseous labyrinth)

endolymph

inside membranous labyrinth (center)

cochlear duct lies between

oval and round window

cochlea “snail shaped” -houses

the organ of hearing vibrations of middle ear taken from stapes

Organ of Corti

has receptors called hair cells (on basilar membrane) \n that extend into endolymph of cochlear duct, between scalas

Nervous pathway

vestibulocochlear nerve → cerebellum → thalamus → cerebral cortex

temporal lobes

auditory cortices

Semicircular canals

function in dynamic equilibrium (help maintain equilibrium during movement)