UNIT 4 SPECIAL SENSES

lacrimal caruncle

contains glands producing thick secretions

conjunctiva

covers inner surface of eyelids & covers anterior surface of eye

conjunctivitis - pink eye

lacrimal gland

produces tears that contain an antibacterial enzyme (superior & lateral)

lacrimal sac

collect tears (inferior & medial)

nasolacrimal duct

delivers tears to nasal cavity

sclera

outer most layer

cornea

transparent part of outer layer of eye

iris

changes diameter of pupil, color of eye

pupil

controls the amount of light that enters eye

papillary muscles

change diameter of pupil

ciliary muscles

alter shape of lens to focus

ciliary body

contains ciliary muscle and ciliary processes which attach to suspensory ligaments of lens

suspensory ligaments

connect muscles to lens

choroid

vascular layer that separates fibrous and neural tunics, delivers oxygen and nutrients to retina

retina

contains visual receptors and associated neurons

pigmented retina

outer layer that absorbs light

neural retina

inner layer that contains photoreceptors

photoreceptors

cells that detect light

rods

highly sensitive to light, do not discriminate light colors

cones

provide color vision, densely clustered in fovea, at center of macula

macula

center of retina, all cones - no rods

fovea centralis

center of macula, sharpest vision

optic disc

medial to fovea, optic nerve and blood vessels enter and exit eye

blind spot

optic disc has no photoreceptors

anterior cavity

anterior to lens

anterior chamber

extends from cornea to iris

posterior chamber

between iris and lens

aqueous humor

fluid circulates within eye

intraocular pressure

fluid pressure in aqueous humor, retains eye shape

posterior cavity

posterior to lens

vitreous cavity

gelatinous mass located in posterior cavity, retains eye shape

lens

lies posterior to cornea, focuses light on retina

cataract

when lens has lost its transparency

accommodation

shape of lens changes to focus image on retina

image reversal

image on retina is upside down and backwards, brain reverses image

visual acuity

clarity of vision, normal rating is 20/20

myopia

nearsighted

hyperopia

farsighted

astigmatism

light passing through cornea and lens is not refracted properly, image is distorted

retinal

is synthesized from vitamin A

night blindness

results from deficiency of vitamin A

color blindness

inability to detect certain colors

visual pathway

photoreceptor → bipolar cell → ganglion cell → optic disc → optic nerve → optic chiasm → optic tract → superior colliculus & lateral geniculate → visual cortex of cerebral hemispheres

field of vision

each eye receives slightly different images

depth perception

interpretation of 3D relationships by comparing images from both eyes

auricle

provides directional sensitivity

tympanic membrane

eardrum

cerumen

earwax

auditory tube

permits equalization of pressures on either side of tympanic membrane

bony labyrinth

layer of dense bone

perilymph

fluid inside bony labyrinth, surrounds membranous

membranous labyrinth

soft tissue, fluid filled tubes

endolymph

fluid inside membranous labyrinth

saccule

monitors gravity and linear acceleration

utricle

monitors gravity and linear acceleration

semicircular canals

stimulated by movement of head

cochlea

bony chamber (snail)

oval window

connected to base of stapes, covers vestibular duct

vestibular duct (scala vestibuli)

provide sense of hearing

cochlear duct

provide sense of hearing

round window

covers tympanic duct

tympanic duct (scala tympani)

provide sense of hearing

equilibrium

balance, sensations provided by hair cells of vestibular complex

semicircular ducts

provide equilibrium, sensations - head movement

hair cells

basic receptors of inner ear, provide information about direction and strength of mechanical stimuli

anterior, posterior, and lateral semicircular ducts

ampulla with gelatinous cupula (contains the hair cells)

pathways for equilibrium sensations

1. vestibular ganglia

2. vestibular branch

3. vestibulochochlear nerve (VIII)

4. vestibular nuclei

functions of vestibular nuclei

1. integrates sensory information about balance and equilibrium from both sides of head

2. relay information from vestibular complex to cerebellum

3. relay information from vestibular complex to cerebral cortex provides conscious sense of head position and movement

4. send commands to motor nuclei in brain stem and spinal cord

nystagmus

have trouble controlling eye movements, caused by damage to brain stem or inner ear

meniere’s disease

dizziness, loss of balance, possible hearing loss

tinnitus - ringing in the ears

cochlear duct

lie between vestibular dict and tympanic duct, hair cells lie within organ of corti - contains basilar & tectorial membranes

basilar membrane

separates cochlear duct from tympanic duct, contain the hair cells

tectorial membrane

is attached to inner wall of cochlear duct

hearing process

1. sound waves arrive at tympanic membrane

2. tympanic membrane vibrates, malleus, incus, stapes

3. stapes at oval window establishes pressure waves

4. waves distort basilar membrane

5. vibration of hair cells against tectorial membrane

6. region and intensity of stimulation relayed to CNS

cochlear branch pathway

1. spiral ganglion → cochlear branch

2. medulla oblongata

3. dorsal and ventral cochlear nuclei

4. inferior colliculus

5. medial geniculate nucleus of thalamus

6. auditory cortex of temporal lobe