Chapter 12- Equilibrium and Eyes

mechanoreceptors in semicircular canals

rotational equilibrium

mechanoreceptors in vestibule

gravitational equilibrium

parts associated with equilibrium

proprioreceptors in muscles + joints, photoreceptors, cerebellum, ear

gravitational (static)

depends on uricle and saccule in vestibule, contains hair cells with steriocillia embedded in otolithic membrane

uricle

sensitive to horizontal movements

saccule

senstiive to veritcal movements

otoliths

calcium carbonate structures in ears, detect gravity and tilt

when head moves

otoliths displace and membrane is disturbed, steriocillia head toward or away from kinocillium

cerebellum + brain centers

use sensory info to maintain balance

rotational (dynamic)

semicircular canals, contains hair cells with steriocillia embedded in cupula

ampula

enlarged base of 3 canals, each responds to head rotation in different place of space

capula

displaced causes steriocillia to bend creatine changes in nerve impulses traveling through vestibular nerve to brain

vision

eyelids, eyelashes, lacrimal apparatus, extrinsic eye muscles

eyebrow

shade from sun + protect from perspiration/debris

eyelids

continuations of the skin, keep eye lubricated

conjunctiva

inner eyelid, and anterior surface of eye except cornea, protects eye

eyelashes

block debris

glands

secretions lubricate eye

lacrimal apparatus

produce tears in glands, collect in lacrimal sac and drain into nose by nasolacrimal duct

eye upward

CN III, sup rect

eye downward

CN III inf rect

eye outward

CN VI lat rect

eye inward

CIII med rect

eye counterclockwise

CN IV sup obl

eye clockwise

CN III inf obl

eye anatomy

sclera, choroid, lens, retina, optic nerve, photoreceptors

sclera

outer coat, white and fibrous

cornea

transparent window to the world

choroid

middle lyer, vasculairze, becomes iris

iris

front colored portion, regulates pupil size

ciliary body

behind iris, contains muscle that controls shape of lens

lens

focuses image on retina, divides eye in 2 compartments, anterior + posterior

anterior eye compartment

aqueous humor

posterior eye compartment

retina + vitreous humor

retina

inner coat, contains photoreceptors

optic nerve

formed from sensory fibers in retina

photoreceptors

in retina, rods and cones

rod cells

night + peripheral vision

cone cells

colors, fovea centralis

fovea centralis

cone cells are densely packed

accomodation

focusing objects on retina, lens changes shape

ciliary muscles

relaxes and contracts to change lens

ciliary relaxes

distant image, tightens suspensory ligaments and flattens lens

ciliary contracts

near image, loosens suspensory ligament, lens bulges

refraction

heading light waves passing at angle between mediums off diff densities

convex lens

light waves comverge (cornea + lens)

concave lens

light waves diverge

focusing

bends light so image falls on fovea capitis in eye

image in retina

upside down and reversed visual cortex corrects it

abnormalities

myopia, hyperopia, astigmatism

myopia

near-sightedness, elongated eyeball, far focuses in front of retina, correct with concave

hyperopia

far-sightedness, short eyeball, near focuses behind retina, correct with convex

astigmatism

oval shaped cornea or irregular lens, lens ground to compensate

visual pigments

rhodopsin, one in rods, 3 in cones

cones rhodopsin

red blue and green, color blindness is absence of color pigments

rods and cones absord light

rhodopsin splits into opsin and retinal

light stimulus

stops release of neurotransmitter molecule from synaptic vesicles, nerve impulses travel to visual cerebral cortex

optic nerve

carry impulses to chiasma

chiasma

where nerves cross paths

fibers

stay on their respective right/left sides; synpase in thalamus

visual axons

carry impulse to visual areas of occipital lobes by optic radiations, visual cortex rebuilds image