Lecture Quiz 5 Flashcards
What percentage of sensory receptors are in the eye?
70%
What protects the eye?
a cushion of fat
the bony orbit
What are the accessory structures to the eye?
eyebrows eyelids conjunctiva lacrimal apparatus extrinsic eye muscles
Give a general overview of the structure of the eyeball
slightly irregular hollow sphere with anterior and posterior poles
wall is composed of three tunics - fibrous, vascular, and sensory
internal cavity is filled with fluids called humors
lens separates the internal cavity into anterior and posterior segments
What is the fibrous tunic composed of?
outermost coat of the eye
composed or opaque sclera (posterior) and clear cornea (anterior)
What is the purpose of the sclera?
protects the eye and anchors extrinsic muscles
What is the purpose of the cornea?
lets light enter the eye
What are the three regions of the vascular tunic?
choroid
ciliary body
iris
What does the choroid region do?
a dark brown membrane that forms the posterior portion of the uvea
supplies blood to all eye tunics
What does the ciliary body do?
thickened ring of tissue surrounding the lens
composed of smooth muscle bundles (ciliary muscles)
anchors the suspensory ligament that holds the lens in place
What is the iris consisted of?
the colored part of the eye
the pupil
What does the pupil do?
regulates the amount of light entering the eye
When do the pupils constrict? Dilate?
Constrict for close vision and bright light, or when subject matter is appealing or requires problem-solving skills
Dilate for distant vision and dim light
What does the retina consist of?
delicate two-layered membrane
pigmented layer is the outer layer
neural layer inner layer
What does the pigmented layer of the retina do?
absorbs light and prevents its scattering
What does the neural layer of the retina contain?
photoreceptors - transduce light energy
bipolar cells and ganglion cells
amacrine and horizontal cells
Where are the ganglionic cell axons in the eyeball?
run along the inner surface of the retina
leave the eye as the optic nerve
What is the optic disc?
the site where the optic nerve leaves the eye lacks photoreceptors (blind spot)
What do rods do in the eyeball?
respond to dim light
are used for peripheral vision
What do the cones do in the eyeball?
respond to bright light
have high-acuity color vision
Where are cones found in the eyeball?
macula lutea
concentrated in the fovea centralis
How is the eye separated into chambers?
the lens separated the internal eye into anterior and posterior segments
What does the vitreous humor of the posterior segment do?
transmits light
supports the posterior surface of the lens
holds the neural retina firmly against the pigmented layer
contributes to intraocular pressur
How is the anterior segment divided?
anterior chamber between the cornea and the iris
posterior chamber between the iris and the lens
What is the anterior segment filled with?
aqueous humor
What does the aqueous humor of the anterior segment come from?
filters from the capillaries of the cilliary processes
drains via the canal of Schlemm into the scleral venous sinus
What does the aqueous humor of the anterior segment do?
supports, nourishes, and removes wastes
Describe the lens of the eye
bioconvex transparent flexible avascular composed of epithelium and lens fibers
What does the lens of the eye do?
allows precise focusing of the light onto the retina
Describe the lens epithelium
anterior cuboidal cells that differentiate into lens fibers
Describe lens fibers
cells filled with the transparent protein crystallin
What happens to the lens with age?
lens becomes more compact and dense
loses its elasticity
What is electromagnetic radiation?
all energy waves from short gamma rays to long radio waves
What do our eyes respond to in regards to electromagnetic radiation?
a small portion of the spectrum
visible spectrum
different cones in the retina respond to different wavelengths of the visible spectrum
What happens when a light passes from one transparent medium to another?
its speed changes and it refracts
What happens when light passes through a convex lens?
it is bent so that the rays converge to a focal point
What happens when a convex lens forms an image?
the image is upside down and it is reversed right to left
What is an emmetropic eye?
normal eye with light focused properly
What is a myopic eye?
nearsighted
the focal point is in front of the retina
eyeball is usually too long
How do you correct a myopic eye?
concave lens
What is a hyperopic eye?
farsighted
the focal point is behind the retina
eyeball too short
How do you correct a hyperopic eye?
convex lens
What is the pathway of light entering the eye?
cornea aqueous humor lens vitreaous humor neural layer of the retina to the photoreceptors
Where is light refracted in the eye?
at the cornea
entering the lens
leaving the lens
What does lens curvature and shape allow for?
fine focusing on an image
How does the eye adjust for focusing for distant vision
sympathetic system
light from a distance needs little adjustment for proper focusing
What is the far point of vision?
the distance beyond which the lens does not need to change shape to focus (~20 ft)
What does close vision require (3)?
accommodation
constriction
convergence
How is accommodation achieved in the eye?
changing the lens shape by ciliary muscles to increase refractory power
How is constriction achieved in the eye?
the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye
How is convergence achieved in the eye?
medial rotation of the eyeballs toward the object being viewed
What is photoreception?
process by which the eye detects light energy
What do rods and cones both contain?
visual pigments
aka photopigments
How do rods and cones perceive light?
rods are sensitive to dim light and best suited for night vision, and absorb all wavelengths of visible light
cones need bright light for activation and have low sensitivity
How do rods and cones perceive colors?
rods perceive input in gray tones only
cones have pigments that furnish a vividly colored view
How do rods and cones communication with the CNS?
sum of visual input from many rods feeds into a single ganglion cell
each cone synapses with a single ganglion cell
What are the results from rod perception vs cone perception?
rods result in fuzzy and indistinct images
cones provide vision that is detailed and has high resolution
What is retinal and what does it do?
light absorbing molecule
combines with opsins to form visual pigments
similar to and is synthesized from Vitamin A
What are the two isomers of retinal?
11-cis retinal - formed from vitamin A
all-trans retinal
What does isomerization of retinal do?
initiates electrical impulses in the optic nerve
phototransduction
What is the visual pigment of rods?
rhodopsin
What happens to rods during the light phase?
rhodopsin breaks down into all-trans retinal + opsin (bleaching of the pigment)
What happens to rods during the dark phase?
all-trans retinal converts to 11-cis form
11-cis retinal + opsin regenerate rhodopsin
What happens during excitation of cones?
visual pigments and method of excitation is similar to rods
How do cones perceive color?
three types of cones - blue, green, and red
intermediate colors are perceived by activation of more than one type of cone
What does adaptation to bright light involve?
dramatic decreases in retinal sensitivity - rod function is lost
switching from the rod to cone system - visual acuity is gained
What does adaptation to dark involve?
cones stop functioning in low light
rhodopsin accumulates in the dark and retinal sensitivity is restored
What forms the optic nerve?
axons of retinal ganglion cells
Where does decussation occur in impulses from the retina?
medial fibers of the optic nerve decussate at the optic chiasma
Where do most fibers of the optic tract travel to?
the lateral geniculate body of the thalamus, where they then travel to the visual cortex
Where are alternative places optic fibers end?
midbrain and then superior colliculi (initiating visual reflexes) pretectal nuclei (involved with pupillary reflexes)
What does melanopsin do and where is it found?
found in a small subset of visual fibers
mediates pupillary light reflexes
sets daily biorhythms
How is depth perception achieved?
achieved by both eyes viewing the same image from slightly different angles
three-dimensional vision results from cortical fusion of the slightly different images
What happens to depth perception if only one eye is used?
depth perception is lost
the observer must rely on learned clues to determine depth
What are the two chemical senses?
gustation - taste
olfaction - smell
What must be true for our chemoreceptors to respond in our chemical senses?
chemicals must be dissolved in solution
taste - saliva
smell - fluids of the nasal membranes
What is the organ of smell?
the olfactory epithelium, which covers the superior nasal concha
Describe olfactory receptors
bipolar neurons with radiating olfactory cilia
surrounded and cushioned by supporting cells
What do you find at the base of olfactory epithelium and why?
stem cells
typical life span of olfactory cells is 30-60 days and they need to be replaced ofted
Where are the cell bodies of olfactory nerves?
olfactory epithelium in nasal mucosa
What happens when olfactory receptors react to odor-causing chemicals?
when bound to a ligand, these proteins initiate G protein mechanism, which uses cAMP as a second messenger
cAMP activates Na+ and Ca+ channels, causing depolarization of the receptor membrane that then triggers an action potential
What is the neural pathway of olfactory cells?
olfactory receptor cells synapse with mitral cells
glomerular mitral cells process odor signals
mitral cells send impulses to the olfactory cortex, hypothalamus, amygdala, and limbic system
this is the only pathway that does not go through the thalamus
How many taste buds are in the tongue and where are they found?
10,000
found in the papillae of the tongue mucosa
Describe the papillae of the tongue
come in three forms based on shape - filiform, fungiform, and circumvallate
filiform is the only type that does not contain taste buds
Describe the structure of a taste bud
gourd shaped taste bud that consists of two major cell types:
basal cells - dynamic stem cells
gustatory cells - taste cells that are replaced every 7-10 days
What causes a sweet sensation?
sugars
saccharin
alcohol
some amino acids
What causes a salty sensation?
metal ions
What causes a sour sensation?
hydrogen ions
What causes a bitter sensation?
alkaloids such as quinine, morphine, nicotine
What causes an umami sensation?
glutamate and aspartate
What needs to happen in order for a chemical to be tasted?
it must be dissolved in saliva
it must contact gustatory hairs
What does binding of the food chemical do?
depolarizes the taste cell membrane, releasing neurotransmitter
initiates a general potential that elicits an action potential
How is the stimulus energy of taste converted into a nerve impulse?
Na+ influx in salty tastes
H+ in sour tastes by directly entering the cell, opening cation channels, or blocking K+ channels
gustducin in sweet, bitter, and umami tastes - G protein receptor mechanism
What cranial nerves are involved in taste?
VII and IX carry impulses from taste buds to the solitary nucleus of the medulla
What is the gustatory pathway of the brain?
these impulses travel to the thalamus, then branch to the gustatory cortex, hypothalamus, and limbic system
What are the other influencers in taste?
taste is 80% smell
thermoreceptors, mechanoreceptors, and nociceptors also influence taste
temperature and texture
What parts of the ear are involved with only hearing?
outer and middle ear
What does the inner ear do?
functions in both hearing and equilibrium
What so receptors for hearing and balance do?
respond to separate stimuli
Describe the auricle
It is composed of the helix (rim) and lobule (earlobe)
Describe the tympanic membrane
thin connective tissue membrane that vibrates in response to sound
transfers sound energy to the middle ear ossicles
boundary between outer and middle ear
What is the middle ear?
small, air-filled, mucosa-lined cavity
flanked laterally by the eardrum
flanked medially by the oval and round windows
What is the pharyngotympanic tube and what does it do?
connects the middle ear to the nasopharynx
equalizes pressure in the middle ear cavity with the external air pressure
What are the three small bones of the tympanic cavity and what do they do?
malleus, incus, and stapes
transmit vibratory motion of the eardrum to the oval window
dampened by the tensor tympani and stapedius muscles
Describe the bony labyrinth of the inner ear
tortuous channels worming their way through the temporal bone
contains the vestibule, cochlea, and semicircular canals
filled with perilymph
Describe the membranous labyrinth of the inner ear
series of membranous sacs within the bony labyrinth
filled with a potassium-rich fluid
Describe the vestibule
central egg-shaped cavity of the bony labyrinth
suspending in it perilymph are two sacs - the saccule and utricle
Where does the saccule extend into?
the cochlea
Where does the utricle extend into?
semicircular canals
What do the sacs of the vestibule do?
house equilibrium receptors called maculae
respond to gravity changes in the position of the head
What are the semicircular canals?
three canals that each define two-thirds of a circle and lie in the three planes of space
What do the semicircular canals do?
membranous semicircular ducts line each canal and communicate with the utricle
What is the ampulla?
the swollen end of each canal and it houses equilibrium receptors called the crista ampullaris
these receptors respond to angular movements of the head
Describe the shape of the cochlea
a spiral, conical, bony chamber that
extends from the anterior vestibule
coils around a bony pillar called the modiolus
contains the cochlear duct which ends at the cochlear apex
contains the organ of Corti (hearing receptor)
What are the three chambers of the cochlea?
scala vestibuli
scala media
scala tympani
Where does scala tympani terminate?
the round window
What are the scalas tympani and vesitbuli filled wtih?
perilymph
What is scala media filled with?
endolymph
What is the “floor” of the cochlear duct composed of?
bony spiral lamina
basilar membrane, which supports the organ of Corti
What nerve is found in the cochlea?
cochlear branch of nerve VIII runs from the organ of Corti to the brain
Describe how sound mechanics work in the ear
sound vibrations beat against the eardrum
eardrum pushes against the ossicles
presses fluid in the inner ear against the oval and round windows
shearing forces pull on hair cells
moving hair cells stimulate the cochlear nerve that sends impulses to the brain
What is sound?
a pressure disturbance originating from a vibrating object
composed of areas of rarefaction and compression
represented by a sine wave in wavelength, frequency, and amplitude
What is frequency?
the number of waves that pass a given point at a given time
What is pitch?
perception of different frequencies
we hear 20-20,000 Hz
What is amplitude?
intensity of a sound measured in decibels (dB)
What is loudness?
subjective to interpretation of sound intensity
What is the pathway of sound to the inner ear?
outer ear - pinna, auditory canal, eardrum
middle ear - malleus, incus, stapes, oval window
inner ear - scalas vestibuli and tympani to the cochlear duct
How do sound waves of low frequency resonate on the basilar membrane?
travel across the helicotrema
do not excite the hair cells
inaudible
How do audible sound waves resonate on the basilar membrane?
penetrate through the cochlear duct
vibrate the basilar membrane
excite specific hair cells according to the frequency of the sound
What is the organ of Corti?
composed of supporting cells and outer and inner hair cells
afferent fibers of the cochlear nerve attach to the base of hair cells
What are the stereocilia?
hairs of organ of corti
protrude into the endolymph
touch the tectorial membrane
What happens when you bend stereocilia?
opens mechanically gated ion channels
causes a graded potential and the release of a neurotransmitter
What does the neurotransmitter do in the organ of Corti?
causes cochlear fibers to transmit impulses to the brain where sound is perceived
What is the auditory pathway to the brain?
impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei
impulses are sent to the superior olivary nucleus and inferior colliculus
impulses pass to tthe auditory cortex
auditory pathways decussate so that both cortices receive input from both ears
How is pitch perceived?
primary auditory cortex
cochlear nuclei
How is loudness perceived?
varying thresholds of cochlear cells
number of cells stimulated
How is localization perceived?
superior olivary nuclei that determine sound
What is conduction deafness?
something hampers sound conduction to the fluids of the inner ear
What is sensorineural deafness?
results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells
What is tinnitus?
ringing or clicking sound in the ears in the absence of auditory stimuli
What is meniere’s syndrome?
labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea, and vomiting
What is the vestibular apparatus?
equilibrium receptors in the semicircular canals and vestibule
What does the vestibular apparatus do?
maintains our orientation and balance in space
What monitors static equilibrium?
vestibular receptors
What monitors dynamic equilibrium?
semicircular canal receptors
What are maculae?
sensory receptors for static equilibrium
contain supporting cells and hair cells
each hair cell has stereocilia and kinocilium embedded in the otolithic membrane
What is the otolithic membrane?
jelly-like mass studded with tiny CaCO3 stones called otoliths
What do utricular hairs do?
respond to horizontal movement
What do saccular hairs do?
respond to vertical movement
What happens when otolithic movement is in the direction of the kinocilia?
depolarizes vestibular nerve fibers
increases the number of action potentials generated
What happens if movement is away from kinocilia?
hyperpolarizes vesttibular nerve fibers
reduces the rate of impulse propagation
brain is told head is changing position
What is the crista ampullaris?
receptor for dynamic equilibrium
located in the ampulla of each semicircular canal
responds to angular movements
Describe the support cells of each crista
support cells and hair cells extend into a gel-like mass called the cupula
dendrites of vesttibular nerve fibers encircle the base of the hair cells
What happens when there is directional hair cell bending in the cristae?
depolarizations and rapid impulses reach the brain at a faster rate
hyperpolarizations and fewer impulses reach the brain
brain is informed of rotational movements of head
What are the three modes of input for balance and orientation?
vestibular receptors
visual receptors
somatic receptors
