Quiz 3-- Visual Pathways and Auditory Flashcards
simplified signal flow from eye
photoreceptors, bipolar, ganglion, lateral geniculate nucleus, v1
what forms the optic nerve
ganglion cells
what happens in the optic chiasm
60% of the fibers cross over to the contralateral side
the optic tract contains information from
both eyes
dorsal lateral geniculate nucleus of thalamus goes to
the primary visual cortex, suprachiasmatic nucleus, pretectum, superior colliculus
pupillary light reflex
ganglion cellls, pretectum, both sides go to the endinger westphal nucleus, go to the oculomotor nerve, ciliary ganglion
ciliary ganglion neurons
regulate constriction of the iris, lowering pupil diameter (this should occur in both eyes)
should the pupillary reflex be in one or both eyes
both
how do objects appear on the retina
inverted, left-right reversed
what are the quadrants of the eye
nasal, temporal
superior, inferior
what info does each eye get
left eye gets majority of left and one part of right
right gets majority of right and one part of left
where does information from the eye go
right visual field to left side and vice versa– ganglion cells in nasal division cross over in optic chiasm, in temporal division stay on the same side
how is the fovea represented
very large in posterior striate cortex, peripheral stimuli are further front
upper visual field is ___ h=the clcarine sulcus
below
lower visual field is
above the calcarine sulcus
meyers loop
part of the path from thalamus to striate cortex– in the temporal cortex, has info about contralateral sperior visual field
baum’s loop
parietal cortex, contralateral inferior visual field
lesion in right optic nerve
loss of vision in right eye
lesion in optic chiasm
edges of visual field are blind in both eyes- temporal side
lesion in right optic tract
left visual field
lesion along meyers loop
vision loss in upper left quadrant of both eyes
anterior striate cortex lesion
contralateral loss with macular sparing
pathway of info from eyes to brain
photoreceptors, bipolar cells, ganglion cells, LGN, V1
3 types of ganglion cells
magnocellular (large, layers 1-2)
parvocellular (small, layers 3-6)
koniocellular (in between)
Parvocellular target
4c beta
magnocellular target
4 c alpha
koniocellular target
patch 2/3
parvocellular pathway
spatial resolution due to small receptive fields and slow, sustained responses
also help with shape, size, color
magnocellular pathway
temporal resolution- large recepion, transient fast responses, lovation, speed, direction of object
koniocellular pathway
some color info
how are neurons in the LGN arranged
similar to retina where center-surround fields and selectivity for increases and decreases in luminance predominate
cells in primary visual cortex
respond selectively to bars and edges, responding most to preferred orientation
axons from lgn terminate primarily
on cells of layer 4c – axons convey activity to other layers
cells in 2/3 layers of visual cortex
project to higher order visual cortices
cells in 5/6
go to lgn and superior colliculus
cortical areas also synapse where in v1
layers 5,4,2,1
columns of neurons in cortical surface
show similar receptive field properties; in other words, centered in same region of visual space and have similar orientation
compare horizontal and vertical columns in v1
horizontal columns had less related receptive fields
intrinsic signal imaging
detects changes in blood flow; colors show average orientation of columns at each location ; neurons in given region have similar orientation except at center of pinwheel
are inputs still separate at lgn and layer 4?
yes, only separate after 4
when eyes are fixed on a point what happens
points beyond or in front of plane project to non corresponding retinal areas, allowing for depth perception
3 types of binocular neurons in primary cortex
far cells- discharge to retinal disparities beyond fixation point
near cells- retinal disparities that arise from in front of point
tuned zero- plane of fixation selective
extrastriate visual areas
usually depend on v1 for activation
cells in mt (middle temporal)
respond to direction of a moving edge
cells in v4
respond selectively to color- no regard to movement
how many separate representations of visual field
at least 10
cerebral akinetopsia
unable to detect motion
cerebral achromatopsia
cone functioning but no color
parietal ____ and temporal _____ pathway
where/what
spatial awareness and giodance of physical actions, selective for direction and speed and lesions cause akinetopsia
object recognition and form, selectivity for shape, color, texture, preferential response to face/objects, also evaluates significance of elements not just a description
sound refers to what
pressure waves generated by vibrating air molecules
wave form of a sound
amplitude against time
how do we hear frequency
as pitch
humans hear frequencies between
20 hz to 20khz
amplitude is perceived as
loudness
what are the decibel threshold levels
> 115 dB: high risk threshold
135 dB: pain threshold
what is the human hearing range?
20-20k Hz, but this range shrinks with age (higher frequencies fade off first)
presbycusis
age-related hearing loss
external and middle ear
collect sound waves, amplify pressure
describe the sound pathway
external ear and middle ear collect sound waves and amplify pressure, sound is transmitted to the cochlea in the inner ear, which breaks down complex sounds into simple sinusoidal components which go to hair cells and auditory fibers
cochlea
breaks down complex waves into simple sinusoidal components
hair cells
encode frequency, amplitude, and phase
hair cells transmit to
auditory fibers
hair cells are represented
along the cochlea
pathway of sound
external ear, middle ear, inner ear, cochlear nucleus, superior olive, inferior colliculus, thalamus, cortex
external ear consists of
pinna, concha, auditory meatus
what does the external ear do
focus sound waves on tympanic membrane, boost sound pressure 30-100 fold, selective for frequencies around 3 khz
why is 3 khz important
external ear is selective for this, 2-5 khz is a frequent range of hearing loss, related to speech processing because consonants have energy in this range
what does the middle ear do
transform airborne sounds into vibrations detected by cells (hair cells in inner ear) since usually this energy would just be reflected. it also boosts air pressure again
tympanic membrane
funnels sound onto small oval window
ossicles
3 ear bones– malleus, incus, stapes- problems can cause conductive hearing loss
conductive hearing loss
loss caused by something that stops sounds from getting through outer or middle ear
tensor tympani and stapedius
two small muscles activated by loud noises and contract to protect inner ear
cochlea
transforms wave forms from sound pressure into neuronal signals
what does the inner ear do to complex waveforms
deconstructs it into simple tones
are normal sounds simple or complex waveforms
complex (multiple frequencies)
sensorineural hearing loss
Occurs after inner ear damage and problems with the nerve pathways from the inner ear
oval window
covers the entrance to the cochlea
tympanic mebrane
aka eardrum, separates outer and inner ear and causes the ossicles to vibrate
round window
energy enters through oval window, transmitted through cochlea, leaves via round window– opposite/out of phase vibrations in comparison to oval window; it allows fluids in cochlea to move
basilar membrane
within the cochlea of the inner ear, separating the two areas called the scala media and scala tympani
tectorial membrane
resides above the hair cells
fluid filled chambers of the cochlea
scala vestibuli and scala tympani (perilymph)
scala media aka cochlear duct (endolymph)
basilar membrane separates scala tympani and scala media
tonotopy
topographical mapping of frequencies along basilar membrane– both the membrane and the nerve fibers prefer specific frequencies with narrow and stiff basal end responding to high frequencies like 10k hz and apical end being more floppy and working better with low frequencies
what are the layers of the cochlea from bottom to top?
scala tympani, basilar membrane, scala media, reissner’s membrane, scala vestibuli
organ of corti
transform pressure waves into action potentials, sits inside cochlear duct between scala vestibuli and the scala tympani
how does basilar membrane react to sound
basilar membrane pushes hair cells against the tectorial membrane as perilymphatic pressure waves pass
vertical motion of the travelling wave along the basilar membrane
induces a shearing motion between the basilar membrane and tectorial membrane. this bends stereocilia on the hair cells, causing hyper or depolarization
inner hair cells
3.5k present: receptors for hearing, constitute 95% of the auditory nerve fibers that project to the brain
outer hair cells
12,000, receive efferent axons from the superior olivary complex in the brain, and amplify the traveling wave
how many hair cells are there
15k in each ear, each with 30-100 stereocilia which are graded in height and bilaterally symmetrical
tip links
connect 2 adjacent stereocilia, this transfers the shearing motion into receptor potential. This movement opens and closes channels
how specific are hair cells/stereocilia
detect movements the size of a gold atom, responds in microseconds
depolarization of hair cells
K+ influx in apical compartment through stereocilia leads to depolarization when tip links are pulled on and opened
are some channels open at rest for stereocilia
Yes
when are stereocilia hyperpolarized
when they are closed
effect of depolarization on hair cell
influx of K+ in stereocilia opens calcium channels that trigger glutamate release and induce action potentials in auditory nerve
describe the appearance of the receptor potential
biphasic- only occurs in direction parallel to symmetry axis
how are different frequencies encoded
tonotopy of basilar membrane is preserved at higher levels in auditory pathway— labeled line coding of frequencies
tuning curve threshold
auditory fibers are tuned to characteristic frequencies– hair cells release nt only when depolarized, auditory nerve fibers fire during the positive phase
how do you treat conductive hearing loss
external hearing aid to amplify sound
treatment of sensorineural hearing loss due to hair cell damage
cochlear implant– microphone and processor create electrical stimulation
full auditory pathway
cochlea, spiral ganglia to non leminiscal pathways and also to leminiscus and superior olive to inferior colliculus to thalamus to A1
auditory nerve innervates the
cochlear nuclei
low frequencies terminate ________, high frequencies terminate _________
ventrally, dorsally
how are auditory projections organized
in parallel
from cochlear nucleus to
medial and lateral superior olive
which ear goes to superior olive
both
superior olive function
bilateral inputs for sound localization
MSO
time differences to localize sound <3khz this is determined by length of axon connection; both action potentials converge on MSO neuron that responds most strongly if arrival is coincident
LSO
intensity differences to localize sound above 3 khz
above 2 khz, head acts as an
obstacle for short, high frequency waves
differences in _____ are used by the _____ and the ________ to locate sound
intensity, lateral superior olive, medial nucleus of the trapezoid body
LSO
receives excitatory ipsilateral and inhibitory contralateral movement, so that highest firing will be when sound directly lateral; for sounds in front, inhibition from contralateral ear balances excitation from ipsilateral ear, almost silencing lso activity for that ear
after olives
inferior colliculus, which has a topographical representation of space, then goes to medial geniculate complex
neurons have
preferred elevation and preferred horizontal direction (also respond to patterns)
auditory thalamus
medial geniculate complex integrates combinations of frequencies in specific time intervals
decussation occurs at
cochlear nucleus
auditory cortex
located in temporal cortex, maintains topographical map of cochlea
auditory cortex
projections from ventral division of medial geniculate thalamus maintain tonotopic map – adjacent belt areas receive projection from medial and dorsal medial geniculate
- combination sensitive neurons, species specific sounds, speech
