Vision (chapter 2) Flashcards
how much of the human\s cerebral cortex is involved in the visual system
thirty percent (more than any other sense)
knoiwledge of how light enery is converted into electrical signals comes primarily from studies of…
Drosophiilia and mice
pathway
- light passes through the cornea (rigid cornea does the initial focusing)
- enters the eye through the pupil
- lense then bends the light so that it focuses on the inner surface of eyeball (sheet of cells called retina)
how dies tge iris regulate how mch light enters
by changing the sixe of the pupil
how does the lens brging near or far objcts into better focus on the retina
lens can thicken or flatten
visual input is mappend directly onto the retina as a two-dimensional reversed image
- objects to right project images onto the left side of retina (vice versa)
what happens after processing by specialized cells in the retina
signals will travel via optic nerves to other parts of brain to undergo further integration and interpretation
three types of neurons in retina
gangion cells, photoreceptors, interneurons
- communicate extensively with each other before information is sent to the brain
where are rods and cones located
- most peripheral layer of the retina
- light travels through the cornea lens then through the ganglion cells and interneurons before reaching the photoreceptors
true/false: ganglion cells repond directly to light
- false. They do not, but they process and relay information from the photoreceptors
what are the axons of ganglion cells
- they exit the retina togehter, and form the optic nerve
how many photoreceptors in each human eye
125 million
transduction
the process of converting one form of energy into another occurs in most sensroy systems
rods allow to see in dim light
cones allow u to cath fine detail and colour
- allows you to engage in activities that require a great deal of visual acuity
three type sof cones in human eye
- each are sensitive to a different range of colours (red, green, blue)
- sensitivties of these cones overlap, different combinations f the three cone’s activity coney info about ever colour
- mic red, green, and blue to generate millions of colours
where is vision the sharpest
- in the center of the retina because it contains many more cones than other retinal areas, sharper than in the periphery
fovea
center oft the retina
- small pitted area where cones are most densely packed
contains only red and green cones
- resolve very fine details
macula
immediately around the ffovea
- critical for reading and driving
leading cause of blidness in developed countries
- death or degeneartion of phptorceptors in the macula (macular degeneration)
macular region input
- each ganglion cell receives input (via one or more interneuons) from one or very few cones which allows u to see very fine details
margins of retina inputs
each ganglion ells receives signals from several photoreceptors
- convergeense of inputs = why periphereral vision is less detailed
receptive field
portion of visual space providing input to a single ganglion cell
what does visual processing begin with
- comparing the anounts of ligth hitting small, adjacent areas on the retina
- receptive fields of ganglion cells “tile” the retina which provides a complete two dimensional representation of the visual scene
how is the receptive field of a ganglion cell activated
when light hits a tiny region on the retina that corresponds to the centre of the field
when is the ganglion cell inhibited
when light hits the donut-shaeped area surrounding the center
- if the light hits both the donut shaped area and the hole (the entire receptive field) the ganglion cells respond only weakly.
what is the key to object-detection
- this inhibition ios the first way our visual system maximizes the perception of contrast which is jey
where do optic nerves travel towards
the back of the brain.. occippital lobes?
what happens at the optic chaism
information from the left sdie of retinas of both eyes continue on let side of brain
- info from right side of both retinas proceeds on the right side of the brain
what happens after the optic chiasm
- visual info is then relyed though the lateral geniculate nucleus (region of thalamus)
- then to primary visual cortex
primary visual cortex
- thin sheet of neural tissue located in the occupuputal oobe
- many layers, densely packed with cells
middle layer of pvc
receivese messages from the thalamus
- has receptive fields like those in the retina and can persevere the retina’s visual map
cells above and below the middle layer
- more complex receptive fields
- register stimulti shaped like bars or edges iwt particular orientations
- ex. specific cells will respond to edges at a certain angel or moving in a certain direction
what happens as visual information from the primary visual cortex is combined in other areas
receptive fields become more complex and selettive]
- some neurons at higher levels of processing respong only to specific objects/faces
where are visual signals fed into
studies in monkeys suggest several parallel but interacting processing streams
what are the rpocessing streams
dorsal (heads up to the parietal lobe)
basically the where stream, combines spatial relationships, motion, timing to create an action plan without need for conscious thought
ventral (down to temporal)
basically the “what” stream
integrates shape, colour with memories and experience for recognition puproses
what does the brain do during recognition
extracts info at several stages, compares with past experiences, passes to higher levels for processing
binocular vision
perceives depth or three dimensions because each eye sees an object from a slightly diff abngle
- only works if eyes’ visual fields overlap
- if both eyes are equally active and properly aligned
strabismus
- person with corssed eyes
- misses out on much depth perception
where is this visual info processed
visual cortex
strabisumus in children
- children with thic condition initially have good vision in each eye, but since they cannot fuse the images coming from both eyes, they
- start to favour one eye
- ## they often lose vision in the other
can vision be restored in these children?
- yes but only if the issue is treated at a young age (after 8, or so m the blidnness becomes permanent)
in the past, how was strabismus treated
- ophthalmologists wwaited until children were four, before operating
- before they would prescribe exercises or an eyepath
- now it is corrected before the age of four
what lies at the heart of many disorders that cause blindess
- loss of function or death of photoreceptors
- many are difficult to treat
what does hearing involve
- a series of steps that convert sound waves in the air into electrical signals that are carried into the brain by nerve cells.
how are sound waves transformed into electrical signals?
- sound in form of air pressure waves reaches the pinnae of your ears
- here, the waves are funneled into each ear canal to reach the eardrum
- eardrum vibrates in reponse to changes in air pressure, sendin the vibrations to three tiny sound-spmplifying bones in the middle ear
- lst bone in the chain (stapes) acts like a tiny piston as it pushes the membrane that seperates the air filled middle era from the fluid filled cochlea of the inner ear
- oval windo converts the mechanical vibrations of the stapes into pressure waves in the fluid of the cochlea where they are trasduced into electrical signals by specialized receptor cells (hari cells)
basilar membrane
- runs along the inside of the cochlea like a winding ramp, spiraling from the otuer coil, near the ovil window to the innermost coil. It is tuned along its length to different frequencies/pitches.
when the pressure waves are in the fluid of the cochlea and it ripples, what happens
- the membrane moves, vibrating to higher-pitched sounds near the oval windo and to lower-ptiched sounds in the center
hair cells on top of the vibrating basiliar membrane
- rows of these hair cells are located on top, and when the membrane moves up and down…
- microscopic hair-like stereocilia extending from the hari cells bend agaisnt an overlying structure called the tectorial membrane.
- they respond most strongly to a narrow range of sound frequences depending on how far along the cochlea it is located.
what occurs after the bedning of the stereocilia
- small channels in the stereociilia are op[ened, and so ions in the surrounding lfuid rush in and convert the physical movement into an electrochemical signals.
- when these hair cells are stimulated escite the audtiory nerve which sends its electrical signals to the brainstem
what is the nect stop for sound processing after the electrical singlas are sent tot he brain stem
the thalamus.
- itis the brain’s relay station for incoming sensory information
what comes after the thalamus in sound processing
- information is sent to the auditory part of the cerebral cortex
How is a sound’s direction and location computed
- Ton the way to the cortex, he brainstem and the thalamus do this by using the iformation from both ears
where are sond qualities such as harmony, rhythm and melody processed
- at higher levels, peyond the primary auditory cortex, neurons are able to do this
- they combine the types of audtiory info iinto a voice or instrument that u can recognize
sound processing on left side
** sound is processed on both sides tho
- ## typically responsible for understanding and producing speech
what happens to hearing if there is damage to the left auditory cortex (especially in the Wernicke’s are)
- this damage can occur during a stroke
- a person is able to hear, but cannot understand what is being said.
what is reponsible for the majority of cases of hearing loss
- loss of hari cells
- once they die, they do not regrow
how are researchers trying to treat this loss of hair cells in the ear?
- eventually hopefully with neurogenesis to replace these damaged hair cells
sense fo taste
gustation
sense of smell
olfaction
what are smell and taste perceptions of
- tiny molcules in the air and in your food
why do taste receptor cells regularly degenerate
because the cells procesing taste and smella re esposed tot he envirnoenment, same scenario with olfactory neurons
oilfactory neurons are…
the only sensory neurons that are continually replaced throughout our lives
what are molecules released by chewing or drinking detected by
taste/gustatory cells within taste buds on tongue and along roof and back of mouth.
how many taste buds do we have
- btwn 5 000 an 10 000 taste buds, which we start to lose around the age of 50
how many sensory cells within each taste bud
50 to 100, each receptibe ot one of at least fiv e diff basic taste qualities:
- sweetm sour, salty, bitter, and umami (savory)
- all tastes are detected acorss tongue
what happens when taste receptor cells are stimulatedf
- they send signals through three cranial nerves (the facial, glossopharyngeal and vagus nerves) to taste regions in the brainstem
- these signals are routed through the thalamus to the gustatory cortex in tthe frontal lobe and insula where specific tase perceptions are identified
what happens when odors enter the nose
- they enter on air currents
- they bind to specialized olfactory cells on a small patch of mucus membrane high inside the nasal cavity.
what happens after the odors bind to the olfacotyr cells
- the axons of the olfactory cells enter the olfactroy bulbs (one for each nostril_ after crossing through tiny holes in the skull.
- information is then sent to the olfactory cortex
WHAT IS THE ONLY SENSORY SYSTEM THAT SENDS SENSORY INFROMATION DIRECTLY TO THE CEREBRAL CORTEX WITHOUT FIRST PASSING THROUGH THE THALAMUS?
smellllll
how amany olfactory cells do we have
around 1000… but we can identiy about twenty times more smells
what are on the tips of olfactory cells
there are hari-like cilia that are receptive to a number of different odor molecules
- many cells respond to the same molecules
- a specific cell will therefore stimulate a unique combination of olfactory cells
- this creates a distinct activity of patter which is then transmitted to the olfactory bulb and on to the primary olfactory cortex located on the nateror surface of the temporal lobe
what happens to olfactory information after it is transmitted to the primary olfactory cortex
- the olfactory information then passes to nearby brain areas where odor and taste info are mixed
- this cretaes a perception of flavor
how quickly can people identiy odors
as wuickly as 110 milliseconds
*** the size of olfactory bulbs and the way neurons are organized can change over time
remember that our smell adds great coplexity to the flavours we perceive
- taste and smell info appear to converge in several central regions of the brain
which system is reposnsible for all the touch sensations we feel
the somatosensory system. (light touch, pressure, virbation, temperature, texture, itch, pain)
body’s main sense organ for touch
the skin
nerve cells in hairy skin
when very hairy, some sensitive neruon endings will wrap around the bases of hairs, and respond to even the slightest hair movement
where do signals from touch receptors travel to
they travel along sensory nerve fibres that connect to neruons in the spinal cord.
- these signals will then move upward towards the thalamus and on to the somatosensory cortex where they are translated into touch perception
fast-traveling information
- information travels quiickly along myelinated nerve fibres with think axons
these are called A-beta fibres
slow-traveling information
- transmitted more slowly along thin, unmyelinated axona
- these are called C-fibres
cortical map
- somatosensory information from all parts of body are spread onto the cortex in a form of a topographic map that curls around the brain like headphones.
stimulation of the regions of the cortex
- VERY SENSITIVE BODY AREAS LIKE LIPS AND FINGERTIPS STIMULATE MUCH LARGER REGIONS OF THE CORTEX THAN LESS SENSIVITE PARTS OF THE BODY
- densely nerve-packed areas
what does the sensitivity of different body regions to tactile and painful stimuli depend on
largely on number of receptors per unit area and the distance between them
what type of receptor will reposnd to painful stimuli
nociceptors (special sensory fibres) repond to stumli that can cause tissue damage
- usually only respond to strong or high-threshold stimuli
itch
aome types of nociceptors respond only to chemical stimuli that cause itch
inflamattion
when tissue injjury occrsm it triggers the release of various chemicals at the site of damage which causes inflammation
- this inflammatory soup triggers nerve impulses that cause u to feel pain
prostaglandins
enhance sensitvity of receptors to tissue damage which makes u feel pain more intensely.
allodynia
- soft touch can even produce pain
(like on really sunburned skin) - contributed to by prostaglandins
what happens when the nervous system is damaged/changed
- enhance and prolong perceived pain even in the absence of pain stimuli (neuropathic pain)- hypersensitivity to pain
diabetic neuropathy
- nerves in the hands or feet are damaged by prolonged exposure to high blood sugar
- send signals of numbness, tingling, burning, or aching pain.
how do pain and itch messages make their way to the spinal cord
via small A-delta fibres and even smaller C fibres
A-fibres and pain
A-delta fibres evoke the immediate, sharp and easily identifibale pain
C-fibres and pain
they transmit slow pan message,s and their nerve endings spread out over a relatively large area to produce a dull and diffused achre or pain sensation (hard to pinpoint)
Pain and itch signals travel path
- up the spinal cord
- throughout the brainstem
- to the thalamus
- relayed to several areas of the cerebral cortex that monitor the state of the body and transform pain and itch messages into conscious experience
what else affects the perception of pain/ pain expereince
strenggth of the stimulus, person’s emoitional state
what else affects the perception of pain/ pain expereince
strenggth of the stimulus, person’s emoitional state, setting in which the injury occurs
periaquedicuctal gray matter
receives pain messages from the cortex
- region of the brainstem
-
what does theperiaquedicuctal gray matter do with its connections with other brainstem nuclei
Through these connections, it activates descending pathways that modulate pain
- these pathways also send messages to networks that release endorphins which relieve pain. It is a drug.
how do endorhpins regulate pain
intercepting the pain signals ascending in the spinal cord and brainste,
cannabis and pain
- successfuly targets the motional component of pain rather than stopping the stimulus itself.
- suprresses activity in just a few pain areas in the brain (especially those that are part of the limbic system the emotional center of the brain)
