Lecture 10: Vision ll, Touch, and Taste Flashcards
what type of cell is located at the furthest back point in the eye?
photoreceptors
photoreceptors’ leak sodium channels are always ____ in the dark
depolarized
how are ON and OFF bipolar cells differentiated?
by whether they inhibit or exhibit glutamate
what is the effect of light on photoreceptors?
they are hyperpolarized and stop releasing neurotransmitters
function of retinal ganglion cells
integrate information from ON and OFF bipolar cells
how are the receptive fields of ganglion cells organized?
“center-surround” organization
how are retinal ganglion cells classified
they are called ON or OFF cells, depending on whether they show increased or decreased spiking activity when light is presented in the center of their receptive field.
ON retinal ganglion cells
excited by the light in the centre and are inhibited by light in the surround
OFF retinal ganglion cells
excited by the light in the surround and are inhibited by light in the centre
function of retinal ganglion cells in the fovea
process colour information
types of receptive fields of retinal ganglion cells
Yellow on, blue off
Blue on, yellow off
Red on, green off
Green on, red off
in a yellow on, blue off receptive field
yellow is at the centre and blue makes up the border
in a blue on, yellow off receptive field
blue is at the centre and yellow makes up the border
where does visual information go after retinal ganglion cells?
Visual information is relayed from the retinal ganglion cells to the thalamus (the lateral geniculate nucleus) to the area V1 in the cerebral cortex (primary visual cortex)
receptive fields of V1 neurons
the sum of many RGCs
simple cells in the primary visual cortex
sensitive to lines of light and their receptive fields are typically organized in a center-surround fashion
difference between neurons in the V1 and retinal ganglion cells
Neurons in the V1 have larger receptive fields than retinal ganglion cells
v1
another word for primary visual cortex
when are neurons in V1 most active?
when a line of light in a particular orientation is detected in the receptive field
what do V1 neurons try to determine?
borders, edges, and corners
how much of the cerebral cortex is dedicated to processing visual information?
20-25%
visual association cortex
part of the occipital lobe that surrounds the primary lobe
t or f: Visual processing extends into the temporal and parietal lobe
true
dorsal stream
encodes where objects are. Starts in the primary visual cortex and ends in the posterior parietal cortex.
ventral stream
encodes what the object is and its colour (mostly information from cone cells). Starts in the primary visual cortex and ends in the inferior temporal cortex.
monocular vision
visual input from one eye
binocular vision
visual input from two eyes
what type of visual input do most V1 cells respond to?
binocular
how does depth perception work?
many monocular cues can be used to estimate depth such as relative size, amount of detail, relative movement as we move our eyes, etc. These are the cues we use to appreciate depth when looking at a 2D image
stereopsis
the perception of depth that emerges from the fusion of two slightly different projections of an image on the two retinas
retinal disparity
the difference between the images from the two eyes
result of retinal disparity
horizontal separation of the two eyes, which improves the precision of depth perception, which is particularly helpful when trying to plan movement to interact with objects in space
agnosia
A deficit in the ability to recognize or comprehend certain sensory information
cause of agnosia
a problem in some sensory association cortex
visual agnosia
People cannot recognize objects but otherwise have normal vision
cause of visual agnosia
relates to damage located downstream of the primary visual cortex
akinetopsia
a deficit in the ability to perceive movement
akinetopsia cause
damage in an area of the dorsal visual stream (in the parietal lobe of the cerebral cortex)
cerebral acrhomatopsia
People with this condition deny seeing any form of colour; they say everything is just shades of grey.
cerebral achromatopsia cause
damage to the ventral visual stream. often comes about from strokes
prosopagnosia
failure to recognize particular people by the sight of their face
prosopagnosia cause
damage to the fusiform gyrus (in the ventral stream)
most pathways in the visual cortex are
bidirectional
Predictive coding theory of perception
Claims that each level of the network is attempting to predict the responses at the next lower level via feedback connections. What propagates up is the prediction error signal, which is used to improve future predictions
3 different visual information pathways
- thalamus (LGN)
- midbrain (superior colliculus)
- hypothalamus
thalamus visual pathway
projects to the primary visual cortex in the occipital lobe of the cerebrum. Visual information is processed in this pathway to determine was you’re looking at. It creates an internal representation of your entire visual space
midbrain visual pathway
visual information is used here to control fast visually-guided movements. The midbrain doesn’t know what you are looking at, but it knows where light is moving in visual space
hypothalamus visual pathway
visual information is used here to control circadian rhythms (such as the sleep-wake cycle.) the hypothalamus doesn’t know where you are looking, but it knows how much light is in the environment
fast-guided movements use ___ pathway
midbrain
circadian rhythms are controlled by ___ pathway
hypothalamus
most visual information is controlled by ___ pathways
thalamus
somatosensory pathways
Provides information about touch, pressure, temperature, and pain, both on the surface of the skin and inside the both
3 parts of the somatosensory pathway
Exteroceptive system, Interoceptive system, Proprioceptive system
exteroceptive system
responds to external stimuli applied to the skin
interoceptive system
provides information about conditions within the body and is responsible for efficient regulation of its internal milieu
proprioceptive system
monitors information about the position of the body, and movement
cutaneous senses
encode different types of external stimuli
Pressure
caused by the mechanical deformation of the skin
vibrations
occur when we move our fingers across a rough surface
temperature
produced by objects that heat or cool the skin
pain
caused by many different types of stimuli, but can primarily damage tissue
epidermis
the outermost layer of the skin (above the dermis)
Cells here get oxygen from the air (not the dermis)
dermis
the middle layer of the skin
hypodermis
the deepest layer of skin (below the dermis)
Glabrous skin
hairless skin (ex. palms)
free nerve endings
Primarily respond to temperature and pain
Meissner’s corpuscles
Primarily respond to temperature and pain
merkel’s discs
respond to local skin indentations (simple touch)
Pacinian corpuscles
respond to skin vibrations
Ruffini corpuscles
sensitive to stretch and the kinesthetic sense of finger position and movement
two categories of thermal receptors
those that detect hot & cold
how is temperature perceived
Temperature-gated-ion channels that open at varying temperatures
myelination of temperature axons
This information is poorly localized and the axons that carry it to the CNS are unmyelinated or thinly myelinated
are proteins that are sensitive to temperature ligand-gated?
some are
perception of pain
mediated by free nerve endings on the skin
nociceptors
pain receptors
mechanoreceptor
pressure receptor cells
2 main pathways from the body to the primary somatosensory cortex
Spinothalamic tract and dorsal column
spinothalamic tract
- immediately crosses over the spinal cord and the first synapse is there.
- The information then ascends to the thalamus through the spinothalamic tract
- Detects crude touch, temperature and pain
- Poorly localized information
dorsal column
- Ascends ipsilaterally through the dorsal column of the spinal cord.
- The first synapse in the pathway is in the medulla.
- From there the information crosses over to the contralateral side as it ascends to the thalamus
- Detects fine touch and kinesthesia
- Highly localized information
where does touch information go after the thalamus?
primary sensory cortex in the parietal lobe
what happens when electrical stimulation is applied to various sites of the primary somatosensory cortex?
patients report somatosensory sensations in specific parts of their bodies
somatotopic map
reflects the relationship between cortical stimulations and body sensations (also referred to as the somatosensory homunculus “little man”)
tactile agnosia
Patients with tactile agnosia have trouble identifying objects by touch alone
However, these patients can often draw objects that they are touching without looking
phantom limb
A form of pain sensation that occurs after a limb has been amputated
phantom limb causes
One idea is that the phantom limb sensation is due to confusion in the somatosensory cortices (primary and association). The brain gets nonsense signals (in the form of cut axons) and it has difficulty interpreting them
transduction of taste information
similar to the chemical transmission that takes place at synapses; Ligand receptor interactions produce a change in membrane potential
how many taste receptor cells are in taste buds?
25-50
how often are taste receptor cells replaced?
every 10 days
how are different tastes generated?
the activation of different types of taste receptor protein; Each taste bud is sensitive to a particular tastant
how do taste receptor cells release neurotransmitters?
in a graded fashion
do taste receptor cells have action potentials?
no
Six different categories of taste receptors
sweetness, umami, bitterness, saltiness, sourness, fat
MSG (monosodium glutamate) activates
both salt and umami receptors
Sugar and umami taste receptors are
instinctively rewarding
Bitter tastes are
instinctively averse
sweetness detects
sugar
umami detects
glutamate
bitterness detects
a variety of different molecules
saltiness detects
ions
sourness detects
pH level
fat detects
fatty acids
how is taste perception developed?
it isn’t developed; it’s innate
what did mice studies reveal about taste perception?
it’s innate
t or f: Each hemisphere gets input from both eyes
t
where does the left visual field go?
right hemisphere
where does the right visual field go?
left hemisphere
how is temperature perception mediated?
free nerve endings
Capsaicin activates
heat receptors
Menthol activates
cold receptors
t or f: Dorsal column and spinothalamic synapse before projecting to the primary somatosensory
t
how many tastants are individual taste buds sensitive to?
one & they express that same taste receptor protein
how do taste receptor cells release neurotransmitters?
in a graded fashion
how is the primary gustatory cortex organized?
Organized by taste within people (not consistent for everyone)
how many metabotropic receptors detect sugar molecules?
1
how many metabotropic receptors detect bitter molecules?
50
what type of receptors detect saltiness
Ion channels permeable to sodium
what type of receptors detect sourness?
Ion channels permeable to free protons
what type of receptors detect fat?
Metabotropic and fatty acid transporters
