BIOS 485 Exam I Study Guide from Thomas Park
Weakly electric fish, homing pigeons, ferrets
-electric fish: can sense electric fields, sensitive to magnetic energy that
we’re unaware of they continuously fire AP in noncontractile muscles to put out
electric pulses to use in murky water to avoid obstacles, identify each other,
gender, etc. (communication), their muscles don’t contract, they use ventral fin
-homing pigeons: if you raise them somewhere, drive 20 miles away, release
them, they will return--they’re sensitive to earth’s magnetic fields (it’s like seeing
lines that orient north and south poles, a sense we don’t have)
-honeybee & white spider: white spider evolved to be white to help attract
honey bees to the flower, the white spider looks good in UV light which honey bees
can see but the birds that prey on those spiders don’t see UV light
-ferrets: when born are blind & deaf
-eye has 2 main projections:
1) synapse in LGN (allows you to see and recognize stuff) then
projects to the visual cortex (synapses there too)
2) Superior colliculus (which is in charge of orienting you towards
interesting things in the environment, w/in the structure there’s
a map of touch & acoustic & visual space all layered on top of
one another--there are multimodal neurons in sup. coll. that
respond to more than one type of stimulus)
-ear has one projection, the cochlea sends info to the inferior colliculus then
synapses in MGN, then goes to the auditory cortex
Normal: eye → LGN → visual cortex
eye → Superior Colliculus
cochlea → Inferior
Colliculus
-experiment: surgically remove superior and inferior colliculi in baby ferrets
(before any connections are made) results in the hearing pathway being
messed up, while the visual pathway is intact
-MGN is intact and it’s saying that it needs a connection to the visual pathway
connect to the MGN and makes synapses and the secondary cell goes to the
cortex--can cause auditory cortex to respond to visual stimuli-- ‘hearing
colors’
Which sensory systems mainly use graded potentials
Graded Potentials: Hearing, Balance, Taste, Vision
-receptor cells generate graded potentials and release graded amounts of
transmitter
Action Potentials: Touch, Olfaction
-receptor cells generate APs and have axons that project centrally
, “Labeled Line Code”
-how modality is communicated
-receptors in different senses are sensitive to specific energy types
-different senses have distinct channels for information about each modality
-each line from the sensory surface to where you receive it in the cortex is
labeled for specific energy data, so for example, flashing light at cochlea won’t do
anything
-Why is labeled line code good? Depolarization by any means will give you
perception appropriate for that sensory system
Example: cochlear prosthetic: someone has a problem in their auditory
system, the cochlea is functioning but sound isn’t able to get to the correct place to
depolarize proper cochlear hair cells, we can put a microphone and have it
transduce signals but instead of going from sound to electrical signals in the brain,
it goes from sound to electrical in an electrode, the device makes sound into
electrical impulses that then stimulate the appropriate part of the cochlea so the
person can hear, again this shows us that depolarization by any means is perceived
as that sensory systems’ energy
Example: if you hit your head and say you ‘saw stars’ or if you poke your eye
you may see a visual pattern--this is bc you are artificially depolarizing
Which sensory systems transduce which types energy?
-mechanical: touch receptors, hearing receptors, and balance receptors
transduce mechanical energy
-chemical: taste receptors and olfactory receptors transduce chemical energy
-thermal
-electromagnetic : photoreceptors transduce electromagnetic energy
-hearing, balance, vision can’t regenerate cells
-taste can regenerate cells
-olfaction has programmed cell death
Is there more than one sensory system that transduces mechanical energy?
YES
Somatosensory, auditory and equilibrium
Interesting note about taste receptors:
-they can also generate APs but the function of them is unknown, theory:
maybe for signaling among receptor cells within a taste bud, but for everyday
function they use graded potentials
Chemoreceptors and photoreceptors use GPCRs and second messenger cascades
-sugar molecule binds → cascade of events the close leaky K channels but
don’t affect Na channel, Na ions will depolarize the cell, the more depolarized the
more nt gets released
, -everytime you go through one step of the cascade you’re able to activate
more and more components--it’s amplified, this is how we are able to sense just
one molecule of sugar
receptive fields in fingertips versus back of the leg
-small receptive field in fingertips, large receptive field on back of leg
-all four sensory nerves have some form of a receptive field, if you stimulate
outside of that receptive field, that neuron doesn’t know the stimulus exists,
you must stimulate within the receptive field for neuron to get stimulation
-some nerve cells have tight receptive fields, others have large
-in touch & photoreceptors, the receptive field describes the region of
sensory surface that can generate a response → receptive fields carry
info about spatial location
-for a stimulus to generate a response it has to be within a receptor’s
“receptive field”
-diff receptor types have diff receptive fields
-receptors are arranged systematically at the sensory surface: a
“topographic” representation of the sensory surface is maintained
throughout the nervous system (this is an important organizational
principle of all sensory systems)
-size and density of receptive fields determine acuity
-acuity increases with more receptors and smaller receptive fields
-in hearing receptors, the receptor field describes the range of frequency that
can generate a response, it’s still a map, but not spatial info
-so how do we know where sound is coming from? Contact inhibition--we
have 2 ears which tell us where sound is coming from by arrival time
and intensity differences, a computational thing
two-point discrimination procedure (What’s it good for?)
-it shows the variability in receptor density: the more dense the receptors, the
smaller the receptive fields are and the more finer your ability to
distinguish stimuli
-a good way to measure receptive field size
intensity coding (various ways)
-for touch receptors: increase in pressure causes increase in response
magnitude
-signaled by population response
-different receptors have different thresholds and greater pressure recruits
additional receptors
muscle spindle fibers (stretch-sensitive mechanoreceptors): use them to figure out
what molecular mechanism of sensory signaling/processing in touch receptors is
-big muscle in leg → doesn’t have a lot of these mechanoreceptor cells (MSF)
-fingertips → has a lot of these MSF
-why do we need a stretch receptor cell in our muscles? bc muscles make our limbs
move, they gives us sensory feedback which allows us to position our muscles
Weakly electric fish, homing pigeons, ferrets
-electric fish: can sense electric fields, sensitive to magnetic energy that
we’re unaware of they continuously fire AP in noncontractile muscles to put out
electric pulses to use in murky water to avoid obstacles, identify each other,
gender, etc. (communication), their muscles don’t contract, they use ventral fin
-homing pigeons: if you raise them somewhere, drive 20 miles away, release
them, they will return--they’re sensitive to earth’s magnetic fields (it’s like seeing
lines that orient north and south poles, a sense we don’t have)
-honeybee & white spider: white spider evolved to be white to help attract
honey bees to the flower, the white spider looks good in UV light which honey bees
can see but the birds that prey on those spiders don’t see UV light
-ferrets: when born are blind & deaf
-eye has 2 main projections:
1) synapse in LGN (allows you to see and recognize stuff) then
projects to the visual cortex (synapses there too)
2) Superior colliculus (which is in charge of orienting you towards
interesting things in the environment, w/in the structure there’s
a map of touch & acoustic & visual space all layered on top of
one another--there are multimodal neurons in sup. coll. that
respond to more than one type of stimulus)
-ear has one projection, the cochlea sends info to the inferior colliculus then
synapses in MGN, then goes to the auditory cortex
Normal: eye → LGN → visual cortex
eye → Superior Colliculus
cochlea → Inferior
Colliculus
-experiment: surgically remove superior and inferior colliculi in baby ferrets
(before any connections are made) results in the hearing pathway being
messed up, while the visual pathway is intact
-MGN is intact and it’s saying that it needs a connection to the visual pathway
connect to the MGN and makes synapses and the secondary cell goes to the
cortex--can cause auditory cortex to respond to visual stimuli-- ‘hearing
colors’
Which sensory systems mainly use graded potentials
Graded Potentials: Hearing, Balance, Taste, Vision
-receptor cells generate graded potentials and release graded amounts of
transmitter
Action Potentials: Touch, Olfaction
-receptor cells generate APs and have axons that project centrally
, “Labeled Line Code”
-how modality is communicated
-receptors in different senses are sensitive to specific energy types
-different senses have distinct channels for information about each modality
-each line from the sensory surface to where you receive it in the cortex is
labeled for specific energy data, so for example, flashing light at cochlea won’t do
anything
-Why is labeled line code good? Depolarization by any means will give you
perception appropriate for that sensory system
Example: cochlear prosthetic: someone has a problem in their auditory
system, the cochlea is functioning but sound isn’t able to get to the correct place to
depolarize proper cochlear hair cells, we can put a microphone and have it
transduce signals but instead of going from sound to electrical signals in the brain,
it goes from sound to electrical in an electrode, the device makes sound into
electrical impulses that then stimulate the appropriate part of the cochlea so the
person can hear, again this shows us that depolarization by any means is perceived
as that sensory systems’ energy
Example: if you hit your head and say you ‘saw stars’ or if you poke your eye
you may see a visual pattern--this is bc you are artificially depolarizing
Which sensory systems transduce which types energy?
-mechanical: touch receptors, hearing receptors, and balance receptors
transduce mechanical energy
-chemical: taste receptors and olfactory receptors transduce chemical energy
-thermal
-electromagnetic : photoreceptors transduce electromagnetic energy
-hearing, balance, vision can’t regenerate cells
-taste can regenerate cells
-olfaction has programmed cell death
Is there more than one sensory system that transduces mechanical energy?
YES
Somatosensory, auditory and equilibrium
Interesting note about taste receptors:
-they can also generate APs but the function of them is unknown, theory:
maybe for signaling among receptor cells within a taste bud, but for everyday
function they use graded potentials
Chemoreceptors and photoreceptors use GPCRs and second messenger cascades
-sugar molecule binds → cascade of events the close leaky K channels but
don’t affect Na channel, Na ions will depolarize the cell, the more depolarized the
more nt gets released
, -everytime you go through one step of the cascade you’re able to activate
more and more components--it’s amplified, this is how we are able to sense just
one molecule of sugar
receptive fields in fingertips versus back of the leg
-small receptive field in fingertips, large receptive field on back of leg
-all four sensory nerves have some form of a receptive field, if you stimulate
outside of that receptive field, that neuron doesn’t know the stimulus exists,
you must stimulate within the receptive field for neuron to get stimulation
-some nerve cells have tight receptive fields, others have large
-in touch & photoreceptors, the receptive field describes the region of
sensory surface that can generate a response → receptive fields carry
info about spatial location
-for a stimulus to generate a response it has to be within a receptor’s
“receptive field”
-diff receptor types have diff receptive fields
-receptors are arranged systematically at the sensory surface: a
“topographic” representation of the sensory surface is maintained
throughout the nervous system (this is an important organizational
principle of all sensory systems)
-size and density of receptive fields determine acuity
-acuity increases with more receptors and smaller receptive fields
-in hearing receptors, the receptor field describes the range of frequency that
can generate a response, it’s still a map, but not spatial info
-so how do we know where sound is coming from? Contact inhibition--we
have 2 ears which tell us where sound is coming from by arrival time
and intensity differences, a computational thing
two-point discrimination procedure (What’s it good for?)
-it shows the variability in receptor density: the more dense the receptors, the
smaller the receptive fields are and the more finer your ability to
distinguish stimuli
-a good way to measure receptive field size
intensity coding (various ways)
-for touch receptors: increase in pressure causes increase in response
magnitude
-signaled by population response
-different receptors have different thresholds and greater pressure recruits
additional receptors
muscle spindle fibers (stretch-sensitive mechanoreceptors): use them to figure out
what molecular mechanism of sensory signaling/processing in touch receptors is
-big muscle in leg → doesn’t have a lot of these mechanoreceptor cells (MSF)
-fingertips → has a lot of these MSF
-why do we need a stretch receptor cell in our muscles? bc muscles make our limbs
move, they gives us sensory feedback which allows us to position our muscles
