Sensory Physiology Flashcards
Starting an AP
Sensory neurons have _______ that are opened or close in response to______
channels
stimulus
Starting an AP
for example, touch receptors have a _______ that is _____
Na channel
opened with deformation of the cell membrane
Starting an AP
Opening of channels produces a _________, similar to _____
local response
sub threshold response or epsp
Starting an AP
sub threshold response in sensory neurons is called
this depolarization is caused a “generator potential”
Starting an AP
getting an AP from stimulus
if the stimulus is strong enough or lasts long enough, the generator potentials will cause the afferent neuron to come to threshold and generate an AP
Starting an AP
where does the AP go
back to the spinal cord/brain
One of the best studied of the receptors that responds to touch
Pacinian Corpuscle
The Pacinian corpuscle is comprised of
alternating layers of membrane with fluid between them, surrounding the nerve ending
when we touch something, what happens to the pacinian corpuscle
all the layers of the membrane are deformed–> opening of mechanosensitive Na channels on the membrane and influx of Na–>generation of an AP back to the CNS
what happens when the stimulus is maintained on a pacinian corpuscle
the action potentials gradually die away as adaptation occurs
The adaptation in a pacinian corpuslce is due to
redistribution of fluid in the corpuscle so that the force is no longer transmitted to the nerve ending.
Much, but not all of the adaptation that occurs is the result of
changes in the periphery (directly altering the afferent)
In some cases of the receptor adaptation, the removal of the stimulus triggers
action potentials as the ending “reforms”
this is known as an afterdischarge
Afterdischarge is associated with
the persistence of the sensation after the stimulus eliciting the discharge has been removed (phantom glasses)
Sensory unit
the sensory nerve and all its branches
Receptive field
the area from which stimulation produces activation of the neuron
The number of ____ is one way of coding the intensity of a stimulus
Number of action potentials. (with greater intensity, we see more action potentials - with further increases we may se patterned discharges like doublets or triplets)
The number of ______ also increases with increased
receptors firing
The number of ______ also increases with increased
receptors firing
Just noticeable difference
the smallest difference that can be detected
a change of about 10% is usually required for conscious recognition of the change
The Relationship between perceived strength and actual (measured) intensity - Oricinaly described as
Weber Fechner Law
Perceived intensity =log(measured intensity)
The Relationship between perceived strength and actual (measured) intensity - New data suggests the following formula
perceived intensity =K(measured intensity)^A
where K and A are constants
The Relationship between perceived strength and actual (measured) intensity - K and A vary depending on
type of sensory receptor
K and A for muscle senses s
both are close to 1
meaning - our perceived intensity matches th actual intensity very closely
K and A for cutaneous senses
more variability
meaingin - what we perceive may diverge from the actual rather substantially
Sensory pathway to the brain for proprioceptive and discriminative touch
Dorsal columns
sensory pathway to the brain for thermal, nociceptive, and crude touch
spinothalamic tract
Spinoreticulothalamic system
nociceptive
In sensitive parts of our bodies, stimulus activates
more than one receptor due to overlap of receptive fields
Presynaptic inhibition is what kind of synapse?
What is the end result?
axo-axonal synapse (the post-synaptic cell is a pre-synaptic terminal)
End result of pre-synaptic transmission: reduced neurotransmitter release from the inhibited pre-synaptic terminal
Presynaptic inhibition - describe
Start with a a normal chemical synapse with NT release from A to B
add another neuron that synapses on the presynaptic terminal (A)
when activated neuron C releases GABA
which activates Cl entrance into neuron A
causing the presynaptic terminal of A to hyper polarize, and allow less Ca to enter
leading to less NT release
reducing the probability of AP in neuron B
Presynaptic inhibition occurs between
neighboring receptors at the first synapse in their pathway
this increases the brains ability to localize the signal
Regardless of which pathway is used, every synapse along the way represents a chance to
modify or respond to the stimulus
The sensory cortex is arranged
somatotopically
The somatosensory cortex is neocortex so it has
six layers
neurons in the somatosensory cortex are arranged in
columns
Each column deals with
one sensory modality in on part of the body
Sensory information arrives at its respective column in layer
IV (via the THALAMUS)
Somatic Sensory Area 1 (S1)
post central gyrus
brodmann;s 1, 2, 3
first stop for most cutaneous senses
Somatotopic representation - toes medial, head lateral
Somatic Sensory Area 2 (S2)
wall of lateral (Sylvian)fissure
receives input from S1
somatotopic representation - not as detailed as S1
Somatic Sensory Area 2 (S2)
wall of lateral (Sylvian)fissure
receives input from S1
somatotopic representation - not as detailed as S1
S1 is involved in
the integration of the information for position sense as well as size, shape discrimination
(I know the characteristics of the object in my hand, but not what the object is)
S1 feeds the processesed information to
S2
Somatic sensory area 2 (S2) is required for
cognitive touch
stereognosis
comparisons between two different tactile sensations
determining whether something becomes a memory
Describe damages to S1 and S2 and how they affect each other
Because of the wiring, damage to S1 will impair the functioning of S2
Damage to S2 will not impair the function of S1
One of the greates differences between human brains and the brains of other species is
the amount of cortex devoted to association areas
PTO association area
the parieto temporal occipital association cortex is required for high level interpretation of sensory inputs - so it receives that input from the different sensory cortical areas, including S1 and S2
PTO functions in
analysis of the spatial coordinates of self/surrondign objects
naming of objects
other functions related to other aspects of cognition
How the cortex can be changed by sensation
modification of input
plasticity
plasticity
early in life many of our experiences enable us to refine the map that is genetically coded in the cortex
this includes anatomically eliminating synapses as well as strengthening others
plasticity - if an area of the body is amputated or otherwise denervated
afferent input from remaining parts of the body will reinnervate the cortex
Plasticity - if an area of the cortex is lost
those afferents will innervate neighboring (remaining) columns
What’s the trade off in that plasticity
gain - the ability to detect the signal from the part of the body that the signal is coming from
given up - some of the precision bc now activating the column that is dedicated to something else
What you feel law
the doctrine of specific nerve energies
doctrine of specific nerve energies states:
stimulation of a sensory pathway at any point leads to the perception of a sensation that is dictated by the nature of the receptor that started the pathway
doctrine of specific nerve energies means
If I stimulate the cortical column that receives input from a pascinin corpuscle, you will perceive the sensation of light touch
Where you feel it law
law of projections
law of projections states
no matter where along the path we stimulate it, the perceived sensation is always referred back to the area of the body in which the receptor is located
law of projections means
that if the cortical column I stimulated receives input from a pacinian corpuscle in your left index finger, you perceive the touch as occurring on your left index finger.
