Exam Two - Somatosensory Physiology Receptors Flashcards
What are sensations?
virtual reality, how the nervous system transduces energy into perception
What is feature extraction?
what our sensory receptors do, these receptors extract different features of a given stimulus and send it to CNS
What is a general problem for all sensory systems?
representing multidimensional stimula with a single language - frequency of action potentials
best stimulus for a specific receptor?
adequate stimulus
- sensory receptors are activated by a specific stimuli
transduction
conversion of specific aspects of stimulus energy into membrane conductance change, that leads to a graded potential
generator potentials can lead to an…
AP
GP are membrane potential changes, that…
- may be summated
- degraded over time and distance
- are not sustained
What are two types of GP?
1 - receptor potentials
2 - synaptic potentials
Receptor potentials
- local responses that occur at a sensory receptor and in regions of the membrane that ghave only ligand gated channels
- graded in amplitude and duration
- proportional to the amplitude and duration of the stimulus
Where do synaptic potentials occur?
- postsynaptic membrane of dendrites, soma, or axon terminals.
- similar to receptor potentials
________ must reach a portion of the axon that contains voltage gated channels for generation an __________
receptor potentials, AP
The portion of the AXON. that is in contact with RECEPTOR does not have “voltage gates” channels, therefore the change in membrane potential is __________ and __________ of the applied stimulus
directly proportional with the intensity, duration
What are two types of graded potentials at the synapse?
EPSP, IPSP
depolarizing membrane potential = ________, hyperpolarizing membrane potential = _____________.
EPSP, IPSP
EPSP is…
local
depolarzing
graded
slow
electronic (passive spread and decremental)
__________ have common features with EPSP, both are graded, local, dissipate if AP is not generated.
receptor potentials
At the ___ or _________, generator potentials may be summated to the point where the threshold level for an AP is reached.
axon hillock, adjacent to sensory receptor (“trigger zone”)
Where is threshold voltage?
-55
what are the two types of graded potential summation?
temporal and spatial summation
temporal summation
- same stimulus
- repeated close together in time (high frequency)
spatial summation
- location of synaptic input
What are the 4 basic dimensions of a stimulus/sensation
1 - modality
2 - intensity
3 - location
4 - timing
modality
what the sensation type is
ex - vision, taste, smell, touch, etc…
submodality
quality of stimulus
- color vision
- touch vibration
intensity
how much of sensation
What is intensity coded by?
frequency code
What is intensity limited by?
absolute refractory period
neural mass
number of axons activated
location
where the sensation originated
receptive field
portion of the sensory space that can evoke neuronal responses upon stimulation
precise location
overlap of RFs increases ability to discriminate location
_______ increase likelihood of discrimination
small RFs
___________ improves discrimination
overlap of RFs
Size of RF varies with location, distal to proximal (increase/decrease)?
increase
size of RF varies with the density of innervation, distal to proximal (increase/decrease)?
decrease
Size of RF varies with stimulus intensity until_________
maximum size is reached
timing
when the stimulus starts and stops
adaptation rate
how long receptors continue to generate AP when the probe is in the RF and motionless
RA stands for?
rapidly adapting receptors
RA receptors
respond to dynamic aspects of the stimulus (movement: velocity and acceleration)
SA stands for?
slowly adapting receptors
SA receptors
respond to static (and dynamic) aspects of the stimulus, respond if the stimulus is there even if its not moving
temporal pattern of coding
receptors respond to the stimulus onset, duration, offset
Absolute threshold
feel it or not
- signmoid curve
- 50% of the time patients say they feel stimulation
why is using AT problematic?
AT changes with emotion state, mood, and distractions
differential threshold (JND)
minimus difference in stimululation that a person can detect 50% of the time
T or F? Differentiating is linear
False! It’s not!
It is better at lower intensity, as we go higher, the difference must be much bigger for perception of the difference
3 factors for differential threshold: point localization
1 - varies with location
2 - best on face and hands
3 - related to RF size
Two point threshold is related to….
1 - RF size
2 - innervation density
3 - RF overlap
How are somatosensory receptors classified? and what are the classifications?
classified by what part of the world they perceive
- exteroceptive
- proprioceptive
- interoceptive
cutaneous and subcutaneous mechanoreceptors
pacinian corpuscle
meissners corpuscle
ruffini ending
merkel cell
pacinian corp chart
ra, AB, contact vibration
meissners corp chart
RA AB contact flutter
ruffini ending chart
SA AB pressure, skin stretch
merkel cell chart
SA AB pressure, texture
muscle, deep mechanoreceptors
muscle spindle
golgi tendon organ
joint capsule-mechanoreceptor
stretch-sensitive free endings
muscle spindle chart
SA Aa muscle length and change in length
golgi tendon organ chart
SA Aa muscle tension, change in tension
joint capsule mechanoreceptors chart
SA AB joint angle and rate of change
stretch-sensitive free endings chart
SA A delta excess stretch or force
thermoreceptors and nociceptors
cool receptors
warm receptors
mechanical nociceptor
thermal nociceptor (2 types)
polymodal nociceptor
cool receptors
SA Adelta skin cooling
warm receptors
SA C skin warming
mechanical nociceptor
SA Adelta sharp pain (fast pain)
thermal nociceptor (2types)
RA Adelta burning pain
RA C freezing pain
polymodal nociceptor
RA C aching, burning pain (slow pain)
What are the receptors in glabrous (hairless) skin?
meissners corpuscle
merkels disks
pacinian corpuscle
what are the receptors in hairy skin?
hair-follicle receptor
tactile disk
ruffini ending
What stimulus does the pacinian corpuscle respond to?
vibration detector
responds to acceleration/deceleration points in skin indentation
why is the RF of pacinian corpuscle large?
because vibration travels easily through body tissues
what is the adaptation rate of pacinian corpuscle?
RA rapidly adapting
What is the receptive field size of pacinian corpuscle?
large
What type of fibers are pacinian corpuscles?
AB
what stimulus does meissner corpuscle respond to?
velocity change (ramps of skin movement)
can respond to slow vibrations called “flutter”
What type of fibers are meissners corpuscle?
AB
What is the adaptation rate of meissners corpuscle?
RA
What is the receptive field size of meissner corpsucle?
small!!
2 facts about meissner corpuscle you need to remember?
- may contribute to high spatial resolution of fingertips, lips, etc.
- capsule consists of flattened epithelial cells
Ruffini ending respond to what kind of stimulus?
responds to velocity ramp (dynamic phase) and the plateau (static phase) of skin indentation
encodes intensity (pressure) really well
describe the AP distribution of ruffini endings
AP during plateau are evenly spaced but frequency of AP increases with intensity
What is the receptive field size of ruffini endings?
large! large, stretch sensitive receptive field
What is the adaptation rate of ruffini endings?
SA
What type of fibers are ruffini endings?
AB fiber
What is special about merkel cells?
an epithelial cell that has a synapse with the neuron
obviously the receptor cannot produce APs
describe the AP distribution of merkel cells?
characteristic irregular discharge pattern during plateau phase
What is the receptive field size of merkel cells?
very small, punctate receptive field
What type of stimulus do merkel cells read?
a good intensity response, known as a “pressure receptor”
What is the adaptation rate of merkel cells
SA
What type of fibers are merkel cells?
AB fibers
______ receptors respond to a given simulus
All!! Each receptor extracts a different type of information from the stimulus
Describe the pathway from the skin receptor to the brain
receptors read stimulus, send it up the the nucleus cuneatus, then to VPL nuclei of the thalamus, and from there to the somatosensory cortex
