Somatosensory System Flashcards
Sensation
Triggering the first sensory neuron in a pathway
Perception
Conscious awareness of sensation
6 sensory systems
Vision Hearing Olfaction Taste Touch Pain/temperature
Why is it that touch and pain/temperature aren’t considered to be the same sensory system?
They use different neurons
Sensory receptor
First neuron involved in sensation
How is our perception of our environment limited by our sensory systems?
Above and below a given range, no change in sensation is detected
3 steps of perception:
1) _____ stimulus binds to _____ neuron
2) ____ stimulus is transformed into _____ signal
3) _____ awareness of ____ signal (____)
1) Physical Sensory 2) Physical Electrical 3) Conscious Electrical Perception
Vision: stimulus, receptor class, cell
Light
Photoreceptor
Rods/cones
Hearing: stimulus, receptor class, cell
Sound
Mechanoreceptor
Hair cells
Taste: stimulus, receptor class, cell
Chemical
Chemoreceptor
Taste bud
Olfaction: stimulus, receptor class, cell
Chemical
Chemoreceptor
Olfactory
Touch: stimulus, receptor class, cell
Mechanical
Mechanoreceptor
Dorsal root ganglia and cranial nerves
Pain: stimulus, receptor class, cell
Mechanical/chemical
Mechanoreceptor/chemoreceptor
Dorsal root ganglia and cranial nerves
Temperature: stimulus, receptor class, cell
Thermal
Thermoreceptor
Dorsal root ganglia and cranial nerves
Stimulus modality measures the ____ of a stimulus, answering what question?
Quality
What kind of stimulus?
Stimulus location answers what question?
Where is the stimulus originating from?
Stimulus intensity measures the _____ of a stimulus, answering what question?
Quantity
How strong is the stimulus?
Stimulus timing answers what question?
When did the stimulus start/stop?
The more intense the stimulus, the ____ the frequency of firing.
Higher
Adaptation determines whether the sensory receptor conveys ____ or _____ properties of the stimulus.
Static
Dynamic
What is the difference between static and dynamic receptor activation?
Dynamic- starting and stopping of firing, even in the presence of stimulus
Static- continuous firing as long as stimulus is present
What does the threshold of sensory receptor refer to?
How intense stimulus must be before sensory information is perceived
What type of receptors are known to have a particularly low threshold, and which ones are known to have a particularly high threshold?
Mechanoreceptors
Pain receptors
2 categories of mechanoreceptors: which responds to external stimuli, and which responds to internal stimuli? Both respond to _____ or _____ of tissue.
Tactile (external)
Propioceptors (internal)
Stretching or contracting
What is the difference between the nerve endings of mechanoreceptors vs pain and temperature receptors?
Mechanoreceptors have encapuslated endings, whereas pain and temperature receptors have free nerve endings
What type of sensory neurons have the biggest axons and are the fastest in conduction?
Proprioception
Proprioceptive neurons are labeled how? How is faster vs slower designated?
Roman numeral with lowercase letter
Lower the number and letter, faster the neuron (Ia is faster than Ib, which is faster than IIa)
Touch and pain neurons are labeled how? How is faster vs slower designated?
Uppercase letter with Greek letter
Lower the letters, faster the neuron (A alpha is faster than A beta, which is faster than B alpha)
Do dorsal root ganglia and cranial nerves have the same developmental origins? Do either of them develop from the neural tube?
No
No
From what region(s) of the body do the cranial nerves receive sensory information? What region(s) of the body do the dorsal root ganglia receive sensory information?
Face and neck
Rest of body
What do the cranial nerves develop from?
Cranial ectodermal placodes (ectoderm)
What do the dorsal root ganglia develop from?
Neural crest
Dorsal root ganglia carry ____ information to the ____ ____.
Sensory
Spinal cord
What is the role of growth cones in development?
Sense environmental signals and guide axons accordingly
What type of receptors are important for dorsal root ganglia axon guidance?
Neurotrophin
Neurons are guided to targets in developing system by _____ made by the targets.
Neurotrophins
Is it the targets in the developing system or the neurons themselves that contain the neurotrophin receptors?
Neurons
What is the name of the type of receptor with which neurotrophins interact?
Trk (“track”)
Can any neurotrophin interact with any Trk receptor, or do neurotrophins show affinity for specific Trk receptors?
Neurotrophins show affinity for specific Trk receptors
What is the name of the neurotrophin receptor to which any neurotrophin can bind?
p75
Do sensory neurons show equal affinity for all neurotrophins, or does each show affinity for one specific neurotrophin?
Show affinity for one specific neurotrophin
In addition to guiding the axon towards its target, what other role do neurotrophins play in the developing nervous system?
Favor survival of the guided neuron
What are the 2 types of neurotrophin signals? Which one acts in the short-term, and which acts in the long-term?
Local (short-term)
Retrograde (long-term)
The local neurotrophin signal is important for ___ ___ to respond to the ____ ____, enabling the axon to grow to the right place.
Growth cone
Guidance signal
The retrograde signal occurs when the neurotrophin binding to neurotrophin receptor triggers ______, and the ____ containing the receptor-ligand complex is transported ______ back to the ____ ____, where it promotes cell _____.
Endocytosis Endosome Retrogradely Cell body Survival
What would be two effects of knocking out neurotrophins or neurotrophin receptors in a developing system? Would these effects occur in all neurons in the system, or just the ones with affinity to the particular neurotrophin?
Axon wouldn’t grow to right place
Neuron could die
Just neurons with affinity to particular neurotrophin
What is the difference in outcome between neurotrophin binding to Trk receptors vs p75 receptors?
Trk receptor binding usually triggers positive outcomes for the neuron (guidance, survival), whereas p75 binding could trigger survival or apoptosis
What do the Trk receptors function as once neurotrophin has bound to them? On what side of the plasma membrane does this function take place? How does the function of p75 receptors differ from that of Trk receptors?
Trk receptors are kinases
Cytoplasmic side
p75 receptors aren’t kinases
What type of sensory neurons favor neurotrophin BDNF?
Merkel disks (tactile)
What type of sensory neurons favor neurotrophin NGF?
Nociceptive
What type of sensory neurons favor neurotrophin NT3?
Proprioceptive
The sensory cortex in the parietal lobe is (rostral/caudal) to the central sulcus.
Caudal (closer to the back of the brain)
Most sensory regions of the brain have a ___ _____ area that directly receives information and an _____ area that processes sensory information and integrates with other sensory information.
Primary sensory
Association
Information coming in from the cranial nerves and dorsal root ganglia is divided into ______.
Dermatomes
Dorsal root ganglia are located on (one/each) side of the spinal cord and service the (same/opposite) side of the body as where they are located.
Each
Same
Each dermatome is specific to a specific _____.
Vertebra
What are the 4 sections of the spinal cord, and what does each one service?
Cervical (shoulders and arms)
Thoracic (mid body)
Lumbar (legs and hips)
Saccral (back of legs, bottom, genital area)
The dermatome that covers the face and part of the neck is serviced by the _____ nerve, or ____ nerve ____.
Trigeminal nerve
Cranial nerve V (5)
All the information from a dermatome comes in through (a single/ multiple) dorsal root ganglia.
A single
Each dorsal root ganglion has many types of sensory neurons that have their ___ ____ in the dorsal root ganglion.
Cell bodies
Information entering dorsal root ganglia comes in through the ____ ____.
Dorsal root
Touch information enters through the ____ ____ and ascends up to the ____.
Dorsal horn
Medulla
Pain neurons have their first synapses in the ____ ___ and have ___ ___ neurons that bring the information up to the brain.
Dorsal horn
Second order
The homunculus shows proportional representation of ____ information in body parts. Which parts of the homunculus are biggest, and what does that say about the amount of space those parts take up in the sensory cortex?
Sensory
Mouth, tongue, lips, hands
Those parts take up the most space in the sensory cortex
The homunculus (sensory cortex) is pre-determined. What does this mean? Can it be changed at all by sensory input?
Develops in the absence of sensory input
Can still be changed by sensory input
First experiment that showed that the homunculus can re-map: after stimulating 2 fingers of a primate, what happened to the cortical area of the brain that was associated with the 2 stimulated fingers?
Area associated with stimulated fingers increased
Second experiment that showed that the homunculus can re-map: after removing a primate’s finger, what happened to the cortical area that had been associated with the removed finger?
The areas associated with neighboring fingers took over the cortical area associated with the amputated finger
The skin somatosensory receptors have their cell bodies in the ___ ___ ___.
Dorsal root ganglia
Somatosensory receptors in the skin are divided into what 2 categories?
Mechanoreceptors
Free nerve endings
Mechanoreceptors: what do the Ruffini receptors measure and are they located in the epidermis or dermis?
Skin stretch
Dermis
Mechanoreceptors: what do the Merkel receptors measure and are they located in the epidermis or dermis?
Light touch, edges, points, and curves
Epidermis
Mechanoreceptors: what do the Meissner receptors measure and are they located in the epidermis or dermis?
Heavy pressure and skin motion
Dermis
Mechanoreceptors: what do the Pacinian receptors measure and are they located in the epidermis or dermis?
Vibration
Dermis
Are hair follicle receptors considered to be mechanoreceptors or free nerve ending receptors?
Mechanoreceptors
Free nerve endings: 3 categories, located in epidermis or dermis
Pain, temperature, chemoreceptors
Epidermis
Threshold of skin mechanoreceptors is measured how and in what unit?
How much the skin is moved before perception takes place
Micrometers
Rate the skin mechanoreceptors in terms of highest to lowest threshold.
Highest: Ruffini
Merkel
Meissner
Pacinian
How is slow vs rapid adaptation defined?
Slow- signal through duration of stimulus
Rapid- fire at beginning of stimulus, then stop firing
What 2 skin mechanoreceptors have slow adaptation?
Ruffini
Merkel
What 2 skin mechanoreceptors have rapid adaptation?
Meissner
Pacinian
How is 2-point discrimination measured? Which parts of the body have the best 2-point discrimination?
With eyes closed, 2 points poke skin- how close can they be together and still be perceived as separate
Fingers and lips
Receptive field
Area served by single sensory receptor
With receptive field, how is receptor density related to discrimination, like in the 2-point discrimination test?
Higher density (more receptors per area), increased discrimination
How is receptive field size related to discrimination, like in the 2-point discrimination test?
Smaller the receptive field, increased discrimination (only if many receptors in that area)
Merkel receptors: relative receptive field size and receptor density, discrimination ability
Small receptive field, high receptor density
High discrimination
Pacinian receptors: relative receptive field size and receptor density, discrimination ability
Large receptive field, low receptor density
Low discrimination
Merkel mechanoreceptors: slow or rapid adapting (S or R), small (1) or large (2) receptive field, low or high threshold, label
Slow
Small
High
SA1
Meisner mechanoreceptors: slow or rapid adapting (S or R), small (1) or large (2) receptive field, low or high threshold, label
Rapid
Small
Low
RA1
Pacinian mechanoreceptors: slow or rapid adapting (S or R), small (1) or large (2) receptive field, low or high threshold, label
Rapid
Large
Low
RA2
Ruffini mechanoreceptors: slow or rapid adapting (S or R), small (1) or large (2) receptive field, low or high threshold, label
Slow
Large
High
SA2
When feeling a row of Braille dots, which skin mechanoreceptor’s response pattern will be the most like that of the stimulation pattern? Which will have a similar response pattern to the stimulation pattern, but not as similar as the first? Which 2 will give the least information? Does receptive field size, threshold, or adaptation rate seem to play the biggest role in determining the ability of a skin mechanoreceptor to respond to touching Braille dots? Are all the skin mechanoreceptors active in this example, or just the one(s) that are best at responding to the given type of stimulus?
Merkel Meissner Pacinian and Ruffini Receptive field size All skin mechanoreceptors
Spatial acuity is related to what? Is it more a property of individual neurons or multiple neurons? Why?
Discrimination
Multiple neurons
Depends on number of neurons present and size of receptive fields
In the dorsal root ganglia, sensory afferents go into the ___ ___ of the spinal cord.
Dorsal horn
Mechanosensory pathway from back 1/3 of head and rest of body as well as face: how many neurons and how many synapses required to get information to somatosensory cortex? In what region is the 3rd synapse?
3 neurons, 2 synapses
3rd synapse is in somatosensory cortex
Mechanosensory pathway from back 1/3 of head and rest of body: first neuron with cell body in ____ ____ ___ ascends (ipsilaterally/ contralaterally) to _____. This neuron is part of the ___ tract if it comes from the lower body and is part of the ____ tract if it comes from the upper body (cervical spine). The first synapse in this pathway is in the ____ or ____ nucleus of the ____, depending on which tract it is part of.
Dorsal root ganglia Ipsilaterally Medulla Gracile Cuneate Gracile or cuneate nucleus Medulla
Mechanosensory pathway from back 1/3 of head and rest of body: second neuron with cell body in ____ ascends (ipsilaterally/contralaterally) through the ___ ___ and synapses in the ____. What is the name for the fibers that cross in the medulla?
Medulla Contralaterally Medial lemniscus Thalamus Internal arcuate fibers
Mechanosensory pathway from back 1/3 of head and rest of body: third neruon with cell body in the ___ ____ ___ part of the ____ ascends into the ____ ____.
Ventral posterior lateral
Thalamus
Somatosensory cortex
Mechanosensory pathway from face: first neuron with cell body in ____ ____ enters (ipsilaterally/contralaterally) via ___ ___ ___. This neuron synapses in the ____.
Trigeminal ganglion
Ipsilaterally
Cranial nerve V
Pons
Mechanosensory pathway from face: second neuron with cell body in ___ ascends (ipsilaterally/contralaterally) through the ___ ___ and synapses in the ____.
Pons
Contralaterally
Medial lemniscus
Thalamus
Mechanosensory pathway from face: third neuron with cell body in the ___ ___ ___ part of the ___ ascends into the ____ ____.
Ventral posterior medial
Thalamus
Somatosensory cortex
Proprioceptors are located on ____ and ___ and give information about position of ____ with respect to the rest of the body.
Joints
Muslces
Limbs
To what part of the brain is proprioceptive information carried? Is it restricted to one side or shared across both sides of spinal cord as it is carried to this part of the brain?
Cerebellum
Shared across both sides of spinal cord
Do neurons that carry pain and temperature information conduct at a relatively fast or slow rate?
Slow
3 types of nociceptors and the type of information they convey
Mechanosensitive (physical)
Thermosensitive (thermal)
Polymodal (physical, chemical, and thermal)
How do thermoreceptors differ from thermosensitive nociceptors?
Thermoreceptors convey temperature information in the non-painful range
Do nociceptors and thermoreceptors have same or different pathways?
Same
Do pain and temperature receptors serve the same or different dermatomes as mechanoreceptors? Do they go up to the somatosensory cortex as the mechanosensory neurons do?
Same dermatomes
Yes
Pain and temperature neurons communicate with _____ neurons in the somatosensory cortex.
Mechanosensory
Different neurons receiving information about different sensory pathways enable _____ of sensations.
Distinction
Thermoreceptors’ increase in magnitude of firing is ____ in its optimum window: below that, ___ firing takes place and above that (in the ____ range), the rate of firing (continues to/doesn’t) increase.
Constant
No
Painful
Doesn’t
Nociceptors start firing once the stimulus is in the ___ range, but increases ____ until ___ ___ has taken place.
Painful
Constantly
Nerve damage
First pain is considered to be ____ pain, whereas second pain is considered to be ___ pain. First pain is (short/long)-lasting and second pain is (short/long)-lasting.
Sharp
Dull
Short
Long
The first pain neurons are designated ____, whereas the second pain neurons are designated ____. Which ones are lightly myelinated, and which ones are unmyelinated? Which ones synapse in more superficial layers of the dorsal horn?
A delta C First pain- lightly myelinated Second pain- unmyelinated Second pain synapse in more superficial layers of dorsal horn
Pain neurons cross to the (ipsilateral/contralateral) side of the dorsal horn and then send their axons through the ___ ___ ___ up to the ____.
Contralateral
Anterolateral white matter
Thalamus
In the 2 point discrimination test, if 2 points are indeed perceived, are the 2 points detected by the same or by different mechanoreceptors?
Different
For first pain coming from the body, the second synapse is in the ___ ___ ___ part of the thalamus and the third synapse is in the ____ ___. How does this pathway differ from that of second pain?
Ventral posterior lateral
Somatosensory cortex
Second pain can travel through many different pathways to many different brain systems
Pain and temperature pathways from back 1/3 of head and rest of body: first order neuron carries information through ___ ___ ___ and synapses in ____ ____.
Dorsal root ganglia
Dorsal horn
Pain and temperature pathways from back 1/3 of head and rest of body: second order neuron with cell body in ____ ____ crosses to (ipsilateral/contralateral) (dorsal/ventral) side and ascends through ____ ____ ____ tract up to the _____ and synapses in the ____ ____ ____ part of this brain region.
Dorsal horn Contralateral Ventral Anterolateral white matter Thalamus Ventral posterior lateral
Pain and temperature pathways from back 1/3 of head and rest of body: third order neuron with cell body in ____ ____ ____ of ____ ascends to and synapses in the ____ ____.
Ventral posterior lateral
Thalamus
Somatosensory cortex
Since pain/temperature and mechanosensory information travel to the same parts of the brain, do their neurons synapse on the same neurons in those parts of the brain? Why or why not?
No
Wouldn’t be able to differentiate pain/temperature from mechanosensory information if neurons were the same
Pain and temperature pathways from face: first order neuron comes in through _____ nerve (_____ nerve ___) and (ascends/descends) from ____ to _____, where it synapses.
Trigeminal Cranial nerve V Descends Pons Medulla
Pain and temperature pathways from face: second order neuron with cell body in ____ crosses to (ipsilateral/contralateral) side and ascends through ____ ____ tract to ____ and synapses in the ____ ____ ___ part of this brain region.
Medulla Contralateral Trigemino-thalamic tract Thalamus Ventral posterior medial
Pain and temperature pathways from face: third order neuron with cell body in ____ ___ ___ of ____ ascends to and synapses in ____ _____.
Ventral posterior medial
Thalamus
Somatosensory cortex
Injury to the spinal cord on one side only would affect touch sensation on the (ipsilateral/contralateral) side below the site of injury. Pain information would be affected on the (ipsilateral/contralateral) side below the site of injury. Why is this the case?
Ipsilateral
Contralateral
Pain ascends on the contralateral side, whereas touch ascends on the ipsilateral side
Damage to what quadrant of the spinal cord (left/right, dorsal/ventral) would affect pain sensation at and below site of injury on the left side? Why?
Right ventral
Information from left side enters through left dorsal horn and crosses to right ventral horn, so information entering site of injury would be coming through right ventral horn
Damage to what quadrant of the spinal cord (left/right, dorsal/ventral) would affect touch sensation at and below site of injury on the left side? Why?
Left dorsal
Information from left side enters through left dorsal horn and ascends through it to brain
Damage to the right ventral posterior lateral of the thalamus would affect pain and touch on what sides of the body? Why?
Left for both
Both pain and touch have crossed to contralateral side by the time the thalamus is reached
What does “referred” pain in internal organs refer to? What causes this phenomenon? How is this demonstrated in the cases of heartburn and heart attack?
Damage to internal organs can be perceived as external pain
Pain neurons that service skin also service internal organs
Heartburn: pain in esophagus is perceived near heart
Heart attack: pain in heart is perceived in left arm
The thermosensitive channels are designated how? What causes them to open up and pass ions? Do they detect only temperature, or do they detect other things?
TRP
Warming of membrane causes conformational change that opens channel
Detect other things (multimodal)
The mechanosensitive channels have how many subunits? What kind of structure is a part of each subunit, and how does it help channel function? What causes them to open up and pass ions?
3 (trimer)
Blade: amplify effects of stretch or vibration
Stretching of membrane causes conformational change that opens channel
TRPV1 can be on (nociceptive/non-nociceptive/either) receptors. What are 3 things that activate it (2 nociceptive/thermoreceptive, 1 spice)? Which one activates from the intracellular side? Why is spice called “hot?”
Either
Heat (nociceptive and non-nociceptive), acid, capsaicin (spice)
Capsaicin activates from intracellular side
Spice is called “hot” because it activates the same receptors responsible for heat
How do anagesic “heating” creams affect TRPV1 and thus pain?
“Heating” creams decrease expression of TRPV1, leading to decrease in pain
Each TRP receptor detects a specific range of ______.
Temperature
Pain propagation through voltage-gated channels: 6 steps
Painful stimulus -> mechanoreceptor -> depolarization -> open VG NaV1.7 -> open VG NaV1.8 -> action potential propagation
What voltage-gated Na+ channels do scorpion toxins normally bind to? What does this cause?
NAv1.7
Increased Na+ current and perception of pain
What about the voltage-gated Na+ channels of grasshopper mice enable the mice to not feel pain from scorpion stings? What type of pain is actually inhibited, first or second?
Mutation in NAv1.8 causes channel to be inhibited by scorpion toxin binding and provides analgesia
Second pain
A mutation to what voltage-gated Na+ channel causes congenital insensitivity to pain? Is it sensation or perception of pain that is blocked in this condition? Why? What kind of condition would occur with a gain-of-function mutation of this voltage-gated Na+ channel?
NAv1.7
Sensation of pain (nociceptive neurons don’t fire)
Person would perceive pain in absence of stimulus
NSAIDS: do they target inflammation or pain, examples
Inflammation
Aspirin, acetaminophen
NSAIDS target what enzyme? What does this enzyme make? What does this product cause in the body and what type of nerve endings does it activate?
COX enzymes
Prostaglandins
Inflammation
Free nerve endings (pain)
In hyperalgesia, what type of stimuli induce pain? What causes this and what is its purpose?
Non-painful
Enhanced sensitivity to stimuli
Protect injury from further damage
Allodynia is similar to (hyperalgesia/algesia) and occurs in the _____. What type of neurons have high activity, and what causes this increase in activity?
Hyperalgesia
CNS
Dorsal root ganglia
LTP-like changes in 2nd order neuron
What is neuropathic pain, and what causes it? What type of neurons are damaged and what is the result?
Pain in absence of painful stimulus
Disease
1st or 2nd order neurons are damaged, causing increased signaling
Descending control of pain: signals from various ____ regions can ____ pain signals at (many/a few) levels.
Brain
Modify
Many
Descending control of pain: descending inputs from the locus coeruleus can release _____ onto the (C fiber/ dorsal horn projection neuron) and descending inputs from the Raphe nucleus can release _____ onto interneurons that then release _____ (endogenous opioid) onto the (C fiber/dorsal horn projection neuron). Descending systems can (upregulate/downregulate/either) transfer of information from C fiber to projection neuron.
Norepinephrine Dorsal horn projection neuron Serotonin Enkephalin C fiber Either
What is phantom limb pain?
Person with amputated limb still “feels” limb and experiences pain
How does motor imagery for phantom limb pain work? Is it more or less helpful than other kinds of therapy?
Person imagines that limb is still there and can be controlled
Less helpful than other kinds of therapy
How does mirror therapy for phantom limb pain work? Is it more or less helpful than motor imagery?
Person puts functional limb in front of mirror and “sees” missing limb through mirror image of functional limb
More helpful than motor imagery
How does phantom motor execution for phantom limb pain work?
Electrodes attached to what’s left of person’s limb pick up signals intended for missing limb- person sees on screen movements of virtual limb
How is phantom limb pain evidence of top-down regulation?
Person experiences pain in amputated limb even though there is no limb to sense pain
