Somatosensory Flashcards
what is signal conduction in the nervous system?
conversion of external stimulus into electricity/chemical signals in the NS (occurs at level of sensory receptor)
what happens when a sensory receptor is stimulated?
stimulus transduction into the NS (ex pressure receptor pushed down when you touch something)
what is somatosensation?
provides us information about what is happening on the surface of our bodies and what is happening internally
what are the two somatosensory pathways?
touch and position
pain/temperature
what are mechanoreceptors?
senses light touch, pressure, vibration
what are Meissner corpuscles’ stimulus and function?
dynamic deformation (skin motion, sensation of rubbing hand on table and feeling it)
very adaptive, rapid adaption
what do Pacinian corpuscles detect and what their function?
vibration
rapid adaption
what do merkel cells detect? what is their speed?
indentation depth (hod hand to sand paper and feel it)
slow adaption
what do ruffini corpuscles detect?
stretch of the skin
slow adapt
what are some things mechanoreceptors cancode?
intensity, duration, location and modality of the stimulus
what mechanisms do mechanoreceptors use for intensity?
frequency code (how many action potentials are coming in from the sensory receptor being stimulated?)
population code (how many receptors are being stimulated)
what is adaption of duration of a stimulus?
process of minimizing sensation of certain sensations (like your cloths touching your skin all day)
what are slow adapting receptors good for?
touch discrimination and strech
what are fast adapting receptors good for?
motion and vibration
how do we encode for stimulus location?
somatic maps (similar to a dermatome)
what are receptive fields?
vary in size and density across the body more receptors in close proximity makes more specific reception
what is modality?
type or quantity of stimulus energy
what is specificity in encoding of motility?
different stimuli are detected by and go through different pathways
what is paresthesia?
usually painless and described as tingling or numbness skin crawling or itching (leg falling asleep when you sit on it wrong)
what is probilistic receptor specificity?
most sensory receptors are optimally sensitive to singe stimulus energy
what is anesthesia?
total loss of sensation
what is hypoesthesia?
reduced sense of touch or sensation
what pathway does info from touch travel on?
dorsal column / lateral lemniscus pathway
where does somatosensory info of the face travel?
trigeminal system
what pathway does pain/temp travel on?
anterolateral pathway / spinothalamic tract
where are the cell bodies first order neurons of the DCMl pathway?
dorsal root ganglia of spinal nerve, axon enters dorsal spinal cord
what dorsal columns does the DCMl pathway travel through and what is the difference between them?
fasciculus gracillis and cuneatis (C is upper bod, Gra is lower)
where do the first order neurons of the DCM terminate?
nuc gracills or cuneatus of lower medulla
In the DCMI, Axons of second order neurons ascend to the _____ and synapse onto third order neurons in the ________
thalamus
ventral posterior lateral nucleus of the thalamus
what are the second order neurons of DCMl called?
internal arcuate fibers (cross midline and travel as a path called medial lemniscus)
DCML third order neurons project to the
primary somatosensory cortex in
the parietal lobe
what is the somatosensoy cortex also know as?
A1
in the trigeminal system neuron 1 Receives projections from mechanoreceptors in face and oral cavity.
THEN Travel to the _____ in the ____
Main Sensory Nucleus in the mid Pons
in the trigeminal system Neuron #2 has Axons that project to _________
VPM of thalamus
in the trigeminal system the third neurons project to
somatosensory cortex for perception of mechanical touch of face
what is pain transmission called?
nociception
what are nocieptors?
free nerve endings located in skin (superficial), bones, joints and blood vessels
Transduction involves what?
ion channels on the thermoreceptor called Transient Receptor Potential (TRP) channels
Opening of channels on nerve ending depolarizes or hyperpolarizes sensory neuron (Na+ or K+)
what are thermal receptors?
free nerve endings in the skin that respond to warmth or coolness (detect in diff temp ranges, work best at middle of each receptors range)
what does the TRPV2 receptor detect?
noxious heat above 125
what does TRPV1 detect?
heat/capsaicin above 109
what does TRPV4 detect?
warmth (body heat and blood temp) above 77
what does TRPV3 detect?
warmth above 88
what des TRPM8 detect?
temps below 82
what does TRPA1 detect?
noxious cold below 64
what are the two clinical states of pain?
physiological pain (ex pain from injury)
neuropathic pain (cause pain from non pain events)
what is neuropathic pain?
result from injury to the peripheral or central nervous system that causes permanent changes in circuit sensitivity and CNS connections.
where is ceII body of the first order neuron of Anterolateral/ Spinothalamic Pathway
dorsal root ganglia just outside the spinal cord
The whole dendrite/axon extension is what kind of fiber?
myelinated AD fiber or an unmyelinated C fiber
in the aI/st The axon extends from the cell body in the DRG into the :
dorsal horn of the spinal cord, then travel approx. two vertebral levels
Anterolateral/Spinothalamic Pathway, The first order neuron then synapses with secondary
neurons in the _________
substantia gelatinosa of Rolando
Anterolateral/Spinothalamic Pathway, The spinothalamic tract has somatotopic organization.
meaning…
Its cervical, thoracic, lumbar, and sacral components are arranged from most medial to most lateral
respectively
Anterolateral/Spinothalamic Pathway, The axons decussate to the other side of the spinal
cord via the anterior white commissure to the
_________
anterolateral corner of the spinal cord.
Anterolateral/Spinothalamic Pathway The axons of the second order neurons terminate in
the________ and synapse onto
third order neurons. From there, signals go to the primary somatosensory cortex, cingulate cortex, and insular cortex.
ventral posteriorlateral thalamus
in the trigeminal path nerves synapse with second order neurons that mostly decussate and ascend in the ventral trigeminal thalamic tract to the _________________ to synapse with third order neurons to the face area of the SS cortex
ventral posterior medial nucleus of the thalamus
what is the pain matrix in central processing?
many higher order centers of the brain receive pain input at the same time and are able to react based on it
what role does S1 play in the pain matrix?
S1 informs pain intensity, modality, and location, but other brain region activities are more closely correlated to the experience of pain
what does the anterior cingulate cortex do in pain processing?
part of the limbic
system involved in emotional learning
what does the insula do in pain processing?
self-awareness, sense of self in pain, sense of visceral pain (gastric distension)
what does the prefrontal cortex do in pain processing?
anticipation of pain
Activated during placebo effect with PAG
what does periaqueductal grey do for pain processing?
important site of endogenous pain inhibition
what is the PAG?
hub of pain inhibition
PAG stimulates noradrenergic,
serotonergic, and opioidergic producing sites, e.g. locus coeruleus (LC), raphe
nucleus, and RVM respectively
what is allodynia?
pain produced by normally non painful stimui
what is hyperalgesia?
heightened response to a pain (hot water feels extra hot when sunburnt)
what is Peripheral sensitization?
Peripheral sensitization is a reduction in threshold and an increase in responsiveness of the peripheral ends of nociceptors (due to action of chems)
how does Peripheral sensitization work?
-These chemicals can bind to receptors on the distal peripheral nerves and depolarize them closer to threshold
-Persistent stimulation can also lead to an increase in Na+ channel number and subtype, and TRP channels, resulting in stronger depolarization events
what is Central sensitization
Central sensitization is an increase in the excitability of neurons within the central nervous system, either due to peripheral or central nerve damage and inflammation
how does Central sensitization happen?
A burst of activity in nociceptors alters the strength of synaptic
connections between the nociceptor and the neurons of the spinal cord
(hyperalgesia)
* Low-threshold sensory fibers activated by light touch begin to activate
neurons in the spinal cord that normally only respond to noxious stimuli
(allodynia)
