Exam2Lec2CutaneousSensation,Touch,andPain Flashcards
What is the somatosensory system?
A network of neurons that help humans recognize objects, discriminate textures, generate sensory-motor feedback and exchange social cues
Somatosensory receptors are what?
free nerve endings (no synaptic terminus, not myelinated)
sensation that they process is based on the shape of the receptor/protein at the receptive end of neurons
Nociception vs pain
Nociception is peripheral stimulation tellingus this can cause damge
pain is cognitive: no pain receptos; the brain motivates us to move away from damage
For modality Mechanoreception, Merkel cell receptor, what is the fiber type and role in perception and adaptation type?
Fiber type: AB
Role in perception: pressure, form, texture
adaptation type: slow
For modality Mechanoreception, Meissner corpuscle receptor, what is the fiber type and role in perception, and adaptation type?
Fiber type: AB
Role in perception: flutter, motion
adaptation type: rapid
For modality Mechanoreception, Ruffni corpuscle receptor, what is the fiber type and role in perception, and adaptation type?
Fiber type: AB
Role in perception: stretch
adaptation type: slow
For modality Mechanoreception, Pacinian corpuscle receptor, what is the fiber type and role in perception and adaptation type?
Fiber type: AB
Role in perception: vibration
adaptation type: rapid
For modality Mechanoreception, free nerve ending receptor, what is the fiber type and role in perception?
Fiber type: C
Role in perception: pressure
unmyelinated
For modality thermoreception, free nerve ending receptors, what is the fiber type and role in perception?
Fiber type: C and AY
Role in perception: C-> Warmth alpha delta->cold
For modality nociception, with the submodality SMALL, MYELINATED what is the receptor, fiber type and role in perception?
receptor: free nerve ending
Fiber type: alpha delta
Role in perception: sharp localized pain
For modality nociception, with the submodality UNMYELINATED what is the receptor, fiber type and role in perception?
receptor: free nerve ending
Fiber type: C
Role in perception: Burning
Mechanoreceptors are responsible for what?
Discriminative touch
What two layers do we have for mechanoreceptors?
Superficial layers and deeper layers
What type of receptors can we find on the superficial layers of mechanoreceptors?
- Meissner corpuscle: flutter, motion, more “general” touch and superficial pressure on skin
- Merkel disks: Pressure, form, texture, identification of “edges and stripes and shapes”
What type of receptors can we find on the deeper layers of mechanoreceptors?
- Ruffini corpuscle: stretch
- Pacinian corpuscle: deep pressure and vibration
What is receptive field?
An area of skin that when stimulated with an adequate stimulus, will cause a specific neuron to alter its activity, may vary in size
a stimulis to which a receptor is most sensitive
The highest density of neurons is where?
Index finger, palms of hands, and thumbs
What is two point discrimination?
The ability to discern that 2 nearby objects are truly 2 distinct points not one.
The ____ the receptive field, the more we are able to distinguish between sensations
SMALLER
the back, limb,s etc have a much higher threshold to discriminate 2 sep points
Explain cutaneous sensory transduction
- When skin is stretched, the membrane of the cell is stretched
- Ion channels open, get ion influx and can reach threshold generating an ap
- this then goes to neurons
channel stretches (mechano) and influx of ions occur
cutaneous receptors transduce degrees of skin deformation (stretch) or thermal energy
Receptors produce a generator potential through?
voltage or ligand gated ion channels
What do receptor code?
- Spatial location
- modality
- stimulation duration
- intensity
Perception of texture and pattern is a function of what two things?
Both rapidly and slowly adapting receptors
What are slow adapting receptors? And what they help us detect?
merkel disks and ruffini’s ending
helps us detect place and duration
keeps firing , respinds over course of stimulius
ex: holding on to a cup of water to maintain muscle control or holding on during tug of war
What are rapidly adapting receptors? and what does it help us detect?
Meissner corpuscle and Pacianian corpuscle
Helps us detect changes in form
rapidly responds to changes in stimulus. Gages what is not impt once the stimulus has been noticed
ex: putting on clothes and not sensing that you have clothes on for the rest of the day
Somatosensory info enters the CNS via what structure?
Via the dorsal root ganglia into the dorsal root
this is outside sc
Once somatosensory info enters the spinal cord, the sensory fibers carrying touch, pressure, and vibration (mechanosensory) info travel up where?
Posterior/dorsal column
Once somatosensory info enters the spinal cord, the sensory fibers pain and temp info travel up where?
Lateral column
remeber it crosses anterolaterally
Where do large myelinated fibers bifurcate?
At the dorsal root entry zone
one branch ascends in the posterior (dorsal) columns
the other branches synapses in deepr laminae of the sc
Where do small, myelinated fibers synapse?
In the dorsal horn of the spinal cord
Explain the dorsal column system for the lower body
- Mechnosensory information from the lower body enters the CNS at the lumbar spinal cord and travels up the gracile tract to the gracile nucleus in the caudal medulla.
- From there, same as upper body, it will CROSS at the internal arcuate fibers in the caudal medulla to continue traveling up on the opposite side. This crossing is known as DESCUSSATION.
- AFTER the internal arcuate fibers decussate, they form the medial lemniscus tract which travels up to the ventral posterior LATERAL nucleus of the thalamus (VPLN).
- Then it goes to primary and secondary somatosesnory cortex to integrate info.
Ventral Posterior (L)ATERAL
Nucleus = (L)otion for the BODY
Explain the dorsal column system for the upper body
- Mechnosensory information from the upper body enters the CNS at the cervical spinal cord and travels up the cuneate tract to the cuneate nucleus in the caudal medulla.
- From there, same as lower body, it will CROSS at the internal arcuate fibers in the caudal medulla to continue traveling up on the opposite side. This crossing is known as DESCUSSATION.
- AFTER the internal arcuate fibers decussate, they form the medial lemniscus tract which travels up to the ventral posterior LATERAL nucleus of the thalamus (VPLN).
- Then it goes to primary and secondary somatosesnory cortex to integrate info
Ventral Posterior (L)ATERAL
Nucleus = (L)otion for the BODY
If there is a LEFT spinal injury, which side of the body would loose mechanosensation?
left
If there is a RIGHT brainstem injury, which side of the body would lose mechosensation?
left
Explain the trigemino-thalamic-cortical pathway
- Mechanosensory information from the FACE enters the brainstem directly via the trigeminal ganglion and synapses in the principal trigeminal nucleus of the caudal medulla.
- Fibers immediately cross the midline and ascend via the trigeminal lemniscus to the ventral posterior MEDIAL nucleus of the thalamus.
- Then it goes to primary and secondary somatosesnory cortex to integrate info
Ventral Posterior (M)EDIAL
Nucleus = (M)akeup for the FACE
What are dermatomes?
Slice of skin that 1 spinal root or one brainstem CN roots carries info from. Helps clinically to localize things
there are 3 dermatomes in face inn by trig nerve
Where do we integrate different kind of touch info?
primary somatosensory cortex
Why do we have so many layers of the primary somatosensory cortex?
B/c we need to to driciminate touch coming in pain, proprioception, and more and we start integrating info and send it out for response.
What uses up the largest area of the ventral posterior complex (VPM; medial) and the somatosensory cortex and why?
The face uses up the largest area b/c a large density of information coming from a large number of neurons with small receptive fields.
What uses a smaller portion of the ventral posterior complex (VPL; lateral) and the somatosensory cortex?
thoracic region of the body
What region of the spinal cord takes up the biggest processing area in thalamus and somatosensory cortex?
cervical
What determines how big the nuceli are?
The density of info NOT amt of body they are responding to
At the level of somatosensory cortex, what structure do we have that represents how much brain processing there is for each body part?
homunculus
A tiny amt of skin in hand has the biggest area of processing , why?
It is b/c this is what we use for identification, it has a high density info and small receptive field
Explain somatosensory plasticity and give an example
It has lots of ability to change in response to stimuli that are coming in.
ex: amputate 3rd finger, the somatosensory complex does not create any dead or wasted space, it starts responding to neighboring neurons that are still sending input by using there processing space and you become more sensitive in other fingers
another example: learning to play piano at a young age, 2 fingers grow in plasticity and allocate more brain procesing space to play instrument
Do we have pain receptors?
NO, nociceptors respond to very
intense and possibly harmful stimuli
only conscoius perception
What is the role of thermoreceptors?
Responds to heat up until a certain threshold then nociceptors kicks in
What is the role of nociceptors?
responds to intense stimuli that can cause tissue damage
Aδ fibers perceives ____ pain type
acute, sharp, sting
cold
C fibers perceive ____ pain type
dull, long lasting
warmth
Are most Aδ fibers and C fibers nociceptors?
yes
Free nerve ending of Aδ fibers are excitatory or inhibitory?
Excitatatory amino acids (glut, aspartate, ATP)
What is capsaicin?
Capsaicin binds to an allosteric binding site on a vanilloid receptor** (VR-1)**. Allowing ion influx
capsaicin, acid, heat all open vr-1 recept. Lvls of capsaicin determines how much you like spicy food
Mechnoreceptive information enters the spinal cord via the dorsal horn and travels up the posterior/dorsal on which side?
ipsilaterally (same side), it will not cross until it reaches the brainstem.
Nociceptive information, on the other hand, will enter the spinal cord via the dorsal horn on which side via what structure?
Cross to the lateral side immediately via the anterior white commissure.
If you have a right sc lesion which side do we lose discriminatory touch and pain/temp perception?
Lose discriminatory touch on right side lose response to pain and temp on left side.
If you have a left sc lesion which side do we lose discriminatory touch and pain/temp perception?
Lose discrimiantory touch if the left side and pain/temp perception on the right side
What is the difference b/w ant. commisure and ant. white commissure?
ant commisure: small bundle of fibers connecting the 2 hemispheres
ant white commisure: this is in the sc, and this is where pain signals enters sc and crosses immediately
After pain signal crosses immediately at the ant white commissure, it travels through the ____ tract.
anterolateral
nociceptor-> enters dorsal root ganglia->deccusate immediate at ant white commissure-> up through ant lat tract of sc-> up into the brain
What is lissauer’s tract?
redundency crossing of nociceptor info @ multiple spinal roots 2-3 segments above and below dorsal root entry zone. Helps us maintain nociptive info
pain info does not come in at 1 spinal root, it comes in and crosses at multiple layers.
If you have a small sc lesion, at one spinal root, can you still get nociceptive info? Why or why not?
Yes you still get nociceptive info b/c it will cross @ another lvl (redudant)
Explain the anterolateral tract (neospinothalamic)
- Nociceptive information from BOTH the upper and lower body enters the CNS via the dorsal root ganglion and IMMEDIATLEY CROSSES at the anterior white commissure to the anterolateral portion of the spinal cord.
- From there, nociceptive information travels up the spinothalamic/neospinothalamic tract to the ventral posterior LATERAL nucleus of the thalamus.
- Finally, the fibers ascend to the primary (SI) and secondary (SII) somatosensory cortex where we begin integrating somatosensory information.
pain!
Explain the trigeminal system
- Nociceptive information enters the CNS at the pons.
- From there it will travel DOWN to the medulla,
- From there, nociceptive information travels up the trigemino-thalamic tract to the ventral posterior MEDIAL nucleus of the thalamus.
- Then it goes to primary and secondary somatosesnory cortex to integrate info
If you injury the medulla on the left side, where do you lose pain info on your face?
Both sides of your face, your whole face!
Injury to the medulla will lead to loss of nociception on both sides of the face.
Nociceptive pathway goes through entire ____ system to get away from painful stimulus now. and avoid in the future
limbic
has memory and emotional component
What are diff targets of the anterolat system?
- Anterior Cingulate/Insular cortex: Avoidance/emotional component that drive behavioral responses
- Amygdala: negative emotion
- Hypothalamus: fight or flight
- Superior colliculus: directs our attention to the source of pain
- Reticular formation: arousal (via release of acetylcholine) in order to respond to pain
- Periaqueductal Gray: pain control
What is referred pain?
It is when someone has somatosensory pain and it feels superficial/external but is actually pain from an organ
ex: heart attack (shoulder or arm pain)
What does allodynia mean?
perception of normally
non-nociceptive stimuli as being
painful
something that shouldn’t be painful, but is
ex:you have a sunburn, you put clothes , it hurts
What is hyperalgesia?
nociceptive stimuli
perceived as being more painful
than expected
feel worse than normal
ex: you have a sunburn, and someone slaps you on where your sunburn is
What is peripheral sensitization?
when you get allodynia
and/or hyperalgesia due to
peripheral mechanisms
ex: more histamine circulation
What is central sensitization?
allodynia
and/or hyperalgesia due to central
mechanisms
perception is exagerrated due to trauma/previous experience
Explain the peripheral sensitiztion inflamatory response/ axon reflex
- Trauma initiates inflammatory response which activates C fibers.
- This causes the release of neuropeptides (substance P, glutamate, etc.
- Now there is local sensitization around the site of the injury
Explain central sensitization
Neurochemistry
* Sensitization of NMDA receptors on spinal interneurons or directly on anterolateral tract neurons alters synaptic efficacy
Anatomic reorganization in spinal cord
* Loss of primary afferents results in sprouting of existing afferents in dorsal horn
Explain descending pain modulation
with the periaq gray
- Spinotectal fibers synapse in the periaqueductal grey (PAG) which projects to:
* Raphe nucleus: serotonergic projections
* Lateral Tegmental Nucleus: noradrenergic projections - These projections synapse on
enkephalinergic interneurons in the dorsal horn
pag releases serotonin and norepi and goes back down to reduce signaling at the lvl of the sc where inj occured and release enkepheline (reduce pain signal in nerv system)
Explain pain control in the spinal column
- You have serotonin and norepi (input coming from raphe nuclei and tegmental ) coming down
- this activates and releases enkephalin neuron at the sc
- this inhibits the C fiber (nocipetor) from synpasing onto the dorsal horn projection neuron to anterolat system
Explain phantom limb loosly
It is when you loose a peripheral body, but you feel like you still have that limb. Trigger points are going to become those areas of skin that were processed proximally as somatosensory cortex
ex: loss one arm, some response in areas of face and shoulder
