CNS/sensory 3 - somatosensory Flashcards
what is somatic - bodily sensation mediated by
several types of receptors
describe the types of receptors - what makes them different
specialized end organss that wrap around afferent in skin
allows you to be sensitive and encode to specific types of energy
describe touch
mehcanoreceptors with specialized end organs that surround nerve terminal
end organs allow only selective info to activate nerve terminal
what mediates touch at superficial layers
meissner’s corpuscle
merkel disk
what mediates touch at deep layers
pacinian corpuscle
ruffini endings
describe meissner’s corpuscle
fluid filled structure enclosing nerve terminal
rapidly adapting
light stroking and fluttering (sensitive to light or weak stimulus energy and since rapidly adapting = sensitive to changes that occur via strokes or light vibrations)
describe merkel disk
small epithelial cells surround nerve terminal
slowly adapting
pressure and texture
describe pacinian corpuscle
large concentric capsules of connective tissue surround nerve terminal
rapidly adapting
strong vibrations (deep in skin)
describe ruffini endings
nerve endings wrap around spindle like structure
slowly adapting
Stretch and bending of skin - shape of object - can know this as you grab and touch object
describe proprioception
muscle spindles provide sense of static position and movement of limbs and body
part of somatosensory but closely related to motor control
what are mechanoreceptors activated by
stretching of cytoskeletal strands
describe activation of mechanoreceptors
mechanical deformation causes membrane of afferent to be deformed and put pressure or tension on cytoskeletal strands
they pull = open ion channels = mechanical transduction process
mechanical opening of ion channels
describe temperature
thermoreceptors are free nerve endings
contain ion channels
Respond to different temperature ranges
can also open via chemical substances
describe cold afferents
0-35 degrees c
Activated by menthol = casue ion channels to open, feels cold but skin not actually cold
describe warm afferents
30-50 degrees c
Activated by capsaicin = chemical compound in chile peppers, can activate warm afferents, if too much = pain
activated by ethanol = makes you feel warm
what do extreme temperatures do
activate pain receptors
temps out of ranges = pain
describe pain
nociceptors are free nerve endings
Contain ion channels that open in response to intense mechanical deformation, excessive temperature or chemicals - things that will/are producing tissue damage
pain afferents are
high modulated
enhanced - bottom up and suppressed - top down (can shut off pain)
descrive visceral pain receptors
activated by inflammation
inside body = respond to intense mechanical problems inside you and you feel pain
what are nociceptors enhanced by
many mediators
give basic pathway of nociceptors
1=tissue damage
2=activate nociceptors - fire aps
3=substance p released in spinal cord (neurotransmitter released to 2nd order neurons)
4= info goes to brain = pain
5 = enhancement of surrounding nociceptors by injured tissue and afferent feedback onto mast cells
6 = dilation of blood vessels, red, inflamed, pain
what is hyperalgesia
increased sensitivity to pain after injury = bottom up
happening by itself - out of your control - tells you damage is there and not to use it
what causes hyperalgesia
release of substance p onto mast cells (release histamine) and dilates blood vessels
also cells rupture and release all kinds of stuff - bradykinin, 5-ht, prostaglandin, k+
how is somatosensory info sent to brain - 2 ways
dorsal columns
anterolateral pathway
what dorsal columns send info about
touch and proprioception
describe dorsal columns pathway
light feather stimulus –> spinal nerve –> dorsal root ganglion –> enters dorsal root and goes up –> dorsal columns –> enters brainstem –> synapse on 2nd order neurons and crosses midline –> medial lemniscus (contralateral touch and proprio) –> thalamus –> somatosensory corext
what does ipsilateral mean
same side
dorsal columns carry ipsilateral touch and proprio
what does contralateral mean
opposite side of midline
what do anterolateral pathways send info about
temp and pain
describe anterolateral pathway
finger on candle –> spinal nerve –> dorsal root ganglion –> dorsal horn –> anterolateral column (spinothalamic), synapse on 2nd order neurons in segment and cross over around midline –> brainstem –> branches into reticular formation –> thalamus –> somatosensory cortex *receives contralateral info
where is lesion if ipsilateral loss of touch and proprioception at and below the level of the lesion
dorsal column lesioned, just one = ipsilateral touch and proprio
if left cervical dorsal columns lesioned - name symptoms
Loss of touch and proprioception perception starting at the left hand and proceeding down to the toes.
Touch and proprioception are normal on the right side of the body.
Pain and temperature perception are normal on both sides of the body.
where is lesion if bilateral loss of touch and proprioception from bellybutton down to toes but pain and temp intact
both dorsal columns
what happens in lesion right in middle of gray matter of spinal segment
Bilateral loss of pain and temperature in a thin strip at the level of my lower chest.
Touch and proprioception are intact.
describe brown sequard lesion
loss of touch, proprioception, temp and pain on left side
loss of touch and proprioception and motor on left side
loss of temp and pain on right side
lesions =
damage anterolateral columns - temp and pain from contralateral side
Damage dorsal column = loss of touch and proprio at level of lesion and below on ipsilateral side
damage single spinal segment = dorsal root is blocked so all somatosensory info blocked on ipsilateral side
left hemisection of spinal cord = where lesions are
describe somatosensory cortex
contralateral representation
has organized layout
what is order from lateral to medial
head
arms
legs
what has highest acuity
hands then head - face and lips
low acuity = back
what does somatosensory cortex drawing show
how much area is taken up by portion of body is porprotional to number of afferents that innervate area
small receptive fields = many afferent = high acuity
what happens if contralateral loss of all somatosensation corresponding to head
damage to lateral somatosensory cortex
what is referred pain
visceral and somatic pain afferents commonly synapse on same neurons in spinal cord
perception of pain = on skin, but activation of pain afferent = inside body
synapse on same 2nd order neuron so body does not know where it comes from
brain usually assigns to skin
heart attacks commonly produce pain in left arm
why does referred pain happen
labeled line code - brain knows modality and every location of afferents
has label
EXCEPT PAIN
what do descending pathways do
regulate nociceptive information
top down
describe descending pathways
periaqueductal gray matter (midbrain)
reticular formation (medulla)
dorsolateral funiculus - activates descending pathway
synapse on pain afferents = shut down pain, and substance p being released
analgesia
how can pain be reduced
presynaptic inhibition
describe reduction of pain through presynaptic inhibition
descending pathways from brainstem = release opiate neurotransmitters - presynaptic inhibition and inhibits substance p
same effect as morphine - site of action of opiates
