CNS/sensory 3 - somatosensory

Question 1

what is somatic - bodily sensation mediated by

Answer 1

several types of receptors

Question 2

describe the types of receptors - what makes them different

Answer 2

specialized end organss that wrap around afferent in skin
allows you to be sensitive and encode to specific types of energy

Question 3

describe touch

Answer 3

mehcanoreceptors with specialized end organs that surround nerve terminal
end organs allow only selective info to activate nerve terminal

Question 4

what mediates touch at superficial layers

Answer 4

meissner’s corpuscle
merkel disk

Question 5

what mediates touch at deep layers

Answer 5

pacinian corpuscle
ruffini endings

Question 6

describe meissner’s corpuscle

Answer 6

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)

Question 7

describe merkel disk

Answer 7

small epithelial cells surround nerve terminal
slowly adapting
pressure and texture

Question 8

describe pacinian corpuscle

Answer 8

large concentric capsules of connective tissue surround nerve terminal
rapidly adapting
strong vibrations (deep in skin)

Question 9

describe ruffini endings

Answer 9

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

Question 10

describe proprioception

Answer 10

muscle spindles provide sense of static position and movement of limbs and body
part of somatosensory but closely related to motor control

Question 11

what are mechanoreceptors activated by

Answer 11

stretching of cytoskeletal strands

Question 12

describe activation of mechanoreceptors

Answer 12

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

Question 13

describe temperature

Answer 13

thermoreceptors are free nerve endings
contain ion channels
Respond to different temperature ranges
can also open via chemical substances

Question 14

describe cold afferents

Answer 14

0-35 degrees c
Activated by menthol = casue ion channels to open, feels cold but skin not actually cold

Question 15

describe warm afferents

Answer 15

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

Question 16

what do extreme temperatures do

Answer 16

activate pain receptors
temps out of ranges = pain

Question 17

describe pain

Answer 17

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

Question 18

pain afferents are

Answer 18

high modulated
enhanced - bottom up and suppressed - top down (can shut off pain)

Question 19

descrive visceral pain receptors

Answer 19

activated by inflammation
inside body = respond to intense mechanical problems inside you and you feel pain

Question 20

what are nociceptors enhanced by

Answer 20

many mediators

Question 21

give basic pathway of nociceptors

Answer 21

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

Question 22

what is hyperalgesia

Answer 22

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

Question 23

what causes hyperalgesia

Answer 23

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+

Question 24

how is somatosensory info sent to brain - 2 ways

Answer 24

dorsal columns
anterolateral pathway

Question 25

what dorsal columns send info about

Answer 25

touch and proprioception

Question 26

describe dorsal columns pathway

Answer 26

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

Question 27

what does ipsilateral mean

Answer 27

same side dorsal columns carry ipsilateral touch and proprio

Question 28

what does contralateral mean

Answer 28

opposite side of midline

Question 29

what do anterolateral pathways send info about

Answer 29

temp and pain

Question 30

describe anterolateral pathway

Answer 30

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

Question 31

where is lesion if ipsilateral loss of touch and proprioception at and below the level of the lesion

Answer 31

dorsal column lesioned, just one = ipsilateral touch and proprio

Question 32

if left cervical dorsal columns lesioned - name symptoms

Answer 32

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.

Question 33

where is lesion if bilateral loss of touch and proprioception from bellybutton down to toes but pain and temp intact

Answer 33

both dorsal columns

Question 34

what happens in lesion right in middle of gray matter of spinal segment

Answer 34

Bilateral loss of pain and temperature in a thin strip at the level of my lower chest. Touch and proprioception are intact.

Question 35

describe brown sequard lesion

Answer 35

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

Question 36

describe somatosensory cortex

Answer 36

contralateral representation has organized layout

Question 37

what is order from lateral to medial

Answer 37

head arms legs

Question 38

what has highest acuity

Answer 38

hands then head - face and lips low acuity = back

Question 39

what does somatosensory cortex drawing show

Answer 39

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

Question 40

what happens if contralateral loss of all somatosensation corresponding to head

Answer 40

damage to lateral somatosensory cortex

Question 41

what is referred pain

Answer 41

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

Question 42

why does referred pain happen

Answer 42

labeled line code - brain knows modality and every location of afferents has label EXCEPT PAIN

Question 43

what do descending pathways do

Answer 43

regulate nociceptive information top down

Question 44

describe descending pathways

Answer 44

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

Question 45

how can pain be reduced

Answer 45

presynaptic inhibition

Question 46

describe reduction of pain through presynaptic inhibition

Answer 46

descending pathways from brainstem = release opiate neurotransmitters - presynaptic inhibition and inhibits substance p same effect as morphine - site of action of opiates