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S2 Neuroscience > Somatosensation > Flashcards

Somatosensation Flashcards

1
Q

pathways carrying somatosensation for the body enter the spinal cord how and where

A

in a segmental fashion

over the dorsal root of each spinal nerve

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2
Q

somatotopic organization

-describe what this means

A

throughout the transfer of information from the periphery to the brain, the segmental arrangement is maintained as a topographic map within the pathways and nuclei carrying each sensation

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3
Q

where do we see a representation of somatotopic organization ?

A

in the homunculus positioned over both primary somatosensory cortex and primary motor cortex

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4
Q

dorsal column/medial lemniscus system

-carries what sensations

A

conscious

  • proprioception
  • discriminative touch (two-point discrimination; light touch)
  • vibration
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5
Q

what carries proprioception, discriminative touch, and vibration for the face

A

CN V

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6
Q

DCML sensations are

  • encoded by…
  • enter spinal cord over what fibers
A

encoded by encapsulated nerve endings

enter spinal cord over Ia, Ib, and type II fibers

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7
Q

what is proprioception

A

information concerning movement and position of body parts

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8
Q

what are the two types of proprioception

A

conscious

unconscious

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9
Q

conscious proprioception is involved in…

-what is this?

A

kinesthesia

-sense of perception of movement of joints

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10
Q

stereognosis

  • what is it
  • what sensations are necessary to have it
A

ability to identify an object by feel

need proprioception and discriminative touch

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11
Q

unconscious proprioception is mediated (carried) by what tracts

A

spinocerebellar

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12
Q

DCML 1st order neuron

  • cell body is where
  • type of neuron
  • level of peripheral processes myelination
A

cell body is in dorsal root ganglia from S5 through C1
pseudounipolar neurons
peripheral processes are heavily myelinated (Ia, Ib, II)

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13
Q

DCML 1st order neuron

  • central processes level of myelination
  • central processes ascend via what tracts?
A

high level of myelination
tracts
-fasciculus gracilis
-fasciculus cuneatus

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14
Q

fasciculus gracilis

-carries fibers from what segmental entry points?

A

S5-T7

-lower trunk and lower limb

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15
Q

fasciculus cuneatus

-carries fibers from what segmental entry points

A

T6-C1

-upper trunk and upper limb

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16
Q

fasciculus gracilis and fasciculus cuneatus comprise what?

A

dorsal (posterior) columns

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17
Q

fasciculus gracilis and fasciculus cuneatus spacial organization within the dorsal columns

A

added sequentially in a topographic fashion from medial (lower extremities) to lateral (upper extremities)

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18
Q

DCML 1st order neuron

-how much of it is ipsilateral and contralateral to receptor that encoded sensation

A

entirely ipsilateral

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19
Q

DCML 2nd order neuron

  • location of cell bodies
  • these nuclei (from 1st part of question) are located at level of…
  • ascending fibers in dorsal columns synapse on…
A

cell bodies located in the nucleus gracilis and nucleus cuneatus, respectively
both nuclei are located at the level of the closed or caudal medulla
ascending fibers in the dorsal columns synapse on these nuclei

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20
Q

axons of DCML 2nd order neurons form…

-what do these do?

A

form the internal arcuate fibers

-these cross the midline to form the contralateral medial lemniscus

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21
Q

medial lemniscus

-projects to…

A

ventral posterolateral nucleus of the thalamus (VPL)

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22
Q

DCML 2nd order neuron

  • cell body ipsilateral or contralateral to 1st order neuron
  • what does the axon do?
A

ipsilateral

axon crosses the midline to eventually terminate in the contralateral thalamus

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23
Q

DCML 3rd order neuron

  • cell body location
  • axons go where?
A

cell bodies in VPL
axons of these neurons project through the posterior limb of the internal capsule to the primary somatosensory cortex (areas 3, 1, 2; postercentral gyrus in the parietal lobe)

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24
Q

DCML 3rd order neuron

  • projections to the postcentral gyrus is organized how?
  • what areas receive a greater representation within the cortex?
A

organized in a somatotopic fashion
areas of body that are most sensitive have greatest representation
3rd order neuron entirely contralateral to location of stimulus

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25
Q

DCML 3 neuron pathway exception

A

proprioception of the LE

  • includes Nucleus Z (part of Nucleus Gracilis) and Clarke’s Nucleus (sipinal cord levels T1-L2)
  • extra neuron is added between the dorsal root ganglion and the nucleus Gracilis
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26
Q

DCML alternative pathway

-what is the pathway

A

some large diameter 1st order fibers end in the ipsilateral dorsal nucleus of Clarke
2nd order neuron sends its axon out ipsilaterally to ascend in the dorsolateral fasciculus, adjacent to the dorsal spinocerebellar tract
-synapses in Nucleus Z
axons of nucleus Z join the internal arcuate fibers and cross to ascend as part of the contralateral medial lemniscus
rest of pathway is same as others

27
Q

location of Nucleus Z

A

rostral end of nucleus Gracilis

28
Q

DCML alternative pathway proposed purpose

A

possible neural pathway by which some conscious perception of proprioception for the LE is maintained when the dorsal column system is damaged due to trauma or degenerative illnesses

29
Q

anterolateral or spinothalamic system

-carries what sensations?

A

pain
temperature
non-discriminative touch

30
Q

spinothalamic system

-primary pathways

A

lateral spinothalamic pathway

anterior spinothalamic pathway

31
Q

how are the sensations of the spinothalamic system transported in anterior 2/3 of the face, oral and nasal cavities

A

trigeminal nerve and its cetnral nuclei and tracts

32
Q

lateral spinothalamic system carries what sensations

A

pain
temperature
(more localizable sensations)

33
Q

lateral spinothalamic system

-how does it get its name

A

named for the position of the fiber bundle of axons from the 2nd neuron

34
Q

lateral spinothalamic system 1st order neuron

  • type of neuron
  • cell body location
  • peripheral receptors are what type of nerve ending
  • fiber types
A

pseudounipolar neuron
located in dorsal root ganglia
peripheral receptors are free nerve endings
A-delta fibers (light myelinated)

35
Q

lateral spinothalamic system 1st order neuron

-A-delta fibers carry what sensation

A

pricking pain that is fairly localizable

36
Q

lateral spinothalamic system 1st order neuron

  • central processes enter spinal cord where?
  • bifurcate where?
A

enter spinal cord laterally

bifurcate in the Lissauer’s tract

37
Q

lateral spinothalamic system 1st order neuron

-how/where do they synapse?

A

may ascend or descend several segments, or enter dorsal horn at that level and then synapse on neurons in substantia gelatinosa/nucleus Proprius (Lamina of Rexed II, III)

38
Q

lateral spinothalamic system 1st order neuron

-what is the likely neurotransmitter in this pathway

A

glutamate

39
Q

lateral spinothalamic system 1st order neuron

-ipsi or contra to location of stimulus

A

ipsi

40
Q

lateral spinothalamic system 2nd order neuron

-cell body location

A

cell body location not known with certainty

-probably located in substantia gelatinosa and nucleus proprius

41
Q

lateral spinothalamic system 2nd order neuron

  • where do the axons go?
  • what do they form and where
A

axons move across midline, through anterior white commissure, in an ascending and oblique (1-2 segments) direction to form the lateral spinothalamic tract on the contra side of cord

42
Q

lateral spinothalamic system 2nd order neuron

-describe the somatotopic organization

A

lateral fibers carry pain and temerature sensations from lower body segments
medial fibers carry sensation from higher levels of spinal cord

43
Q

lateral spinothalamic system 2nd order neuron

-where does it end?

A

ascends through spinal cord and brainstem to reach the ventral postolateral thalamic nucleus (VPL) and intra-laminar thalamic nuclei

44
Q

lateral spinothalamic system 3rd order neuron

  • cell body location
  • ipsi or contra to stimulus
  • somatotopic distribution
A 
cell body is located in VPL
positioned contra to stimulus
somatotopic distribution
-lateral: LE
-medial: higher up
45
Q

lateral spinothalamic system 3rd order neuron

-axon location

A

ascend to primary somatosensory cortex via the superior thalamic radiations (medial part of the posterior limb of the internal capsule)

46
Q

location of primary somatosensory cortex

A

postcentral gyrus, cortical areas 3, 1, 2

47
Q

lateral spinothalamic system 3rd order neuron
-due to the somatotopic organization (same representation as in other neurons), the result is a representation of the contralateral body called…

A

a homunculus (little man)

48
Q

homunculus appearance

A

upside down, as if it is hanging by the lower limb with the leg representation in the midline cortex and the rest of the body on the lateral surface with the neck and head towards the lateral sulcus

49
Q

lateral spinothalamic system 3rd order neuron

-loss of these will result in…

A

loss of localization of pain, but not the affective emotional response to pain

50
Q

precision in the lateral spinothalamic system makes it useful to…

A

define lesion sites
possible to identify the level of a spinal cord lesion by the loss of painful stimulation
-termed anesthesia

51
Q

loss of pain over half the body would be a…

A

hemi-anesthesia

52
Q

parallel systems to the lateral spinothalamic tract

A

spinocervicothalamic
spinoreticulothalamic
spinomesencephalic

53
Q

spinocervicothalamic pathway

  • contains what that the lateral spinothalamic does not
  • what does it carry
  • this information is…
A

contains an extra neuron that originates in the dorsal horn and ascends ipsilaterally to a group of cells located at the level of the cervical dorsal horn
-these fibers joint the medial lemniscal system
carries
-modalities of conscious proprioception, discriminative touch, pain, temperature
information in this pathway is non-localizable

54
Q

spinoreticulothalamic pathway

  • have a synapse in the _____ of the brain stem
  • pathway eventually reaches…
A

synapse in reticular formation of brain stem
pathway eventually reaches medial and intralaminar thalamic nuclei that project to widespread cortical areas including the limbic system

55
Q

spinoreticulthalamic pathways

  • limbic system connections involve…
  • purpose of this connection
A

hypothalamus

activates or influences the ANS

56
Q

spinoreticulothalamic pathway

-purpose

A

functions to help in analyzing the stimulus within the emotional domain
activates the SNS response

57
Q

spinomesencephalic (spinotectal) pathway

  • projects to…
  • pathway can activate…
A

projects to the superior colliculus and periaqueductal gray in the midbrain
pathway can activate descending pathways that are critical for modulating incoming painful stimuli

58
Q

spinoreticulothalamic and spinomesencephalic pathways

-similarities in regards to ability to activate…

A

can activate descending pathways originating from Raphe’ nuclei (serotonin) and locus ceruleus (norepinephrine) of the reticular formation

59
Q

function of Raphe’ nuclei and locus ceruleus of the reticular formation

A

have descending projections to the spinal cord that function in the proposed circuitry used in the modification of the transmission of painful sensations

60
Q

anterior spinothalamic pathway

  • function
  • 1st order neuron fiber type
  • 1st order neuron neurotransmitter
A

carry light or non-discriminative touch and pain sensation
non-specific temperature information
C-fibers
carry sensation of burning pain, as well as thermal nociceptive impuses
neurotransmitter
-substance P

61
Q

anterior spinothalamic pathway

-location of neuron cell bodies (1, 2, and 3)

A

same as for lateral spinothalamic tract

62
Q

anterior spinothalamic pathway

-how do you demonstrate this sensation?

A

brush a piece of cotton across the skin

-patient is aware of being touched but is unable to identify texture or precise limits of the stimulation

63
Q

anterior spinothalamic pathway

-trajectory of 2nd order neuron axon

A

random

-may travel up or down 10 to 12 segments before it crosses through anterior white commissure

64
Q

anterior spinothalamic pathway 2nd order neuron

  • once axons have crossed, they form…
  • where does this go?
A

forms the anterior spinothalamic pathway

pathway ascends to VPL

S2 Neuroscience (25 decks)

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