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Neuro 1 > Somatosensory Pathways > Flashcards

Somatosensory Pathways Flashcards

1
Q

adequate stimulus vs. modaility

A

adequate stimulus = light

sensory modality = vision

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2
Q

receptor (generator) potential

A

potential generated that is proportional to strength of stimulus

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3
Q

Where is somatosensory cortex?

A 
Postcentral gyrus (anatomical name)
Brodmann's Area: 3,1,2
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4
Q

how does NS encode information about the stimulus’s modality and intensity?

A

modality = Labeled line code: sensory coding for the modality, if stimulated by an adequate stimulus.

intensity = population code (increased number of receptors activated with increased intensity) and frequency code (increased int. = inc. rate of AP generation.)

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5
Q

receptive field

A

part of environment to which a neuron responds

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6
Q

resolution

A

ability to distinguish 2 seperate stimuli

  • if receptive field is small, then resolution will be high
  • low density of primary affarents in an area = large receptive field = decreased resolution = decreased affarents reaching cx
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7
Q

2 point discrimination

A

based on density of afferents in an area.
lips/tongue: 1-2 mm
fingertips: 3-5 mm
back/thigh: 4-7 cm

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8
Q

Posterior Column-Medial Lemniscus (PCML)

A

ascending sensory tract carrying proprioception, fine (discriminitive touch) and vibrations sense.
- comes from C1-S5

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9
Q

axons of PCML

A

very large diameter, heavily myelinated = very rapidly conducting
Aalpha fibers

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10
Q

damage to PCML causes…

A

ispilateral loss of vibratory sense, position sense and discrimitive touch below level of lesion (stereoanesthesia)
- rostral to decussation, medial lemniscus lesions result in contralateral losses that include the entire body excluding the head.

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11
Q

where are receptors of proprioception located?

A

proprioceptors found in:

  1. joint capsules (joint receptors),
  2. golgi tendon organs (tension in tendons),
  3. muscle spindles (measure change in m. length)
  4. skin mechanoreceptors (register contact with surfaces)
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12
Q

graphesthesia

A

discrimintive touch, ability to know what number is being traced in hand

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13
Q

stereogenesis

A

discrimitive touch, allows recognition of object placed in hand.

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14
Q

How is fine touch/proprio/vibration sensed in arm?

A

DCML/PCML

  • primary affarent with cell body in dorsal root ganglion comes into through the dorsal horn, and goes into dorsal columns (posterior funiculus) of the cervical enlargement
  • it ends up laterally in the fasciculus cuneatus
  • it ascends to the nucleus cuneatus in the caudal medulla where it synapses on a prethalamic relay neuron.
  • the secondary neuron then decussates at the internal arcuate fibers of the medulla and ascends through the pons in the medial lemniscus.
  • It synapses in ventral posterolateral nucleus of thalamus (VPL) medially to the leg. It then ascends through the internal capsule to the cortex.
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15
Q

How is fine touch/proprio/vibration sensed in leg?

A
  • primary order GSA from leg with cell body in dorsal root ganglia enters the lumosacral enlargement at the posterior horn and enters the posterior funiculus.
  • The fibers then ascend to the medulla via the fasciculus gracilis where they synapse in the nucleus gracilis on secondary affarents in caudal medulla.
  • The prethalamic relay neurons then decussate via the internal arcuate fibers.
  • They then run through the pons via the medial lemniscus
  • They pass through the midbrain and synapse on third order neurons laterally in the VPL.
  • Third order neurons then go through the internal capsule to the SS cx where they synapse on cortical neurons of the longitudinal fissure.
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16
Q

whats relationship of legs to arms in posterior funiculus for DCML?

A

leg tracts medial

arm tracts lateral

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17
Q

relationship of arms to legs in medial at decussation for DCML?

A

arms posterior
legs anterior
(stays this way into the medulla)

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18
Q

relationship of arm/leg in pons for DCML?

A
  • legs move from ventral postion to lateral position

- arms stay medial

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19
Q

sensory ataxia

A

dysmetria (a lack of coordination of movement typified by the undershoot or overshoot of intended position)
- wide base/stance
- stumbling
truncal sway
** lesion in cervical spinal cord will result in this lack of coordination **

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20
Q

relationship of arm/leg in internal capsule for DCML?

A

leg: inferior/caudal/posterior
arm: superior/rostral/anterior

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21
Q

what does anterolateral system sense?

A

GSA modalities of:

  • nociception (pain)
  • thermoreception (temp)
  • crude touch
  • 4 tracts, only 1 ends in cortex
22
Q

where are four tracts of ALS located in spinal cord?

A

in the anterolateral region of the cord

23
Q

four tracts of ALS?

A
  1. spinothalamic (projects to primary SS cx via thalamus - conscious perception)
  2. spinoreticular tract (focus attn)
  3. spinomesencephalic tract (pain modulation)
  4. spinohypothalamic tract (autonomic and emotional response)
24
Q

spinothalamic tract of ALS?

A

projects to SS cx. via thalamus

  • conscious perception
  • has ok localization because only runs unilaterally
25
Q

spinoreticular tract

A

projects to reticular formation

- important in alterting cx, focusing attention to noxious stimuli.

26
Q

spinomesencephalic tract?

A

goes to midbrain

  • info sent to periaqueductal grey (group of neurons near mesocephalic aquduct) which helps regulate pain modulation
  • subset spinotectal tract: sends info from spinal cord to superior colliculus which functions in visual reflexes: when noxious stimulus comes in - focus eyes there “visual reflex”
27
Q

spinohypothalamic tract

A
  • projects to hypothalamus
  • carries autonomic responses to stimuli
  • projects to limbic system so that there is an emtotional response to pain
27
Q

Anteriolateral system?

A
  • pain, temp, crude touch
  • primary affarents come in to dorsal horns where they synapse on secondary neurons.
  • they give off a motor neuron here to control reflex
  • second neurons ascend in in tract of lissauer (posterolateral tract) prior to decussation for a few levels.
  • they then will decussate through the anterior white comissure and will join the anterolateral system.
28
Q

axons of ALS?

A

Axons are smaller and can be lightly myelinated or unmyelinated.

  • ABeta = touch, temp
  • Adelta (small lightly myelinated) = fast initial pain with good resolution
  • C fibers = (small unmyelinated) slow pain with poor localization/resolution
  • somatotopy is good in spinothalamic and poor in others
  • spinothalamic = contralateral projection
  • others = bilateral projection
29
Q

orientation in ALS?

A

legs are more lateral
trunk/arms are more medial
- in VPL: the arms are more rostral/anterior and the legs are more caudal/posterior

30
Q

vascular lesion in lateral medulla?

A

lesion in posterior inferior cerebellar artery or lateral pons (anterior inferior cerebellar artery) result in loss of pain and thermal sensations over entire contralateral side of body and ipsilateral face.

31
Q

what supplies somatosensation to most of head?

A

CN V: Trigeminal n.

also the muscle of mastication - branchial arch origin

32
Q

three divisions of trigeminal nerve?

A

V1: opthalmic (sensory only)
V2: Maxillary (sensory)
V3: Mandibular (sensory and motor)

33
Q

where are trigeminal cell bodies?

A

almost all are in trigeminal ganglion.

- proprioceptive fibers however are located in the Mesencephalic nucleus.

34
Q

spinal nucleus of five:

A

ascends from pons into medulla and relays information about pain temperature and crude touch from V1,2,3
- The cell bodies located in spinal nucleus are analagous to dorsal horn prethalamic relay neurons.

35
Q

Pontine sensory nucleus of five

A

(Chief, Main, Principle) is responsible for proprioception, vibration and fine touch. These cell bodies are analagous to cell bodies in the nucleus cuneatus and nucleus gracilis

36
Q

Where do the spinal nucleus and pontine sensory nucleus of five go to?

A

local reflex arcs

  • thalamus (VPM) so that it can go to cx
  • RF
  • hypothalamus
  • cerebellum
37
Q

mesencephalic nucleus of V?

A

responsible for proprioception

39
Q

pain/crude touch and temp of face pathway?

A
  • primary affarent cell bodies located in trigeminal ganglion.
  • The fibers then enter the pons via the trigeminal nerve and descend to the medulla via the spinal tract of V. where they synapse with second order neurons at spinal nucleus of V.
  • second order neurons then will ascend and decussate in medulla and ascend through the pons to the ventral trigeminal thalamic tract (VTT) and eventually synapse in VPM of the thalamus.
  • third order neuron will then travel out to the lateral cortex.
  • somatotopy: Face (rostral), ear, head (caudal)
39
Q

trigeminal motor nucleus

A

the mesencephalic nucleus of V also sends fibers that synapse on the trigeminal motor nucleus.

  • trigeminal motor nucleus sends LMNs to mm. of mastication without input from the cortex.
  • axons are part of the V3 mandibular division
40
Q

how is sensory oriented in the trigeminal nerve SS pathways?

A

Face is more rostral (superior) in brain stem

  • ear in middle
  • head (more caudal/inferior in brainstem)
41
Q

trigeminal motor nucleus

A

the mesencephalic nucleus of V also sends fibers that synapse on the trigeminal motor nucleus.

  • trigeminal motor nucleus sends LMNs to mm. of mastication without input from the cortex and regulates the proprioception of mastication.
  • axons are part of the V3 mandibular division
42
Q

somatotopy of spinal nucleus of V?

A

upside down head
V1= most anterior
V2: middle
V3= most posterior

43
Q

Where are the branchial efferent LMNs?

A

trigeminal motor nerves to mm. of mastication

- located in trigeminal motor nucleus

45
Q

where are the branchial efferent UMNs?

A
  • trigeminal motor nerves to mm. of masticaion
  • UMNs are in corticobulbar tracts
  • origin area 4
  • run through the genu of external capsule to the trigeminal motor nucleus bilaterally
  • thus lesion superior to brainstem will not produce paralysis of masticatory muscle
46
Q

How do you sense pain/temp/crude touch in legs and arms?

A
  • primary affarents come in to dorsal horns (cell bodies in dorsal root ganglia) where they synapse on secondary neurons.
  • they give off a motor neuron here to control reflex
  • second neurons ascend in in tract of lissauer (posterolateral tract) prior to decussation for a few levels.
  • they then will decussate through the anterior white comissure and will join the contralateral anterolateral system.
  • The second order neurons will then ascend contralaterally in the ALS and will eventually reach the VPL where they will synapse on third order neurons
  • The third order neurons will project to the somatosensory cortex (arm rostral/anterior, leg caudal/posterior) through the internal capsule.
47
Q

Proprioception of the face?

A
  • proprioceptive primary affarent fibers enter the pons and ascend to the mesencephalic nucleus of V where they leave their cell bodies, then return back to the pontine nucleus of V where they synapse on second order neurons. The second order neurons project up contralaterlly through the VTT to eventually synapse on third order neurons of VPM, they are then sent out to post-central gyrus.
48
Q

UMN vs LMN lesion differences?

A

UMN: increased tone, increased reflexes, present babinski, no atrophy, weakness present and fasciculations absent

LMN: decreased tone and reflexes, no babinski, large atrophy and weakness. fasciculations are present.

48
Q

UMN vs LMN lesion differences?

A

UMN: increased tone, increased reflexes, present babinski, no atrophy, weakness present and fasciculations absent

LMN: decreased tone and reflexes, no babinski, large atrophy and weakness. fasciculations are present.

49
Q

where do nerve roots exit?

A

C1-7 exit above their cords
C8- exits between C7 and T1
all other nerve roots exit below their respective vertebrae.

Neuro 1 (14 decks)

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