10. Somatosensory Pathways 1 Flashcards

1
Q

The somatosensory pathway transmits and analyzes touch or tactile info from external locations, such as discriminative touch, vibratiion, proprioception. Transmitted via what two pathways?

A

Posterior column/medial lemniscal

trigeminothalamic pathway

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2
Q

The posterior column - medial lemniscal system (PCMLS) is involed in what ?

A

perception and appreciation of stimuli (tactile/proprioception)

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3
Q

PCMLS has somatotopic organization (homunculus) and allows two-point discrimination, which is?

A

ability to discriminate between two stimuli simultaneously

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4
Q

Peripheral receptor density gradient exists between various parts of the body. Which areas would have more or less?

A
Digits and perioral have increase density of tactile recep
Back and (legs) have decreased density of receptors
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5
Q

A receptive field is area of skin innervated by somatic afferent fibers, a small field has what?

A

high receptor density as compared to a large field with low density (back)

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6
Q

Primary afferent fibers consist of pseudounipolar cell body in the posterior/dorsal root ganglion (DRG) and has what processes?

A

Peripheral process to free nerve ending
Central process from DRG to CNS
dermatomes formed due to this

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7
Q

PCMLS specific afferent fibers enter the spinal cord via what?

A

medial division of poterior root and then branch

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8
Q

The largest set of branches will ascend to form the what? which collective are called posterior columns?

A

Fasciculus gracilis (LE/Lower Thoracics) or fasciculus cuneatus (UE/ Upper thoracics)

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9
Q

Fibers from medial to lateral within the fasciculus gracilis have sacral, then lumbar through T6. What about fasciculus cuneatus?

A

added laterally as they join the LE, thoracic levels above T6, lower cervical, upper cervical, which is the most lateral in the fasciculus cuneatus

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10
Q

A SC lesion in the fasciculus cuneatus or gracilis would result in?

A

ipsilateral loss of proprioception/touch to that level and below

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11
Q

What is it called when there is a loss of muscle stretch reflexes and proprioceptive loss from extremeties due to lack of sensory input?

A

Sensory Ataxia

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12
Q

The second order neurons of the PCMLS, which receive input from first order neurins, can be found in what, where?

A

in the nucleus gracile and nucleus cuneatus in the posterior medulla

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13
Q

From the second or neurons of the PCMLS, it sends axons to the contralateral thalamus via?

A

internal arcuate fibers

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14
Q

The internal arcuate fibers of the PCMLS cross the midline as the sensory decussation and ascend as what on the opposite side?

A

Medial Lemniscus ML

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15
Q

As the medial lemniscus moves rostrally, is rotates laterally in the pons, so the LE/UE fibers are located where inside?

A

UE are medial and LE are lateral

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16
Q

The medial lemniscus with the UE fibers medial and LE fibers lateral moves to the thalamus where is synapses where?

A

Ventral Posterolateral Nucleus (VPL)

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17
Q

What is the main blood supply to the cuneatus and gracilis fasciculus in the SC?

A

posterior spinal A

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18
Q

What is the main blood supply to the medial lemniscus and pyramids of the medulla?

A

anterior spinal A

19
Q

Damage of the BS in the midbrain of the medial lemniscus would lead to what? Why?

A

CONTRALATERAL deficits of touch and proprioception because the fibers of the PCMLS crossed in the medulla via internal arcuate fibers to ascend as the ML

20
Q

The ventral posterior nuclei are located in the caudal thalamus and are comprised of what?

A

ventral posterolateral and posteromedial nucleus (VPL/VPM) which are separated by arcuate lamina

21
Q

What is the blood supply to the VPL and VPM, which if compromised can result in loss of touch and sensation over contralateral body/head?

A

thalamogeniculate branches of posterior cerebral A

22
Q

The medial lemniscus terminates in the VPL with fibers from cuneatus and gracile nuclei terminating where?

A

cuneatus medially and gracile laterally within the VPL

23
Q

The VPL for the trunk and extremities contain two populations of neurons?

A
  1. third order neurons **majority

2. local circuit interneurons (inhibitory to stop firing rate of 3rd order neurons)

24
Q

From the VPL, most of the axons terminate in the third order neurons there which send axons that traverse what to where?

A

traverse the posterior limb of the internal capsule and terminate in primary/secondary somatosensory cortex

25
Q

From the posterior limb of the internal capsule, the third order neurons from the thalamus terminate in the somatosensory cortex, which is comprised of what?

A

postcentral and posterior paracentral gyri

26
Q

LE is medial, UE is medial, and face is lateral in the parital part of the brain. Which have the largest amt of receptors?

A

hands, feet, face

27
Q

If the ACA or MCA blood supply was cut to the left side of the brain, primarily at the somatosensory cortex, what would be seen?

A

the RIGHT side (cause fibers crossed) would have no touch sense or proprioception
(aca is LE, mca is upper body and face)

28
Q

What brodmann areas make up the primary somatosensory cortex from posterior to anterior? (4)

A

3a, 3b, 1, 2

29
Q

The secondary somatosensory cortex lies deep in the lateral sulcus, and gets input from what?

A

ventral posterior inferior nucleus of thalamus

30
Q

parietal cortical regions receive tactile inputs including areas 5 and 7 posterior to bordmann 2 area. Lesions here lead to agnosia which is?

A

limb is not recognized as part of the patients body

31
Q

Trigeminal carries main sensory for head and motor for mastication M. Afferents extend from cell bodies to trigeminal (semilunar) ganlgion which then does what?

A

forms continous cell column that extends from spinomedullary junction to rostral levesl of midbrain

32
Q

What are the two main sensory nucleus of the trigeminal inputs that relay info on touch and proprioceptions?

A
Main/cheif/princple sensory nucleus (msT) : touch and pressure
Mesencephalic nucleus (mes): proprioceptive from TMJ/mastication M
33
Q

The main sensory nucleus receives info on tacile and proprioceptive sensations. there is a dorsomedial and ventrolateral division which receive afferents from?

A

dorsomedial: oral cavity
Ventrolateral: V1,V2,V3

34
Q

Afferents from trigmenal N synapse in trigeminal ganglion and send axons to the main sensory nucleus, ventro is V1-3 and dorsomedial is from oral cavity. What happens next?

A

2nd order fibers from dorsomedial division travel IPSILATERALLY via posterior trigeminothalamic tract
2nd order fibers from ventrolateral division travel CONTRALATERALLY via anterior trigeminothalamic tract

35
Q

The posterior and anterior trigeminothalamic tracts have the same target of?

A

ventral posteromedial (VPM) nucleus in thalamus (oral cavity is medial and V1-3 is lateral)

36
Q

3rd order axons/fibers from the VPM nucelus in the thalamus project to what to get to the primary somatosensory cortex?

A

posterior limb of the internal capsule

37
Q

Tactile and proprioceptive information from UE/LE is relayed via PCMLS while head and neck is via

A

main sensory nucleus of trigeminal w some PCMLS

38
Q

The mesencephalic nucleus is comprised of pseudounipolar neurons and is the only nucleus in the CNS. What does it convey?

A

unconscious proprioceptive and pressure info from muscles of oral region

39
Q

What is this reflex: afferent limb: mesencephalic trigeminal neuron whose peripheral process innervates a masseter muscle and whose central process synapses on a trigeminal motor neuron (efferent)?

A

jaw-jerk reflex

40
Q

Mesecephalic nucleus via spinal nucleus (pars interpolaris) allows proprioceptive input from jaw/chewing via?

A

supeiror cerebellar peduncle

41
Q

From main sensory nucleus some 2ndary neurons project anterior to the vermis of the cerebellum via?

A

superior cerebellar peduncle

42
Q

What is important information that is relayed via trigeminocerebellar pathways?

A

jaw placement during mastication

43
Q

Cross sensory syndrome are different deficits that depend on where fibers cross. Brainstem: UE/LE is contralateral while face is ipsilateral. SC lesions can result in?

A

proprioceptive deficits on the right but anesthesia on the left (lack pain)

44
Q

SI leasions usually include larger areas and frequenctly result in more what?

A

global deficits, as compared to brainstem/brain injuries