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Neuroscience > Lab 3 - Sensory and Motor Circuits > Flashcards

Lab 3 - Sensory and Motor Circuits Flashcards

1
Q

what are the 4 somatosensory circuits?

A

conduct sensory info from body’s skin, muscles, and joints; first 3 serve trunk/limbs, last for head/neck

  1. lemniscal
  2. anterolateral
  3. spino-cerebellar
  4. trigeminal
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2
Q

what does the lemniscal system carry and what does that mean?

A

epicritic sense (from trunk/limbs)

  • vibration (high frequency stimulation)
  • tactile form (2-point discrimination; separate location of 2 simultaneous touches near each other)
  • position sense (state position of limb w/o cues)
  • simple touch
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3
Q

what does the anterolateral (spinothalamic) system carry and what does that mean?

A

proprioceptive sense (from trunk/limbs)

  • pain
  • temperature sense
  • simple touch
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4
Q

what does the spino-cerebellar system carry and what does that mean?

A 
proprioreceptive sense (from trunk/limbs)
-muscle/joint information
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5
Q

what does the trigeminal system carry and what does that mean?

A

all sensation from head/neck

  • epicritic
  • protopathic
  • proprioceptive
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6
Q

how does information get to the lemniscal system?

A

comes to spinal cord via large diameter dorsal root axon

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7
Q

what are large neurons especially vulnerable to, and what does that mean for early symptoms of peripheral nerve disease?

A

vulnerable to ischemia, toxicity, bacteria

-means that early symptoms are “epicritic” (via lemniscal) instead of protopathic (anterolateral/spinothalamic)

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8
Q

how do dorsal root axons from lower trunk/limbs ascend spinal cord?

A

enter at lower thoracic and lumbosacral levels, send segmental collateral to dorsal gray matter, and ascend as gracile fasciculus (medial)

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9
Q

how do dorsal root axons from upper trunk/limbs ascend spinal cord?

A

enter at upper thoracic and cervical levels, and ascend as cuneate fasciculus (lateral)

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10
Q

how do epicritic losses on one side of the body correspond to fasciculus sides?

A

since fasciculi ascend cord on same side of the body they serve, damage to one side of body (left) would cause losses on same (left) side

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11
Q

where do the fasciculi synapse and what picks up the info? where do these axons exit? what do they become? where does it go now?

A

axons end in medulla, and info is picked up by second-order neurons whose cell bodies lie in gracile and cuneate nuclei

  • these axons exit nuclei and CROSS to other side in medulla to become medial lemniscus
  • ML ascends to thalamus
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12
Q

how do epicritic losses on one side of the body correspond to medial lemniscus and internal capsule sides?

A

since gracile/cuneate nuclei exit nuclei and cross to other side of medulla (and become ML), damage to one side of the ML or IC (right) would cause epicritic symptoms on patient’s other side (left)

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13
Q

where does the medial lemniscus synapse? what picks this up? where and how is it carried?

A

ML synapses in ventral posterolateral nucleus of thalamus, and info is picked up by 3rd-order neurons that carry it to postcentral gyrus via internal capsule

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14
Q

how does information get to the anterolateral/spinothalamic system? where do they travel? where do axons synapse?

A

small-diameter dorsal root axon
-travel in tract on dorsolateral aspect of SC (Lissauer’s tract, or dorsolateral fasciculus) up or down one or two spinal segments only, then synapse immediately in dorsal horn of SC (at/near level they enter)

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15
Q

where do axons go after synapsing in dorsal horn?

A

axons carrying information ascend in white matter of spinal cord as anterolateral (AL) or spinothalamic (ST) tract/system

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16
Q

do AL tract neurons cross the midline before or after ascending to brain? what does this mean for damage affecting sides?

A 
MOSTLY before (not all)
-thus, damage to AL tract on one side cause protopathic symptoms on opposite side of body
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17
Q

how do AL axons synapse? where do most terminate, and where do they go from there? where do the “few” terminate?

A

synapse diffusely and at every level in the brainstem

  • most: reticular formation
  • few: thalamus w/in VPL, dorsomedial and intralaminar nuclei
  • all relay info to same VPL of thalamus
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18
Q

how do spino-cerebellar system signals enter CNS? where do they carry it?

A

signals from muscle spindles and joint receptors enter CNS via dorsal roots
-after synapsing, SC tracts carry this info to same side of the cerebellum

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19
Q

how do spino-cerebellar axons from leg and lower trunk ascend? where do 2nd order neurons ascend within?

A

as part of gracile fasciculus (like lemniscal system)

  • terminate in dorsal nucleus of Clarke (or Clarke’s nucleus) in thoracic cord
  • 2nd order neurons ascend to cerebellum along lateral rim of white matter as dorsal spinocerebellar tract
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20
Q

how do spino-cerebellar axons from arm and upper torso ascend? where do 2nd order neurons ascend within?

A

as part of cuneate fasciculus to medulla (like lemniscal system)

  • synapse on accessory/lateral cuneate nucleus
  • 2nd order neurons carry signals to cerebellum as cuneocerebellar tract
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21
Q

do spino-cerebellar tracts cross?

A

usually not, but if they do, they usually re-cross prior to ending in cerebellum, so damage always corresponds to the same side

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22
Q

are clinical effects of damage to spino-cerebellar system seen often?

A

not really, b/c rarely damaged in isolation

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23
Q

where do trigeminal axons conveying epicritic sensation synapse? where do 2nd order neurons go?

A

immediately in principal/chief sensory nucleus of CN V and pontine part of spinal nucleus of CN V
-2nd order neurons leave nuclei, cross midline, and join medial lemniscus to VPN, which are then forwarded to postcentral gyrus (like lemniscal system)

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24
Q

what does the pathology of pontine portion of trigeminal system mean for head/neck damage?

A

epicritic losses on the same side if pathology before crossing (CN V or nuclei), and opposite side if after crossing (medial lemniscus, thalamus, cortex)

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25
Q

where do trigeminal axons conveying protopathic sensation synapse? where do 2nd order neurons go?

A

descend toward SC as spinal tract of CN V, synapsing in caudal part of spinal nucleus of CN V
-2nd order neurons leave caudal part, cross midline, and project to reticular formation, which go to VPN and other parts of thalamus (like anterolateral system)

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26
Q 
what do trigeminal lesions in:
-spinal trigeminal tract (medulla)
-nucleus of CN V
-pontine or midbrain level
cause?
A

first two cause protopathic losses on same side of head

last affects opposite side of head (b/c after crossing; reticular formation)

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27
Q

what can surgical lesions in spinal tract or nucleus in medulla do?

A

selectively relieve intractable pain in head/neck w/o impairing epicritic sensation

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28
Q

where do trigeminal axons conveying proprioceptive sensation synapse? where do 2nd order neurons go?

A

axons in CN V are continuous w/ neurons of mesencephalic nucleus of CN V
-travel as mesencephalic tract of CN V to synapse with neurons of motor nucleus of CN V (for jaw) and reticular formation before going to cerebellum

29
Q

what is the motor component of the trigeminal nerve?

A

axons arise from motor nucleus of CN V in pons, and innervate muscles of mastication on same side

  • pathology reduces both facial sensation and weakens jaw of patient
  • jaw may jut to side of injury when opened
30
Q

what are the 2 motor circuits and what do they do? are these damaged together or separately more often?

A

descending networks that carry motor commands to brainstem

  1. pyramidal - direct cortical input
  2. brainstem-spinal (AKA extra-pyramidal) - indirect cortical control

usually damaged together, causing marked weakness or outright paralysis of affected muscles

31
Q

what are the component tracts, origins, and controls of pyramidal motor circuits?

A

components: cortico-bulbar, -pontine, -rubro-olivary, and -spinal
origin: all areas of neocortex, esp. frontal and parietal lobes
controls: CN nuclei, cerebellum via pontine nucleus and cortico-rubro-olive circuit, and spinal motor neurons

32
Q

what are the component tracts, origins, and controls of extra-pyramidal motor circuits?

A

components: vestibulo-, tecto-, reticulo-, and rubro-spinal
origin: vesticular nuclei, tectum, reticular formation, and red nucleus
controls: indirect control via brainstem spinal pathway to spinal motor neurons

33
Q

where does the cortico-bulbar tract descend and what does it control?

A

through the brainstem, and controls neurons of all CN nuclei

34
Q

what will unilateral pathology of cortico-bulbar tract do?

A

weaken movement of head and neck on opposite side of body (b/c cross just rostral to level of CN being affected)

  • however, also ipsilateral CB, so that’s why not significant weakness, since bilateral projections sustain movement
  • only CN XII (tongue) and VII (face) affected
35
Q

where does the cortico-bulbar tract end and where does that signal go?
-is isolated damage common?

A

ends on pontine nuclei at base of pons

  • axons forward signals to cerebellum on opposite side
  • isolated damage doesn’t occur clinically
36
Q

what is the cortico-rubro-olivary circuit?

A

cortex sends connections to a projection of the red nucleus, that project to inferior olive that projects to cerebellum

37
Q

where does the cortico-spinal tract descend and what does it control? do they usually stay on the same side or not?

A

descends through brainstem and spinal cord

  • controls motor neurons of trunk and limbs
  • most cross midline in caudal medulla (pyramidal decussation), but a small number continue ipsilaterally
  • thus, brainstem pathology usually affects opposite side of body, while spinal cord pathology affects same side
38
Q

how does pyramidal pathology affect sides of the body?

A

since they generally mimic pyramidal tracts:

  • pathology in brainstem affects movement on opposite side of the body
  • pathology in spinal cord affects movement on same side of body
39
Q

what controls both pyramidal and brainstem spinal pathways?

A

motor cortex

40
Q

why do frontal lobe lesions often cause severe paralysis?

A

because precentral (motor) and premotor areas of cortex contribute to both direct and indirect pathways

41
Q

how does visual information enter the optic tract? and do they cross at any time?

A
  1. information leaves retina by way of 2 optic nerves
  2. at optic chiasm, the two nerves partially decussate
  3. axons from nasal half (temporal visual field) of each retina cross, but temporal half (nasal visual field) don’t
  4. retinal axons enter optic tract, which wraps around thalamus and crus cerebri
42
Q

what is the most important pathway and what happens if it’s damaged?

A

geniculo-calcarine pathway; damage has most severe effect on vision

43
Q

where do most axons from the eyes terminate? where do the rest go?

A

most: lateral geniculate nucleus of thalamus
the rest: continue past LGN in brachium of superior colliculus to pretectal area of nucleus on either side of posterior commissure; others to superior colliculus

44
Q

where do neurons from the LGN project?

A

to the occipital lobe via optic/visual radiations, terminate in primary visual cortex
-thus axons fan out and wrap around lateral ventricles

45
Q

where do axons carrying info about upper half of visual field pass? what does this mean pathology-wise?

A

deep to cortex of temporal lobe, and terminate in lingual gyrus
-pathology of temporal lobe or lingual gyrus causes scotomas upper visual field

46
Q

where do axons carrying info about lower half of visual field pass? what does this mean pathology-wise?

A

deep to parietal lobe, and terminate in cuneus gyrus

-damage to parietal lobe or cuneus gyrus causes scotomas in lower visual field

47
Q

other than the most important, where else do optic tracts send axons?

A
  • hypothalamus
  • pretectum
  • superior colliculus
48
Q

what does the hypothalamus govern vision-wise?

A

long-term reactions to light (resetting daily biological rhythms, detecting seasonal changes in light)

49
Q

what is the pineal body?

A

projection from hypothalamus that receives optic input

-related to seasonal changes in light

50
Q

what does the pretectum do vision-wise? how is it connected? where does info project?

A

connected via projection via posterior commissure

  • functions as light meter, getting bilateral input and calculating total light energy entering eyes
  • cross midline to other pretectal nucleus, or project to (parasympathetic) Edinger-Westphal nucleus of same side
  • pregang EW axons project w/ CN III to innervate ciliary ganglion to constrict pupil in response to light
51
Q

what will loss of Edinger-Westphal nucleus cause?

A

inability for pupil to constrict to light, created dilated pupils

52
Q

what does the superior colliculus govern vision-wise

A

function is uncertain, and no visual symptoms attend physiology-wise

  • involved in moving eyes, head, and axial muscles
  • optic input to colliculus allows rapid orientation of eyes and body to visual event
53
Q

where does CN VIII terminate? what do they carry?

A

dorsal and ventral cochlear nuclei, which lie on surface of inerior cerebellar peduncle at transition of medulla and pons
-each one carries info from only one ear (so left CN VIII, cochlea, or coclear nuclei causes deafness in left ear)

54
Q

where do 2nd order neurons from CN VIII arise and go?

A

arise in cochlear nuclei, and project to several nuclei in both sides of the brain, crossing mainly in caudal pons near medial lemniscus (in trapezoid body)

55
Q

when is there bilateral mixing of auditory information?

A

half of info ascends brainstem on left side, the other half on right side

  • so already at the 2nd order of neurons, much bilateral mixing
  • mixing continues at every level thereafter
56
Q

what does it mean when:

  • unilateral brainstem lesion at 2nd order axon and beyond (before cochlear nuclei)
  • patient has hearing loss in one ear
  • patient has hearing loss in both ears
A
  • no hearing loss, b/c much of info from both ears escapes injury
  • pathology in ear, CN VIII, or cochlear nuclei, but no deeper
  • bilateral pathology
57
Q

where do cochlear nuclei eventually terminate?

A
  • superior olive and other nuclei (trapezoid body, lateral lemniscus, etc.), or bypass
  • all info eventually ascends in lateral lemniscus
  • -much terminates in inferior colliculus –> medial geniculate nucleus of thalamus via brachium of inferior colliculus –> Heschl’s (transverse temporal) gyrus via internal cotex
58
Q

what is called the primary auditory cortex? where does this info go? what is it important for?

A

Heschl’s (transverse temporal) gyrus

  • primary sensory cortex for audition, important for distinguishing sound patterns
  • projects to surrounding secondary auditory areas
  • -importantly, Wernicke’s area in left hemisphere for perception of language
59
Q

what does unilateral damage to Heschl’s gyrus do compared to bilateral damage?

A

uni: little deficit (b/c processed bilaterally)
bi: inability to understand spoken language, since auditory info cut off from Wernicke’s area (word deafness)
- also if damage to left auditory cortex and corpus callosum, since left Heschl’s gyrus gets projections from right Heschl’s gyrus through CC)

60
Q

anterior nucleus

  • location
  • input
  • target
  • function
A
  • anterior tubercule
  • mammillary bodies (hypothalamus)
  • cingulate gyrus
  • emotions (?)
61
Q

dorsomedial/mediodorsal nucleus

  • location
  • input
  • target
  • function
A
  • medial to internal medullary lamina
  • amygdala, hypothalamus, spinal trigeminal nucleus, ALS
  • frontal lobe anterior to motor areas and orbital cortex
  • emotions and non-motor frontal lobe functions
62
Q

ventral anterior nucleus

  • location
  • input
  • target
  • function
A
  • lateral to internal medullary lamina
  • globus pallidus and cerebellum
  • premotor cortex
  • motor
63
Q

ventral lateral nucleus

  • location
  • input
  • target
  • function
A
  • posterior to ventral anterior nucleus
  • globus pallidus and cerebellum
  • precentral gyrus and premotor cortex
  • motor
64
Q

ventral posterolateral nucleus

  • location
  • input
  • target
  • function
A
  • posterior to ventral lateral nucleus
  • medial lemniscus (dorsal column nuclei)
  • postcentral gyrus
  • somatic sensation, body
65
Q

ventral posteromedial nucleus

  • location
  • input
  • target
  • function
A
  • medial to ventral posterolateral nucleus
  • medial lemniscus (trigeminal sensory nuclei)
  • postcentral gyrus (near lateral fissure)
  • somatic sensation, head
66
Q

pulvinar nucleus

  • location
  • input
  • target
  • function
A
  • posterior thalamus
  • superior colliculus, occipital, temporal, parietal lobes
  • occipital, temporal, parietal lobes
  • visual perception, language
67
Q

medial geniculate nucleus

  • location
  • input
  • target
  • function
A
  • posterior ventral surface of thalamus
  • inferior colliculus
  • auditory cortex
  • audition
68
Q

lateral geniculate nucleus

  • location
  • input
  • target
  • function
A
  • posterior ventral surface of thalamus
  • optic tract
  • visual cortex
  • vision
69
Q

intralaminar nucleus

  • location
  • input
  • target
  • function
A
  • embedded in internal medullary lamina
  • reticular formation, spinal cord, spinal trigem nucleus, ALS, globus pallidus
  • basal ganglia, diffusely to cortex
  • attention, arousal

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