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Brain and Behavior Exam 2 > Lec 28 Motor System Neuroanatomy > Flashcards

Lec 28 Motor System Neuroanatomy Flashcards

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1
Q

What composes the pyramidal tract? Where do these fibers go?

A
  • descending cortical fibers from sensory + motor areas of cerebral cortex
  • fraction of these extend into spinal cord via cotical spinal tracts
  • the rest terminate in brainstem nuclei in mid/pons/med
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2
Q

What is the difference between anterior [ventral] and lateral corticospinal tracts?

A
  • lateral = contralateral fibers that crossed in the pyramidal decussation
  • anterior = ipsilateral, smaller tract of fibers
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3
Q

What motor pathways make up the lateral group? function?

A

lateral and anterior corticospinal tracts
rubrospinal tract

  • these tracts target motoneuronal pools important for fine motor control of distal muscles
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4
Q

Where does lateral corticospinal tract [LCST] originate? path? terminate? role?

A

originate: motor and sensory cortex
path: crosses at medulla, descends contralaterally
terminate: contralateral spinal interneurons, LMNs
role: fine motor control of distal muscles

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5
Q

Where does rubrospinal tract originate? path? terminate? role?

A

originate: red nucleus [midbrain]
path: crosses, descends contralaterally
terminate: contralateral spinal interneurons
role: activate flexor aMNs, inhibit extensor aMNs

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6
Q

Where does tectospinal tract originate? path? terminate? role?

A

originate: superior colliculus [midbrain]
path: crosses, ends at cervical spinal cord
terminate: interneurons, CN 3, 4, 6 nuclei
role: postural reflexes of head, neck rotation

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7
Q

Where does lateral lateral vestibulospinal tract originate? path? terminate? role?

A

originate: lateral vestibular nucleus [pons]
path: ipsilateral
terminate: ipsilateral γMNs, interneurons
role: maintain posture, tonic excitation of axial extensors

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8
Q

What motor pathways make up the medial group? function?

A
  • tectospinal tract
  • lateral vestibulospinal tract
  • medial reticulospinal tract
  • lateral reticulospinal tract

function: mostly target motoneuronal pools that control axial and proximal muscles. control body posture and reflex adjustments to posture [act against gravity]

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9
Q

Where does medial reticulospinal tract originate? path? terminate? role?

A

originate: pons reticular nuclei [pons]
path: ipsilateral tract
terminate: ipsilateral γMNs, interneurons
role: maintain posture, facilitate axial extensors

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10
Q

Where does lateral reticulospinal tract originate? path? terminate? role?

A

originate: medullary reticular nuclei [medulla]
path: bilateral tract
terminate: interneurons
role: maintain posture, inhibit axial extensors

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11
Q

Where in spinal cord does anterior [ventral] corticospinal tract terminate?

A

extends only to upper thoracic levels

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12
Q

What types of neurons do corticospinal axons terminate on?

A
  • mostly spinal interneurons

- some monosynaptic connections directly to alpha motoneurons

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13
Q

What is the medial vestibulospinal tract? function?

A

origin: medial vestibular nucleus
path: descend in MLF
terminate: terminate on spinal interneurons in cervical spinal cord
function: neck posture, facilitates neck extensors

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14
Q

What is fasciculus proprious?

A

fiber tract adjacent to central grey at all levels

  • arises from intrinsic interneurons of spinal cord
  • forms ipsilateral and contralaterl ascending and descending intersegmental connections

function: integrate motor activity at different spinal levels [eg in reflexes]

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15
Q

What is organization within lateral corticospinal and spinothalamic tracts?

A

legs [lumbosacral] are lateral –> cervical is medial

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16
Q

what is organization within dorsal column tracts?

A

organized as you are –> arms outside, legs inside

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17
Q

Which descending motor tract is responsible for head/neck rotation, begins at the superior colliculus in midbrain, and ends at cervical spinal cord?

A

tectospinal tract [medial group]

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18
Q

Match these tracts and the sites of their origin:

  1. medial reticulospinal
  2. lateral reticulospinal

A. medulla
B. pons

A 
medial = pons
lateral = medulla
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19
Q

Which descending motor tract is bilateral and inhibits axial extensors?

A

lateral reticulospinal tract [LRST]

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20
Q

What is mech of anti-gravity muscle control of static posture? which 5 structures involved?

A
  • VST, lateral RST, medial RST, cerebral cortex, cerebellum

lateral VST and medial RST –> tonic excitation of antigravity extensors]

purkinje cells of cerebellum –> inhibit lateral VST

cerebral cortex –> stimulates lateral RST –> inhibits extensors

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21
Q

What are 2 types of inhibitory input to balance out tonic excitation of anti-gravity extensors by lateral VST and medial RST?

A

purkinje cells of cerebellum –> inhibit lateral VST

cerebral cortex –> stimulates lateral RST –> inhibits extensors

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22
Q

Are vestibulospinal tracts under cortical or cerebellar control? how?

A
  • under cerebellar control
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23
Q

What is decerebrate rigidity model?

A
  • brainstem transected cat at intercollicular level has excessive hypertonia of extensor anti-gravity muscles
  • lesion knocks out cortical inhibitory input to lateral RST; have unbalanced γMNs [from lateral VST and medial RST]

also called gamma rigidty

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24
Q

How do you alleviate decerebrate/gamma rigidity?

A
  • section the dorsal root [DRG] input from extensor muscles –> breaking the 1a/2 afferent arc
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25
Q

What is hypertonia?

A

excessive muscle tone = increased resistance to passive limb manipulation

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26
Q

What are signs of spasticity?

A
  • hyperactive stretch reflexes
  • hypertonia of anti-gravity muscles [arm flexors, axial extensors]
  • clasp-knife resistance [initial strong resistance to passive manipulation that decreases as manipulation maintained
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27
Q

What causes spasticity?

A
  • damage to upper motor neurons [UMNs], motor cortex, cortical tracts [internal capsule, corticospinal tract]
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28
Q

What causes rigidity?

A
  • parkinsons

- damage to basal ganglia

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29
Q

What are signs of rigidity?

A
  • hypoactive muscle reflexes
  • hypertonia in both extensors and flexors
  • cog-wheel resistance [limb moves like a ratchet when manipulated]
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30
Q

Where is primary motor cortex? function?

A

M1 area 4

location: precentral gyrus
function: motor execution

31
Q

Where is premotor cortex? function?

A

PM, area 6

location: anterior to M1
function: sensory guided movement planning

32
Q

Where is supplemental motor area? function?

A

SMA or M2, area 6

location: above cingulate gyrus
function: internally generated movement planning

33
Q

What are some features of all motor cortical areas?

A
  • neurons active prior to movement onset
  • low threshold of excitability
  • granular: lack prominent layer 4
  • receive inputs from thalamic nuclei
  • contribute to pyramidal tract either directly on spinal MNs via corticospinal tract or via indirect descending brainstem projections
34
Q

What does it mean that motor cortical areas are granular?

A
  • lack prominent layer 4 [major somatosensory layer]
35
Q

What are brodmann’s areas corresponding to S1 [primary somatosensory cortex]?

A

areas 3a, 3b, 1, 2

36
Q

What is brodman’s area corresponding to M1?

A

area 4

37
Q

what is brodmann’s area corresponding to PM [premotor cortex]?

A

area 6 [lateral]

38
Q

what is brodmann’s area corresponding to SMC/SMA/M2?

A

area 6 [medial]

39
Q

Do motor cortical neurons fire after or before movement onset?

A

before!

40
Q

Do motor cortical neurons have high or low threshold for activation?

A

low threshold [because direct connect with spinal cord]

41
Q

What thalamic inputs does M1 receive? where does that thalamic nucleus get it’s own input?

A

cerebellum –> VLp –> M1

42
Q

What thalamic inputs do PM + SMA receive? where does that thalamic nucleus get it’s own input?

A

globus pallidus –> VLa –> PM and SMA

43
Q

How is M1 organized?

A 
somatotopically
legs = medial; face = lateral
disproportionate: hands, feet, mouth
all contralateral
organized in interconnected micro columns
44
Q

What is difference small vs large [betz] cells in M1?

A

small = 90% of neurons, fire proportional to force generation, directionally selective, get sensory feedback,
function: control delicate movement

large [betz] = 10%, all or non firing, no sensory feedback,
function: ballistic/powerful movement/grasping

45
Q

What is effect of M1 lesions?

A
  • permanent loss of fine motor control

- loss of individual finger movements

46
Q

What is function of premotor cortex?

A
  • neurons discharge prior to M1 activity
  • prepares upcoming motor acts based on sensory-related instructional cue [gets input from parietal/visual/auditory/striatum]

ex. the monkey who has to anticipate when the light goes on he goes

47
Q

What is effect of PM lesions?

A

impairment in performing sensory-guided motor tasks

48
Q

What is function of the SMA/SMC? organization?

A
  • self generated motor planning, bimanual coordination

- bilateral representation

49
Q

What is effect of SMC/SMA lesion?

A
  • impairment in self-initiated tasks
  • impairment in tasks that require bimanual coordination
  • forced grasping [hard to let go]
50
Q

Where does PM get input from in the thalamus??

A

VLa

51
Q

What happens in UMN lesion?

A
  • spastic paralysis
  • hyperrefflexia
  • hypertonia
  • weakness of upper extensors + lower flexors
  • positive babinskiy
  • arm swing in gait
  • clonus may be present
52
Q

What happens in LMN lesion?

A
  • falccid paralysis
  • hyporeflexia
  • hypotonia
  • muscle atrophy
  • distribution in one nerve, root, or plexus
  • fasciculations/fibrillations = abnormal firing LMNs
  • absent clonus
53
Q

What is positive babinski sign of UMN damage?

A
  • when do babinski –> fanning of toes, get dorsiflexion

normal = toes down

54
Q

How can facial weakness tell you upper vs lower motor neuron?

A

UMN lesion = only inferior half of one side of face

LMN = all [inferior + superior] of one side of face

55
Q

What is pseudobulbar palsy?

A
  • inability to control facial movements, swallowing, spastic speech

due to damage to corticobulbar tract

56
Q

What is function of spinal cord ventral horn motor neurons in the descending motor system?

A

they are the final common pathway neurons [LMNs]

- site of integration of all descending and reflex paths

57
Q

What part of brain is responsible for concept of extra personal space?

A

areas 5 and 7 of parietal lobe

58
Q

What is function of extrapyramidal structures?

A

initiate movement, smooth movement, motor learning

59
Q

what is function of cerebellum in extrapyramidal path?

A
  • integrate movements into smooth sequence
60
Q

what is function of basal ganglia in extrapyramidal path?

A
  • involved in rapid adjustments of movement [ex sudden turning]
61
Q

What is the difference extrafusal vs intrafusal muscle fibers?

A

extrafusal: force generating
intrafusal: control and adjust sensitivity of muscle spindle

62
Q

What do alpha motorneurons innervate?

A

extrafusal muscle

  • large aMNs innervate fast/fatigable extrafusals
  • small aMNs innervate slow/fatigue resistant extrafusals
63
Q

What do gamma motor neurons innervate?

A

intrafusal muscle, control sensitivty of muscle spindle in detecting changes in muscle length

64
Q

What is a motor unit?

A

one motor neuron and all the muscle fibers it innervates

65
Q

What is ration of motor neurons to muscle fibers?

A

varies from 1:10 to 1:2000

66
Q

What are the first type of motor neurons to respond to low-level afferent inputs?

A

small aMNs and gamma MNs

67
Q

What are the last type of motor neurons to respond to afferent input?

A

large MNs require strong stimulus

68
Q

What information to muscle spindles record?

A

they are stretch receptors

- record muscle length and rate of change

69
Q

What are the two functional regions of muscle spindle and what innervates each part?

A

central region: non-ccontractile, sensory innervation from group 1a and 2 sensory afferents

polar: contractile intrafusal fiber, motor innervation from gamma MNs

70
Q

What is alpha-gamma motoneurona coactivation?

A
  • needed to detect muscle length
  1. surrounding muscle is stretched –> spindles stretched –> 1a and 2 fibers fire
  2. 1a/2 fibers stimulate both alpha and gamma
  3. aMNs –> contraction of extrafusal –> muscle shortens
  4. activated gamma –> contraction of intrafusal –> keeps spindle taught while muscle is shortening so that 1a/2 fibers keep firing
71
Q

What is function of the golgi tendon organs?

A
  • records tension generated at myotendinous junction during contraction
  • composed of group 1b fibers –> fire when muscle contracted –> stimulated spine interneurons that in turn terminate active muscle contraction
72
Q

What is the path of myotatic [stretch, deep tendon] reflex?

A
  1. afferent: group 1a and group 2 sense some sort of stimulus at muscle spindle [ie. muscle stretched]
  2. intraspinal:
    - afferents terminate monosynaptically on aMNs innervating the same [homonymous] muscle and on synergist [heteronymous] muscles
    - also activate type 1a inhibitory interneuron which inhibits aMNs innervating antagonistic muscles
  3. efferent: aMN causes stretched muscle to shorten [contract]
73
Q

What is path of the inverse myotatic reflex?

A
  • tension feedback reflex to reduce over-contraction
  1. afferent: group 1b afferents sense tension on fGTO
  2. intraspinal:
    - 1b fibers inhibit homonymous a-MNs and synergists
    - excite antagonistic aMNs
  3. efferent: as muscle contract with increasing forcefulness, increased number of GTOs discharge function to minimize over contraction

Brain and Behavior Exam 2 (21 decks)

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