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NSC 4354 Integrative Neuroscience > Exam 2- Motor Systems > Flashcards

Exam 2- Motor Systems Flashcards

1
Q

skeletal muscle contraction is initiated by

A

lower motor neurons in the spinal cord

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2
Q

cell bodies of lmns are located in

A

the ventral horn of the spinal cord

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3
Q

lmns are also known as

A

alpha motor neurons

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4
Q

where do lmns send axons

A

to skeletal muscles

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5
Q

lmns are known as

A

the final common pathway for transmitting information to the skeletal muscles

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6
Q

what are upper motor neurons

A

neurons in the brainstem or cortex that descent to synapse with circuit neurons or LMNs directly; the help initiate movement and complex spatiotemporal sequences of skilled movement

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7
Q

what do lower motor neurons receive input from

A

sensory inputs, local circuit neurons, which then go to skeletal muscles

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8
Q

what do upper motor neurons receive input from

A

basal ganglia and cerebellum, then go down to local circuit and motor neuron pools to the skeletal muscles

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9
Q

basal ganglia

A

prevents UMNs from initiating unwanted movement, prepares motor circuit for initiation of movement, regulates transition from one pattern of movement to another

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10
Q

disorders of the basal ganglia

A

parkinsons, huntingtons

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11
Q

cerebellum

A

detects and attenuates the difference/motor error between an intended movement and the actual movement, mediating real-time and long term reductions in these errors

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12
Q

cerebellar damage leads to

A

incoordination with persistent errors in controlling direction and amplitude of ongoing movements

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13
Q

each lower motor neuron innervates

A

muscle fibers in a single muscle

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14
Q

motor neuron pool

A

a group of lower motor neurons innervating muscle fibers in a single muscle

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15
Q

organization of lower motor neurons

A

columnar organization in ipsilateral ventral horn

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16
Q

topographical organization of the ventral horn

A

cervical- neck/arms
thoracic- abs
lumbar/sacral- legs/pelvis

medial to lateral arrangement with medial being more proximal and lateral being more distal (fingers and toes most lateral)

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17
Q

pathways in medial part of spinal cord

A

control posture and locomotion and are bilateral

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18
Q

interneurons in medial part

A

cover many segments vertically

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19
Q

pathways in lateral spinal cord

A

control fine movement in distal extremities– interneurons here are strictly local and ipsilateral

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20
Q

2 types of lmn

A

alpha motor neurons and gamma motor neurons

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21
Q

alpha motor neurons

A

innervate extrafusal, striated, force producing muscles needed for posture and movement

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22
Q

gamma motor neurons

A

innervate intrafusal muscle fibers (muscle spindles), helping with stretch detection and setting them to an appropriate length

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23
Q

a single alpha motor neuron innervates

A

multiple extrafusal muscle fibers in the same muscle, which helps spread force across muscle and reduces the chance that loss of one neuron results in loss of muscle function

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24
Q

what generates muscle contraction

A

an action potential from a motor neuron

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25
Q

motor unit

A

an alpha motor neuron and the muscle fibers it innervates

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26
Q

sizes of alpha motor neurons

A

slow, fast fatigue resistant, fast fatigable

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27
Q

fast fatigable neurons

A

large neurons, high threshold, fastest conduction

the unit is large, easily fatigued, and used for brief force like running and jumping

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28
Q

fast fatigue resistant

A

neurons are medium size, medium threshold, medium conduction

unit is medium force, fatigue and function is for things like walking

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29
Q

slow

A

neurons are small, low threshold, slow conduction

unit produces small force and slow fatigue, function is sustained things like standing

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30
Q

recruitment of motor neuron pool

A

larger recruitment means more force

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31
Q

at low frequencies, every AP

A

generates a muscle twitch

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32
Q

at higher frequencies, action potentials

A

summate twitches

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33
Q

higher force requirements

A

recruit more and more motor units– so with more force, number and rate of firing of active motor units increases

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34
Q

tetanus

A

prolonged contraction of a muscle caused by repeated stimuli

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35
Q

group 1a and 2 afferents

A

largest axons in peripheral nerves so also very fast

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36
Q

group 1a afferents

A

coiled around the middle region of intrafusal fibers, forming annulospiral primary endings, respond phasically (so fire then accommodate) to small stretch

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37
Q

1a activity is dominated by

A

signals transduced by the dynamic subtype of nuclear bag fiber, which is sensitive to the velocity of fiber stretch

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38
Q

group 2 afferents

A

innervate static nuclear bag fibers and the nuclear chain fibers, signal the level of sustained fiber stretch, fire tonically (continuously) at a frequency proportional to the degree of stretch with little dynamic sensitivity

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39
Q

solution to stretch reflex

A

group 2 afferents continuously signal sustained stretch for muscle tone, adding a load stretches the muscle spindle and activates 1a afferents, which excites the alpha motor neuron and inhibits antagonist muscle

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40
Q

myotatic reflex

A

hammer stretches tendon, stretching sensory receptors (muscle spindles) in extensor- quadriceps

sensory neuron (1a afferent) synapses w/ and excites motor neuron in spinal cord and interneuron, which inhibits flexor muscles

alpha motor neuron conducts AP to synapses on extensor, causing contraction, flexor relaxes due to inhibition, leg extends

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41
Q

motor nuclei of the basal ganglia

A

striatum (caudate, putamen)

globus pallidus (gp): external and internal segments

substantia nigra: pars reticulate and pars compacta (globus pallidus and DA neurons)

subthalamic nucleus

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42
Q

role of basal ganglia

A

permission for the initiation of movement by upper motor neurons

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43
Q

corticostriatal pathway

A

projections from association, temporal, insular, and cingulate cortices

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44
Q

caudate receives input from

A

multimodal frontal and motor cortices, controlling eye movement

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45
Q

putamen

A

receives input from higher order sensory cortices, premotor, and motor cortices

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46
Q

projections to caudate and putamen

A

are parallel and segragated, which is maintained in output too

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47
Q

msns are located

A

in the striatum

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48
Q

msns in the striatum receive

A

excitatory glutamatergic synapses from cortical neurons

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49
Q

msns have large

A

dendritic trees, allowing them to collect and integrate input from local, thalamic, brainstem, dopamine serotonin

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50
Q

firing of msns is associated with

A

impending movement

51
Q

caudate fires

A

before eye movements

52
Q

putamen

A

fires before limb and trunk movements

53
Q

t or f: msns have high spontaneous activity

A

false– needs many excitatory inputs

54
Q

msns send out

A

converging inhibitory GABAergic projections to the globus pallidus and substantia nigra pars reticulata, which send gabaergic projections to superior colliculus and va/vl thalamus

55
Q

organization of the basal ganglia thalamocortical motor circuit

A

loops

56
Q

neurons in sn and gp

A

tonically inhibit superior collicular cells and va/vl thalamus to prevent unwanted movement

57
Q

gabaergic projection from msn in striatum

A

inhibits inhibition of sn and gp, causing disinhibition, causing initiation of movement

58
Q

excitatory nt of basal ganglia

A

glutamine– primary and premotor cortices, also prefrontal, parietal, temporal, cingulate, subthalamic

59
Q

why are y-motor neurons important

A

allows for fine adjustments in movements, increasing in activity if a movement is more difficult/precise

60
Q

when alpha motor neurons are stimulated without y motor neurons, 1a fiber decreases as muscle contracts

A

when both a and y are activated, no decreasing in 1a firing during muscle contraction, showing us that y motor neurons regulate the gain (muscle force generated) of muscle spindles so they can operate efficiently at any length

61
Q

golgi vs muscle spindle

A

muscle spindle– muscle length
golgi– muscle force

62
Q

golgi tendon organs

A

encapsulated afferent nerve endings at the junction of a muscle and a tendon

63
Q

gto is innervated by

A

a single group 1b sensory axon

64
Q

when a muscle actively contracts

A

force acts on tendon, leading to tension of collagen in gto, causing compression of nerve endings, the acons contact gabaergic circuit neurons that synapse and innervate the same musccle– this means gto is negative feedback so decreases muscle activation when large forces generated

65
Q

gto effect

A

increases contraction of antagonist muscle, relaxes stretched muscle

66
Q

passive stretch

A

ms and gto activated, ms to a greater extent

67
Q

active muscle contraction

A

ms are unloaded, activity decreases, gto are activated

68
Q

painful sensory stimuli leads to

A

flexion reflex (inhibition of extensor, activation of flexor on affected side so leg withdraws, also crossed extension reflex so extensor on other side activates to support leg

69
Q

local spinal cord circuitry

A

also contributes to rhythmic movements like locomotion and swimming

70
Q

local circuits in spinal cord

A

called central pattern generators– control timing and coordination

71
Q

transection of thoracic spinal cord

A

continued locomotion

72
Q

locomotion is

A

independent of sensory input and descending projections

73
Q

lower motor neuron syndrome

A

paralysis, paresis (weakness), loss of reflexes and muscle tone, fibrilations and fasciculations, atrophy

74
Q

als

A

aka lou gherigs disease, slow degenration of alpha motor neurons in ventral horn and brainstem and motor cortex, progressive weakness, wasting

75
Q

motor cortex neurons

A

descend via lateral white matter, allowing for voluntary expression of precise, skilled movements of distal parts of limbs

76
Q

brainstem neurons

A

descent via anterior medial white matter, helping with posture, balance, orienting mechanisms, and initiation and regulation of stereotyped, rhythmic behavior

77
Q

premotor and motor cortex

A

premotor is in front of primary motor

78
Q

upper motor neurons in cortex

A

planning and initiation of temporal sequences of voluntary movements , receive input from cerebellum and ganglia via ventrolateral thalamus and somatosensory cortex

79
Q

umn of primary motor cortex

A

pyramidal cells of primary motor cortex– descending projections of axons to brainstem and spinal cord via corticobulbar and corticospinal tract

80
Q

corticospinal and corticobulbar tracts

A

upper motor neuron axons descend through internal capsule, go thru cerebral peduncle and pontine fibers, form medularry pyramids, corticobulbar innervates cranial nerve nuclei, reticular formation, red nucleus, corticospinal decussates so 90% of lateral corticospinal tract cross midline, 10% of ventral terminate ipsilaterally

81
Q

lateral corticospinal tract

A

direct pathway from cortex neurons to local circuitry in ventral horn, some synapse on alpha motor neurons for forearms and hands

82
Q

lesion of lower motor neurons in facial motor nucleus or axons in facial nerve

A

affects all muscles of facial expression on side of lesion

83
Q

umns in cortex lesion

A

difficulty controlling contralateral mouth muscles, upper facial muscles still function on both sides because of umns in cingulate gyrus that bifurcate and bilaterally innervate the same area

84
Q

fritch and hitzig

A

electrical stimulation of motor cortex elicits contralateral muscle contraction

85
Q

john hughlings jackson

A

motor cortex contains a complete map of body’s musculature

86
Q

charles sherrington

A

spatial representation of body’s muscle in great apes

87
Q

wilder penfield

A

400 neurosurgical patients– human motor cortex also topographical, motor homunculus

88
Q

icms

A

small currents initiated excitation of several muscles, motor map is less precise than somatotopic map, high overlap

89
Q

motor maps represent

A

maps of organized movement

90
Q

stimulation of arm regions in primary cortex elicits

A

movements of arm towards central space

91
Q

upper motor neurons are broadly tuned

A

discharrges prior to movements in many directions

92
Q

can individual upper motor neurons specify direction of arm movement

A

no but directional preferences are present

93
Q

premotor cortex

A

complex mosaic of interconnected frontal lobe areas contributing to motor function, receives multisensory input and complex signals related to motivation and intention

94
Q

direct premotor pathway

A

axons through corticobulbar and corticospinal pathways to local circuits; 30% of corticospinal axons from premotor cortex

95
Q

indirect premotor pathway

A

extensive reciprocal connections with primary motor cortex, premotor cortex uses info from cortical regions to select movements appropriate to context/goal of action

96
Q

premotor has more or less monosynaptic connections to alpha motor neurons in spinal cord

A

fewer

97
Q

m1 action goal encoding

A

localized to personal space w/in arms length

98
Q

premotor goal encoding

A

localized to extrapersonal space

99
Q

responses of premotor cortex are

A

linked in time to ocurrence of movemtns, firing most strongly before and during movements in a specific direction

100
Q

when do umns in premotor fire

A

before and during movements made in a specific direction, fire at the appearance of a cue and encode intention for a movement– selection of movements based on external events

101
Q

neurons that fire while monkey performs food grabbing task

A

also fires when observing similar action by experimenter’s hand , even behind barrier, but not with a tool

102
Q

supplementary motor area

A

mediates movement selection, initiating movements by internal self initiated cues, lesion reduces number of self initiated or spontaneous movements, activated when individuals perform motor sequences from memory (autopilot)

103
Q

brain machine interfaces

A

restore lost function, acquire brain signals and implement signals to operate systems, sensory feedback generated

104
Q

brainstem umn pathway

A

nuclei of vestibular complex, reticular formation, superior colliculus

105
Q

role of brainstem umns

A

balance, posture, locomotion, gaxe, work with motor cortex for skilled and reflexive activiries

106
Q

vestibular nuclei

A

inputs from 8th cranial nerve, semicircular and otolith organs, descending axons that terminate in medial region of spinal cord

107
Q

medial vrstibulospinal tract

A

inputs from semicricular canals, terminates bilaterally in medial ventral horn, regulates head position

108
Q

lateral vestibulospinal tract

A

input from otolith organs, terminates ipsilaterally among medial lmn pools governing proximal muscles, activates limb extensor muscles, also control eye movement

109
Q

reticular formation

A

network of circuits in core of brainstem, numerous neuronal clusters with many functions, cardiovascular and respiratory control, sensorimotor reflexes, eye movements, sleep/wakefulness

110
Q

reticulospinal pathway

A

terminate in medial parts of gray matter, influence local circuit neurons coordinating axial and proximal limb muscles, bilaterally to medial ventral horns, feedforward adjustments for posture

111
Q

reticulospinal pathway helps with

A

anticipatory feed-forward mechanism

112
Q

upper motor neuron syndrome

A

damage to motor cortex or descending upper motor axons, flacidity of contralateral muscles, hypotonia called spinal shock , babinski sign, spasticity with increased muscle tone, hyperactive stretch, clunus, inability to perform fine movements

113
Q

striatum at rest

A

gp is active, inhibiting thalamus, so no excitation of upper motor neuron

114
Q

active striatum

A

gp inhibited so thalamus disinhibited, leading to upper motor neuron excitation

115
Q

eyes fixating on a target

A

UMNs in SC tonically inhibited by substantia nigra cells

116
Q

target moves

A

cortical input excites msn to inhibit inhibitory SN to release UMNs in SC

117
Q

direct pathway

A

internal globus pallidus, which tonically inhibits va/vl

118
Q

indirect pathway

A

involves external gp, inhibition from msn in striatum to tonically active inhibitory neurons in external segment of gp

119
Q

disinhibition of subthalamic nucleus to internal gp

A

excites gpi, leading to less movement

120
Q

range of direct and indirect pathways

A

focused in direct, diffuse in indirect, which balance eachother and facilitate selection of motor programs, suppresses competing motor programs – center surround organization

121
Q

dopaminergic cells in sn pars compacta

A

msns in striatum receive and project to compacta, which sends projections back to msns

122
Q

d1 dopamine receptors

A

excitatory g protein coupled, excites direct pathway

123
Q

d2 receptors

A

inhibitory, gpcr, inhibit indirec so both d1 and d2 decrease inhibitory outflow of bg to increase excitability of upper motor neurons

NSC 4354 Integrative Neuroscience (5 decks)

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