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Year 2: Neurobiology II > Lecture 5: Motor Control Part II > Flashcards

Lecture 5: Motor Control Part II Flashcards

1
Q

where is the corticospinal tracts in humans vs in vertebrate animals

A

humans = mainly in ventral horn and slightly in intermediate zone; S1 doesn’t contribute much

vertebrates = ventral and dorsal horns; takes up almost the whole gray matter in some animals

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2
Q

where are the rubrospinal and reticulospinal tracts located in the spinal cord

A

rubrospinal = intermediate zone

reticulospinal = ventral horn

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3
Q

LMN somatotopy distribution from medial to lateral in SC

A

trunk to distal extremity

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4
Q

LMN somatotopy distribution from anterior to posterior in SC

A

extensors to flexors

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5
Q

where does the medial vestibulospinal tract end and what does it control

A

ends in neck and upper thoracic region

controls B neck extensors

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6
Q

what does the medial corticospinal tract control

A

B postural flexor mm control

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7
Q

what does the pontine reticulospinal tract control

A

B proximal extremity extensors

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8
Q

what does the lateral vestibulospinal tract control

A

ipsilateral proximal extremity extensors

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9
Q

what does the medullary reticulospinal tract control

A

B distal extremity flexors

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10
Q

what does the rubrospinal tract control and where does it end in the SC

A

controls distal UE flexors

ends in neck and upper thoracic

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11
Q

what does the lateral corticospinal tract control

A

distal extremity flexors

fine motor

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12
Q

what is a motor neuron pool

A

LMNs for one mm all aligned in a column

more cranial portion of the column = proximal mm

more distal portion of column = distal mm

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13
Q

what is a motor unit; describe its integration

A

all mm fibers innervated by one LMN

fibers are intermingled, not homogenous

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14
Q

describe type I mm fibers

A

mainly found in red mm

slow twitch (S)

fatigue resistant

high concentration mitochondria

less glycogen

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15
Q

where are type II mm fibers mainly found

A

mainly in white mm

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16
Q

describe type IIa mm fibers

A

fast twitch
fatigue resistant (FR)
medium concentration of mitochondria and glycogen

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17
Q

describe type IIb mm fibers

A

fast twitch

fatiguable (FF)

low concentration of mitochondria

more glycogen

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18
Q

how can mm fibers be transformed

A

they can go between any form to another with strenuous work

type II can become type I

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19
Q

what type of mm contain what fiber types

A

all mm contain all 3 fiber types just with different ratios depending on the use of the mm

each type of mm fibers mingle together but they form individual motor units

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20
Q

describe small LMNs and their function

A

innervate type I fibers

less powerful but they can last for hours

used with fine motor and postural control

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21
Q

describe medium LMNs and their function

A

innervate type IIa fibers

more powerful and last about 1 hour

used for gross motor tasks (in between small and large LMNs)

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22
Q

describe large LMNs and their function

A

innervate type IIb fibers

most powerful but only last about 1 min

used for gross motor and power

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23
Q

describe the motor unit used for gross motor function, the types of fibers that make up that unit, and the purpose of this set up

A

gross motor = large motor unit (1 LMN innervates hundreds/thousands of mm fibers)

type IIa/IIb fibers controlled by medium and large LMNs

mm example: gastroc (FR/FF)

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24
Q

describe the motor unit used for fine motor function, the types of fibers that make up that unit, and the purpose of this set up

A

fine motor = small motor unit (1 LMN innervates several mm fibers)

less fibers to control per LMN = more accurate

type I mm fibers controlled by small LMN

mm example: extraoccular mm - 1:3 ratio of LMN to mm fibers; slow twitch

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25
Q

how are saccades still fast with extraoccular mm even though they are slow twitch mm

A

due to the ratio of LMN to mm fibers (1:3)

still fast movement

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26
Q

generally, 1 LMN controls one motor unit only; what is the exception to this

A

facial expression mm

multiple LMNs overlap different facial mm

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27
Q

intensity of a stimuli is encoded by what

A

action potential

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28
Q

what are the steps for LMN activation/force production

A
  1. presynaptic membrane AP travels to LMN axon terminal
  2. postsynaptic membrane AP frequency travels along mm fibers
  3. force is then produced by mm fiber contraction; force production directly related to AP frequency

**there is a lag at each step due to the process of signal conduction

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29
Q

what is tetanus

A

AP over 80 Hz

sustained mm contraction

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30
Q

what is spatiotemporal summation

A

different motor units at different locations

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31
Q

describe the size principle of motor unit recruitment

A

UMNs are all the same size; LMNs have 3 sizes

small size LMNs (type I) activated first

Ohms law - Voltage = current x resistance

UMN activation signals (ACh release) induce the same current (I), but smaller LMNs have higher resistance (R) compared to Larger LMNs

thus smaller LMNs create a larger voltage

works like voltage gated ion channels to form action potential

type IIa and IIb follow type I when more force is needed; this is regulated by GTOs

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32
Q

3 types mm contraction

A

concentric = shortening fibers

isometric = stay same length

eccentric = elongating mm fibers

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33
Q

active vs passive insufficiency

A

active = mm too short to create optimal force

passive = mm too long to create optimal force

these insufficiencies are found in multiple joint mm

34
Q

2 structural types of muscle spindles

A

nuclear chain = nuclei aligned in chain/line

nuclear bag = nuclei concentrated as in a bag

35
Q

3 functional types of mm spindles

A

nuclear bag
1. static - detect length
2. dynamic - detect velocity

nuclear chain
3. only static type - for length

every spindle has at least 2 nuclear bag cells (1 static and 1 dynamic)

36
Q

relationship between mirror neurons and mm spindles

A

mirror neurons transform sensory info to motor

mm spindles transform motor info to sensory

37
Q

extrafusal mm innervation

A

alpha motor neuron and free n endings

38
Q

intrafusal mm innervation

A

gamma motor neurons

39
Q

primary type Ia n innervate what type of intrafusal mm

A

central nuclear bag and chain cells

both static and dynamic

40
Q

secondary type II nn innervate what type of intrfusal mm

A

static nuclear bag and chain cells

does NOT innervate dynamic bag cells; dynamic bag cells only innervated by type Ia and gamma motor neurons

41
Q

what happens at the mm spindle with an isometric contraction

A

increase in Ia/II fibers from static nuclear bag and nuclear chain cells

b/c mm is remaining static

42
Q

what happens at the mm spindle with eccentric contraction

A

increase Ia on dynamic nuclear bag cells

43
Q

what happens at the mm spindle with concentric mm contraction

A

decrease in dynamic stretch on mm spindle and this a decrease in Ia activity from nuclear bag cells

44
Q

what motor neuron type will be activated with concentric contraction of intrafusal fibers

A

gamma motor neuron

45
Q

what mm fibers give feedback to motor actions in regard to position sense and kinesthesia

A

position sense (stretch) = Ia and II from static nuclear bag and nuclear chain; info sent to cerebellum via posterior spinocerebellar tract

kinesthesia (velocity) = Ia from dynamic nuclear bag cell

46
Q

Number of CNs with motor function

A

9

47
Q

what cranial nn are NOT controlled by corticospinal tract

A

III, IV, and VI

48
Q

which CNs do not have B control but rather contralateral control bias

A

CNs V and XII

vagus and hypoglossal

49
Q

how is CN VII unique in its motor control

A

facial expression mm motor unit can be innervated by 2 or 3 LMNs

facial expression is essential for social congnition

50
Q

all head mm spindle Ia and II innervations are from what CN

A

CN V

51
Q

what are the 3 ways UMNs can separately control LMNs for facial mm

A

cingulate motor cortex:
- level IV
- controls B scalp
- from dorsal motor nucleus CN VII

motor cortex and posterior parietal cortex:
- level IV and III
- controls contralateral face
- from ventral motor nucleus

deep brain structures:
- level II
- controls face and scalp
- from amygdala, basal nuclei, and brainstem nuclei

52
Q

LMNS for facial mm control what portion of the face

A

ipsilateral face and scalp

53
Q

why does a regional injury to the CN VII anastomosis not affect facial expression

A

CN VII LMN can innervate different motor units

54
Q

inter CN V and CN VII anastomosis controls what

A

proprioception of facial mm

55
Q

what are the components of the spinal/brainstem reflex

A

receptor
afferent = somatic or visceral sensory input
may/may not have interneurons for integration
efferent = somatic or visceral motor output
effectors = muscles and glands

56
Q

intrasegmental reflex

A

afferent and efferent signals at the SAME SPINAL LEVEL

57
Q

intervsegmental reflex

A

afferent and efferent at MULIPLE SPINAL LEVELS

58
Q

what type of loop is used in the spinal/brainstem reflex

A

bottom up/closed loop

no higher level motor control

59
Q

what is the flexor reflex

A

via cutaneous receptors

aka withdrawal reflex/nociceptive reflex

60
Q

how does the flexor reflex work

A

noxious stimuli is sent to SC via nociceptive axons (a delta fibers)

interneuons in higher and lower segments elicit an intersegmental reflex

axon terminals ascend/descend through lissauer’s tract

efferent outcome:
flexors are excited and extensors are inhibited (limb is pulled away from noxious stimuli)
- this only happens in UE flexor reflex

61
Q

describe how the crossed extension reflex works

A

built upon flexor reflex

noxious stimuli is recieved and travels to SC via nociceptive axons

interneurons alternate excitatory vs inhibitory

efferent result:
- ipsilateral side = flexors are excited and extensors are inhibited (flexor reflex)
- contralateral side = extensors are excited and flexors are inhibited

this combo of effects allows the affected limb to withdrawal while allowing the unaffected limb to extend to maintain balance

62
Q

describe how the mm stretch reflex works (aka DTR or myotatic reflex)

A

example = patellar tendon reflex

afferent = mm spindle in quads

alpha motor neurons in quads are activated
- myotatic reflex- monosynaptic
- intrasegmental reflex - afferent/efferent at same lvl

alpha motor neurons in HS are inhibited
- via interneurons
- intersegmental reflex - afferent/efferent at diff. lvl

total effect = knee ext/knee jerk reflex

63
Q

biceps reflex spinal level and nerve

A

C5

musculocutaneous

64
Q

brachioradialis reflex spinal level and nerve

A

C6

radial n

65
Q

triceps reflex spinal level and nerve

A

C7

radial n

66
Q

patellar (quads) reflex spinal level and nerve

A

L4

femoral n

67
Q

achilles (gastroc/soleus) reflex spinal level and nerve

A

S1

tibial n

68
Q

true deep tendon reflex is controlled by what? how does this work?

A

controlled by GTO

excitatory AND inhibitory neurons

total effect depends on which interneurons are activated

has temporal/serial and spatial/parallel patterns

motor units exerting heavily will be inhibited (protective)

involved in size principle during motor recruitment; helps the right size mm fibers be recruited

69
Q

importance of GTO reflex

A

allows fine adjustments of force production during ordinary motor activities

initiates additional forms of autogenic inhibition at higher tension levels

70
Q

what causes the clinical presentation of “clasp knife effects”

A

constant resistance results to autogenic inhibition through GTO reflex

like PNF?

71
Q

describe how reflexes can be modulated by the UMN system

A

mm spindle- Ia fiber conducts signal to SC

various segments = spinal reflex

higher levels = conscious perception and unconscious information of mm contraction

can be overwritten by higher level cortical motor systems

i.e. some people have to be distracted to test DTR

72
Q

how are CPGS foundational for locomotion

A

can control rhythmic alternating mobility pattern

no supraspinal control - cat can still walk on treadmill with SC cut

no sensory feedback needed

i.e. stepping reflex in babies

73
Q

CPG neurons

A

propriospinal neurons (specialized interneurons)

74
Q

CPG neurons form what tract and what does it control

A

fasciculus proprius

tracts coordinate 4 limb locomotion

75
Q

at what points with walking do you need control from UMN regions

A

gait patterns, reach, grasp, etc

at start and stop of movement

i.e. if you are walking and suddenly trip on something and need to catch yourself

76
Q

CPGs relation to locomotion provides a new hope for what

A

locomoting pathologies

i.e. stroke, TBI, PD, SCI, etc

77
Q

voluntary locomotor regions are continuous components of what

A

reticular formation

78
Q

what are the 2 voluntary locomotor regions

A
  1. diencephalic locomotor region (DLR) - in thalamus
  2. mesencephalic locomotor region (MLR) - boundary of midbrain and pons/pedunculopontine junction
79
Q

function/regulation of voluntary locomotor regions

A

still regulated by hierarchical control system

functions to coordinate CPGs

80
Q
A

Year 2: Neurobiology II (10 decks)

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