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PN3313 > Motor Systems > Flashcards

Motor Systems Flashcards

1
Q

What are the 3 main categories of motor systems?

A

Reflexive - involuntary in response to peripheral stimuli
Rhythmic - occilating controlled by brain stem and spinal cord
Voluntary - goal directed, higher centres involved

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2
Q

How is the motor system hierarchally organised?

A

spinal cord -> brain stem -> cortex

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3
Q

How does the brainstem feedback to other motor systems?

A
  • Feedback to cortex and spinal cord to regulate planning and execution
    (affected in Parkinsons, Huntington’s and Cerebral ataxia)
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4
Q

What are the two areas of output of the spinal cord?

A

Dorsal -> sensory

Ventral -> motor

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5
Q

What are the two different categories of motor neurons?

A

Lateral - limb buds

Medial - axial muscles

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6
Q

What are local interneurons?

A

Confined to the same or adjascent segments, local networks and rythmic neurons

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7
Q

What are propriospinal neurons?

A

Axons that project to distant segments

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8
Q

What are projection neurons?

A

Axons that ascend to higher brain areas

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9
Q

What are the medial brainstem pathways?

A
  • Control basic posture control
  • Vestibulospinal, reticulospinal and tectospinal tracts
  • Terminate on ventromedial interneurons and some medial interneurons
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10
Q

Describe the lateral brainstem pathways?

A
  • Goal directed
  • Lateral motorneurons
  • Dosolateral interneurons
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11
Q

What does the cortex control?

A
  • Coordination of individual joint and whole limb actions
  • Complex goal directed and precise movements
  • Code parameters such as direction and force
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12
Q

What does the ventral corticospinal tract control?

A

Posture, ventral medial motor neurons

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13
Q

What does the lateral corticospinal tract control?

A

Activates lateral neurons (limbs)

Loss of these affects fine digit control

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14
Q

What do the axons of the primary motor cortex ennervate?

A
  • Single neuron synapses with motor neurons innervating a number of muscles
  • Different groups activate different combinations of spinal interneuron networks
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15
Q

What are premotor areas influential in?

A

Complex movements, motor planning and learning

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16
Q

What are mirror neurons?

A
  • Discharge when motor act is performed and done by another individual
  • Activated also by sounds of task
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17
Q

Describe the role of the basal ganglia in motor systems

A

Gets input from cortex which it relays through the thalamus
striotum - major recipient of inputs
globus pallidus - major output projections of the basal ganglia

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18
Q

What is the direct pathway?

A

Facilitates desired movement

  • inhibits GPi input (thalamus) and allows more activity in the cortex
  • Absent in Parkinsons
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19
Q

What is the indirect pathway?

A
  • Inhibits GP less

- Inhibits movement

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20
Q

Define locomotion

A

Rythmic and alterating movements of the body which generate propulsion involving functional agonists

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21
Q

In limbed animals what are the two modes of locomotion?

A

Power stroke - stance (extensor)

Return stroke - swing (flexor)

22
Q

What were the earliest studies of locomotion?

A

Marey and Muybridge used high speed photography to show that horses had all legs off the ground at point during a gallop

23
Q

What changes during the different gaits in the locomotion of quadripeds?

A

Swing phase changes a little however stance phase becomes much shorter with speed

24
Q

What did Charles Sherrington propose?

A

That simple reflexes are the basic units of movement

25
Q

What did T. Graham Brown find?

A
  • Isolated spinal chords can still produce rythmic motor activity
  • Central pattern generators -> half centre hypothesis
26
Q

What has been the more recent addition to the half-life hypothesis?

A
  • Reflexes integrated with cpg to produce adaptive movements
    e. g sstimulation of high threshold, small diameter afferents in cat spinal chords treated with L-DOPA led to rythmic activity
27
Q

What is the function of the mesencephalic locomotor region?

A
  • Exites interneurons in the medial reticular formation
  • Axons descend to the spinal locomotor system via the ventrolateral funiculus
  • Increasing stimulation strength changes gait and speed of circuit
28
Q

What are the descending pathways of locomotion in the brain?

A
  • MLR activates locomotion
  • Processing of afferent signals involving the cerebellum refines the motor pattern
  • Limb movements guided by visual input
29
Q

What are central pattern generators?

A

Rhythm generating networks which may be conveyed to pattern forming circuits for appropriate spatial and temporal muscle pattern activity

30
Q

What is the output of central pattern generators determined by?

A
  • Intrinsic properties e.g ion channels, neurotransmitters
  • Synaptic connectivity between neurons
  • Synaptic properties
  • Neuromodulation
31
Q

Where is rostro-caudal delay found?

A

In invertebrates

32
Q

What can the rhythmicity of a CPG reflect?

A
  • Occilating neural networks

- Endogenous bursters (pacemaker cells)

33
Q

What is the half-centre hypothesis?

A

Idea of 2 neurons that receive tonic exitation also exite inhibitory neurons connecting the two resulting in occilating activity (reciprocal inhibition) where the inhibitory neuron fatigues

34
Q

What is the hyperpolarisation-activated inward current (Ih)?

A
  • Mixed cationic (N+/K+) current activated by hyperpolarisation
  • Activates and deactivates slowly causing slow depolarisation
  • Can give rise to a post-inhibitory rebound potential
35
Q

What are low voltage activated calcium currents(ILVA)?

A
  • Transient (inactivating) Ca2+ currents activated at low v
  • Can also mediate post-inhibitory rebound potentils
  • Can boost membrane depolarisation threshold
36
Q

What are transient K+ channels (IA)?

A
  • Transient outward current
  • Require hyperpolarisation to remove inactivation
  • Can delay spike and burst initiation
37
Q

What are persistent Na+ currents (INAP)?

A
  • Non-inactivating persistent
  • Low activation threshold
  • Can contribute to plateau potentials
  • Help initiate depolarisation and are then important for maintenance
38
Q

What are high voltage activated calcium currents (IHVA)?

A
  • Activated by depolarisation from resting potential
  • Various subtypes with slow/little activation
  • Mediate persistent inwards currents which contribute to plateau potentials
  • Help initiate and main depolarisation and maintain it
39
Q

What are slow non-selective cationic current (ICAN) ?

A
  • Calcium activated current
  • Non-inactivating and persistent with no voltage sensitivity
  • Maintains depolarisation
40
Q

What are two channels which contribute to the termination of action potential firing?

A
  • Inactivation of fast inactivating sodium currents (INA) which inactivate when depolarised
  • KCa channels which produce long hyperpolarising pauses in activity
41
Q

What is the Calcium activated K current (IKCA)?

A
  • Activated by Ca2+ entry via voltage activated channels
  • Underlies post action potential hyperpolarisation (AHP)
  • Can control spike timing leading to spike frequency adaptation
42
Q

How are isolated rodent spinal cords used to study locomotion?

A
  • Early spinal tissue kept alive
  • Motor activity induced by stimulating brainstem or applying NMDA and serotonin or dopamine (older)
  • Attach electrodes to ventral roots of left and right extensor (L2 )and extensor (L5)
  • See alternating burst of activity
43
Q

Where is the vertebrate CPG believed to be located?

A
  • In the ventral horn of the spinal cord

- Distributed along the lumbar cord however has a rostrocaudal exitability gradient

44
Q

How are interneurons studied in the vertebrate spinal cord?

A
  • Identification of transciption factors involved in the differentiation of specific types of spinal neurons
  • Labeling of specific interneurons with fluorescent markers
45
Q

What are genetic knock-outs?

A

Knock-outs of specific genes using homologous recombination to replace gene of interest with an inoperable version

46
Q

How does the cre-lox system work?

A
  • Cre mediates recombination between two loxP sites
  • Pair gene of interest with Cre and flank gene we want to cut out with loxP
  • Can be used for conditional deletion and expression at the level of specific tissues
47
Q

What are the criteria for rhythm generating neurons in vertebrates?

A

Must be ipsilaterally projecting glutaminergic excitatory neurons

48
Q

Why might HB9 expression neurons be rhythm generating?

A
  • Glutaminergic with intrinsic bursting (revealed by TTX)
  • Rhythmically active in time with fictive locomotion
  • Coupled by gap junctions (allows coordination)
  • Ipsilaterally projecting neurons
49
Q

What are the characteristics of Dbx-1 (V0) expressing interneurons and what might they be involved in?

A
  • Have monosynaptic connections with motor neurons
  • knockout of these leads to increased number of cobursts between left and right
  • Could be involved in left-right coordination
50
Q

What are V1 motor neurons and what do they appear to control?

A
  • Express Pax6 and En1
  • Inhibitory and ipsilareally projecting
  • When deleted locomotor burst duration increases and rhythm slows - could therefore control speed
51
Q

What is the advatage of inducible silencing techniques?

A

Avoids compensation

52
Q

What do deletions of activity during fictive locomotion suggest?

A

A layered organisation of the CPG with a central rythm generator (clock) and a bottom pattern forming layer which distribute this rhythm

PN3313 (9 decks)

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