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Motor System > Motor system > Flashcards

Motor system Flashcards

1
Q

4 Systems Control Movement

A

1 - Local SC & brainstem circuits: located in grey matter of Sc & tegmentum of brainstem
2 - Descending control centers in the cerebral cortex & brainstem
3 - Cerebellum
4 - Basal ganglia

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2
Q

1 - SC & Brainstem circuits = Local level - cells include:

A

1 - Lower motor neurons: send axons out of brainstem & Sc to innervate skeletal muscles of head & body
2 - Local circuit neurons - major source of synaptic input to all lower motor neurons

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3
Q

2 - Descending Systems = Middle level; consists of:

A

1 - UMN (upper motor neurons) from cortex - planning & initiation of voluntary movement of muscles
2 - UMN from brainstem - regulating muscle tone & orienting eyes, head & body with respect to vestibular, somatic, auditory, visual sensory info

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4
Q

3 & 4 - Cerebellum & Basal Ganglia = Middle level

A

massive complex neural circuits with output pathways that have no direct access to either LCN or LMN
Control movement indirectly by regulating activity of UMNs

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5
Q

Function of cerebellum vs basal ganglia

A

Cerebellum - co-ordination of ongoing movement

Basal ganglia - prevents UMN from initiating unwanted movements & prepares motor circuits for initiation of movements

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6
Q

Which motor neurons located most medially in ventral horn of SC:

A

Motor neurons that innervate the axial musculature (postural muscles of the trunk)
LMN innervate the proximal muscles

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7
Q

Which motor neurons located more laterally in ventral horn of SC:

A

Motor neurons that innervate the muscles of the shoulders

LMN that innervate distal muscles

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8
Q

Define motor unit

A

a single motor neuron & all of the muscle fibres it innervates
(each alpha motor neuron synapses w multiple fibers in the muscle)

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9
Q

Types of motor units

A

1 - Slow motor units : resistant to fatigue, contract slowly
2 - Fast fatigable (FF) motor units: little mitochondria (easily fatigued)
3 - Fast Fatigue resistant (FR) motor units: not as fast as FF; generate twice the force & fatigue resistant

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10
Q

5 Components of a reflex arc:

A 
1 - Sensory receptor
2 - Sensory neuron
3 - Information processing in CNS
4 - motor neuron
5 - effector
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11
Q

Reflexes by early development:

A
  1. Innate reflexes: Basic neural reflexes formed before birth, genetically programmed, e.g. withdrawal to pain, chewing, visual tracking
  2. Acquired Reflexes: Rapid, automatic learned motor patterns, repetition enhances, e.g. braking car in emergency
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12
Q

Reflexes by motor response:

A
  1. Somatic Reflexes: control skeletal muscle contractions, superficial reflexes (skin/mucous membranes), immediate, eg. pattellar (knee jerk)
  2. Visceral reflexes (autonomic reflexes): control other effectors - smooth muscle, cardiac muscle, glands
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13
Q

Reflexes by complexity of neural circuit:

A
  1. Monosynaptic reflex: Single synapse - simplest reflex arc; sensory neuron synapses directly w motor neuron; fast response e.g. stretch reflex
  2. Polysynaptic reflex: at least 1 interneuron between sensory neuron & motor neuron (most common); slower response; intersegmental reflex arcs: many spinal cord segment interact (variable response), e.g.Flexor/Crossed Extensor reflex
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14
Q

What cells do the lateral premotor cortex contain:

A

Mirror cells

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15
Q

What are mirror neurons

A

Mirror neurons are neurons that fire both when an animal acts and when the animal observes the same action performed by another

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16
Q

Which part of the brainstem is important in feedforward control of posture:

A

Reticular formation

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17
Q

Name the two tracts from the corticospinal tract

A

Lateral Corticospinal tract & Anterior corticospinal tract

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18
Q

What are considered pyramidal tracts?

A

Pass through medullary pyramids –> descend onto LMN in SC

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19
Q

Lateral corticospinal tract

A

90% of fibers from corticospinal tract decussate at medullary pyramid & descend in lateral SC (Lateral CST)
Detailed movements of distal muscles

20
Q

Anterior corticospinal tract

A

10% of CST fibers descend ipsilaterally in ventral SC (anterior CST) (do not decussate)
Axial & proximal muscles

21
Q

Collaterals of CST

A

Collaterals extend to red nucleus & reticular formation

22
Q

Corticobulbar Tract

A

Brain –> spinal nerves
Control facial, neck muscles
Pathway: 1 motor cortex - through corona radiata —> midbrain –> exit brainstem at appropriate level to synapse on LMN of cranial nerves
ONLY nerves controlling muscles of lower face decussate

23
Q

DAMGE to corticobulbar tract:

A

Unilateral - only involves face

Bilateral - pseudobulbar pasly (inability to control facial muscles)

24
Q

Extra-Pyramidal pathways

A

Motor neurons from motor cortex that don’t pass through pyramids of medulla - tracts run through pons & medulla
Damage - various types of dyskinesias (involuntary movement disorders)

25
Q

RUBROSPINAL TRACT

A 
Not sure if exists in humans
Originates in red nucleus projects to SC
Runs adjacent to CST
Projection participates together with direct pathway from motor cortex control of arms
Damage - temporary slowness of movement
26
Q

Vestibulospinal Tract

A

Lateral & Medial Vestibulospinal tract
Lateral - originates in lateral vestibular nucleus
medial - originates medial vestibular nucleus
Activates extensors; inhibits flexors
Maintains upright balance & posture
Receives input form cerebellum

27
Q

Reticulospinal Tract

A

Coordinates autonomic locomotion & posture movements
Pons (pontine) medial reticulospinal tract
Medullary (lateral) reticulospinal tract
both originate from reticular formation in corresponding areas (pons & medulla)

28
Q

Somatotopic organisation in motor cortex

A

not as finely represented as in the ssx
More overlapping, multiple representations, no strict somatotopy:
- A single corticospinal axon may supply multiple columns of LMN in ventral horn
- A single spike in corticospinal axon may activate 4 different muscles in the forelimb
More movement representation than muscle representation

29
Q

Babinski Reflex

A

Sole of foot is stimulated
Normal plantar response - toes down (Flexion)
Extensory plantar response - fanning of toes (babinski sign - sign of pathology)

30
Q

Basal Ganglia Structures:

A

Striatum (caudate nucleus & putamen)
Globus Pallidus (external & internal segments)
Substantia nigra
Subthalamic nuclei

31
Q

Two distinct regions of substantia nigra

A 
Pars compacta (Snc) - dopaminergic
Pars retiuclata (Snr) - GABAergic
32
Q

Disorders of Substantia Nigra

A

Parkinson’s Disease

Loss of dopaminergic neurons of substantia nigra (pars compacta (Snc)

33
Q

Affect of degeneration of pars compacta

A

Reduce inhibition via indirect pathway, reduce excitation via direct pathway

34
Q

Treatment for Parkinson’s

A 
Aim to increase dopamine levels
L-DOPA (dopamine precursor)
Dopamine Agonist (bromocriptine) binds to postsynaptic dopaminergic receptors
MAO-B inhibitors: inhibit dopamine breakdown by MAO
35
Q

Huntington’s disease

A

Disease caused by destruction of striatal, cortical, cholinergic neurons, inhibitory GABAergic neurons
Presents with chorea (writhing movements), dementia

36
Q

Located in precentral gyrus of frontal lobe

Function: control skeletal muscle movement

A

Primary motor cortex

37
Q

Located anterior precentral gyrus

Function: controls learned motor skills & coordinates movement of several muscle groups

A

Premotor cortex

38
Q

true or false: motor neurons are scattered haphazardly all over the SC

A

FALSE

39
Q

Lateral descending tracts are associated with the function of a) and medial tracts are associated with the function of b)

A

a) distal

b) proximal

40
Q

A reflex are includes:

A

At least 2 sequential neurons

41
Q

T/F: Reflex actions include the inhibition of sensory receptors

A

false

42
Q

Patellar reflex is an example of a) reflex and the flexor reflex is an example of a b) reflex

A

a) monosynaptic

b) polysynaptic

43
Q

Class = monosynaptic; stimulus = muscle stretch, effect = muscle contraction

A

Stretch reflex

44
Q

Class = polysynaptic, stimulus = pain, effect = flexion of afferent limb

A

Flexor/withdrawal reflex

45
Q

In the flexor withdrawal reflex, contraction of flexor muscles is associated with reciprocal inhibition of:

A

Ipsilateral extensor muscles

46
Q

Descending motor tracts:

A

Corticospinal tract
Corticobulbar tract
Reticulospinal tract

47
Q

Corticospinal tract originate from

A

a) premotor area in frontal lobe
b) supplementary motor area in frontal lobe
c) somatosensory area in parietal lobe

Motor System (1 decks)

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