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NEUROSCIENCE 2 > LECTURE 12 - motor systems 1 > Flashcards

LECTURE 12 - motor systems 1 Flashcards

1
Q

What are the main components of the motor system?

A

Spinal cord

  • motor neurons (controls muscle contraction)
  • sensory input (we know what we are moving)
  • local reflexes

Descending motor pathways

  • later (=voluntary)
  • ventromedial (brainstem control)

Cerebral cortex

  • voluntary movement
  • motor cortex
  • sensory input
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2
Q

What are the main features of the motor system?

A
  1. Hierarchical organisation
  2. Feedback loops
  3. Somatotopic representation (particular part of musculature connected to particular neurones
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3
Q

What are the basic types of movement?

A
  • reflex
  • rhythmic motor patters
  • voluntary
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4
Q

What is a reflex?

A
  • protective e.g. limb withdrawn
  • motor patterns generated in spinal cord
  • closed loop
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5
Q

What is a rhythmic motor pattern?

A
  • e.g. chewing, walking, breathing

- combination of reflex and voluntary

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6
Q

What is voluntary movement?

A
  • purposeful, goal-directed
  • command originates from higher centres
  • open loop, can override and modify
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7
Q

What do alpha motor neurones do?

A

Directly control muscle contraction ALONE
- final common pathway of motor control
(they are lower motor neurones)

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8
Q

What inputs affect spina motoneuron activity?

A
  1. Sensory input - local feedback control (ongoing movement) via dorsal roots
  2. Spinal interneurones - circuitry generating motor programmes
  3. Upper motor neurones initiation and control
    (1 & 2 = reflexes)
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9
Q

Can movement of spinal cord be generated in isolation?

A
  • even when descending influences are severed, coordinated movements can occur
  • central pattern generators - circuits within the spinal cord are responsible
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10
Q

What is descending input from upper motoneurons?

A
  • sophisticated, adaptable patterns of movement
  • involves input descending from the BRAIN
  • (super)imposed upon the intrinsic circuitry of the spinal cord
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11
Q

What is distal musculature?

A
  • hands, feet, digits
  • fine motor control
  • innervated by lateral motoneurons (in spinal cord)
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12
Q

What is proximal and axial musculature?

A

proximal = elbows, knees etc
axial = trunk muscles
- for posture control
- both innervated by medial motoneurons

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13
Q

What are the lateral descending pathways for?

A
  • controlling distal muscles
  • controlling flexors
  • voluntary movement

motor cortex –> spinal cord
+
motor cortex –> red nucleus –> spinal cord

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14
Q

What are the ventromedial descending pathways for?

A
  • posture control
  • unconscious motor behaviour
  • axial muscles
  • extensors

motor cortex –> brain stem nuclei –> spinal cord
e.g. reticular nuclide, superior colliculus and vestibular nuclei

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15
Q

What are the main lateral pathways?

A
  1. Corticospinal tract

2. Rubrospinal tract

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16
Q

What is the corticospinal tract?

A

= pyramidal tract

  • a direct line contralateral projection from cortex to lateral spinal motor neurons
  • monosynaptic contact with alpha motoneurons
  • majority of axons from neurone with cell bodies in the motor cortex (areas 4 and 6)
  • innervate aMNs controlling distal muscles, particularly flexors
17
Q

What is the rubrospinal tract?

A
  • contralateral projections from red nucleus running down the lateral column of the spinal cord
  • similar role to corticospinal tract
  • much smaller component of the lateral pathway
  • can compensate if there is damage to corticospinal tract
18
Q

What are the main features of the ventromedial motor pathways?

A
  • extra pyramidal tracts
  • all originate from brain stem nuclei
  • both contra and ipsilateral descending projections
  • all unconscious control
  • -> control of motor output to proximal and axial muscles
  • -> control of body position and posture
19
Q

What are the main ventromedial pathways?

A

4 pathways but can be seen as 2 pairs
1. Reticular nuclei
(pontine reticulo-spinal + medullary reticulo-spinal)

  1. Superior colliculus and vestibular nuclei
    (vestibulo-spinal + tecto-spinal)
20
Q

What is the pontine reticulo-spinal tract?

A
  • enhances anti-gravity reflexes of spinal cord

- facilitates leg extensors to maintain standing posture

21
Q

What is the medullary recticulo- spinal tract?

A
  • has opposing effect to pontine
  • frees antigravity muscles from reflex control
  • allows voluntary override e.g. to sit down
22
Q

What is the vestibulospinal tract?

A
  • relays gravitational sensory info from vestibular labyrinth (inner ear) and stretch receptors in axial muscles
  • maintains head and neck position, as well as legs
23
Q

What is the tectospinal tract?

A
  • relays visual sensory info from retina and visual cortex

- orientates head and eyes to visual and auditory stimuli

24
Q

Why does voluntary movement involve almost all of the neocortex?

A

movement involves not just the execution but also:

  • sensory input
  • planning
  • deciding appropriate action
  • holding plan in memory

principle areas involved identified through electrical stimulation and recording from cortical surface

25
Q

What is area 4 of the motor cortex and what is it used for?

A

Primary motor cortex (M1)

  • control of distal musculature
  • has the best connection with alpha motor neurons as it has the lowest stimulus threshold => strong synaptic link
26
Q

What is area 6 of the motor cortex and what is it used for?

A

Premotor cortex (lateral)

  • control of proximal musculature (posture, balance)
  • control of movement sequencing
  • preparation for movement, initiation

Supplementary motor area (front/medial)

  • role in planning and initiation
  • bi-manual coordination

Area 6 for more complex movements

27
Q

What are primary motor cortical output neurone?

A
  • upper motor neurons
  • contribute ~50% of corticospinal tract axons
  • pyramidal type, cell body in cortical layer V (Betz cell)
  • somatotopically organised
  • activate small groups of muscles rather than single ones
  • individually encode the force OR direction of movement
28
Q

What happens if there is damage to upper motor neurones?

A
  • initial muscle weakness
  • eventual spasticity (increased resistance to passive movement)
  • -> increased muscle tone (hypertonia)
  • -> increased reflex responses (hyper-reflexia)
  • affects side contralateral to damage
  • recovery possible - M1 circuitry shows some adaptive alterations

Can be caused by stroke, tumour

NEUROSCIENCE 2 (32 decks)

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