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Neuroscience Y2 > Motor System > Flashcards

Motor System Flashcards

1
Q

What neurones innervate skeletal muscle

A

Alpha motor neurones

  • cell bodies in Ventral root
  • motor axons exit ventral root
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2
Q

What is a motor unit

A

Alpha motor neurone + all innervated muscle fibres

  • each muscle fibre receives input from one motor neurone
  • each motor neurone innervates several muscle fibres
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3
Q

What controls voluntary movement

A
  1. Descending motor controls
  2. Controlled by higher motor areas
  3. Upper&lower motor neurones
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4
Q

What controls involuntary movement

A
  1. Response evoked from peripheral stimulation
  2. Coupling sensory input to motor output
  3. Spinal reflexes
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5
Q

Describe Cutaneous reflexes

A

Flexion withdrawal reflex

  1. Cutaneous receptors detect noxious stimuli
  2. Primary afferent activated
  3. Synergistic activation and inhibition of muscles

Rapidly removes limb from harmful stimuli

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6
Q

Describe the Myotatic reflex

A

Prevents over-stretching the muscle

  1. One synapse
  2. Stimuli stretches attached muscle
  3. Subsequent contraction of same muscle restores muscle length
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7
Q

Describe how a muscle detects stretch

A
  1. Muscle spindles (proprioceptors)
  2. Sensory neurones in spindle encode information of muscle length
  3. Ia and II afferents monitor extent of stretch and synapse with motor neurones in the spinal cord
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8
Q

Describe the polysynaptic reflex

A
  1. Two or more synapses
  2. Stimulus is muscle stretch
  3. Inhibitory interneurones synapse alpha motor neurones
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9
Q

Role of Gamma motor neurones

A
  1. Innervates intrafusal fibres
  2. Adjusts sensitivity of muscle spindle
  3. Increased range of function
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10
Q

What are the three types of interneurones involved in motor system

A

A. Inhibitory interneurones
B. Excitatory interneurones
C. Renshaw cells

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11
Q

Role of inhibitory interneurones

A
  • activated by PANs
  • inhibits alpha motor neuron
  • inhibits contraction of associated muscle
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12
Q

Role of excitatory interneurones

A
  • activate Y motor neurone
  • synapse onto intrafusal muscle fibre
  • increased sensitivity of spindle
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13
Q

Role of Renshaw cells

A
  • inhibitory interneurones
  • activated by alpha motor neurone
  • also inhibits alpha neurones (andromic inhibition)
  • inhibits interneurones and y motor neurones
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14
Q

Describe the 3 types of spinal cord organisation

A
  1. Segmental
    - basic circuits and connections at each level
    - basic spinal reflexes mediate these
  2. Prospinal system
    - connecting different levels of SC
    - enables coordination
  3. Descending motor tracts
    - controls muscle tone
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15
Q

Describe the crossed extensor reflex

A

Maintains balance

  • flexion withdrawal removes ipsilateral limb
  • simultaneous extension of contralateral limb
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16
Q

Law of reciprocal innervation

A

When contraction of a muscle is stimulated, there is a simultaneous inhibition of its antagonist
- essential for coordinated movement

17
Q

What circuits are required to generate rhythmic movements

A

Only Spinal cord intrinsic circuits

- although modified and initiated by descending commands and sensory feedback

18
Q

Define a Central pattern generator

A

Biological neural network that produces rhythmic patterned outputs without sensory feedback

19
Q

Describe the half-centre hypothesis

A

Generation of alt activity involves two neuronal centres with mutual reciprocal inhibition

  • two groups of spinal cord neurones
  • mutually inhibiting each other
  • capable of producing basic rhythm when coupled to each other
20
Q

Describe half-centre oscillator theory

A
  1. Segmental pathways activated by high-threshold flexor reflex afferents (FRA)
  2. Excitation of flexors (by ipsilateral FRA) and of extensors (contralateral side)
  3. Reciprocally inhibitory interactions

TRANSMISSION IN ONE PREVENTS SIMULTANEOUS TRANSMISSION IN THE OTHER

21
Q

Describe pacemaker neurones/ concept

A

Pacemaker neurone directing continuous rhythmic movement

22
Q

What are the two types of motor system organisation

A

Parallel: each level issues commands that act directly on the lowest level

Okay hierarchical: motor system organised into a series of functional levels- higher command lower

23
Q

What are the four major components of the motor system

A
  1. Pre-motor cortex
  2. Primary motor cortex
  3. Brainstem
  4. Spinal cord
    Both parallel and hierarchical organisation
24
Q

Describe the differences between higher and lower level damage

A

Lower: obvious specific deficit

Higher: higher commands lose ability to coordinate lower levels resulting in new patterns of activity

25
Q

Difference between upper and lower motor neurones

A

Upper: from cerebrum or brainstem with connections to spinal cord

Lower: in cranial nerve nuclei in brainstem or spinal cord with connections to muscle/ periphery

26
Q

Why is the Babinski sign (toes curl upwards) a sign of high motor neurone damage

A

Lesions to higher control frees lower centres from their normal functioning

27
Q

Describe lesion at level of C1

A
  1. Spinal cord divided from CNS
  2. Lower motorneuones spared
  3. Flaccid paralysis (loss of voluntary muscle control and muscle tone)
28
Q

Describe lesions at level of colliculi

A
  1. Dividing upper and lower brainstem
  2. Extensor muscles contract leading general stiffness
  3. Higher centres disconnected thus releasing lower levels of control
29
Q

Name 3 organisational features of motor system

A
  1. Body maps
    - distal branch of ventral horn controls distal muscles
  2. Sensory feedback
    - each level receives sensory feedback to correct movement
  3. Descending motor control
    - higher levels modulate levels of sensory input into motor system
30
Q

Name two side loops of the motor system

A
  1. Basal ganglia

2. Cerebellum

31
Q

What are the three types of stroke

A

Ischaemic- due to closure of blood vessel by blood clot
Haemorrhagic- blood vessel rupture and bleeding
Transient ischaemic attach (TIA)- temporary blockage of blood flow

32
Q

What is an insufficient blood supply called

What is permanent brain damage called

A

Ischaemia

Infraction

33
Q

Describe the corticospinal pathway

A

From motor area of cortex to spinal cord, synapsids in brainstem nuclei

With rubrispinal pathway Known as the lateral descending motor pathway

34
Q

Describe the corticobulbar pathway

A

From brainstem nuclei to spinal cord

Medial white matter tract

35
Q

What does the lateral descending motor pathway control

A

Distal musculature

Fine movement

Neuroscience Y2 (12 decks)

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