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Y2 Neuroscience and Mental Health > Neuromuscular and spinal cord control of movements > Flashcards

Neuromuscular and spinal cord control of movements Flashcards

1
Q

What is the function of the synapse

A

Allows for contact from neurone to muscle or from neurone to neurone

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2
Q

Describe synapses

A

Structure is similar throughout the nervous system
May be simple or complex
Contact ratio ranges from 1:1 (muscle) to 10^3:1 (CNS)
synaptic cleft = 10-50nm

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3
Q

What are the two directions in which a membrane potential of the post synaptic neurone can be altered

A

-ve = further away from threshold for firing (inhibitory post synaptic potentials)

+ve = brought closer to threshold for firing (excitatory post synaptic potential)

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4
Q

What is summation

A

Graded effects of synaptic transmission
Occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.
Excitatory post synaptic potentials and inhibitory post synaptic potentials can summate
The degree of summation will determine how readily a neurone can reach threshold to produce an AP

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5
Q

Describe the neuromuscular junction

A

Specialised synapse between the motor neurone and the motor end plate, the muscle fibre cell membrane

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6
Q

How is the neuromuscular junction activated§

A
  1. AP arrives
  2. Calcium influx
  3. ACh release
  4. ACh binds to receptor on motor end plate
  5. Ion channels open to allow sodium to influx -> AP
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7
Q

What are mature end-plate potentials

A

At rest, individual vesicles release ACh at a very low rate

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8
Q

Describe the alpha motor neurone

A

Lower motor neurones of the brainstem and spinal cord
Innervates the extramural muscle fibres of the skeletal muscles
Activation causes contraction

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9
Q

What is the motor neurone pool

A

Contains all alpha motor neurons innervating a single muscle

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10
Q

What is a motor unit

A

Single motor neurone together with all the muscle fibres that it innervates
Smallest functional unit to produce force
Stimulation of one motor unit causes contraction of all the muscle fibres in that unit

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11
Q

What are the 3 types of motor unit

A

Slow (S, type I)
Fast, fatigue resistant (FR, Type IIA)
Fast, fatiguable (FF, type IIB)

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12
Q

Describe slow motor units

A

Smallest diameter cell bodies
Small dendritic trees
Thinnest axons
Slowest conduction velocity

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13
Q

Describe fast, fatigue resistant motor units

A

Larger diameter cell bodies
Larger dendritic trees
Thicker axons
Faster conduction velocity

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14
Q

Describe fast, fatiguable motor units

A

Larger diameter cell bodies
Larger dendritic trees
Thicker axons
Faster conduction velocity

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15
Q

What are the 3 motor unit types classified according to

A

Amount of tension generated
Speed of contraction
Fatiguability

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16
Q

What is recruitment

A

Mechanism by which the brain regulates the force a single muscle can produce

Governed by the size principle - smaller motor units are recruited first (generally slow twitch)
More force required -> more units required
Allows fine control (e.g. writing), under which low force levels are required

17
Q

What is rate coding

A

Mechanism by which the brain regulates the force a single muscle can produce

Motor units can fire at a range of frequencies
Slow units = lower frequency
As firing rate increases, force produced increases
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.

18
Q

What are neurotrophic factors

A

Type of growth factor
Prevents neuronal death
Promotes growth of neurones after injury

19
Q

What are the effects of neurotrophic factors

A

Motor unit and fibre characteristics are dependent on the nerve which innervates them.

If a fast twitch muscle and a slow muscle are cross innervated, the soleus becomes fast and the FDL becomes slow.

The motor neurone has some effect on the properties of the muscle fibres which it.

20
Q

Describe the plasticity of motor units/muscle fibres

A

Fibre types can change properties under conditions

Training = IIB -> IIA
Severe deconditioning/ spinal cord injury = =I -> II
Microgravity in spaceflight = slow -> fast
Ageing = loss of type I slower contraction

21
Q

What is the vestibulospinal tract involved in

A

Ventral
regulates posture to maintain balance, and facilitates mainly α motoneurones of the postural, anti-gravity (extensor) muscles

22
Q

What are the Sacral and anterior corticospinal tracts involved in

A

Control voluntary movements

23
Q

What is the role of the reticulospinal tract

A

Coordinates automated movements of locomotion and posture e.g. to painful stimuli

24
Q

What is the role of the rubrospinal tract

A

Automatic movements of arm in response to posture/balance changes

25
Q

What is a reflex

A

An automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness.

26
Q

What are the components of a reflex arc

A 
Sensory receptor 
Sensory neuron 
Integrating center 
Motor neuron
Effector
27
Q

Describe the monosynaptic (stretch) reflex

A
  1. Stretching stimulates the sensory receptor (muscle spindle)
  2. Sensory neuron is excited
  3. Sensory neuron activates motor neurones in the integrating centre (spinal cord)
  4. Motor neuron excited
  5. Effector contracts and relives the stretching
  6. Inhibitory neurone activated
  7. Motor neurone to antagonistic muscles inhibited
  8. Antagonistic muscles relax
28
Q

What is the Hoffman reflex

A

-

29
Q

Describe a polysynaptic reflex

A

Flexion withdrawal

  1. Stepping on a tack stimulates the sensory receptor
  2. Excited sensory neurone
  3. Sensory neurones activates interneurones in several spinal cord segments, ascending and descending
  4. Motor neurones are excited
  5. Effector contracts
30
Q

Describe the supra spinal control of reflexes

A

Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex
Inhibitory control dominates in normal conditions
Decerebration reveals the excitatory control from supra spinal nerves

31
Q

How may rigidity and spasticity occur via supra spinal reflex control

A

Brain damage giving over-active or tonic stretch reflex.

32
Q

What are the mechanisms by which higher centres influence reflexes

A

Activating:

  1. Alpha neurones
  2. Inhibitory interneurones
  3. Propriospinal neurons
  4. Gamma motor neurons
  5. Terminals of afferent fibres
33
Q

Which higher centres and pathways are involved in supra spinal control of reflexes

A

Cortex – corticospinal (fine control of limb movements, body adjustments)

Red nucleus – rubrospinal (automatic movements of arm in response to posture/balance changes)

Vestibular nuclei – vestibulospinal (altering posture to maintain balance)

Tectum – tectospinal (head movements in response to visual information).

34
Q

What is the gamma reflex loop

A

If the knee is extended and the muscles fo slack, the spindle is shortened to maintain its sensitivity

35
Q

What is hyper-reflexia

A

Below normal or absent reflexes
Loss of descending inhibition
Mostly associated with lower motor neuron diseases
May be due to stroke

36
Q

Describe the structure of the alpha motor neuron

A

Extensors are more ventral, flexors dorsal

Grey matter is more proximal

Y2 Neuroscience and Mental Health (22 decks)

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