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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.

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5
Q

What does the degree of summation determine

A

how readily a neurone can reach threshold to produce an AP

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6
Q

How is the neuromuscular junction activated

A
  1. AP arrives at the pre-synaptic terminal causing opening of VGCa2+ channels and Ca2+ moves in
  2. Ca2+ causes the ACh vesicles to bind to the pre-synaptic membrane
  3. Ach is released into the synaptic cleft
  4. ACh binds to the receptors on the nicotinc ACh receptor (nAChR) and opening it
  5. Na+ moves into the sarcolemma and causes an AP here often leading to muscle contraction
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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 extrafusal muscle fibres of the skeletal muscles
Activation causes contraction

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9
Q

What are the alpha motor neurons made up of and where is it

A

Cell bodies in grey matter of the spinal cord/brainstem
Cranial and spinal nerves included

In the spinal cord and brainstem

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10
Q

What is a motor unit

A

Single motor neurone together with all the muscle fibres that it innervates
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 is recruitment

A

The acquisition of more motor units as more force is required
Allows fine control (e.g. writing), under which low force levels are required
(basically spatial summation)

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16
Q

In what order does recruitment occur in

A

Governed by the size principle - smaller motor units are recruited first (generally slow twitch)
S to FR to FF

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17
Q

What is Rate Coding

A

The increase in firing rate to generate more force by the motor unit
As firing rate increases, force produced increases
(basically temporal summation)

18
Q

Explain how rate coding is associated with summation

A

Summation/tetany occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.

19
Q

Describe the plasticity of motor units/muscle fibres

A

Fibre types can change properties under conditions

20
Q

What are the changes in motor units during training

A

FF(IIB) to FR(IIA)

21
Q

What are the changes in motor units in ageing

A 
Loss of Type I and II, but more II
S type (I) mainly
22
Q

Where is the vestibulospinal tract and what is it involved in

A

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

23
Q

Where is the anterior corticospinal tract and what is it involved in

A

Dorsal to vestibulospinal tract

Control voluntary movements

24
Q

Where is the rubrospinal tract and what is it involved in

A

Lateral

Automatic movements of arm in response to posture/balance changes

25
Q

Where is the reticulospinal tract and what is it involved in

A

Dorsal to the anterior corticospinal tract

Coordinate automated movements of locomotion and posture (e.g. to painful stimuli)

26
Q

What are the components of a reflex arc

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

What are the types of spinal reflexes

A

Stretch reflex
Flexion reflex
Crossed extensor reflex

28
Q

Describe the general reflex pathway

A
  1. Receptors sense the stimuli
  2. Sensory neurones stimulated
  3. Synapse with interneurons in posterior horn
  4. Synapse with motor neurones in anterior horn
  5. Effector activated
29
Q

Describe the stretch reflex pathway

A

Monosynaptic

Same as the normal reflex but there is an inhibitory signal to the antagonistic muscle causing relaxation

30
Q

What is the Hoffman reflex

A

If you stimulate a muscle fibre then it will be stimulated by:
The direct stimulation to the motor neurone and cause contraction (SHORT ROUTE) also creating an M wave
The sensory neurone going back through the spinal cord to the motor neurone and causing contraction (LONG ROUTE) also creating an H wave
Hence you end up with 2 contractions of the muscle

31
Q

Describe the flexion reflex

A

Polysynaptic (as there is an interneurone stimulated in the spinal cord)
Several spinal segments are stimulated from one sensory neurone
Causes contraction of the flexor muscles and therefore withdraws the arm/leg

32
Q

Describe the crossed extensor reflex

A

Polysynaptic
The sensory neurone synapses with several interneurons including those from the other side and so you get flexion of the stimulated side and extension of the non-stimulated side (in this case)
So there is excitatory stimulation to both flexor and extensor muscles on both sides

33
Q

What are muscle spindles

A

Specialised receptors within the skeletal muscles to detect changes in length and proprioception
avoid damage/overuse/pain

34
Q

What do gamma neurones do

A

They keep the muscle spindles sensitive by causing intrafusal muscle contraction to keep up with the changing muscle fibre length caused by alpha motor neurons

35
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

36
Q

Give an example fo supra spinal control of reflexes

A

1 .If your bicep muscle is at normal length (N) then if a weight is suddenly dropped on your hand it will move to a stretched length(S)

  1. When it moves to S then the spindles within the muscle fib§res are stretched and cause the a reflex to occur and contract your bicep (as there are sensory neurons wrapped around the spindle)
  2. So your extrafusal muscle fibres have shortened but your spindles are still stretched
  3. Supraspinal areas control the gamma motor neurones, causing stimulation of these to contract the spindle back to the correct now contracted length and keep the muscle sensitive to any other changes (Like if you dropped the weight suddenly)
37
Q

Where does UMN originate and terminate

A

originate in cerebral cortex and terminate in the spinal cord/brainstem

38
Q

Where does LMB ornate and terminate

A

LMN originate in the spinal cord/brainstem and terminate at the effector muscle

39
Q

What causes hyperreflexia

A

loss of the supraspinal reflex control when the UMNs are damaged and so the reflexes are present and very active as there is no suppression

40
Q

What causes hyporeflexia

A

LMNs are not functioning to effectively contract the muscles in the reflex loop

41
Q

What occurs in an upper motor neurone lesion

A 
Hypertonia 
Hyperreflexia 
No atrophy 
Clonus prescient 
Lesion from motor cortex through to anterior horn
42
Q

What occurs in a lower motor neurone lesion

A

Hypotonia
Hyporeflexia
Severe atrophy
Fasciculations and fibrillations

Y2 Neuroscience and Mental Health (22 decks)

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