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Neuroscience and Mental Health > 9. Neuromuscular and spinal cord > Flashcards

9. Neuromuscular and spinal cord Flashcards

1
Q

What is the range of contact ratio of synapses in the body?

A

1:1 to 10^3:1

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2
Q

What is the resting potential difference over the membrane?

A

-70mV (inside is 70mv more negative than outside)

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3
Q

How can the membrane potential of the post-synaptic neurone be altered (2 directions)?

A

• Can be made less negative
- brought closer to the threshold for firing
- excitatory post-synaptic potential (EPSP)
• Can be made more negative
- brought further away from threshold for firing
- inhibitory post-synaptic potential (IPSP)

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4
Q

What is summation?

A
  • Process that determines whether or not an action potential will be generated by the combined effects of excitatory and inhibitory signals
  • Both from multiple simultaneous inputs (spatial summation), and from repeated inputs (temporal summation)
  • Summation may or may not reach the threshold voltage to trigger an action potential
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5
Q

Outline how a motor neurone can induce an action potential in a muscle fibre

A
  • Ca2+ influx causes ACh release
  • ACh diffuses across the synapse and binds to receptors on motor end plate
  • Ion channel opens - Na+ influx causes action potential in muscle fibre
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6
Q

What are extrafusal and intrafusal muscle fibres?

A
  • Extrafusal - standard skeletal muscles that cause contraction
  • Intrafusal - contain specialised sensory organs that give the CNS information
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7
Q

What are alpha motor neurones?

A
  • Lower motor neurones of the brainstem and the spinal cord
  • Alpha motor neurones are the final neurones going from the CNS to the muscle
  • Innervate the extrafusal muscle fibres of the skeletal muscles
  • Activation causes muscle contraction
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8
Q

What is it called when all of the neurones go to a single muscle?

A
  • Motor neurone pool

* This occurs with many alpha motor neurones innervating a single muscle

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9
Q

Where are alpha motor neurones found in the CNS?

A
  • Anterior/ventral horn of the grey matter

* these neurones are aka ventral/anterior horn cells

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10
Q

What do flexors and extensors allow?

A
  • Flexors - flex the muscles and allow you to curl up into a ball
  • Extensors - allow you to be as tall and long as possible
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11
Q

What does a motor unit describe?

A
  • A nerve and all of the muscle fibres that it innervates

* The smallest functional unit to produce a contraction

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12
Q

How many motor units can innervate a single muscle fibre?

A

Only 1 - no muscle fibre is innervated by more than one motor unit

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13
Q

How many muscle fibres does each motor neurone supply?

A

Each motor neurone supplies about 600 muscle fibres

420,000 motor neurones and 250million skeletal muscle fibres in a human

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14
Q

What are the 3 different types of motor units?

A
  • Slow (S)
  • Fast (FR) - fatigue resistant
  • Fast (FF) - fatiguable
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15
Q

What are the 3 different motor unit types classified by?

A
  • Amount of tension generated
  • Speed of contraction
  • Fatiguability of the motor unit
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16
Q

Describe slow motor units

A
  • Smallest diameter cell bodies
  • Small dendritic trees
  • Thinnest axons
  • Slowest conduction velocity
  • Don’t generate much force
  • Don’t tire out - continue indefinitely
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17
Q

Describe fast (FR and FF) motor units?

A
  • Larger diameter
  • Larger dendritic trees
  • Thicker axons
  • Faster conduction velocity
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18
Q

What are the 2 mechanisms by which the brain regulates the force that a single muscle can produce?

A
  • Recruitment - changing the number of motor units active at any one time
  • Rate coding - changing the frequency of action potentials to the muscle

• Both happen together

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19
Q

How are motor units recruited?

A
  • Size principle
  • Smaller units are recruited first (slow twitch units)
  • As more force is required, more units are recruited
  • This allows fine control, under which low force levels are required
  • Slow => fatigue resistant (FR) => fatiguable (FF)
  • Happens in reverse when coming down from a contraction
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20
Q

What happens when units fire at a frequency too fast and why (as part of ‘rate coding’)?

A
  • Summation

* Allows the muscle to relax between arriving action potentials

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21
Q

Where is my will to live?

A

not here.

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22
Q

What are neutrotrophic factors?

A
  • Type of growth factor
  • Prevent (peripheral) neuronal death and promote growth of neurones after injury
  • CNS neurones don’t regenerate after injury unlike peripheral neurones
23
Q

What is the general explanation for the inability of CNS neurones to repair?

A
  • Millions of axons in the CNS as opposed to a few thousand

* Consequences of rewiring incorrectly is not worth it

24
Q

What happens if a fast twitch and slow muscle are cross-innervated, and what does this mean?

A
  • Slow muscle becomes fast
  • Fast muscle becomes slow
  • Therefore, action potentials can’t be the only thing being delivered to the muscle - something else governs the way the muscle behaves
25
Q

How can fibre types change from type IIA (FR) to type IIB (FF) and vice versa?

A 
• FR to FF
- normally no way
- possible in cases of sever deconditioning or spinal cord injury
• FF to FR
- most common following training
26
Q

What affect does microgravity during spaceflights have on the fibre types?

A

Slow to fast muscle fibres

27
Q

What affect does ageing have on muscle fibre types?

A
  • Loss of type I (S) and II fibres
  • Preferential loss of type II
  • Larger proportion of type I - evidence: slower contraction times
28
Q

What is a loss of muscle mass, quality and strength due to ageing called?

A

Sarcopenia

29
Q

Which tracts control voluntary movements and automatic movements?

A
  • Voluntary - corticospinal/pyramidal tract

* Automatic - extrapyramidal tracts

30
Q

Where do the upper motor neurones cross over and meet the lower motor neurone?

A
  • Cross at decussation of the pyramids

* Synapses in the ventral horn of grey matter

31
Q

What does a lower motor neurone join with to form a peripheral nerve?

A

Sensory nerve

32
Q

What is the rubrospinal tract involved in?

A

Automatic movements of arms in response to posture/balance changes

33
Q

What is the reticulospinal tract involved in?

A

Coordinated movements of locomotion/posture resulting from painful stimuli

34
Q

What is the vestibulospinal tract involved in?

A

Regulates posture to maintain balance - allow us to maintain head/neck position

35
Q

What is a reflex?

A
  • Automatic and often inborn response to a stimulus

* Elicited by peripheral stimuli

36
Q

What is the integrating centre?

A
  • One or more regions within the CNS that relay impulses from sensory to motor neurones
  • Part of reflex arc
  • Includes the interneuron
37
Q

What does it mean if you can voluntary contract a muscle but there is no reflex?

A

Damage of the sensory neurone

38
Q

How do flexors and extensors work together?

A
  • Afferent signal travels to the spinal cord
  • Afferent signal stimulates certain motor neurones (e.g. those supplying the flexor) and inhibits others (e.g. those supplying the extensor) to allow for movement
  • Allows for a monosynaptic connection with the efferent
  • An inhibitory signal from an interneuron allows this
39
Q

When you strike the patellar ligament with a tendon, which muscles do you excite and inhibit?

A
  • Excite the quadriceps muscle

* Inhibit the hamstrings

40
Q

What is the Hoffman reflex used for?

A
  • Used clinically to asses which set of nerves may be affected by a disorder
  • The stimulus is identical every time the reflex is tested so it is more useful in identifying problems due to a change in reflex
  • This is not the case when using the knee-jerk reflex, which is less reliable
41
Q

Why do you see 2 twitches if you stimulate the nerve at the back of the knee?

A

1) M (motor) wave - direct motor response
• From motor neurone that has been stimulated, directly to the muscle causing contraction
2) H (Hoffman) wave - reflex
• AP in sensory neurone going to the spinal cord and exciting the motor neurone
• Second twitch - longer path

42
Q

Are you more likely to get a response from a sensory or motor nerve stimulation?

A
  • Sensory (H wave) rather than the M wave

* Sensory nerves are more amenable to electrical stimuli as they are larger

43
Q

Explain why the H-waves peaks earlier then gets smaller as the M wave peaks?

A
  • H wave peaks as sensory stimulus increases
  • As the M wave increases, more antidromic (wrong way) action potentials are propagated, as the stimulus is in the middle of the motor neurone
  • At a certain level, the sensory signal will be cancelled out by the antidromic motor impulse
  • M wave continues to get bigger as stimulus increases, until no more neurones can be activated
44
Q

What is it called when you have a reflex it move your leg away to a painful stimulus?

A

Flexion withdrawal

45
Q

What is the reflex that occurs to prevent you from falling over called?

A

Crossed extensor

46
Q

What is the Jendrassik manoeuvre?

A
  • Clenching teeth and interlocking hands when having patellar tendon tapped
  • This action can prevent conscious inhibition of the patellar reflex
47
Q

How does disease affect the influence of the CNS higher centres on stretch 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 supraspinal areas
  • Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex
  • Explanation for brisk reflexes and spasticity in someone who’s had a stroke
48
Q

How do higher centres of the CNS influence reflexes?

A
  • Activating alpha motor neurones (contraction)
  • Activating inhibitory interneurons
  • Activating propriospinal neurones (posture)
  • Activating gamma motor neurones
  • Activating terminals of afferent fibres
49
Q

Which higher centres and pathways are involved in the influence of reflexes?

A
  • Cortex - corticospinal
  • Red nucleus - rubrospinal
  • Vestibular nuclei - vestibulospinal
  • Tectum - tectospinal (head movements in response to visual information)
50
Q

What are gamma neurones involved in?

A
  • Supply the sensory parts of the muscle
  • Change the sensitivity of the sensory organ
  • Senses the extent of contraction or stretch
  • Affects the alpha motor neurone creating a gamma reflex loop
51
Q

What is clonus?

A

Muscular spasm involving repeated, often rhythmic, contractions

52
Q

What is Babinski’s sign?

A

Plantar extension when stroking the bottom of the foot (with condition or a child <18 months due to undeveloped corticospinal tract)

53
Q

What is hypo-reflexia mostly associated with?

A

Lower motor neurone lesions

Neuroscience and Mental Health (17 decks)

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