Neuromuscular and Spinal Cord Flashcards

1
Q

What is the difference between EPSP (excitatory post-synaptic potential) and IPSP (inhibitory post-synaptic potential) in terms of membrane potential?

A

EPSP – makes the membrane potential less negative (bringing it closerto the threshold potential)
IPSP – makes the membrane potential more negative (hyperpolarisation)
You get graded effects – whether the neurone fires or not is dependent on the summation of inputs

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2
Q

Which proteins are involved in the release of acetylcholine at synapses?

A

SNARE proteins

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3
Q

What trigger acetylcholine release?

A

Calcium influx

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4
Q

If you record the post-synaptic membrane potential at any one time, you will see some small changes in membrane potential. What are these caused by?

A

Miniature end plate potentials

They are caused by the constant dumping of acetylcholine into the synapse

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5
Q

What is the difference between intrafusal and extrafusal muscle fibres?

A

Intrafusal – these are skeletal muscle fibres that serve as sensory organs (proprioceptors) that detect the amount and rate of change of length of a muscle
Extrafusal – standard skeletal muscle fibres that are innervated by alpha motor neurones and generate tension by contracting, thereby allowing for skeletal muscle movement

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6
Q

What are alpha motor neurones? State some other names given to alpha motor neurones.

A

Anterior horn cells, ventral horn cells or lower motor neurones
They are motor neurones that innervate the extrafusal fibres of skeletal muscle

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7
Q

What is the name given to the sensory receptors in muscle that feedback to the CNS and allow an excitatory reflex to be generated?

A

Spindles

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8
Q

What is a motor neurone pool?

A

Collection of lower motor neurones that innervate a single muscle

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9
Q

Describe the arrangement of alpha motor neurones within the ventral horn.

A

Dorsal – flexors
Ventral – extensors
Medial – proximal
Lateral - distal

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10
Q

What is an important rule to remember regarding the connections between alpha motor neurones and muscle fibres?

A

One motor neurone can innervate several muscle fibres

But every muscle fibre can only be innervated by one motor neurone

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11
Q

Under what conditions can this rule be broken?

A

Under pathological conditions (e.g. severed nerve), the axonal regeneration can result in the innervation of muscle fibres that are already innervated

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12
Q

Define motor unit.

A

A single motor neurone together with all the muscle fibres that it innervates - it is the smallest functional unit that can generate force.

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13
Q

Describe and explain the difference in innervation ratio across different muscles in the body using examples.

A

Muscles that require very fine control (e.g. extrinsic eye muscles) havea low innervation ratio (few fibres innervated by a single neurone)
Muscle that are required to generate a lot of power have a high innervation ratio because when the motor unit fires, it will cause the contraction of a large mass of muscle fibres thus generating power (e.g. quadriceps)

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14
Q

What are the 3 types of motor unit?

A

Slow (Type 1)
Fast fatigue-resistant (Type 2A)
Fast fatiguable (Type 2B)

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15
Q

Describe the structural and functional differences between slow and fast twitch muscle fibres.

A
Slow fibres have: 
 Smallest diameter cell bodies 
 Small dendritic trees
 Thinnest axons 
 Slowest conduction velocity 
Fast fibres have: 
 Larger diameter cell bodies 
 Large dendritic cells 
 Thicker axons 
 Faster conduction velocity
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16
Q

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

A

Recruitment – recruiting more motor units for the muscle contraction
Rate Coding – increasing the frequency of action potentials travelling down the nerves to the muscle fibres

17
Q

What principle governs recruitment?

A

Size principle

Smaller units are recruited first, which are generally slow fibres

18
Q

Describe the order of recruitment of motor units with increasing force generation.

A

Slow –> Fast Fatigue-Resistant –> Fast Fatiguable

19
Q

What are neurotrophic factors?

A

Factors produced within the nerves and are transported throughout the nerve to maintain the nerves integrity and function.
They are a type of growth factor that prevents neuronal death and promotes the growth of neurones after injury.

20
Q

What happens to a slow fibre when a fast nerve is transplanted onto it and what does this show?

A

It becomes fast
This shows that the function of the muscle fibre is very much determined by the type of nerve that innervates it.
The action potentials can’t be the only thing being delivered to the muscles by the nerves.

21
Q

How easy is it to switch from one motor unit type to another?

A

Type 2B to Type 2A can happen with training
There is usually no way of changing from type 2 to type 1 or vice versa except in the case of severe deconditioning e.g. zero gravity or spinal injury

22
Q

How does muscle composition change with ageing?

A

Ageing is associated with a loss of type 1 and type 2 fibres with preferential loss of type 2 fibres
This means that a large proportion of muscle fibres in ages muscle are type 1
This loss of muscle is called sarcopenia

23
Q

What tract is responsible for voluntary movements?

A

Pyramidal/Corticospinal tract

24
Q

What is the role of extrapyramidal tracts?

A

It is responsible for automatic movements in response to stimuli (these are movements that your body makes without you being aware of it)

25
Q

What is a reflex?

A

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

26
Q

What are the components of a reflex arc?

A

Afferent signal
Relay neurone
Motor neurone

27
Q

What are the two signals that are generated when the patellarligament is tapped?

A

There is an excitatory signal going to the quadriceps

There is also an inhibitory signal going to the hamstrings (antagonist)

28
Q

Why is there a difference in the time taken for these signals to reach the relevant muscles?

A

The signal going to the quadriceps only has one synapse (monosynaptic) whereas the signal to the hamstrings goes via an inhibitory interneurone so there are two synapses.
This means that the signal to the quadriceps arrives slightly faster than the signal to the hamstrings.

29
Q

How did Hoffman plan on standardising the reflex test?

A

He considered bypassing the stretch that is caused by the tendon hammer on the patellar ligament and directly stimulating the nerve, which has sensory and motor fibres.
This would mean that the stimulus is identical every time (in duration and amplitude) and the magnitude of the reflex elicited will not be due to variations in input (how hard you tap the patellar tendon/where you tap it)

30
Q

What are the two twitches that are seen when you stimulate the nerve behind the knee?

A

M wave – twitch due to the direct conduction of the impulse down the motor neurone to the muscle fibre
H wave – due to the action potential passing down the sensory neurone back to the spinal cord and then coming out via a motor neurone to stimulate the muscle

31
Q

Why do sensory nerves show a response at lower stimulus intensity than motor nerves?

A

They are more amenable to electrical stimuli because they’re larger

32
Q

What names are given to the polysynaptic reflexes?

A

Flexion withdrawal Crossed extensor

33
Q

Describe the supraspinal control of reflexes.

A

There is a large descending control over reflexes that only becomes noticeable when these descending controls are removed.

34
Q

What is the Jendrassik manoeuvre?

A

Tap someone’s patellar tendon with a tendon hammer whilst they are clenching their teeth. The response elicited is 2-3 times greater.

35
Q

If you decerebrate an animal (but keep them alive) and test their reflexes, what would you expect to observe?

A

Hyperreflexia

Increased muscle tone

36
Q

What is the gamma reflex loop?

A

It shortens the spindles in muscle to maintain its sensitivity
There is also facilitation from higher centres, which increase the sensitivity of the motor neurone to afferent input

37
Q

What signs are seen with upper motor neurone lesions?

A

Hyperreflexia
Clonus
Babinski’s Sign