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LCRS 2 > Neuromuscular and Spinal Cord > Flashcards

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 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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7
Q

What is a motor neurone pool?

A

Collection of lower motor neurones that innervate a single muscle

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8
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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9
Q

Under what conditions can the rule muscle fibres can only be innervated by one motor neurone 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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10
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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11
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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12
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

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13
Q

What principle governs recruitment?

A

Size principle

Smaller units are recruited first, which are generally slow fibres

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14
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.

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15
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.

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16
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

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17
Q

What tract is responsible for voluntary movements?

A

Pyramidal/Corticospinal tract

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18
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)

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19
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

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20
Q

What are the components of a reflex arc?

A

Afferent signal
Relay neurone
Motor neurone

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21
Q

What are the two signals that are generated when the patellar ligament is tapped?

A

There is an excitatory signal going to the quadriceps

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

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22
Q

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

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.

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23
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

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24
Q

What names are given to the 2 polysynaptic reflexes?

A

Flexion withdrawal

Crossed extensor

25
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.

26
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.

27
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

28
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

29
Q

What signs are seen with upper motor neurone lesions?

A

Hyperreflexia
Clonus
Babinski’s Sign

30
Q

What determines how readily a neuron can reach its action potential

A

Summation of all the ISPSs and ESPSs

31
Q

What are alpha motor neurones

A

Lower motor neurones that innervate extrafusal muscle fibres

32
Q

Where are they found

A

Either originating from brainstem (trigeminal nucleus) or ventral horn

33
Q

What is the motor neuron pool

A

Where all alpha motor neuron innervating a single muscle are found

34
Q

Somatotopic mapping of ventral horn

A

Distal pools more lateral

Proximal more medial

35
Q

Functional mapping of ventral horn

A

Extensors more ventral

Flexors more dorsal

36
Q

What is a motor unit

A

The motor neuron and the muscle fibres it innervates

37
Q

What is smallest functional unit we talk about to give a force

A

Motor unit

38
Q

3 types of motor unit

A

Slow
Fast fatigue resistant
Fast fatiguable

39
Q

Order at which motor units are brought in

A

Slow then fast resistant then fast fatiguing

40
Q

Differences between slow and fast motor units

A

Small have lower axon and cell body diameters
Smaller dendritic trees
Slow conduction

41
Q

Alternative names for types of motor units

A

Slow can be type 1 or S
Fast resistant can be type 2a or FR
Fast fatiguing can be type 2b or FF

42
Q

How to classify motor units

A

Force produced
Speed of contraction
Fatiguing

43
Q

Importance of cross innervation

A

Possible for a fast twitch muscle and slow muscle to be cross innervated where motor neurone supplying them changes resulting in a change in fibre characteristics

44
Q

Plasticity of a motor unit

A

Common for fibre types to change

45
Q

Change in fibre types brought about from training

A

Type 2 b to 2A

46
Q

Cause of change in T1 to T2

A

Severe deconditioning or spinal chord injury

47
Q

Change brought about from space flights

A

T1 to T2

48
Q

Example of polysynaptic withdrawal

A

Flexion withdrawal

49
Q

What makes flexion withdrawal polysynaptic

A

Certain muscles have numerous motor units which also come at different spinal levels, these have to also have to receive the transmission. There is also issue with giving appropriate message to other leg as you don’t want that leg to flex as well. You need to stimulate the extensor in the other leg to maintain balance

50
Q

Jendrassik manouever

A

Clenching teeth and making fists can potentials pterodactyl patellar reflex

51
Q

What is the supraspinal effect on stretch reflexes

A

Higher centres of CNS exert excitatory and inhibitory regulation on reflexes

52
Q

Proof of supraspinal control on reflexes

A

Decerebration revealed excitatory control as can leave muscles tonically stretched

53
Q

How can higher centres influence reflexes

A 
Activating 5 neurones:
Alpha motor
Inhibitory interneurones
Propriospinal
Gamma motor 
Terminals of afferent fibres
54
Q

Propriospinal neurones

A

Give information about where we are in space

55
Q

4 higher centres and their pathways in reflex control

A

Cortex- corticospinal
Red nucleus- rubrospinal
Vestibular nucleus- vestibulospinal
Tectum- tectospinal

56
Q

Tectospinal pathway

A

Head movements in response to visual info

57
Q

Gamma loop reflex

A

If knee is extended and goes slack the. The spindle is shortened to maintain sensitivity

58
Q

Why does hyper-reflexia occur

A

Loss of descending inhibition

59
Q

Causes of hyporeflexia

A

Normally lower motor neurone problem

LCRS 2 (44 decks)

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