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YR2: Neuroscience and Mental Health > Neuromuscular and Spinal Cord > Flashcards

Neuromuscular and Spinal Cord Flashcards

1
Q

What is the difference between EPSP and IPSP in terms of membrane potential? What do these result in?

A

EPSP: makes the membrane potential less negative (bringing it closer to the threshold potential)
IPSP: makes the membrane potential more negative (hyperpolarisation- further away from threshold for firing)
Graded effects- activity is a result of 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

Caused by constant low rate release of ACh into the synapse

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5
Q

What is the difference between intrafusal and extrafusal skeletal muscle fibres?

A

Intrafusal: serve as sensory organs (proprioceptors) that detect the amount + rate of change of length of a muscle
Extrafusal: innervated by alpha motor neurones + 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
Motor neurones that innervate the extrafusal fibres of skeletal muscle
Activation causes muscle contraction

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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

1 motor neurone can innervate several muscle fibres

But every muscle fibre can only be innervated by 1 motor neurone

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11
Q

When is a muscle fibre innervated by >1 motor neurone?

A

Under pathological conditions (e.g. severed nerve): 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 (the smallest functional unit that can generate force.)
Stimulation of 1 motor unit causes contraction of all muscle fibres in that unit

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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) have a 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: Smallest diameter cell bodies, Small dendritic trees, Thinnest axons, Slowest conduction velocity
Fast: 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 AP’s travelling down the nerves to the muscle fibres

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17
Q

What principle governs recruitment?

A

Size principle

Smaller units are recruited first (generally slow twitch units)

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18
Q

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

A

Slow –> Fast Fatigue-Resistant –> Fast Fatiguable

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19
Q

What are neurotrophic factors?

A

= a type of growth factor that prevent neuronal death + promote 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

Function of the muscle fibre is determined by the type of nerve that innervates it.

21
Q

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

A

Type 2B to Type 2A occurs with muscle training

Type 2 to type 1 occurs in 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 + type 2 fibres with preferential loss of type 2 fibres
Results in a larger proportion of type 1 fibres in aged muscle (slower contraction times)

23
Q

What tract is responsible for voluntary movements?

A

Pyramidal/Corticospinal tract

24
Q

What is the role of extrapyramidal tracts?

A

Automatic movements in response to stimuli

25
Q

What is a reflex?

A

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

26
Q

What are the 2 signals that are generated when the patellar ligament is tapped?

A

Excitatory signal to quadriceps= contraction

Inhibitory signal to hamstrings (antagonist)= relaxation

27
Q

Why is there a difference in the time taken for signals to reach the quadriceps and hamstrings in the patellar reflex?

A

Signal going to quadriceps only has 1 synapse (monosynaptic) whereas the signal to the hamstrings goes via an inhibitory interneurone so there are 2 synapses.
Thus, signal to quadriceps arrives slightly faster than signal to hamstrings.

28
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

29
Q

What names are given to the polysynaptic reflexes?

A

Flexion withdrawal

Crossed extensor

30
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.

31
Q

What is the Jendrassik manoeuvre?

A

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

32
Q

If you decerebrate an animal and test their reflexes, what would you expect to observe?

A

Revelation of excitatory control from supraspinal areas

Rigidity + spasticity result from brain damage giving over active or tonic stretch reflex

33
Q

What are gamma motor neurones reactive to?

A

Activity of muscle itself

control contraction of muscle fibers located within the muscle spindle based on afferent input

34
Q

What signs are seen with upper motor neurone lesions?

A

Hyperreflexia (loss of descending inhibition)
Clonus (tonic involuntary behaviour of foot)
Babinski’s Sign (great toe will flex, small toes fan out)

35
Q

What is the neuromuscular junction?

A

A specialised synapse between the motor neurone + motor end plate (muscle fibre cell membrane)

36
Q

What does recruitment allow?

A

Fine control (e.g. when writing) under which low force levels are required

37
Q

In rate coding, when does summation occur?

A

When units fire at frequency too fast to allow muscle to relax between arriving AP’s

38
Q

What is the reticulospinal tract involved in?

A

Coordinating automated movements of locomotion + posture e.g. to painful stimuli

39
Q

What is the rubrospinal tract involved in?

A

Automatic movements of arm in response to posture/ balance changes

40
Q

What is the vestibulospinal tract involved in?

A

Regulating posture to maintain balance + facilitates mainly alpha motor neurones of the postural, extensor muscles

41
Q

What determines magnitude and timing of a reflex?

A

Intensity + onset of stimulus

42
Q

How do reflexes differ from voluntary movement?

A

Once they are released, they can’t be stopped

43
Q

Describe what is seen in a flexion withdrawal and crossed extensor reflex

A

Pain sensation
Sensory neurone excited
Activation of interneurones in several spinal cord segments
Stimulation of flexor muscle to allow withdrawal from pain
Stimulation of extensor muscle in other leg to contract to maintain balance

44
Q

What is the Gamma reflex loop?

A

Feedback loop in nervous system that regulates level of tension in muscles
Shortens the spindles in muscle to maintain its sensitivity

45
Q

What is hypo-reflexia?

A

Below normal or absent reflexes

Mostly associated with lower motor neurone disease

YR2: Neuroscience and Mental Health (20 decks)

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