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LCRS - neuro > Neuromuscular and spinal cord > Flashcards

Neuromuscular and spinal cord Flashcards

1
Q

Give another name for a presynaptic terminal.

A

Bouton

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2
Q

How long is a synaptic cleft?

A

10-50nm

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3
Q

What is the role of a synapse?

A

Allow for communication/contact between neurones or neurone –> muscle

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4
Q

How does the contact ratio of synapses vary?

A

1:1 muscle

103:1 in the CNS

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5
Q

What is summation?

A

The graded effects of combined EPSPs and IPSPs on the neurone membrane potential.

The degree of summation determines whether an AP will be generated.

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6
Q

What is the difference between an IPSP and an EPSP.

A

An EPSP makes the neurones potential less negative, vice versa.

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7
Q

What is a neuromuscular junction?

A

Specialised synapse between a motor neurone, a motor end plate and the muscle fibre cell membrane.

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8
Q

Diagram of NMJ.

A
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9
Q

How is the NMJ activated?

A

AP arrives at terminal bouton.

Ca2+ influx.

ACh vesicles fuse with pre-synaptic membrane + diffuses across cleft.

ACh binds to post-synaptic receptors.

Na+ influx stimulated.

AP in muscle fibre.

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10
Q

what are miniature end-plate potentials?

A

At rest individual vesicles release ACh at a very low rate causing minimal stimulation.

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11
Q

Where are alpha motor neurons found?

A

Brainstem and spinal cord.

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12
Q

What do alpha motor neurons innervate?

A

The muscle fibres of skeletal muscle - activation causes contraction.

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13
Q

What is a motor neuron pool?

A

all the alpha motor neurons innervating a single muscle.

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14
Q

Cross section of vertebrae showing where in grey matter alpha motor neurons are located.

A
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15
Q

What is a motor unit?

A

A motor neuron and all the muscle fibres innervated by that particular motor neuron.

Stimulation of one motor unit causes contraction of all muscle fibres in that unit.

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16
Q

How many motor neurons and skeletal muscle fibres does a human have?

A

420,000 motor neurons

250 million skeletal muscle fibres.

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17
Q

How many muscles fibres are supplies by each motor neuron?

A

Approx. 600

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18
Q

Table comparing types of motor unit:

Slow (type 1)

Fast, fatigue resistant (type IIA)

Fast, fatiguable (type IIB).

Compare cell body diameter, no. dendritic trees, axon thickness, velocity of conduction,

A
19
Q

In what 3 ways can different motor units be classified?

A

Amount of tension generated.

Velocity of conduction.

Fatiguability of motor unit.

20
Q

Compare the tension, contraction speed, and fatiguability of Type I, Type IIA and Type IIB motor units.

A

Type IIB - fast twitch, high tension, high fatigue.

Type IIA - less fast twitch, moderate tension, somewhat fatigue resistant.

Type I - slow twitch, low tension, fatigue resistant.

21
Q

What two mechanisms does the brain use to regulate the force that a single muscle produces?

A

Recruitment and rate coding.

22
Q

Explain recruitment.

A

Recruit different motor units to build the force of contraction.

Smaller units recruited first - slow twitch.

Slow –> FR –> FF.

23
Q

Explain rate coding.

A

Different motor units fire at different frequencies.

Slow units fire at a lower frequency.

As firing rate increases, force produced by the unit increases.

Summation occurs when units fire too fast to allow muscle to relax between arriving APs.

24
Q

What are the roles of the motor cortex, brainstem, and cerebellum/basal ganglia in the motor system?

A

Motor cortex - receive info from other cortical areas and relays them to brainstem and thalamus.

Brainstem - passes command to spinal cord for body muscles and directly to muscles of face, head and neck.

Cerebellum/basal ganglia - adjust commands from other parts of motor system before outputting them to the thalamus and brainstem.

25
Q

What are neurotrophic factors?

A

growth factors that prevent neuronal death and promote growth after injury

26
Q

Explain normal relative to crossed innervation.

A

normal innervation - slow units have slow nerve fibres innervating them, while fast units have rapid ones.

Crossed innervation - fast and flow innervation is swapped so slow units become faster and fasr units become slower (e.g. Soleus faster, FDL slower).

27
Q

Define plasticity and give some examples of it

A

The ability of fibre type to change.

IIB –> IIA after training

I –> II after severe deconditioning or spinal cord injury (or space microgravity)

Ageing - preferential loss of type II.

28
Q

What is the role of pyramidal corticospinal tracts?

A

Control voluntary movements

29
Q

What is the role of reticulospinal tracts?

A

coordinate automated movements of locomotion and posture e.g. To painful stimuli

30
Q

What is the role of the vestibulospinal tract?

A

regulate posture to maintain balance and uses anti-gravity muscles.

31
Q

What is the role of the rubrospinal tract?

A

automatic movements of arm in response to posture/balance changes.

32
Q

Which tags correspond to the:

lateral and antrerior corticospinal tracts (pyramidal)

rubrospinal, reticulospinal, vestibulospinal, olivospinal tracts (extrapyramidal)?

A
  1. a,b
  2. a,b,c,d
33
Q

What is a reflex?

A

involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli.

34
Q

Diagram showing components of a reflex arc.

A
35
Q

Compare monosynaptic stretch reflexes with polysynaptic flexion withdrawal reflexes.

A

Polysynaptic involves activated interneurons at several spinal cord levels

36
Q

Diagram showing monosynaptic reflex.

A
37
Q

Give the steps of a polysynaptic flexion withdrawal reflex.

A
  1. step on painful stimulus –> sensory receptor stimulated –> sensory neurone stimlated.
  2. sensory neurone activates interneurons in several spinal cord segments within integrating centre
  3. interneurons as/descend several levels and stimulate motor neurones from several levels to contract flexor muscles to move leg.
38
Q

Explain crossed extension.

A

interneurons cross the cord and stimulate effectors on opposite limb to contract and extens other limb.

39
Q

Define hyporeflexia.

A

below normal/absent reflexes. mostly associated with LMN disease.

40
Q

Define hyperflexia.

A

supra-normal reflexes.

41
Q

Explain supraspinal control of reflexes.

A

Higher CNS centres regulate stretch reflex. Under normal conditions, inhibitory control dominates.

Decerebration: reveals excitatory control from supraspinal areas - leading to rigidity and spasticity (overactive and tonic stretch reflex)

42
Q

Via which neurons do higher centres of the CNS regulate reflexes?

A
  1. Activating alpha motor neurons
  2. Activating inhibitory interneurons
  3. Activating propriospinal neurons
  4. Activating gamma motor neurons
  5. Activating terminals of afferent fibres
43
Q

What spinal pathways are involved in reflex regulation?

A

Rubrospinal: red nucleus for arms in balance

Vestibulospinal: vestibular nuclei for balance

Tectospinal: head movements due to visual information

LCRS - neuro (16 decks)

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