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Neuro > Neuromuscular and Spinal Cord > Flashcards

Neuromuscular and Spinal Cord Flashcards

1
Q

Membrane potential value

A

-70mV

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2
Q

2 directional alterations to membrane potential of post-synaptic neurones

A

It can be made less negative – i.e. brought closer to threshold for firing; this is an excitatory post synaptic potential (EPSP)

Or it can be made more negative – i.e. brought further away from threshold for firing; this is an inhibitory post-synaptic potentials (IPSP)

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3
Q

Sequence at the NMJ

A

When an action potential arrives at the MNJ, Ca2+ influx causes ACh release

ACh binds to receptors on motor end plate

ACh diffuses across the synapse, activate ACh receptors and propagate AP

Ion channel opens – Na+ influx causes action potential in muscle fibre

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4
Q

mEPP

A

At rest, individual vesicles release ACh at a very low rate causing miniature end-plate potentials (mEPP). These potentials tend to be graded.

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5
Q

Alpha motor neurone

A

Lower motor neurone (α): final neurone going from the CNS to the muscle

They innervate the extrafusal muscle fibres of the skeletal muscles
(standard skeletal muscles that cause contraction)

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6
Q

Intrafusal muscle fibres

A

Contain specialised sensory organs that tell the CNS information

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7
Q

Motor Neurone pool

A

All of the neurones going to a single muscle

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8
Q

Arrangement of alpha motor neurones

A

They are found in the anterior/ventral horn of grey matter

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9
Q

Motor Unit

A

Made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron’s axonal terminals.

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10
Q

How many motor units can a muscle fibre be innervated by

A

Only 1

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11
Q

Types of motor unit

A

Slow (S)

Fast (FR and FF)

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12
Q

Characteristics of slow motor units

A

Smallest diameter cell bodies

Small dendritic tress

Thinnest axons

Slowest conduction velocity

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13
Q

Characteristics of Fast fatigue resistant

A

Resistant to fatigue

Large diameter cell bodies

Larger dendritic trees

Thickets axons

Faster conduction velocity

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14
Q

Characteristics of Fast fatiguable

A

Fatigue easily

Larger diameter cell bodies

Larger dendritic trees

Thickets axons

Faster conduction velocity

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15
Q

Recruitment

A

Changing the number of motor units active at any one time

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16
Q

Sequence of recruitment

A

Smaller units are recruited first (these are generally the slow twitch units).

As more force is required, more units are recruited. This allows fine control (e.g. when writing), under which low force levels are required.

We go from slow, to fatigue resistant, to fast fatigable.

17
Q

Define Rate coding

A

Change he frequency with which action potentials travel down to the muscle

18
Q

Process of rate coding

A

A motor unit can fire at a range of frequencies. Slow units fire at a lower frequency. As the firing rate increases, the force produced by the unit increases. Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.

Coding changes at the same time recruitment changes. As the motor unit coding increases, frequency increases. At low levels of force, you expect the slow motor units to be recruited, but within an individual set of motor units, impulses are changing in frequency at the same time.

19
Q

Neurotrophic Factors

A

Growth factors- produced in the nerve and transported throughout nerve to maintain nerve integrity and function

Allows growth after injury

20
Q

Plasticity of motor unit/muscle fibres- which muscle fibres change

A

Fibre types can change properties under many different conditions.

The change from type IIB (fast fatigable) to IIA (fast fatigue resistant) is most common following training

There is normally NO WAY of changing fast to slow (or vice versa)

The change from type I to II possible in cases of severe deconditioning or spinal cord injury

Microgravity during spaceflight results in shift from slow to fast muscle fibre types

Ageing is associated with loss of type I and II fibres but also preferential loss of type II fibres

This results in a larger proportion of type I fibres in aged muscle (evidence: slower contraction times)

This loss of muscle is called sarcopenia

21
Q

Motor tracts in the spinal cord

A

Corticospinal /pyramidal Tract = voluntary movement pathway (it goes from the motor cortex to the spinal cord)

There are many extrapyramidal tracts that are concerned with automatic movements in response to stimuli.
* RUBROSPINAL TRACT: involved in automatic movements of arms in response to posture/balance changes

  • RETICULOSPINAL TRACT: coordinated movements of locomotion/posture resulting from painful stimuli
  • VESTIBULOSPINAL TRACT: regulates posture to maintain balance – allow us to maintain head/neck position
22
Q

Pathway of upper and lower neurone

A

The upper motor neurone crosses over at the decussation of the pyramids in the medulla and synapses with a lower motor neurone in the ventral horn of grey matter. Pyramidal tracts are the major voluntary pathways (tracts outside of this are the extrapyramidal tracts).

The lower motor neurone then projects out of the spinal cord and joins with a sensory nerve coming in to form a peripheral nerve.

23
Q

Define Reflex

A

An automatic and often inborn response to a stimulus

24
Q

Components of a reflex arc

A
  • Sensory receptor
  • Sensory neurone
  • Integrating centre- the point at which the neurons that compose the grey matter of the spinal cord or brainstem synapse
  • Motor neurone
  • Effector
25
Q

Using reflex tests to determine where the damage is

A

If you can voluntarily contract the muscle then there is probably nothing wrong with the motor neurones. If you then hit the tendon and nothing happens, since you can voluntarily contract it, is indicates a sensory

26
Q

How many synapses in a reflex arc

A

If the afferent fibres from the muscle are stimulated you will get a monosynaptic connection with the efferent to get contraction (excitatory). It can also synapse with an interneuron, which inhibits the motor neurone supplying another muscle (inhibitory).

27
Q

The monosynaptic (stretch) reflex

A

When you hit the patellar ligament with a tendon hammer, not only do you excite the quadriceps muscle, you also INHIBIT the hamstrings

  • This sends an afferent signal that excites the efferents to the quadriceps and inhibits the efferents to the hamstrings - the leg kicks up
28
Q

The Hoffman Reflex

A

The stimulus can be identical every time the reflex is tested

APs are sent down the motor neurone to the muscle (quick). Simultaneously, it sends sensory signals to the spinal cord, which synapse onto the motor neurone, and come back to the same motor nerve - contract the muscle again (slower, longer). There are 2 contractions.

M wave- from motor neurone
H(Hoffman) wave- from sensory

This allows us to see what part of the system is injured

29
Q

Supraspinal control of 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
30
Q

How higher centres influence reflexes

A
  1. Activating alpha motor neurons (contraction)
  2. Activating inhibitory interneurons (inhibit)
  3. Activating propriospinal neurons (posture)
  4. Activating gamma motor neurons
  5. Activating terminals of afferent fibres
31
Q

Higher centres and pathways involved in reflexes

A

o Cortex – corticospinal (fine control of limb movements, body adjustments)

o Red nucleus – rubrospinal (automatic movements of arm in response to posture/balance changes)

o Vestibular nuclei – vestibulospinal (altering posture to maintain balance)

o Tectum – tectospinal (head movements in response to visual information).

32
Q

Gamma motor neurone

A

Supply sensory organs of the muscle

These neurones change the sensitivity of the sensory organ in order to sense the extent of contraction

33
Q

Stroke causes what lesions- and what this then results in

A

Causes upper motor neurone lesions

Strokes lead to a loss of descending inhibition of reflexes so you get hyperreflexia

  • Clonus
  • Babinski’s sign
34
Q

Clonus

A

Muscular spasm involving repeated, often rhythmic, contractions

35
Q

Babinski’s Sign

A

If you stroke the bottom of the foot you see plantar extension (the toes fan out

36
Q

Causes of hypo-reflexia

A

Mostly associated with Lower motor neurone lesions

Neuro (9 decks)

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