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eLCRS - 뉴로 > Neuro 7: Neuromuscular + spinal cord > Flashcards

Neuro 7: Neuromuscular + spinal cord Flashcards

1
Q

What are synapses ?

A
  • allows contact from:
  • -> neurons to muscle
  • -> neurone to neurone
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2
Q

how can the memb potential of post synaptic neurone can be altered in 2 direction by inputs

A

a) can be made less -ve
- -> i.e brought closer to threshold for firing
- -> excitatory post synaptic potential (EPSP)

OR

b) can be made more negative
- -> i.e brought further away from threshold
- -> inhibitory post synaptic potentials (IPSP)

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3
Q

What is a neuromuscular junction.

A
  • NMJ = specialized synapse btw motor neurone + motor end plate on muscle fibre cell memb
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4
Q

How is NMJ activated?

A
  • AP arrives at NMJ
  • Ca2+ influx causes Ach release
  • Ach binds to receptors on motor end plate
  • ion channel opens
  • Na+ influx causes AP in muscle fibre
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5
Q

What does the degree of summation determine?

A
  • determines how readily a neuron can reach threshold to produce an AP
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6
Q

What are Miniature End plate potentials?

A
  • when at rest

individual vesicles release Ach at a low rate –> causing mEPP

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7
Q

What is an alpha motor neuron?

A

alpha motor neuron = lower motor neurons of the brainstem + spinal cord

–> they innervate the extrafusal muscle fibres of the skeletal muscles

–> activation causes muscle contraction

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8
Q

What is meant by intrafusal?

A

intrafusal : skeletal muscle fibres that acts as sensory organs that detects amount + rate of change in length of a muscle

  • houses the sensory organs
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9
Q

What is meant by extrafusal ?

A

extrafusal: standard skeletal muscle fibre that are innervated by alpha motor neurones

  • and they generate tension by contracting
  • -> allowing skeletal muscle movement
  • contains sensory organs = for reflex responses
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10
Q

What is a motor neurone pool?

A

motor neurone pool= collection of lower motor neurones that innervate a single muscle

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11
Q

describe the arrangement of alpha motor neurones.

A
  • they are found in the anterior/ ventral horn of grey matter
  • there are flexors + extensors
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12
Q

What is the difference between flexors and extensors

A

flexors = flexes the muscles –> allows you to curl up into a ball

extensors = allows you to be as tall + long as possible.

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13
Q

Define a motor unit:

A

motor unit - a single motor neurone together with all the muscle fibres that it innervates.
–> it is the smallest functional unit with which to produce force

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14
Q

note: stimulation of 1 motor unit –> causes contraction of all the muscle fibres in that unit.

A

-

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15
Q

What are the 3 types of motor unit?

A
  1. slow (S, type I)
  2. Fast, fatigue resistant (FR, Type 2a)
  3. Fast, fatiguable (FF, type 2b)
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16
Q

postural muscles = mainly _____ muscles

A

postural muscles = mainly slow muscles

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17
Q

Distinguish between the 3 different types of motor unit

A

SLOW, TYPE 1

  • cell bodies = smallest diameter
  • has small dendritic trees
  • thinnest axon
  • slowest conduction velocity

FR, TYPE 2A

  • cell bodies = larger diameter
  • has larger dendritic trees
  • has thicker axons
  • has faster conduction velocity

FF, TYPE 2B

  • cell bodies = larger diameter
  • has larger dendritic trees
  • has thicker axons
  • has faster conduction velocity
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18
Q

the 3 diff motor unit types = classified by:

A

the 3 diff motor unit types = classified by:

  • amount of tension generated
  • speed of contraction
  • fatiguability of the motor unit
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19
Q

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

A
  1. recruitment

2. rate coding

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20
Q

fatigue resistant muscles produce more/less force than slow fibres
and force = produced more quickly/slowly

A

fatigue resistant muscles produce MORE force than slow fibres + force = produced more QUICKLY

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21
Q

explain the difference between recruitment and rate coding

A

RECRUITMENT
= recruiting more motor units
- as muscles increase in force, more units are recruited
- smaller units are recruited first

RATE CODING
= changing the freq at which you send AP down the nerves
-

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22
Q

at ____ levels of force, the bottom motor unit = firing all the time

A

at LOW levels of force, the bottom motor unit = firing all the time

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23
Q

what is the order of recruitment?

A

slow –> fast fatigue resistant –> fast fatiguable

24
Q

what are neurotrophic factors?

A
  • neurotrophic factors = host of factors/ type of growth factor produced within the nerve
  • -> transported through nerve to maintain nerve integrity + function
25
Q

What do neurotrophic factors do?

A
  • prevent neuronal death

- promote growth of neurons after injury

26
Q

note: motor unit and characteristics are dependent on the nerve which innervates them –> if you cut a e.g slow nerve and switch it onto a different muscle type –> the muscle takes on the characteristics of the nerve and the muscle itself also becomes slow

A

-

27
Q

most commonly type ___ may change to ____

following training

A

most commonly type 2B may change to 2A

following training

28
Q

When might Type 1 change to change 2

A
  • when there is severe deconditioning / spinal cord injury

-

29
Q

Aging = associated with loss of what type of muscle fibre?

A

-loss of both type 1 + 2

but has preferential loss of type 2 fibres

–> so when you’re old there is a larger proportion of type 1 fibres (which are slower obv)

30
Q

Why do aged muscle generally have slower contraction times?

A
  • when you age –> there is preferential loss of type 2 fibres
  • so there is a large proportion of type 1 fibre

–> so has slower contraction times

31
Q

What is sarcopenia?

A
  • loss of muscle
32
Q

what does pyramidal tract largely control?

A

voluntary movements

33
Q

define reflex

A

reflex = an automatic/ often inborn response to a stimulus

  • that involves a nerve impulse passing inward from a receptor to a nerve centre
  • -> then outward to an effector
  • without reaching level of consciousness
34
Q

the magnitude + timing of a coordinated muscle contraction/relaxation = determined by what 2 factors?

A
  1. intensity of the stimulus

2 onset of the stimulus

35
Q

Why are reflexes important??

A
  • important in maintaining upright posture

- and to reduce damage to parts of the body

36
Q

what 3 things do you need for a reflex?

A
  1. an afferent signal
  2. some kind of relay neurone
  3. a motor neurone
37
Q

describe how a reflex test is conducted

A
  • muscle = stretched

- -> and amount of force the muscle produces in reflex action is recorded

38
Q

What does a reflex test tell us?

A
  • reflex testing can help determine whether there has been a sensory or a motor loss
  • if you can voluntarily contract muscle –> motor neurone = normal
  • if hit the tendon + nothing happens –> sensory loss
39
Q

describe the difference between monosynaptic and disynaptic reflex

A

(MONOSYNAPTIC) - excitatory
stimulate extensor afferent –> you get response in extensor efferent –> causing contraction

(DISYNAPTIC) - inhibitory
if you excite flexor afferent nerve - there is an interneurone which inhibits the excitation of the extensor efferent

note:

time difference to generate an AP –> reflects difference in no. of synapses between monosynaptic(usually only 1) and disynaptic (usually more than 1)

40
Q

How would a monosynaptic (stretch) reflex work

A
  • when you strike the patellar tendon
  • -> it makes the quadriceps stretch
  • which sends an afferent signal
  • this excites the efferents that goes to the quadriceps
  • and inhibits the efferent to the hamstrings.
41
Q

What is a key feature of the hoffman reflex?

A
  • stimulus = identical each time a reflex is tested
    (same duration + amplitude)
  • so you know any change in reflex size = not due to the input
42
Q

what does the hoffman reflex test?

A
  • it tests the integrity of the reflex pathways .
43
Q

Describe what would happen if you stimulate the nerve at the back of the knee:

A
  • you will observe 2 twitches
    1. M wave:
  • direct motor response
  • goes from motor neurone to muscle –> causing contraction
  1. H wave:
    - caused by AP in sensory neurone
    - which goes back to the spinal cord + excites the motor neurone
44
Q

Why are sensory nerves more amendable to electrical stimuli?

A
  • because they are larger

- so you can get a response from sensory nerve (H wave) at a lower stimulus intensity than the M wave

45
Q

reflex responses
comprises of flexion withdrawal and crossed extensor.

explain how these work in response to a painful stimuli

A

e.g you step on pin multiple muscles on one limb contracts

Polysynaptic reflexes

  • flexion withdrawal –> lifting leg up + make other leg straight
  • crossed extensor –> allows you to stand in upright position even with one leg
46
Q

What is the Jendrassik maneuver?

A

when testing the knee jerk, reflex on someone –> and you ask them to clench your teeth,
reflex will be 2-3x greater.

47
Q

note: there is control from the brain

- pull hind leg of cat 
cat was decerebrated 
- pull hind leg of cat again 
- bigger response in the leg 
- because you take away the inhibitory control (that is usually dominant at rest)

CONCEPT IS SIMILAR FOR PATIENT WITH HYPERREFLEXIA

A

-

48
Q

In supra spinal control of reflexes, what are the 5 ways in which higher centers influence reflexes?

A
  1. activating alpha motor neurons
  2. activating inhibitory interneurons
  3. activating propriospinal neurons
  4. activating gamma motor neurons
  5. activating terminal of afferent fibres
49
Q

What is a gamma reflex loop?

A
  • -> spindle of muscle is shortened

- -> to maintain its sensitivity

50
Q

What is hyper reflexia?

A
  • loss of descending inhibition

- due to e.g a stroke

51
Q

What is a clonus?

A
  • muscular spasm involving repeated / rhythmic contractions

- has hypertone in muscles

52
Q

What is the babinski’s sign?

A
  • if you stroke bottom of foot
  • -> you will see plantar extension
  • -> so toes fan out
53
Q

What is hypo reflexia?

A
  • below normal / absent reflexes

–> usually associated with lower motor neurone lesions –> because signal don’t go out / come out of spinal cords

54
Q

what is the order of recruitment?

A

fast fatiguable –> fast fatigue resistant –> slow

55
Q

whats does the vestibulospinal tract do?

A
  • it regulates posture to maintain balance and facilitates mainly alpha motor neurones of the postural, anti-gravity (extensor) muscles
56
Q

When you tap the patellar ligament - Why is there a difference in the time taken for these signals to reach the relevant muscles? (quadricep + hamstring)

A
  • Signal to quadriceps = monosynaptic
  • Signal to hamstring = disynaptic (polysnaptic)
  • So signal to quadriceps = slightly faster

eLCRS - 뉴로 (16 decks)

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