- allows contact from: - -> neurons to muscle - -> neurone to neurone

Neuro 7: Neuromuscular + spinal cord Flashcards by P R

What are synapses ?

allows contact from:
-> neurons to muscle
-> neurone to neurone

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

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

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

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What is a neuromuscular junction.

NMJ = specialized synapse btw motor neurone + motor end plate on muscle fibre cell memb

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How is NMJ activated?

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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What does the degree of summation determine?

determines how readily a neuron can reach threshold to produce an AP

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What are Miniature End plate potentials?

when at rest

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

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What is an alpha motor neuron?

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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What is meant by intrafusal?

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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What is meant by extrafusal ?

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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What is a motor neurone pool?

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

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describe the arrangement of alpha motor neurones.

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

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What is the difference between flexors and extensors

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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Define a motor unit:

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

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What are the 3 types of motor unit?

slow (S, type I)
Fast, fatigue resistant (FR, Type 2a)
Fast, fatiguable (FF, type 2b)

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postural muscles = mainly _____ muscles

postural muscles = mainly slow muscles

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Distinguish between the 3 different types of motor unit

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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the 3 diff motor unit types = classified by:

amount of tension generated
speed of contraction
fatiguability of the motor unit

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

recruitment

2. rate coding

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

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

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explain the difference between recruitment and rate coding

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

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

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what is the order of recruitment?

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slow –> fast fatigue resistant –> fast fatiguable

what are neurotrophic factors?

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

What do neurotrophic factors do?

- prevent neuronal death | - promote growth of neurons after injury

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

most commonly type ___ may change to ____ following training

most commonly type 2B may change to 2A following training

When might Type 1 change to change 2

- when there is severe deconditioning / spinal cord injury -

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

-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)

Why do aged muscle generally have slower contraction times?

- 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

What is sarcopenia?

- loss of muscle

what does pyramidal tract largely control?

voluntary movements

define reflex

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

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

1. intensity of the stimulus | 2 onset of the stimulus

Why are reflexes important??

- important in maintaining upright posture | - and to reduce damage to parts of the body

what 3 things do you need for a reflex?

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

describe how a reflex test is conducted

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

What does a reflex test tell us?

- 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

describe the difference between monosynaptic and disynaptic reflex

(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)

How would a monosynaptic (stretch) reflex work

- 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.

What is a key feature of the hoffman reflex?

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

what does the hoffman reflex test?

- it tests the integrity of the reflex pathways .

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

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

Why are sensory nerves more amendable to electrical stimuli?

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

reflex responses comprises of flexion withdrawal and crossed extensor. explain how these work in response to a painful stimuli

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

What is the Jendrassik maneuver?

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

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

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

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

What is a gamma reflex loop?

- -> spindle of muscle is shortened | - -> to maintain its sensitivity

What is hyper reflexia?

- loss of descending inhibition | - due to e.g a stroke

What is a clonus?

- muscular spasm involving repeated / rhythmic contractions | - has hypertone in muscles

What is the babinski's sign?

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

What is hypo reflexia?

- below normal / absent reflexes --> usually associated with lower motor neurone lesions --> because signal don't go out / come out of spinal cords

what is the order of recruitment?

fast fatiguable --> fast fatigue resistant --> slow

whats does the vestibulospinal tract do?

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

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)

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

Neuro 7: Neuromuscular + spinal cord Flashcards

(56 cards)