Neuromuscular and Spinal Cord Control of Movement

Question 1

What mechanism causes the graded effects of neuronal transmission

Answer 1

Summation

Question 2

• The degree of summation will determine how readily a neurone can ….

Answer 2

reach threshold to produce an AP

Question 3

3 steps of activation at a NMJ:

Answer 3

1. When an AP arrived at the MNJ, Ca2+ influx causes ACh release
2. ACh binds to receptors on the motor end plate
3. Ion channel opens- Na+ influx causes an AP in the muscle fibre

Question 4

What causes MINIATURE END-PLATE POTENTIALS

Answer 4

At rest, individual vesicles release ACh at a very low rate in a motor neuron

Question 5

What is the motor unit:

Answer 5

NAME GIVEN TO A SINGLE MOTOR NEURON TOGETHER WITH ALL THE MUSCLE FIBRES THAT IT INNERVATES- IT IS THE SMALLEST FUNCTIONAL UNIT WITH WHICH TO PRODUCE FORCE

Question 6

Stimulation of one motor unit causes contraction of how many fibres

Answer 6

all the muscle fibres in that unit

Question 7

THE ALPHA MOTOR NEURON is the….

Answer 7

lower motor neurons of the brainstem and the spinal cord (the last neurons before the muscle fibre)

Question 8

THE ALPHA MOTOR NEURON is located in…

Answer 8

the ventral horn of the spinal cord

Question 9

motor neuron pool contains …

Answer 9

all alpha motor neurons innervating a single muscle

Question 10

The 3 different motor unit types are:

Answer 10

Slow S type 1
Fast fatigue resistant, FR TIIA
Fast fatiguable FF, TIIB

Question 11

Which motor unit has the largest diameter cell bodies, dendritic tress, axon thickness, and fastest conduction velocity

Answer 11

FF TIIB

Question 12

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

Answer 12

RECRUITMENT

RATE CODING

Question 13

Explain recruitment in regulating force produced by a motor neuron

Answer 13

• Motor units are not randomly recruited- there is an order to this
• Governed by the ”SIZE PRINCIPLE”- smaller units are recruited first (these are generally the slow twitch units)
• As more force is required, more units are recruited
• This allows for fine control e.g. writing, under which low force levels are required

Question 14

Which type of motor unit is recruited first

Answer 14

Smaller units and so generally slow twitch

Question 15

Explain rate coding in regulating force produced by a motor neuron

Answer 15

• 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 ire at frequency too fast to allow the muscle to relax between arriving APs

Question 16

Which type of motor unit has the lowest firing frequency

Answer 16

Slow twitch T1

Question 17

• Summation occurs when units are at frequency too fast to …

Answer 17

allow the muscle to relax between arriving APs

Question 18

Motor unit and fibre characteristics are dependent on …

Answer 18

the nerve which innervated them

Question 19

If a fast twitch muscle and a slow muscle are cross innervated (their innervation is switched) what happens to speed of twitching

Answer 19

the slow becomes fast and the fast becomes slow

Question 20

Type I to II muscle fibre switching is possible in cases of … example of when this occurs.

Answer 20

severe deconditioning or spinal cord injury

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

Question 21

• Ageing is associated with loss of type I and II fibres but also preferentially loss of what type of fibre. What is evidence of this

Answer 21

type II

evidenced from slower contraction times

Question 22

REFLEX definition:

Answer 22

AN AUTOMATIC AND OFTEN INBORN RESPONSE TO A PERIPHERAL STIMULUS THAT INVOLVES A NERVE IMPULSE PASSING INWARD FROM A RECEPTOR TO A NERVE CENTRE AND THEN OUTWARD TO AN EFFECTOR (AS A MUSCLE OR GLAND) WITHOUT REACHING THE LEVEL OF CONSCIOUSNESS

Question 23

Reflex response size is proportional to …

Answer 23

the size of the stimulus

Question 24

Describe the reflex pathway starting with the sensory receptor

Answer 24

Sensory receptor -> sensory neuron -> (interneuron -> inhibits antagonistic muscle) motor neuron -> effector

Question 25

What is a Volley, e.g. afferent volley or effect volley

Answer 25

collection of APs

Question 26

What detects stretch in the reflex arc

Answer 26

Muscle spindle

Question 27

What is the Hoffman reflex

Answer 27

- Stimulate the nerve that you want to stimulate the muscle of interest electrically - Stimulate a mixed nerve right in the centre and it will send signals up to the spinal cord and down to the muscle - This allows you to achieve the same identical stimulation each time - Should result in a quick response resulting from immediate motor activation, and a slower response resulting from sensory and THEN motor activation (the second is called the Hoffman reflex)

Question 28

What test can enable us to work out which part of the NS is damaged

Answer 28

Hoffman Reflex

Question 29

Explain crossed extensor reflex

Answer 29

If you step on a plug, Not only is a response on the ipsilateral side to the stimulus required e.g. moving your foot off of the plug, but a response on the contralateral side is needed e.g. repositioning your other leg to stay balanced This is what we mean by crossed extensor

Question 30

How do you enhance the kneejerk reflex

Answer 30

ching our teeth or making a fist when having our patellar tendon tapped

Question 31

what is the Jendrassik manoeuvre

Answer 31

enhance the kneejerk reflex by clenching our teeth or making a fist when having our patellar tendon tapped- this is called the JENDRASSIK manoeuvre

Question 32

Explain the Jendrassik manoeuvre

Answer 32

- Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex - Inhibitory control dominates in normal conditions (N) - Decerebration reveals the excitatory control from supraspinal areas - Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex

Question 33

HIGHER CENTRES INFLUENCE REFLEXES BY: (5)

Answer 33

``` 1) activating alpha motor neurone activating inhibitory interneurons activating propriospinal neurons activating gamma motor neurons activating terminals of afferent fibres ```

Question 34

HIGHER CENTRES AND PATHWAYS INVOLVED in reflexes are? (4)

Answer 34

Cortex Red nucleus Vestibular nucleus Tectum

Question 35

Pathway the cortex controls in reflexes? and this does?

Answer 35

Corticospinal (fine control of limb movements and body adjustments)

Question 36

Pathway the Red nucleus controls in reflexes?

Answer 36

Rubrospinal (automatic movements of arm in response to posture/balance changes)

Question 37

Pathway the Vestibular nucleus controls in reflexes?

Answer 37

vestibulospinal (altering posture to maintain balance)

Question 38

Pathway the Tectum controls in reflexes?

Answer 38

tectospinal (head movements in response to visual information)

Question 39

HYPER-REFLEXIA is a classic symptom of ....

Answer 39

upper motor neurone disorders e.g. stroke

Question 40

CLONUS definition? Often seen in?

Answer 40

series of involuntary, rhythmic muscular contractions and relaxations (often seen in upper motor neurone disorders)

Question 41

BABINSKI SIGN is... often seen in people with ....

Answer 41

Stimulation on sole of foot with blunt instrument leads to an uncontrolled upward extension of the hallux (toe) in people with upper MN disorders

Question 42

Hyporeflexia is associated with XXXX diseases

Answer 42

lower motor neurone