Neuromuscular control

Question 1

What are the alpha neurones?

Answer 1

lower motor neurones of the brainstem and spinal cord

innervate extrafusal muscle fibres of the skeletal muscles
Activation causes contraction

Question 2

What does the motor neurone pool contain?

Answer 2

All alpha motor neurones innervating a single muscle

Question 3

What is a motor unit?

Answer 3

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 4

How many muscle fibres does a motor neurone supply?

Answer 4

About 600 muscle fibres

Stimulation of one motor unit, contracts all the muscle fibres in that unit

Question 5

What are the different types of motor unit fibres?

Answer 5

Slow, type I
Fast fatigue resistant FR, IIA
Fast fatigue able FF, IIB

Question 6

describe slow motor unit fibres?

Answer 6

smallest diameter cell bodies​

small dendritic trees​

thinnest axons​

slowest conduction velocity

Question 7

Describe FR fibres?

Answer 7

larger diameter cell bodies​

larger dendritic trees​

thicker axons​

faster conduction velocity

Question 8

Describe FF?

Answer 8

larger diameter cell bodies​

larger dendritic trees​

thicker axons​

faster conduction velocity​

Question 9

What are the motor units classified by?

Answer 9

amount of tension generated
speed of contraction
fatiguability
LOOK AT GRAPHS

Question 10

What is recruitment?

Answer 10

Not randomly recruited.
size principle -> smaller units are recruited first

as more force is required more units are recruited

this allows fine control

Question 11

What is rate coding?

Answer 11

motor units can fire at a range of frequencies.
slow units will fire at lower frequencies

as firing rate increases, the force produced by the unit increases

summation occurs when the units fire at a frequency too fast to allow the muscle to relax between arriving action potentials.

Question 12

What are neurotrophic factors?

Answer 12

are a type of growth factors, which prevent neuronal death -> promote growth of neurons after injury

Question 13

Talk to me about cross innervation?

Answer 13

characterises of the muscle depend on the nerve which innervates them,
if fast twitch and slow twitch are cross innervated the muscles alternate

Question 14

Do motor units have plasticity?

Answer 14

Fibre types can change properties under many conditions.
IIB -> IIA
I -> II in severe deconditioning or spinal injury and microgravity in a spaceflight can do the same

Question 15

How does ageing affect fibres?

Answer 15

loss of type I + II but also loss of type II fibres

so you result into more type I fibres

Question 16

What is a reflex?

Answer 16

automatic response to a stimulus which involves a nerve impulse from receptor to the nerve centre and then to the effector
no level of consciousness

Question 17

What does magnitude and timing of reflex depend on?

Answer 17

Intensity and onset of stimulus

Question 18

What is the Jendrassik manoeuvre

Answer 18

exaggerated reflex when doing another movement (eg clenching teeth)

Question 19

How does the manoeuvre work?

Answer 19

CNS centres send inhibitory and excitatory regulation upon reflex reflex

inhibitory is key in normal conditions
decerebration reveals excitatory control from supraspinal areas

(rigidity and spasticity can result from brain damage giving over reactive or tonic stretch reflex)

LOOK AT SUPRASPINAL REFLEX CONTROL

Question 20

What is hyperreflexia

Answer 20

overreactive reflexes
loss of descending inhibition
UM lesions

Question 21

What is hyper reflexia/ clonus?

Answer 21

involuntary and rhythmic muscle contraction
loss of descending inhibition
associated with UMN lesion

Question 22

What is the Babinski sign?

Answer 22

it is a sign of hyper reflexia

sole is stimulated with blunt instrument, big tow

curl downwards -> normal
curl upwards -> abnormal in adults, as it is Babinski
sign
UMN lesions

toe curls upwards in infants

Question 23

What is hypo reflexia

Answer 23

below normal

associated with LMN disease