1b Neuromuscular Control

Question 1

what are alpha motor neurones?

Answer 1

The lower motor neurones of the brainstem and the spinal cord that innervate the extrafusal muscle fibres of skeletal muscles

Question 2

What does activation of the alpha motor neurones cause?

Answer 2

Muscle contraction

Question 3

What is a motor neurone pool?

Answer 3

Pool which contains all the alpha motor neurones which innervate a single muscle

Question 4

what is a motor unit?

Answer 4

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 5

What are Type 1 muscle fibres?

Answer 5

Slow - smallest cell bodies and smalled dendritic trees, thinnest axons and slowest conduction velocity

Question 6

What are Type 2A muscle fibres?

Answer 6

Fast, fatigue resistant - larger diameter cell bodies, larger dendritic trees, thicker axons and faster conductions

Question 7

What are Type 2B muscle fibres?

Answer 7

Fast, fatiguable - larger diameter cell bodies, larger dendritic trees, thicker axons and faster conductions

Question 8

Which type of muscle fibre produces the largest amount of force?

Answer 8

Type 2B

Question 9

How are the three motor unit types classified?

Answer 9

amount of tension generated, speed of contraction and fatiguability.

Question 10

What are the two mechanisms by which the brain regulates the amount of force a single muscle produced?

Answer 10

rate coding and recruitment

Question 11

What is recruitment?

Answer 11

When smaller units are recruited first, and as more force is required, larger units are then recruited - this allows for fine control when necessary

Question 12

What is rate coding?

Answer 12

When different units can fire at different frequencies - higher firing rate is larger force

Question 13

When does summation occur?

Answer 13

When the muscle units fire at a frequency which is too fast to allow the muscle to relax between AP’s

Question 14

what are neurotrophic factors?

Answer 14

a type of growth factors which prevent neuronal death and promote the growth of the neurones after injury

Question 15

How does cross innervation work?

Answer 15

If a fast twitch muscle and a slow muscle are cross innervated, the soleus becomes fast and the FDL becomes slow.

The motor neuron has some effect on the properties of the muscle fibres it innervates.

Question 16

What causes a change from IIB to IIA fibres?

Answer 16

Training

Question 17

What causes a change from Type I to Type II?

Answer 17

Severe deconditioning or spinal cord injury, or microgravity

Question 18

What change is ageing associated with?

Answer 18

with loss of type I and II fibres but also preferential loss of type II fibres.

Question 19

What is the evidence that ageing results in a loww of type 1 and 2 fibres, with a preferential loss of type 2?

Answer 19

Larger proportion of type 1 fibres = slower contraction times

Question 20

What is a reflex?

Answer 20

An automatic response to a 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 21

What is the Jendrassik Manoeuvre?

Answer 21

Try clenching the teeth, making a fist, or pulling against locked fingers when having patellar tendon tapped. The reflex becomes larger

Question 22

What type of control dominates in normal conditions?

Answer 22

Inhibitory control

Question 23

What reveals the excitatory control from the supraspinal areas?

Answer 23

Decerebration

Question 24

What can be the result of brain damage that causes a tonic stretch reflex?

Answer 24

Rigidity and spasticity

Question 25

What is hyper-reflexia?

Answer 25

Overactive reflexes due to a loss of descending inhibition, and is associated with upper motor neuron lesions

Question 26

What is Clonus (As a type of hyper-reflexia)?

Answer 26

Involuntary and rhythmic muscle contractions

Loss of descending inhibition

Upper motor lesion

Question 27

What is the Babinski Sign?

Answer 27

When the sole of the foot is stimulated with a blunt instrument, the big toe curls upwards (in adults, this is abnormal)

Question 28

When the sole of the foot is stimulated with a blunt object, what is the normal and pathological response in adult and kids?

Answer 28

Adults - Normal = Down, Pathological = Upwards
Children - Normal = Upwards

Question 29

What type of lesion is babinski sign associated with?

Answer 29

Upper motor lesions

Question 30

What is hyporeflexia?

Answer 30

Below normal or absent reflex - associated with lower motor neurone disease