Neuromuscular control

Question 1

What are the roles of UMNs?

Answer 1

Inhibit the excitability of stretch receptors

Question 2

What are alpha motor neurons?

Answer 2

-LMNs of the brainstem and spinal cord
-Innervate extrafusal muscle fibres of skeletal muscles to contract

Question 3

What is a motor neuron pool?

Answer 3

All alpha motor neurons innervating a single muscle

Question 4

What is a motor unit?

Answer 4

A single motor neuron with all the muscle fibres

Question 5

What is innervation ratio?

Answer 5

The number of motor fibres a single motor neuron innervates

Question 6

When is high innervation ratio useful?

Answer 6

For powerful movement

Question 7

When is low innervation ratio important?

Answer 7

For fine, well controlled movement

Question 8

What are the 3 types of motor units?

Answer 8

-Type I = slow, low force, long period of time
-Type IIA = fast, fatigue resistant, high force, short period of time
-Type IIB = fast, fatiguable, high force, short period of time

Question 9

What are the 2 ways the brain regulates muscle force?

Answer 9

-Recruitment
-Rate coding

Question 10

What does recruitment of motor units mean?

Answer 10

-Smaller units (slow) are recruited first then as more force is required more units are recruited
-This allows fine control
-Ordered

Question 11

What does rate coding mean?

Answer 11

-Firing rate increases causing increased force produced by the unit
-Summation= units fire too fast to allow muscle to relax between APs

Question 12

What does motor unit and fibre characteristics depend on?

Answer 12

The nerve that innervates them

Question 13

Why would a muscle become atrophied?

Answer 13

Lack of nerve supply

Question 14

What can muscle training cause?

Answer 14

Change in motor units from type IIB to IIA

Question 15

What can severe deconditioning/ spinal cord injury cause?

Answer 15

Change in motor units from type I to II

Question 16

What happens to motor units during ageing?

Answer 16

Loss of type I and II fibres but greater proportion of type I

Question 17

What is the Jendrassik manoeuvre?

Answer 17

-Clenching teeth, making a fist, pulling against locked finger makes the reflex larger

Question 18

Why do we use the Jendrassik manoeuvre?

Answer 18

To distract the CNS and elicit the reflex

Question 19

Under normal conditions what dominates over reflexes?

Answer 19

Inhibitory control

Question 20

What is the cause of hyper reflexia?

Answer 20

-Loss of descending inhibition
-Associated with UMN lesions

Question 21

What is clonus?

Answer 21

Involuntary and rhythmic muscle contractions

Question 22

What is Babinski’s sign?

Answer 22

-When sole stimulated with blunt instruments the big toe will curl upwards
-Should normally curl downwards

Question 23

What causes hypo reflexia?

Answer 23

LMN lesions

Question 24

Describe the knee jerk reflex?

Answer 24

1. Patellar tendon is hit with a patellar hammer
2. Impulse sent down sensory neurone
3. Travels through dorsal horn and splits into 2
4. Synapses with the 2 separate motor neurones
5. 1 motor neurone travels to biceps femoris and causes it to relax
6. Other motor neurone travels to quadriceps femoris and causes it to contract
7. This causes the leg to kick out