21.1 Lower Motor Neuron Pools

Question 1

What are the lower motor neurons?

Answer 1

Efferent fibres running from the spinal cord to the peripheral areas, providing control over the various muscle units.

Question 2

Where do lower motor neurons originate?

Answer 2

Ventral horn of spinal cord

Question 3

What is the primary fibre type of lower motor neurons?

Answer 3

A-alpha

Question 4

What are the three subtypes that alpha-motor neurons can be classified into?

Answer 4

I, IIa, IIb

Question 5

Which neurotransmitter do all lower motor neurons use?

Answer 5

ACh

Question 6

What is the contraction time of type I, IIa, IIb muscle fibres?

Answer 6

I: Slow
IIa: Fast
IIb: Very fast

Question 7

What is the level of fatigue resistance of type I, IIa, IIb muscle fibres?

Answer 7

I: High
IIa: Moderate
IIb: Low

Question 8

What is the relative muscle fiber size of type I, IIa, IIb muscle fibres?

Answer 8

I: Small
IIa: Large
IIb: Medium

Question 9

Which muscle fibre is needed for long distance?

Answer 9

Type I

Question 10

Which muscle fibres are needed for power and speed?

Answer 10

Type IIa and IIb

Question 11

What is the relative generating force of type I, IIa, IIb muscle fibres?

Answer 11

I: Small
IIa: Moderate
IIb: Very high

Question 12

Are motor axons myelinated?

Answer 12

Yes

Question 13

What is meant by Henneman’s size principle?

Answer 13

Smaller motor units are recruited before larger ones

Question 14

Why is there an exponential relationship between recruitment and power?

Answer 14

smaller fibres are the most easily recruited, and stimulate the smallest number of motor units (Henneman’s principle)

Question 15

What is spatial facilitation?

Answer 15

Increasing muscle force by increasing motor unit recruitment

Question 16

What is temporal facilitation?

Answer 16

Increasing muscle force by increasing firing and recruitment frequency

Question 17

Where is the overall pattern for muscle movement generated?

Answer 17

CNS

Question 18

Where are patterns for basic locomotion generated?

Answer 18

Spinal cord

Question 19

Where are patterns for well-learned movements generated?

Answer 19

Brainstem/cerebellum

Question 20

Where are patterns for novel, internally formed movements generated?

Answer 20

Cortex

Question 21

What is reciprocal inhibition?

Answer 21

While one muscle stretches, the opposing muscle is inhibited

Question 22

Why is reciprocal inhibition important?

Answer 22

It prevents muscles from working against each other –> efficient, effective coordination

Question 23

What are the symptoms of lower motor neuron damage?

Answer 23

• Hypotonia (decreased muscle tone)
• Hyporeflexia (diminished reflex responses)
• Wasting
• General flaccid paralysis
• Fasciculation

Question 24

What is a fasciculation?

Answer 24

A spontaneous, involuntary muscle twitch