Fast and Slow Muscle

Question 1

small motor units

Answer 1

less than 10 muscle fibres

Question 2

large motor units

Answer 2

more than 100 muscle fibres

Question 3

The force of muscle contraction is increased mainly by two

means:

Answer 3

• By activating more motor units i.e. recruitment
• By activating motor units more i.e. by increasing stimulus
frequency to cause summation or tetanus of individual motor
units

Question 4

electromyography -EMG

Answer 4

The electrical activity of skeletal muscle can be recorded (electromyogram or EMG) using electrodes in or near the muscle

Question 5

When will a clinician order an EMG

Answer 5

if a patient has signs or symptoms that may indicate a nerve or muscle disorder.

Question 6

importance of EMG

Answer 6

often necessary to help diagnose or rule out a number of conditions such as:

Question 7

myasthenia gravis

Answer 7

Diseases affecting the connection between the nerve and the muscle,

Question 8

examples of disorders that affect motor units in brain or spinal cord

Answer 8

amyotrophic lateral sclerosis or polio

Question 9

what are slow muscles adapted for

Answer 9

slow, sustained, tonic,

fatigue-resistant contractions e.g. postural muscles

Question 10

fast muscles are adapted for

Answer 10

rapid, intense, phasic,

easily fatigued contractions e.g. gastrocnemius

Question 11

muscle fibres are characterised based on

Answer 11

speed of contraction and ATP production

Question 12

3 types of muscle fibres

Answer 12

– Type I: Slow-oxidative (small diameter)
– Type IIa: Fast-oxidative (intermediate diameter)
– Type IIb: Fast-glycolytic (large diameter)

Question 13

fast muscle ATP production

Answer 13

= higher Myosin ATPase activity

Question 14

oxidative

Answer 14

ATP produced by oxidative phosphorylation (Red Fibres)

– Much more efficient than glycolysis – more resistant to fatigue

Question 15

glycolytic

Answer 15

generate ATP via anaerobic glycolysis (White Fibres)

– Inefficient method which also produces lactic acid

Question 16

fast twitch speed

Answer 16

15-40 ms

Question 17

slow twitch speed

Answer 17

50-100 ms

Question 18

difference between cells and muscles

Answer 18

individual cells are either fast or slow
whole muscles have fast AND slow cells
whole muscle is seen as fast or slow depending on the majority of fast or slow cells

Question 19

size of motor neurons in slow fibres in comparison to fast fibres

Answer 19

motor neurons in slow fibres are smaller than fast fibres

Question 20

when will small cell bodies be recruited

Answer 20

Their cell bodies are more excitable and are the first

to be recruited during moderate contractions.

Question 21

when will fast cell bodies be recruited

Answer 21

during more intense contractions

Question 22

does training have an effect on fast and slow fibre numbers

Answer 22

Training has little effect on fast and slow fibre numbers
• Training regimens cannot alter fiber type or the
expression of myosin isoforms.
• Elite sprinters have high numbers of fast fibres

Question 23

training can

Answer 23

Improve oxidative capacity (more resistant to fatigue)
• Increase blood supply/number of mitochondria
– Change muscle fibre diameter - hypertrophy - in short high intensity anaerobic exercise

Question 24

atrophy

Answer 24

Muscle decreases in mass if not routinely used

Question 25

lesion of motor nerves in skeletal muscle causes

Answer 25

A lesion of the motor nerves to skeletal muscle (lower motor neuron lesion) causes flaccid paralysis

Question 26

Fasciculations

Answer 26

Visible twitching caused by release of Ach from

degenerating motoneurons

Question 27

where does Type I and type II atrophy occur

Answer 27

peripheral neuropathies, disuse (bedrest,

spaceflight, immobilization), myasthenia gravis etc

Question 28

where does type II atrophy mainly occur

Answer 28

with Duchenne muscular dystrophy and ageing

sarcopaenia

Question 29

Type II hypertrophy occurs

Answer 29

with weight training

Question 30

psuedohypertrophy

Answer 30

in calf muscles in Duchenne muscular dystrophy (“false

enlargement,” because the muscle tissue is abnormal.)

Question 31

neuropathy

Answer 31

(disease affecting nerves) in the central or

peripheral nervous system or both (peripheral nerves,

Question 32

example of neuropathy

Answer 32

multiple sclerosis

Question 33

junctionopathy

Answer 33

disease affecting (Neuromuscular junctions,

Question 34

example of junctionopathy

Answer 34

myasthenia gravis

Question 35

myopathy

Answer 35

(disease affecting muscle,

Question 36

examples of myopathy

Answer 36

muscular

dystrophies