fast and slow muscles & muscle disorders

Question 1

what is a motor unit?

Answer 1

consists of a motor neuron and all of the muscle fibres that it innervates

Question 2

what kind of muscles have large vs small motor units?

Answer 2

• postural muscles - large MU
• muscles requiring precise control - extraocular and hand muscles

Question 3

by what 2 ways can the force of muscle contraction be increased?

Answer 3

1. recruitment - activating more MU’s
2. increasing stimulus freq to cause summation or tetanus

Question 4

how can the electrical activity be recorded on skeletal muscle?

Answer 4

by electromyography

Question 5

what kind of muscle disorder and pathologies can be diagnosed or ruled out by an electromyography?

Answer 5

• muscular dystrophy - muscle disorder - hereditary condition
• myasthenia gravis - autoimmune disorder - decreasing no of Ach receptors
• amyotrophic lateral sclerosis/ motor neuron disease

Question 6

why would a clinician order an electromyography?

Answer 6

to detect a nerve or muscle disorder

Question 7

what are slow muscles adapted for?

Answer 7

slow sustained and fatigue resistant contractions
eg postural muscles

Question 8

what are fast muscles adapted for?

Answer 8

• rapid, intense and easily fatigued contractions
• eg gastrocnemius muscle

Question 9

what 2 things are the 3 types of muscle fibres characterised on?

Answer 9

• speed of contraction
• ATP production

Question 10

what are the 3 types of muscle fibres?

Answer 10

• Type I - slow oxidative
• Type IIA- fast oxidative
• Fast IIb- fast - glycolytic

Question 11

do the fast or slow muscle fibres have a higher myosin ATPase?

Answer 11

• fast muscle fibres

Question 12

by what method do type iib fibres generate atp?

Answer 12

by anaerobic glycolysis

Question 13

why are slow muscles red?

Answer 13

• mitochondria
• myoglobin
• high level of vascularity

Question 14

why are fast muscles white?

Answer 14

due to lack of mitochondria, myoglobin and vascularity

Question 15

what is the function of myosin ATPase?

Answer 15

• catalyses the reaction that breaks down ATP into ADP and phosphate
• ie ATP hydrolysis

Question 16

do whole muscles consist of both fast and slow muscle fibres?

Answer 16

yes they consist of both slow oxidative and fast oxidative and glycolytic fibres

Question 17

what type of muscle fibres are usually recruited first?

Answer 17

slow oxidative fibres

Question 18

what can training change in a muscle fiber?

Answer 18

• can imporve oxidative capacity - ie increase number of mitochondria
• change muscle diameter - ie hypertrophy or increase in muscle size

Question 19

what is atrophy?

Answer 19

decrease in muscle mass / muscle wasting

Question 20

what can happen as a result of a lower motor neuron lesion (lesion in peripheral nerve)?

Answer 20

• flaccid paralysis
• hyporeflexia
• atrophy

Question 21

what is flaccid paralysis?

Answer 21

• neurological condition characterised by weakness or paralysis and reduced muscle tone
• may be caused by disease or trauma affecting the nerves

Question 22

what is muscle fasciculation characterised by?

Answer 22

• visible twitching caused by release of ACH from degenerating motorneurons

Question 23

what can a failure to regenerate the nerves result in?

Answer 23

type 1 and 11 fibre atrophy

Question 24

what conditions and situations lead to type I and II atrophy?

Answer 24

• peripheral neuropathies
• disuse - eg bedrest, immobilisation
• myasthenia gravis
• muscular dystrophy
• ageing - sarcopenia - age related loss of muscle

Question 25

what is a junctionopathy?

Answer 25

pathology affecting the NMJ eg myasthenia gravis

Question 26

what is myopathy?

Answer 26

disease affecting the muscle eg muscular dystrophies