T3 L3: Physiology of skeletal muscle

Question 1

How does muscle grow?

Answer 1

By hypertrophy

There is synthesis of myofilaments, addition of sarcomeres, satellite cell activation, angiogenesis, and vascularisation

Question 2

What is the effect of endurance exercise on muscles?

Answer 2

Increased fibre diameter, blood supply, and mitochondrial content

There will be more oxidative enzymes

Fibres will become slower (transformation from IIx to IIa fibres)

Question 3

What is the effect of non-endurance exercise?

Answer 3

Conversion of IIa into IIx fibres

There is increase in IIx fibre size due to increased numbers of sarcomeres and myofilaments

Results in much larger muscle

Question 4

What is the effect of ice on muscles?

Answer 4

It reduces swelling by reducing perfusion

Good after an acute injury like a sprain, or after overuse injury

Question 5

What is the effect of heat on muscles?

Answer 5

It helps to relax and loosen muscles

Used before activities that irritate chronic injuries like strains because it increases blood flow

Question 6

What is the mechanism behind Aspirin?

Answer 6

It inhibits COX which reduces the synthesis of prostaglandins and part of the arachidonic acid

Question 7

What are the side effects of blocking prostaglandins and arachidonic acid?

Answer 7

Gastro-intestinal adverse effects

Eg. stomach bleeding, ulcers

Question 8

What are the anabolic effects of testesterone?

Answer 8

• Increases protein synthesis
• Decreases catabolism
• Reduces fat (increases BMR and increases differentiation to muscles rather than fat cells)

Question 9

What is catabolism?

Answer 9

Breaking down of large molecules

Question 10

What is BMR?

Answer 10

Basal metabolic rate

Question 11

What are the effects of anabolic steroid abuse?

Answer 11

They’re used to increase muscle size and strength.

Large doses are needed

Male- testicular atrophy, sterility, baldness
Female- breast/uterus atrophy, menstrual changes, facial hair, deepening of voice

Question 12

What is the effect of bed-rest of muscles?

Answer 12

Weight-bearing muscles atrophy

• Decreased muscle protein synthesis
• Myofibrillar breakdown
• Reduced strength
• Loss of type I fibres

Transition of type I to type IIa

Treated by resuming minor activity early

Question 13

How does a contracture form?

Answer 13

If the limb is immobilised for a long period of time, the process of growth is reversed so sarcomeres are removed and the muscle shortens

Question 14

Why do multinucleate cells not divide?

Answer 14

Because mitosis with multiple nuclei is usually impossible

Question 15

How are muscles regenerated?

Answer 15

Satellite cells are activated which proliferate, differentiate, and fuse onto fibres and contribute to forming multinucleate myofibers

Question 16

What are the progenitor cells of muscles?

Answer 16

Satellite cells

Question 17

What is myalgia?

Answer 17

Muscle pain caused by injury, overuse, infections, or autoimmune

Question 18

What is myopathy?

Answer 18

Muscular weakness due to muscular fibre dysfunction

Question 19

What is paresis?

Answer 19

Weakness, partial loss, or impaired voluntary movements,

Question 20

What are fasciculations?

Answer 20

Involuntary large visible neurogenic twitches in single motor units
-Usually occur in lower motor neurone diseases

Question 21

What are fibrillations?

Answer 21

Small involuntary myogenic spontaneous contractions of individual muscle fibres

Can be identified by electromyography

Question 22

What is rhabdomyolysis?

Answer 22

Rapid breakdown of skeletal muscle

Causes: trauma, drugs, hyperthermia, ischaemia to skeletal muscle

Symptoms: muscular pain, vomiting, confusion, dark urine

Question 23

What is the treatment for Rhabdomyolysis?

Answer 23

Intravenous fluid to treat shock and haemodialysis to clear the blood

Question 24

How is Rhabdomyolysis diagnosed?

Answer 24

Urine will be very dark and will be tested for myoglobin

Hyperkalaemia is tested for because when muscle cells lyse, they release K+

Question 25

What is myasthenia gravis?

Answer 25

Progressive muscle weakness and fatigability

Caused by a depletion of nicotinic ACh receptors because of autoimmune destruction of the receptors

Question 26

What are some initial symptoms of myasthenia gravis?

Answer 26

Ptosis and diplopia because those muscles are so weakened

Question 27

What is the treatment for myasthenia gravis?

Answer 27

-AChE inhibitors
Eg. Pyridostigmine increases ACh activity at the NMJ
Eg. Edrophonium is used for diagnosis because it should temporarily improve symptoms

• Thymectomy reduces 70% of symptoms
• Immunosuppressive drugs
• Plasmapheresis: removal of anti-AChR antibodies from the blood

Question 28

What is Spinal muscular atrophy (SMA)?

Answer 28

AKA floppy baby syndrome

It’s caused by the death of lower motor neurones in the anterior horn of the spine

Aetiology: autosomal recessive gene

Question 29

What is meant by fibre type grouping?

Answer 29

Different types of muscle fibres grouped together

Question 30

What is malignant hyperthermia?

Answer 30

A rare genetic susceptibility to gas anaesthetics causing SERCA to work too hard

Symptoms: increased O2 consumption, CO2, acidosis, tachypnea, muscles overheat, the body overheats, muscles are damaged (rhabdomyolosys), hyperkalaemia, muscles become rigid

Question 31

What is the treatment for malignant hyperthermia?

Answer 31

Dantrolene sodium will stop the abnormal calcium release by inhibiting the ryanodine receptor

Question 32

What is Gower’s sign?

Answer 32

A sign of muscular dystrophy where the patient is too weak to stand up so has to use their hands

Question 33

What is duchenne muscular dustrophy?

Answer 33

An X-linked disease caused by a mutation on the dystrophin protein