Alteration In Skeletal Muscle Function

Question 1

Replacement of muscle

Answer 1

Is a continual process
- contractile protein replaced every two weeks
ATROPHY
- destruction > replacement (muscle wastes away)
HYPERTROPHY
- replacement > destruction (muscle increases in cell size)

Question 2

Skeletal muscle and exercise

Answer 2

• metabolic adaption
• sarcoplasmic reticulum swells
• increased volume of mitochondria
• increased Z band width
• increased ATPase
• increased density of T tubules systems
• increased number of contractile proteins
• little evidence of hyperplasia

Question 3

Function

Answer 3

• movement
• posture
• joint stability
• heat generation

Question 4

Exercise

Answer 4

High Resistance e.g. weightlifting
- stimulates contractile protein synthesis (actin and myosin) leads to fatter muscle fibres and larger muscles
- increases muscle mass and strength - may lead to hypertrophy of myosatellite cells
Endurance e.g. jogging
- increased endurance without hypertrophy
- stimulates synthesis of mitochondrial proteins, vascular changes allow for greater oxygen utilisation
- shift to oxidative metabolism (e.g. of lipids)

Question 5

Atrophy

Answer 5

Disuse atrophy
- due to bed rest, limb mobilisation, sedentary behaviour, etc.
- loss of protein –> reduced fibre diameter –> loss of power
Atrophy with age
- +30 years muscle mass begins to decrease
- by 80 years 50% of muscle mass lost - sarcopenia
- can lead to hypothermia due to inadequate temperature regulation
Denervation (neurogenic muscular) atrophy
- signs of lower motor neutron lesions, weakness, flaccidity, muscle atrophy
- re-innervation within 3 months of recovery (after this time there is an increased risk of paralysis)

Question 6

Adjustment of muscle length

Answer 6

• increases by sustained stretching
• addition of sarcomeres, changes in neurology and viscoelastic properties
• reduced length of muscle if immobilised (e.g. limb in plaster)

Question 7

Neuromuscular junction disorders

Answer 7

• autoimmune destruction of the end-plate of ACh receptors
• loss of junctional folds of end-plate
• widening of synaptic cleft
  Less acetyl CoA receptors, less surface area and a larger diffusion distance over the synaptic cleft

Question 8

Myasthenia Gravis

Answer 8

SYMPTOMS
Fatiguability and sudden falling
- due to reduced ACh release
Primary signs
- ptosis (dropping upper eyelid), double vision because eyes don’t move in synchronisation
Effected by General state of health, fatigue and emotion, symptoms fluctuate
TREATMENT
- acetylcholinesterase inhibitors - keeps ACh in the synaptic cleft got longer to sustain muscle contraction for longer
- immune suppressants
- plasmapheresis - washes the blood
- thymectomy

Question 9

Muscular Dystrophies

Answer 9

• genetic disorders that lead to progressive muscle weakness and wasting
  Duchenne-Type and Becker-Type are the most severe

Question 10

Muscle fibre damage in Duchenne Muscular Dystrophy

DMD

Answer 10

Consequence of protein abnormality
- muscle fibres tear themselves apart on contraction
- creatine phosphokinase is liberated into the serum
- calcium enters the cell causing cell death (necrosis)
- pseudohypertrophy (swelling) before fat and connective tissue replaces muscle fibres
Early onset
Gower’s sign (arms used to push and extend legs)
Contractures - imbalance between agonist and antagonist muscles
- steroid therapy (prednisolone)
Genetic research - gene therapy, stem cells, etc.

Question 11

Skeletal muscle disorders

Answer 11

MYOPATHIES (primary muscle disease) 
- muscular dystrophies 
- inflammatory myopathies
- myopathies secondary to systemic disease 
DENERVATION 
- neurological causes 

Inflammatory e.g. Influenza
Electrolyte imbalance e.g. Hypokalaemia - low potassium
Thyrotoxicosis e.g. increased BMR
Hypothyroidism e.g. Hypocalcaemia causing tetany (muscle spasms)
Channelopathies e.g. Malignant hyperthermia - high temperature can be fatal

Question 12

Origins of skeletal muscle problems

Answer 12

• neurological
• metabolic
• immunological
• neuromuscular junction
• muscle tissue