Structure and mechanics of skeletal muscle Flashcards
What is fasciculation?
The normal random twitch of fascicles. Excessive in motor neurone disease.
What are agonists?
The prime movers, the main muscle responsible for a particular movement eg biceps brachii
What are antagonists?
They oppose prime movers to allow smooth movement, eg triceps
What are synergists?
They assist prime movers to neutralise any extra movement and keep the movement in one direction, eg brachialis
What are fixators?
They stabilise the action of the prime mover by fixing non-moving joints
What is isotonic contraction?
Muscle has constant tension, changes length to move the load eg biceps
What are the two types of isotonic contraction?
Concentric- muscle shortens to exert force eg biceps when lifting a load with the arm
Eccentric- muscle extends to exert force eg walking downhill
What is isometric contraction?
Muscle is constant length, variable tension eg hand grip when carrying a large suitcase.
Describe Type I muscle fibres
Slow twitch Red in colour (high mitochondria) Aerobic resp High myoglobin Rich capillary supply Fatigue resistant Endurance activities eg posture
Describe Type IIa muscle fibres
Grey/pink colour Aerobic resp High myoglobin Rich capillary supply Some fatigue resistance Walking, sprinting
Describe Type IIb muscle fibres
White colour (low mitochondria) Anaerobic glycolysis Low myoglobin Poorer capillary supply Rapidly fatigued Short, intense movements eg weight lifting
What is proprioception?
Feedback control of movement.
Proprioreceptors are muscle spindles = specialised fibres that feedback to brain how much tension and stretch there is in the muscle, which allows the brain to know the limb position.
What is a motor unit?
A motor neurone and the muscle fibres it innervates. (Can be 3-3000 muscle fibres)
What is crosstalk?
Communication between neurones and muscles via signalling molecules, ie atrophy of the nerve leads to atrophy of muscle and vice versa.
Communication is via neurotrophins, cytokines and insulin-like growth factors
How is muscle tone controlled?
By motor control centres in the brain via afferent fibre signals from the muscle.
Baseline tone is present in muscle at rest due to motor neurone activity and muscle elasticity.
What is hypotonia and what can it be due to?
Low muscle tone due to:
Cerebral or spinal neural shock, lesions of the cerebellum/spinal cord.
Lesion of sensory or lower motor neurones (eg polyneuristis)
Primary degeneration of the muscle (myopathies)
How do muscle relaxants work?
Inhibit acetylcholinesterase so high ACh level us maintained. Increased initial contraction, but then the sites become blocked and muscle relaxes.
What is spatial summation?
More motor neurones activated so more muscle fibres are recruited to develop more force.
Controlled by feedback pathway
What is temporal summation?
Increased frequency of action potentials to muscle fibres.
1 AP leads to a twitch
Infused tetanus needed for continuous muscle force.
What are the functions of skeletal muscle?
Movement
Stability of joints
Posture
Heat generation
How is electromyography used to diagnose motor neurone disease?
Electrodes are placed above/in muscles to record electrical activity.
Usually when more force is applied more motor units are recruited but this does not occur in individuals with MND
What are the 4 sources of ATP for muscles?
- Short term stores of ATP in the muscle fibre
- Creative phosphate
- Glycolysis
- Oxidative phosphorylation
What is peripheral fatigue?
Depletion of muscle glycogen stores, occurs in 1 minute if blood flow interrupted
What is intermittent claudication?
Intermittent muscle pain, goes away in rest. Caused by reduced blood flow to a muscle eg. due to atherosclerosis
What is a muscle contracture?
A state of continuous contraction when ATP is depleted, as the myosin heads are unable to detach from the actin filaments.
