MS2: Skeletal Muscle Flashcards
How can muscles be arranged? 7 ways?
Convergent Circular Fusiform Unipennate Bipennate Multipennate Parallel
Four functions of skeletal muscle
Movement
Posture
Stability of joints
Heat generation (80 % energy lost as heat)
DeScribe the histologial appearance of skeletal muscle
Muscle fibre (nuclei) made of myofibrils surrounded by endomysium.
In bundles (fascicles) wrapped by perimysium
Fascicles and blood vessels are all contained within the muscle wrapped by epimysium
Ends peri Epi
Describe the structure and organisation of skeletal muscle
Under voluntary control
Striated muscle
Multiple peripheral nuclei
Can look like adipose tissue but not so white
Explain the mechanism of contraction of skeletal muscles (9 steps)
Action potential travel towards the NMJ
Stimulates calcium influx
Neurotransmitter released (AcH) an binds to nicotinic receptors (ligand gated Na channels)
Depolarisation of sarcoplasmic reticulum membrane (Na influx)
Travels down T tubules causing voltage gated calcium channels to open - floods sarcoplasmic reticulum
Calcium binds to troponin, displacing tropomyosin and exposing myosin binding site
Myosin (bound to ATP) is hydrolysed releasing ADP Pi and binds to exposed side: cross link
Pulls actin towards the M line
Remains attached until more ATP binds and displaces it.
Define a motor unit
A motor unit is a motor neurone and the muscle fibres it innervates,
1 can innervates 1-3000 fibres! Fine to crude control
Describe muscle tone and its relation to hypertonia and hypotonia
There is baseline tone at rest due to motor neurone activity and muscle elasticity
Tone is controlled by:
-motor control centres e.g, brain and CNS
-afferent signals from muscle e.g sensory fibres
Hypotonia caused by:
Lesions in cerebellum (neural shock), sensory afferent fibres, motor neurones, or from degeneration of muscle (myopathies)
Explain the mechanism of contraction of skeletal muscles
Each muscle fibre is innervates by motor neurones at the neuro muscular junctions.
They are stimulated by excitation of the neurone, which excites the myofibrils (excitation contraction coupling)
The myofibril undergoes tension due to the cross bridge cycle and shortens the fibre
Collective shortening of the group of myofibrils causes contraction of the muscles and therefore a movement,
Describe simply the physiological mechanisms which underlie variation in the force of contraction of a muscle
Movement is controlled by proprioception
Feedback control using muscle spindles (proprioceptiors) located in the muscle belly: monitor muscle force and stretch and help muscle memory.
Contraction is all or none. Need many neurones to be stimulated at the same time for an effect (spatial summation). More neurones activated = more force of contraction
Or increase frequency of the contraction (temporal summation) increases frequency of AP to fibres,
How do cells communicate between nerve and muscle
Signalling molecules Neurotrophin NT3 Cytokines (cardiotrophin) Insulin like growth factors (GF) Stroppy of the nerve or muscle caused atrophy of the corresponding nerve or muscle
Differentiate the sources of energy for muscle contraction and relate these to muscular fatigue
ATP is needed to detach the myosin head
Stores
- short term ATP stores in fibres
Creatine phosphate (kinase released - marker)
Glycolysis
Oxidative phosphorylation
(Anaerobic glycolysis- pyruv to lactate - cramps)
Muscle fatigue occurs when depletion of muscle glycogen.
If blood flow disrupted, pain in 1 min: intermittent claudication
Differentiate the sources of energy for muscle contraction and relate these to muscle fibre type and types of muscle contraction
Isotonic: constant tension
- concentric (force when muscle shortens)
- eccentric (exerts force when extended)- e.g walking downhill
Isometric: hand grip, muscle same length but varies tension. Increases BP
Different types of muscle fibres
Type 1, red, high myoglobin and mitochondria
Slow oxidative
Aerobic, Endurance and posture
Type 2a: fast oxidative
Red/pink, Mitochondria, good blood,
Walking and sprinting
Type 2b: fast glycolytic
Anaerobic glycolsis
Pale: poor capillary, low myoglobin, few mitochondria, tire easily
Short intense movement
Describe the biomechanics of muscle movement
Levers: three classes
1: head and neck
2: pivot eg wheelbarrow-
3: fishing rod type- most muscles
Agonists, antagonists, synergistic, fixation
