Muscle structure and function Flashcards
What can muscle structures be influenced by? (4)
Resistance training
Age
Chronic or acute muscle wasting
Rehab
What are the 7 muscle functions?
- Protein synthesis
- Carbohydrate oxidation
- Mitochondrial function
- Lipid oxidation
- Strength loss and increased fatigue
- Protein digestion
- Muscle lactate production
What is skeletal muscle surrounded by?
Epimysium
What is within skeletal muscle?
Fascicles (encapsulated by perimysium)
What are the layers of skeletal muscle outwards in: (7)
Skeletal muscle Epimysium Perimysium - gives the striated look Fascicles Endomysium Muscle fibre Myofibril
What is the structure of a muscle fibre? (7)
Endomysium Sarcolemma Nucleus Striations Sarcoplasm Myofibrils Filaments
What are the 2 types of filaments?
Actin and myosin
What is a motor unit?
A motor neuron plus the muscle fibres it innervates
Within a muscle fibre what can you see and what are their functions? (6)
Sarcoplasmic reticulum - calcium ion store
Mitochondrion
T tubule - quick, effective and even depolarisation
Sarcolemma - spread the potential quickly
Thick myofilament (myosin)
Thin myofilamnet (actin)
What is the structure of the filaments?
- Thin filament - actin(blue)
- Thick filament - myosin (red)
- Z disc - connects each myofibril, stability, titin nebulin
- I band - light actin tropomyosin and troponin extend partially into the A band
- A band contains myosin, fully contained
- H zone is only thick filaments
What is the sarcomere boundary?
I band to I band
Under a microscope what can you see in a muscle?
I-band (light zone)
A-band (dark zone)
H-zone (middle of the a band)
M-line (middle of the H-zone)
What type of head does myosin have?
Globular
What is the process of neuromuscular transmission? (4)
Synaptic vesicles containing ACh are released in axon terminal
Fusion with synaptic membrane
ACh diffuses across synaptic cleft
Bind to receptors on the sarcolemmas fibre
What is special about the sarcolemma?
Many folds to increase surface area
Where are action potentials sent down once inv the muscle fibre and what causes tension
T tubules
Calcium causes tension (released from sarcoplasmic reticulum
What causes depolarisation of the T tubules?
ACh
What releases calcium?
Sarcoplasmic reticulum
What happens once calcium is released? (3)
Attaches to troponin
Troponin causes tropomyosin to shift
Causes the actin active site to be revealed
Describe the action of a myosin head? (4)
- Attaches to the actin myofilament - causing a cross bridge
- Inorganic phosphate is released, initiating the power stroke, myosin head pivots and pulls on the actin towards the M line, ADP released
- Cross bridge detaches and new ATP attaches to myosin head
- ATP is split to ADP + P and myosin head is energised
What muscle motor units are recruited first and last?
Muscles recruit slow motor units first (small) then recruit fast motor units
When are sarcomeres bunched up and the shortest?
When the muscle is relaxed and at its shortest
What is and what are the pros and cons of isotonic contraction?
Pulling towards you (curling)
Pros: Constant muscle tension
Cons: Cant be done anywhere, speed will vary
What is and what are the pros and cons of isokinetic contraction?
Movement through a range of motion at a fixed velocity
Pros: Force velocity relationship is controlled for complete muscle fibre recruitment
Cons: Specialist equipment required
