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Questions and Answers
What occurs during the relaxation phase of a twitch contraction?
What occurs during the relaxation phase of a twitch contraction?
Which type of muscle contraction does not produce any work?
Which type of muscle contraction does not produce any work?
Which contraction type is characterized by the muscle generating force while lengthening?
Which contraction type is characterized by the muscle generating force while lengthening?
What is primarily responsible for tension or force generation in muscle fibers?
What is primarily responsible for tension or force generation in muscle fibers?
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In Henneman’s size principle, which type of motor unit is recruited first?
In Henneman’s size principle, which type of motor unit is recruited first?
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Which method is NOT used for assessing muscle strength?
Which method is NOT used for assessing muscle strength?
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What is the primary consequence when all troponin bind with calcium ions?
What is the primary consequence when all troponin bind with calcium ions?
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How does a twitch contraction differ from tetanus?
How does a twitch contraction differ from tetanus?
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What triggers the release of calcium ions during excitation-contraction coupling?
What triggers the release of calcium ions during excitation-contraction coupling?
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What is the correct order of events in the crossbridge cycle?
What is the correct order of events in the crossbridge cycle?
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What role do troponin and tropomyosin play in muscle contraction?
What role do troponin and tropomyosin play in muscle contraction?
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Which structure in muscle fibers facilitates the propagation of action potentials?
Which structure in muscle fibers facilitates the propagation of action potentials?
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Which component of muscle tissue is responsible for the striated appearance in skeletal muscle?
Which component of muscle tissue is responsible for the striated appearance in skeletal muscle?
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What happens to the I-band during muscle contraction?
What happens to the I-band during muscle contraction?
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What is the function of the neuromuscular junction?
What is the function of the neuromuscular junction?
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Which type of filament is primarily responsible for muscle contraction?
Which type of filament is primarily responsible for muscle contraction?
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Study Notes
Applied Sciences - Muscle Physiology Part 1
- Course code: PT4050 and PT7001
- Lecturer: Chris Chamberlin and Dr Ben Hunter
- Email: [email protected]
Learning Outcomes
- Neuromuscular junction
- Muscle structure
- Contraction types
- Cross-bridge formation
- Motor units
Structure
- Sarcolemma: The plasma membrane of a muscle cell
- Sarcoplasm: The cytoplasm of a muscle cell
- Myofibrils: Contractile proteins within muscle cells
- Mitochondria: Cellular energy producers
- Sarcoplasmic reticulum: Smooth ER, stores and releases calcium
- Transverse tubule (T tubule): Network that carries action potentials
Neuromuscular Junction (NMJ)
- Action potential travels down a motor neuron axon terminal
- Calcium channels open, releasing acetylcholine (ACh)
- ACh binds to receptors on the motor end plate
- Ligand-gated sodium channels open
- Action potential generated, following “all-or-nothing” principle
- Action potential propagates along sarcolemma
Excitation-Contraction Coupling
- ACh released at NMJ, receptor, AP
- Action potential down T tubules
- AP triggers Ca²⁺ release from Sarcoplasmic Reticulum (SR)
- Ca²⁺ binds to troponin, exposing myosin-binding sites
- Cross-bridge cycling occurs
- Ca²⁺ re-uptake actively
- Myosin binding sites blocked
Striations
- Skeletal muscles exhibit striations when viewed longitudinally.
- Highly organized intracellular structures called myofibrils are responsible for striations.
Muscle Structure - Levels of Organisation
- Epimysium: Surrounds the entire muscle.
- Perimysium: Surrounds fascicles (bundles of muscle fibers).
- Endomysium: Surrounds individual muscle fibers.
Structure of a Myofibril / Sarcomere
- Myofibril: Elongated protein structures within muscle fibers.
- Sarcomere: The basic contractile unit of a myofibril; it's the region between two Z lines
- Z lines: Define the borders of a sarcomere.
- M lines: Located in the center of the sarcomere.
- A band: Contains the entire length of the thick filaments.
- I band: Contains only thin filaments.
- H zone: Center of a sarcomere, and only thick filaments.
- Thin filaments: Primarily made of actin.
- Thick filaments: Primarily made of myosin.
- Cross-bridges: Myosin heads that extend and interact with actin.
Myofilaments
- Actin: A contractile protein.
- Troponin: A regulatory protein.
- Tropomyosin: A regulatory protein
Myosin
- Myosin molecules have heads and tails.
- Two myosin molecules bound at their tails—forming cross-bridges
The Crossbridge Cycle
- Binding of myosin to actin
- Power stroke (low energy state)
- Rigor (low energy state) Unbinding of myosin and actin
- Cocking of myosin head (high energy state)
Sliding Filaments
- Myosin/actin filaments do not shorten
- A-band remains the same length
- I-band shortens
- H-band shortens
Length-Tension Relationship
- Optimal length for maximum force generation.
- Relevance in physiotherapy
Twitch Contraction
- Contraction produced in response to a single action potential
- All or nothing for a given muscle fibre
- Latency: time delay between stimulation (nerve AP or direct electrical) – E-C coupling
- Contraction phase - cross-bridge cycling
- Relaxation phase - Ca²⁺ uptake
Types of Muscle Contraction
- Isometric: Muscle does not shorten, load > tension
- Isotonic: Constant force, work is done, load < tension. Types: concentric (muscle shortens), eccentric (muscle lengthens)
Frequency and Summation
- Action potential: 2 ms.
- Muscle contraction: 10-200 ms. The tension force depends on [Ca²⁺]
- When the system is saturated, tetanus (long lasting contraction): freq. of stim.↑, Ca²⁺ release > uptake, [Ca²⁺] ↑
Motor Unit
- One motor neuron innervates many fibres.
- One fibre innervated by only one neuron.
- Same type of fibres within the motor unit.
- All the muscle fibres in a motor unit will simultaneously contract when it "fires".
Recruitment
- MU recruitment occurs in a specific order according to Henneman's size principle.
- Smallest MUs recruited first (type I), largest MUs recruited last (type II).
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Description
This quiz focuses on the fundamentals of muscle physiology, covering key concepts such as the neuromuscular junction, muscle structure, and types of contractions. It also delves into the components of muscle cells, including sarcolemma, myofibrils, and mitochondria. Test your knowledge on these essential topics!
