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Questions and Answers
What initiates the release of calcium ions (Ca2+) from the sarcoplasmic reticulum during muscle contraction?
What initiates the release of calcium ions (Ca2+) from the sarcoplasmic reticulum during muscle contraction?
What event occurs at the sarcolemma when acetylcholine (ACh) binds with its receptors?
What event occurs at the sarcolemma when acetylcholine (ACh) binds with its receptors?
In the process of cross-bridge cycling, what binds to the myosin heads to allow them to detach from the actin filaments?
In the process of cross-bridge cycling, what binds to the myosin heads to allow them to detach from the actin filaments?
What is the role of calcium ions (Ca2+) in the excitation-contraction coupling process?
What is the role of calcium ions (Ca2+) in the excitation-contraction coupling process?
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Which of the following describes the function of the neuromuscular junction?
Which of the following describes the function of the neuromuscular junction?
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What are the two main components of thick filaments?
What are the two main components of thick filaments?
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What structural feature allows myosin heads to bind during muscle contraction?
What structural feature allows myosin heads to bind during muscle contraction?
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How do T tubules contribute to muscle contraction?
How do T tubules contribute to muscle contraction?
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In which process do myosin heads repeatedly bind and detach during contraction?
In which process do myosin heads repeatedly bind and detach during contraction?
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Which component of the sarcoplasmic reticulum is crucial for regulating calcium levels during muscle contraction?
Which component of the sarcoplasmic reticulum is crucial for regulating calcium levels during muscle contraction?
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How does the sliding filament model describe muscle contraction?
How does the sliding filament model describe muscle contraction?
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What role does ATP play in muscle contraction?
What role does ATP play in muscle contraction?
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What is the primary role of tropomyosin in muscle contraction?
What is the primary role of tropomyosin in muscle contraction?
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What initiates the process of muscular contraction?
What initiates the process of muscular contraction?
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During the power stroke phase of cross bridge cycling, what happens?
During the power stroke phase of cross bridge cycling, what happens?
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What is the role of ATP in muscle contraction?
What is the role of ATP in muscle contraction?
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What occurs when Ca2+ binds to troponin?
What occurs when Ca2+ binds to troponin?
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Which statement accurately describes excitation-contraction coupling?
Which statement accurately describes excitation-contraction coupling?
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What happens to tropomyosin during muscle contraction?
What happens to tropomyosin during muscle contraction?
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How does the myosin head return to a high-energy state?
How does the myosin head return to a high-energy state?
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What is the correct sequence of events in cross bridge cycling?
What is the correct sequence of events in cross bridge cycling?
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Study Notes
Muscular System: Lecture 1 & 2
- The muscular system is covered in lectures 1 & 2 of MEDI101/HSF-1.
- The lectures were given by Hassaan A. Rathore, PhD, Associate Professor in the College of Pharmacy at Qatar University.
- The syllabus indicates 2 lectures and 1 lab (3 hours) for week 8 (October 13-17, 2024) and 2 lectures and 1 lab (3 hours) for week 9 (October 20-24, 2024).
- Lab 5 covers the appendicular skeleton in week 8
- Lab 6, SCL-2 (OSPE practice), is in week 9
- Expected learning outcomes include defining the roles of endomysium, perimysium, and epimysium.
- Describing the sliding filament model of muscle contraction.
- Explaining the neuromuscular junction.
- Distinguishing graded responses of muscle contraction.
- Muscles form the main tissue in the heart, blood vessels and walls of hollow organs.
- Muscles make up almost half of the body's mass.
- Skeletal and smooth muscle cells are elongated and called muscle fibers.
- Muscle contraction relies on two types of myofilaments: actin and myosin.
Muscle Terminology
- Sarcolemma - muscle plasma membrane
- Sarcoplasm - cytoplasm of a muscle cell
- Prefixes myo, mys, and sarco all relate to muscle.
Types of Muscles
- Three types of muscle tissue: skeletal, cardiac, and smooth
- These tissue types differ in structure, location, function, and method of activation.
Functions of Muscles
- Movement: Skeletal muscles move the skeleton (locomotion). Smooth muscles move fluids and substances through hollow organs (digestion, veins). Cardiac muscles propel blood through the body.
- Maintenance of body posture and position: Muscles enable sitting and standing.
- Joint stabilization: Muscle tendons, such as those around the shoulder, provide joint stability.
- Heat generation: Muscle contractions produce heat which helps maintain normal body temperature.
Functional Characteristics of Muscle Tissue
- Excitability/Irritability: Ability to receive and respond to stimuli.
- Contractility: Ability to shorten forcibly.
- Extensibility: Ability to be stretched or extended.
- Elasticity: Ability to recoil and return to its original resting length.
Types of Muscles (Detailed)
- Skeletal muscle tissue: Packaged into skeletal muscles, makes up 40% of body weight. Skeletal muscle cells are striated, multinucleated (at periphery), and voluntary.
- Cardiac muscle tissue: Found in the heart walls. Cardiac muscle cells are striated, uni-nucleated, and branching with intercalated discs. They are involuntary.
- Smooth muscle tissue: Occupies hollow organs and lacks striations (non-striated). Cells are uni-nucleated and this tissue is involuntary.
Basic Features of Skeletal Muscles
- Most skeletal muscles run from one bone to another.
- One bone moves, the other remains fixed.
- Origin: The fixed end of the muscle.
- Insertion: The movable end of the muscle.
- Muscles attach to origin and insertion by connective tissue.
- Indirect attachments use tendons (connective tissue).
- Bone markings (tubercles, trochanters, tuberosities, crests) are where tendons meet bones.
Skeletal Muscle Function
- Force production used for locomotion and breathing (diaphragm).
- Force production used for postural support.
- Heat production during cold stress.
Skeletal Muscle Fiber & Connective Tissue
- The structure and organization of connective tissue, including tendons and fascicles, within skeletal muscle.
Skeletal Muscle Micro-Anatomy
- Endomysium, Perimysium, and Epimysium: The connective tissue coverings surrounding individual muscle fibers, fascicles, and the whole muscle, respectively.
Myofibrils
- Myofibrils are rod-like contractile elements that are densely packed within muscle fibers.
- A perfectly aligned series of dark A bands and light I bands is evident in their arrangement.
Sarcomere
- The smallest contractile unit of a muscle fiber (cell) located between two successive Z discs.
- Composed of myofilaments (thick and thin) made up of contractile proteins.
Myofilaments – Thick Filaments
- Composed primarily of myosin protein.
- Each myosin molecule consists of a rod-like tail and two globular heads.
- Tails are interwoven.
- Heads are called cross bridges.
Myofilaments – Thin Filaments
- Composed mainly of actin protein.
- Each actin molecule is a helical polymer of G-actin subunits.
- Actin subunits have active binding sites, where myosin heads attach during muscle contraction.
- Tropomyosin & troponin are regulatory subunits bound to actin.
Sarcoplasmic Reticulum
- An elaborate, smooth endoplasmic reticulum surrounding each myofibril.
- Paired terminal cisternae create perpendicular cross channels.
- Functions in regulating intracellular calcium levels.
- Elongated T tubules penetrate into the cell at the A-I band junction, and form triads with terminal cisternae.
T Tubules
- Continuous with the sarcolemma.
- Conduct impulses to the deepest regions of the muscle.
- Trigger Ca2+ release from terminal cisternae.
- T tubules and SR provide tightly linked signals for muscle contraction.
- T tubule proteins are voltage sensors.
- SR foot proteins regulate Ca2+ release from SR cisternae.
Sliding Filament Model
- Actin filaments slide past thick myosin filaments, causing actin and myosin filaments overlapping a greater degree.
- This overlap occurs more in a contracted state compared to a relaxed state.
- Myosin heads bind to actin during stimulation.
Sequential Events of Contraction
- Cross-bridge formation: Myosin cross-bridge attaches to actin filament.
- Working (power) stroke: Myosin head pivots and actin filament pulled toward M line.
- Cross-bridge detachment: ATP attaches to myosin head and the cross-bridge detaches.
- "Cocking" of the myosin head: Energy from ATP hydrolysis cocks myosin head into a high-energy state.
Excitation-Contraction Coupling
- Communication between electrical events and mechanical muscle events in response to stimulus.
- Action potentials propagate along the sarcolemma, then down the T tubules which triggers Ca2+ release from terminal cisternae.
- Ca2+ binds to troponin which causes the blocking action of tropomyosin to cease and actin active binding sites to be exposed.
- Myosin cross bridges alternately attach and detach.
- Thin filaments move toward the center of the sarcomere through ATP hydrolysis.
- Ca2+ is removed into the SR, tropomyosin blockage is restored, and the muscle fiber relaxes.
Neuromuscular Junction
- Junction between the motor nerve and skeletal muscle fiber
- Action potentials in the sarcolemma lead to the release of acetylcholine (ACh) into the synaptic cleft.
- ACh binds to its receptors, initiating an action potential.
Role of Acetylcholine (ACh)
- ACh binds to its receptors at the motor end plate (on sarcolemma).
- Binding opens chemically (ligand)-gated channels.
- Na+ diffuses inwards and interior of the sarcolemma. This is called depolarization.
Depolarization Spread
- Initially, a local electrical event called end-plate potential.
- Later, it starts an action potential, spreading in all directions across the sarcolemma.
Graded Responses
- Twitch, Summing of contractions (incomplete), and Fused tetanus (complete) responses of a whole muscle to different stimulus.
- Muscle response is graded to meet the needs of the body.
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Description
This quiz covers key concepts from Lectures 1 & 2 of the Muscular System in MEDI101/HSF-1, led by Dr. Hassaan A. Rathore. Students will explore topics such as the roles of various connective tissues, the sliding filament model, and the structure of muscle fibers. Prepare to test your understanding of muscle contraction and the neuromuscular junction!
