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What is the main function of the T-system in muscle fibers?
What is the main function of the T-system in muscle fibers?
Slow muscle fibers have shorter twitch durations compared to fast muscle fibers.
Slow muscle fibers have shorter twitch durations compared to fast muscle fibers.
False
What initiates the process of Excitation-Contraction coupling in muscle fibers?
What initiates the process of Excitation-Contraction coupling in muscle fibers?
The release of calcium ions from the sarcoplasmic reticulum.
In isometric contraction, there is no decrease in the ______ of the muscle fiber.
In isometric contraction, there is no decrease in the ______ of the muscle fiber.
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Match the following muscle fiber types with their characteristics:
Match the following muscle fiber types with their characteristics:
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Which drug is NOT classified as having acetylcholine-like action?
Which drug is NOT classified as having acetylcholine-like action?
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Myasthenia gravis causes muscle paralysis due to excessive transmission of nerve signals to muscle fibers.
Myasthenia gravis causes muscle paralysis due to excessive transmission of nerve signals to muscle fibers.
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What happens to cardiac muscle fibers during phase 0 of the action potential?
What happens to cardiac muscle fibers during phase 0 of the action potential?
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The absolute refractory period in cardiac muscle means a normal cardiac impulse cannot re-excite an already ________ area of cardiac muscle.
The absolute refractory period in cardiac muscle means a normal cardiac impulse cannot re-excite an already ________ area of cardiac muscle.
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Match the following drugs to their actions at the neuromuscular junction:
Match the following drugs to their actions at the neuromuscular junction:
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What is the main function of gap junctions in cardiac muscle?
What is the main function of gap junctions in cardiac muscle?
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The resting membrane potential (RMP) of cardiac muscle is approximately -70 mV.
The resting membrane potential (RMP) of cardiac muscle is approximately -70 mV.
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Which channels are primarily responsible for the prolonged plateau phase in cardiac muscle action potential?
Which channels are primarily responsible for the prolonged plateau phase in cardiac muscle action potential?
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What is the primary function of dense bodies in smooth muscle?
What is the primary function of dense bodies in smooth muscle?
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The relative refractory period of smooth muscle is characterized by its ability to be easily excited by normal stimuli.
The relative refractory period of smooth muscle is characterized by its ability to be easily excited by normal stimuli.
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What is the role of calcium ions (Ca++) in smooth muscle contraction?
What is the role of calcium ions (Ca++) in smooth muscle contraction?
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Smooth muscle is primarily found in the walls of ________.
Smooth muscle is primarily found in the walls of ________.
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Match the type of smooth muscle with its characteristics:
Match the type of smooth muscle with its characteristics:
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Which of the following describes the resting membrane potential (RMP) of visceral smooth muscle?
Which of the following describes the resting membrane potential (RMP) of visceral smooth muscle?
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Troponin is present in smooth muscle tissue.
Troponin is present in smooth muscle tissue.
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What are the two main types of smooth muscle?
What are the two main types of smooth muscle?
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Muscle fibers are made up of ______ which are divided into filaments that are made up of contractile proteins.
Muscle fibers are made up of ______ which are divided into filaments that are made up of contractile proteins.
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Which of the following proteins is NOT a component of the thin filament in skeletal muscle?
Which of the following proteins is NOT a component of the thin filament in skeletal muscle?
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Skeletal muscle fibers lack anatomical and functional connections between individual muscle fibers.
Skeletal muscle fibers lack anatomical and functional connections between individual muscle fibers.
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What is the role of Troponin I in the process of muscle contraction?
What is the role of Troponin I in the process of muscle contraction?
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Match the following components of the skeletal muscle with their descriptions:
Match the following components of the skeletal muscle with their descriptions:
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The globular heads of myosin contain an actin binding site and a ______ site that hydrolyzes ATP.
The globular heads of myosin contain an actin binding site and a ______ site that hydrolyzes ATP.
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The thin filaments are made up of two chains of actin that form a double helix.
The thin filaments are made up of two chains of actin that form a double helix.
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Study Notes
Muscle Physiology
- Muscle cells, like neurons, respond to chemical, electrical, or mechanical stimuli to generate an action potential that propagates along the cell membrane.
- Unlike neurons, muscle cells possess a contractile mechanism triggered by action potentials (excitation-contraction coupling).
Types of Muscles
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Skeletal Muscle:
- Exhibits well-defined cross-striations.
- Requires nervous stimulation for contraction.
- Lacks direct connections between muscle fibers.
- Controlled voluntarily.
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Cardiac Muscle:
- Also displays cross-striations but contracts rhythmically without external stimulation due to pacemaker cells.
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Smooth Muscle:
- Lacks cross-striations.
- Actin and myosin are present but not arranged in regular arrays.
- Contains dense bodies analogous to Z-lines in skeletal and cardiac muscle.
- Troponin is absent.
- Sarcoplasmic reticulum is poorly developed.
Skeletal Muscle Structure
- Skeletal muscles are composed of muscle fibers arranged in parallel and joined to tendons.
- Each fiber is a long, cylindrical, multinucleated cell surrounded by the sarcolemma.
- Muscle fibers are made up of myofibrils further divided into filaments (actin and myosin).
- Contractile proteins in skeletal muscle include myosin II, actin, tropomyosin, and troponin.
Skeletal Muscle Morphology
- Striations: Created by the arrangement of thick (myosin) and thin (actin, tropomyosin, troponin) filaments.
- Myosin: Possesses globular heads, each with an actin-binding site and ATPase activity.
- Thin filaments: Consist of two actin chains forming a double helix. Troponin and tropomyosin regulate muscle contraction by interacting with myosin.
Troponin
- Troponin molecules are globular proteins located along tropomyosin.
- Troponin T connects troponin to tropomyosin.
- Troponin I inhibits myosin-actin interaction.
- Troponin C has calcium-binding sites, which initiate muscle contractions.
Arrangement of Contractile Proteins
- Diagram illustrating the arrangement of actin, myosin, and associated proteins within a sarcomere structure.
Sarcotubular System
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Made up of T-tubules and sarcoplasmic reticulum (SR).
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T-tubules: Transverse tubules that are continuous with the sarcolemma; crucial for rapid transmission of action potentials throughout the muscle fiber.
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SR: Stores calcium ions (Ca²⁺), crucial for muscle contraction; has terminal cisternae and T-tubules
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Action potential travels down T tubules, triggering release of Ca++ from SR.
Neuro-Muscular Junction
- Specialized synapse between a motor neuron and a skeletal muscle fiber.
Skeletal Muscle Action Potential (AP)
- Resting membrane potential (RMP) of skeletal muscle is −80 to −90 mV.
- Action potentials must penetrate myofibrils along T-tubules triggering the release of Ca++.
- Excitation-contraction coupling is the process connecting the nerve signal to muscle contraction.
General Mechanisms of Skeletal Muscle Contraction
- Action potentials travel along a motor neuron.
- Acetylcholine (ACh) is released, activating membrane channels.
- Sodium (Na⁺) ions influx initiating action potential in muscle fiber.
- Action potentials propagate along the sarcolemma and T-tubules.
- This triggers calcium (Ca²⁺) release from the sarcoplasmic reticulum (SR).
- Sliding filament theory: Myosin heads bind to actin filaments causing the sliding of actin filaments toward the center of the sarcomere, which shortens the muscle fiber and leads to contraction.
- Ca²⁺ is returned to SR, muscle relaxes.
The Muscle Twitch
- A single action potential causes a brief contraction (twitch) followed by relaxation.
- Twitch duration varies based on muscle type (fast or slow).
Muscle Fiber Types
- Fast Fibers: Fine, rapid movements; short twitch duration (approximately 7.5 ms).
- Slow Fibers: Long, sustained contractions used in posture maintenance (e.g., back muscles); longer twitch duration.
Types of Contraction
- Isometric: Muscle contracts without changing length (e.g., holding a weight).
Electromyography (EMG)
- Recording and analyzing the electrical activity of muscles.
Drugs Affecting Neuromuscular Junction
- Stimulatory Drugs: Mimic or enhance acetylcholine (ACh) action (e.g., methacholine, carbachol, nicotine)
- Inhibitory Drugs (Anticholinesterase Inhibitors): Inhibit the breakdown of ACh, increasing its concentration at the synapse(e.g., neostigmine, physostigmine)
- Curariform Drugs: Block action of ACh on receptors preventing nerve impulse transmission to muscle .
Myasthenia Gravis
- Autoimmune condition causing muscle weakness due to impaired neuromuscular transmission.
- Treated with anticholinesterase drugs.
Cardiac Muscle Morphology
- Striated muscle with branching fibers connected via intercalated discs.
- Myofibrils are composed of actin, myosin, tropomyosin, and troponin.
Cardiac Muscle Electrical Properties
- Resting membrane potential is approximately −90 mV.
- Action potential phase 0 is rapid depolarization due to opening voltage-gated Na + channels.
- Phase 1: Initial rapid repolarization.
- Phase 2: Prolonged plateau caused by slow opening voltage-gated Ca 2+ channels.
- Phase 3 & 4: Final repolarization to resting membrane potential due to closing of Ca++ channels and K+ channels efflux.
Refractory Period of Cardiac Muscle
- Cardiac muscle, like other excitable tissues exhibits refractory periods preventing repetitive contractions during AP.
- Absolute refractory period is the time muscle cannot respond to stimulation.
- Relative refractory period is the time when muscle is more difficult to stimulate than normally but possible with a stronger stimulus
Smooth Muscle Structure
- Smooth muscle lacks striations, consisting of actin and myosin filaments arranged in irregular arrays.
- Contraction mechanism differs from skeletal and cardiac muscle.
- Dense bodies are anchored to the cell membrane and are analogous to Z-lines.
Types of Smooth Muscles
- Visceral (Unitary): Contract as a single unit interconnected via gap junctions (e.g., gut, blood vessels).
- Multi-unit: Individual muscle cells contracting independently under nervous stimulation (e.g., eye muscles).
Electrical and Mechanical Activities of Visceral Smooth Muscle
- resting membrane potential is approximately -50 to -60mV.
- Slow-wave potentials are fluctuations in membrane potential.
Control of Smooth Muscle Contraction
- Smooth muscle contraction is regulated via nervous and hormonal signals.
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Description
Test your knowledge on muscle fibers, excitation-contraction coupling, and neuromuscular junction actions. This quiz covers various aspects of muscle physiology, including differences between muscle fiber types and cardiac muscle action potentials. Challenge yourself with a series of questions that gauge your understanding of these critical topics.
