Textbook Question
The hamstring and quadriceps muscle groups are antagonists of each other, and each group is a prime mover in its own right. What action does each muscle group perform?
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Ch. 6 The Muscular System
Marieb13th EditionEssentials of Human Anatomy & PhysiologyISBN: 9780135624340
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Table of contents
- Ch. 1 The Human Body: An Orientation23
- Ch. 2 Basic Chemistry22
- Ch. 3 Cells and Tissues20
- Ch. 4 Skin and Body Membranes13
- Ch. 5 The Skeletal System38
- Ch. 6 The Muscular System26
- Ch. 7 The Nervous System26
- Ch. 8 Special Senses12
- Ch. 9 The Endocrine System24
- Ch. 10 Blood22
- Ch. 11 Cardiovascular System29
- Ch. 12 The Lymphatic System and Body Defenses21
- Ch. 13 The Respiratory System7
- Ch. 14 The Digestive System and Body Metabolism13
- Ch. 15 The Urinary System23
- Ch. 16 The Reproductive System15
Marieb13th EditionEssentials of Human Anatomy & PhysiologyISBN: 9780135624340Not the one you use?Change textbook
Chapter 6, Problem 12
Describe the events that occur from the time calcium ions enter the axon terminal at the neuromuscular junction until muscle cell contraction occurs.
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Calcium ions (Ca²⁺) enter the axon terminal when an action potential reaches the presynaptic neuron at the neuromuscular junction. This triggers the opening of voltage-gated calcium channels, allowing Ca²⁺ to diffuse into the axon terminal.
The influx of Ca²⁺ causes synaptic vesicles containing the neurotransmitter acetylcholine (ACh) to fuse with the presynaptic membrane. Acetylcholine is then released into the synaptic cleft via exocytosis.
Acetylcholine diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors on the motor end plate of the muscle cell membrane (sarcolemma). This binding opens ligand-gated sodium (Na⁺) channels, leading to an influx of Na⁺ into the muscle cell and depolarization of the sarcolemma.
The depolarization triggers an action potential that propagates along the sarcolemma and down the T-tubules. This action potential stimulates the release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum into the cytosol of the muscle cell.
The released Ca²⁺ binds to troponin on the thin filaments of the sarcomere, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin. This allows myosin heads to bind to actin, initiating the cross-bridge cycle and muscle contraction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Calcium Ion Role in Neurotransmission
Calcium ions (Ca²⁺) play a crucial role in neurotransmission at the neuromuscular junction. When an action potential reaches the axon terminal, voltage-gated calcium channels open, allowing Ca²⁺ to flow into the terminal. This influx triggers the release of neurotransmitters, specifically acetylcholine, into the synaptic cleft, which is essential for muscle contraction.
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Neurotransmitter Receptors
Acetylcholine and Muscle Activation
Acetylcholine (ACh) is a neurotransmitter released at the neuromuscular junction that binds to receptors on the muscle cell membrane. This binding initiates a series of events, including the opening of sodium channels, leading to depolarization of the muscle cell membrane. This depolarization is critical for generating an action potential in the muscle fiber, ultimately resulting in muscle contraction.
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Excitation-Contraction Coupling
Excitation-contraction coupling refers to the physiological process linking the electrical signal from the nerve to the mechanical response of muscle contraction. Following the generation of an action potential in the muscle fiber, calcium ions are released from the sarcoplasmic reticulum, leading to the interaction of actin and myosin filaments. This interaction causes the muscle fibers to contract, completing the process initiated by the entry of calcium ions at the axon terminal.
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5:47B. Excitation-Contraction Coupling
Related Practice
Textbook Question
Why are the connective tissue wrappings of skeletal muscles important? Name these connective tissue coverings, beginning with the finest and ending with the coarsest.
b.
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Textbook Question
Define neuromuscular junction, motor unit, tetanus, graded response, aerobic respiration, anaerobic glycolysis, muscle fatigue, and neurotransmitter.
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In addition to acting to flex the spine and compress the abdominal contents, the abdominal muscles are extremely important in protecting and containing the abdominal viscera. What is it about the arrangement of these muscles that makes them so well suited for their job?
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Muscle tone keeps muscles healthy. What is muscle tone, and what causes it? What happens to a muscle that loses its tone?
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Textbook Question
Why are the connective tissue wrappings of skeletal muscles important? Name these connective tissue coverings, beginning with the finest and ending with the coarsest.
c.
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