Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

9. Muscle Tissue

Steps of Muscle Contraction

Anatomy & Physiology

9. Muscle Tissue

Steps of Muscle Contraction

Previous problemNext problem

2: minutes

Problem 12

Textbook Question

Describe the events that occur from the time calcium ions enter the axon terminal at the neuromuscular junction until muscle cell contraction occurs.

Verified step by step guidance

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.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

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.

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.

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.

Watch next

Master Overview of Muscle Contraction with a bite sized video explanation from Bruce Bryan

Start learning

Related Videos

Related Practice

Textbook Question

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Stimulation by a motor neuron before a muscle fiber has fully relaxed results in a condition called wave summation.

617

views

Textbook Question

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

A muscle fiber changes length during isotonic concentric and isotonic eccentric contractions.

Tell where each of the three types of muscle tissue would be found in the body. What is meant by the statement, 'Smooth muscles are involuntary in action'?

401

views

Textbook Question

Linda's father suffers an apparent heart attack and is rushed to the emergency room of the local hospital. The doctor on call tells her that he has ordered some blood work and that he will be able to tell if her father actually had a heart attack by looking at the blood levels of CK and cardiac troponin. Why would knowing the level of CK and cardiac troponin help to indicate if a person suffered a heart attack?

416

views

Textbook Question

After ACh attaches to its receptors at the neuromuscular junction, what is the next step?

a. Sodium channels open

b. Calcium binds to regulatory proteins on the thin filaments

c. Cross bridges attach

d. ATP is hydrolyzed

558

views

Textbook Question

Chemical A binds and blocks acetylcholine receptors of muscle cells. Chemical B floods the cytoplasm of muscle cells with calcium ions. Which chemical would make the best muscle relaxant, and why?

415

views

Textbook Question

What structural feature of a skeletal muscle fiber propagates action potentials into the interior of the cell?

487

views

Textbook Question

What forms of energy reserves do resting skeletal muscle fibers contain?

425

views

Show more practices