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

11. Nervous Tissue and Nervous System

Graded Potentials

Anatomy & Physiology

11. Nervous Tissue and Nervous System

Graded Potentials

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3:55 minutes

Problem 16

Textbook Question

Briefly explain how nerve impulses are initiated and transmitted, and why conduction at synapses is always one-way.

Verified step by step guidance

Step 1: Nerve impulses are initiated when a stimulus causes the resting membrane potential of a neuron to reach the threshold level. This occurs due to the opening of voltage-gated sodium (Na⁺) channels, allowing Na⁺ ions to rush into the cell, depolarizing the membrane.

Step 2: Once the membrane is depolarized, the action potential propagates along the axon as voltage-gated sodium channels sequentially open, followed by the opening of voltage-gated potassium (K⁺) channels to repolarize the membrane. This creates a wave-like transmission of the impulse.

Step 3: At the axon terminal, the arrival of the action potential triggers the opening of voltage-gated calcium (Ca²⁺) channels. Calcium ions enter the terminal, causing synaptic vesicles to release neurotransmitters into the synaptic cleft via exocytosis.

Step 4: The neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane. This binding initiates a response in the postsynaptic neuron, such as depolarization or hyperpolarization, depending on the type of neurotransmitter and receptor.

Step 5: Conduction at synapses is always one-way because neurotransmitters are released from the presynaptic neuron and receptors are located on the postsynaptic neuron. The structural and functional organization of synapses ensures that signals cannot travel backward.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nerve Impulse Initiation

Nerve impulses, or action potentials, are initiated when a neuron reaches a certain threshold of depolarization, typically due to the influx of sodium ions through voltage-gated ion channels. This rapid change in membrane potential propagates along the axon, allowing the signal to travel quickly over long distances. The all-or-nothing principle ensures that once the threshold is reached, the impulse will fully propagate without diminishing.

Transmission of Nerve Impulses

Transmission of nerve impulses occurs through a process called saltatory conduction in myelinated axons, where the impulse jumps between nodes of Ranvier, enhancing speed and efficiency. At the axon terminals, the arrival of the action potential triggers the release of neurotransmitters into the synaptic cleft, facilitating communication between neurons. This process is crucial for the rapid relay of information throughout the nervous system.

One-Way Conduction at Synapses

Conduction at synapses is always one-way due to the structural and functional organization of synaptic transmission. Neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron, initiating a response. The absence of receptors on the presynaptic side and the directional flow of neurotransmitter release ensure that signals travel in a single direction, preventing backward transmission and maintaining the integrity of neural communication.

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