Physiology of the Nervous System

Questions and Answers

What primarily causes the resting membrane potential to be negative?

Organic anions that can diffuse across the membrane.

The influx of Na+ ions during action potentials.

A higher permeability of K+ ions compared to Na+ ions. (correct)

The Na+-K+ pump moving more K+ ions outside than Na+ ions inside.

What characterizes myelinated neurons compared to unmyelinated neurons?

They have slower transmission speeds due to more ion exchanges.

They always have a thicker axon diameter than unmyelinated neurons.

They utilize saltatory movement for faster signal propagation. (correct)

They have no myelin sheath which allows constant ion exchange.

What is the role of the Na+-K+ pump in maintaining membrane potential?

It creates a concentration gradient by actively moving ions against their gradient. (correct)

It passively allows Na+ influx and K+ efflux.

It moves 3 Na+ ions inside and 2 K+ ions outside.

It is responsible for initiating the action potential.

During depolarization in an action potential, what happens primarily?

Na+ channels are activated, allowing Na+ to enter the cell. Signup and view all the answers

Which component of the neuron contains the majority of voltage-gated ion channels?

Axon hillock. Signup and view all the answers

What is the effect of leakage of K+ ions during the resting state of a neuron?

It establishes a negative interior relative to the exterior. Signup and view all the answers

What characteristic of action potentials is key to their function in neural signaling?

They are rapid and transient electrical changes in membrane potential. Signup and view all the answers

What is the primary role of the myelin sheath in the central nervous system?

To insulate the axon and facilitate faster signal transmission. Signup and view all the answers

What triggers the opening of the voltage-gated Na+ channel?

A minimum stimulus power at threshold Signup and view all the answers

Which statement accurately describes the function of the Na-K+ pump following an action potential?

It maintains the resting membrane potential by pumping Na+ out of the cell. Signup and view all the answers

During the repolarization phase of an action potential, what causes the inner surface to become hyperpolarized?

Continued outward diffusion of K+ due to slowly closing K+ channels Signup and view all the answers

What is the relationship between stimulus strength and the time required to produce a response called?

Strength-duration curve Signup and view all the answers

Which type of potential occurs when the membrane potential reaches +35 mV?

Overshoot Signup and view all the answers

What characterization best describes the condition in which the action potential spreads in one direction only?

It occurs due to the unequal distribution of Na+ and K+ channels across the axon. Signup and view all the answers

What defines the 'negative after potential' during repolarization?

A temporary state where the inner surface is more negative than resting potential Signup and view all the answers

What is the main difference between the gates of Na+ channels and K+ channels?

Na+ channels have an outer and an inner gate while K+ channels only have an inner gate. Signup and view all the answers

Study Notes

Neuron Structure

Units of the nervous system consist of the cell body (soma), dendrites, axon (nerve fiber), and axon terminals.
The plasma membrane is crucial for maintaining neuron function.
Myelin sheath provides insulation for faster signal transmission along the axon.

Types of Nerve Fibers

Myelinated fibers are present mostly in the central nervous system (CNS), facilitating faster impulses with less energy due to ion exchanges occurring only at nodes (saltatory conduction).
Unmyelinated fibers transmit signals more slowly.

Action Potential (AP)

Generally originates at the axon hillock due to a high concentration of voltage-gated ion channels.
AP is unidirectional, propagating from the neuron soma towards the axon.

Membrane Potential

Membrane potential arises from differences in ion concentrations between intracellular and extracellular fluids.
Key ions:
- Intracellular: high concentrations of K+ and organic anions (e.g., phosphate, sulfate).
- Extracellular: high concentrations of Na+ and Cl-.

Resting Membrane Potential

The resting potential for large nerve fibers is approximately -90 mV, indicating a polarized state.
Factors contributing to resting potential:
- K+ outflow is 100 times more permeable than Na+ influx.
- The Na+-K+ pump maintains concentration gradients (3 Na+ out, 2 K+ in).
- Presence of organic anions inside the neuron.

Stages of Action Potential

Depolarization (ascending limb): Voltage-gated Na+ channels open rapidly when the threshold is reached (-50 to -60 mV).
Maximum depolarization occurs at +35 mV (overshoot).
Repolarization (descending limb): Na+ channels close, while voltage-gated K+ channels open, restoring the negative membrane potential.

Stimulus Threshold

Minimum stimulus required to open voltage-gated Na+ channels is called the stimulus threshold.
Once the first Na+ channel opens, additional channels open progressively, resulting in AP propagation.
AP spreads directionally from the soma to the axon due to higher density of voltage-gated channels at the axon hillock.

Channels and Gates

Na+ channel consists of two gates: an outer gate and an inner gate.
K+ channel has only an inner gate.

Spike Potential

Characterized by a steep rise during depolarization followed by a rapid decline during repolarization.
Includes a negative after-potential where the inner surface becomes more negative than at rest due to slowly closing K+ channels, leading to hyperpolarization.

Stimulus Strength and Types

Stimulus strength ranges from subminimal to maximal, with specific types including mechanical, thermal, chemical, and electrical.
The strength-duration curve illustrates the relationship between stimulus strength and the time required to elicit a response.
Rheobase represents the minimum strength required for stimulation to occur.

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Description

Explore the complex structures of the nervous system and their functions with Dr. Eman Negm. This quiz covers neuron structure, types of nerve fibers, and the roles of myelin in the central nervous system. Test your understanding of this essential biological system.