Neurobiology: Action Potentials and Neurons

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Questions and Answers

Which property of a neuron helps to ensure that action potentials propagate over long distances?

High membrane resistance (correct)

Low internal resistance

High capacitance

Short length constant

What is the primary role of myelin in the conduction of action potentials?

To insulate the axon and facilitate saltatory conduction (correct)

To slow down the conduction speed

To increase the capacitance of the axon

To generate action potentials at the nodes

What is the function of glial cells in the context of action potential propagation?

To directly transmit impulses between neurons

To increase the internal resistance of the neuron

To generate action potentials in neurons

To provide structural support and insulation (correct)

How does saltatory conduction enhance the speed of action potential propagation?

By causing the action potentials to jump between myelinated segments Signup and view all the answers

What initiates the propagation of an action potential along an excitable membrane?

Influx of Na+ ions Signup and view all the answers

What prevents an action potential from propagating backwards along an axon?

Refractory period due to inactivated Na+ channels Signup and view all the answers

What type of synapse allows ions to freely pass between adjacent neurons?

Electrical synapse Signup and view all the answers

What is the main characteristic of chemical synapses?

Synaptic cleft is about 200 Å wide Signup and view all the answers

What is the primary trigger for the release of neurotransmitters from vesicles in axon terminals?

Ca++ ions influx Signup and view all the answers

What is the role of the postsynaptic membrane in a chemical synapse?

To have specific protein receptors for neurotransmitter binding Signup and view all the answers

What is the role of voltage-gated Na+ channels in excitable cells?

They are responsible for generating action potentials. Signup and view all the answers

Which type of cell is capable of conducting action potentials over long distances?

Muscle cells Signup and view all the answers

As signals travel along a neuron, what is the function of the myelin sheath?

It insulates the axon and increases the speed of signal transmission. Signup and view all the answers

What is the primary advantage of saltatory conduction?

It reduces energy expenditure over long distances. Signup and view all the answers

Which component of the neuron is responsible for integrating input signals?

Cell body Signup and view all the answers

What is the synapse responsible for in neuronal communication?

Allowing communication between axon terminals and postsynaptic cells. Signup and view all the answers

Which of the following statements about glial cells is true?

They provide support and insulation for neurons. Signup and view all the answers

In a neuron, the initial segment of the axon is crucial for what process?

Generating action potentials. Signup and view all the answers

What do excitable cells lack that prevents them from generating action potentials?

Voltage-gated Na+ channels Signup and view all the answers

When a voltage is applied across a membrane in a biological tissue, what type of current is initially generated?

Passive current Signup and view all the answers

Study Notes

Impulse Conduction

Action potentials (APs) are initiated when Na+ influx reverses the membrane potential from negative to positive.
The local reversal generates a depolarizing current that propagates to adjacent membranes.
Once initiated, APs propagate along the axon without diminishing.

Excitable Cells

Excitable cells, such as neurons and muscle cells, possess voltage-gated Na+ channels essential for AP generation.
Non-excitable cells can conduct passive currents but lack the capacity to generate APs.
Neurons have long axons, which act as conduits for transmitting APs over distances.

Structure of a Neuron

Neurons consist of several key components:
- Cell body (nucleus)
- Dendrites (input region)
- Axon (transmission region) split into axon hillock and initial segment.
- Myelin sheath (insulator to speed up conduction)
- Postsynaptic neuron (target cell receiving signals).

Functional Dynamics of Action Potentials

APs cannot reverse direction due to the refractory period, rendering Na+ channels inactivated after depolarization.
APs propagate in one direction towards synaptic terminals where they signal the release of neurotransmitters.

Synapses

Synapses form the functional association of neurons with other neurons or effector organs (muscles or glands).
Two main types of synapses exist: electrical and chemical.

Electrical Synapses

Electrotonic synapses (gap junctions) feature membranes approximately 35Å apart.
Connexins connect adjacent cells, facilitating the passage of small ions and depolarization waves.

Chemical Synapses

Neurotransmitter release occurs in the synaptic cleft, a specialized space about 200 Å wide.
Presynaptic terminals (boutons) contain vesicles with neurotransmitters, while postsynaptic membranes have receptors for these transmitters.
The cleft is crucial for neurotransmission efficiency and specificity.

Axon Terminal and Vesicle Release

Axons conclude in boutons loaded with vesicles containing neurotransmitters, which are released upon appropriate stimulation.
Exocytosis of vesicles is triggered by the influx of Ca++ ions.

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Description

Explore the dynamics of action potentials and the anatomy of neurons in this quiz. Understand how excitable cells generate and propagate signals, and learn about the key components of neuron structure. Perfect for students studying neurobiology at an advanced level.