Neuroscience: Action Potentials Overview

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Questions and Answers

What is the outcome when two EPSPs occur simultaneously?

Inhibition occurs

An action potential is generated (correct)

Grip is decreased

No action potential is generated

How do local anesthetics like Novocaine and Lidocaine function?

They enhance action potentials

They block voltage gated Na+ channels (correct)

They inhibit excitatory synaptic potentials

They facilitate synaptic transmission

What type of potential must occur in high enough frequency to generate an action potential?

Local potentials

EPSPS (correct)

Refractory potentials

IPSPS

What effect does increasing inhibition (IPSP) have when combined with excitation (EPSP)?

Prevents action potentials from occurring Signup and view all the answers

What is a potential consequence of tetrodotoxin (TTX) exposure?

Paralysis and respiratory distress Signup and view all the answers

What defines action potentials in nerve cell axons?

Small identical electrical changes in individual parts of a neuron Signup and view all the answers

Why do action potentials propagate in one direction along an axon?

Inactivation of sodium channels after they open prevents back propagation Signup and view all the answers

What role does the myelin sheath play in nerve physiology?

Facilitates saltatory conduction of action potentials Signup and view all the answers

Which mechanism is involved in synaptic transmission?

Diffusion of neurotransmitters across the synaptic cleft Signup and view all the answers

What distinguishes local anaesthetics from neurotoxins in their mechanism of action?

Local anaesthetics prevent action potentials, while neurotoxins increase excitability Signup and view all the answers

What type of cells are responsible for transmitting sensory information?

Specialised sensory cells that detect external stimuli Signup and view all the answers

What is the significance of the time taken for ions to achieve 99% equilibrium in a nerve?

It highlights the importance of diffusion in nerve function Signup and view all the answers

What limits the size of graded potentials in neurons?

The amplitude of the incoming stimulus and its dispersion Signup and view all the answers

What triggers the opening of sodium channels during an action potential?

A change in membrane potential to -55 mV Signup and view all the answers

What happens to the membrane potential during the phase leading to an action potential?

It must reach -55 mV Signup and view all the answers

Which condition describes the resting membrane potential?

The inside of the neuron is negative relative to the outside Signup and view all the answers

During which phase do voltage-gated sodium channels play a critical role?

The action potential phase Signup and view all the answers

What is the effect of increased sodium concentration inside the axon?

It raises the membrane potential towards a threshold Signup and view all the answers

What defines graded potentials in a neuron?

They can lead to action potentials with sufficient strength Signup and view all the answers

Which event occurs first after the membrane potential reaches -55 mV?

Sodium channels open Signup and view all the answers

What is the role of potassium (K+) channels during action potentials?

They allow repolarization of the membrane Signup and view all the answers

How is the membrane potential at -70 mV characterized?

It represents a stable resting membrane potential Signup and view all the answers

What occurs at the decision point of an action potential?

The overall membrane potential reaches a threshold Signup and view all the answers

What is the primary effect of opening voltage-gated Na+ channels on the neuron's membrane potential?

Depolarization of the membrane Signup and view all the answers

What is the result of K+ ions leaving the cell when K+ channels are open?

Repolarization or hyperpolarization of the membrane Signup and view all the answers

How quickly does the fast excitatory response occur upon the opening of Na+ channels?

5 milliseconds Signup and view all the answers

What characterizes an excitatory post-synaptic potential (EPSP)?

It is likely to trigger action potentials. Signup and view all the answers

What is the role of iberiotoxin in the context of K+ channels?

It blocks K+ channels. Signup and view all the answers

Which response is described as occurring slowly due to ligand binding and conformational changes?

Slow response - indirect channel opening Signup and view all the answers

What does the hyperpolarization in a post-synaptic cell indicate?

It is called an inhibitory post-synaptic potential (IPSP). Signup and view all the answers

What is the rate at which Na+ ions can enter the cell when Na+ channels open?

10^8 ions/sec Signup and view all the answers

What is the main mechanism of action associated with ionotropic responses?

Mediated by an ion channel Signup and view all the answers

Which of the following primarily leads to an increase in voltage across the membrane rapidly?

Na+ entering the cell through open channels Signup and view all the answers

What happens to the graded potential at the axon hillock when the stimulus on a sensory cell ceases?

It falls below -55 mV. Signup and view all the answers

Why do action potentials propagate in one direction along nerve cell axons?

Because of the refractory period of the previous segment. Signup and view all the answers

What effect would blocking voltage-gated Na+ channels have on nerve impulses?

It would prevent the generation of action potentials. Signup and view all the answers

Which of the following best describes the role of neuroglia and the myelin sheath in the context of action potentials?

They prevent ion leakage and speed up impulse conduction. Signup and view all the answers

What is a direct consequence of a graded potential falling below -55 mV?

No new action potentials are generated. Signup and view all the answers

How do local anaesthetics function within the neural pathway?

By blocking ion channels critical for action potentials. Signup and view all the answers

What is the relationship between synapses and neuronal circuits?

Synapses facilitate communication between neurons in circuits. Signup and view all the answers

What would be the impact of reducing the number of synapses in a neuronal circuit?

Diminished signal transmission and processing. Signup and view all the answers

What mechanism underlies synaptic transmission in the nervous system?

Release and binding of neurotransmitters. Signup and view all the answers

Which scenario best describes the resting state of a neuron?

The neuron has a membrane potential around -70 mV. Signup and view all the answers

Study Notes

Action Potentials

Action potentials are generated by the movement of ions across the cell membrane.
They are rapid changes in membrane potential.
The movement of ions is facilitated by voltage-gated sodium and potassium channels.
Sodium ions flow into the cell during depolarization.
Potassium ions flow out of the cell during repolarization.

Propagation of Action Potential

Action potentials propagate in one direction because of the refractory period.
The refractory period is a brief period of time after an action potential when the neuron cannot fire another action potential.
This is because the sodium channels are inactivated after they open.
The refractory period ensures that the action potential travels in one direction.

Role of Neuroglia and Myelin Sheath

Neuroglia are supporting cells that play a crucial role in the nervous system.
They provide structural support, nourishment, and insulation for neurons.
Myelin sheath is a fatty substance that insulates axons, speeding up the conduction of action potentials.

Synaptic Transmission

Synaptic transmission is the communication between neurons.
Neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron.
There are two types of synaptic transmission:
- Fast - mediated by ion channels and occurs very quickly.
- Slow - mediated by second messenger systems and occurs more slowly.
Excitatory postsynaptic potentials (EPSPs) increase the likelihood of an action potential occurring in the postsynaptic neuron.
Inhibitory postsynaptic potentials (IPSPs) decrease the likelihood of an action potential occurring in the postsynaptic neuron.

Local Anaesthetics

Local anaesthetics (e.g. novocaine, lidocaine) block voltage-gated sodium channels.
This prevents action potentials from being generated, resulting in pain relief.
They have a local effect on neurons, preventing pain signals from reaching the brain.

Neurotoxins

Neurotoxins (e.g. tetrodotoxin) block voltage-gated sodium channels.
This prevents nerve impulses from being sent, leading to paralysis.
Tetrodotoxin is a very potent neurotoxin and can be fatal.
Tetrodotoxin is found in pufferfish.

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Description

This quiz covers the fundamentals of action potentials in neurons, including their generation, propagation, and the roles of neuroglia and the myelin sheath. Test your knowledge on the ion movements, depolarization, and the refractory period vital for neuronal signaling.