Nerve Impulse and Action Potential
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Questions and Answers

What is primarily responsible for making the dendrite more susceptible to structural changes during learning?

  • Increased sodium concentration outside the cell
  • Depolarization of the neuron membrane
  • Rapid influx of potassium ions
  • Action potential back-propagation (correct)

During which phase of the action potential do sodium channels remain tightly shut, preventing any action potential from occurring?

  • Polarization
  • Relative refractory period
  • Absolute refractory period (correct)
  • Depolarization

What happens to the membrane potential during the relative refractory period?

  • It becomes more negative than usual. (correct)
  • It is at its peak voltage.
  • It remains at a resting state.
  • It is fully depolarized.

Which of the following describes the role of the sodium-potassium pump in neuronal function?

<p>It repeatedly transports three sodium ions out and two potassium ions in. (B)</p> Signup and view all the answers

What two forces push sodium ions into the neuron when it is at rest?

<p>Electrical gradient and concentration gradient (A)</p> Signup and view all the answers

What occurs during the depolarization phase of an action potential?

<p>Sodium channels open, allowing sodium ions to enter. (A)</p> Signup and view all the answers

What effect does the selective permeability of the membrane primarily have on ion movement?

<p>It allows potassium to leak out while restricting sodium. (B)</p> Signup and view all the answers

Which statement accurately describes the absolute refractory period?

<p>The membrane cannot produce an action potential regardless of the stimulus. (A)</p> Signup and view all the answers

What does an ionotropic receptor do when a neurotransmitter binds to it?

<p>It opens a channel to allow one type of ion to pass through. (D)</p> Signup and view all the answers

Which neurotransmitter is typically associated with excitatory ionotropic effects?

<p>Glutamate (D)</p> Signup and view all the answers

How do metabotropic synapses differ from ionotropic synapses in terms of duration of effects?

<p>Metabotropic effects last longer and begin more slowly. (A)</p> Signup and view all the answers

What type of ion does GABA typically allow to enter the neuron?

<p>Chloride ions (B)</p> Signup and view all the answers

What role does the G protein play in metabotropic receptor activity?

<p>It is released to initiate metabolic reactions elsewhere in the cell. (A)</p> Signup and view all the answers

In which situation are ionotropic synapses primarily utilized?

<p>For immediate sensory inputs such as vision and hearing. (C)</p> Signup and view all the answers

Which statement about the effects of ionotropic and metabotropic synapses is accurate?

<p>Metabotropic synapses influence activity in much or all of the cell. (B)</p> Signup and view all the answers

What is the primary advantage of metabotropic synapses in terms of function?

<p>They provide sustained responses to stimuli like taste and pain. (C)</p> Signup and view all the answers

What is the primary role of calcium in neurotransmitter release?

<p>Calcium opens voltage-dependent channels to trigger exocytosis. (B)</p> Signup and view all the answers

Which statement accurately describes the behavior of neurotransmitters after release?

<p>Released neurotransmitters may be recycled or can diffuse away. (A)</p> Signup and view all the answers

What distinguishes nitric oxide from other neurotransmitters?

<p>Nitric oxide is released immediately upon formation. (B)</p> Signup and view all the answers

Which neurotransmitter is closely related to both epinephrine and norepinephrine?

<p>Dopamine (C)</p> Signup and view all the answers

What occurs when neurotransmitters bind to receptors on the postsynaptic neuron?

<p>The activity of the postsynaptic neuron is altered. (A)</p> Signup and view all the answers

What process follows calcium entry into the presynaptic terminal?

<p>Exocytosis occurs leading to neurotransmitter release. (B)</p> Signup and view all the answers

How do postsynaptic cells communicate with presynaptic cells?

<p>By transmitting reverse messages to control neurotransmitter release. (A)</p> Signup and view all the answers

What is the source of most neurotransmitters in neurons?

<p>Synthesis from amino acids obtained from dietary proteins. (D)</p> Signup and view all the answers

What mechanism enhances the speed of action potentials in axons?

<p>Myelin sheath surrounding the axon (A)</p> Signup and view all the answers

Why does potassium tend to flow out of the cell despite the electrical gradient attracting it in?

<p>Potassium is more concentrated inside the cell (B)</p> Signup and view all the answers

What is the term for the process by which action potentials jump from node to node?

<p>Saltatory conduction (A)</p> Signup and view all the answers

What happens to a single subthreshold excitation in a postsynaptic neuron over time?

<p>It decays before another excitation can occur (A)</p> Signup and view all the answers

How does saltatory conduction conserve energy in myelinated axons?

<p>By concentrating sodium entry at nodes (C)</p> Signup and view all the answers

What primarily causes the rapid influx of sodium ions during an action potential?

<p>Opening of sodium channels (B)</p> Signup and view all the answers

What characterizes temporal summation in neuronal signaling?

<p>Repeated stimuli leading to a combined effect in a short time (C)</p> Signup and view all the answers

What is the role of the sodium-potassium pump in relation to potassium ions?

<p>It transports potassium into the neuron continuously (C)</p> Signup and view all the answers

What is the main difference between action potentials and graded potentials?

<p>Graded potentials can be excitatory or inhibitory. (A)</p> Signup and view all the answers

How does spatial summation differ from temporal summation in neuron activity?

<p>Spatial summation combines inputs from different locations, while temporal summation combines successive inputs. (D)</p> Signup and view all the answers

What occurs within the neuron during the initiation of an action potential?

<p>Sodium ions enter, causing depolarization. (C)</p> Signup and view all the answers

What role does an interneuron play in a reflex action, such as a dog lifting its leg?

<p>It inhibits the extensor muscles of the leg being raised and the flexor muscles of other legs. (A)</p> Signup and view all the answers

What effect do excitatory postsynaptic potentials (EPSPs) have on a neuron's firing rate?

<p>They increase the firing rate above the spontaneous firing rate. (C)</p> Signup and view all the answers

What happens to the postsynaptic cell when inhibitory synapses are activated?

<p>The postsynaptic cell hyperpolarizes, moving its charge farther from the threshold. (C)</p> Signup and view all the answers

Which step is NOT part of neurotransmitter chemical transmission?

<p>Neurotransmitters are broken down at the presynaptic terminal. (B)</p> Signup and view all the answers

What is the effect of the spontaneous firing rate of most neurons?

<p>It allows for periodic action potentials even without input. (A)</p> Signup and view all the answers

What is the primary function of sodium channels during the action potential?

<p>To initiate the depolarization of the axon membrane. (C)</p> Signup and view all the answers

What does the all-or-none law state regarding action potentials?

<p>An action potential will occur only if the stimulus is strong enough. (A)</p> Signup and view all the answers

During which phase of the action potential do potassium ions flow out of the axon?

<p>After the depolarization phase. (D)</p> Signup and view all the answers

What causes the propagation of the action potential down the axon?

<p>The influx of sodium ions that depolarizes neighboring areas. (A)</p> Signup and view all the answers

Which statement about the action potential is correct?

<p>It maintains a constant magnitude as it travels along the axon. (C)</p> Signup and view all the answers

What happens at the peak of the action potential?

<p>The sodium gates snap shut to stop the influx of sodium ions. (C)</p> Signup and view all the answers

What occurs after the action potential begins to propagate?

<p>The adjacent membrane areas become depolarized due to sodium influx. (B)</p> Signup and view all the answers

How does the axon convey information about weak or strong stimuli?

<p>By changing the timing or frequency of its action potentials. (B)</p> Signup and view all the answers

Flashcards

Absolute Refractory Period

The period following an action potential where the neuron cannot fire another action potential, regardless of stimulus strength.

Relative Refractory Period

The period following an action potential where the neuron can fire another action potential, but only with a stronger than usual stimulus.

Back-propagation

The process by which an action potential travels backwards into the dendrites of a neuron, increasing its susceptibility to structural changes associated with learning.

Membrane Potential

The difference in electrical charge between the inside and outside of a neuron's membrane, determined by the concentration of ions.

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Concentration Gradient

The difference in concentration of ions across the neuron's membrane, driving the movement of ions.

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Electrical Gradient

The difference in electrical charge across the neuron's membrane, influencing the movement of charged particles.

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Sodium-Potassium Pump

A protein pump that actively transports sodium ions out of the neuron and potassium ions into the neuron, maintaining the membrane potential.

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Selective Permeability

A property of cell membranes that allows some substances to pass through while blocking others.

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Threshold

The critical level of depolarization that must be reached for an action potential to occur. When the threshold is reached, voltage-gated sodium channels open, allowing an influx of sodium ions.

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Action Potential

The rapid change in electrical potential across a neuron's membrane when stimulated. This is caused by an influx of sodium ions, followed by an outflow of potassium ions.

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Propagation of the Action Potential

The movement of an action potential down the axon. It's a regenerative process where the signal is constantly renewed.

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Refractory Period

The period after an action potential where the neuron is less likely to fire another action potential. It's like a 'recharging' period for the neuron.

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All-or-None Law

The principle that the amplitude and speed of an action potential are independent of the strength of the stimulus. All or nothing!

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Frequency Coding

The strength of a stimulus is coded by the frequency of action potentials. More frequent action potentials mean a stronger stimulus.

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Repolarization

The process by which the sodium gates close and potassium gates open, leading to repolarization of the membrane and returning the neuron to its resting potential.

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Resting Potential

The resting potential of the neuron, typically around -70mV. This is the baseline electrical charge of the neuron.

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Potassium flow in a neuron

The electrical gradient attracts potassium into the cell, but the concentration gradient pushes it out. This creates a balance where some potassium flows out of the cell, while the sodium-potassium pump pulls it back in.

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Myelin sheath

A specialized covering on axons that insulates them and speeds up nerve impulse transmission.

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Nodes of Ranvier

Short gaps in the myelin sheath that allow for the regeneration of the action potential.

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Saltatory conduction

The process of nerve impulse transmission where the action potential jumps from one node of Ranvier to the next.

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Presynaptic neuron

A neuron that sends a signal to another neuron.

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Postsynaptic neuron

A neuron that receives a signal from another neuron.

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Temporal summation

The combined effect of multiple weak stimuli that occur within a short time frame.

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Summation

The process where repeated stimuli within a short time frame add their effects together to cause a response.

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Spatial Summation

When multiple neurons communicate with a single neuron simultaneously, their individual signals combine to produce a larger signal.

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Excitatory Postsynaptic Potential (EPSP)

A type of graded potential that makes a neuron more likely to fire an action potential. It's caused by sodium ions entering the neuron, making it more positive.

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Inhibitory Postsynaptic Potential (IPSP)

A type of graded potential that makes a neuron less likely to fire an action potential. It's caused by negatively charged ions entering the neuron, making it more negative.

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Spontaneous Firing Rate

The natural tendency of a neuron to fire action potentials at a regular rate even without any input from other neurons.

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Chemical Transmission

The process by which neurons communicate with each other, using chemicals called neurotransmitters to send signals across the synapse.

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Synapse

The junction between two neurons, where a signal is transmitted from one neuron to another.

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Neurotransmitters

Chemicals that are released by neurons to carry signals across the synapse to other neurons or cells.

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What are neurotransmitters?

Chemical messengers released by neurons at synapses to communicate with other neurons or target cells.

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What is the synaptic cleft?

The space between a presynaptic neuron and a postsynaptic neuron, where neurotransmitters are released and bind to receptors.

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What is exocytosis?

The process by which neurotransmitters are released from vesicles in the presynaptic terminal into the synaptic cleft.

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What are neurotransmitter receptors?

Specific proteins on the postsynaptic membrane that bind to neurotransmitters, initiating a response in the postsynaptic cell.

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What is reuptake?

The process where neurotransmitters are reabsorbed back into the presynaptic terminal for reuse after being released.

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What is serotonin?

A neurotransmitter that is often involved in relaxation and sleep, and is boosted by eating foods rich in tryptophan.

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What is dopamine?

A neurotransmitter involved in alertness, attention, and mood. It is synthesized from the amino acid tyrosine.

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What is norepinephrine?

A neurotransmitter involved in arousal, stress response, and memory. It is synthesized from tyrosine, just like dopamine.

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What is an ionotropic effect?

This process occurs when a neurotransmitter binds to a receptor causing a change in the receptor that opens a channel allowing one type of ion to pass through. This creates a fast but short-lived effect.

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What is a metabotropic effect?

A neurotransmitter, that is a chemical that binds to a receptor, can also trigger a slower but longer-lasting effect. This involves a chain of metabolic reactions that start slowly but continue for a longer time.

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Which neurotransmitter is typically associated with excitatory ionotropic effects?

A neurotransmitter that typically triggers excitatory ionotropic effects. It opens sodium channels, allowing positively charged ions to flow into the neuron, causing depolarization and increasing the likelihood of an action potential.

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Which neurotransmitter is typically associated with inhibitory ionotropic effects?

A neurotransmitter that typically triggers inhibitory ionotropic effects. It opens chloride channels, allowing negatively charged ions to flow into the neuron, hyperpolarizing the cell and decreasing the likelihood of an action potential.

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What are G proteins involved in?

These are proteins that are attached to the inside of the cell membrane. When a neurotransmitter binds to a metabotropic receptor, it bends the receptor protein, which detaches the G protein. This G protein then goes on to activate other processes within the cell.

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What are the effects of ionotropic synapses?

These occur in one specific location on the cell membrane, affecting only that particular area. They produce quick, localized effects.

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What are the effects of metabotropic synapses?

These have a more widespread effect, affecting much or all of the cell and lasting for a longer duration. They can even influence activity in other neurons connected to the cell.

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Which type of synapse is best suited for tasks requiring quick, fleeting information?

The type of synapse responsible for the quick and brief information needed for senses like vision and hearing.

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Study Notes

Nerve Impulse

  • Neurons transmit signals through nerve impulses.
  • All neuron parts are covered by a membrane, allowing chemical passage.
  • Polarization: A difference in electrical charge between the inside and outside of the cell
  • At rest, the inside of the membrane is slightly negative (-70mV).
  • The resting potential prepares the neuron for rapid response.
  • Excitation opens sodium channels, allowing rapid sodium entry.
  • Hyperpolarization: Increasing the negative charge inside a neuron.
  • Depolarization: Decreasing a neuron's polarization.
  • Action Potential: A significant depolarization reaching a threshold triggers sodium and potassium channel opening & reversal of membrane charge.
  • Action potentials regenerate along the axon maintains constant magnitude.
  • All-or-none law: Action potential amplitude and velocity are independent of stimulus intensity (above threshold). Axon signals frequency changes to signal stimulus strength.

Action Potential Propagation

  • Action potentials transmit along the axon.
  • Positive charge flows downstream causing neighboring regions to reach threshold.
  • Sodium channels open rapidly, depolarizing the next region.
  • Potassium channels open, repolarizing the membrane.
  • Propagation regenerates along the axon without loss of strength
  • Refractory period: A period after an action potential where the membrane cannot produce another action potential (absolute), or a greater than usual stimulus is needed (relative).

Synaptic Transmission

  • Synapses are junctions between neurons.
  • Neurotransmitters are released across the synaptic cleft by the presynaptic neuron.
  • Neurotransmitters attach to receptors on the postsynaptic neuron.
  • Receptors trigger ionotropic (fast) or metabotropic (slow) effects.
  • Temporal summation: Repeated stimuli in brief time.
  • Spatial summation: Potentials from different locations.
  • EPSPs (excitatory postsynaptic potentials): depolarizations.
  • IPSPs (inhibitory postsynaptic potentials): hyperpolarizations.
  • Neurotransmitters are synthesized, stored, and released via calcium channels and exocytosis.

Neurotransmitters and Receptors

  • Neurotransmitters are chemicals released at synapses.
  • Neuron synthesis of neurotransmitters, either in cell body or axon terminal.
  • Action potentials at presynaptic terminal cause calcium entry, releasing neurotransmitters into the synaptic cleft.
  • Neurotransmitter interaction with receptors alters the activity of the postsynaptic neuron.
  • Ionotropic Receptors: Fast direct channel opening.
  • Metabotropic Receptors: Induce a sequence of metabolic reactions.

Types of Neurotransmitters

  • Amino Acids (glutamate, GABA)
  • Modified Amino Acids
  • Monoamines (dopamine, serotonin)
  • Neuropeptides
  • Purines
  • Gases like Nitric Oxide

Functions of Neurotransmitters

  • Many neurons release nitric oxide.
  • Neurotransmitters are synthesized from amino acids.
  • Synthesized compounds (eg., dopamine, epinephrine, norepinephrine) are also important.
  • Neurotransmitters are stored in vesicles.

Summary

  • Nerve impulse involves resting potential, action potential, propagation, refractory period.
  • Synaptic transmission occurs at synapses through neurotransmitters and receptors.
  • Neurotransmitters, classified as amino acids, modified amino acids, monoamines, neuropeptides, purines, and gases , are released by presynaptic neurons to affect postsynaptic neurons.
  • Different types exert various effects (ionotropic, metabotropic).

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Description

This quiz explores the mechanisms of nerve impulses, including the roles of polarization, depolarization, and action potential in neuron signaling. Understand how neurons transmit signals and the significance of resting potential and action potentials in communication. Test your knowledge of neurophysiology concepts and their implications in the nervous system.

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