Action Potential in Neurons

Questions and Answers

What is a characteristic of an action potential?

It is an all-or-none response. (correct)

Its size varies depending on the strength of the incoming signal.

It only occurs at the dendrites of a neuron.

It is a graded potential.

What happens to the membrane potential when the sodium channels open during an action potential?

It becomes positive.

It becomes less negative. (correct)

It becomes more negative.

It remains the same.

What is the purpose of the sodium-potassium pump?

To generate action potentials.

To close potassium channels.

To restabilize the membrane potential. (correct)

To open sodium channels.

What is the absolute refractory period?

The duration in which no amount of stimulation can stimulate another action potential. Signup and view all the answers

What is the membrane potential when the potassium channels open during an action potential?

+50 mV Signup and view all the answers

What happens to the membrane potential after the absolute refractory period?

It returns to its resting state. Signup and view all the answers

What triggers the release of neurotransmitters and exocytosis in the presynaptic neuron?

An influx of calcium ions in the presynaptic membrane Signup and view all the answers

Where are small neurotransmitters often aggregated?

Near the voltage-gated calcium channels in the presynaptic membrane Signup and view all the answers

What type of receptors are ion channels?

Ionotropic receptors Signup and view all the answers

What is the characteristic of the release of small neurotransmitters?

It is a rapid, pulsing release Signup and view all the answers

What is the primary advantage of functional magnetic resonance imaging (fMRI) over MRI?

No need for injection of contrast agents Signup and view all the answers

What is necessary for the release of neuropeptides?

A gradual increase in the firing rate of action potentials Signup and view all the answers

What is the primary function of the capacitor in a Transcranial Magnetic Stimulation (TMS) machine?

To prevent the flow of current Signup and view all the answers

What is the term for anything that binds to a protein?

Ligand Signup and view all the answers

What type of signal is emitted by water molecules in the blood supply with high oxygen levels?

A stronger radio frequency signal Signup and view all the answers

What is the effect of ionotropic receptors on the postsynaptic neuron?

They lead to a quick, short-lasting change in the postsynaptic potential Signup and view all the answers

What is the primary limitation of functional magnetic resonance imaging (fMRI)?

Low temporal resolution Signup and view all the answers

What is the purpose of Transcranial Magnetic Stimulation (TMS)?

To stimulate specific regions of the cerebral cortex Signup and view all the answers

What type of receptors are more common than ionotropic receptors?

Metabotropic receptors Signup and view all the answers

What happens when the capacitor in a TMS machine is discharged?

All of the current flows through the circuit Signup and view all the answers

What is the name of the signal emitted by water molecules in the blood supply?

The BOLD signal Signup and view all the answers

What is the result of the magnetic field around the coils in a TMS machine?

It induces an electrical current in neural tissue Signup and view all the answers

What is the purpose of a stereotaxic atlas in lesion technique?

To map the location of structures in the brain Signup and view all the answers

What is the role of the head holder in a stereotaxic instrument?

To hold the brain in place during surgery Signup and view all the answers

What is the term for lesioning a structure on both sides?

Bilateral Signup and view all the answers

What is the significance of the 'bregma' landmark in stereotaxic surgery?

It provides a reference point for the z-axis Signup and view all the answers

What is the primary advantage of intracellular unit recording?

It provides moment-by-moment changes in the membrane potential of a single neuron Signup and view all the answers

In extracellular unit recording, what is the purpose of the ground electrode?

To provide a neutral reference point for the recording Signup and view all the answers

What is the primary purpose of lesion technique in neuroscience research?

To damage or destroy specific areas of the brain Signup and view all the answers

What can be done to either side of the brain in lesion technique?

Lesions can be done to either side of the brain Signup and view all the answers

What type of information can be obtained from extracellular unit recording?

Signals about electrical disturbances in the extracellular environment Signup and view all the answers

What is the purpose of the microelectrode in intracellular unit recording?

To measure the charge around the microelectrode with respect to the ground electrode Signup and view all the answers

What is the relationship between different stages of sleep and EEG activity?

Different stages of sleep are associated with distinct patterns of EEG activity Signup and view all the answers

What is NOT a type of electrophysiological recording method?

Neuropsychological testing Signup and view all the answers

What is the function of myelination in axons?

To allow action potentials to jump over large distances Signup and view all the answers

Which type of neuron has either no axons or small axons?

Interneuron Signup and view all the answers

What is a characteristic of action potentials?

The size is not graded and is always the same Signup and view all the answers

What is the term used to describe the instantaneous conduction of an action potential from one node of Ranvier to another?

Saltatory conduction Signup and view all the answers

How does the diameter of an axon affect the speed of conduction?

The larger the diameter, the faster the conduction Signup and view all the answers

What is the primary difference between action potentials and postsynaptic potentials?

Action potentials are not graded, while postsynaptic potentials are Signup and view all the answers

What is the minimum membrane potential required to generate an action potential?

-65 mV Signup and view all the answers

What type of integration occurs when EPSPs and IPSPs are generated at the same time but in different locations?

Spatial summation Signup and view all the answers

How do action potentials provide indication of strength of signal?

By frequency of stimulation Signup and view all the answers

What is the maximum frequency of stimulation that can be achieved by an action potential?

1000 hertz Signup and view all the answers

What type of conduction occurs when an action potential travels in the opposite direction it normally would?

Antidromic conduction Signup and view all the answers

How do myelination and conduction velocity relate?

Myelination increases conduction velocity Signup and view all the answers

What happens to the resting membrane potential of a neuron when neurotransmitters bind to postsynaptic receptors?

It becomes more positive (depolarization) Signup and view all the answers

What is the result of a net excitation at the axon initial segment?

The neuron is stimulated to produce an action potential Signup and view all the answers

What happens to the action potential as it travels away from the site of origin?

It remains the same amplitude Signup and view all the answers

What is the direction of travel for an action potential under normal conditions?

Away from the cell body Signup and view all the answers

What is the significance of the threshold (-65 mV) in a neuron?

It is the minimum potential required for an action potential to occur Signup and view all the answers

How do postsynaptic potentials travel in the cell membrane?

They travel fast and decrease in size Signup and view all the answers

What is the significance of integrating postsynaptic potentials?

To decide whether to activate an action potential or not Signup and view all the answers

What is the effect of inhibitory postsynaptic potentials on the membrane potential?

It becomes more negative Signup and view all the answers

What is the significance of neurotransmitters in chemical communication between cells?

They are the chemical messengers that communicate between cells Signup and view all the answers

What is the result of a single postsynaptic neuron receiving thousands of signals?

A net effect that is either excitatory, inhibitory, or no response Signup and view all the answers

What occurs during the relative refractory period of an action potential?

The action potential can be generated, but requires more stimulation than normal. Signup and view all the answers

What type of synapse occurs when an axon contacts the dendrites of a neuron?

Axodentritic synapse Signup and view all the answers

What is the primary characteristic of directed synapses?

The site of release and reception of neurotransmitters are close together. Signup and view all the answers

What is the term for the swelling on the postsynaptic site of contact in an axodentritic synapse?

Dendritic spine Signup and view all the answers

What type of synapse occurs when an axon contacts the soma of a neuron?

Axosomatic synapse Signup and view all the answers

What is the primary characteristic of non-directed synapses?

The site of release and reception of neurotransmitters are far apart. Signup and view all the answers

What is the term for the swelling along the axon where neurotransmitters are released in non-directed synapses?

Varicosity Signup and view all the answers

What is the region between two cells where chemical communication takes place?

Synapse Signup and view all the answers

What is the precursor molecule for catecholamines?

Tyrosine Signup and view all the answers

What is the role of retrograde transmission in the nervous system?

Transmitting signals from postsynaptic to presynaptic neurons Signup and view all the answers

What type of neurotransmitters are nitric oxide and carbon monoxide?

Soluble gas neurotransmitters Signup and view all the answers

What is the primary function of computed tomography (CT) scans in neuroscience research?

Visualizing internal brain structures Signup and view all the answers

What is the characteristic of neuropeptides?

They are named based on their location in the body Signup and view all the answers

What is the role of acetylcholine in the nervous system?

Causing muscle contraction Signup and view all the answers

What is the precursor molecule for serotonin?

Tryptophan Signup and view all the answers

What is unique about unconventional neurotransmitters?

They affect presynaptic neurons Signup and view all the answers

What is the main difference between small and large neurotransmitters?

Their site of synthesis in the neuron Signup and view all the answers

What is the role of microtubules in neurotransmitter transport?

To transport vesicles from the cell body to the synaptic terminal Signup and view all the answers

What is the characteristic of varicosities in axons?

They give axons a beaded appearance Signup and view all the answers

What is the term for the coexistence of a neuropeptide and a small neurotransmitter in a single neuron?

Coexistence Signup and view all the answers

What is the process by which synaptic vesicles release their contents into the synapse?

Exocytosis Signup and view all the answers

What type of receptors are activated by neuropeptides?

Metabotropic receptors Signup and view all the answers

What is the site of small neurotransmitter synthesis?

Synaptic terminals Signup and view all the answers

What is the purpose of Electroencephalography (EEG)?

To look at the pattern of compound brain activity across different regions of the scalp Signup and view all the answers

What is picked up by a single electrode in Electroencephalography (EEG)?

The sum of any neural activity present underneath it Signup and view all the answers

What is the function of golgi complexes in neurotransmitter synthesis?

To package neurotransmitters in vesicles Signup and view all the answers

What is stimulated by eddy currents in the brain?

Neural tissue Signup and view all the answers

What is the significance of standardized positions of electrodes in Electroencephalography (EEG)?

It enables the comparison of results across different participants Signup and view all the answers

What does the machine in Electroencephalography (EEG) pick up?

Electrical signals, action potentials, and postsynaptic potentials of the skin, eye, and brain Signup and view all the answers

What do different patterns of activity in Electroencephalography (EEG) reflect?

Different states of consciousness Signup and view all the answers

What happens to the protons in a water molecule when a strong magnetic field is applied?

They align themselves instantly in the direction of the magnetic field Signup and view all the answers

What is the signal emitted by the protons in an fMRI scan based on?

The amount of oxygenated blood supplied to active areas of the brain Signup and view all the answers

Why do different areas of the brain have different signal strengths in an MRI scan?

Because of differences in water amount in different areas of the brain Signup and view all the answers

What is the primary advantage of functional magnetic resonance imaging (fMRI) over MRI?

Non-invasive and provides functional and structural imaging Signup and view all the answers

What happens when the capacitor in a TMS machine is discharged?

A quick flow of current through the coils Signup and view all the answers

What is the main difference between the signal emitted by protons in an MRI and an fMRI scan?

The origin of the signal (water molecules or oxygenated blood) Signup and view all the answers

What is necessary for an fMRI scan to be taken?

A strong magnetic field and a task to be performed by the person Signup and view all the answers

What type of signal is emitted by water molecules in the blood supply with high oxygen levels?

A radio frequency signal Signup and view all the answers

What is the primary limitation of functional magnetic resonance imaging (fMRI)?

Low temporal resolution Signup and view all the answers

What do protons in a water molecule emit when they align themselves in a strong magnetic field?

A signal Signup and view all the answers

What is the purpose of fMRI?

To create a functional image of the brain based on oxygenated blood supply Signup and view all the answers

What is the purpose of Transcranial Magnetic Stimulation (TMS)?

To stimulate the brain non-invasively Signup and view all the answers

What is the primary difference between MRI and fMRI?

The type of image produced (structural vs functional) Signup and view all the answers

What is the name of the signal emitted by water molecules in the blood supply?

BOLD signal Signup and view all the answers

What is the effect of Transcranial Magnetic Stimulation (TMS) on the brain?

It turns different areas of the brain on or off Signup and view all the answers

What is the component of a TMS machine that prevents the flow of current?

Capacitor Signup and view all the answers

What is the main purpose of a stereotaxic atlas in lesion technique?

To provide a precise map of the brain for lesioning Signup and view all the answers

What is the function of the head holder in a stereotaxic instrument?

To hold the brain in place during surgery Signup and view all the answers

What is the term for lesioning a structure on both sides of the brain?

Bilateral lesion Signup and view all the answers

What is the significance of the 'bregma' landmark in stereotaxic surgery?

It marks the zero point on the z-axis Signup and view all the answers

What is the primary advantage of lesion technique in neuroscience research?

It allows for the study of the effects of lesioning on brain function Signup and view all the answers

What is the relationship between different stages of sleep and EEG activity?

Different stages of sleep are associated with different patterns of EEG activity Signup and view all the answers

Study Notes

Action Potential

Size of action potential is the same regardless of the incoming signal that initiated it
Net postsynaptic potential at axon initial segment determines the threshold, which is -65mV
Depolarization occurs when sodium channels open, allowing sodium ions to rush inside the cell
Repolarization occurs when potassium channels open, allowing potassium ions to leave the neuron
Refractory period is the duration in which no amount of stimulation can stimulate another action potential

Neurotransmitter Release and Activation

Release of neurotransmitters (NTs) occurs in response to an influx of calcium ions in the presynaptic membrane
Small NTs are released rapidly in pulses due to their proximity to the presynaptic membrane
Neuropeptides are released slowly and gradually due to their distance from calcium channels
NTs bind to postsynaptic receptors, which are proteins containing the binding site for a few NTs
Ionotropic receptors are quick to activate and have short-lasting effects, while metabotropic receptors are more common and have longer-lasting effects

Functional Neuroimaging

Functional magnetic resonance imaging (fMRI) measures changes in blood oxygenation in response to neural activity
Blood oxygen level-dependent (BOLD) signal is the change in magnetic signal in response to changes in oxygenation
Advantages of fMRI include non-invasiveness, provision of functional and structural imaging, and better spatial resolution
Disadvantages include low temporal resolution, making it unsuitable for studying changes in activity over time

Transcranial Magnetic Stimulation (TMS)

TMS stimulates specific regions of the cerebral cortex by inducing a magnetic field
Composed of a capacitor that holds a charge, which is suddenly discharged to create a large current flow
The magnetic field around the coils induces a current in the neural tissue underneath

Lesion Technique

Lesion technique involves damaging, destroying, or inactivating part of the brain
Stereotaxic surgery is used to precisely position experimental devices into the brain
Stereotaxic atlas is a map of the brain used to guide the surgery
Lesions can be done unilaterally (on one side) or bilaterally (on both sides)

Electrophysiological Recordings

Intracellular unit recording allows researchers to record moment-by-moment changes in the membrane potential of a single neuron
Extracellular unit recording records electrical disturbances in the extracellular environment, indicating neural activity but not providing moment-by-moment membrane potential changes

Chemical Communication between Cells

Chemical communication between two cells takes place in the space between the presynaptic neuron and the postsynaptic neuron.
Neurotransmitters (chemical messengers) are released by the presynaptic neuron and bind to receptors on the postsynaptic neuron.
This binding causes a change in the resting membrane potential of the postsynaptic neuron, which can be either excitatory (less negative or more positive) or inhibitory (more negative or less positive).

Postsynaptic Potentials

Postsynaptic potentials are graded, meaning the size of the potential depends on the strength of the signal.
Two characteristics of postsynaptic potentials:
- They travel very fast.
- They are decremental, meaning their size decreases as they travel away from the area of origin.

Integration of Postsynaptic Potentials

A single postsynaptic neuron receives thousands of signals from presynaptic neurons, which are a mix of excitatory and inhibitory.
These signals are integrated to produce a net effect at the axon initial segment.
Integration can occur over space (spatial summation) or time (temporal summation).
The purpose of integration is to decide whether to activate an action potential or not.

Action Potential

An action potential is a very short-lasting change in the membrane potential that travels in one direction along the axon.
It can travel in one direction due to the absolute refractory period.
Action potential frequency, not amplitude, indicates the strength of the signal.
Action potentials are non-decremental and can travel long distances without decreasing in size.

Effects of Myelination

Myelination allows for saltatory conduction, where the action potential jumps from one node of Ranvier to another.
This increases the speed of conduction and allows the potential to travel long distances quickly.

Interneurons

Interneurons are a special case, with either no axons or small axons.
Conduction takes place mostly through postsynaptic potentials rather than action potentials.

Differences between Action Potential and Postsynaptic Potential

Action potential size is not graded and is not dependent on the strength of the incoming signal.
Action potentials have a fixed direction of travel, whereas postsynaptic potentials can travel in multiple directions.

Synaptic Structure

Axodendritic synapse: the ends of an axon contact the dendrites of a neuron.
Other types of synapses: axosomatic, axoaxonic, axomyelenic, and dendrodendritic.
Synapses can be broadly categorized into two types: directed and non-directed.

Neurotransmitters

Monoamines: catecholamines (made from tyrosine) and indolamines (made from tryptophan).
Acetylcholine: released from neurons onto skeletal muscles, causing them to contract.
Unconventional neurotransmitters: soluble gases (nitric oxide and carbon monoxide), endocannabinoids (anandamide), and neuropeptides.
Unconventional neurotransmitters affect the presynaptic neuron rather than the postsynaptic neuron.

Research Methods

Techniques to visualize the brain: computed tomography (CT).
CT scans provide researchers with the ability to visualize internal structures of the brain.

Varicosities and Neurotransmitter Synthesis

Varicosities give axons the appearance of beads on a string
Two broad categories of neurotransmitters (NTs):
- Small NTs:
Made in the cytoplasm of synaptic terminals
Packaged in vesicles by Golgi complexes in the terminals
Activate ionotropic receptors
- Large NTs (neuropeptides):
Small chains of amino acids (3-36)
Made in the cytoplasm of the cell body using ribosomes
Placed in spherical vesicles by Golgi complexes in the cell body
Transported from cell body to synaptic terminal through microtubules
Activate metabotropic receptors
Coexistence: a single neuron usually contains a neuropeptide and a small NT

Neurotransmitter Release

Exocytosis: synaptic vesicles release contents into the synapse
Vesicle membrane fuses with the presynaptic membrane
Signals are released, generating a structural image

Functional Magnetic Resonance Imaging (fMRI)

Measures signal based on oxygenated blood supply to active areas of the brain
Uses magnetic properties of oxygenated blood to create a functional image
Advantages:
- Non-invasive
- Provides functional and structural imaging
- Better spatial resolution
Disadvantages:
- Low temporal resolution
- Not used to look at changes in activity over time

Technique to Stimulate the Brain

Transcranial Magnetic Stimulation (TMS):
- Turns different areas of the brain on or off
- Stimulates regions of the cerebral cortex
- Uses a capacitor to hold a charge, then releases it quickly
- Creates a magnetic field, inducing electrical currents (eddy currents) in the brain
- Eddy currents stimulate neural tissue

Psychophysiological Recording

Electroencephalography (EEG):
- Used to study compound brain activity across different regions of the scalp
- Participant wears a cap with electrodes placed at standardized positions
- Electrodes pick up neural activity, action potentials, and postsynaptic potentials
- Purposes: look at pattern of activity, not individual activities
- Different patterns reflect different states of consciousness (e.g., sleep stages)

Lesion Technique

Part of the brain is damaged, destroyed, or inactivated
Stereotaxic surgery:
- Used to precisely position experimental devices into the brain
- Requires a stereotaxic atlas (map of the brain) and stereotaxic instrument
- Instrument contains a head holder and an electrode holder
- Electrode can be moved in the x, y, and z directions
Lesions can be done to the brain on either side

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Description

Learn about the mechanisms of action potential in neurons, including the threshold, depolarization, repolarization, and refractory period.