Neuroscience: Neurons and Membrane Potential

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Questions and Answers

What characterizes multipolar neurons?

They have many dendrites. (correct)

They lack axons.

They only transmit sensory information.

They have a single dendrite.

What contributes to the resting membrane potential of a neuron?

An even distribution of sodium and potassium ions.

The uniform concentration of ions inside and outside the cell.

The higher concentration of Na+ and Cl- outside the cell. (correct)

A constant movement of K+ ions into the cell.

How is the resting membrane potential primarily maintained?

By the passive leakage of Na+ ions into the cell.

By the trapping of K+ ions in the extracellular fluid.

Through active transport of anions across the membrane.

Through the movement of sodium and potassium ions. (correct)

What is the role of nongated ion channels in resting membrane potential?

They are always open and facilitate the passage of certain ions. Signup and view all the answers

What occurs during the process of simple diffusion in neurons?

Na+ and Cl- ions move inside the cell, while K+ and A- remain outside. Signup and view all the answers

What effect does aging have on white matter according to DTI studies?

It causes deterioration of white matter leading to slower processing. Signup and view all the answers

Which imaging method allows for the study of receptor distribution and metabolic activity?

Positron emission tomography (PET) Signup and view all the answers

In the context of the dopamine hypothesis of schizophrenia, what role does raclopride play?

It is a competitive antagonist that emits radiation. Signup and view all the answers

What is indicated by a higher displacement of raclopride in the striatum during PET studies?

Higher dopamine release into the striatum. Signup and view all the answers

Why is PET considered to have lower spatial resolution compared to MRI?

It is unable to distinguish between closely located brain structures. Signup and view all the answers

What is the primary function of the sodium-potassium pump?

To maintain resting membrane potential by moving ions across the membrane. Signup and view all the answers

What occurs during the depolarization phase of an action potential?

Sodium ions rush into the neuron due to a concentration gradient. Signup and view all the answers

Which statement describes an IPSP?

A postsynaptic potential that inhibits action potential firing. Signup and view all the answers

How do voltage-gated ion channels respond during an action potential?

They open in response to changes in the membrane's voltage. Signup and view all the answers

What triggers the release of neurotransmitters from presynaptic neurons?

The arrival of an action potential leading to calcium influx. Signup and view all the answers

What is the role of autoreceptors in neurotransmitter regulation?

They provide feedback to decrease neurotransmitter release. Signup and view all the answers

During the repolarization phase of an action potential, which ion is primarily exiting the neuron?

Potassium ions Signup and view all the answers

What distinguishes EPSPs from IPSPs?

EPSPs increase the likelihood of action potential firing, while IPSPs decrease it. Signup and view all the answers

What criteria must a substance meet to be classified as a neurotransmitter?

It must be deactivated within the synaptic cleft. Signup and view all the answers

Which phase occurs when the neuron's membrane potential becomes more positive than resting potential?

Depolarization Signup and view all the answers

What is spatial integration in the context of postsynaptic potentials?

The summation of potentials arriving at various locations on the neuron. Signup and view all the answers

Which neurotransmitter release mechanism is associated with calcium influx?

Exocytosis from presynaptic vesicles Signup and view all the answers

How does the sodium-potassium pump contribute to action potential generation?

By maintaining the resting membrane potential between action potentials. Signup and view all the answers

What is the effect of hyperpolarization on a neuron?

It creates a more negative membrane potential, inhibiting action potentials. Signup and view all the answers

What is the primary role of ionotropic receptors?

They directly open ion-gated channels upon neurotransmitter binding. Signup and view all the answers

How do neuromodulators differ from neurotransmitters?

Neuromodulators modulate the activity of groups of neurons over a longer timescale. Signup and view all the answers

What is a key function of G-protein coupled receptors (GPCRs)?

They activate second messenger pathways upon neurotransmitter binding. Signup and view all the answers

What happens when neurotransmitters bind to autoreceptors?

They inhibit the release of subsequent neurotransmitters. Signup and view all the answers

Which pathway is primarily associated with reward and drug-taking behavior?

Meso-limbic pathway Signup and view all the answers

What is neuroplasticity most fundamentally about?

The ability of the brain to reorganize and form new synaptic connections. Signup and view all the answers

Which brain regions are known to produce new neurons in adults?

Hippocampus and subventricular zone Signup and view all the answers

What role do second messengers typically play in cellular signaling?

They amplify the signal within the cell following receptor activation. Signup and view all the answers

How does alcohol influence fetal brain development?

It can disrupt various developmental processes crucial for brain formation. Signup and view all the answers

What is the primary measurement in functional MRI (fMRI) scans?

Blood oxygenation level and blood flow changes. Signup and view all the answers

What is a consequence of the drug-induced changes occurring as a teratogen during pregnancy?

Disruption of critical periods of neuron proliferation and connectivity. Signup and view all the answers

What is a defining characteristic of metabotropic receptors?

They trigger a cascade of secondary signaling events within the cell. Signup and view all the answers

What effect do cytoarchitectural constraints have on brain connectivity?

They restrict the ability to form new connections, especially outside critical periods. Signup and view all the answers

Study Notes

Neurons

Specialized cells that receive, process, and convey information in the form of electrical signals.
Polar cells: Possess a defined directionality in their structure and function.
Multipolar neurons: Have multiple dendrites and an axon.
Dendrites: Receive incoming signals from other neurons.
Synaptic terminals: Specialized structures at the end of axons where signals are transmitted to other neurons.
Dendrites and synaptic terminals contain: mitochondria, rough endoplasmic reticulum (RER), ribosomes, and Golgi apparatus.
Mitochondria are transported back and forth between dendrites and synaptic terminals.

Resting Membrane Potential

The electrical potential difference across the neuronal membrane when the neuron is not transmitting a signal.
Outside the cell: 0 mV.
Inside the cell: -70 mV.
Maintained by an uneven distribution of ions (sodium, potassium, chloride, and anions).
Na+ and Cl- are more concentrated outside the cell, K+ and A- are more concentrated inside.
Sodium-potassium pump: actively moves 3 Na+ ions out of the cell and 2 K+ ions into the cell, contributing to the resting membrane potential.

Factors Maintaining Resting Membrane Potential

Simple diffusion: Ions move down their concentration gradients from areas of high concentration to low concentration.
Electrostatic pressure: Opposite charges attract, and like charges repel.
Differential permeability: The neuron's membrane is selectively permeable to different ions, allowing some ions to pass through more easily than others.
Ion pumps: Actively transport ions against their concentration gradients, requiring ATP.

Action Potential

A rapid, short-lasting change in the electrical potential across the neuronal membrane.
All-or-none principle: An action potential either occurs fully or not at all.
Threshold: The voltage (-50 mV) at which an action potential is triggered.
The strength of an action potential is always the same, but the frequency of firing can vary.

Post-synaptic Potential (PSP)

Changes in the electrical potential of a postsynaptic neuron in response to neurotransmitter release from a presynaptic neuron.
Excitatory post-synaptic potential (EPSP): Depolarizes the neuron, making it more likely to fire an action potential.
Inhibitory post-synaptic potential (IPSP): Hyperpolarizes the neuron, making it less likely to fire an action potential.
Temporal integration: Summation of PSPs that occur close in time.
Spatial integration: Summation of PSPs that occur at different locations on the neuron.

Action Potential Process

Depolarization: The membrane potential becomes less negative, moving towards 0 mV.
Repolarization: The membrane potential returns to its resting state.
Hyperpolarization: The membrane potential becomes more negative than the resting potential.

Steps in Action Potential:

Reaching threshold: Depolarization reaches -50 mV, triggering the opening of voltage-gated sodium channels.
Sodium influx: Sodium ions rush into the cell, driven by concentration gradient and electrostatic pressure, rapidly depolarizing the neuron.
Potassium efflux: As the membrane potential reaches approximately +40 mV, sodium channels close, and voltage-gated potassium channels open. Potassium ions flow out of the cell, repolarizing the membrane.
Hyperpolarization: Potassium channels close gradually, allowing for a brief period of hyperpolarization.
Restoring resting potential: The sodium-potassium pump actively restores the resting membrane potential.

Synapse

The junction between two neurons where communication occurs via the release of neurotransmitters.

Neurotransmitters (NTs)

Chemical messengers synthesized in presynaptic cells, stored in vesicles, and released into the synaptic cleft in response to an action potential.

Synaptic Transmission

Action potential arrives at the presynaptic terminal.
Calcium influx: Voltage-gated calcium channels open, allowing calcium ions to enter the terminal.
Vesicle fusion and neurotransmitter release: Calcium influx triggers vesicle fusion with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft..
Neurotransmitter binding to receptors: Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron.

Ending Synaptic Action

Neurotransmitter breakdown: Enzymes in the synaptic cleft degrade the neurotransmitter.
Reuptake: Neurotransmitters are transported back into the presynaptic terminal.
Breakdown within the cell: Neurotransmitter is broken down by enzymes within the presynaptic cell.

Autoreceptors and Heteroreceptors

Autoreceptors: Localized on presynaptic neurons; provide feedback on the amount of neurotransmitter released by binding with the same neurotransmitter.
Heteroreceptors: Localized on presynaptic neurons; respond to neurotransmitters released by other neurons or chemicals released from postsynaptic neurons.

Criteria for Neurotransmitters

Synthesized within the neuron.
Released in response to depolarization.
Binds to receptors on postsynaptic cells, influencing their activity.
Deactivated in the synaptic cleft.

Steps in Neurotransmitter Action

Synthesis from precursors with the help of enzymes.
Storage in vesicles.
Degradation of leaked neurotransmitters by enzymes.
Release into synapse by vesicle fusion.
Binding to autoreceptors, inhibiting future release.
Binding to postsynaptic receptors, leading to cellular changes..
Deactivation by reuptake or enzymatic degradation.

Neuromodulators

Chemicals released by neurons that modulate the activity of groups of neurons, acting over longer timescales than neurotransmitters.
They can influence either presynaptic or postsynaptic activity.
They are usually released in larger amounts and diffuse farther than neurotransmitters.
Examples: Endorphins, cannabinoids.

Receptors

Protein molecules in the postsynaptic membrane to which neurotransmitters bind.

Ionotropic Receptors

Binding sites are directly coupled to ion channels.
Neurotransmitter binding leads to conformational changes in the receptor proteins, opening the ion channels.
Allows ion influx/efflux, changing membrane potential.

Metabotropic Receptors

Indirectly influence the activity of ion channels through G protein-coupled receptors (GPCRs).
Neurotransmitter binding activates a G protein subunit, which can:
- Activate/inhibit nearby ion channels.
- Initiate second messenger cascades.

Second Messengers

Molecules synthesized within the cell in response to the activation of GPCRs.
Can influence the functioning of ion channels and receptors, promoting long-lasting cellular changes.
Example: cAMP (cyclic adenosine monophosphate)

Brain Circuits

Groups of interconnected neurons that work together to perform specific functions.

Dopamine Pathways:

Nigrostriatal pathway: Involved in movement control, originating from the substantia nigra and projecting to the striatum.
Mesolimbic pathway: Involved in reward and motivation, originating from the ventral tegmental area (VTA) and projecting to the nucleus accumbens (NAC) and the prefrontal cortex (PFC).
Mesocortical pathway: Involved in motivation and emotions, originating from the VTA and projecting to the cortex (including the PFC).
Tuberoinfundibular pathway: Involved in hormone regulation, originating from the hypothalamus and projecting to the pituitary gland.

Brain Development

Proliferation: Generation of new neurons and glial cells.
Migration: Movement of newly formed neurons to their final destination in the brain.
Differentiation: Specialization of neurons into distinct types.
Synaptogenesis: Formation of connections between neurons (synapses).
Myelination: Formation of a myelin sheath around axons, increasing signal transmission speed.

Teratogens

Substances that can interfere with the development of the fetus, including alcohol, drugs, and viruses.

Neurogenesis

The birth of new neurons in the adult brain.
Occurs in the hippocampus and subventricular zone.

Neuroplasticity

The brain's ability to change its structure and function in response to experience.
Allows for learning and adaptation.
Some brain connections are more stable than others and are more difficult to modify beyond critical periods of development.

Brain Imaging Techniques

Tools used to study brain function and structure.

Magnetic Resonance Imaging (MRI)

Non-invasive technique that uses magnets and radio waves to generate detailed images of the brain.
Provides good spatial resolution and contrast resolution.

Functional Magnetic Resonance Imaging (fMRI)

Measures brain activity by detecting changes in blood flow, as active brain regions require more oxygen.
Provides good spatial resolution but limited temporal resolution.

Diffusion Tensor Imaging (DTI)

Measures the diffusion of water molecules in the brain, revealing the direction of white matter fiber bundles.
Provides information about the integrity of white matter and its role in signal transmission.

Positron Emission Tomography (PET)

Uses radioactive tracers to study brain activity.
Tracers bind to specific receptors or metabolic pathways to quantify their activity.
Provides information about receptor distribution, metabolic activity, and changes in receptors over time.

Dopamine Hypothesis of Schizophrenia

Posits that schizophrenia is associated with an overactivity in dopaminergic pathways.
Supported by:
- Psychosis symptoms induced by stimulant drugs.
- Effectiveness of antipsychotic drugs that block dopamine receptors.
- PET studies showing increased dopamine release in the striatum of patients with schizophrenia.

Conclusion

The study of the nervous system continues to expand our understanding of how neurons communicate and how this communication impacts behavior, learning, and various neurological conditions.

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Description

This quiz covers the fundamental concepts of neurons and resting membrane potential. It addresses the structure and function of specialized neurons, including dendrites and synaptic terminals, as well as the electrical properties of neuronal membranes. Test your understanding of these essential topics in neuroscience.