Neuroscience Chapter: Resting Membrane Potential

Questions and Answers

What is the typical range for resting membrane potential in neurons?

Negative 70 to negative 90 millivolts (correct)

Negative 50 to negative 70 millivolts

Negative 60 to negative 80 millivolts

Negative 90 to negative 110 millivolts

Resting membrane potential exists only in neurons.

False

What role do sodium-potassium ATPases play in maintaining resting membrane potential?

They pump three sodium ions out and two potassium ions into the cell.

The resting membrane potential is typically around _____ millivolts.

negative 70 Signup and view all the answers

Match the following components with their functions in maintaining resting membrane potential:

Sodium-Potassium ATPases = Pumps sodium out and potassium in Leaky Potassium Channels = Allows passive potassium flow Leaky Sodium Channels = Allows sodium ions to flow into the cell Ion Concentration Gradients = Drives movement of ions based on concentration Signup and view all the answers

What is the main effect of leaky potassium channels on resting membrane potential?

Increase in internal negativity Signup and view all the answers

The concentration of sodium is higher inside the cell than outside.

False Signup and view all the answers

What is the Nernst potential equation for potassium?

E(K) = 61.5 / z × log([K outside] / [K inside]) Signup and view all the answers

The typical concentration of potassium outside the cell is _____ mM.

5 Signup and view all the answers

Why does the permeability of the membrane to potassium contribute more to resting potential than that to sodium?

The membrane is more permeable to potassium than sodium Signup and view all the answers

What is the threshold voltage for action potential stimulation?

-55 millivolts Signup and view all the answers

Potassium has a greater impact on resting potential stabilization than sodium.

True Signup and view all the answers

What is the typical resting membrane potential of a neuron?

-70 millivolts Signup and view all the answers

During depolarization, the membrane potential moves towards ________ millivolts.

positive 30 Signup and view all the answers

Match the following ionic movements with their effects on the membrane potential:

Sodium influx = Depolarization Potassium efflux = Hyperpolarization Calcium influx = Neurotransmitter release Chloride influx = Inhibition Signup and view all the answers

What happens during the absolute refractory period?

No stimulus can initiate another action potential Signup and view all the answers

Graded potentials only move the membrane potential further from the action potential threshold.

False Signup and view all the answers

What role do voltage-gated calcium channels play during an action potential?

They allow calcium to enter the axon terminal for neurotransmitter release. Signup and view all the answers

The process of exocytosis in neurotransmitter release is facilitated by ________ binding to SNARE proteins.

calcium Signup and view all the answers

Which of the following describes hyperpolarization?

Membrane potential becomes more negative than the resting state Signup and view all the answers

What is the main consequence of a cell reaching a membrane potential of negative 55 millivolts?

Action potential is triggered. Signup and view all the answers

Graded potentials always lead to action potentials.

False Signup and view all the answers

What effect do excitatory postsynaptic potentials (EPSPs) have on the membrane potential?

They bring the membrane potential closer to the threshold for action potentials. Signup and view all the answers

During depolarization, the cell's internal charge becomes more ________ as sodium ions enter.

positive Signup and view all the answers

Match the following voltages with their corresponding actions or states:

-70 mV = Resting membrane potential -55 mV = Threshold potential +30 mV = Peak depolarization -90 mV = Hyperpolarization Signup and view all the answers

Which ion influx is primarily responsible for initiating the action potential?

Sodium (Na+) Signup and view all the answers

Hyperpolarization increases the electrical charge of the inside of the cell above the resting potential.

False Signup and view all the answers

What role do voltage-gated potassium channels play after an action potential?

They help return the membrane potential back to resting state by allowing K+ to exit. Signup and view all the answers

The absolute refractory period occurs after the ________ of an action potential.

peak depolarization Signup and view all the answers

Which mechanism allows neurotransmitter release into the synapse?

Exocytosis Signup and view all the answers

What primarily establishes the negative charge inside the cell?

Potassium efflux through leaky channels Signup and view all the answers

The sodium-potassium ATPase pump moves more sodium ions into the cell than potassium ions it moves out.

False Signup and view all the answers

State the typical resting membrane potential in millivolts.

-70 Signup and view all the answers

The _____ concentration of sodium is higher outside the cell.

sodium Signup and view all the answers

Match the ion with its primary concentration location.

Sodium = Outside the cell Potassium = Inside the cell Calcium = Outside the cell Chloride = Outside the cell Signup and view all the answers

Which of the following ions primarily dictates the resting membrane potential?

Potassium Signup and view all the answers

Leaky sodium channels have a higher permeability compared to leaky potassium channels.

False Signup and view all the answers

What is the role of leaky potassium channels in neurons?

They allow potassium ions to flow in and out passively, creating a more negative internal environment. Signup and view all the answers

The equilibrium potential for potassium based on typical concentrations is approximately _____ millivolts.

-90 Signup and view all the answers

Which mechanism helps maintain the ion concentration gradients essential for resting membrane potential?

Sodium-Potassium ATPases Signup and view all the answers

What function do astrocytes perform regarding potassium ions during action potentials?

Absorb excess potassium from extracellular space Signup and view all the answers

Astrocytes are only found in the central nervous system.

False Signup and view all the answers

What are the three layers of the blood-brain barrier?

Endothelial cells with tight junctions, basal lamina, foot processes from astrocytes Signup and view all the answers

The area postrema samples blood for _____ and triggers a vomiting response.

toxins Signup and view all the answers

Match the following brain regions with their function regarding the blood-brain barrier:

Area postrema = Triggers vomiting response Osmoreceptors = Regulates fluid balance Hypothalamic-pituitary axis = Hormone signaling Signup and view all the answers

Which substance can easily cross the blood-brain barrier?

Oxygen Signup and view all the answers

Astrocytes increase tight junction formation within the blood-brain barrier by secreting growth factors.

True Signup and view all the answers

What neurotransmitter do astrocytes help regulate by converting it to glutamine?

Glutamate Signup and view all the answers

Astrocytes can redistribute excess potassium through _____ between each other.

gap junctions Signup and view all the answers

What is one of the primary functions of the blood-brain barrier?

To protect the brain from toxins Signup and view all the answers

Which of the following cell types is responsible for myelinating axons in the central nervous system?

Oligodendrocytes Signup and view all the answers

Glutamine is converted back into glutamate in astrocytes before being transported to neurons.

False Signup and view all the answers

What is the role of microglia in the central nervous system?

Microglia are immune cells that respond to pathogens and neuronal damage. Signup and view all the answers

Astrocytes regulate glucose levels for neurons by breaking down glycogen into ________.

glucose Signup and view all the answers

Match the types of cells with their corresponding roles in the nervous system:

Astrocytes = Regulate nutrient metabolism Schwann Cells = Myelinate axons in PNS Oligodendrocytes = Myelinate axons in CNS Ependymal Cells = Produce and circulate cerebrospinal fluid Signup and view all the answers

Which type of fiber is characterized by having a high conduction velocity due to high myelination?

Type A fibers Signup and view all the answers

Schwann cells are unable to regenerate after damage.

False Signup and view all the answers

What is the composition of myelin?

Myelin is mainly composed of lipids and proteins. Signup and view all the answers

The gaps between myelin sheaths on axons are known as ________.

nodes of Ranvier Signup and view all the answers

What happens to conduction velocity as axon diameter increases?

Conduction velocity increases Signup and view all the answers

What type of cells are found only in the central nervous system (CNS)?

Astrocytes Signup and view all the answers

The blood-brain barrier allows for the easy passage of charged ions and larger molecules without transport proteins.

False Signup and view all the answers

What is the primary function of astrocytes in relation to potassium ions during action potentials?

To absorb excess potassium and redistribute it. Signup and view all the answers

The blood-brain barrier consists of three layers: endothelial cells, basal lamina, and ________ processes from astrocytes.

foot Signup and view all the answers

Match the following regions of the brain with their function related to the blood-brain barrier:

Area postrema = Triggers vomiting response Osmoreceptors = Regulates fluid balance Hypothalamic-pituitary axis = Hormone signaling Medulla = Autonomic functions Signup and view all the answers

Which substance can easily cross the blood-brain barrier?

Lipid-soluble substances Signup and view all the answers

Astrocytes enhance the formation of tight junctions within the blood-brain barrier by secreting growth factors.

True Signup and view all the answers

What enzyme do astrocytes use to convert excess glutamate to glutamine?

Glutamine synthetase Signup and view all the answers

Astrocytes play a role in regulating _______, which is crucial for neurotransmission in the brain.

glutamate Signup and view all the answers

What is one primary function of the blood-brain barrier?

To control the movement of molecules between blood and nervous tissue Signup and view all the answers

What is the primary function of astrocytes in glucose metabolism for neurons?

They regulate glucose transport and storage. Signup and view all the answers

Oligodendrocytes can regenerate after injury in the central nervous system.

False Signup and view all the answers

What is the main consequence of demyelination in the peripheral nervous system?

Guillain-Barre Syndrome Signup and view all the answers

Astrocytes assist in the synthesis of GABA from glutamate via the enzyme ________.

glutamate decarboxylase Signup and view all the answers

Match the following types of cells with their primary functions:

Astrocytes = Regulate nutrient metabolism and neurotransmitter levels Schwann Cells = Myelinate axons in the peripheral nervous system Microglia = Act as immune cells in the central nervous system Ependymal Cells = Produce and circulate cerebrospinal fluid Signup and view all the answers

Which type of transporter is involved in glucose uptake in astrocytes?

GLUT1 Signup and view all the answers

Nodes of Ranvier are concentrated areas of potassium channels on myelinated axons.

False Signup and view all the answers

What is the role of the neurolemma in Schwann cells?

Crucial for regeneration following damage Signup and view all the answers

Microglia respond to pathogens by releasing ________ substances.

pro-inflammatory Signup and view all the answers

Which type of neuron fibers is associated with the fastest conduction velocity?

Type A fibers Signup and view all the answers

What is the role of dendrites in a neuron?

Act as the receptive zone for incoming signals. Signup and view all the answers

The cell body of a neuron is mainly involved in conducting electrical impulses.

False Signup and view all the answers

What process involves the transcription of DNA into mRNA in neurons?

Protein synthesis Signup and view all the answers

The region where the axon begins is known as the __________.

axon hillock Signup and view all the answers

Match the following neuronal components with their functions:

Dendrites = Receive incoming signals Axon = Conduct electrical impulses away from the cell body Axon terminals = Release neurotransmitters Cell body = Synthesize proteins and maintain cell functions Signup and view all the answers

Which motor protein facilitates anterograde transport in neurons?

Kinesin Signup and view all the answers

Action potentials are mainly propagated through the axon by the movement of potassium and sodium ions.

True Signup and view all the answers

Which part of the neuron contains the nucleus?

Cell body Signup and view all the answers

Neurotransmitters are packaged into vesicles by the __________ for delivery along the axon.

Golgi apparatus Signup and view all the answers

What type of potential do EPSPs represent?

Graded potential leading to depolarization Signup and view all the answers

Which transport mechanism is used by certain viruses like polio and rabies to move toward the cell body?

Dynein Signup and view all the answers

Nerve growth factors are transported retrogradely to stimulate the cell body for neuronal repair.

True Signup and view all the answers

What is the primary role of the axon terminal?

Neurotransmitter release and reuptake Signup and view all the answers

The _____ concentration of potassium is higher inside the neuron compared to outside.

K+ Signup and view all the answers

Match the following types of neurons with their functions:

Sensory neurons = Carry signals from receptors to the CNS Motor neurons = Transmit signals from the CNS to effector organs Interneurons = Connect sensory and motor pathways Multipolar neurons = Found in motor cortex and cerebellum Signup and view all the answers

What is the role of calcium ions during neurotransmitter release?

Triggers vesicle fusion with the plasma membrane Signup and view all the answers

SSRIs work by promoting the enzymatic degradation of serotonin in the synapse.

False Signup and view all the answers

What outcome occurs when the varicella zoster virus reactivates?

Production of viral particles affecting skin tissue Signup and view all the answers

Interneurons are essential for mediating _____ actions within the spinal cord.

reflex Signup and view all the answers

During which phase of action potentials does sodium ion influx occur?

Depolarization Signup and view all the answers

Study Notes

Resting Membrane Potential

Defined as the voltage difference across the cell membrane when a neuron is at rest.
Exists in all cell types, not just neurons, highlighting its universal biological significance.
Typical range for resting membrane potential in neurons is between negative 70 to negative 90 millivolts, with negative 70 millivolts being the average.

Mechanisms Contributing to Resting Membrane Potential

Sodium-Potassium ATPases
- Pumps three sodium ions out of the cell and two potassium ions into the cell.
- Establishes a slight negative charge inside the cell and maintains ion concentration gradients: higher sodium outside and higher potassium inside.
Leaky Potassium Channels
- Always open, allowing potassium ions to flow in and out of the cell passively.
- Higher potassium concentration inside drives potassium ions to exit, leading to a more negative internal environment.
- Loss of potassium creates unoccupied negative charges (anions) inside, increasing negativity up to around negative 90 millivolts.
Leaky Sodium Channels
- Also allow sodium ions to flow, but the permeability of the membrane to potassium is much higher than that to sodium.
- Sodium influx contributes less to resting membrane potential adjustment, as much of its concentration remains outside the cell.

Ion Concentration Gradients

Sodium concentration is higher outside, while potassium concentration is higher inside due to the action of pumps.
The movement of ions occurs based on their respective concentration gradients, contributing to the overall membrane potential.

Nernst Potential

Calculated for various ions (e.g., potassium and sodium) to determine their equilibrium potential across the membrane.
For potassium:
- Equation used: E(K) = 61.5 / z × log([K outside] / [K inside])
- Typical concentrations: 5 mM outside, 150 mM inside yield approximately negative 90 millivolts.
For sodium:
- Equation: E(Na) = 61.5 / z × log([Na outside] / [Na inside])
- Typical concentrations: 140 mM outside, 10 mM inside yield approximately positive 70 millivolts.

Overall Impact

The resting membrane potential is determined primarily by the equilibrium potentials of potassium and sodium.
Significant shifts in membrane potential are primarily due to changes in permeability to potassium, rather than sodium, emphasizing the greater impact of potassium on resting potential stabilization.### Membrane Potentials
Resting membrane potential is typically around negative 70 millivolts.
The equilibrium potential for potassium influences the cell voltage when potassium ions move out.
A cell with 90% permeability to potassium and 10% to sodium would average near negative 70 millivolts.

Graded Potentials

Graded potentials adjust the resting membrane potential towards the threshold for action potentials.
Threshold voltage for action potential stimulation is approximately negative 55 millivolts.
Depolarization moves the membrane potential closer to threshold; hyperpolarization makes it more negative.
Excitatory postsynaptic potentials (EPSPs) bring the membrane potential closer to threshold.
Inhibitory postsynaptic potentials (IPSPs) move the potential further from threshold.

Neuronal Communication

Presynaptic neurons release neurotransmitters (e.g., glutamate for EPSPs, GABA for IPSPs) at the synapse to influence the postsynaptic neuron.
Ligand-gated ion channels open in response to neurotransmitter binding, allowing ion flow.
Sodium (Na+) and calcium (Ca2+) influx increases the cell's positive charge.
Chloride (Cl-) influx or potassium (K+) efflux makes the cell interior more negative, inducing hyperpolarization.

Summation of Potentials

EPSPs and IPSPs compete to influence membrane potential, with the aim to have more EPSPs to trigger action potentials.
Temporal summation involves rapid repeated firing from a single presynaptic neuron, cumulatively raising potential.
Spatial summation involves simultaneous firing from multiple presynaptic neurons, increasing total EPSP effect.

Threshold and Action Potential

Action potentials are triggered when the threshold of negative 55 millivolts is reached at the axon hillock.
Voltage-gated sodium channels, concentrated at the axon hillock, open rapidly upon reaching threshold.
Sodium influx during action potential can elevate membrane potential to positive 30 millivolts, reversing the polarity.
Once the threshold is reached, voltage-gated channels create an all-or-nothing response, triggering the action potential.### Action Potential and Ion Channels
Resting Membrane Potential: Neurons have a resting membrane potential around -70 millivolts.
Threshold Potential: An action potential is initiated when the membrane potential reaches approximately -55 millivolts.
Voltage-Gated Sodium Channels:
- Activation gate opens at -55 millivolts, allowing sodium (Na+) ions to rush in.
- Positive feedback leads to rapid depolarization, peaking around +30 millivolts.
- Inactivation gate closes at +30 millivolts, preventing further Na+ entry.

Depolarization and Action Potential Propagation

Depolarization: Movement from a negative to a positive internal charge, specifically when Na+ enters the cell.
Propagation: The depolarizing wave moves along the axon towards the terminal bulb.
Voltage-Gated Calcium Channels: Activated at +30 millivolts, allowing calcium (Ca2+) to enter the axon terminal necessary for neurotransmitter release.

Neurotransmitter Release Mechanism

Synaptic Vesicle Fusion: Calcium binds to SNARE proteins, facilitating the fusion of vesicles with the cell membrane.
Exocytosis: Release of neurotransmitters into the synaptic space to interact with adjacent neurons.

Repolarization and Hyperpolarization

Repolarization: Returning the membrane potential back to resting state (-70 millivolts).
Voltage-Gated Potassium Channels: Open at +30 millivolts, allowing potassium (K+) to exit and move the potential towards -90 millivolts.
Hyperpolarization: Occurs when the potential goes below -70 millivolts due to excess K+ leaving before returning to resting potential.

Key Definitions

Depolarization: Making the inside of the cell more positive.
Repolarization: Returning from a positive back to a negative resting potential.
Hyperpolarization: Increasing negativity beyond the resting potential.

Recovery to Resting Membrane Potential

Restoration Mechanisms: Involvement of sodium-potassium ATPase and leak channels help stabilize the membrane potential back to -70 millivolts.
Refractory Periods:
- Absolute Refractory Period: Follows peak depolarization where no stimulation can initiate another action potential, regardless of stimulus strength.
- Relative Refractory Period: Occurs after the absolute phase when a stronger-than-normal stimulus is needed to initiate a new action potential.

Summary of Voltage-Gated Channel States

At Rest: Activation gate closed, inactivation gate open.
During Depolarization: Activation gate opens, inactivation gate begins to close.
At Peak Depolarization: Activation gate open, inactivation gate closed.
During Repolarization: Activation gate begins to close, K+ channels open.
Post Action Potential: Recovery to resting state configuration upon reaching -70 millivolts.

Resting Membrane Potential

Voltage difference across the cell membrane in a resting neuron, typically around -70 to -90 millivolts.
Universal phenomenon observed in all cell types, not just neurons.

Mechanisms Contributing to Resting Membrane Potential

Sodium-Potassium ATPases: Pumps 3 Na+ ions out and 2 K+ ions in, creating a slight negative interior and maintaining concentration gradients.
Leaky Potassium Channels: Always open, allowing K+ to exit, enhancing negative charge inside the cell.
Leaky Sodium Channels: Less impact on resting potential due to lower permeability; primarily sodium remains outside.

Ion Concentration Gradients

Sodium concentration is higher outside (140 mM) and potassium is higher inside (150 mM).
Ion movement driven by these gradients influences membrane voltage.

Nernst Potential

Equilibrium potential calculated to determine ion movement across membranes.
Potassium: E(K) calculation shows potential around -90 mV based on typical ion concentrations.
Sodium: E(Na) is approximately +70 mV based on differing concentrations inside and outside.

Overall Impact

Resting membrane potential highly influenced by potassium equilibrium potential and its permeability.
Shifts in membrane potential primarily occur due to changes in potassium permeability rather than sodium.

Membrane Potentials

Average resting membrane potential is about -70 mV.
Higher potassium permeability results in a more stable resting potential around this value.

Graded Potentials

Facilitate adjustments to resting potential, moving towards action potential threshold of approximately -55 mV.
EPSPs bring the potential closer to threshold while IPSPs push it further away.

Neuronal Communication

Neurotransmitters (e.g., glutamate for EPSPs, GABA for IPSPs) released by presynaptic neurons impact the postsynaptic neuron.
Ligand-gated ion channels open upon binding of neurotransmitters, allowing ion flow that alters charge inside the neuron.

Summation of Potentials

EPSPs and IPSPs balance to affect membrane potential; more EPSPs needed to trigger action potentials.
Temporal summation combines rapid sequential firing from a single neuron.
Spatial summation accumulates effects from concurrent firings of multiple neurons.

Threshold and Action Potential

Action potential triggered at -55 mV at axon hillock, where voltage-gated sodium channels open.
Rapid depolarization occurs as Na+ influx raises potential to +30 mV, reversing polarity.

Action Potential and Ion Channels

Resting membrane potential around -70 mV; action potential initiation requires reaching the threshold.
Voltage-gated sodium channels rapidly open at threshold, allowing Na+ entry and causing depolarization.

Depolarization and Action Potential Propagation

Depolarization occurs when Na+ floods into cells, creating a positive charge.
Propagation of depolarization signals travels along the axon toward the terminal.
Voltage-gated calcium channels open at +30 mV, critical for neurotransmitter release.

Neurotransmitter Release Mechanism

Calcium binds to SNARE proteins aiding vesicle fusion with the membrane for exocytosis of neurotransmitters.

Repolarization and Hyperpolarization

Repolarization brings the membrane back to about -70 mV.
Voltage-gated potassium channels open at +30 mV, causing K+ to exit and potential to drop towards -90 mV.
Hyperpolarization occurs when the potential falls below -70 mV due to excess K+ outflow.

Key Definitions

Depolarization: Inside of cell becomes more positive.
Repolarization: Return from a positive back to negative resting potential.
Hyperpolarization: Increased negativity beyond resting potential.

Recovery to Resting Membrane Potential

Sodium-potassium ATPase and leak channels help stabilize the membrane back to -70 mV.
Refractory Periods:
- Absolute Refractory Period: No further action potentials can be initiated post-depolarization.
- Relative Refractory Period: Follows absolute period; requires a stronger stimulus to generate a new action potential.

Summary of Voltage-Gated Channel States

At Rest: Activation gates closed, inactivation gate open.
During Depolarization: Activation gate opens; inactivation gate starts closing.
At Peak: Both activation gates are open; inactivation gate closes to stop Na+ entry.
During Repolarization: K+ channels open, returning the cell to a negative state.
Post Action Potential: Channels recover to resting state configuration as the potential returns to -70 mV.

Resting Membrane Potential

Voltage difference across the cell membrane in a resting neuron, typically around -70 to -90 millivolts.
Universal phenomenon observed in all cell types, not just neurons.

Mechanisms Contributing to Resting Membrane Potential

Sodium-Potassium ATPases: Pumps 3 Na+ ions out and 2 K+ ions in, creating a slight negative interior and maintaining concentration gradients.
Leaky Potassium Channels: Always open, allowing K+ to exit, enhancing negative charge inside the cell.
Leaky Sodium Channels: Less impact on resting potential due to lower permeability; primarily sodium remains outside.

Ion Concentration Gradients

Sodium concentration is higher outside (140 mM) and potassium is higher inside (150 mM).
Ion movement driven by these gradients influences membrane voltage.

Nernst Potential

Equilibrium potential calculated to determine ion movement across membranes.
Potassium: E(K) calculation shows potential around -90 mV based on typical ion concentrations.
Sodium: E(Na) is approximately +70 mV based on differing concentrations inside and outside.

Overall Impact

Resting membrane potential highly influenced by potassium equilibrium potential and its permeability.
Shifts in membrane potential primarily occur due to changes in potassium permeability rather than sodium.

Membrane Potentials

Average resting membrane potential is about -70 mV.
Higher potassium permeability results in a more stable resting potential around this value.

Graded Potentials

Facilitate adjustments to resting potential, moving towards action potential threshold of approximately -55 mV.
EPSPs bring the potential closer to threshold while IPSPs push it further away.

Neuronal Communication

Neurotransmitters (e.g., glutamate for EPSPs, GABA for IPSPs) released by presynaptic neurons impact the postsynaptic neuron.
Ligand-gated ion channels open upon binding of neurotransmitters, allowing ion flow that alters charge inside the neuron.

Summation of Potentials

EPSPs and IPSPs balance to affect membrane potential; more EPSPs needed to trigger action potentials.
Temporal summation combines rapid sequential firing from a single neuron.
Spatial summation accumulates effects from concurrent firings of multiple neurons.

Threshold and Action Potential

Action potential triggered at -55 mV at axon hillock, where voltage-gated sodium channels open.
Rapid depolarization occurs as Na+ influx raises potential to +30 mV, reversing polarity.

Action Potential and Ion Channels

Resting membrane potential around -70 mV; action potential initiation requires reaching the threshold.
Voltage-gated sodium channels rapidly open at threshold, allowing Na+ entry and causing depolarization.

Depolarization and Action Potential Propagation

Depolarization occurs when Na+ floods into cells, creating a positive charge.
Propagation of depolarization signals travels along the axon toward the terminal.
Voltage-gated calcium channels open at +30 mV, critical for neurotransmitter release.

Neurotransmitter Release Mechanism

Calcium binds to SNARE proteins aiding vesicle fusion with the membrane for exocytosis of neurotransmitters.

Repolarization and Hyperpolarization

Repolarization brings the membrane back to about -70 mV.
Voltage-gated potassium channels open at +30 mV, causing K+ to exit and potential to drop towards -90 mV.
Hyperpolarization occurs when the potential falls below -70 mV due to excess K+ outflow.

Key Definitions

Depolarization: Inside of cell becomes more positive.
Repolarization: Return from a positive back to negative resting potential.
Hyperpolarization: Increased negativity beyond resting potential.

Recovery to Resting Membrane Potential

Sodium-potassium ATPase and leak channels help stabilize the membrane back to -70 mV.
Refractory Periods:
- Absolute Refractory Period: No further action potentials can be initiated post-depolarization.
- Relative Refractory Period: Follows absolute period; requires a stronger stimulus to generate a new action potential.

Summary of Voltage-Gated Channel States

At Rest: Activation gates closed, inactivation gate open.
During Depolarization: Activation gate opens; inactivation gate starts closing.
At Peak: Both activation gates are open; inactivation gate closes to stop Na+ entry.
During Repolarization: K+ channels open, returning the cell to a negative state.
Post Action Potential: Channels recover to resting state configuration as the potential returns to -70 mV.

Glial Cells Overview

Nervous tissue is composed of neurons and glial cells.
Glial cells are present in both the central nervous system (CNS) and peripheral nervous system (PNS).

Astrocytes

Found exclusively in the CNS, astrocytes perform various functions, including maintaining the blood-brain barrier (BBB).

Blood-Brain Barrier Structure

The BBB comprises three layers:
- Endothelial cells with tight junctions.
- Basal lamina, a connective tissue layer.
- Foot processes from astrocytes that help in forming the barrier.

Blood-Brain Barrier Function

Regulates the transport of molecules between blood and nervous tissue.
Lipid-soluble substances and gases (e.g., CO2, O2) cross the BBB easily.
Charged ions and larger molecules require specialized transport proteins to pass through.
Astrocytes secrete growth factors to strengthen tight junctions, enhancing the barrier's selectivity.

Areas with Compromised Blood-Brain Barrier

Certain brain regions permit molecular exchange due to a compromised BBB:
- Area postrema: Detects blood toxins and triggers vomiting.
- Osmoreceptors near the hypothalamus: Monitor blood salts and glucose for fluid balance regulation.
- Hypothalamic-pituitary axis: Facilitates hormone signaling between hypothalamus and pituitary gland.

Potassium Buffering

Astrocytes absorb excess potassium ions during neuronal action potentials to maintain neuronal excitability.
They redistribute potassium among themselves via gap junctions, preventing dangerous extracellular potassium increases.

Neurotransmitter Regulation

Astrocytes manage glutamate and GABA levels:
- Uptake excess glutamate from synapses and convert it to glutamine through glutamine synthetase.
- Glutamine is transported back to neurons, where it is reconverted to glutamate.
- Synthesize GABA from glutamate using glutamate decarboxylase.

Glycogen and Glucose Metabolism

Astrocytes store glycogen and manage glucose levels for neurons.
They sense low ATP levels in neurons, breaking down glycogen to release glucose.
Glucose is transformed into pyruvate and lactate, which is sent to neurons for ATP production.
Glucose enters astrocytes through GLUT1, while neurons use GLUT3.

Glut Transporters

The BBB contains one type of glut transporter.
Neurons have three distinct types of glut transporters.

Astrocytes and Synaptic Connections

Astrocytes enhance synaptic connections between neurons, though the underlying mechanisms remain unclear.

Satellite Cells

Satellite cells serve as the PNS counterpart to astrocytes.
They regulate nutrient metabolism, neurotransmitter levels, and potassium homeostasis without involvement in the BBB.

Locations of Satellite Cells

Present in the dorsal root ganglia and autonomic ganglia:
- Dorsal root ganglia: Contain cell bodies outside the spinal cord, surrounded by satellite cells.
- Autonomic ganglia: Include sympathetic (pre-vertebral and para-vertebral) and parasympathetic ganglia (near target organs).

Oligodendrocytes vs. Schwann Cells

Oligodendrocytes myelinate axons in the CNS, covering multiple axons (30-60 per cell).
Schwann cells myelinate axons in the PNS, covering distinct segments of individual axons.

Myelination in the Nervous System

Damaged oligodendrocytes result in irreversible demyelination with no regeneration capacity.
Schwann cells have regenerative potential, facilitating remyelination in damage scenarios like Guillain-Barre Syndrome.

Demyelination Diseases

Multiple sclerosis affects demyelination in the CNS.
Guillain-Barre Syndrome refers to demyelination in the PNS.

Structure and Function of Schwann Cells

Schwann cells envelop axons with "arms" forming concentric layers, creating the myelin sheath.
The neurolemma, the outer layer of Schwann cells, is crucial for post-injury regeneration.

Myelin Composition and Function

Myelin primarily consists of lipids and proteins, serving as an electrical insulator to enhance action potential propagation.
Myelinated axons facilitate saltatory conduction, leading to faster signal transmission compared to non-myelinated axons, which transmit signals continuously.

Nodes of Ranvier

Gaps between the myelin sheath on axons are called nodes of Ranvier, densely packed with voltage-gated sodium channels.
Action potentials leap from node to node, boosting conduction speed.

Factors Affecting Conduction Velocity

Myelination and axon diameter both increase conduction velocity; larger diameters reduce resistance to signal flow.
Neuron types vary:
- Type A fibers (alpha, beta, gamma, delta) have the fastest conduction due to high myelination.
- Type B fibers have moderate myelination and conduction speed.
- Type C fibers are unmyelinated or minimally myelinated, resulting in low conduction speeds.

Ependymal Cells

Ependymal cells line brain ventricles and create a blood-cerebrospinal fluid barrier.
They regulate molecule movement (water, glucose, ions) and produce cerebrospinal fluid (CSF) via ciliary movement.

Microglia

Microglia are immune cells in the CNS, derived from bone marrow monocytes.
They react to pathogens and injury by releasing inflammatory substances, which can harm healthy tissues.
Capable of phagocytosing pathogens and presenting antigens to T cells, thus amplifying the immune response.
Overactive microglia can lead to demyelination and contribute to conditions such as encephalitis, particularly in diseases such as HIV.

Glial Cells Overview

Nervous tissue is composed of neurons and glial cells.
Glial cells are present in both the central nervous system (CNS) and peripheral nervous system (PNS).

Astrocytes

Found exclusively in the CNS, astrocytes perform various functions, including maintaining the blood-brain barrier (BBB).

Blood-Brain Barrier Structure

The BBB comprises three layers:
- Endothelial cells with tight junctions.
- Basal lamina, a connective tissue layer.
- Foot processes from astrocytes that help in forming the barrier.

Blood-Brain Barrier Function

Regulates the transport of molecules between blood and nervous tissue.
Lipid-soluble substances and gases (e.g., CO2, O2) cross the BBB easily.
Charged ions and larger molecules require specialized transport proteins to pass through.
Astrocytes secrete growth factors to strengthen tight junctions, enhancing the barrier's selectivity.

Areas with Compromised Blood-Brain Barrier

Certain brain regions permit molecular exchange due to a compromised BBB:
- Area postrema: Detects blood toxins and triggers vomiting.
- Osmoreceptors near the hypothalamus: Monitor blood salts and glucose for fluid balance regulation.
- Hypothalamic-pituitary axis: Facilitates hormone signaling between hypothalamus and pituitary gland.

Potassium Buffering

Astrocytes absorb excess potassium ions during neuronal action potentials to maintain neuronal excitability.
They redistribute potassium among themselves via gap junctions, preventing dangerous extracellular potassium increases.

Neurotransmitter Regulation

Astrocytes manage glutamate and GABA levels:
- Uptake excess glutamate from synapses and convert it to glutamine through glutamine synthetase.
- Glutamine is transported back to neurons, where it is reconverted to glutamate.
- Synthesize GABA from glutamate using glutamate decarboxylase.

Glycogen and Glucose Metabolism

Astrocytes store glycogen and manage glucose levels for neurons.
They sense low ATP levels in neurons, breaking down glycogen to release glucose.
Glucose is transformed into pyruvate and lactate, which is sent to neurons for ATP production.
Glucose enters astrocytes through GLUT1, while neurons use GLUT3.

Glut Transporters

The BBB contains one type of glut transporter.
Neurons have three distinct types of glut transporters.

Astrocytes and Synaptic Connections

Astrocytes enhance synaptic connections between neurons, though the underlying mechanisms remain unclear.

Satellite Cells

Satellite cells serve as the PNS counterpart to astrocytes.
They regulate nutrient metabolism, neurotransmitter levels, and potassium homeostasis without involvement in the BBB.

Locations of Satellite Cells

Present in the dorsal root ganglia and autonomic ganglia:
- Dorsal root ganglia: Contain cell bodies outside the spinal cord, surrounded by satellite cells.
- Autonomic ganglia: Include sympathetic (pre-vertebral and para-vertebral) and parasympathetic ganglia (near target organs).

Oligodendrocytes vs. Schwann Cells

Oligodendrocytes myelinate axons in the CNS, covering multiple axons (30-60 per cell).
Schwann cells myelinate axons in the PNS, covering distinct segments of individual axons.

Myelination in the Nervous System

Damaged oligodendrocytes result in irreversible demyelination with no regeneration capacity.
Schwann cells have regenerative potential, facilitating remyelination in damage scenarios like Guillain-Barre Syndrome.

Demyelination Diseases

Multiple sclerosis affects demyelination in the CNS.
Guillain-Barre Syndrome refers to demyelination in the PNS.

Structure and Function of Schwann Cells

Schwann cells envelop axons with "arms" forming concentric layers, creating the myelin sheath.
The neurolemma, the outer layer of Schwann cells, is crucial for post-injury regeneration.

Myelin Composition and Function

Myelin primarily consists of lipids and proteins, serving as an electrical insulator to enhance action potential propagation.
Myelinated axons facilitate saltatory conduction, leading to faster signal transmission compared to non-myelinated axons, which transmit signals continuously.

Nodes of Ranvier

Gaps between the myelin sheath on axons are called nodes of Ranvier, densely packed with voltage-gated sodium channels.
Action potentials leap from node to node, boosting conduction speed.

Factors Affecting Conduction Velocity

Myelination and axon diameter both increase conduction velocity; larger diameters reduce resistance to signal flow.
Neuron types vary:
- Type A fibers (alpha, beta, gamma, delta) have the fastest conduction due to high myelination.
- Type B fibers have moderate myelination and conduction speed.
- Type C fibers are unmyelinated or minimally myelinated, resulting in low conduction speeds.

Ependymal Cells

Ependymal cells line brain ventricles and create a blood-cerebrospinal fluid barrier.
They regulate molecule movement (water, glucose, ions) and produce cerebrospinal fluid (CSF) via ciliary movement.

Microglia

Microglia are immune cells in the CNS, derived from bone marrow monocytes.
They react to pathogens and injury by releasing inflammatory substances, which can harm healthy tissues.
Capable of phagocytosing pathogens and presenting antigens to T cells, thus amplifying the immune response.
Overactive microglia can lead to demyelination and contribute to conditions such as encephalitis, particularly in diseases such as HIV.

Structure of Neurons

Neurons consist of key components: dendrites, cell body (soma), axon, axon hillock, and axon terminals.
Dendrites extend from the neuron, acting as the primary receptive zone for incoming signals.
The cell body houses the nucleus and organelles essential for neuron function.
Axons conduct electrical impulses away from the soma to the axon terminal.
The axon hillock is the starting point of the axon, notable for a high density of voltage-gated sodium channels.

Functions of Neurons

Dendrites receive neurotransmitters through ligand-gated ion channels, leading to excitatory (EPSP) or inhibitory (IPSP) graded potentials.
EPSPs promote action potentials; conversely, IPSPs diminish the likelihood of action potentials.
The soma engages in graded potentials and is vital for synthesizing proteins, including neurotransmitters and membrane components.

Protein Synthesis Process

Protein synthesis begins with transcription, where DNA is converted into mRNA, which travels to the rough endoplasmic reticulum (Nissl bodies) for translation into proteins.
Post-synthesis, proteins are packaged into vesicles by the Golgi apparatus and transported along the axon.

Axon Functions

The axon transmits action potentials via a depolarization followed by repolarization phase.
Action potentials are initiated at the axon hillock and propagated down the axon using voltage-gated sodium and potassium channels.

Axonal Transport Mechanisms

Kinesin is the motor protein responsible for anterograde transport, delivering materials from the soma to the axon terminal.
Dynein carries out retrograde transport, moving materials from the axon terminal back to the soma.
Anterograde transport includes neurotransmitters, membrane proteins, and organelles like mitochondria.
Retrograde transport can recycle organelles and transmit nerve growth factors, crucial for signaling damage.

Clinical Relevance

Some viruses, like polio and rabies, exploit axonal transport mechanisms, utilizing dynein to travel from nerve terminals to the soma for replication and neuronal damage.

Summary of Action Potentials

Action potentials consist of a depolarization phase (sodium influx) followed by a repolarization phase (potassium efflux).
Voltage-gated sodium channels facilitate the depolarization process, while voltage-gated potassium channels restore the negative membrane potential during repolarization.

Additional Notes

Retrogradely transported nerve growth factors can stimulate the soma to enhance protein production for neuronal repair and growth in response to injury.

Shingles and Viral Mechanism

Shingles originates from the varicella zoster virus, which can remain inactive post-infection and can be reactivated under stress or immunosuppression.
The virus utilizes kinesin for transport back down the axon, which can affect skin tissues.

Axon Terminal Functions

The axon terminal is critical for the release and reuptake of neurotransmitters.
Action potentials trigger depolarization at the axon terminal via voltage-gated sodium channels, leading to calcium influx through voltage-gated calcium channels, which initiates neurotransmitter release.

Neurotransmitter Release Process

Neurotransmitter vesicles contain v-SNAREs, while the axon terminal features t-SNAREs, with calcium enabling vesicle fusion to the plasma membrane.
Released neurotransmitters interact with receptors on adjacent neurons or muscles, exerting their effects.

Neurotransmitter Termination

Neurotransmitter action is terminated by reuptake or enzymatic degradation.
Specific proteins mediate the reuptake of neurotransmitters for recycling in the axon terminal, with SSRIs like Prozac inhibiting reuptake to enhance serotonin availability in synapses, beneficial in treating depression.

Structural Classification of Neurons

Neurons are categorized as multipolar, bipolar, or pseudo-unipolar based on their structures.
Multipolar neurons feature multiple dendrites and are commonly located in areas like the motor cortex.
Bipolar neurons, possessing a single dendritic extension, are mainly found in sensory organs like the retina.
Pseudo-unipolar neurons have one process that forks into peripheral and central branches, often found in dorsal root ganglia.

Functional Classification of Neurons

Neurons are classified as sensory (afferent), motor (efferent), or interneurons.
Sensory neurons convey signals from receptors to the CNS and include various specialized types.
Motor neurons transmit signals from the CNS to effectors, categorized into visceral and somatic types.
Interneurons serve as relays between sensory and motor pathways and constitute a significant portion of the CNS.

Importance of Interneurons

Interneurons facilitate immediate reflex actions by connecting sensory inputs to motor outputs in the spinal cord.
They are essential for processing information in the brain and spinal cord, supporting a variety of neural pathways.

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Description

Explore the fundamental concept of Resting Membrane Potential in neurons and other cell types. Understand the roles of Sodium-Potassium ATPases and Leaky Potassium Channels in establishing and maintaining this essential biological state.