Podcast
Questions and Answers
What is the process called when the membrane potential decreases and the cell interior becomes less negative?
What is the process called when the membrane potential decreases and the cell interior becomes less negative?
During which stage does the membrane become very permeable to sodium ions, allowing them to diffuse into the cell?
During which stage does the membrane become very permeable to sodium ions, allowing them to diffuse into the cell?
What happens during hyperpolarization?
What happens during hyperpolarization?
What is the term for the restoration of the normal resting membrane potential after depolarization?
What is the term for the restoration of the normal resting membrane potential after depolarization?
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What initiates the depolarization of a neuron?
What initiates the depolarization of a neuron?
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What is the threshold in the context of membrane potentials?
What is the threshold in the context of membrane potentials?
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What role does repolarization play in cellular signaling?
What role does repolarization play in cellular signaling?
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What characterizes the resting membrane potential of a cell?
What characterizes the resting membrane potential of a cell?
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What initiates neurotransmission in a neuron?
What initiates neurotransmission in a neuron?
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What type of synaptic transmission involves the receptor protein also serving as an ion channel?
What type of synaptic transmission involves the receptor protein also serving as an ion channel?
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Which neurotransmitter is primarily associated with excitatory postsynaptic potentials (EPSP)?
Which neurotransmitter is primarily associated with excitatory postsynaptic potentials (EPSP)?
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What type of potential is caused by excitatory synapses leading to membrane depolarization?
What type of potential is caused by excitatory synapses leading to membrane depolarization?
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Which of the following ions can be involved in inhibitory postsynaptic potentials (IPSP)?
Which of the following ions can be involved in inhibitory postsynaptic potentials (IPSP)?
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What characterizes slow synaptic transmission compared to fast synaptic transmission?
What characterizes slow synaptic transmission compared to fast synaptic transmission?
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What is one of the primary factors that influence membrane potential?
What is one of the primary factors that influence membrane potential?
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What effect does the Na/K-ATPase pump have on the membrane potential?
What effect does the Na/K-ATPase pump have on the membrane potential?
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What effect does opening K+ or Cl- channels generally have on the membrane potential?
What effect does opening K+ or Cl- channels generally have on the membrane potential?
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What is the primary function of ligand-gated ion channels?
What is the primary function of ligand-gated ion channels?
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What does increasing membrane permeability to Na+ ions do to the membrane potential?
What does increasing membrane permeability to Na+ ions do to the membrane potential?
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Which statement about the Nicotinic Acetylcholine Receptors is true?
Which statement about the Nicotinic Acetylcholine Receptors is true?
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What type of gating occurs when channels respond to membrane deformation?
What type of gating occurs when channels respond to membrane deformation?
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How do changes in membrane potential arise?
How do changes in membrane potential arise?
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When is an action potential generated in a neurone?
When is an action potential generated in a neurone?
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What is typically the role of the presynaptic neurone in synaptic transmission?
What is typically the role of the presynaptic neurone in synaptic transmission?
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Study Notes
Membranes and Receptors - Session 3
- Lecture 3.2: Changing Membrane Potentials
- Changes in membrane potential are fundamental to cell signaling, both between cells and within a single cell.
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Examples:
- Action potentials in nerve and muscle cells
- Triggering and controlling muscle contractions
- Regulating hormone and neurotransmitter secretion
- Transduction of sensory information into electrical signals
- Postsynaptic actions in fast synaptic transmission
Depolarization
- A decrease in membrane potential from its normal value.
- The cell interior becomes less negative.
- Example: A change from −70 mV to −50 mV.
- Occurs when sodium ions enter the cell.
Hyperpolarization
- An increase in the size of the membrane potential from its normal value.
- The cell interior becomes more negative.
- Example: A change from −70 mV to −90 mV.
- Occurs when potassium ions leave the cell.
Repolarization
- The return to the resting membrane potential after depolarization or hyperpolarization.
- Moves back towards −70 mV.
Threshold
- The membrane potential value that triggers the opening of voltage-gated sodium channels.
- This is the point where the first voltage-regulated sodium channel opens.
Positive Charge for Depolarization
- To depolarize a cell, a positive charge must be introduced into the cell.
Depolarization Stage
- Membrane permeability to sodium ions suddenly increases.
- Large numbers of positively charged sodium ions enter the axon.
- The normal polarized state (−90 mV) is neutralized, and the potential rapidly rises in the positive direction—this is depolarization.
Repolarization Stage
- Within milliseconds of depolarization, sodium channels close.
- Potassium channels open more than usual.
- Rapid potassium ion diffusion out of the axon re-establishes the normal negative resting membrane potential—this is repolarization.
Voltage-Gated Sodium Channels
- Channels that open and close at specific membrane potentials.
- These channels are crucial for action potentials.
- Different stages:
- Inactivated or delayed (+35 to -90 mV)
- Resting (-90 mV)
- Activated (-90 to +35 mV)
Voltage-Gated Potassium Channels
- Channels that respond to changes in membrane potential.
- They play a role in repolarization and return to the resting state.
- Stages:
- Resting (-90mV)
- Slow activation (+35 to -90mV)
Action Potential Graph
- Describes voltage changes over time.
- Shows the phases of depolarization, repolarization, and refractory period.
Changing Membrane Ion Permeability
- Membrane permeability changes influence membrane potential changes.
- The potential moves towards the equilibrium potential for the ion.
- Equilibrium potentials for key ions:
- K⁺: −95 mV
- Na⁺: +70 mV
- Ca²⁺: +122 mV
- Cl⁻: −96 mV
Less Selective Channels (Example: Nicotinic Acetylcholine Receptors)
- Channels that aren't exclusively selective to one type of ion.
- The nicotinic acetylcholine receptors allow both Na⁺ and K⁺ ion passage but block anions.
- Situated at the neuromuscular junction.
Controlling Channel Activity
- Channels can open or close, and this is termed gating.
-
Types of Gating:
- Ligand Gating: Channels open or close in response to chemical ligands, e.g., neurotransmitters at synapses.
- Voltage Gating: Channels respond to changes in membrane potential; crucial for action potentials.
- Mechanical Gating: Channels respond to membrane deformation, e.g., mechanoreceptors.
Synaptic Transmission
- Action potentials travel across synapses via neurotransmission.
- Neurotransmission begins with the presynaptic neuron releasing a neurotransmitter.
- Neurotransmitters travel across the synaptic cleft and bind to receptors on the postsynaptic membrane.
- The postsynaptic neuron responds appropriately, and the neurotransmitter is removed or deactivated.
Generic Neurotransmitter System
- Illustrates the process of neurotransmitter release, binding, and subsequent degradation/removal.
Synaptic Connections
- Synapses occur between nerve cells, nerve-muscle cells, and nerve-gland cells.
- At each synapse, a chemical transmitter from the presynaptic cell interacts with receptors on the postsynaptic membrane.
Fast Synaptic Transmission
- Receptor proteins are ion channels.
- Transmitter binding directly opens the channel.
Excitatory Synapses
- Excitatory transmitters open ligand-gated channels that increase membrane permeability to Na⁺ and Ca²⁺.
- Membrane depolarization results, creating an EPSP (excitatory postsynaptic potential).
- Examples include glutamate and acetylcholine.
Inhibitory Synapses
- Inhibitory transmitters open ligand-gated channels that increase membrane permeability to K⁺ or Cl⁻.
- Membrane hyperpolarization occurs, creating an IPSP (inhibitory postsynaptic potential).
- Examples include GABA and glycine.
Postsynaptic Potentials (ERP and IPSP)
- Postsynaptic potentials resulting from excitation and inhibition.
Slow Synaptic Transmission
- Receptor proteins and ion channels are distinct.
- Two basic mechanisms:
- Direct G-protein gating
- Gating via an intracellular messenger (e.g., receptor-G-protein channels).
Two Other Factors Influencing Membrane Potential
- Ion Concentration Changes: Extracellular potassium concentration is especially significant, affecting membrane excitability; alterations can occur clinically (e.g., hyperkalemia).
- Electrogenic Pumps: Na+/K+-ATPase pumps contribute to membrane potential by moving ions across the membrane; some drugs affect this pump.
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Description
Explore the intricate dynamics of membranes and receptors in this quiz, which delves into key concepts like depolarization, hyperpolarization, and repolarization. Understand the importance of membrane potential changes in cell signaling, including examples from nerve and muscle cells. Test your knowledge on how these processes contribute to muscle contractions and sensory information transduction.
