Membranes and Receptors - Session 3

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Questions and Answers

What is the change in membrane potential called when it becomes less negative?

  • Repolarization
  • Depolarization (correct)
  • Resting potential
  • Hyperpolarization

What triggers depolarization in a cell?

  • Sodium entering the cell (correct)
  • Calcium entering the cell
  • Potassium exiting the cell
  • Chloride entering the cell

During which phase does the membrane potential return to its normal state after depolarization?

  • Hyperpolarization
  • Repolarization (correct)
  • Action potential phase
  • Threshold phase

What happens to the cell's interior during hyperpolarization?

<p>It becomes more negative (A)</p> Signup and view all the answers

What is the threshold in the context of membrane potentials?

<p>The point at which sodium channels first open (C)</p> Signup and view all the answers

Which ions are primarily involved in repolarization?

<p>Potassium ions exiting (C)</p> Signup and view all the answers

Which of the following represents a typical change in membrane potential during an action potential?

<p>From -70 mV to +30 mV (A)</p> Signup and view all the answers

Which process occurs immediately after the depolarization stage in a typical action potential?

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

What happens during neurotransmission after neurotransmitter binds to postsynaptic receptors?

<p>The neurotransmitter is removed or deactivated. (B)</p> Signup and view all the answers

Which type of synaptic transmission involves the receptor protein also functioning as an ion channel?

<p>Fast synaptic transmission (D)</p> Signup and view all the answers

What characterizes excitatory synapses?

<p>They facilitate membrane depolarization. (C)</p> Signup and view all the answers

Inhibitory post-synaptic potentials (IPSP) are typically permeable to which ions?

<p>K+ and Cl- (C)</p> Signup and view all the answers

What does the Na/K- ATPase do in terms of ion movement?

<p>Moves 3 Na+ out and 2 K+ in (D)</p> Signup and view all the answers

What occurs during slow synaptic transmission?

<p>Receptor and channel are separate proteins. (B)</p> Signup and view all the answers

Which neurotransmitter is primarily associated with excitatory synapses?

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

How can changes in ion concentration affect membrane potential?

<p>They can cause significant changes in membrane excitability. (B)</p> Signup and view all the answers

What effect does increasing membrane permeability to Na+ have on the membrane potential?

<p>It moves the membrane potential towards + 70 mV. (B)</p> Signup and view all the answers

Which type of ion channel is influenced by the binding of acetylcholine at the neuromuscular junction?

<p>Nicotinic acetylcholine receptors. (D)</p> Signup and view all the answers

In which type of gating do channels respond to changes in membrane potential?

<p>Voltage gating. (C)</p> Signup and view all the answers

What is the equilibrium potential for K+ as mentioned in the content?

<ul> <li>95 mV (A)</li> </ul> Signup and view all the answers

What is a characteristic of a ligand-gated channel?

<p>It opens or closes in response to a chemical ligand. (C)</p> Signup and view all the answers

What type of channels are involved in action potentials?

<p>Voltage-gated channels. (A)</p> Signup and view all the answers

What happens when K+ or Cl- channels are opened?

<p>It causes hyperpolarization. (B)</p> Signup and view all the answers

What is the role of the presynaptic neurone in a synapse?

<p>It sends the signal. (A)</p> Signup and view all the answers

Flashcards

Depolarization

A decrease in the size of the membrane potential from its normal value. The cell interior becomes less negative.

Hyperpolarization

An increase in the size of the membrane potential from its normal value. The cell interior becomes more negative.

Repolarization

The return of the membrane potential to its resting value after depolarization or hyperpolarization.

Threshold

The point at which the first voltage-gated sodium channel opens, triggering an action potential.

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Sodium Influx

The rapid influx of positively charged sodium ions into the cell during depolarization.

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Potassium Efflux

The rapid efflux of positively charged potassium ions out of the cell during repolarization.

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Action Potential

The change in membrane potential that occurs in nerve and muscle cells, allowing for the transmission of signals.

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Resting Membrane Potential

The state of the membrane potential when a neuron or muscle cell is not actively transmitting a signal.

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Voltage-Gated Sodium Channel

A protein channel embedded in the cell membrane that opens and closes in response to changes in voltage across the membrane. These channels are crucial for nerve impulse propagation, as they allow rapid influx of sodium ions during depolarization.

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Voltage-Gated Potassium Channel

A protein channel embedded in the cell membrane that opens and closes in response to changes in voltage across the membrane. These channels are responsible for repolarizing the membrane after depolarization, restoring the resting potential.

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Membrane Potential

The difference in electrical potential between the inside and outside of a cell membrane. It is determined by the distribution of ions across the membrane. A negative membrane potential indicates that the inside of the cell is more negative than the outside.

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Equilibrium Potential

The theoretical point at which the electrical driving force and the chemical driving force for an ion are balanced, resulting in no net movement of the ion across the membrane.

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Ligand-Gated Channel

A type of ion channel that opens or closes in response to the binding of a specific chemical ligand, usually a neurotransmitter. These are crucial for synaptic transmission.

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Synaptic Transmission

The process by which a nerve impulse is transmitted from one neuron to another across a synapse. It involves the release of neurotransmitters from the presynaptic neuron and their binding to receptors on the postsynaptic neuron.

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Presynaptic Neuron

The neuron that releases the neurotransmitter at the synapse. It transmits the signal.

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Postsynaptic Neuron

The neuron that receives the neurotransmitter at the synapse. It receives the signal.

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What is neurotransmission?

A neurotransmitter is released from the presynaptic neuron, diffuses across the synapse, binds to receptors on the postsynaptic neuron, causing a response, and is then removed or deactivated.

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What is a synapse?

The junction between two neurons where communication occurs.

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Where do synaptic connections occur?

Synapses are the sites of communication between neurons and other cells, such as muscle cells or gland cells. They involve the release of chemical transmitters that bind to receptors and initiate responses.

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What is fast synaptic transmission?

A type of synaptic transmission that involves the receptor protein also being an ion channel, allowing for rapid changes in membrane potential.

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What are excitatory synapses?

Synapses that cause depolarization of the postsynaptic membrane, making it more likely to fire an action potential. They are permeable to Na+ and Ca2+. Common excitatory neurotransmitters include glutamate and acetylcholine.

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What are inhibitory synapses?

Synapses that cause hyperpolarization of the postsynaptic membrane, making it less likely to fire an action potential. They are permeable to K+ or Cl-. Common inhibitory neurotransmitters include GABA and glycine.

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What are postsynaptic potentials?

These are changes in the potential of the postsynaptic membrane due to excitation or inhibition.

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What is slow synaptic transmission?

A type of synaptic transmission that involves a delayed response due to the receptor and channel being separate proteins. It often involves G-proteins and second messengers.

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Study Notes

Membranes and Receptors - Session 3

  • This lecture focuses on the resting cell membrane and changing membrane potentials.
  • The lecturer is Dr. Safa Amir.
  • Changes in membrane potential are fundamental to cell signaling, both between and within cells.

Changing Membrane Potentials

  • Examples of processes involving changing membrane potentials:
    • Action potentials in nerve and muscle cells
    • Muscle contraction initiation and regulation
    • Hormone and neurotransmitter secretion control
    • Sensory information transduction into electrical signals
    • Synaptic transmission (especially fast synaptic transmission)
  • Depolarization: A decrease in membrane potential from its normal value, making the cell interior less negative.
    • Example: A change from -70 mV to -50 mV.
  • Hyperpolarization: An increase in membrane potential from its normal value, making the cell interior more negative.
    • Example: A change from -70 mV to -90 mV.

Voltage-Gated Sodium Channels

  • Sodium ion channels are involved in action potential generation.
  • The specific ion channels have different stages:
    • Inactivated
    • Activation gate
    • Inactivation gate
    • Resting

Voltage-Gated Potassium Channels

  • Potassium channels are also crucial for action potentials and return to the resting state. Like sodium channels, these can be categorized in different states.
    • Resting
    • Slow activation

Action Potential Summary

  • This graph shows the voltage changes over time in an action potential.
  • Key stages to remember:
    • Depolarization
    • Repolarization
    • Refractory Period.

Changing Membrane Ion Permeability

  • Membrane permeability changes influence the membrane potential according to the equilibrium potential of the ions.
  • Equilibrium potentials for specific ions (important in determining permeability) :
    • K+: -95 mV
    • Na+: +70 mV
    • Ca2+: +122 mV
    • Cl-: -96 mV
  • Changes in membrane potential arise from changes in ion channel activity.

Nicotinic Acetylcholine Receptors

  • These receptors are found at neuromuscular junctions.
  • They have an intrinsic ion channel and open in response to acetylcholine.
  • They allow both sodium (Na+) and potassium (K+) ions to pass but not anions.
  • They shift membrane potential toward 0 mV, intermediate between ENa and EK.

Controlling Channel Activity

  • Channels can be gated (open or close in response to stimuli).
  • Types of gating:
    • Ligand Gating: Channels respond to the binding of chemical ligands, like neurotransmitters or hormones. (e.g., at synapses)
    • Voltage Gating: Channels open or close in response to changes in membrane potential, as in action potentials.
    • Mechanical Gating: Channels respond to mechanical forces that stretch or deform the membrane.

Synaptic Transmission

  • Synapses are gaps between neurons or neurons and other cells (e.g., muscle cells, gland cells) allowing signal transmission.
  • A signal travels from the pre-synaptic neuron, across the synapse using neurotransmitters to the postsynaptic neuron.
  • Starts with neurotransmitter release from the pre-synaptic neuron to connect with receptors on the post-synaptic membranes.
  • Neurotransmitters are removed after their task to allow another transmission cycle.

Fast Synaptic Transmission

  • In fast synaptic transmission, the receptor protein is an ion channel.
  • Neurotransmitter binding opens the channel, allowing ion flow and altering the postsynaptic membrane potential

Excitatory and Inhibitory Synapses

  • Excitatory Postsynaptic Potentials (EPSPs): Excitatory transmitters depolarize the postsynaptic membrane. (e.g., Glutamate, some types of acetylcholine).
  • Inhibitory Postsynaptic Potentials (IPSPs): Inhibitory transmitters hyperpolarize the postsynaptic cell membrane (e.g., GABA, glycine).

Postsynaptic Potentials

  • Postsynaptic potentials (PSPs) can be excitatory or inhibitory.

Slow Synaptic Transmission

  • Receptors and channels are separate proteins.
  • Types:
    • Direct G-protein gating
    • Gating via an intracellular messenger (like Receptor G-protein Channel)

Other Factors Affecting Membrane Potential

  • Changes in ion concentration (particularly extracellular potassium) can affect membrane excitability.
  • Electrogenic pumps (e.g., Na+/K+ ATPase) contribute to membrane potential directly in some cells.

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