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Questions and Answers
What type of ion channel lacks an inactivation gate?
Potassium ion channels are responsible for depolarization during the action potential.
False
What is the primary role of voltage-gated Na+ channels during the action potential?
To allow sodium ions to enter the cell, causing depolarization.
During repolarization, there is a time lag in closing all ______ channels, which leads to temporary hyperpolarization.
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Match the following segments of a neuron with their descriptions:
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Which statement correctly describes leak channels?
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Leak channels are responsible for generating action potentials.
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What is the resting membrane potential of an unstimulated axon?
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During ________________, sodium ions rapidly enter the cell, causing a change in the membrane potential.
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Match the channel type to its function:
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Which type of ion channel opens when the membrane reaches the threshold potential?
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The action potential travels in both directions along the axon.
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What happens during the repolarization phase of an action potential?
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What type of channels are primarily responsible for the resting membrane potential?
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K+ leak channels allow potassium ions to move into the cell during resting potential.
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How do leak channels contribute to the resting membrane potential?
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The ____ pump is responsible for maintaining the concentration gradients of Na+ and K+ across the membrane.
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Match the following terms related to resting membrane potential with their functions:
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Which of the following correctly describes the state of Na+ and K+ channels at resting potential?
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The resting membrane potential is typically around -70mV.
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What is the main role of the Na+/K+ pump in relation to leak channels?
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Study Notes
Voltage-gated K+ channels
- Do not have an inactivation gate
Inactivation of Sodium Ion Channels and Activation of Potassium Ion Channels Starts Repolarization
- Sodium channels are inactivated and potassium channels are activated, which allows for the repolarization of the membrane.
Time Lag in Closing All Potassium Ion Channels Leads to Temporary Hyperpolarization
- There is a delay in the closing of all potassium channels, leading to temporary hyperpolarization of the membrane.
Nerve Cell Conduction
- Signal movement is unidirectional: from dendrite to axon terminal.
- Nodes of Ranvier are gaps in the myelin sheath that allow for saltatory conduction: faster signal transmission along the axon by jumping from one node to another.
- The myelin sheath is a fatty substance that insulates the axon and increases the speed of signal transmission.
- The axon is the long extension of the neuron that carries signals away from the cell body.
- The nucleus is the control center of the cell body and contains the cell's DNA.
- Collaterals are branches of the axon that allow for the transmission of signals to multiple target cells.
- A node is a gap in the myelin sheath.
- The cell body contains the nucleus and other organelles.
- The dendrite is the extension of the neuron that receives signals from other neurons.
- The axon terminal is the end of the axon where signals are transmitted to other neurons.
Continuous vs. Saltatory Conduction
- Continuous conduction is slower and occurs in unmyelinated neurons.
- Saltatory conduction is faster and occurs in myelinated neurons.
Neuron at Rest: Gated Channels and Ion Gradients
- Chemically gated cation channel: opens when a neurotransmitter binds to it, allowing positive ions to flow through.
- Chemically gated K channel: opens when a neurotransmitter binds to it, allowing potassium ions to flow through.
- Chemically gated Cl- channel: opens when a neurotransmitter binds to it, allowing chloride ions to flow through.
- Voltage-gated K+ channel: opens in response to changes in membrane potential, allowing potassium ions to flow through.
- Voltage-gated Na+ channel: opens in response to changes in membrane potential, allowing sodium ions to flow through.
- Voltage-gated Ca^2+ channel: opens in response to changes in membrane potential, allowing calcium ions to flow through.
Concentration Gradients
- Maintained by ion channels
- Sodium ions move from the intracellular fluid to the extracellular fluid.
- Potassium ions move from the extracellular fluid to the intracellular fluid.
Different types of ion channels:
- Leak channels: always open
- Ligand gated: open when a chemical signal binds to it
- Voltage gated: open when the membrane potential changes
- Mechanically gated channels: open when the membrane is stretched
Na+ inactive state
- The sodium channel is in an inactive state when it is closed and cannot open again
Events of an Action Potential
- Unstimulated axon has a resting membrane potential of -70 mV.
- Graded potentials summate at the initial segment to reach threshold (-55 mV).
- Depolarization occurs when threshold is reached; Na+ rushes in, reversing polarity from negative to positive (-55 mV to +30 mV).
- Repolarization occurs as Na+ channels inactivate and K+ channels open; K+ exits, reversing polarity from positive to negative (+30 mV to -70 mV).
- Hyperpolarization occurs as K+ channels remain open longer than needed, making the membrane potential more negative than resting (-70 mV to -80 mV).
- Voltage-gated K+ channels close, and the Na+/K+ pumps restore the resting conditions (-80 mV to -70 mV).
Resting membrane potential to Action Potential
- A graded potential initiates an action potential by depolarizing the membrane to threshold potential.
- Once threshold is reached, voltage-gated sodium channels open, causing rapid depolarization.
Absolute refractory period to Relative refractory period
- Absolute refractory: no stimulus can trigger an action potential due to inactivation of sodium channels.
- Relative refractory: a strong stimulus is needed to trigger an action potential because of the lingering effect of open potassium channels.
Neuron to Neuron
- Excitable membrane: a membrane that can generate action potentials.
- Synapse: the point of communication between two neurons or a neuron and an effector cell.
- Neurotransmitters: chemical messengers that are released from presynaptic neurons to affect postsynaptic neurons.
Synapse
- Presynaptic neuron: the neuron that releases neurotransmitters at the synapse.
- Synaptic cleft: the space between the presynaptic and postsynaptic neurons.
- Postsynaptic neuron: the neuron that receives neurotransmitters at the synapse.
How does a signal move through the nervous system?
- Dendrite: receives signal from other neurons.
- Cell body: integrates incoming signals.
- Axon: transmits signal away from the cell body.
- Axon terminal: releases neurotransmitters at the synapse.
- Nucleus: control center of the neuron.
- Myelin sheath: insulates the axon, increasing signal transmission speed.
- Node: gap in the myelin sheath, allowing for saltatory conduction.
- Collateral: branches of the axon, allowing signal transmission to multiple targets.
- Direction of signal movement: from dendrite to axon terminal.
Neuron at rest
- Resting potential: the electrical potential difference across the plasma membrane of a neuron when it is not transmitting a signal.
- Cell membrane: a phospholipid bilayer that separates the inside of the cell from the outside.
- Concentration outside of the cell: high in sodium ions (Na+) and chloride ions (Cl-).
- Concentration inside of the cell: high in potassium ions (K+) and negatively charged proteins.
- Chemical gradient: the difference in concentration of a substance across a membrane.
Electrical gradient, Electrochemical gradient, Resting membrane potential
- Electrical gradient: the difference in electrical charge across a membrane.
- Electrochemical gradient: the combined force of the chemical gradient and the electrical gradient acting on an ion.
- Resting membrane potential: the electrical potential difference across the plasma membrane of a neuron when it is not transmitting a signal, typically around -70 mV.
Active Transport:
- Maintains RMP: the Na+/K+ pump moves ions against their concentration gradients, maintaining the resting membrane potential.
- How many Na+ are moved & in which direction? Three sodium ions are moved out of the cell.
- How many K+ are moved and in which direction? Two potassium ions are moved into the cell.
- What is necessary for the Na+/K+ Pump to work? The pump requires ATP, which is the main energy currency of the cell, to move ions against their concentration gradients.
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Description
This quiz covers the mechanisms of nerve cell conduction, focusing on the roles of voltage-gated potassium channels and sodium ion channels in repolarization. It explores the process of hyperpolarization and the significance of the myelin sheath and Nodes of Ranvier in facilitating faster signal transmission. Test your understanding of these essential neurophysiological concepts.
