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Questions and Answers
What is the effect of inactivation gates on sodium channels?
What is the effect of inactivation gates on sodium channels?
During the resting membrane potential, what is the state of voltage-gated K+ channels?
During the resting membrane potential, what is the state of voltage-gated K+ channels?
What triggers the explosive depolarization of the membrane potential?
What triggers the explosive depolarization of the membrane potential?
What is the primary ion responsible for depolarization?
What is the primary ion responsible for depolarization?
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During repolarization, what is the primary ion responsible for efflux?
During repolarization, what is the primary ion responsible for efflux?
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What is the effect of the simultaneous decrease in sodium influx and increase in potassium efflux?
What is the effect of the simultaneous decrease in sodium influx and increase in potassium efflux?
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What is the purpose of the inactivation gate in sodium channels?
What is the purpose of the inactivation gate in sodium channels?
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During the resting membrane potential, what is the membrane potential?
During the resting membrane potential, what is the membrane potential?
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What is the sequence of events in an action potential?
What is the sequence of events in an action potential?
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What is the ionic basis of hyperpolarization?
What is the ionic basis of hyperpolarization?
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Study Notes
Excitable Tissue
- Nerves and muscles are called excitable tissue because they respond to chemical, mechanical, and electrical stimuli.
- Muscles demonstrate by contraction, while nerves by integration and transmission.
Electrical Signals in Neurons
- Production of signals depend on two basic features of the plasma membrane of excitable cells: resting membrane potential and ion channels.
Ion Channels
- Ion channels open and close due to the presence of gates.
- There are four kinds of ion channels:
- Leakage channels: open and close randomly
- Voltage-gated channels: open in response to a change in membrane potential (voltage)
- Ligand-gated channels: open and close in response to chemical stimulus, such as Ach
- Mechanical gated channels: open or close in response to mechanical stimulus
Resting Membrane Potential (RMP)
- Definition: The difference in voltage across the cell membrane when a neuron or muscle cell is not producing an action potential.
- A typical value is: -70 mV (-50 to -90)
- A cell that exhibits a membrane potential is said to be polarized.
- RMP is negative inside the cell relative to the outside because:
- The resting membrane is 10-100 times more permeable to K+ than to Na+
- Potassium inside the cell is 140meq/L and outside is 4meq/L
- K+ tends to leak out of the cell down its concentration gradient, carrying +ve charge with it
Forces Acting on Cell Membrane at Rest
- Diffusion: movement of molecules from a region of higher concentration to a region of lower concentration
- Electrical gradient: +ve ions move to the –ve area and –ve ions move to +ve area
- Active transport: transport ions against their concentration gradient (e.g., Na+-K+ pump)
The Action Potential (AP)
- Definition: A sudden reversal of membrane polarity by a stimulus
- Importance: AP occurs in living organisms to produce physiological effects such as transmission of impulses along nerve fibers and release of neurosecretions or chemical transmitters in synapses
- Action potential takes place as a result of the triggered opening and subsequent closing of 2 specific types of channels: voltage-gated Na+ channels and voltage-gated K+ channels
Voltage-Gated Na+ Channels
- Most important channels during AP
- Have two gates: activation gate and inactivation gate
- Activation gate opens when membrane potential becomes less negative than during resting state
- Inactivation gate closes when membrane potential becomes less negative, leading to Na+ influx
Voltage-Gated K+ Channels
- Open during RMP, but are closed
- Same stimulus that opens voltage-gated Na+ channels also opens voltage-gated K+ channels
- Due to slow opening of these channels, they open just as Na+ channels are beginning to close
- Simultaneous decrease in Na+ influx and increase in K+ outflux cause repolarization
Phases of Action Potential
- Depolarization
- Repolarization
- Hyperpolarization
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Description
This quiz covers the basics of neurons and excitable tissue, including membrane potentials, electrical signals, and how nerves and muscles respond to stimuli.
