Neuroscience Chapter on Membrane Potential

Questions and Answers

What characterizes graded potentials in neurons?

They can travel long distances within the body.

They generate action potentials.

They always result in depolarization.

They are used for short-distance communication only. (correct)

Which type of ion channels are important for the generation and conduction of action potentials?

Mechanically gated channels

Ligand-gated channels

Voltage-gated channels (correct)

Leakage channels

What is the role of leakage (nongated) channels in neurons?

They conduct action potentials exclusively.

They open in response to neurotransmitters.

They respond to mechanical stimuli.

They remain always open and influence resting potential. (correct)

Which statement about action potentials is true?

They can travel short and long distances within the body. Signup and view all the answers

What is depolarization in the context of membrane potential changes?

A decrease in the electrical difference across the membrane. Signup and view all the answers

Which of these conditions would likely lead to the opening of voltage-gated channels?

A change in membrane potential Signup and view all the answers

What causes the resting membrane potential of -70 mV in neurons?

Higher permeability to K+ than Na+ Signup and view all the answers

How do ligand-gated ion channels function?

They respond to specific chemical ligands. Signup and view all the answers

What is the primary role of interneurons in the nervous system?

Process and integrate information within the central nervous system. Signup and view all the answers

Which type of neuroglial cell is found in the peripheral nervous system and aids in myelination?

Neurolemmocytes Signup and view all the answers

What distinguishes afferent neurons from efferent neurons?

Afferent neurons conduct action potentials towards the CNS, while efferent neurons conduct them away. Signup and view all the answers

Which of the following is NOT a primary function of the nervous system?

Environmental adaptation Signup and view all the answers

What is the significance of the voltage difference across the neuron's membrane?

It enables the excitability of neurons necessary for action potentials. Signup and view all the answers

Astrocytes, a type of neuroglial cell, primarily serve what function?

Providing structural support and nutrition to neurons. Signup and view all the answers

Which statement about the nervous system's classification is accurate?

The nervous system can be classified by both its structure and function. Signup and view all the answers

Which cellular component primarily conducts action potentials within the neuron?

Axon Signup and view all the answers

What initiates the action potential formation?

A chemical or mechanical stimulus causing a graded potential Signup and view all the answers

During depolarization, what primarily causes the membrane potential to rise?

Na+ ions flowing into the cell Signup and view all the answers

What is the result of the opening of voltage-gated K+ channels during an action potential?

Hyperpolarization as K+ exits the cell Signup and view all the answers

What does the term 'all or none principle' signify in the context of action potentials?

Once the threshold is reached, an action potential either occurs fully or not at all Signup and view all the answers

What membrane potential is typically considered the threshold for triggering an action potential?

-55mV Signup and view all the answers

Why is the opening of voltage-gated Na+ channels considered a positive feedback process?

It results in a depolarization that opens even more Na+ channels Signup and view all the answers

Which of the following best describes what occurs during hyperpolarization?

The membrane potential becomes more negative than resting level Signup and view all the answers

How many Na+ ions typically enter the cell during the action potential process?

20,000 Na+ ions Signup and view all the answers

What is the main characteristic of the absolute refractory period?

Na+ channels are inactivated and must be reset to generate another AP. Signup and view all the answers

Which of the following describes the function of ionotropic receptors?

They form an ion channel pore that opens upon activation. Signup and view all the answers

What happens during the relative refractory period of an action potential?

A suprathreshold stimulus can initiate an action potential. Signup and view all the answers

Which neurotransmitter is inactivated by acetylcholinesterase?

Acetylcholine (ACh) Signup and view all the answers

What is the primary effect of an excitatory postsynaptic potential (EPSP)?

Depolarization that increases the likelihood of an action potential. Signup and view all the answers

Which summation occurs when multiple presynaptic inputs fire onto one neuron?

Spatial summation Signup and view all the answers

What is the role of neurotransmitter transporters?

They remove neurotransmitters from the synaptic cleft. Signup and view all the answers

What occurs when a ligand-gated K+ channel opens in a neuron?

Hyperpolarizes the neuron, making it less likely to fire. Signup and view all the answers

What is the primary effect of voltage-gated sodium channels opening during an action potential?

Signup and view all the answers

What is the primary consequence of the slow voltage-gated K+ channels opening during the action potential process?

Membrane potential falls as K+ flows out. Signup and view all the answers

What happens as a result of the closing of slow voltage-gated K+ channels?

The membrane potential hyperpolarizes slightly. Signup and view all the answers

Which mechanism is responsible for restoring the resting membrane potential after an action potential?

The Na+/K+ ATPase actively transports ions. Signup and view all the answers

As sodium channels close during the falling phase of an action potential, which of the following occurs?

Membrane potential begins to fall further. Signup and view all the answers

What is the threshold potential typically required to initiate an action potential?

-55 mV Signup and view all the answers

During the action potential, which channel's activity is primarily responsible for the rapid depolarization of the membrane?

Voltage-gated Na+ channels Signup and view all the answers

What is hyperpolarization in the context of an action potential?

Increase in membrane potential beyond resting levels. Signup and view all the answers

What is the effect of the Na+/K+ ATPase during the action potential cycle?

It maintains the concentration gradients of Na+ and K+. Signup and view all the answers

Why does the action potential only travel in one direction along the neuron?

Na+ channels are inactivated immediately after opening. Signup and view all the answers

Study Notes

Nervous System Overview

The nervous system (NS) serves three primary functions: sensory (gathering information), integrative (processing and interpreting sensory input), and motor (responding to stimuli).
NS is categorized based on structure and function, comprising neurons and neuroglia.

Neurons

Neurons are the functional units of the NS, specialized to transmit stimuli.
Neurons are classified functionally into:
- Afferent neurons: Carry action potentials (APs) to the central nervous system (CNS).
- Interneurons: Conduct APs within the CNS.
- Efferent neurons: Carry APs to the peripheral nervous system (PNS).
Structure includes a cell body (containing nucleus and organelles) with dendrites (input extensions) and axons (output extensions).

Neuroglia

Supportive cells in the NS, divided into:
- CNS Neuroglia: Astrocytes, oligodendrocytes, microglia, ependymal cells.
- PNS Neuroglia: Neurolemmocytes (Schwann cells), satellite cells.

Electrical Signals in Neurons

Neurons are electrically excitable due to voltage differences across membranes.
Two types of electrical signals:
- Graded potentials: Local changes for short-distance communication.
- Action potentials: Long-distance signals throughout the body.

Ion Channels

Membrane potential is influenced by ion channels, which can be:
- Leakage (nongated) channels: Always open, allowing ion movement (more K+ than Na+).
- Gated ion channels: Open/close in response to stimuli.
  - Voltage-gated channels: Respond to changes in membrane potential.
  - Ligand-gated channels: Respond to chemicals like neurotransmitters.
  - Mechanically gated channels: Respond to mechanical stimuli (e.g., sound, pressure).

Changes in Membrane Potential

Polarized state: + outside, - inside at rest.
Depolarization: Membrane potential increases (e.g., Na+ enters cell).
Repolarization: Returns to resting state (e.g., K+ exits cell).
Hyperpolarization: Becomes more negative (e.g., K+ exits cell).

Action Potential

Action potential is a sequence of changes that elevates membrane potential from -70mV to +30mV (depolarization) and back to -70mV (repolarization).
Triggered when a stimulus causes a graded potential to reach the threshold of -55mV.
Key steps include:
- Opening of voltage-gated Na+ channels causing Na+ influx (depolarization).
- Positive feedback mechanism where a small amount of Na+ significantly alters membrane potential.
- Slow opening of voltage-gated K+ channels leading to K+ efflux (repolarization).

Summary of Action Potential Formation

Process begins with a resting membrane potential of -70mV.
Upon stimulation, Na+ influx occurs through chemically gated channels.
If a threshold is reached, all voltage-gated Na+ channels open dramatically increasing permeability and leading to a rapid rise in membrane potential.### Action Potentials
Action potentials depolarize the membrane to approximately +30 mV.
Voltage-gated sodium (Na+) channels play a crucial role in this process.
Following initial depolarization, slow voltage-gated potassium (K+) channels open, allowing K+ to flow out, causing the membrane potential to fall.

Refractory Period

The refractory period prevents the generation of successive action potentials.
Absolute refractory period: No stimulus can initiate a new action potential; inactivated Na+ channels must return to resting state.
Relative refractory period: A suprathreshold stimulus can initiate a new action potential; Na+ channels are ready while K+ channels remain open.

Signal Transmission

Neuron signals can be transmitted electrically or chemically.
Chemical synapses involve neurotransmitter release and receptor interaction.

Neurotransmitter Receptors

Ionotropic receptors: Form an ion channel pore that opens upon activation, allowing Na+, K+, or Cl- to flow.
Metabotropic receptors: Activate second messenger systems, altering neuronal responses.

Excitatory and Inhibitory Potentials

Excitatory postsynaptic potential (EPSP): Involves opening of ligand-gated Na+ channels, increasing likelihood of action potential initiation.
Inhibitory postsynaptic potential (IPSP): Occurs via opening of ligand-gated K+ or Cl- channels, making the postsynaptic cell more negative or hyperpolarized.

Removal of Neurotransmitters

Neurotransmitters are eliminated via:
- Diffusion: Movement down concentration gradients.
- Enzymatic degradation: Example includes acetylcholinesterase breaking down acetylcholine.
- Uptake: Recycled by neurons or glial cells via neurotransmitter transporters.

Summation of Signals

Spatial summation: Effect of neurotransmitters released from multiple presynaptic neurons onto a single postsynaptic neuron.
Temporal summation: Effect of consecutive releases of neurotransmitters from the same presynaptic neuron impacting a postsynaptic neuron rapidly.

Small-Molecule Neurotransmitters

Acetylcholine (ACh): Found in the peripheral nervous system (PNS) and central nervous system (CNS); acts excitatory at the neuromuscular junction but inhibitory elsewhere; inactivated by acetylcholinesterase.
Amino Acids: Glutamate serves as an excitatory neurotransmitter in the brain; it is inactivated through reuptake mechanisms.

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Explore the concepts of membrane depolarization and voltage-gated sodium channels in this quiz. Test your understanding of how these channels affect membrane potential and action potential generation in neurons. Perfect for neuroscience students!