C Na, K in action potential, graded potential

What are the anatomical divisions of the nervous system?

Central Nervous System (CNS) and Peripheral Nervous System (PNS)

What are the functional divisions of the nervous system?

Somatic Nervous System and Autonomic Nervous System

What is the structure of a typical neuron?

A neuron consists of a cell body, dendrites, and an axon.

What are the functions of dendrites in a neuron?

Dendrites receive signals from other neurons.

What is the function of the axon in a neuron?

The axon transmits electrical impulses away from the cell body.

How are neurons classified based on their structure?

Neurons can be classified as unipolar, bipolar, or multipolar.

What are neuroglia?

Neuroglia are supportive cells in the nervous system that maintain homeostasis, form myelin, and provide support and protection for neurons.

What is resting membrane potential?

Resting membrane potential is the electrical potential difference across the membrane of a non-active cell, typically around -70mV.

How is resting membrane potential established?

It is established by the distribution of ions, primarily sodium (Na+) and potassium (K+), across the cell membrane.

What is an action potential?

An action potential is a rapid change in membrane potential that occurs when a neuron sends a signal.

What factors affect the speed of action potential propagation?

The speed is affected by the myelination of the axon and the diameter of the axon.

What is the structure of a synapse?

A synapse consists of a presynaptic terminal, synaptic cleft, and postsynaptic membrane.

What are neurotransmitters?

Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another.

What is the role of the sodium/potassium pump?

The sodium/potassium pump moves 3 sodium ions out of the cell and 2 potassium ions into the cell, using ATP to maintain ion concentration gradients.

What are ion channels?

Ion channels are pores in the cell membrane that allow specific ions to cross in response to concentration gradients.

What are leakage channels?

Leakage channels are passive ion channels that randomly allow ions to move across the membrane.

What are chemically gated ion channels?

Chemically gated ion channels open in response to the binding of specific chemicals, such as neurotransmitters.

What are mechanically gated ion channels?

Mechanically gated ion channels respond to physical distortion of the membrane, such as pressure or touch.

What are voltage-gated ion channels?

Voltage-gated ion channels open in response to changes in membrane potential.

Where are voltage-gated ion channels found?

They are found in the axons of neurons and the sarcolemma of skeletal and cardiac muscle cells.

What is electrochemical exclusion?

Electrochemical exclusion refers to the property of ion channels being specific to the charge of ions that can pass through.

What is the role of transmembrane proteins in the cell membrane?

Transmembrane proteins, including channel proteins, facilitate the movement of ions across the cell membrane.

What happens during the generation of an action potential?

During action potential generation, depolarization occurs, followed by repolarization and hyperpolarization.

What is membrane potential?

A distribution of charge across the cell membrane, measured in millivolts (mV).

How is membrane potential measured?

By comparing the charge inside the cell to the outside, which is considered zero.

What is the resting membrane potential of a typical cell?

-70 mV.

What ion concentration is higher outside the cell at rest?

Sodium ions (Na+).

What ion concentration is higher inside the cell at rest?

Potassium ions (K+) and negatively charged proteins.

What role do leakage channels play in resting membrane potential?

They allow Na+ to slowly enter the cell and K+ to slowly exit.

What initiates an action potential?

A ligand-gated Na+ channel opens when a neurotransmitter binds, or a mechanically gated Na+ channel opens due to a physical stimulus.

What is the threshold potential for initiating an action potential?

-55 mV.

What happens during depolarization?

Na+ rushes into the cytosol, causing the inner membrane surface to change from negative to positive.

What is the peak voltage reached during an action potential?

+30 mV.

What occurs after the peak of depolarization?

Inactivation of Na+ channels and activation of K+ channels, leading to repolarization.

What is hyperpolarization?

The membrane potential briefly becomes more negative than the resting potential, reaching -90 mV.

What is the all-or-none principle in action potentials?

Any stimulus that reaches the threshold will trigger an action potential; all action potentials are the same size.

What are the two types of voltage-gated channels involved in action potentials?

Voltage-gated Na+ channels and voltage-gated K+ channels.

What is the refractory period?

The time during which the membrane cannot respond normally to additional stimuli.

What is the absolute refractory period?

The period when all voltage-gated Na+ channels are open or inactivated, and the membrane cannot respond to further stimulation.

What is the relative refractory period?

The period when Na+ channels regain resting condition, and only a strong stimulus can initiate another action potential.

How does an action potential propagate along an axon?

It develops at the initial segment, causing local currents that depolarize adjacent segments to threshold.

What is the speed of action potential propagation?

Approximately 1 m/sec.

What happens during repolarization?

K+ moves out of the cytosol, returning the membrane potential to resting levels.

What is the role of the Na+/K+ pump?

It restores the concentrations of Na+ and K+ after an action potential.

What is the significance of the slight charge difference at the membrane surface?

It generates electrical signals in neurons and muscle cells.

What is the typical concentration ratio of Na+ outside to inside the cell at rest?

10 times greater outside.

What occurs during the inactivation of Na+ channels?

The inactivation gates close after a brief period, preventing further Na+ entry.

What is the role of neurotransmitters in initiating action potentials?

They bind to ligand-gated Na+ channels, causing them to open.

What happens to the membrane potential during the action potential cycle?

It rises to +30 mV during depolarization, then falls back down during repolarization.

What is the relationship between action potentials and stimuli strength?

Action potentials are not affected by the strength of the stimulus once the threshold is reached.

Continuous propagation of action potentials

A type of action potential propagation that occurs in unmyelinated axons, affecting one segment of the axon at a time.

Saltatory propagation of action potentials

A faster type of action potential propagation that occurs in myelinated axons, where local current jumps from node to node, requiring less energy.

Myelin

A fatty substance that insulates axons, preventing continuous propagation of action potentials and allowing for faster saltatory propagation.

Nodes of Ranvier

Gaps in the myelin sheath where depolarization occurs during saltatory propagation of action potentials.

Energy efficiency in action potential propagation

Saltatory propagation requires less energy than continuous propagation due to the jumping of local currents between nodes.

Effect of myelin on action potentials

Myelin prevents continuous propagation and facilitates faster transmission of action potentials through saltatory propagation.

What initiates an action potential in a neuron?

Opening of voltage-gated sodium channels at the start of the axon.

What happens to the membrane potential when sodium enters the neuron?

It rises to about +30 mV, creating the action potential.

What is the resting membrane potential of a neuron?

Approximately -70 mV.

How does sodium affect the next segment of the axon?

Sodium spreads sideways, creating a local current that depolarizes the next segment.

What is the threshold potential that segment ② must reach to fire an action potential?

About -60 mV.

What happens to segment ② after it reaches threshold?

It fires its own action potential, rising to +30 mV.

What is the refractory period?

The time when a segment of the axon cannot fire again immediately after an action potential.

What is continuous propagation?

The process where action potentials affect one segment of an unmyelinated axon at a time.

What is saltatory conduction?

The jumping of action potentials between nodes of Ranvier in myelinated axons.

Why is saltatory conduction faster than continuous propagation?

It skips the myelinated sections, activating only at exposed nodes.

What happens at node ① during saltatory conduction?

An action potential occurs as sodium rushes into the axon.

What is the role of local current in action potential propagation?

It depolarizes adjacent segments or nodes to reach threshold.

What ensures that the action potential moves forward and not backward?

The refractory state of the previous segment prevents it from firing again immediately.

What is the significance of myelin in action potential propagation?

Myelin insulates the axon, allowing faster signal transmission and reducing energy use.

How does the action potential propagate down the axon?

By a chain reaction of depolarization and repolarization across segments or nodes.

What is continuous conduction?

A slow process where voltage-gated Na+ channels open, allowing Na+ to rush into the cell.

What is saltatory conduction?

A faster process where the action potential jumps from one node to the next, renewing depolarization.

How does the diameter of an axon affect conduction speed?

Larger diameters lower resistance and increase conduction speed.

What are Type A fibers?

Myelinated fibers with a large diameter that transmit information rapidly (120 m/sec) to and from the CNS.

What type of information do Type A fibers transmit?

Sensory information such as position and balance, and motor impulses to skeletal muscles.

What are Type B fibers?

Myelinated fibers with a medium diameter that transmit information at intermediate speeds (18 m/sec).

What are Type C fibers?

Unmyelinated fibers with a small diameter that transmit information slowly (1 m/sec).

What type of information do Type C fibers typically carry?

Most sensory information.

How are messages routed by nerves?

According to priority, with critical information transmitted through Type A fibers.

What kind of information do Type A fibers carry that is critical for survival?

Sensory information about threats and motor commands that prevent injury.

What is the speed of transmission for Type A fibers?

120 m/sec.

What is the speed of transmission for Type B fibers?

18 m/sec.

What is the speed of transmission for Type C fibers?

1 m/sec.

What is the role of myelination in axon conduction?

Myelination increases the speed of action potential propagation.

What does the term 'saltare' mean in relation to saltatory conduction?

It means 'to leap', referring to how the action potential jumps between nodes.

What happens to the depolarized membrane during saltatory conduction?

The new influx of Na+ renews the depolarized state.

What is the relationship between axon diameter and conduction speed?

Larger diameter axons have lower resistance and faster conduction speeds.

What type of fibers are responsible for rapid transmission of sensory and motor information?

Type A fibers.

Why is continuous conduction considered slow?

Because it involves a continuous opening of voltage-gated Na+ channels.

What is the primary difference between Type B and Type C fibers?

Type B fibers are myelinated and transmit at intermediate speeds, while Type C fibers are unmyelinated and transmit slowly.

Opening of sodium channels in the axon membrane causes

A. depolarization. B. repolarization. C. hyperpolarization. D. inhibition.

A

Which of the following statements about the action potential is false?

A. During the depolarization phase, membrane potential becomes positive.

B. Repolarization occurs as potassium ions leave the axon.

C. During the repolarization phase, sodium channels close and potassium channels open.

D. The rapid depolarization phase is caused by the entry of potassium ions.

D (should be entry of sodium ions)

What is an action potential compared to?

A light switch turned on.

What initiates the depolarization in an action potential?

A stimulus that reaches a threshold.

What are graded potentials

Temporary changes in membrane voltage that depend on the size of the stimulus.

Where do graded potentials usually occur?

In the dendrites of a neuron.

What determines the amount of change in membrane potential during graded potentials?

The size of the stimulus that causes it.

What are the two types of graded potentials?

Depolarizing and hyperpolarizing.

What causes depolarizing graded potentials?

Na+ or Ca2+ entering the cell.