Neurophysiology Refractory Periods Quiz

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Questions and Answers

What is the primary mechanism of neurotransmitter release at chemical synapses?

Vesicle fusion triggered by calcium ions (correct)

Direct ion flow between cells

Electrical signal propagation along the axon

Passive diffusion through the membrane

Which protein is NOT involved in the docking of synaptic vesicles for neurotransmitter release?

SNAP-25

Syntaxin

Synaptobrevin

Actin (correct)

Which type of receptor is characterized by being an ion channel and allowing rapid ion flow upon ligand binding?

G-protein coupled receptor

Enzymatic receptor

Ionotropic receptor (correct)

Metabotropic receptor

What role do calcium ions play in neurotransmitter release?

They trigger vesicle fusion with the membrane. Signup and view all the answers

Which characteristic distinguishes electrical synapses from chemical synapses?

Chemical synapses use neurotransmitters to transmit signals. Signup and view all the answers

What effect does the inactivation of Na⁺ channels have on the initiation of a second action potential?

It enables a second action potential only with a stronger-than-normal stimulus. Signup and view all the answers

What causes hyperpolarization during the relative refractory period?

Open K⁺ channels allowing K⁺ to exit the cell. Signup and view all the answers

How many sodium ions are expelled from the cell by the sodium-potassium pump in one cycle?

3 Signup and view all the answers

What is the primary function of myelin in neural conduction?

To insulate axons and promote saltatory conduction. Signup and view all the answers

Where in the neuron do action potentials typically originate?

At the axon hillock (trigger zone). Signup and view all the answers

What is saltatory conduction?

A method by which action potentials jump between nodes of Ranvier. Signup and view all the answers

Which cellular mechanism is primarily responsible for restoring ion gradients after an action potential?

Sodium-potassium pump. Signup and view all the answers

During the relative refractory period, what is needed to initiate an action potential?

A stronger-than-normal stimulus. Signup and view all the answers

What is the primary function of GABA in the central nervous system (CNS)?

To reduce neural excitability Signup and view all the answers

What neurotransmitter is synthesized from tyrosine?

Dopamine Signup and view all the answers

What is the role of acetylcholinesterase in relation to acetylcholine?

It breaks down acetylcholine in the synaptic cleft Signup and view all the answers

GABA receptors primarily function as which type of receptor?

Ionotropic receptors Signup and view all the answers

What is the consequence of GABA dysregulation?

It may cause overstimulation of neurons Signup and view all the answers

Which of the following statements about dopamine is correct?

It regulates reward and motivation Signup and view all the answers

How is GABA primarily synthesized in neurons?

From glutamate Signup and view all the answers

What type of receptors do acetylcholine and GABA bind to?

Both ionotropic and metabotropic receptors Signup and view all the answers

What occurs during the depolarization phase of an action potential?

Na⁺ channels open and Na⁺ rushes into the neuron. Signup and view all the answers

During which phase does the membrane potential reach approximately +30 mV?

Depolarization Signup and view all the answers

What is happening during the hyperpolarization phase of an action potential?

K⁺ channels remain open, making the membrane potential more negative than at resting state. Signup and view all the answers

Which ion flows out of the neuron during the repolarization phase?

K⁺ Signup and view all the answers

What characterizes the absolute refractory period?

No second action potential can be initiated regardless of stimulus strength. Signup and view all the answers

Which of the following statements about the sodium-potassium pump is true?

It helps maintain resting potential by moving 3 Na⁺ out for every 2 K⁺ in. Signup and view all the answers

What happens during the falling phase of an action potential?

K⁺ channels open while Na⁺ channels close, allowing K⁺ to flow out. Signup and view all the answers

What is the reason for the undershoot phase in an action potential?

K⁺ channels remain open longer than needed. Signup and view all the answers

What is a primary function of astrocytes in the brain?

Regulating nutrient supply from the bloodstream Signup and view all the answers

Which part of a neuron is responsible for transmitting electrical impulses away from the cell body?

Axon Signup and view all the answers

What initiates action potentials in a neuron?

Axon hillock Signup and view all the answers

How do neurons communicate with each other?

By releasing neurotransmitters at synapses Signup and view all the answers

What role does the myelin sheath play in neuron function?

Insulates the axon and speeds up signal transmission Signup and view all the answers

What is the primary component that distinguishes neurons from other cell types?

Their excitable nature and ability to generate action potentials Signup and view all the answers

Which structure in the neuron serves as the location for integrating signals?

Soma Signup and view all the answers

What is maintained by astrocytes to support neuronal function?

Nutrient balance and ion homeostasis Signup and view all the answers

Study Notes

Refractory Periods

Absolute Refractory Period: Occurs during depolarization and most of repolarization. No second action potential can be triggered, regardless of stimulus strength. This is caused by the inactivation of Na⁺ channels, preventing them from reopening until the membrane potential returns to a certain level.
Relative Refractory Period: Occurs during the latter part of repolarization and undershoot. A second action potential can be initiated, but only with a stronger-than-normal stimulus. This is caused by open K⁺ channels leading to hyperpolarization, requiring a stronger stimulus to reach the threshold.

Sodium-Potassium Pump

The sodium-potassium pump continuously works to maintain potassium and sodium distributions, restoring the initial ion concentrations after an action potential.
It pumps 3 sodium ions out of the cell and 2 potassium ions into the cell against their concentration gradients.
This requires a significant amount of ATP as it works against the concentration gradient.

Action Potential Origin and Travel

Action potentials originate at the axon hillock (trigger zone).
They travel down the axon toward the axon terminals by depolarizing sections of the membrane in a wave-like manner.
Sodium (Na+) ions enter the cell, while potassium (K+) ions exit during depolarization.

Myelin and Saltatory Conduction

Myelin is a fatty substance that insulates axons.
It is produced by Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS).
Myelinated axons conduct action potentials faster through saltatory conduction, where the signal jumps between Nodes of Ranvier.
Voltage-gated sodium channels are only located at the Nodes of Ranvier.

Electrical vs. Chemical Synapses

Electrical synapses: Direct ion flow between cells via gap junctions. They are fast but less flexible and simpler than chemical synapses. More common in invertebrates.
Chemical synapses: Use neurotransmitters to transfer signals across a synaptic cleft. They are slower but highly adaptable and act on specific receptors on the receiving cell's surface.

Neurotransmitter Release: Proteins and Ions

Calcium ions (Ca²⁺): Trigger vesicle fusion.
SNARE proteins: (syntaxin, SNAP-25, synaptobrevin) are essential for vesicle docking and neurotransmitter release. Found on the membrane of the vesicles and the neuronal membrane.

Neurotransmitter Release: Sequence of Events

Action potential reaches the axon terminal.
Voltage-gated Ca²⁺ channels open, allowing calcium to enter.
Synaptic vesicles fuse with the membrane, releasing neurotransmitters.
Neurotransmitters diffuse across the synapse and bind to receptors.

Ligands and Receptors

Ligand: A molecule that binds to a receptor (e.g., neurotransmitter).
Receptor: A protein on the cell surface that ligands bind to, initiating a response.

Ionotropic vs. Metabotropic Receptors

Ionotropic receptors: The receptor itself is an ion channel. Ions rapidly flow through when it is open (depending on driving force). These are also called "transmitter-gated ion channels".
Metabotropic receptors: The receptor activates a signaling pathway, indirectly affecting channels or other cellular processes. Slower acting, modulatory effects.

Glia Types and Functions

Astrocytes: Found in the CNS. They provide structural support, regulate the blood-brain barrier, help deliver nutrients, clear excess neurotransmitters and metabolic waste, and maintain ion balance.
Oligodendrocytes: Found in the CNS. They produce myelin to insulate axons.
Schwann cells: Found in the PNS. They produce myelin to insulate axons.

Neuron vs. Other Cell Types

Excitability: Neurons can generate and propagate electrical impulses (action potentials).
Synaptic transmission: Communicate via neurotransmitter release at synapses.
Unique structure: Dendrites (receive signals), axon (transmit signals), soma (cell body).
Polarity: Signals flow in one direction from dendrites to axon terminal.

Neuron Parts

Dendrites: Receive signals from other neurons.
Cell body (soma): Contains nucleus and organelles, integrates signals.
Axon: Transmits electrical impulses away from the soma.
Axon hillock: Where the axon connects to the soma; action potentials are initiated.
Myelin sheath: Insulates axon, speeding up signal transmission.
Nodes of Ranvier: Gaps in the myelin sheath where action potentials are regenerated..
Axon terminal: Releases neurotransmitters to communicate with other neurons.

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Description

Test your understanding of the absolute and relative refractory periods in neurophysiology. This quiz covers key concepts like sodium and potassium ion dynamics, as well as the role of the sodium-potassium pump in maintaining ion balance during action potentials.