Neuroscience Chapter on Neurotransmitters

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Questions and Answers

What occurs when a neurotransmitter binds to a metabotropic receptor?

It leads to immediate depolarization of the postsynaptic neuron.

Movement of ions occurs through metabolic steps. (correct)

The membrane potential is always hyperpolarized.

Ions move directly through the channel.

What are the two main types of postsynaptic potentials?

Depolarizations and repolarizations

Hyperpolarizations and ionotropic potentials

Threshold potentials and resting potentials

Excitatory postsynaptic potentials and inhibitory postsynaptic potentials (correct)

Which mechanism is NOT involved in the termination of neurotransmitter signaling?

Reuptake of neurotransmitters

Diffusion of neurotransmitters away from the synapse

Enzymatic breakdown of neurotransmitters

Increased ion movement into the neuron (correct)

What severe effect does nerve gas sarin have on neurotransmitter signaling?

It inhibits the enzyme that breaks down neurotransmitters. Signup and view all the answers

In what way do temporal and spatial summation differ?

Temporal summation occurs over time, while spatial summation involves the summation of potentials from different locations. Signup and view all the answers

What type of neuron is responsible for transmitting signals to muscle cells?

Motor neurons Signup and view all the answers

What is the resting potential of a neuron?

The voltage difference when the neuron is not sending signals Signup and view all the answers

Which type of ion channel is primarily responsible for the resting membrane potential?

Nongated Channels Signup and view all the answers

What is the role of sodium-potassium pumps in neurons?

To maintain K+ and Na+ concentration gradients Signup and view all the answers

Which statement accurately describes sensory neurons?

They transmit information about external stimuli Signup and view all the answers

What is the primary role of the axon in a neuron?

To transmit signals to other cells at synapses Signup and view all the answers

What type of signal is primarily used for long-distance communication in neurons?

Electrical signals Signup and view all the answers

Which structure in a neuron is primarily responsible for receiving signals?

Dendrites Signup and view all the answers

What is a characteristic of voltage-gated channels?

They generate and propagate action potentials Signup and view all the answers

What occurs at the synapse?

Electrical signals are converted to chemical signals Signup and view all the answers

How do graded potentials differ from action potentials?

Graded potentials can vary in magnitude, while action potentials are all-or-nothing Signup and view all the answers

What best describes the nature of nerve signal transmission?

It is fast and depends on the signal’s pathway Signup and view all the answers

Where is the axon hillock located in a neuron?

At the cone-shaped base of an axon Signup and view all the answers

What defines the information conveyed by a signal in the nervous system?

The specific location of the signal's pathway Signup and view all the answers

What is the function of neurotransmitters at the synapse?

To facilitate communication between neurons Signup and view all the answers

What is the significance of the electrochemical gradient in neurons?

It plays a role in the initiation and conduction of action potentials Signup and view all the answers

What prevents the action potential from traveling backwards along the axon?

Inactivated Na+ channels behind the zone of depolarization. Signup and view all the answers

What is the primary role of the myelin sheath in axons?

To insulate and speed up signal conduction. Signup and view all the answers

Which phase of the action potential would be most affected by a toxin that binds to voltage-gated sodium channels?

Depolarization phase. Signup and view all the answers

What primarily influences the resting potential of a neuron?

K+ channel permeability Signup and view all the answers

Which ion channel opening results in hyperpolarization of the neuron?

Opening potassium (K+) channels Signup and view all the answers

How is the electrical current transmitted at electrical synapses?

Through gap junctions. Signup and view all the answers

What characterizes saltatory conduction in myelinated axons?

Jumping of action potentials from node to node. Signup and view all the answers

What characterizes action potentials in neurons?

They are all-or-none events. Signup and view all the answers

What is the primary consequence of the lipids in the myelin sheath?

They provide electrical insulation. Signup and view all the answers

What is the primary function of voltage-gated Na+ channels during depolarization?

They allow Na+ to diffuse into the cell. Signup and view all the answers

What role do oligodendrocytes play in the central nervous system?

They wrap axons with layers of myelin. Signup and view all the answers

Which statement about graded potentials is true?

They can lead to action potentials if sufficiently strong. Signup and view all the answers

What is the effect of slow restorative actions of the sodium-potassium ATPase?

It helps to restore resting membrane potential. Signup and view all the answers

What term describes the level of membrane potential necessary to trigger an action potential?

Threshold potential Signup and view all the answers

What happens during the repolarization phase of an action potential?

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

Which statement about the sodium-potassium pump is correct?

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

What initiates the release of neurotransmitters at the presynaptic terminal?

Voltage-gated Ca2+ channels opening Signup and view all the answers

What is the role of neurotransmitters in synaptic transmission?

To bind to receptors on the postsynaptic cell Signup and view all the answers

How can a single neurotransmitter affect different postsynaptic cells?

By binding to different types of receptors Signup and view all the answers

What is the primary function of ligand-gated ion channels in the postsynaptic cell?

To facilitate the entry of ions upon neurotransmitter binding Signup and view all the answers

What occurs at the end of the axon before neurotransmitter release?

Calcium ions enter the presynaptic terminal Signup and view all the answers

What characterizes chemical synapses compared to electrical synapses?

Chemical synapses use neurotransmitters for communication Signup and view all the answers

Which of the following describes the effect of neurotransmitter binding on postsynaptic cells?

It might generate an excitatory or inhibitory response Signup and view all the answers

What mechanism allows neurotransmitters to cross the synaptic cleft?

Simple diffusion across the cleft Signup and view all the answers

Study Notes

Neurons

Neurons are cells that exemplify the close fit between form and function.
Cell body—contains most organelles.
Dendrites—highly branched extensions that receive signals from other neurons. Axons—often much longer extensions that transmit signals to other cells at synapses
The cone-shaped base of an axon is called the axon hillock.
A synapse is a junction between an axon and another cell. The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters.
Sensory neurons transmit information about external stimuli (light, touch, smell).
Interneurons analyze and interpret information
Motor neurons transmit signals to muscle cells, causing them to contract.
Signaling a short distance is chemical.
Signaling a long distance is electrical.

Topics covered

Neurons and electrochemical gradient generation
Resting and membrane potential changes
Action potentials
Conduction of the action potential
Transmission of action potentials (synapses)

Action Potentials

Depolarization—a reduction in the magnitude of the membrane potential
Hyperpolarization—an increase in the magnitude of the membrane potential.
If a depolarization shifts the membrane potential sufficiently, the result is a massive change in membrane voltage called an action potential
Action potentials have a constant magnitude, are all-or-none, and transmit signals over long distances
Action potentials arise because some ion channels are voltage-gated channels(opening or closing when the membrane potential passes a certain level called threshold)

Generation of Postsynaptic Potentials

Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell.
Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential
Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold.
Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from threshold.

Myelinated axons

Myelin sheath - The electrical insulation that surrounds vertebrate axons
Myelin sheath is produced by glial cells (oligodendrocytes in the CNS, Schwann cells in the PNS)
Myelin sheath's membranes are mostly lipid, which is a poor electrical conductor and thus a very good insulator.
Action potentials "jump" from node to node resulting in Saltatory conduction.

Transmission of a Signal: Synapse

At electrical synapses, the electrical current flows from one neuron to another through gap junctions.
At chemical synapses, a chemical neurotransmitter carries information between neurons.
Most synapses are chemical synapses.
Neurotransmitter molecules are cleared from the synaptic cleft in two mechanisms:
- Enzymatic breakdown of NT
- Reuptake of the NT.

Formation of Resting Potential

In most neurons, the concentration of K+ is higher inside the cell, while the concentration of Na+ is higher outside the cell.
Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane.
These concentration gradients represent chemical potential energy.

Ion Concentrations Inside/Outside Mammalian Neurons

Table 48.1: Shows Potassium (K+), Sodium (Na+), Chloride (Cl-), and other ions' concentrations inside and outside mammalian neurons.

Voltage-gated Ion Channels

Open or close in response to changes in voltage across the plasma membrane.
When gated, they open/close in response to a change in voltage
Nongated channels are responsible for resting membrane potential and responsible for the resting membrane potential.
Voltage-gated channels are responsible for the generation and propagation of the action potential.
Chemically-gated channels are responsible for synaptic potentials.

The "undershoot" Phase

The 'undershoot', or after-hyperpolarization, phase after the action potential is due to sustained opening of voltage-gated potassium channels.

Nerve Gas Sarin

Nerve gas sarin blocks the process of neurotransmitter breakdown leading to paralysis and death by inhibiting the enzyme involved.

Flow of Information

Sensory input—information flows from a sensor to integration.
Integration—information is processed.
Motor output—information exits integration to an effector.

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Test your knowledge on neurotransmitter signaling and its various mechanisms with this quiz. Explore topics such as metabotropic receptors, postsynaptic potentials, and the effects of nerve agents like sarin on neurotransmission. Ideal for students studying neuroscience or related fields.