psych 261 lecture 3

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Questions and Answers

What is the primary mode of communication between neurons according to the provided text?

Direct physical contact between axons

Chemicals called neurotransmitters (correct)

A combination of electrical and magnetic impulses

Electrical signals carried by dendrites

What is the main function of axons as described in the provided text?

To form the physical gap of the synapse

To conduct electrical signals (correct)

To receive chemical signals

To synthesize neurotransmitters

The concept of the 'synapse', as referenced in the text was introduced by whom?

Sir Charles Scott Sherrington (correct)

An anonymous researcher

A collective scientific body

A group of early neuroscientists

According to the provided text, what is the nature of the physical connection at the synapse?

A point of contact with a gap Signup and view all the answers

What does the term 'synapse' mean according to the text?

'Joining together' Signup and view all the answers

According to the provided diagrams, where are microglia located within the nervous system?

Throughout the brain including the cortex, corpus callosum, and hippocampus Signup and view all the answers

What is a key characteristic of action potential propagation down the axon?

The action potential size remains constant as it travels. Signup and view all the answers

What is one of the primary roles of microglia, as depicted in the provided diagrams?

To remove excessive synapses Signup and view all the answers

Which of the following best describes the resting potential of a cell?

The inside of the cell is more negative than the outside. Signup and view all the answers

Besides excess synapses, what other cellular components are microglia shown to remove?

Live glioma cells, and neuronal precursors Signup and view all the answers

In an action potential, what is the approximate peak voltage inside the cell?

+40 mV Signup and view all the answers

What best describes the action of microglia on neuronal components such as synapses and dendritic spines, according to the diagrams?

They prune and remove synapses, and may affect dendritic spines Signup and view all the answers

According to the provided illustrations, which of the following is true about squid giant axons?

They are large enough to insert microelectrodes for study. Signup and view all the answers

According to the diagrams provided, what is the overall impact of microglia on neuronal connections?

They selectively remove and refine neuronal connections, ensuring effective network function Signup and view all the answers

Which region of the neuron is the action potential shown to propagate along?

Axon Signup and view all the answers

Which of the following correctly identifies the role of microglia depicted, in relation to neurons?

They engulf and remove live, stressed neurons alongside other elements in the brain Signup and view all the answers

What cellular process most accurately describes how microglia interact with synapses, as depicted in these diagrams?

Phagocytosis of synapses Signup and view all the answers

According to the provided illustrations, what are the relative charges outside and inside the cell at resting potential?

Outside positive, inside negative Signup and view all the answers

Based on the diagrams, which of these cells are targeted by microglia, in addition to neurons and their components?

Neutrophils, live glioma cells, and neuronal precursors occur with neurons and their components Signup and view all the answers

What was the key contribution by Hodgkin and Huxley mentioned in the text in relation to action potentials?

Quantifying the mechanism of action potentials using the giant axon of a squid Signup and view all the answers

Where does the action potential travel after it leaves the axon?

Presynaptic Terminal Signup and view all the answers

What is the state of sodium (Na+) channels at resting potential?

Closed Signup and view all the answers

What happens to the potassium (K+) channels immediately following depolarization?

They open very slowly Signup and view all the answers

What voltage is reached when Na+ channels open rapidly?

+40 mV Signup and view all the answers

What is the state of potassium (K+) channels at resting potential?

Partly open Signup and view all the answers

What triggers the cell to reach the threshold?

Depolarizing stimulation Signup and view all the answers

What happens to sodium (Na+) channels after they open rapidly?

They close Signup and view all the answers

At which point do potassium (K+) channels reach maximal opening?

After Na+ channels close Signup and view all the answers

What happens to potassium (K+) channels once the cell is repolarized?

They close Signup and view all the answers

During which phase of the action potential does the membrane potential become more negative than the resting membrane potential?

Afterhyperpolarization Signup and view all the answers

What is the primary purpose of the sodium-potassium pump in maintaining neuronal membrane potential?

To establish and maintain the concentration gradients of sodium and potassium ions. Signup and view all the answers

According to the provided figure of an action potential, approximately how long does it take for a neuron to complete an action potential?

Approximately 4 milliseconds Signup and view all the answers

Which ion is most responsible for the repolarization phase of an action potential?

Potassium ($K^+$) Signup and view all the answers

What role do negatively charged proteins primarily play in a neuron?

They contribute to the resting membrane potential. Signup and view all the answers

Based on the diagram of the potassium channel, what is the difference between the 'closed' and 'open' state of the channel?

The channel conformation changes, creating or obstructing an ion-conducting pore. Signup and view all the answers

Which of the following ion channels play a major role during the depolarization phase of an action potential?

Voltage-dependent sodium channels Signup and view all the answers

What would happen to the resting membrane potential of a neuron if the sodium-potassium pumps were disabled?

The membrane potential would eventually approach $0 mV$. Signup and view all the answers

During the rising phase of an action potential, which of the following best describes the state of ion channels?

Sodium channels open rapidly, and potassium channels open very slowly. Signup and view all the answers

What is the approximate membrane potential (in mV) at which an action potential is triggered, also known as the threshold?

-7 Signup and view all the answers

What role does the sodium-potassium pump play in maintaining the resting membrane potential?

Moves 3 Na+ ions out of the cell for every 2 K+ ions moved in. Signup and view all the answers

During the absolute refractory period, it is impossible to trigger another action potential because:

The sodium channels are in a closed state and cannot be activated yet. Signup and view all the answers

When does the membrane potential reach its peak positive value during an action potential?

When sodium channels open rapidly, and before the potassium channels open. Signup and view all the answers

According to the 'all-or-none' law, what happens to the amplitude of an action potential if the stimulus strength increases?

The amplitude of an action potential remains the same. Signup and view all the answers

What primarily determines the resting membrane potential of a neuron?

The partially open potassium channels, with other channels closed. Signup and view all the answers

During the relative refractory period, a stronger than normal stimulus may trigger an action potential. Why?

Some sodium channels have recovered from inactivation and are able to open. Signup and view all the answers

Study Notes

Neuron Communication

Communication between neurons occurs via chemicals called neurotransmitters.
Axons transmit electrical signals.

Sir Charles Scott Sherrington

Introduced the concept of the synapse.
Synapse describes the gap between nerve cells, allowing for changes in the nervous impulse as it passes from one cell to the next.

Neuron Types

Efferent Axon: Carries signals away from an area.
Afferent Axon: Carries signals to an area.

Glia

Supporting cells in the nervous system.

Astrocytes

Star-shaped glial cells.
Help form the blood-brain barrier.
Create scaffolding that holds neurons in place.
Serve as conduits for nutrients between blood and neurons.

Blood-Brain Barrier

A selective barrier that controls the passage of substances between the blood and the brain.
Lipid-soluble agents and some gases can passively cross.
Tight junctions restrict the passage of water-soluble substances.
Astrocytes and pericytes help create the barrier.

The Tripartite Synapse

Includes a presynaptic neuron, a postsynaptic neuron, and an astrocyte.
Astrocytes help synchronize activity among multiple synapses.
Astrocytes play a role in regulating neurotransmitter release.

Schwann Cells

Glial cells in the peripheral nervous system.
Form myelin sheaths around axons.
Help maintain the integrity of axons in the peripheral nerves.

Oligodendrocytes

Glial cells in the central nervous system.
Form myelin sheaths around axons.
Can myelinate multiple axons simultaneously.

Polydendrocytes (NG2 Cells)

Precursors to oligodendrocytes.
Help remyelinate axons after injury.
Can form synapses with neurons.

Microglia

Small, immune-like glial cells.
Remove debris, foreign invaders, and damaged cells to maintain brain health.
Involved in synaptic pruning and the removal of synapses.
Interact with synapses.

Radial Glia

Supporting cells that guide migrating neurons during development.
Provide scaffolding for neurons to reach their final destinations in the brain.

The Action Potential

The action potential is an electrical signal that travels down an axon.
It is initiated at the axon hillock.
The magnitude remains constant regardless of stimulation strength (all-or-none law).
The action potential has a specific sequence of events involving ion channels.
There is an absolute and relative refractory periods to ensure one-way propagation of nerve impulses down the axon.

Ion Concentrations

Ion concentration gradients across the neuronal membrane help create and maintain the resting potential.
Differences in ion concentration drive the flow of ions across the membrane.

Ion Movement

Diffusion moves ions from high to low concentration.
Electrostatic forces move ions based on their charge.

Hodgkin & Huxley Model

Developed a model describing the action potential.
Used squid giant axons to study ion channels and currents.

The Action Potential: Characteristics

Electrical signal that travels down the axon.
Initiated at the axon hillock.
All-or-none law: magnitude remains the same regardless of stimulation strength.

Action potential varieties

The shape of the action potential varies according to the neuron type.
Characterized by specific properties, including duration, peak voltage.

The Sodium-Potassium Pump

Active transport mechanism that maintains ion gradients.
Moves 3 sodium ions out for every 2 potassium ions it moves in.

Refractory periods

Absolute refractory period: neuron cannot fire another action potential.
Relative refractory period: neuron can fire, but greater stimulation is needed.

The Potassium Channel

Contributes to controlling the action potential.
Opens very slowly compared to sodium channel.

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Description

Test your understanding of the communication between neurons, the role of axons, and the concept of the synapse with this quiz. Explore the functions of microglia and the mechanics of action potentials as described in your neuroscience class materials.