Week 2: Neurons and Action Potentials

What is conductance?

The ability of ions to flow through a medium.

What is permeability?

The property of a membrane that allows substances to pass through.

What is an ion channel?

A protein structure that allows ions to pass through a cell membrane.

What is resting membrane potential?

The difference in electrical charge across the membrane at rest.

What is depolarization?

The process of reducing the membrane potential difference.

What is hyperpolarization?

The process of increasing the membrane potential difference.

What is an action potential?

An electric impulse that travels along the neuron.

What is the action potential threshold?

The membrane potential level that must be reached to initiate an action potential.

What is the difference between ionotropic and metabotropic receptors?

Ionotropic receptors directly control ion channels, while metabotropic receptors activate signaling pathways.

What is EPSP?

Excitatory postsynaptic potential, a change in membrane potential that makes a neuron more likely to fire.

What is continuous conduction?

The unmyelinated propagation of action potentials along an axon.

What is saltatory propagation?

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

Why is the action potential referred to as 'all-or-none'?

Because no partial action potentials exist; it either occurs fully or not at all.

Why do action potentials travel in only one direction?

Because the membrane just behind the action potential is refractory due to inactivated sodium channels.

Why is an excitatory synapse on the soma more effective in evoking action potentials?

Because it is closer to the spike-initiation zone, allowing for more effective depolarization.

What is the correct definition of resting membrane potential?

A) Difference in electrical charge across the membrane at rest.

Which major charge carriers are involved in the conduction of electricity in neurons?

B) Cations.

How do action potentials differ from passively conducted electrical signals?

D) Action potentials are signals of fixed size and duration; passively conducted signals are not.

Which of the following is true of ion channels?

a) They permit the passage of ions through a cell membrane

b) They are composed of proteins that form pores in the cell membrane

c) They are responsible for passive transport of ions through the cell membrane

all of the above

Which of the following might cause a neuron to fire?

All of the above.

A)EPSPs triggered by activity at five synapses at the same time

b) EPSPs triggered by activity at five nearby synapses

c) Multiple EPSPs at the same synapse triggered in rapid succession

all of the above

Neurons

Neurons function to receive, integrate and transit information

About a hundred billion neurons

Neurons receive an avg of 5000 synaptic contacts

Glia

Glia means glue

3 types:

-Astrocytes; buffer ion concentration, metabolic fuel

-Oligodendrocytes & Schwann celll wrap around axon to create insulation, oligo-CNS Schwann-PNS

-Microglia; clean up cellular derbies produced by damage

Neuron Doctrine

The hypothesis that the brain is composed of separate cells that are distinct structurally, metabolically, and functionally.

Basic Structure of Neuron

Soma, Nucleus, Dendrites, Axon hillock, axon, myelin, node of ranvier, axon collateral, presynaptic terminal, synaptic vesicles, synaptic cleft, postsynaptic density

Functional Zones of a neuron

input zone, integration zone, conduction zone, output zone

Cellular structure: Soma & dentrites

Functional Zone: Input

Events: Post Synaptic Potential

Molecular Structure: Postsynaptic Receptors: ligand-gated ion channels

Ion: NA+ Cl-

Cellular Structure: Axon Hillock

Functional Zone: Integration

Events: action potential initiation

Molecular Structure: Voltage gated ion channels

Ion: Na+

Cellular Structure: Axon

Functional Zone: Conduction

Events: Action Potential Conduction

Molecular Structure: Voltage gated ion channels

Ion: NA+ K+

Cellular Structure: Terminal Bouton

Functional Zone: Output

Events: Action potential triggered neurotransmitter release

Molecular Structure: Voltage gated ion channels

Ion: Ca 2+

sodium-potassium pump

a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

In a neuron moves

2 potassium ions in

3 sodium ions out

consuming 1 ATP

Action potential undershoot

At rest, the neuron's membrane does not allow much Na⁺ to enter, but some K⁺ leaks out. During the rising phase of the action potential, Na⁺ channels open and Na⁺ rushes into the axon, causing depolarization. During the falling phase, Na⁺ channels close and K⁺ channels open, allowing K⁺ to leave the cell and repolarize the membrane.

After this, K⁺ channels close and the membrane returns to its resting state. If the membrane becomes more negative than its resting potential, it is called hyperpolarization, which makes it harder to fire another action potential.

Action potential propagation

the movement of an action potential along an axon; in myelinated axons, it occurs via saltatory conduction

myelinated axons

axons covered with myelin sheaths

unmyelinated axons

rest in invaginations of Schwann cells or oligodendrocytes. Not wrapped around the axon; gray matter.

Axon Diameter and Propagation Speed

The larger the axon diameter, the lower the resistance and the faster the speed

changes in membrane potential

A sudden increase or decrease in membrane potential caused by movement of ions across the cell membrane

neurons release neurotransmitters that bind sodium-channels, causing them to open. The immediate effect of this on the post-synaptic neuron would be

an EPSP

spatial summation

Integration by a postsynaptic neuron of inputs (EPSPs and IPSPs) from multiple sources.

temporal summation

Summation by a postsynaptic cell of input (EPSPs or IPSPs) from a single source over time.

Integrate-and-fire neurons