Neuronal Physiology and Synaptic Transmission

Forty Q&A flashcards reviewing key concepts from the lecture on neuronal ion transport, membrane potentials, action potentials, synaptic transmission, and channel types.

What is the primary function of the sodium-potassium pump in neurons?

To actively move 3 Na⁺ out of the cell and 2 K⁺ into the cell, maintaining ion gradients and the negative resting potential.

During one full cycle of the sodium-potassium pump, how many positive ions leave and how many enter the neuron?

Three Na⁺ leave and two K⁺ enter.

What net electrical change occurs inside the neuron after one pump cycle?

A net loss of one positive charge, making the interior 1 unit more negative.

What is a typical resting membrane potential for a neuron?

About –70 millivolts (mV).

Where is sodium concentration highest when a neuron is at rest?

Outside the cell.

Where is potassium concentration highest when a neuron is at rest?

Inside the cell.

Why can’t Na⁺ and K⁺ ions freely cross the lipid bilayer?

Because they are charged particles that cannot pass through the hydrophobic membrane core without channels or pumps.

What do we call a membrane channel that is always open?

A leakage (non-gated) channel.

Which channel type opens when the membrane is physically deformed?

A mechanically gated channel.

Which channel type opens in response to a specific voltage change?

A voltage-gated channel.

What opens a ligand-gated ion channel?

Binding of a specific chemical ligand such as a neurotransmitter.

When a voltage-gated sodium channel opens, in which direction does Na⁺ move?

Into the cell, down its electrochemical gradient.

What immediate effect does Na⁺ influx have on membrane potential?

It depolarizes the membrane (makes it less negative).

What voltage threshold generally triggers an action potential?

Approximately –55 mV.

What name is given to the all-or-none electrical signal that travels along an axon?

An action potential.

Which ion movement mainly causes repolarization during an action potential?

K⁺ efflux through voltage-gated potassium channels.

What is hyperpolarization?

The membrane potential becoming more negative than the resting level after an action potential.

Why do myelinated axons conduct impulses faster?

Myelin insulates the axon, causing action potentials to jump between nodes of Ranvier via saltatory conduction.

What is saltatory conduction?

The rapid “jumping” of action potentials from one node of Ranvier to the next along a myelinated axon.

Approximately how many neurons are in the human brain?

About 86 billion.

Define a synapse.

The junction between an axon terminal and another cell where neural communication occurs.

Do presynaptic and postsynaptic membranes touch in a chemical synapse?

No; they are separated by the synaptic cleft.

List the seven basic steps of chemical synaptic transmission.

1) Action potential reaches terminal; 2) Depolarization opens voltage-gated Ca²⁺ channels; 3) Ca²⁺ enters terminal; 4) Ca²⁺ triggers vesicle fusion; 5) Neurotransmitter is released; 6) Neurotransmitter binds postsynaptic receptors; 7) Ion flow creates a postsynaptic potential that may reach threshold.

Which ion’s influx triggers neurotransmitter release at the presynaptic terminal?

Calcium ions (Ca²⁺).

What do synaptic vesicles contain?

Neurotransmitter molecules.

When neurotransmitters bind ligand-gated sodium channels on the postsynaptic membrane, which ion moves and in what direction?

Na⁺ moves into the postsynaptic cell.

What is an EPSP?

An excitatory postsynaptic potential that depolarizes the neuron toward threshold.

What is an IPSP?

An inhibitory postsynaptic potential that hyperpolarizes the neuron away from threshold.

How do graded potentials differ from action potentials?

Graded potentials vary in size, decay with distance, and can summate, whereas action potentials are all-or-none and propagate without decrement.

What process sums all incoming EPSPs and IPSPs at the axon hillock?

Summation (spatial and temporal).

What is the most common type of synapse based on neuronal parts?

An axodendritic synapse.

Name two other synapse types besides axodendritic.

Axosomatic and axoaxonic synapses.

Why do Na⁺ and K⁺ both have a +1 charge?

They each lose one electron and belong to the first column of the periodic table.

In the bank analogy, what does withdrawing $3 and depositing $2 represent in a neuron?

Pumping out 3 Na⁺ and bringing in 2 K⁺, yielding a net loss of one positive charge.

What term describes the membrane potential when a neuron is inactive and “just chilling”?

Resting potential.

Can a neuron fire a partial action potential?

No; action potentials follow the all-or-none principle.

What prevents small random depolarizations from triggering unwanted action potentials?

The threshold of excitation (about –55 mV) providing a safety margin.

Why does Na⁺ rush into a neuron when its channels open?

Both the concentration gradient and the negative interior (electrical gradient) drive Na⁺ inward.

In physiology, what does the term “ligand” mean?

A molecule that binds to a receptor, such as a neurotransmitter.

Which neurotransmitter mentioned is primarily inhibitory and which is primarily excitatory?

GABA is inhibitory; glutamate is excitatory.