Initiating and Propagating an Action Potential

What is an action potential?

A temporary reversal of membrane potential in a neuron, characterized by depolarization, overshoot, repolarization, and hyperpolarization.

What initiates an action potential?

Action potentials are most often initiated by graded potentials, which are smaller depolarizations of the cell membrane.

What are the properties of graded potentials?

Graded potentials have variable amplitude, are easily generated by various signals, fade with time and distance, and do not have a refractory period.

What are the properties of action potentials?

Action potentials have a fixed amplitude, are all-or-none, require a minimum threshold to be generated, do not fade, and have a refractory period.

What causes the depolarization in an action potential?

Depolarization occurs when voltage-gated Na+ channels open, allowing Na+ to enter the neuron rapidly.

What happens after the peak of an action potential?

After the peak, Na+ channels close and voltage-gated K+ channels open, allowing K+ to exit the neuron, leading to repolarization.

What is saltatory conduction?

Saltatory conduction is the process by which action potentials jump from one Node of Ranvier to another in myelinated axons, increasing the speed of conduction.

What triggers neurotransmitter release at the synapse?

The arrival of an action potential at the presynaptic terminal opens voltage-gated Ca2+ channels, allowing Ca2+ influx that triggers neurotransmitter release.

What is the role of neurotransmitters?

Neurotransmitters are chemicals that stimulate target cells by binding to receptors on the postsynaptic membrane, leading to graded potentials.

What are EPSPs and IPSPs?

EPSPs (excitatory postsynaptic potentials) depolarize the postsynaptic membrane, while IPSPs (inhibitory postsynaptic potentials) hyperpolarize it.

How are neurotransmitters removed from the synaptic cleft?

Neurotransmitters are removed by enzymatic degradation, reuptake into the presynaptic neuron, or diffusion away from the cleft.

What is the threshold potential for generating an action potential?

The threshold potential is usually about -55 mV.

What is the significance of the refractory period in action potentials?

The refractory period prevents the immediate re-excitation of a neuron, ensuring that action potentials only travel in one direction along the axon.

What are the two main types of neurotransmitter receptors?

Chemically-gated (ligand-gated) ion channels and G-protein coupled receptors.

What is the function of neuromodulators?

Neuromodulators alter the effect of neurotransmitters, enhancing or diminishing their impact on the postsynaptic cell.

What neurotransmitter is primarily associated with the cholinergic system?

Acetylcholine (Ach), which has muscarinic and nicotinic subtypes.

What role do biogenic amines play in neurotransmission?

Biogenic amines, such as dopamine, norepinephrine, and serotonin, act as neurotransmitters and are involved in various physiological processes.

What is the major excitatory neurotransmitter in the mammalian CNS?

Glutamate.

What is the major inhibitory neurotransmitter in the mammalian CNS?

GABA (Gamma-aminobutyric acid).

What factors affect synaptic integration and strength?

Factors include the amount of neurotransmitter released, Ca++ influx, recent polarization state of the postsynaptic membrane, and the number of postsynaptic receptors.

What happens during the overshoot phase of an action potential?

The membrane potential peaks at approximately +30 mV due to rapid Na+ influx.

What is the role of SNARE proteins in neurotransmitter release?

SNARE proteins facilitate the fusion of synaptic vesicles with the presynaptic membrane, leading to the exocytosis of neurotransmitters.

What is the effect of drugs on neurotransmitter receptors?

Drugs can act as receptor agonists or antagonists, modifying the effects of neurotransmitters on their receptors.