Neurons, Glia, Synapses, and Neurotransmission
The Neuron as an Electrical Cell
Membrane excitability
Neurons generate electrical signals because ion gradients across the membrane create a resting potential, and voltage-gated channels allow rapid changes in membrane voltage.
Core membrane concepts
Mechanistic point
The sodium-potassium pump maintains gradients over time, but the immediate shape of the action potential is driven mainly by voltage-gated sodium and potassium channels.
Which ion channel opening is most directly responsible for the rapid depolarization phase of an action potential?
Rapid depolarization is caused by sodium influx through voltage-gated sodium channels.
Correct answer: Voltage-gated sodium channels
What is saltatory conduction?
Myelin speeds conduction by allowing current to jump node to node.
Correct answer: Conduction of action potentials between nodes of Ranvier in myelinated axons
Synapses and Neurotransmitters
Chemical signaling
At chemical synapses, presynaptic depolarization opens calcium channels, triggering vesicle fusion and neurotransmitter release. Postsynaptic receptors then generate excitatory or inhibitory effects.
Major neurotransmitter systems
Glutamate
- Primary excitatory transmitter
- Important for learning and synaptic plasticity
GABA
- Primary inhibitory transmitter
- Important for preventing excessive network firing
Which neurotransmitter is the main inhibitory transmitter in the adult CNS?
GABA is the principal inhibitory neurotransmitter in the adult central nervous system.
Correct answer: GABA
What event triggers neurotransmitter release at a chemical synapse?
Calcium entry into the presynaptic terminal initiates vesicle fusion with the membrane.
Correct answer: presynaptic calcium influx
Glia and Network Support
Why glia matter
Glial cells are not passive scaffolding. Astrocytes regulate extracellular ions and neurotransmitters, oligodendrocytes myelinate CNS axons, Schwann cells myelinate peripheral axons, and microglia function as immune sentinels.
Which glial cell forms myelin in the peripheral nervous system?
Schwann cells myelinate peripheral nerves.
Correct answer: Schwann cell
Why is glial dysfunction clinically important?
Many neurologic diseases involve glial injury or dysregulation, not just neuron loss.
Correct answer: Because glia control myelination, metabolic support, and inflammatory responses