Neuronal Electrical Activity & Neurotransmitter Release

A set of Q&A flashcards summarizing key points about graded potentials, action potentials, ion channels, and neurotransmitter release in neurons.

What two major types of cells in the body are classified as excitable?

Neurons and muscle cells

At what membrane voltage must the axon hillock reach to trigger an action potential?

Approximately –55 millivolts, known as threshold

How does a graded potential differ from an action potential in terms of strength?

Graded potentials vary in amplitude and weaken over distance, while action potentials are all-or-nothing and maintain strength along the axon

What two factors cause a graded potential to lose strength as it spreads across the cell body?

Cytoplasmic resistance and potassium leakage through always-open K⁺ channels

Which type of ion channel is commonly found on dendrites and opens when a chemical ligand binds?

Ligand-gated sodium (Na⁺) channels

What event specifically opens the first voltage-gated sodium channel at the axon hillock?

The membrane reaching threshold (–55 mV)

Why is propagation of an action potential compared to a row of falling dominoes?

Because opening the first voltage-gated Na⁺ channel reliably triggers sequential opening of all downstream channels, ensuring the signal reaches the terminals

Which ion enters the axon terminal through voltage-gated channels to initiate neurotransmitter release?

Calcium ions (Ca²⁺)

What cellular process is triggered by Ca²⁺ influx in the axon terminal?

Calcium-induced exocytosis of synaptic vesicles containing neurotransmitters

Why must the initial depolarization at the dendrites be greater than –55 mV?

To compensate for voltage loss while it travels to the axon hillock so that threshold is still reached

What are the two forms of communication used by neurons?

Electrical signaling via action potentials and chemical signaling via neurotransmitters

Give two possible ligands that could open dendritic ligand-gated Na⁺ channels.

Examples include hormones, neurotransmitters, heat, or odor molecules (any stimulus activating the receptor)

What role do potassium leakage channels play in neuronal resting potential?

They allow K⁺ to continually exit the cell, helping return the membrane toward its negative resting value

Where does the conversion from electrical to chemical signaling occur in a neuron?

At the axon terminals when Ca²⁺ triggers neurotransmitter release into the synaptic cleft

What is meant by the term “all-or-nothing” with respect to an action potential?

Once threshold is met, the full action potential travels the entire axon without diminishing; if threshold is not met, no action potential occurs