20.3: Electrical cell-cell communication

Photoreceptors

Sensory neurons that detect light.

Neurons

Cells of the nervous system that transmit electrical signals.

Soma (cell body)

Contains the nucleus of a neuron.

Dendrites

Highly branching structures on neurons that receive signals from other neurons at synapses.

Synapse

Junctions where neurons receive signals from other neurons.

Axon

long fibre extending from soma which transmits signals away from cell body towards terminal

Axon hillock

Where the cell body meets the axon; generates the action potential.

Myelin sheath

Fatty sheath made by glial cells that insulates the axon.

Nodes of Ranvier

Gaps in the myelin sheath where the action potential is regenerated.

Terminal

End of the axon, containing synaptic vesicles filled with neurotransmitter molecules.

Neurotransmitters

Molecules released into the synaptic cleft to transmit signals to the next cell.

Synaptic cleft

space between the presynaptic and postsynaptic neuron at a synapse.

Action potential

Specific change in charge across a cell membrane that propagates electrical signals.

Resting membrane potential

The difference in electrical potential between the inside and outside of the membrane of a neuron at rest (approx. -70 mV).

Reuptake proteins

Proteins on presynaptic cells responsible for recycling neurotransmitters.

what happens when neuron receives a signal

membrane potential either hyperpolarise (decrease) or depolarise (increase)

what happens when neurons depolarise

The membrane potential becomes more positive, leading to the generation of an action potential if the threshold is reached.

Process that follows if threshold is reached

voltage gated sodium channels open = sodium ions enter cell down their gradient = increased concentration = positive charge = rapid increase in membrane potential to around +40 mV (peak of action potential) = sodium channels close= potassium channels open = potassium ions exit cell down its gradient = reduces membrane potential

how is resting potential restored

The resting potential is restored through the action of the sodium-potassium pump, which actively transports sodium out of the cell and potassium into the cell, re-establishing the original ion concentrations.

what is the concentration of sodium and potassium when neurons are at rest

When neurons are at rest, sodium concentration is higher outside the cell and potassium concentration is higher inside the cell