Cell-cell communication is essential for the survival of anorganism. There are a variety of ways cells communicate including by directcontact, local signaling, and long-distance signaling. Direct-contact signalinginvolves the plasma membrane and occurs via cell junctions (gap junctions inanimal cells and plasmodesmata in plant cells) and surface molecules, whichallow cells to recognize and communicate with one another from their respectivesurface proteins.
Local signaling includes paracrine signaling (e.g. growthfactors released to neighboring cells). Long-distance signaling is endocrine signaling;cells release hormones that travel in the circulatory system to cells allaround the body.
Typically, cells communicate using chemical signals—a cellreleases a chemical (ligand) and it binds to a receptor in the target cell,creating a response. Non-target cells do not have the necessary receptor forthe ligand. I will be discussing synaptic signaling in more detail. Neuronscommunicate with neurons and other cells via synaptic signaling (also knows as neurotransmission).When a pre-synaptic neuron reaches threshold, an action potential (an electricalimpulse) is fired. The threshold potential is the voltage at which an actionpotential can be triggered due to sodium concentration. The action potentialtravels down the axon and results in the release of neurotransmitters, whichare signaling molecules, from the axon terminal.
The neurotransmitters diffuseacross the synapse, the space in between two neurons, and bind to receptors inthe post-synaptic neuron. The effect can be either excitatory or inhibitory andthe resulting changes can be ephemeral or long-living.