AP Biology Notes: Cell Communication

Four Things to Know About Cell Communication

  1. There are two major ways animal cells communicate: through signaling molecules secreted by cells and through receptor molecules that rest on the cells’ surfaces.
  2. Responses to signal transduction (the conversion of an extracellular signal to a change in an intracellular process) may be stimulatory or inhibitory.
  3. Endocrine signaling refers to the secretion of chemical messengers for widespread distribution throughout the entire organism. Paracrine signaling refers to the process of signaling only nearby cells. Synaptic signaling occurs between a nerve cell and either another nerve cell, a gland cell, or a muscle cell.
  4. The cells of many tissues contain pores known as gap junctions that allow for direct cell-to-cell communication, which allows for incredibly fast, undisrupted signal transmission across large areas. Plasmodesmata are plant cells’ equivalent of gap junctions.

Key Topics–Cell Communication

Remember that the AP Biology exam tests you on the depth of your knowledge, not just your ability to recall facts. While we have provided brief definitions here, you will need to know these terms in even more depth for the AP Biology exam.


  • Neuron: A nerve cell
  • Soma: The whole body of an organism or the cell body, exclusive of the germ cells
  • Dendrite: The part of the neuron that transmits impulses to the cell body
  • Axon: A nerve fiber
  • Myelin: Fatty lipid material that forms an insulating sheath around nerve fibers

Action Potentials

  • Action potential: The change in electrical potential across a nerve or muscle cell when stimulated, as in a nerve impulse
  • Resting membrane potential: Electrical state in an excitable cell where the membrane potential is more negative inside the cell than outside
  • Electrochemical gradient: Diffusion gradient of an ion, including potential and kinetic energy of the ion
  • Neurotransmitters: Messenger molecules that affect the behavior of neurons
  • Synapse: The junction or gap between the axon terminal of one neuron and the dendrites of another neuron

Nervous System Organizations

  • Nerve: A bundle of nerve axons
  • Central nervous system (CNS): Encompasses the brain and the spinal cord
  • Autonomic nervous system: The part of the nervous system that regulates the involuntary muscles, such as the walls of the alimentary canal; includes the parasympathetic and sympathetic nervous systems
  • Adrenaline (epinephrine): An “emergency” hormone stimulated by anger or fear; increases blood pressure and heart rate to supply the emergency needs of the muscles

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