AP Biology

AP Biology Notes: Nervous Systems

Four Things to Know about Nervous Systems

  1. A neuron (or nerve cell) processes and transmits information via electrical and chemical signaling. Chemical signals occur across a synapse via neurotransmitters. Electrical signals along the axon depend upon the flow of ions across the axon membrane and cell body membrane. The opening and closing of sodium and potassium voltage-gated channels are responsible for the transmission of electrical signals.
  2. The nervous system is broken down into two main parts: the central nervous system and the peripheral nervous system. The central nervous system contains the brain and spinal column and is used to control animal behavior based on input from the environment. The peripheral nervous system connects the central nervous system to all other parts of the body.
  3. The autonomic nervous system regulates the body’s internal environment without the aid of conscious control. It is composed of two subdivisions, the sympathetic and the parasympathetic nervous systems. The sympathetic division is responsible for the “fight-or-flight” responses that ready the body for action. The parasympathetic division acts to conserve energy and restore the body to resting activity levels following exertion.
  4. The body has several types of special sensors and sensory receptors to monitor its internal and external environments: interoceptors, proprioceptors, and exteroceptors. The chemical senses are taste and smell. The ears transduce sound energy (pressure waves) into impulses and are responsible for maintaining equilibrium, while the eyes use light input for vision.

Key Topics–Nervous Systems

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

Click the button to the right for our printable notes!