A01

• How many neurons are in the human nervous system?

  100 billion
• What percentage of neurons are located in the brain?

  80%
• How do neurons communicate within the nervous system?

  By transmitting signals electrically and chemically
• What are the three types of neurons?

  • Sensory neurons
  • Relay neurons
  • Motor neurons
• What is the function of sensory neurons?

  They carry signals from sensory receptors
• What is the role of relay neurons?

  They connect sensory and motor neurons
• What do motor neurons do?

  They carry signals to muscles and glands
• What is the basic structure shared by all neurons?

  Cell body, dendrites, and axon
• What does the cell body (soma) contain?

  A nucleus with genetic material
• What are dendrites responsible for?

  Carrying nerve impulses towards the cell body
• What is the function of the axon?

  To carry impulses away from the cell body
• What is the myelin sheath?

  A fatty layer that protects the axon
• What happens if the myelin sheath is continuous?

  It slows down the electrical impulse
• What are nodes of Ranvier?

  Gaps in the myelin sheath
• How do nodes of Ranvier affect impulse transmission?

  They speed up the transmission by forcing jumps
• What are terminal buttons?

  They communicate with the next neuron across the synapse
• Where are the cell bodies of motor neurons located?

  In the central nervous system (CNS)
• Where are sensory neurons located?

  Outside of the CNS in the PNS
• What percentage of neurons are relay neurons?

  97%
• What is the resting state of a neuron?

  The inside is negatively charged
• What is created when a neuron becomes positively charged?

  An action potential occurs
• What occurs when a neuron is activated by a stimulus?

  The inside becomes positively charged
• What travels down the axon after an action potential?

  An electrical impulse