Neuron Classification Notes

Neuron Classification

Structural Classification of Neurons (Based on Anatomy)

  • Neurons are polar cells, meaning different parts of the cell have different appearances.
  • Classification based on the number of processes (extensions) coming out of the cell body (soma).
1. Unipolar Neurons
  • Have a single process extending from the cell body.
  • Often referred to as pseudo-unipolar neurons.
  • The single process branches into two arms of the axon.
2. Bipolar Neurons
  • Have two processes (neurites) extending from the cell body.
  • One dendrite and one axon extend from the soma.
3. Multipolar Neurons
  • Have multiple processes extending from the cell body.
  • Multiple dendrites and one axon extend from the soma.
Structural Aspects & Function
  • Reception/Sensation: Occurs across multi, bi, or unipolar neurons.
  • Integration/Processing: Occurs in or near the cell body.
  • Conduction: Carried out by the axon (acts as a tunnel or channel).
  • Transmission: Occurs at the axon terminals, where the signal is transmitted to other cells.
Summary of Structural Classification
  • Unipolar: One process extends from the cell body.
  • Pseudo-Unipolar: One process extends and then branches into two arms.
  • Bipolar: Two distinct processes extend from the cell body.
  • Multipolar: Multiple dendrites extend from the cell body with one axon.

Functional Classification of Neurons

  • Based on the function/role of the neuron in the nervous system.
  • Relates to the basic functions of the nervous system: sensation, integration, and motor output (afferent, integration, efferent).
1. Sensory (Afferent) Neurons
  • Located in the peripheral nervous system.
  • Detect changes in the environment (temperature, pressure, pain, pH).
  • Convey signals to the central nervous system.
2. Interneurons
  • ~90% of all neurons are interneurons.
  • Located in the central nervous system.
  • Integrate and process information received from sensory neurons.
  • Decide on a response and relay it via motor neurons.
3. Motor (Efferent) Neurons
  • Receive messages from the central nervous system and execute instructions.
  • Convey messages from the central nervous system to effector organs (muscles and glands).
Example of Functional Neuron Interaction (Cup of Tea Scenario)
  1. Sensory neurons in fingertips detect the temperature of the tea cup.
  2. This information is relayed to interneurons in the central nervous system (spinal cord/brain).
  3. Interneurons process the information (potential burn threat).
  4. Motor neurons send a message to muscles in the hand/arm to put the cup down or drop it.
  5. This closes the negative feedback loop, protecting the body from harm.
Flowchart of Communication
  1. Afferent Neuron (Sensory): Receives information via receptors.
  2. Information is passed down the axon to axon terminals.
  3. Interneurons: Integrate, process, and translate information.
  4. Efferent Neuron (Motor): Issues commands to muscles or gland cells.
  • Illustrates the roles of the central nervous system and peripheral nervous system in communication.
Summary of Neuron Types
  • Structurally: Uni, bi, and multipolar neurons.
  • Functionally: Sensory (afferent), interneurons, and motor (efferent) neurons.