Neurons and Their Functions

Neuron Structure and Function

• Neurons

  • Do not undergo mitosis, hence cannot replicate themselves.
  • Loss of neurons can lead to diseases like Alzheimer's.
  • Neurons have extreme longevity; the ones you are born with are the ones you will keep for life.
  • Once a neuron dies, it is not replaced.

• Processes of Neurons

  • Composed of dendrites, axons, and the soma (cell body).
  • Soma:
  • Contains organelles (e.g., nucleus, rough and smooth ER).
  • Has more units of ribosomes than any type of organelle due to its need for protein synthesis.
  • Ribosomes in neurons known as Nissl bodies.
  • Dendrites:
  • Branch-like structures that collect information.
  • Cannot respond to signals; they only transmit information to the soma.
  • Axon:
  • Long structure that transmits signals away from the soma.
  • Bundles of axons form nerves in the PNS and tracts in the CNS.

• Cell Division

  • Neurons are described as amitotic (cannot undergo cell division).
  • They have a high metabolic rate, primarily consuming glucose from the bloodstream.

Neuron Anatomy and Classification

• Cell Body (Soma)

  • Contains organelles and cytosol with a higher concentration of ribosomes.
  • The cluster of cell bodies in the CNS is referred to as nuclei, while in the PNS, it is called ganglia.

• Neural Processes

  • Processes are extensions that connect to the soma.
  • Two major types: dendrites and axons.
  • Action Potentials and Graded Potentials:
  • Graded Potential: Travels from dendrites to the soma — short distance and duration.
  • Action Potential: Travels from soma to axon terminal — long distance and can last longer.

Types of Neurons

• Classification by Anatomy

  • Multipolar Neurons:
  • Most common type; numerous processes attached to the soma.
  • Function primarily as motor neurons.
  • Bipolar Neurons:
  • Two processes attached directly to the soma.
  • Generally located in sensory organs (vision, hearing).
  • Unipolar Neurons:
  • One singular process that branches into two; typically sensory neurons.

• Neuronal Structure

  • Dendrites are short and collect information, while axons are long and transmit signals.
  • Neurons can vary based on their processes:
  • Multipolar: multiple dendrites and one axon.
  • Bipolar: one dendrite and one axon.
  • Unipolar: one primary process that splits.

Important Terminologies:

• Chromatophilic (Nissl Bodies): Ribosomes in neurons that are color-coded.
• Ligand: The chemical that binds to a channel to open it (related to graded potentials).
• Voltage Gated Channels: Channels that open based on changes in membrane potential; crucial for action potentials.