Understanding Neurons and Their Functions

Sep 8, 2024

Lecture Notes: Neurons and Their Functions

Overview of Neurons

  • Neurons are the basic units of the brain.
  • Main function: Send electrical signals over distances in the body.
  • Neurons are electrically and chemically excitable.

Structure of a Neuron

  • Components:
    • Dendrites
    • Cell Body (Soma)
    • Axon (including Axon Hillock)
    • Presynaptic Terminal

Dendrites

  • Branch out in a tree-like fashion from the cell body.
  • Main target for incoming signals from other cells.
  • Complexity of dendritic branching determines the number of inputs received.
  • Spines: Small protrusions on dendrites that increase surface area for synaptic contact.

Cell Body (Soma)

  • Contains nucleus and cellular organelles (e.g., endoplasmic reticulum, Golgi apparatus, mitochondria, ribosomes, secretory vesicles).
  • Nucleus: Houses DNA, template for protein synthesis.
  • Organelles manage cellular mechanisms like protein synthesis and respiration.

Axon

  • Long process beginning at axon hillock, extending from the cell body.
  • May branch to communicate with multiple target cells.
  • Transmits an electrical signal (action potential) from axon hillock to presynaptic terminal.

Action Potential

  • Brief change in electrical potential (negative to positive and back).
  • Many axons covered by myelin sheath, increasing signal speed.
  • Nodes of Ranvier: Uncovered regions regenerating the action potential through saltatory conduction.

Axon Characteristics

  • Length variable, depending on neuron location and function.
    • Example: Sensory neuron axon from toe to spinal cord.
  • Diameter affects signal propagation speed; larger diameter = faster travel.

Presynaptic Terminal

  • Where axon terminates, forms a synapse with postsynaptic neuron or cell.
  • Action potential triggers neurotransmitter release into synapse.
  • Neuronal Communication: Involves electrical (action potential) and chemical (neurotransmitter) signals.

Synapse

  • Contact primarily with dendrites, but can also involve cell bodies or axons.
  • Neurons can synapse with non-neuronal cells (e.g., muscle cells, glands).
  • Terms:
    • Presynaptic: Releases neurotransmitters.
    • Postsynaptic: Receives neurotransmitters.

Variations in Neuron Structure

  • Unipolar Neurons: One branch from cell body, with dendrites and axon terminals projecting from it.
  • Bipolar Neurons: One axonal and one dendritic branch.
  • Multipolar Neurons: Many processes branching from the cell body.
  • Despite variations, all neurons share common features of cell body, dendrites, and axon.

These notes cover the essential components and functions of neurons, including their structural variety and how they facilitate communication within the nervous system.