Neurons and Their Components

Nucleus and Cell Body Description

  • Nucleus: A collection of cell bodies associated with the neural structure.
    • Cell Body: Also referred to as Soma or Perikaryon.
    • Organelles Contained: Includes the usual cellular organelles such as:
      • Nucleus
      • Ribosomes
      • Rough Endoplasmic Reticulum (ER) which contains chromatophilic substance
      • Golgi apparatus
      • Mitochondria
    • Neurofibrils: Structures within the cell body that maintain cell shape and integrity.

Grey Matter

  • Grey Matter Characteristics:
    • Lacks myelin, which is typical in parts of the central nervous system (CNS).
    • Contains a high density of cell bodies.
    • Notable structures include:
    • Nuclei (clusters of cell bodies in the CNS)
    • Ganglia (clusters of cell bodies in the peripheral nervous system (PNS))

Dendrites

  • Definition & Structure:
    • Branching extensions that arise from the cell body, containing cytoplasm and organelles.
  • Function:
    • Provides an increase in surface area for receiving input signals.

Axon

  • Definition:
    • A single projection of the cell body responsible for transmitting information.
    • A neuron typically contains only one axon.
  • Location:
    • Arises from the axon hillock, which is the part of the neuron that initiates action potentials.
  • Characteristics:
    • Length can vary, reaching up to 1 meter in some cases (referred to as a nerve fiber).
    • May possess branches known as axon collaterals.
  • Axon Terminals:
    • Usually, an axon can have around 10,000 terminal branches.
    • The terminals act as the secretory component of neurons, primarily involved in neurotransmitter (NT) release.
    • Contains organelles but lacks endoplasmic reticulum (ER) or Golgi apparatus, relying on the cell body for protein synthesis.
  • Damage Response:
    • Axons tend to decay quickly when damaged, which impacts signal transmission.
  • Structural Components:
    • Axolemma: Plasma membrane surrounding the axon.
    • There is a constant two-way traffic of molecules within the axon:
    • Anterograde Transport: Movement from the cell body to the axon terminal includes:
      • Mitochondria
      • Replacement molecules for axolemma
      • Molecules for neurotransmitter synthesis.
    • Protein involved: Kinesin, which facilitates the transport.
    • Retrograde Transport: Movement from the axon terminal back to the cell body includes:
      • Molecules and organelles designated for degradation and recycling.
      • Protein involved: Dynein, which assists in transporting materials back to the cell body.

Cytoskeletal Transport Mechanism

  • Mechanism:

    • Motor molecules can attach to receptors on vesicles or organelles and carry these components along microtubule pathways of the cytoskeleton.

  • Energy Source:

    • The transport process is powered by ATP (adenosine triphosphate).

  • Visual Representation:

    • Motor molecules are depicted as engaging with vesicles, facilitating their movement along defined microtubule tracks within the cytoskeleton, aiding in transport of cellular materials as necessary for neuron function.