Anatomy of the Nervous System Cells

Anatomy of the Nervous System Cells

Overview of Neurons

  • Definition: Neurons (nerve cells) are fundamental units of the nervous system responsible for transmitting information.
    • Structure of a Neuron:
    • Dendrites: Receive incoming signals; can have 1 to 1,000 dendrites.
    • Cell Body: Contains nucleus and organelles for protein synthesis (e.g., neurotransmitters like acetylcholine).
    • Axon: Conducts nerve impulses; may have branches called terminal arborization which communicate with other cells via synapses.

Neuron Structure Details

Dendrites
  • Function: Collect incoming messages towards the neuron.
  • Connectivity: Branches create pathways for processing information.
Cell Body
  • Components: Houses the nucleus and machinery for neurotransmitter production.
  • Neurotransmitter Packaging: Golgi complex packages neurotransmitters in synaptic vesicles for transport.
Axon
  • Originates at the axon hillock (trigger zone) and conducts impulses away from the cell body.
  • Terminates in synaptic knobs that connect with other cells (muscles, glands, or other neurons).
  • Motor Units: Comprised of one neuron and muscle fibers it controls; can stimulate many muscle fibers.

Myelin Sheath and Axon Transport

  • Myelin: Lipid-rich insulation for axons; not present on cell bodies or dendrites.
    • Nodes of Ranvier: Gaps in the myelin sheath critical for impulse conduction.
  • Axonal Transport:
    • Anterograde (toward synaptic knob): Carries neurotransmitters; typically fast.
    • Retrograde (toward cell body): Recycles vesicles; viruses (e.g., rabies) can exploit this for movement to the brain.

Types of Neurons

  1. Multipolar Neurons:

    • Structure: Multiple dendrites, one axon.
    • Location: Common in the brain and spinal cord.
    • Function: Efferent (carry signals away from CNS).

  2. Bipolar Neurons:

    • Structure: One dendrite, one axon.
    • Location: Found in the retina, inner ear, nasal cavity.
    • Function: Afferent (carry signals toward CNS).

  3. Unipolar Neurons:

    • Structure: Single process (dendrite and axon fused); cell body is off to the side.
    • Location: Sensory areas like skin and organs.
    • Function: Afferent (carry signals toward CNS); often grouped in ganglia.

Neuroglia: Support Cells

  • Oligodendrocytes: Form myelin in the CNS.
  • Ependymal Cells: Line CNS fluid cavities; produce cerebrospinal fluid (CSF).
  • Astrocytes: Star-shaped; maintain blood-brain barrier and regulate CSF composition; form scar tissue.
  • Microglia: Act as macrophages in the CNS, remove debris and pathogens.
  • Schwann Cells: Myelinate axons in the PNS, promote regeneration after axonal injury.
  • Satellite Cells: Regulate chemical environment in PNS ganglia.

Implications of Neurotransmitter Imbalance

  • Mental Disorders: Example - Depression results from altered neurotransmitter levels. Treatment often involves medication to correct these imbalances.
    • Antidepressants: Help restore normal neurotransmitter function.

Disease Considerations

  • Neurons have limited ability to divide after puberty, leading to tumors (gliomas) developing from neuroglial cells.
    • Malignant nature: These can grow rapidly, affected by the protective blood-brain barrier.