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Overview of the Nervous System

Oct 21, 2024

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Fundamentals of the Nervous System

Nervous System Structure and Function

  • Central Nervous System (CNS):
    • Composed of the brain and spinal cord.
    • Seat of all mental activity, interpreting sensory input and dictating motor responses.
  • Peripheral Nervous System (PNS):
    • Composed of cranial and spinal nerves; communication lines between CNS and the body.
    • Divisions:
      • Sensory Division (Afferent): Conducts impulses from sensory receptors to CNS.
      • Motor Division (Efferent): Conducts impulses from CNS to muscles and glands.
        • Somatic Nervous System: Controls voluntary movements.
        • Autonomic Nervous System (ANS): Controls involuntary responses.
          • Sympathetic: Mobilizes body during emergencies (fight or flight).
          • Parasympathetic: Conserves energy during rest (rest and digest).

Function of the Nervous System

  • Sensory receptors monitor changes (input).
  • Nervous tissue processes sensory input (integration).
  • Response to stimuli (motor output).
  • Maintains homeostasis.

Neural Tissue

  • Composed of neurons and glial cells.

Neurons

  • Characteristics:
    • Excitable and conduct nerve impulses.
    • Longevity and high metabolic rate.
    • Can be large and are generally amitotic.
  • Structure:
    • Cell Body (Soma): Contains nucleus; site of metabolic activity.
    • Processes:
      • Dendrites: Receive signals.
      • Axon: Transmits impulses; surrounded by axolemma.
      • Myelin Sheath: Insulates axons; speeds impulse transmission.
  • Classification by Structure:
    • Bipolar: One dendrite, one axon.
    • Unipolar: Continuous dendrite and axon.
    • Multipolar: One axon, multiple dendrites.

Neuroglial Cells

  • CNS Glial Cells:
    • Astrocytes: Support and nourish neurons; form blood-brain barrier.
    • Microglia: Act as macrophages.
    • Oligodendrocytes: Form myelin sheath in CNS.
    • Ependymal Cells: Line brain and spinal cord cavities; circulate cerebrospinal fluid.
  • PNS Glial Cells:
    • Schwann Cells: Form myelin sheath in PNS.
    • Satellite Cells: Support neuron cell bodies.

Neurophysiology

  • Electrical Currents: Flow of ions across membranes.
  • Resting Membrane Potential:
    • Polarized cell membrane (~-70mV).
    • Sodium high outside; potassium high inside.
  • Graded Potentials:
    • Change in membrane potential.
    • Can lead to action potentials.
  • Action Potentials:
    • All-or-none response.
    • Saltatory conduction in myelinated axons.

Action Potential Phases

  1. Depolarization: Sodium channels open, sodium enters.
  2. Propagation: Action potential moves down axon.
  3. Repolarization: Sodium channels close, potassium exits.
  4. Hyperpolarization: Potassium channels slow to close.
  5. Restoration: Sodium-potassium pumps restore resting potential.

Neurotransmitters and Receptors

  • Neurotransmitter Types: Acetylcholine, dopamine, serotonin, etc.
  • Receptor Types:
    • Ionotropic: Direct channel opening.
    • Metabotropic: Indirect, through second messengers like cAMP.

Key Concepts

  • Synaptic Transmission: Communication across synapses.
  • Summation: EPSP and IPSP effects can sum to produce action potentials.

This concludes our overview of the nervous system and neural tissue, covering the structure, function, and fundamental processes involved in neural communication.

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