Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Divisions of the Nervous System

• Central Nervous System (CNS):

  • Comprised of the brain and spinal cord.
  • Located centrally along the midline.

• Peripheral Nervous System (PNS):

  • Comprised of nerves outside the brain and spinal cord.
  • Contains cranial nerves (emerging from the brain) and spinal nerves (emerging from the spinal cord).
  • Functions as a two-way delivery system for nerve impulses.
  • Sensory Division (Afferent): Conducts impulses towards CNS, responsible for acquiring sensory information.
  • Motor Division (Efferent): Conducts impulses away from CNS, responsible for responding to sensory information.
    • Somatic Nervous System: Controls voluntary skeletal muscle movements and reflexes.
    • Autonomic Nervous System (ANS): Involuntary control of cardiac and smooth muscles, glands. Maintains homeostasis via sympathetic and parasympathetic divisions.

Nervous Tissue

• Neurons:

  • Basic functional unit, specialized for transmitting electrical signals (nerve impulses).
  • Structure includes:
    • Dendrites: Receive impulses and conduct them to the cell body.
    • Axon: Conducts impulses away from the cell body.
    • Axon Hillock: Tapered area where axon begins; initiation site for nerve impulses.

• Neuroglia (Glia):

  • Supportive cells, provide structural and functional support to neurons.

Neuron Function and Types

• Sensory Neurons: Conduct impulses towards CNS (input from receptors).

• Motor Neurons: Conduct impulses away from CNS to effectors (muscles or glands).

• Interneurons: Communication between sensory and motor neurons.

• Reflex Arc Example:

  • Stimulus detected by receptors, converted to nerve impulse.
  • Impulse travels via sensory neuron to CNS, relayed by interneuron to motor neuron, leading to response by effector organ (e.g., muscle contraction).

Neuron Morphology

• Multipolar Neurons: Many extensions (dendrites and axon), common shape for motor neurons and interneurons.
• Bipolar Neurons: Two extensions (one dendrite, one axon), found in special senses.
• Unipolar Neurons: Single extension (axon), common for sensory neurons.

Myelination

• Myelinated Axons: Wrapped in myelin sheath (protein and lipid), produced by Schwann cells in PNS and oligodendrocytes in CNS.
  • Nodes of Ranvier: Gaps in myelin sheath, facilitate rapid nerve impulse conduction (saltatory conduction).

Membrane Potential and Nerve Impulses

• Membrane Potential: Difference in charge concentration inside vs. outside of the cell.

  • Resting membrane potential is negative inside.
  • Sodium-Potassium Pump: Maintains resting potential by pumping out 3 Na+ ions for every 2 K+ ions in, resulting in net negative charge inside.

• Nerve Impulse (Action Potential):

  • Self-propagating wave of electrical activity across neuron membranes.
  • Reverses resting potential, allowing for communication across neurons.