Chapter 7: The Nervous System

Lecture by Patty Bostwick-Taylor, Florence Darlington Technical College

Functions of the Nervous System

• Sensory Input: Monitors changes inside and outside the body.
• Integration: Processes and interprets sensory input to decide on action.
• Motor Output: Responds to stimuli via muscles or glands.

Organization of the Nervous System

• Structural Classification:
  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
• Functional Classification:
  • Sensory (afferent) Division: Carries information to CNS.
  • Motor (efferent) Division: Carries impulses from CNS to effectors.

Structural Classification

• CNS:
  • Organs include the brain and spinal cord.
  • Functions as the integration and command center.
• PNS:
  • Includes nerves extending from the brain and spinal cord.
  • Serves as communication lines among sensory organs, brain, spinal cord, glands, or muscles.

Functional Classification

• Sensory Division: Carries information to CNS.
  • Somatic Sensory Fibers: From skin, skeletal muscles, and joints.
  • Visceral Sensory Fibers: From visceral organs.
• Motor Division:
  • Somatic Nervous System: Voluntarily controls skeletal muscles.
  • Autonomic Nervous System: Automatically controls smooth/cardiac muscles and glands.
    • Subdivided into sympathetic and parasympathetic systems.

Nervous Tissue: Support Cells

• CNS Glial Cells:
  • Astrocytes: Star-shaped cells that anchor neurons to blood capillaries.
  • Microglia: Spiderlike phagocytes that dispose of debris.
  • Ependymal Cells: Line brain/spinal cavities and circulate cerebrospinal fluid.
  • Oligodendrocytes: Wrap around nerve fibers, form myelin sheaths.
• PNS Glial Cells:
  • Schwann Cells: Form myelin sheath around PNS nerve fibers.
  • Satellite Cells: Protect and cushion neuron cell bodies.

Nervous Tissue: Neurons

• Neurons: Specialized nerve cells transmitting messages.
  • Cell Body: Nucleus and metabolic center.
  • Processes (Fibers):
    • Dendrites: Conduct impulses toward the cell body.
    • Axons: Conduct impulses away, ending in axon terminals.
    • Myelin: Fatty insulation covering axons, speeds transmission.

Neuron Terminology

• Nuclei: Clusters of cell bodies in CNS.
• Ganglia: Cell bodies outside CNS in PNS.
• Tracts: Bundles of nerve fibers in CNS.
• Nerves: Bundles in PNS.
• White Matter: Myelinated fibers.
• Gray Matter: Unmyelinated fibers and cell bodies.

Neuron Functional Properties

• Irritability: Responds to stimuli and converts to nerve impulse.
• Conductivity: Transmits impulse to neurons, muscles, or glands.

Reflexes

• Types:
  • Somatic Reflexes: Stimulate skeletal muscles.
  • Autonomic Reflexes: Regulate smooth muscles, heart, glands.
• Reflex Arc Elements:
  1. Sensory receptor reacts to stimulus.
  2. Sensory neuron carries message to CNS.
  3. Integration center processes info and directs motor output.
  4. Motor neuron carries message to effector.
  5. Effector organ (muscle/gland) is stimulated.
• Reflex Arc Types:
  • Two-Neuron Reflex Arc: Simplest type, e.g., knee-jerk.
  • Three-Neuron Reflex Arc: More complex, involves receptor, sensory neuron, interneuron, motor neuron, effector.