Nervous System Functions and Organization

Key Functions of the Nervous System

• Sensory Function:

  • Detects internal stimuli (e.g., increased blood pressure) and external stimuli (e.g., a raindrop on your arm).
  • Sensory information is transmitted to the brain and spinal cord via cranial and spinal nerves.

• Integrative Function:

  • Processes sensory information by analyzing it and determining a response.
  • Delivers an appropriate outcome based on integrated information.

• Motor Function:

  • Activates effectors (muscles or glands) to elicit a response (e.g., muscle contraction, gland secretion).

Example: Dehydration

• Detection: Osmoreceptors detect dehydration.
• Transmission: Sensory info is sent to the spinal cord/brain.
• Integration: Brain processes info, considers context (e.g., access to water).
• Response: Muscles activated to pick up a glass of water and drink.

Structure and Organization of the Nervous System

Central Nervous System (CNS)

• Components: Brain and spinal cord.
• Functions:
  • Processes sensory information.
  • Origin of thoughts, emotions, and memories.
  • Generates signals for muscle contraction or gland secretion.

Peripheral Nervous System (PNS)

• Components:

  • Cranial and spinal nerves.
  • Ganglia (neuronal cell body clusters).
  • Enteric plexuses (networks in gastrointestinal tract walls).
  • Sensory receptors (e.g., touch receptors, photoreceptors, olfactory receptors).

• Divisions:

  • Somatic Nervous System:

    • Sensory neurons from somatic and special (vision, hearing, taste, smell) receptors.
    • Motor neurons to skeletal muscles (voluntary control).

  • Autonomic Nervous System:

    • Sensory receptors in visceral organs (e.g., stomach, lungs).
    • Motor neurons to smooth muscle, cardiac muscle, glands (involuntary control).
    • Divided into:
      • Sympathetic Division: "Fight or flight" responses (e.g., increase heart rate).
      • Parasympathetic Division: "Rest and digest" responses (e.g., decrease heart rate).

  • Enteric Nervous System (ENS):

    • Monitors chemical changes and stretching in gastrointestinal organs.
    • Controls smooth muscle contractions and secretions along the GI tract.
    • Acts independently of the CNS, often referred to as the "brain of the gut."

Summary

• The nervous system is divided into the CNS and PNS.
• CNS: Brain (inside skull) and spinal cord (inside vertebral column).
• PNS: Nervous tissue outside the CNS, including nerves, ganglia, enteric plexuses, and receptors.
• PNS is further divided into somatic, autonomic, and enteric systems.