Fundamentals of the Nervous System

Importance of the Nervous System

• Controls all organs, physiological and psychological reactions
• Superior to the endocrine system

Principal Functions

1. Sensory Input
   • Detection of external stimuli (e.g., spider on skin)
2. Integration
   • Processing of sensory input
   • Decision making (e.g., react to spider)
3. Motor Output
   • Execution of response (e.g., hand removes spider)

Organization of the Nervous System

Central Nervous System (CNS)

• Brain and spinal cord
• Main control center
• Processes sensory input and sends motor output

Peripheral Nervous System (PNS)

• Nerves branching from brain and spinal cord
• Connects CNS to the rest of the body

Sensory (Afferent) Division

• Picks up sensory stimuli and sends to the brain

Motor (Efferent) Division

• Sends instructions from brain to muscles and glands

Somatic (Voluntary) Nervous System

• Controls skeletal muscle movement

Autonomic (Involuntary) Nervous System

• Controls heart, lungs, stomach, etc.
• Two divisions:
  • Sympathetic: Mobilizes body into action
  • Parasympathetic: Calms the body down

Nervous Tissue

• Densely packed with cells
• Less than 20% extracellular space

Types of Cells

Neurons (Nerve Cells)

• Respond to stimuli and transmit signals
• Long-lived, irreplaceable, and high metabolic rate
• Structure:
  • Soma: The cell body containing the nucleus and organelles
  • Dendrites: Receive messages from other cells
  • Axon: Sends messages to other cells

Glial Cells (Neuroglia)

• Support and protect neurons
• Types in CNS:
  • Astrocytes: Abundant, support and anchor neurons
  • Microglial Cells: Immune defense in brain and spinal cord
  • Ependymal Cells: Produce and circulate cerebrospinal fluid
  • Oligodendrocytes: Create myelin sheath around neurons
• Types in PNS:
  • Satellite Cells: Support neuron cell bodies
  • Schwann Cells: Create myelin sheath around axons

Classification of Neurons

Structural

• Multipolar Neurons: Many processes, one axon and multiple dendrites
• Bipolar Neurons: Two processes, one axon and one dendrite
• Unipolar Neurons: One process, mostly in sensory receptors

Functional

• Sensory (Afferent) Neurons: Transmit impulses from sensory receptors to CNS
• Motor (Efferent) Neurons: Transmit impulses from CNS to muscles/glands
• Interneurons: Transmit impulses within CNS, mostly multipolar

Example: Spider on Knee

• Sensory neurons detect spider
• Signal travels to spinal cord via Schwann cells
• Interneurons process signal
• Motor neurons execute response

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• How neurons use chemistry and electricity for communication