Overview of the Nervous System

Introduction

• The nervous system is essential for all physiological and psychological reactions.
• It controls the body's organs and other systems, including the endocrine system.

Functions of the Nervous System

• Sensory Input: Detection of stimuli (e.g., feeling a spider on your knee).
• Integration: Processing of the sensory input and deciding the response.
• Motor Output: Execution of the response by activating body parts (e.g., removing the spider).

Main Parts of the Nervous System

• Central Nervous System (CNS): Comprised of the brain and spinal cord; the main control center.
• Peripheral Nervous System (PNS): Composed of nerves branching out from the CNS to the rest of the body.
  • Sensory (Afferent) Division: Picks up stimuli and sends them to the brain.
  • Motor (Efferent) Division: Sends directions from the brain to muscles and glands.
    • Somatic Nervous System: Controls voluntary movements.
    • Autonomic Nervous System: Controls involuntary actions (heart, lungs, stomach).
      • Sympathetic Division: Mobilizes body action.
      • Parasympathetic Division: Relaxes the body.

Nervous Tissue Composition

• Mostly composed of cells with less than 20% extracellular space.

Types of Cells

• Neurons: Respond to stimuli and transmit signals.
  • Long-lived and amitotic (do not divide).
  • Have a high metabolic rate requiring glucose and oxygen.
• Glial Cells: Supportive cells that protect neurons.
  • Astrocytes: Abundant in the CNS; manage neuron blood supply.
  • Microglial Cells: Defensive cells against microorganisms.
  • Ependymal Cells: Line cavities and circulate cerebrospinal fluid.
  • Oligodendrocytes: Produce myelin sheath in the CNS.
  • Satellite Cells: Support neurons in the PNS.
  • Schwann Cells: Produce myelin sheath in the PNS.

Neuron Structure and Types

• Soma: Neuron's life support, contains the nucleus and other organelles.
• Dendrites: Receive information from other cells.
• Axon: Transmits impulses away from the soma.

Neuron Classification by Structure

• Multipolar Neurons: Most common; have one axon and multiple dendrites.
• Bipolar Neurons: Rare; have one axon and one dendrite.
• Unipolar Neurons: One process; primarily in sensory receptors.

Neuron Classification by Function

• Sensory (Afferent) Neurons: Transmit impulses from sensory receptors to CNS.
• Motor (Efferent) Neurons: Transmit impulses from CNS to muscles/glands.
• Interneurons: Transmit impulses between sensory and motor neurons.

Application: Spider on Knee Example

• Sensory neurons detect the spider.
• Signal travels via Schwann cells to spinal cord, then to interneurons.
• Motor neurons trigger muscle response; brain processes stimuli for further actions.

Conclusion

• The nervous system's organization and functionality are crucial for understanding responses to stimuli.
• Upcoming lessons will explore nerve cell communication through chemistry and electricity.

Acknowledgments

• Course made possible by Subbable subscribers and created by a team including Kathleen Yale and Dr. Brandon Jackson.