Lecture on the Nervous System

Introduction

• The nervous system is responsible for processing and executing actions and responses in the body.
• It controls physiological and psychological reactions, even influencing the endocrine system.
• The lecture will cover the anatomy, organization, communication, and damage of the nervous system.

Functions of the Nervous System

• Sensory Input: Detection of stimuli (e.g., a spider on the knee) by sensory receptors.
• Integration: Processing the sensory input and deciding on an action (e.g., whether to react to the stimulus).
• Motor Output: The physical response executed by the nervous system (e.g., removing the spider).

Organization of the Nervous System

• Central Nervous System (CNS): Includes the brain and spinal cord; acts as the main control center.
• Peripheral Nervous System (PNS): Composed of nerves branching off the CNS, facilitating communication.
  • Sensory (Afferent) Division: Picks up stimuli and sends information to the brain.
  • Motor (Efferent) Division: Sends directions from the brain to muscles and glands.
    • Somatic Nervous System: Controls voluntary skeletal muscle movements.
    • Autonomic Nervous System: Manages involuntary actions (heart, lungs, digestion).
      • Sympathetic Division: Prepares the body for action.
      • Parasympathetic Division: Calms and relaxes the body.

Nervous Tissue Composition

• Composed mainly of densely packed cells, with minimal extracellular space.
• Neurons: Nerve cells that respond to stimuli and transmit signals.
• Glial Cells (Neuroglia): Support and protect neurons, more numerous than neurons.
  • Astrocytes (CNS): Anchor neurons to blood supply, facilitate material exchange.
  • Microglial Cells (CNS): Provide immune defense in the brain and spinal cord.
  • Ependymal Cells (CNS): Produce and circulate cerebrospinal fluid.
  • Oligodendrocytes (CNS): Produce myelin sheath around neurons.
  • Satellite Cells (PNS): Support neuron cell bodies.
  • Schwann Cells (PNS): Produce insulating myelin sheath.

Characteristics of Neurons

• Longevity: Neurons can live as long as the organism.
• Amitotic: Neurons generally do not divide; highly dependent on longevity.
• Metabolic Rate: High energy demand, consuming significant daily calories.

Neuron Structure

• Soma (Cell Body): Contains the nucleus and other organelles.
• Dendrites: Receive messages and convey them to the soma.
• Axon: Transmits signals away from the soma.

Classification of Neurons

• Multipolar Neurons: Majority, with multiple processes extending from the soma.
• Bipolar Neurons: Two processes; rare, found in special sensory organs.
• Unipolar Neurons: Single process; mostly involved in sensory input.

Functional Classification

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

Example: Spider on the Knee Scenario

• Sensory neurons detect the spider, signal travels to CNS.
• Interneurons process the signal, initiating a motor response.
• Motor neurons execute the response, such as moving the leg.

Conclusion

• The nervous system's functions are essential in everyday life, controlling everything from thought processes to reactions.
• Next lesson will explore how nerve cells communicate using chemistry and electricity.

Credits

• Lecture by Crash Course, written by Kathleen Yale, edited by Blake de Pastino, consultant Dr. Brandon Jackson.
• Directed by Nicholas Jenkins and Michael Aranda, graphics by Thought Café.