Fundamentals of the Nervous System

Introduction

• Nervous system's role in day-to-day activities: dreams, sensations, decisions, actions
• Nervous system processes activities via electrical and chemical signals

Importance

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

Key Functions

• Sensory Input: Gathering information via sensory receptors (e.g., feeling a spider on your skin)
• Integration: Processing and interpreting sensory input (deciding how to react to the spider)
• Motor Output: Responding to the integrated inputs (e.g., swatting the spider away)
• Example: Nervous system's role in reacting to a spider on your knee

Organization

Central Nervous System (CNS)

• Components: Brain and spinal cord
• Function: Main control center, processes information, sends out orders

Peripheral Nervous System (PNS)

• Components: Nerves branching off from the brain and spinal cord
• Function: Communication between CNS and the body

Divisions of PNS

• Sensory (Afferent): Picks up sensory stimuli and sends to brain
• Motor (Efferent): Sends directions from brain to muscles and glands
  • Somatic (Voluntary): Controls skeletal muscles
  • Autonomic (Involuntary): Controls involuntary actions (heart, lungs)
    • Sympathetic: Mobilizes body for action (fight or flight response)
    • Parasympathetic: Relaxes body (rest and digest response)

Nervous Tissue

• Neurons: Main cells that respond to stimuli and transmit signals (small part of nervous tissue)
• Neuroglia (Glial Cells): Support, protect, and nourish neurons (larger part of nervous tissue)
  • Types: Astrocytes, Microglial, Ependymal, Oligodendrocytes in CNS; Satellite, Schwann cells in PNS

Glial Cells and their Functions

• Astrocytes: Anchor neurons, exchange materials between neurons and capillaries
• Microglial Cells: Provide immune defense in brain and spinal cord
• Ependymal Cells: Line cavities, create and circulate cerebrospinal fluid
• Oligodendrocytes: Produce myelin sheath for insulation in CNS
• Satellite Cells: Support neuron cell bodies in PNS
• Schwann Cells: Form myelin sheath in PNS

Neuron Characteristics

• Longevity: Long-lived cells, potentially living as long as the person
• Irreplaceability: Amitotic, most neurons do not regenerate
• High Metabolic Rate: Require continuous glucose and oxygen

Neuron Structure

• Soma (Cell Body): Contains nucleus and organelles
• Dendrites: Receive messages from other cells, convey to soma
• Axon: Transmits electrical impulses away from soma to other cells

Neuron Classification

• By Structure: Number of processes from cell body
  • Multipolar Neurons: Multiple processes, including one axon and many dendrites (most common)
  • Bipolar Neurons: Two processes, one axon and one dendrite (rare, e.g., retina)
  • Unipolar Neurons: One process, found mainly in sensory receptors
• By Function: Direction of impulse in relation to CNS
  • Sensory (Afferent) Neurons: Transmit impulses from receptors to CNS (mostly unipolar)
  • Motor (Efferent) Neurons: Transmit impulses from CNS to muscles and glands (mostly multipolar)
  • Interneurons: Transmit impulses within CNS, between sensory and motor neurons (mostly multipolar)

Applied Example: Spider on Knee

• Sensory neurons detect spider
• Signal sent via axon to spinal cord
• Interneurons in spinal cord process and transmit signal to motor neurons
• Motor neurons trigger muscle response (e.g., kicking leg, moving away spider)
• Additional processing in brain for conscious recognition and decision-making

Conclusion

• Nervous system's role in sensory input, integration, motor output
• Overview of CNS and PNS organization
• Role and types of glial cells
• Characteristics and classifications of neurons
• Preview of next lesson on nerve cell communication