Homeostasis and the Nervous System

Role of the Nervous System

• Maintains equilibrium in the body.
• Responds to internal and external stimuli.
• Example: Drinking water involves visual processing and motor response coordinated by the nervous system.

Divisions of the Nervous System

• Central Nervous System (CNS):
  • Consists of the brain and spinal cord.
• Peripheral Nervous System (PNS):
  • Made of sensory neurons (brings info to CNS) and motor neurons (carries info out).
  • Motor Neurons Divided Into:
    • Somatic Nervous System: Controls voluntary movements (skeletal muscles).
    • Autonomic Nervous System: Controls involuntary movements (digestion, breathing).
      • Sympathetic Division: Fight-or-flight response.
      • Parasympathetic Division: Rest and digest.

Cells in the Nervous System

• Glial Cells:
  • Non-conducting; support and metabolism of nerve cells.
  • Hold neurons together ("glue").
• Neurons:
  • Conducting cells that carry electrochemical impulses.
  • Parts of a Neuron:
    • Dendrites: Receptors for stimulation.
    • Cell Body: Contains the nucleus.
    • Myelin Sheath: Insulates and speeds transmission.
    • Node of Ranvier: Gaps in myelin sheath for ion exchange.
    • Axon Endings: Contain synaptic vesicles with neurotransmitters.
    • Schwann Cells: Glial cells forming myelin sheath.
    • Axon: Carries impulses.

Nerve Transmission

• Increased by larger axon diameter and myelin sheath.
• Myelin Sheath: Insulation preventing ion loss, like plastic coating on wires.
• Saltatory Conduction: Signal jumps between nodes, speeding up transmission.
• Nodes of Ranvier: Allow ion exchange for action potential.
• Unmyelinated Neurons: Slower impulse due to continuous conduction.

Multiple Sclerosis (MS)

• Autoimmune disease; immune system destroys myelin sheath.
• Results in inefficient nerve transmission.

Types of Neurons

• Sensory Neurons:
  • Myelinated; carry info from receptors to CNS.
• Interneurons:
  • Unmyelinated; integrate and transmit info within CNS.
• Motor Neurons:
  • Myelinated; carry info from CNS to effectors (muscles/glands).

Spinal Cord

• White Matter: Myelinated outer part.
• Gray Matter: Unmyelinated inner part.

Reflex Arc

• Quick, involuntary, and unconscious response.
• Components:
  1. Effector/Sensory Receptor: Converts stimulus to impulse.
  2. Sensory Neuron: Carries info to CNS.
  3. Interneuron: Transmits info within CNS.
  4. Motor Neuron: Carries info to effector.
  5. Effector: Muscle or gland response.
• Synapses at spinal cord; does not require brain.
• Provides rapid response while also sending info to the brain.