Nervous System

Nervous System Overview

• The nervous system enables organisms to react to stimuli in their environment through a structured response.
• Logical order of responses:
  • Stimulus: Condition is presented to the organism.
  • Response: Organism reacts to the stimulus.
  • Assessment: Evaluation of the stimulus.
  • Response Evaluation: Impact of the response is considered.
  • Communication: Information sent to responding structures.
  • Preparation: The response is organized and executed.

Evolution of the Nervous System

• The nervous system has evolved from simple structures in unicellular organisms to complex systems in multicellular animals.
• Single-Celled Organisms: Use membrane receptors and signaling pathways to respond to environmental changes (e.g., amoebas using chemoreceptors).
• Multicellular Animals: Responses are integrated and coordinated by the nervous system, allowing for collective action across multiple cells.

Components of the Human Nervous System

• Central Nervous System (CNS): Comprising the brain and spinal cord.
• Peripheral Nervous System (PNS): Comprising nerves and ganglia that transmit information to and from the CNS.
• Key Terminology:
  • ANS: Autonomic Nervous System
  • PNS: Peripheral Nervous System
  • Sympathetic and Parasympathetic NS: Branches of the ANS with opposing functions (fight-or-flight vs rest-and-digest).
  • Neurons: Primary functional cells transmitting signals.
  • Glia: Support cells with various functions, such as nourishing and regulating neurons.

The Brain and Its Functions

• Major parts of the brain include:
  • Cerebral Cortex: Involved in sensory perception, motor control, and cognitive functions.
  • Hippocampus: Involved in memory formation and learning (central to the hippocampal trisynaptic circuit).
  • Lateralization: The specialization of functions in the left and right hemispheres of the brain.
• Phases of brain development include the crucial role of glia in neuron migration and the importance of synapse growth and rearrangement.

Nervous System Types in Multicellular Animals

• Types of nervous systems found in different organisms include:
  • Nerve Net: Found in cnidarians, like hydras, with no centralization.
  • Central Nervous System: Present in bilaterally symmetrical animals, includes clusters of neurons (ganglia) and brain structures.
  • Complex Mollusks: Cephalopods like squids have advanced systems for processing information and behaviours.

Autonomic Nervous System

• Functions include regulating involuntary actions and processing stimuli.
• Divided into:
  • Sympathetic Division: Involved in arousal and energy generation (fight-or-flight responses).
  • Parasympathetic Division: Promotes resting states and digestion.
  • Enteric Division: Manages the function of the digestive system.

Cerebrospinal Fluid and Central Nervous System (CNS)

• Cerebrospinal Fluid (CSF): Protects and cushions the brain and is continuously produced, maintaining a stable environment for the CNS.
  • Major functions:
  • Provides mechanical protection.
  • Maintains homeostasis.
  • Assists in nutrient and waste exchange.
• The CNS consists of:
  • Gray Matter: Contains neuron cell bodies and dendrites.
  • White Matter: Composed of myelinated axons for efficient signal transmission.

Brain Development

• The brain develops from the embryonic neural tube.
• Cavities within the neural tube become ventricles that house CSF and provide nutrients.
• Choroid plexus cells secrete CSF, essential for brain function and protection against injuries.

Glia Cell Functions

• Majors types of glia include:
  • Astrocytes: Support neurons by forming blood-brain barrier and regulating blood flow.
  • Oligodendrocytes: Insulate axons in the CNS.
  • Microglial Cells: Function in immune defense within the CNS.
• Glial cells play key roles in the nervous system from development to ongoing maintenance of neural health.