Nervous System

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.

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.

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.

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.

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.

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 (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.

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.

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.