Response to Changes in the Environment
Structure: The system is divided into the Central Nervous System (CNS), comprising the brain and spinal cord, and the Peripheral Nervous System (PNS), consisting of nerves that connect the CNS to the rest of the body.
Neurones and Synapses: Information travels as electrical impulses along specialized cells called neurones. Because neurones do not touch, the gap between them—the synapse—is crossed by chemical messengers called neurotransmitters.
Reflex Arcs: These are rapid, automatic pathways that bypass the conscious brain to protect the body from harm. A typical arc involves a sensory neurone, a relay neurone in the spinal cord, and a motor neurone leading to an effector.
Tropisms: Plants exhibit directional growth responses to stimuli. Phototropism is growth in response to light (shoots grow toward it), while Geotropism (or gravitropism) is growth in response to gravity (roots grow toward it).
The Role of Auxin: Auxin is a plant growth regulator produced in the tips of shoots. It diffuses downwards and stimulates cell elongation. In phototropism, auxin accumulates on the shaded side of the shoot, causing those cells to grow longer and bending the plant toward the light source.
| Feature | Nervous System | Endocrine System |
|---|---|---|
| Message Type | Electrical (Impulse) | Chemical (Hormone) |
| Transmission | Along Neurones | Via Bloodstream |
| Speed | Very Fast | Slower |
| Duration | Short-lived | Long-lasting |
Precision in Terminology: Always distinguish between cell elongation and cell division when discussing plant growth. Auxin causes existing cells to stretch longer; it does not increase the number of cells in that specific response phase.
Ligament vs. Muscle: In eye accommodation questions, remember that ciliary muscles contract or relax, but suspensory ligaments only tighten (become taut) or loosen (become slack). Ligaments are not contractile tissue.
Vasodilation Mechanics: Ensure you explain that arterioles dilate to allow more blood to flow near the skin surface, increasing heat loss via radiation. Avoid saying 'capillaries move closer to the skin'.