1. Animal Nervous System & Neurons
The nervous system is made of a specialized network of nerve cells called neurons. Information travels through a neuron in a specific direction:
Dendrite (receives stimulus) → Cell Body → Axon → Nerve Ending → Synapse (chemical gap)
2. Reflex Arc
An automatic, sudden, and involuntary response to an environmental stimulus that bypasses thinking channels in the brain to prevent injury. The structural pathway involves:
- Receptor Organ (e.g., skin sensing heat) $\rightarrow$ Sensory Neuron $\rightarrow$ Spinal Cord $\rightarrow$ Motor Neuron $\rightarrow$ Effector Muscle (pulls hand away).
3. The Human Brain
The main coordinating center of the body, divided into three major components:
- Forebrain (Cerebrum): Responsible for thinking, memory, intelligence, and voluntary actions.
- Midbrain & Hindbrain (Pons, Medulla): Control involuntary actions like blood pressure, salivation, and vomiting.
- Cerebellum (part of Hindbrain): Coordinates precision, posture, and body balance (e.g., riding a bicycle).
4. Plant Hormones (Phytohormones)
- Auxin: Promotes cell elongation; helps plants bend toward light (**phototropism**).
- Gibberellins: Help in the growth of stems and buds.
- Cytokinins: Promote rapid cell division, found heavily in fruits and seeds.
- Abscisic Acid: A growth inhibitor. Responsible for the wilting of leaves.
CBSE Board Exam Classic Case Study
How does Iodized Salt prevent disease? The thyroid gland requires **Iodine** to manufacture the hormone **Thyroxine**. Thyroxine regulates carbohydrate, protein, and fat metabolism for balanced body growth. A lack of iodine in the diet leads to a deficiency, causing an enlarged thyroid gland known as **Goiter**.