Co-ordination and Control

In living organisms, co-ordination is the process by which different parts of the body work together to perform various activities. This is achieved through the nervous system and the endocrine (hormonal) system.

1. Nervous Co-ordination

The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

The Central Nervous System (CNS)

• Brain: Comprises the Cerebrum (intelligence, memory, voluntary actions), Cerebellum (posture and balance), and Medulla Oblongata (involuntary actions like heartbeat and breathing).
• Spinal Cord: Coordinates reflex actions and transmits impulses between the brain and the rest of the body.

Transmission of Impulses

Impulses travel along neurons (Sensory, Relay, and Motor). The junction between two neurons is called a synapse, where chemical neurotransmitters transmit the signal.

Reflex Actions

• Simple Reflex: Automatic, fast response (e.g., blinking, knee jerk).
• Conditioned Reflex: Learned responses (e.g., riding a bicycle, salivation at the sound of a food bell - Pavlov’s experiment).

2. The Sense Organs

• Skin: Detects touch, pressure, pain, and temperature.
• Nose & Tongue: Detect chemical stimuli (smell and taste).
• Eye: Responsible for sight. Common defects include Myopia (Short-sightedness, corrected with concave lenses) and Hypermetropia (Long-sightedness, corrected with convex lenses).
• Ear: Responsible for hearing and maintaining body balance (via semi-circular canals).

3. Hormonal Control

Animal Hormones

• Pituitary: The 'Master Gland'; secretes growth hormone and ADH.
• Thyroid: Produces thyroxine for metabolism.
• Adrenal: Produces adrenaline for 'fight or flight' responses.
• Pancreas: Produces insulin (lowers blood sugar) and glucagon (raises blood sugar).
• Gonads: Testes (testosterone) and Ovaries (oestrogen/progesterone).

Plant Hormones (Phytohormones)

• Auxins: Promote cell elongation and phototropism.
• Gibberellins: Promote stem elongation and seed germination.
• Cytokinins: Promote cell division.
• Ethylene: Stimulates fruit ripening.
• Abscisic Acid: Inhibits growth and promotes leaf fall.

4. Homeostasis

Homeostasis is the maintenance of a constant internal environment.

• Thermoregulation: The skin regulates temperature through sweating and vasodilation/vasoconstriction.
• Osmoregulation: The kidneys regulate water and salt levels, controlled largely by the Anti-Diuretic Hormone (ADH).