Control and Coordination

A reflex action is an automatic, rapid response to a stimulus without conscious thought, like pulling your hand away from a hot object. Walking, however, is a voluntary action that involves conscious decision-making and coordination by the brain. Reflex actions are mediated by the spinal cord, while walking involves the brain's motor cortex.

At the synapse, the electrical impulse from the first neuron triggers the release of chemicals called neurotransmitters. These neurotransmitters cross the synaptic gap and bind to receptors on the next neuron, generating a new electrical impulse. This process ensures the transmission of signals between neurons.

The cerebellum, located at the back of the brain, is responsible for maintaining posture and equilibrium. It coordinates voluntary movements and ensures smooth, balanced actions by processing information from the inner ear and sensory receptors.

Smell is detected by olfactory receptors in the nose. When odor molecules from the agarbatti enter the nose, they bind to these receptors, generating electrical signals. These signals are transmitted to the brain's olfactory bulb, which interprets them as specific smells.

While reflex actions are primarily controlled by the spinal cord, the brain is informed about the action after it occurs. The brain can modulate reflexes and initiate voluntary responses if needed, ensuring appropriate reactions to stimuli.

Plant hormones are chemical messengers that regulate growth, development, and responses to environmental stimuli. Examples include auxins, which promote cell elongation, and gibberellins, which stimulate stem growth. These hormones are produced in one part of the plant and transported to another.

The movement of sensitive plant leaves is a rapid, non-growth response to touch, mediated by changes in cell water content. In contrast, shoot movement towards light (phototropism) is a slow, growth-based response driven by auxin distribution, causing cells on the shaded side to elongate more.

Auxin is a plant hormone that promotes growth by stimulating cell elongation. It is produced at the shoot tip and moves to darker areas, causing cells to grow longer and the plant to bend towards light, a process known as phototropism.

When a tendril touches a support, auxins accumulate on the opposite side, causing cells there to grow faster. This differential growth makes the tendril curl around the support, enabling the plant to climb and access more sunlight.

Plant seeds in a pot with moist soil on one side and dry soil on the other. Over time, roots will grow towards the moist side, demonstrating hydrotropism. This shows roots' ability to detect and grow towards water, a vital adaptation for survival.

Chemical coordination in animals involves hormones secreted by endocrine glands. These hormones travel through the bloodstream to target organs, where they regulate functions like growth, metabolism, and reproduction. For example, insulin regulates blood sugar levels.

Iodised salt provides iodine, essential for the thyroid gland to produce thyroxin hormone. Thyroxin regulates metabolism, growth, and development. Iodine deficiency can lead to goitre, characterized by a swollen thyroid gland, making iodised salt crucial for health.

Adrenaline prepares the body for 'fight or flight' by increasing heart rate, dilating pupils, and redirecting blood to muscles. This response enhances physical performance in emergencies, ensuring rapid reaction to threats or stress.

Diabetes patients may lack sufficient insulin, a hormone that regulates blood sugar. Insulin injections help lower blood sugar levels by promoting glucose uptake by cells. Without insulin, high blood sugar can damage organs and lead to complications.

Sensitive plant movement is a rapid, non-growth response to touch, involving changes in cell water pressure. Leg movement is a voluntary action controlled by the brain, involving muscle contractions and coordinated by the nervous system for precise motion.

Nervous mechanisms use electrical impulses for fast, precise responses, like reflex actions. Hormonal mechanisms use chemical signals for slower, widespread effects, like growth regulation. Both systems work together to maintain homeostasis and coordinate body functions.

Control and coordination ensure that an organism responds appropriately to environmental changes and maintains internal balance. This system integrates sensory input, processes information, and directs responses, enabling survival, growth, and reproduction in varying conditions.

Involuntary actions, like heartbeat, are controlled by the autonomic nervous system and occur without conscious thought. Reflex actions are rapid, automatic responses to stimuli, mediated by the spinal cord. Both are essential for survival but differ in complexity and control.

The fore-brain processes thought, memory, and sensory input. The mid-brain relays visual and auditory information. The hind-brain controls vital functions like breathing and balance. Together, they ensure coordinated and efficient functioning of the body.

Plants respond to stimuli through chemical signals and growth movements. For example, auxins mediate phototropism by redistributing in response to light. These mechanisms allow plants to adapt to their environment without a nervous system.

The spinal cord acts as the primary control center for reflex actions, bypassing the brain for faster responses. It receives sensory input and directly sends motor commands, ensuring quick reactions to potential harm, like withdrawing a hand from a hot surface.

The endocrine system complements the nervous system by providing slower, longer-lasting chemical signals. While the nervous system handles rapid responses, hormones regulate prolonged processes like growth and metabolism, ensuring comprehensive control and coordination.

Growth hormone deficiency in childhood can lead to dwarfism, characterized by stunted growth and short stature. This hormone is crucial for normal development, and its absence affects bone and muscle growth, highlighting the importance of hormonal balance.

Feedback mechanisms maintain hormone levels by detecting imbalances and adjusting secretion. For example, high blood sugar triggers insulin release, which lowers sugar levels, reducing insulin production. This dynamic balance ensures optimal bodily functions.