Control and Coordination in Humans and Plants

6.1.1 Analysis of Reflex Actions

• Definition and Common Usage: The term 'reflex' is commonly used to describe a sudden action performed in response to a stimulus in the environment.

• Examples of Reflexive Behavior:

  • Jumping out of the way of a bus reflexly.

  • Pulling the hand back from a flame reflexly.

  • Mouth watering reflexly when feeling hungry.

• Core Concept: A reflex involves performing an action without conscious thought or a feeling of being in control of the reaction. It is a method of achieving control and coordination in urgent or dangerous situations.

• The Problem of Conscious Thinking:

  • Thinking is a complex activity involving the complicated interaction of nerve impulses from many neurons.

  • The thinking tissue consists of dense networks of intricately arranged neurons located at the forward end of the skull.

  • Process of Thinking: The brain receives signals from the body, thinks about them, and then instructs muscles to move via nerves.

  • Time Constraint: If a response to a hot object required conscious thinking, the time taken to process the pain and decide to move would be long enough for the person to get burnt.

• Reflex Arcs:

  • To solve the time problem, nerves that detect heat (input) are connected directly to the nerves that move muscles (output).

  • Reflex Arc Connection Point: The best location for these connections is where input and output nerves first meet. This occurs in the spinal cord, which is a bundle of nerves from all over the body on their way to the brain.

  • Function of Spinal Cord in Reflexes: Reflex arcs are formed in the spinal cord. While the arc is processed locally for speed, the information also continues to the brain.

  • Evolutionary Perspective: Reflex arcs evolved in animals because the brain's thinking process is often not fast enough for immediate survival. Many animals lack complex neuron networks for thinking, making reflex arcs their primary efficient way of functioning.

6.1.2 Structure and Function of the Human Brain

• Central Nervous System (CNS): Composed of the brain and the spinal cord. It is the main coordinating center of the body, receiving and integrating information from all parts of the body.

• Peripheral Nervous System (PNS): Facilitates communication between the CNS and the rest of the body. It consists of:

  • Cranial Nerves: Arising from the brain.

  • Spinal Nerves: Arising from the spinal cord.

• Major Regions of the Brain:

  • Fore-brain: The main thinking part. It contains:

    • Specialized areas for sensory impulses: hearing, smell, sight, etc.

    • Association Areas: Where sensory information is interpreted by combining it with information from other receptors and stored memories.

    • Motor Areas: Control the movement of voluntary muscles (e.g., leg muscles used for walking).

    • Hunger Center: A distinct part of the fore-brain associated with the sensation of feeling full.

  • Mid-brain and Hind-brain: Control many involuntary actions.

• Functions of the Hind-brain:

  • Medulla: Controls involuntary actions such as blood pressure, salivation, and vomiting.

  • Cerebellum: Responsible for the precision of voluntary actions and maintaining the posture and balance of the body. Examples include walking in a straight line, riding a bicycle, or picking up a pencil.

  • Pons: Included as a structural part of the hind-brain (visible in Fig. $6.3$).

• Voluntary vs. Involuntary Actions:

  • Voluntary: Based on deciding what to do next (e.g., writing, talking, moving a chair, clapping).

  • Involuntary: Actions we cannot easily control by thinking (e.g., heartbeat, breathing, digestion, change in pupil size).

6.1.3 Protection of Nervous Tissues

• Brain Protection:

  • Bony Box (Cranium/Skull): Provides the primary hard outer shell.

  • Fluid-filled Balloon: Inside the bony box, the brain is contained in a fluid that provides shock absorption.

• Spinal Cord Protection: Protected by the vertebral column (backbone), which is the hard, bumpy structure felt down the middle of the back.

6.1.4 Mechanism of Action in Muscle Tissue

• The Final Job: Nervous tissue collects, processes, and conveys decisions, but muscle tissue performs the actual action.

• Cellular Movement: Muscle cells move by changing their shape, specifically by shortening.

• Molecular Basis of Movement: Muscle cells contain special proteins that change their shape and arrangement in response to nervous electrical impulses.

• Classification (Class IX review): Muscles are categorized into voluntary and involuntary muscles based on how they are controlled.

6.2 Coordination in Plants

• Comparison to Animals: Plants have no nervous system and no muscles.

• Types of Plant Movement:

  • Growth-Independent (Immediate Response): Movement that does not involve growth, such as the leaves of a sensitive plant folding up.

  • Growth-Dependent (Tropic Movements): Directional movement caused by growth, such as a seedling's root going down and stem coming up.

6.2.1 Immediate Response to Stimulus in Plants

• Example: The sensitive plant (Mimosa pudica or 'chhui-mui').

• Mechanism of Communication: Information about touch is conveyed through electrical-chemical means from cell to cell. There is no specialized tissue for conduction.

• Mechanism of Movement: Plant cells change shape by altering the amount of water in them. This results in swelling or shrinking, causing the leaves to move. This happens at a point different from the original point of touch.

6.2.2 Movement Due to Growth: Tropic Movements

• Tendrils: Found in plants like the pea. They are sensitive to touch. When a tendril contacts a support, the part in contact grows slower than the part away from the support, causing it to circle and cling to the object.

• Environmental Triggers: Stimuli such as light and gravity change the direction of plant growth.

• Phototropism:

  • Shoots: Show positive phototropism by bending towards light.

  • Roots: Show negative phototropism by bending away from light.

• Geotropism: Response to the pull of earth or gravity.

  • Roots: Grow downwards (positively geotropic).

  • Shoots: Grow upwards and away from the earth (negatively geotropic).

• Hydrotropism: Directional growth in response to water.

• Chemotropism: Directional growth in response to chemicals. Example: Growth of pollen tubes towards ovules.

• Speed of Movement: Plant movements vary in speed; the sensitive plant moves quickly, sunflowers move slowly (day/night), and growth-related movements are the slowest.

6.3 Hormones in Animals: The Endocrine System

• Limitations of Electrical Impulses: Electrical impulses reach only cells connected by nervous tissue. Chemical signals (hormones) can reach all cells of the body to provide wide-ranging changes.

• Adrenaline:

  • Source: Secreted by the adrenal glands.

  • Context: Secreted during 'fight or flight' situations (e.g., a squirrel in danger).

  • Pathway: Secreted directly into the blood and carried to target organs.

  • Effects on Heart: Heart beats faster to supply more $O_2$ to muscles.

  • Blood Diversion: Blood flow to the digestive system and skin is reduced due to contraction of muscles around small arteries, diverting blood to skeletal muscles.

  • Respiratory Effects: Breathing rate increases due to contractions of the diaphragm and rib muscles.

• Thyroxin:

  • Source: Thyroid gland.

  • Requirement: Iodine is essential for its synthesis.

  • Function: Regulates carbohydrate, protein, and fat metabolism for optimal growth balance.

  • Deficiency: Leads to goitre, characterized by a swollen neck.

• Growth Hormone:

  • Source: Pituitary gland.

  • Function: Regulates growth and development. Deficiency in childhood leads to dwarfism.

• Puberty Hormones:

  • Testosterone: Secreted in males by the testes.

  • Oestrogen: Secreted in females by the ovaries.

• Insulin:

  • Source: Produced by the pancreas.

  • Function: Regulates blood sugar levels. Deficiency or improper secretion causes diabetes, resulting in high blood sugar and harmful effects.

• Hypothalamus: Plays a role in releasing hormones. It releases 'releasing hormones' (e.g., growth hormone releasing factor) to stimulate the pituitary gland.

Feedback Mechanisms in Hormone Regulation

• Importance of Precision: Hormones must be secreted in precise quantities.

• The Mechanism: The timing and amount are regulated by feedback loops.

• Sugar Level Example:

  • High blood sugar is detected by pancreas cells.

  • The pancreas responds by producing more insulin.

  • As blood sugar falls, insulin secretion is reduced.

Summary Table of Hormones and Functions

• Growth Hormone (Pituitary): Stimulates growth in all organs.

• Thyroxin (Thyroid): Regulates metabolism for body growth.

• Insulin (Pancreas): Regulates blood sugar level.

• Testosterone (Testes): Development of male sex organs and secondary characteristics.

• Oestrogen (Ovaries): Development of female sex organs, regulation of menstrual cycle.

• Adrenaline (Adrenal): Prepares the body for emergency situations.

• Releasing Hormones (Hypothalamus): Stimulates pituitary gland to release hormones.

Questions & Discussion

• Q: What is the difference between a reflex action and walking?

• A: Reflex actions are sudden, involuntary responses to stimuli controlled usually by the spinal cord without thinking. Walking is a voluntary action controlled by the fore-brain and cerebellum, involving conscious decision-making.

• Q: What happens at the synapse between two neurons?

• A: (Contextual inference from transcript) It is the point where information is transmitted from one neuron's axon to the next neuron's dendrite via chemical signals.

• Q: Which part of the brain maintains posture and equilibrium of the body?

• A: The cerebellum, located in the hind-brain.

• Q: How do we detect the smell of an agarbatti (incense stick)?

• A: Specific sensory regions in the fore-brain receive impulses from olfactory receptors to interpret the smell.

• Q: What is the role of the brain in reflex action?

• A: While the reflex arc is completed in the spinal cord for speed, the brain receives the sensory information for processing and memory.

• Q: Why is the use of iodised salt advisable?

• A: To ensure the thyroid gland has enough iodine to synthesize thyroxin, which regulates metabolism and prevents goitre.

• Q: Why are some patients of diabetes treated by giving injections of insulin?

• A: To lower their blood sugar levels, which the body cannot regulate on its own due to insufficient insulin production by the pancreas.

• Reflex Actions:

  • Quick, involuntary responses to stimuli.

  • Examples: Jumping from a bus, pulling back from a flame.

  • Occur without conscious thought via reflex arcs in the spinal cord.

  • Brain processes information afterwards.

• Nervous System:

  • Central Nervous System (CNS): Consists of brain and spinal cord. Coordinates thought and movement.

  • Peripheral Nervous System (PNS): Connects CNS to the rest of the body.

  • Involuntary Actions: Breathing and heartbeat (automatic).

  • Voluntary Actions: Decisions like walking and talking.

• Plant Responses:

  • No nervous system; respond to stimuli through movements.

  • Immediate responses (e.g., sensitive plant closing leaves).

  • Growth-dependent movements (e.g., roots growing toward water).

• Animal Hormones:

  • Regulate various body functions (e.g., adrenaline increases heart rate, insulin regulates blood sugar).