Notes on Control and Coordination

Introduction to Control and Coordination in Living Organisms

• Movement as a Sign of Life: Traditionally, visible movement is associated with being alive. Examples include a cat running, children playing on swings, or buffaloes chewing cud.

• Types of Movement:

  • Growth-Related Movement: In plants, a seed germinates and grows, pushing soil aside. If growth is inhibited, these movements stop.

  • Non-Growth Movements: Movements such as a cat running or a person whispering are not linked to growth but are often responses to environmental changes.

• Function of Movement: organisms move as a response to changes in their environment or to use environmental changes to their advantage:

  • Plants grow toward sunshine.

  • Children swing for pleasure.

  • Buffaloes chew cud to break down tough food for better digestion.

  • Humans move away from bright light or hot objects to protect themselves.

• The Need for Control and Coordination: Environmental changes evoke specific, appropriate responses. This requires a system to recognize environmental events and trigger the correct response. In multicellular organisms, specialized tissues are dedicated to provide these control and coordination activities.

The Animal Nervous System

• Specialized Tissues: In animals, control and coordination are primarily managed by nervous and muscular tissues.

• Detection of Stimuli through Receptors: All information from the environment is detected by the specialized tips of nerve cells called receptors, typically located in sense organs:

  • Gustatory Receptors: Detected in the tongue, responsible for taste.

  • Olfactory Receptors: Detected in the nose, responsible for smell.

• Structure and Function of a Neuron (Nerve Cell):

  • Information Acquisition: Information is acquired at the dendritic tip of a nerve cell.

  • Path of the Impulse:

    1. A chemical reaction at the dendrite creates an electrical impulse.

    2. The impulse travels from the dendrite to the cell body.

    3. The impulse proceeds along the axon to its end.

  • Synapse: At the end of the axon, the electrical impulse triggers the release of chemicals. These chemicals cross the gap, known as the synapse, and start a similar electrical impulse in the dendrite of the next neuron.

  • Neuromuscular Junction: This is the point where nervous impulses are delivered from neurons to other cells, such as muscle cells or glands.

Reflex Actions and the Reflex Arc

• Definition of Reflex: A sudden, unconscious action in response to an environmental change (e.g., pulling a hand back from a flame or salivating when hungry).

• The Mechanism of Thinking: Thinking is a complex activity involving intricate networks of neurons in the forward end of the skull (the brain). Because thinking involves complex interactions of many nerve impulses, the response time is slower than a reflex.

• The Reflex Arc: To avoid harm (like being burnt by a hot object), the body uses a faster connection that bypasses the complex thinking process of the brain.

  • Path: Input nerve (detecting stimulus) -> Spinal cord -> Output nerve (moving muscle).

  • Location: Reflex arcs are formed in the spinal cord because all nerves from the body meet there on their way to the brain. While the information is also sent to the brain, the response is executed immediately at the spinal level.

  • Evolutionary Significance: Reflex arcs evolved as an efficient way for animals to function when the thinking process is too slow or absent.

The Human Brain

• Central Nervous System (CNS): Composed of the brain and the spinal cord. It serves as 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. Contains:

  • Cranial Nerves: Arise from the brain.

  • Spinal Nerves: Arise from the spinal cord.

• Major Regions of the Brain:

  • Fore-brain: The main thinking part. It contains areas for hearing, smell, and sight.

    • Association Areas: These interpret sensory information by combining it with information from other receptors and stored memory.

    • Motor Areas: Control voluntary muscle movements (e.g., leg muscles).

    • Hunger Centre: A separate part of the fore-brain that detects the sensation of feeling full.

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

    • Medulla (Hind-brain): Specifically controls blood pressure, salivation, and vomiting.

    • Cerebellum (Hind-brain): Responsible for the precision of voluntary actions and maintaining posture and body equilibrium (e.g., walking in a straight line, riding a bicycle, picking up a pencil).

Protection and Response Mechanisms

• Protection of Nervous Tissue:

  • Brain Protection: The brain sits in a bony box (skull). Inside the box, it is surrounded by a fluid-filled balloon that acts as a shock absorber.

  • Spinal Cord Protection: The spinal cord is protected by the vertebral column, also known as the backbone.

• Mechanism of Muscle Action:

  • When an impulse reaches a muscle, the muscle fibre must move by changing its shape.

  • Cellular Level: Muscle cells contain special proteins that change their shape and arrangement in response to nervous electrical impulses. This results in the shortening of the muscle cell to produce movement.

Coordination in Plants

• Absence of Nervous System: Plants lack nerves and muscles but still respond to stimuli.

• Types of Plant Movement:

  • Immediate Response to Stimulus (Non-Growth): Seen in the Mimosa family (e.g., the sensitive plant or "touch-me-not" / chhui-mui).

    • Information about touch is communicated through electrical-chemical means from cell to cell.

    • Movement occurs because plant cells change shape by altering the amount of water in them, causing swelling or shrinking.

  • Movement Due to Growth (Tropic Movements): Slow, directional growth movements.

    • Tendrils: In climbing plants like peas, tendrils are sensitive to touch. Upon contact with a support, the part of the tendril in contact grows slower than the part away from it, causing it to circle and cling to the support.

    • Phototropism: Growth toward light (shoots) or away from light (roots).

    • Geotropism: Response to gravity; roots grow downward (positive geotropism), while shoots grow upward (negative geotropism).

    • Hydrotropism: Growth in response to water.

    • Chemotropism: Growth in response to chemicals (e.g., pollen tubes growing toward ovules).

Plant Hormones

• Function: Chemical compounds that coordinate growth, development, and environmental responses. They move by diffusion from the site of synthesis to the site of action.

• Specific Hormones:

  • Auxin: Synthesized at the shoot tip. When light comes from one side, auxin diffuses to the shady side, causing cells there to grow longer, making the plant appear to bend toward the light.

  • Gibberellins: Help in the growth of the stem.

  • Cytokinins: Promote cell division; found in high concentrations in fruits and seeds.

  • Abscisic Acid: Inhibits growth and causes the wilting of leaves.

Animal Hormones and the Endocrine System

• Adrenaline: Secreted by the adrenal glands during scary or urgent situations (fight or flight).

  • Effects: Heart beats faster to supply more oxygen to muscles; blood is diverted from digestive system/skin to skeletal muscles; breathing rate increases due to diaphragm and rib muscle contractions.

• The Thyroid Gland: Requires iodine to synthesize thyroxin. Thyroxin regulates carbohydrate, protein, and fat metabolism for growth balance. Deficiency of iodine leads to goitre, characterized by a swollen neck.

• The Pituitary Gland: Secretes growth hormone, which regulates the body's growth and development. Deficiency in childhood results in dwarfism.

• Sex Hormones: Testosterone (males) and oestrogen (females) cause the dramatic physical changes during puberty (ages 10–12).

• Pancreas and Insulin: The pancreas produces insulin, which regulates blood sugar levels. Lack of insulin causes diabetes, where blood sugar levels rise to harmful levels.

• Feedback Mechanism: The timing and amount of hormone release are self-regulated. For example, high blood sugar levels trigger the pancreas to produce more insulin; as sugar levels fall, insulin secretion reduces.

• Hypothalamus: Plays a role in releasing hormones, such as releasing growth hormone releasing factor to stimulate the pituitary gland.

Table of Important Hormones and Functions

Questions & Discussion

• Detecting the smell of an agarbatti (incense stick): This is detected by olfactory receptors in the nose, with information transmitted to the fore-brain for interpretation.

• Synapse Activity: Chemicals are released at the end of an axon, cross the synapse, and trigger an electrical impulse in the next neuron.

• Reflex Action vs. Walking: Walking is a voluntary action controlled by the cerebellum/fore-brain, whereas a reflex is an automatic, involuntary response controlled via the spinal cord.

• Posture and Equilibrium: Primarily maintained by the cerebellum in the hind-brain.

• Diabetes Treatment: Patients are given insulin injections because their pancreas does not secrete enough insulin to regulate blood sugar levels.