Control and Coordination in Animals and Plants

Responses to Stimuli

• Organisms respond to stimuli (e.g., shivering to cold, plants bending towards sunlight).
• Responses protect organisms from dangerous stimuli.

Systems for Responses

• Nervous System and Hormonal System help produce responses.
• Neurons are nerve cells crucial for detecting stimuli.
• Neurons have parts: cell body, nucleus, dendrites, axon, and nerve endings.

Receptors

• Specialized tips on neurons detect stimuli and convert them into electrical impulses.
• Types of receptors:
  • Olfactory receptors: detect smell
  • Gustatory receptors: detect taste
  • Other receptors: detect pain, temperature, etc.

Nerve Conduction

• Nerve impulses collected by dendrites and passed through nerve endings.
• Synapse: Junction between nerve endings of one neuron and dendrites of another, where impulses are converted from electrical to chemical signals.
• Sensory Neurons: Carry information from sense organs to spinal cord/brain.
• Motor Neurons: Carry commands from brain/spinal cord to muscles/glands.

Pathways in Responses

1. Long Pathway: Information goes from stimulus to spinal cord, then to brain, and back to spinal cord, resulting in slower responses.
2. Reflex Actions (Short Pathway): Information is processed in spinal cord for quick responses, bypassing the brain.
   • Reflex Arc Components:
     • Receptors
     • Sensory neurons
     • Relay neurons
     • Motor neurons
     • Effectors (muscles or glands)

Nervous System Structure

• Central Nervous System: Brain and spinal cord.
• Peripheral Nervous System: Nerves connecting CNS to rest of the body.

Brain Protection

• Brain is covered by meninges (three layers) and cerebrospinal fluid for protection.
• Cranium (Skull): Hard outer case protecting the brain.

Brain Functions

• Main coordinating center for thinking, decision making, storing information, producing emotions, controlling functions.
• Functions are classified as:
  • Voluntary Functions: Controlled actions (writing, talking).
  • Involuntary Actions: Automatic functions (digestion, heartbeat).

Brain Parts

1. Forebrain: Thought processes, sensory impulses, decision making.
2. Midbrain: Visual/auditory reflexes and eye movements.
3. Hindbrain: Involuntary functions control (pons, medulla oblongata, cerebellum).
   • Pons: Sleep/wake cycle and breathing.
   • Medulla: Heart rate, breathing, blood pressure.
   • Cerebellum: Coordination of voluntary actions.

Plant Responses to Stimuli

• Plants respond to stimuli like sunlight, water, soil, and touch, mainly through movement.
• Movements in plants are not through nervous or muscular systems; instead, they are caused by growth or shape changes of cells.
  • Tropic Movements: Directional movements in response to stimuli (phototropism, geotropism, hydrotropism, thigmotropism, chemotropism).

Phytohormones

• Auxin: Causes cell elongation, responsible for tropic movements.
• Gibberellins: Promote stem and root elongation.
• Cytokinins: Promote cell division and growth.
• Abscisic Acid: Acts as a growth inhibitor.
• Ethylene: Stimulates fruit ripening.

Hormonal Control in Animals

• Endocrine System: Hormonal coordination through glands (pituitary, thyroid, adrenal, etc.).
• Hormones control growth, repair, reproduction; act on target tissues/organs.

Hormone Functions

• Adrenaline: Secreted during "fight or flight" situations; increases oxygen and glucose supply to muscles.
• Thyroxin: Produced by thyroid; controls metabolism of nutrients.
• Insulin: Manages blood glucose levels; deficiency leads to diabetes.

Hormonal Growth Regulation

• Growth Hormone: Regulates growth; deficiency causes dwarfism, excess causes gigantism.
• Testosterone: Male hormone affecting secondary sexual characteristics.
• Estrogen: Female hormone affecting secondary sexual characteristics.

Importance of Iodine

• Iodine is necessary for thyroxin production; deficiency leads to goiter (swollen neck).

Conclusion

• Control and coordination in animals and plants involve complex interactions between nervous and hormonal systems to respond effectively to stimuli.