Control and Coordination Overview

Overview

• Topic: Control and coordination in animals and plants.
• Focus: Stimuli and responses, nervous and endocrine systems in animals, reflex arc, brain structure and functions, plant responses, plant hormones, major animal hormones and disorders.
• Purpose: Summarize key concepts, definitions, and functions for study.

Stimuli and Responses

• Stimulus: Any change in environment that causes a response (e.g., cold, sunlight, ice cream).
• Response: Organism's reaction to a stimulus (e.g., shivering, bending, salivation).
• Most responses protect organisms from dangerous stimuli.

Nervous System Basics

• Neuron (nerve cell) parts: cell body, nucleus, dendrites, axon, nerve endings.
• Receptors: Specialized tips on sensory neurons that detect stimuli and convert them to electrical impulses.
• Types of receptors: olfactory (smell), gustatory (taste), pain, temperature, etc.
• Nerve conduction: impulses collected at dendrites and passed via nerve endings.
• Synapse: Gap between nerve endings of one neuron and dendrites of another.
• Chemical transmission: electrical impulse converts to chemical signal at terminal, crosses synapse, and reconverts to electrical impulse in next neuron.

Types of Neurons

• Sensory Neurons: carry information from sense organs to brain/spinal cord.
• Motor Neurons: carry commands from brain/spinal cord to muscles or glands.
• Relay Neurons: connect sensory and motor neurons, process signals in spinal cord/brain.

Reflex Actions and Reflex Arc

• Reflex action: rapid automatic response processed in spinal cord to protect from danger (e.g., withdrawing from hot object).
• Reflex arc components:
  • Receptor: detects stimulus.
  • Sensory neuron: transmits signal to spinal cord.
  • Relay (inter) neuron: processes and generates response.
  • Motor neuron: carries response to effector.
  • Effector: muscle or gland that executes response.

Organization of Nervous System

• Central Nervous System (CNS): brain and spinal cord.
• Peripheral Nervous System (PNS): nerves linking CNS to body.

Brain Protection and Structure

• Brain protected by skull (cranium), three-layered meninges, and cerebrospinal fluid.
• Main functions: thinking, decision making, memory, emotions, and control of voluntary and involuntary actions.
• Voluntary actions: under conscious control (e.g., writing, talking).
• Involuntary actions: not under conscious control (e.g., heartbeat, digestion).

Major Brain Regions and Functions

| Part | Main Functions | | Forebrain | Thought processing; receives and analyzes sensory input; decision making; centers for hearing, smell, sight; controls voluntary muscle movements and hunger/fullness. | | Midbrain | Controls visual and auditory reflexes; controls eye and eyelid movements. | | Hindbrain | Contains pons, medulla oblongata, cerebellum; controls involuntary functions and coordination. | | Pons | Controls sleep–wake cycle and breathing rhythm. | | Medulla Oblongata | Regulates heart rate, breathing, blood pressure, other involuntary functions. | | Cerebellum | Maintains posture, balance, and precision of voluntary actions (walking, cycling, drawing). |

Plant Responses to Stimuli

• Plants respond to stimuli (light, water, soil, touch, chemicals) mainly by movements driven by growth or cell shape changes.
• Types of growth-driven directional movements (tropisms):
  • Phototropism: movement toward light (stem bending).
  • Geotropism: movement toward gravity/soil (roots growing down).
  • Hydrotropism: movement toward water (roots).
  • Thigmotropism: movement in response to touch (tendrils coiling).
  • Chemotropism: movement toward chemical stimulus (pollen tube growth toward ovule).

Causes of Plant Movements

• Phytohormones (plant hormones) regulate cell elongation, division, inhibition, ripening.
• Auxin: stimulates cell elongation; concentrated in young shoot and root tips; responsible for tropic bending.
• Differential elongation: auxin causes one side cells to elongate more, producing bending.

Major Plant Hormones and Functions

| Hormone | Function / Location | | Auxin | Stimulates cell elongation; responsible for tropisms; concentrated in shoot and root tips. | | Gibberellins | Promote stem and root elongation; support overall plant growth. | | Cytokinins | Promote cell division; abundant in fruits and seeds; aid growth by increasing cell number. | | Abscisic Acid (ABA) | Acts as growth inhibitor; promotes leaf wilting, yellowing, abscission. | | Ethylene | Gaseous hormone that stimulates fruit ripening. |

Endocrine System (Animals)

• Endocrine glands secrete hormones into blood: pituitary, thyroid, adrenal, pancreas, testes, ovaries.
• Exocrine glands (e.g., salivary glands, liver ducts) are not endocrine.
• Hormones are secreted in minute quantities and transported via blood.
• Hormones act only on target organs that have appropriate receptors.

Examples: Hormone Actions and Effects

• Adrenaline (epinephrine): secreted by adrenal glands during "fight or flight" situations.
  • Increases heart rate and breathing, diverts blood to skeletal muscles, raises glucose and oxygen supply.
  • Affects eyes, blood vessels, heart, lungs, and muscles.
• Thyroxine: produced by thyroid gland; requires iodine to synthesize.
  • Regulates metabolism of carbohydrates, proteins, and fats.
  • Iodine deficiency reduces thyroxine → goiter (swollen neck).
• Growth Hormone (GH): secreted by pituitary gland; regulates skeletal muscle and bone growth.
  • Deficiency → dwarfism (stunted growth).
  • Excess → gigantism (excessive height).
• Sex Hormones:
  • Testosterone (male): develops male secondary sexual characteristics and sperm production.
  • Estrogen (female): develops female secondary sexual characteristics and reproductive maturation.
• Insulin: secreted by pancreas; controls blood glucose.
  • Normal blood glucose ≈ 99 mg per 100 ml.
  • Insufficient insulin or malfunctioning pancreatic cells → diabetes (high blood sugar).
  • Dietary advice (reduce sugar/starch) given for diabetic patients.

Key Terms and Definitions

• Stimulus: environmental change causing response.
• Receptor: sensory structure that detects stimuli.
• Neuron: nerve cell transmitting electrical impulses.
• Synapse: junction between neurons where chemical transmission occurs.
• Reflex Arc: neural pathway mediating a reflex action.
• Tropism: directional growth response of plant toward/away from stimulus.
• Phytohormone: plant hormone controlling growth and responses.
• Endocrine Gland: gland secreting hormones into bloodstream.
• Target Organ: organ that responds to a specific hormone.

Action Items / Next Steps (for Students)

• Review neuron structure and label parts on a diagram.
• Memorize the reflex arc components and sequence.
• Practice identifying brain regions with their primary functions.
• Learn major plant hormones and their roles with examples.
• Understand endocrine glands, hormones, and disorders: goiter, diabetes, dwarfism, gigantism.
• Solve short-answer and diagram questions on tropisms and hormone effects.