Nervous System, Plant Responses, and Hormones in Animals

Jul 11, 2024

Nervous System, Plant Responses, and Hormones in Animals

Key Concepts

  • Response to Stimulus: Essential for survival and involves the nervous and hormonal systems.

Nervous System

Neurons

  • Neurons detect stimuli and conduct impulses.
  • Parts: Cell body, nucleus, dendrites, axon, nerve endings.
  • Receptors: Specialized tips in sense organs.
    • Olfactory receptors: Nose (smell)
    • Gustatory receptors: Tongue (taste)
  • Nerve Conduction: Neurons pass impulses via dendrites and nerve endings through synapse (gap).
    • Electrical impulses convert to chemical signals at nerve terminals.
  • Types of Neurons:
    • Sensory neurons: Carry information to brain/spinal cord.
    • Motor neurons: Carry information from brain/spinal cord to muscles/glands.

Reflex Actions

  • Long Pathway: Involves brain for response, takes time.
  • Short Pathway (Reflex Arc): Quick responses via spinal cord.
    • Components: Receptors, sensory neurons, relay neurons, motor neurons, effectors.

Central vs. Peripheral Nervous System

  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS): Nerves connecting CNS to the body.

Brain Structure and Functions

  • Protection: Meninges and cerebrospinal fluid, cranium (bony case).
  • Functions: Coordination, thinking, decision-making, emotions, body functions.
  • Voluntary (e.g., writing) vs. involuntary (e.g., heartbeat) actions.

Brain Parts

  • Forebrain: Thought processing, sensory impulse reception, voluntary muscle movement.
  • Midbrain: Visual/auditory reflexes, eye movement.
  • Hindbrain: Involuntary actions.
    • Pons: Sleep-wake cycle, breathing.
    • Medulla: Heart rate, breathing, blood pressure.
    • Cerebellum: Precision in movements, posture, balance.

Plant Responses

Stimuli and Movements

  • Plants respond to light, water, soil, touch, chemicals via movements.
  • Movements by growth or shape change of cells.
  • Tropic Movements: Directional responses.
    • Phototropism: Movement towards sunlight (e.g., stem bending).
    • Geotropism: Movement towards soil (e.g., roots).
    • Hydrotropism: Movement towards water.
    • Thigmotropism: Response to touch (e.g., tendrils).
    • Chemotropism: Movement towards chemicals (e.g., pollen tube).
  • Phytohormones: Control plant movements.
    • Auxin: Growth signals, especially in shoot/root tips.
    • Gibberellins: Stem/root elongation.
    • Cytokinins: Promote cell division, in fruits and seeds.
    • Abscisic Acid: Growth inhibitor, causes wilting.
    • Ethylene: Ripens fruits.

Hormones in Animals

Endocrine System & Glands

  • Glands: Pituitary, thyroid, adrenal, pancreas, testis, ovaries.
  • Function: Control growth, repair, reproduction via hormones.
  • Hormone Distribution: Through bloodstream.

Specific Hormones and Functions

  • Adrenaline: Fight or flight response, increases glucose/oxygen supply to muscles.
  • Thyroxine: Metabolism control—requires iodine.
  • Growth Hormone: Body growth—deficiency causes dwarfism, excess causes gigantism.
  • Testosterone: Male sex hormone—develops secondary sexual characters.
  • Estrogen: Female sex hormone—develops secondary sexual characters.
  • Insulin: Regulates blood sugar levels—deficiency leads to diabetes.

Importance of Iodized Salt

  • Iodine necessary for thyroxine production to avoid goiter and maintain metabolic functions.