Control and Coordination - Detailed Notes

Control and Coordination

Introduction

  • Living organisms perform maintenance functions.
  • Movement is often associated with life.
    • Some movements are due to growth (e.g., plants).
    • Other movements are not related to growth (e.g., a cat running).
  • Movement is a response to changes in the environment.
    • Examples: cat running after a mouse, plants growing towards sunlight, children swinging.
  • Living organisms attempt to use environmental changes to their advantage.
  • Responses to the environment are carefully controlled.
  • Controlled movement requires:
    • Recognition of events in the environment.
    • Correct movement in response.
  • Living organisms use systems providing control and coordination.
  • Multicellular organisms use specialized tissues for control and coordination.

Animals – Nervous System

  • In animals, control and coordination are provided by nervous and muscular tissues.
  • Touching a hot object requires detection and response.
  • Information from the environment is detected by specialized nerve cell tips called receptors.
  • Receptors are located in sense organs (inner ear, nose, tongue, etc.).
    • Gustatory receptors detect taste.
    • Olfactory receptors detect smell.
  • Information acquisition:
    • A chemical reaction is triggered at the dendritic tip of a nerve cell, creating an electrical impulse.
    • The impulse travels from the dendrite to the cell body, then along the axon to its end.
    • At the axon's end, the electrical impulse triggers the release of chemicals.
    • These chemicals cross the synapse (gap) and start a similar electrical impulse in the next neuron's dendrite.
  • Synapses also allow impulses to be delivered from neurons to other cells (muscle cells, gland cells).
  • Nervous tissue is made of a network of neurons specialized for conducting information via electrical impulses.
  • A neuron consists of:
    • Dendrites: where information is acquired
    • Axon: through which information travels as an electrical impulse
    • Synapse: where electrical impulse is converted into a chemical signal

Reflex Actions

  • Reflex actions are sudden responses to environmental stimuli without conscious thought.
    • Examples: jumping out of the way of a bus, pulling a hand back from a flame, mouth watering when hungry.
  • These actions occur without feeling in control.
  • Touching a flame requires an urgent response.
  • Consciously thinking about the pain and possibility of getting burnt takes too long.
  • Thinking involves the creation of nerve impulses.
  • Thinking tissue consists of dense networks of neurons in the brain.
  • The brain receives signals from the body and instructs muscles to move.
  • This process would take too long in a dangerous situation.
  • Instead, a reflex arc connects the nerves that detect heat directly to the nerves that move muscles.
  • Reflex arcs are formed in the spinal cord.
  • Nerves from the body meet in a bundle in the spinal cord on their way to the brain.
  • Reflex arcs evolved because the brain's thinking process is not fast enough.
  • Many animals lack complex neuron networks for thinking.
  • Reflex arcs are more efficient for quick responses, even in organisms with complex neuron networks.

Human Brain

  • The spinal cord also supplies information to the brain for thinking.
  • Thinking involves complex mechanisms and neural connections concentrated in the brain.
  • The brain and spinal cord form the central nervous system.
  • The central nervous system receives and integrates information from the body.
  • The brain also sends messages to muscles for voluntary actions.
  • The peripheral nervous system facilitates communication between the central nervous system and the body using cranial nerves (from the brain) and spinal nerves (from the spinal cord).
  • The brain allows thinking and actions based on that thinking.
  • Different parts of the brain integrate different inputs and outputs.
  • The brain has three major regions:
    • Fore-brain:
      • Main thinking part.
      • Receives sensory impulses from receptors (hearing, smell, sight, etc.).
      • Has association areas where sensory information is interpreted with information from other receptors and stored information.
      • Decisions are made about how to respond and information is passed to motor areas to control voluntary muscles.
      • Contains a centre associated with hunger giving the sensation of feeling full.
    • Mid-brain
    • Hind-brain:
      • Controls involuntary actions (blood pressure, salivation, vomiting) via the medulla.
      • The cerebellum is responsible for precision of voluntary actions and maintaining posture and balance.

Protection of the Brain and Spinal Cord

  • The brain is protected by:
    • A bony box (skull).
    • A fluid-filled balloon for shock absorption.
  • The spinal cord is protected by the vertebral column (backbone).

Nervous Tissue and Action

  • Nervous tissue collects, sends, and processes information, makes decisions, and conveys decisions to muscles for action.
  • Muscle tissue performs the final action or movement.
  • When a nerve impulse reaches a muscle, the muscle fiber moves.
  • Muscle cells move by changing their shape to shorten.
  • Muscle cells contain special proteins that change their shape and arrangement in response to nervous electrical impulses.
  • Different kinds of muscles exist: voluntary and involuntary.

Coordination in Plants

  • Plants lack a nervous system and muscles.
  • Plants respond to stimuli in different ways:
    • Leaves of a sensitive plant (chhui-mui) fold up and droop when touched.
    • A seed germinates, the root goes down and the stem comes up.
  • Plants show two types of movement:
    • Independent of growth (e.g., sensitive plant).
    • Dependent on growth (e.g., seedling).

Immediate Response to Stimulus

  • Sensitive plants move leaves in response to touch without growth.
  • Plants use electrical-chemical means to convey information from cell to cell, but lack specialized tissue for conduction.
  • Plant cells change shape by changing the amount of water in them, leading to swelling or shrinking.

Movement Due to Growth

  • Plants like pea plants climb using tendrils that are sensitive to touch.
  • The part of the tendril in contact with support grows slower, causing the tendril to circle and cling.
  • Plants respond to stimuli slowly by growing in a specific direction in response to environmental triggers (light, gravity).
  • Tropic movements are directional movements towards or away from the stimulus.
    • Phototropism: Shoots bend towards light, roots bend away.
    • Geotropism: Roots grow downwards, shoots grow upwards in response to gravity.
    • Hydrotropism: Growth in response to water.
    • Chemotropism: Growth in response to chemicals (e.g., pollen tube growth towards ovules).

Electrical impulses vs chemical communication:

  • Electrical impulses enable faster responses, but are limited to cells connected by nervous tissue.
  • Electrical impulses cannot be continually created and transmitted (cells need to reset).
  • Chemical communication (hormones) is slower but can reach all cells in the body.

Plant Hormones

  • Plant hormones coordinate growth, development, and responses to the environment.
  • Hormones are synthesized away from their site of action and diffuse to that area.
    • Auxin: synthesized at the shoot tip, promotes cell elongation. In response to unilateral light, auxin concentrates on the shady side of the shoot causing it to bend towards light.
    • Gibberellins: promote stem growth.
    • Cytokinins: promote cell division, found in areas of rapid cell division (fruits, seeds).
    • Abscisic acid: inhibits growth, causes wilting of leaves.

Hormones in Animals

  • Hormonal means of information transmission are used in animals.
  • In scary situations, animals prepare for fighting or running away.
  • These activities require a great deal of energy.
  • Chemical signals reach all cells of the body and initiate needed changes
    • Adrenaline: secreted from the adrenal glands, prepares the body for action. It increases heart rate (resulting in more oxygen to muscles), reduces blood flow to the digestive system and skin (diverting blood to skeletal muscles), and increases breathing rate.
  • Animal hormones are part of the endocrine system.
  • Animal hormones control directional growth and maintain body design.
    • Thyroxin: requires iodine for synthesis, regulates carbohydrate, protein, and fat metabolism. Iodine deficiency can lead to goiter (swollen neck).
    • Growth hormone: secreted by the pituitary gland, regulates growth and development. Deficiency leads to dwarfism.
    • Testosterone (males) and oestrogen (females): cause changes associated with puberty.
    • Insulin: produced by the pancreas, regulates blood sugar levels. Insufficient secretion leads to diabetes.
      Hormone Levels Regulation:
  • Hormone secretion is regulated by feedback mechanisms.
  • E.g., when blood sugar levels rise, the pancreas produces more insulin. As blood sugar level falls, insulin secretion is reduced.
  • The hypothalamus releases growth hormone releasing factor which stimulates the pituitary gland to release growth hormone when growth hormone level is low.