Control and Coordination Notes

Control and Coordination

Introduction

  • Living organisms exhibit movement, which is often a response to changes in the environment.

  • Movement can be related to growth (e.g., plants) or independent of growth (e.g., animals).

  • Movement is often an attempt to use environmental changes to an organism's advantage.

  • Controlled movement requires recognition of environmental events and appropriate responses.

  • Living organisms use systems providing control and coordination, often involving specialized tissues.

Animals - Nervous System

  • In animals, control and coordination are provided by nervous and muscular tissues.

  • Sense organs contain specialized nerve cell tips called receptors that detect information from the environment.

  • Receptors:

    • Gustatory receptors: detect taste.

    • Olfactory receptors: detect smell.

  • Information acquired at the dendritic tip of a nerve cell sets off a chemical reaction that creates an electrical impulse.

  • The impulse travels from the dendrite to the cell body, and then along the axon to its end.

  • At the end of the axon, the electrical impulse sets off the release of chemicals that cross the synapse and start a similar electrical impulse in a dendrite of the next neuron.

  • Synapses allow delivery of impulses from neurons to other cells, such as muscle cells or gland cells.

  • Nervous tissue is made up of an organized network of nerve cells or neurons specialized for conducting information via electrical impulses.

  • Neuron Structure

    • Information is acquired at the dendrites.

    • Information travels as an electrical impulse through the axon.

    • The impulse is converted into a chemical signal for onward transmission at the axon terminal.

Reflex Actions

  • Reflex actions are sudden, involuntary responses to environmental stimuli.

  • They occur without conscious thought or control.

  • Touching a flame is an example of an urgent and dangerous situation that requires a quick response.

  • Thinking involves complex interactions of nerve impulses from many neurons, which takes time.

  • Reflex arcs provide a quicker response by connecting sensory and motor nerves in the spinal cord.

  • Reflex Arc: A pathway in which nerves that detect heat are connected to the nerves that move muscles in a simpler way so that the signal or the input and responding to it by an output action is completed quickly.

  • The spinal cord is where nerves from all over the body meet on their way to the brain; reflex arcs are formed here.

  • Reflex arcs evolved as efficient ways of functioning in the absence of true thought processes.

  • Reflex arcs continue to be more efficient for quick responses, even after complex neuron networks have come into existence.

Human Brain

  • The spinal cord also supplies information to the brain for thinking.

  • Thinking involves more complex mechanisms and neural connections concentrated in the brain.

  • The brain and spinal cord constitute the central nervous system.

  • The brain integrates information from all parts of the body.

  • Voluntary actions (e.g., writing, talking) are based on decisions about what to do next.

  • The brain sends messages to muscles to initiate actions.

  • The peripheral nervous system facilitates communication between the central nervous system and other body parts; it consists of cranial nerves (from the brain) and spinal nerves (from the spinal cord).

  • The brain allows us to think and take actions based on that thinking.

  • The brain has three major parts: the fore-brain, mid-brain, and hind-brain.

    • Fore-brain: The main thinking part of the brain. It has regions that receive sensory impulses from various receptors. Areas are specialized for hearing, smell, sight, etc. Association areas interpret sensory information, integrating it with stored information. Decisions are made about how to respond, and information is passed to motor areas that control voluntary muscles.

    • The sensation of feeling full is controlled by a center associated with hunger in a separate part of the fore-brain.

    • Mid-brain and Hind-brain: Control involuntary actions (e.g., blood pressure, salivation, vomiting) through the medulla.

    • Hind-brain: The cerebellum is responsible for precision of voluntary actions and maintaining posture and balance.

Protection of Nervous Tissue

  • The brain is protected by the bony box of the skull.

  • The brain is contained in a fluid-filled balloon for shock absorption.

  • The vertebral column (backbone) protects the spinal cord.

How Nervous Tissue Causes Action

  • Muscle tissue performs the final job of action or movement.

  • When a nerve impulse reaches a muscle, the muscle fiber must move.

  • Muscle cells move by changing their shape to shorten.

  • Muscle cells have special proteins that change their shape and arrangement in response to nervous electrical impulses.

  • New arrangements of these proteins give the muscle cells a shorter form.

Coordination in Plants

  • Plants do not have a nervous system or muscles.

  • Plants respond to stimuli through movements independent of growth and movements dependent on growth.

    • Independent of growth: The leaves of the sensitive plant move very quickly in response to touch.

    • Dependent of growth: The directional movement of a seedling.

Immediate Response to Stimulus

  • Information that a touch has occurred must be communicated.

  • Plants use electrical-chemical means to convey information from cell to cell, but there is no specialized tissue for conduction.

  • Plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking.

Movement Due to Growth

  • Tendrils are sensitive to touch. The part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object, which causes the tendril to circle around the object and cling to it.

  • Plants respond to stimuli slowly by growing in a particular direction.

  • Environmental triggers, such as light or gravity, will change the directions that plant parts grow in.

  • Tropic movements: Directional movements toward or away from a stimulus.

    • Phototropism: Shoots bend towards light, while roots bend away from it.

    • Geotropism: Roots grow downwards, and shoots grow upwards, in response to gravity.

    • Hydrotropism: Growth in response to water.

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

  • Electrical impulses are a rapid means of transmission but are limited to cells connected by nervous tissue and cannot be continually generated.

  • Chemical communication is slower but can reach all cells and be done steadily and persistently.

  • Hormones coordinate growth, development, and responses to the environment.

  • Auxin: A hormone that helps cells to grow longer. It is synthesized at the shoot tip and diffuses towards the shady side of the shoot when light is coming from one side of the plant. This stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

  • Gibberellins: Hormones that help in the growth of the stem.

  • Cytokinins: Promote cell division and are present in greater concentration in areas of rapid cell division, such as in fruits and seeds.

  • Abscisic acid: A hormone that inhibits growth. Its effects include wilting of leaves.

Hormones in Animals

  • Hormones are used for chemical information transmission in animals.

  • Animals prepare for fighting or running away in scary situations.

  • Adrenaline is secreted from the adrenal glands directly into the blood and carried to different parts of the body.

  • Effects of Adrenaline:

    • Heart beats faster, resulting in supply of more oxygen to our muscles.

    • Blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs which diverts the blood to our skeletal muscles..

    • Breathing rate also increases because of the contractions of the diaphragm and the rib muscles.

  • Animal hormones are part of the endocrine system.

Hormones and Coordinated Growth

  • Iodine is necessary for the thyroid gland to make thyroxin hormone.

  • Thyroxin regulates carbohydrate, protein, and fat metabolism in the body to provide the best balance for growth.

  • Iodine deficiency can lead to goitre, a swollen neck.

  • Growth hormone: Secreted by the pituitary. It regulates growth and development of the body. If this hormone is deficient in childhood, it leads to dwarfism.

  • Testosterone in males and oestrogen in females cause changes associated with puberty.

  • Insulin: A hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted properly, the blood sugar level rises, causing many harmful effects.

  • The timing and amount of hormone released are regulated by feedback mechanisms.

  • If sugar levels in blood rise, they are detected by the cells of the pancreas which respond by producing more insulin. As the 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 the level of growth hormone is low.