Control and coordination are the functions of the nervous system and hormones in our bodies.
1. ANIMALS – NERVOUS SYSTEM
- The responses of the nervous system can be classified as reflex action, voluntary action or involuntary action.
- The nervous system uses electrical impulses to transmit messages.
- The nervous system gets information from our sense organs and acts through our muscles.
- All information from our environment is detected by the specialised tips of some nerve cells.
- These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on.
- So gustatory receptors will detect taste while olfactory receptors will detect smell.
How nervous impulses travel in the body?
This information, acquired at the end of the dendritic tip of a nerve cell sets off a chemical reaction that creates an electrical impulse.
This 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 some chemicals.
These chemicals cross the gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron. This is a general scheme of how nervous impulses travel in the body. A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscles cells or gland
nervous tissue is made up of an organised network of nerve cells or neurons, and is specialised for conducting information via electrical impulses from one part of the body to another.
1.1 What happens in Reflex Actions?
‘Reflex’ is a word we use very commonly when we talk about some sudden action in response to something in the environment.
Reflex arc : the nerve pathway involved in a reflex action, including at its simplest a sensory nerve and a motor nerve with a synapse between.
1.2 Human Brain
The brain and spinal cord constitute the central nervous system. They receive information from all parts of the body and integrate it.
Voluntary actions : Writing, talking, moving a chair, clapping at the end of a programme are examples of voluntary actions which are based on deciding what to do next.
The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord.
The brain thus allows us to think and take actions based on that thinking.
The brain has three such major parts or regions, namely the fore-brain, mid-brain and hind-brain.
Fore-brain: The fore-brain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors. Separate areas of the fore-brain are specialised for hearing, smell, sight and so on.
Involuntary actions:- Some functions are involuntarily performed, such as breathing, digestion, heart beating, eye reflexes, etc.,
- Many of these involuntary actions are controlled by the mid-brain and hind-brain.
- All these involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain.
Cerebellum: It is responsible for precision of voluntary actions and maintaining the posture and balance of the body.
- Activities like walking in a straight line, riding a bicycle, picking up a pencil. These are possible due cerebellum.
1.3 How are these Tissues of brain protected?
- For this, the body is designed so that the brain sits inside a bony box.
- Inside the box, the brain is contained in a fluid-filled balloon which provides further shock absorption.
- If you run your hand down the middle of your back, you will feel a hard, bumpy structure. This is the vertebral column or backbone which protects the spinal cord.
2 . COORDINATION IN PLANT
Some examples of the COORDINATION in plants are ,
- When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop.
- When a seed germinates, the root goes down, the stem comes up into the air.
In animals, some cells must change shape in order for movement to happen. Instead of the specialised proteins found in animal muscle cells, plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.
Movement Due to Growth
- Environmental triggers such as light, or gravity will change the directions that plant parts grow in. These directional, or tropic, movements can be either towards the stimulus, or away from it.
- So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it.
Geotropism:- Plants show tropism in response to other stimuli as well. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth. This upward and downward growth of shoots and roots, respectively, in response to the pull of earth or gravity is, called geotropism .
Hydrotropism:- the growth or turning of plant roots towards or away from moisture.
Chemotropism:- The growth or movement of a plant or plant part in response to a chemical stimulus. An example is the growth of a pollen tube down the style during fertilization in response to the presence of sugars.
The movement of sunflowers in response to day or night, on the other hand, is quite slow. Growth-related movement of plants will be even slower.
When growing plants detect light, a hormone called auxin, synthesised at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin 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.
Another example of plant hormones are gibberellins which, like auxins, help in the growth of the stem. Cytokinins promote cell division, and it is natural then that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds. These are examples of plant hormones that help in promoting growth
Abscisic acid is one example of a hormone which inhibits growth. Its effects include wilting of leaves.
HORMONES IN ANIMALS
Adrenaline:- Adrenaline is a hormone released from the adrenal glands and its major action, together with noradrenaline, is to prepare the body for ‘ fight or flight’.
- Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles.
- The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles.
- The breathing rate also increases because of the contractions of the diaphragm and the rib muscles.
- All these responses together enable the animal body to be ready to deal with the situation.
- Such animal hormones are part of the endocrine system which constitutes a second way of control and coordination in our body.
- Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth.
- Iodine is essential for the synthesis of thyroxin.
- In case iodine is deficient in our diet, there is a possibility that we might suffer from goitre. One of the symptoms in this disease is a swollen neck.
- lodine is necessary for the thyroid gland to make thyroxin hormone.
Growth hormone is one of the hormones secreted by the pituitary. As its name indicates, growth hormone regulates growth and development of the body. If there is a deficiency of this hormone in childhood, it leads to dwarfism.
Testosterone and Oestrogen
Their arr many Changes in appearance of boys and girls when they approached 10–12 years of age. These changes associated with puberty are because of the secretion of testosterone in males and Oestrogen in females.
This is a hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted in proper amounts, the sugar level in the blood rises causing many harmful effects such as diabetes.
The timing and amount of hormone released are regulated by feedback mechanisms. For example, if the 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.