Control and coordination in animals
The nervous system
Neurons form the basis of the functional as well as the structural unit of the nervous system. The main job of these neurons is to receive the external stimuli and then send it to the brain, so that the brain in turn can read those signals and direct them to the necessary parts of the body to take proper action. For example, when you touch something really hot, then the neurons will transmit this message to the brain that you are touching something really hot and the brain will then send a message back to the hands through the neurons, due to which you will immediately move your hand from there. This transfer of messages takes place through electrical impulses which move throughout the body through nerve fibres.
Take a look at the structure of a neuron. See the dendrites? These are nerve ending tips that are specialised for receiving the outside stimuli and is present in our sense organs. The moment these dendrites receive a stimuli a chemical reaction gets sparked off due to which electrical impulses are generated which in turn moves from the dendrite to the nucleus then to the axon and then finally to the nerve endings. There is a gap present in between two nerve cells which is known as synapse. From the nerve endings of one neurone, the synapse takes in the message and then transmits it to the consecutive neuron and thus through a chain action, these electrical impulses are carried from one part of the body to another to reach the brain.
The central nervous system
Any understanding of the control and coordination will be incomplete without the understanding of the CNS or the Central Nervous System. The brain and the spinal chord together form the CNS. All the electrical impulses are interpreted in the brain which then prompts actions. The human brain is divided mainly into three parts, depending on the type of function they perform. While the forebrain is concerned with activities like thinking, the hindbrain and the midbrain take care of the basic involuntary actions (actions which we do involuntarily). The hindbrain is in turn divided into the medulla and the cerebellum. When you cough or sneeze or the beating of your heart etc is controlled by the medulla. The cerebellum is responsible for maintaining balance and the proper functioning of the muscles.
What is a reflex action?
The sudden and automatic response that we have to an external stimulus is known as a reflex action. For example, our immediate moving away of the hand when we touch something too hot is a reflex action. One needs to understand the reflex arc or the pathway through which a reflex action takes place.
When you touch something hot, the receptors receive the signal and then the sensory neuron carries that message to the CNS, which then interprets the signal and sends back a reaction to the affected part of the body with the help of motor neurons. Then the effectors give a reaction to the stimuli, like immediately moving away the hand from the hot object.
The hormone system
All the actions of coordination and control cannot be performed by the nervous system alone. This is because the electrical impulses which are used by the nervous system for transmitting information cannot be accessed by all the cells, especially the ones which are not connected to the nerve tissue. And on top of that cells need some time to generate impulses and carry them from one place to another. This is why the endocrine gland of our body, secretes hormones which get mixed into our bloodstream and can reach all the target cells. Hormones perform the function of chemical messengers.
Let us take a look at the different hormones and the functions each of them perform:
|Growth hormone||Secreted from the pituitary gland|
Controls and coordinates the growth of an individual
Its deficiency can lead to dwarfism
|Insulin||Maintains and controls the sugar level in blood|
Secreted from the pancreas
Its deficiency might result in a rise in the sugar level in blood
|Sex hormones||Helps to develop the sexual features of an individual|
Different for males (testosterone) and females (estrogen).
Secreted from the reproductive glands of the body
|Thyroxin||Thyroid gland secretes this hormone with the help of iodine|
Controls the metabolism of fat
When present in lesser quantity, may result in goitre which is characterised by a swollen neck
Plants control and coordinate their movement with the help of hormones like auxin, gibberellins, abscisic acid and cytokinins. Their movements may or may not be dependent on their growth.