CHAPTER 2 CONTROL AND COORDINATION
In animals, control and coordination are provided by nervous and muscular tissues. All the information from our environment is detected by the specialised tips of nerve cells. These receptors are located in our sense organs. The 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 how nervous impulses travel in the body.
Reflex is some sudden action in response to something in the environment. Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain.
The brain is the main coordinating centre of the body. The brain sends messages to muscles. The communication between of 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 has three major parts or regions: the fore-brain, mid-brain and hind-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. Based on the information received by from all these receptors, a decision is made about how to respond and the information is passed on to the motor areas which control the movement of voluntary muscles.
Many involuntary actions are controlled by the mid-brain and the hind-brain. A part of the hind-brain called the cerebellum is responsible for precision of voluntary actions and maintaining the posture and balance of the body.
COORDINATION IN PLANTS
Plants use electrical-chemical means to convey information from cells to cells. Some cells must change shape in order for movement to happen. Plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.
HORMONES IN ANIMALS
Hormones produced in one part of an organism move to another part to achieve the desired effect.
A feedback mechanism regulates the action of the hormones.