Chapter – 6

Control and Coordination

3.1. Control and coordination are the functions of animals’ nervous systems and hormones. Plants do not have a nervous system but coordinate via the hormones. The working together of various systems in the body is called coordination.

3.2. Nervous System: The nervous system along with the muscular tissue is the Control Centre of the body in animals including humans.
* It consists of highly specialized cells called neurons, nerves and neural organs that link, coordinate and control the captivities of different organs in the body.
* All information from environment is detected by the specialized tips of some nerve cells called receptors. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue and so on. Gustatory receptors will detect taste while olfactory receptors will detect smell.

3.3. Neuron or Nerve Cell: The information from the environment is detected by the nerve cells called neutrons. They are structural and functional units of the nervous system.
* A neuron is the longest cell of human body which is about 90-100 cm long.
* The nerve tissue is made up of network of nerve cells or neurons. These are specialized for conducting information through electrical impulses from one part of the body to other.
3.3.1.Structure of Neuron or Nerve Cell
It consists of the following main parts:
(i) Cell body or Cyton: It is the broad rounded part of neuron. It has a central nucleus surrounded by cytoplasm and various cell organelles except centrioles.
(ii) Dendrites or dendrons: These are hairlike processes connected to the cyton. They receive stimulus, which may be physical, chemical, mechanical, or electrical, and pass it on to the cyton.
(iii) Axon: These are long, fibre-like cytoplasmic processes. They conduct impulses away from the cell body. The axon may be covered by a protective sheath called myelin sheath.
(iv) Nerve Ending: These are the fine branch-like termination of neurons.

3.3.2. Transmission of a Nerve Impulse
* The transmission of a nerve impulse in the body has a general scheme of flow. All the information from the environment is detected by the receptors (sense organs) present in the body, which transfer it to sensory neurons.
* The information acquired at the end of the dendritic tip of a neuron causes a chemical reaction that produces an electrical impulse.
* This impulse, travels from the dendrite of the sensory neuron to its cells body (cyton) and then along the axon to its end of axon, the electrical impulse causes the release of some chemicals (neurotransmitters).
* These chemicals cross the gap (synapse) and start a similar electrical impulse in the dendrite of the next neuron.
* A similar synapse allows the delivery of such impulses from neurons to other cells, such as muscle cells or glands.
3.3.3. Neuromuscular Junction: The point where a muscle fibre in contact with a motor neuron carrying nerve impulses from the Central Nervous System (CNS). The neurotransmitter for the transmission of nerve impulse from neuron to the muscle fibre releases in the same way as impulses are transmitted across a synapse between two neurons.

3.3.4. Limitations to the use of electrical impulse
(i) The electrical impulse will reach only those cells that are connected by nervous tissue, not each and every cell in the animal body.
(ii) Once an electrical impulse is generated in a cell and transmitted, the cell will take some time to reset its mechanism before it can generate and transmit an new impulse.