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Introduction |
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As the complexity of the individuals, plants or animals increases the different cells and organs become separated from each other by greater distance. Thus it becomes necessary to have a system by which the different parts of the organisms can function as a single unit. This is possible only if the different parts can coordinate with each other and carry out a particular function. |
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Coordination in Plants |
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In case of plants, growth and development is in a coordinated manner. The higher plants do not show locomotion. However, locomotion is seen in structures like sperm cells of ferns and mosses that swim towards the egg. The other movements shown by the plants are associated with the growth of the plants. |
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Growth Regulators |
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Growth substances are also called the phytohormones. The phytohormones have been put in five different categories based on their actions. |
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Control and Coordination in Animals |
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Animals are different from plants because of their ability of locomotion. This ability probably developed as they have to search for food, unlike the plants that are autotrophic. Since they move from one place to another, the animals have to continuously encounter changes in their environment. In order to maintain a steady state within the body (homeostasis), all animals should be able to perceive these changes and adapt to them. |
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Nervous Control in Human Beings - Nervous System |
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It controls and coordinates all the activities of the muscles in response to the changes outside. It also maintains the internal environment of the body by coordinating the functions of the various internal organs and the involuntary muscles. |
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Units of Nervous System |
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Around the cell body are short sensory projections called the dendrons. The fine branches of dendrons are called the dendrites. These short fibres receive messages and pass them on to the cell body or the cyton. The messages from the cyton are carried away by the long axon which ends in many fine branches. |
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Transmission of Messages |
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The messages are transmitted in the form of electrical impulses along the fibres of the neurons. |
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Types of Neurons |
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The neurons that conduct impulses from the receptors or sense organs to the central nervous system are called the sensory neurons. |
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Nerve Fibres and Nerves |
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The long axons of neurons along with the associated structures are called the nerve fibres. The fibres may be enclosed within sheaths called as myelin sheath. However, the action potential is not generated in the areas where there is a sheath over the fibre. Along the fibres there are regions where the myelin sheath is absent. These regions are called the nodes of Ranvier. The action potential jumps from one node to the other. |
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Types of Nerves |
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They are made up of only sensory neurons. For example, the cranial nerves that conduct impulses from the organs to the central nervous system. |
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Receptors and Effectors |
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Receptors are structures at the ends of the nerve fibres that collect the information to be conducted by the nerves. These receptors may be specialised sense organs like the Meissner's corpuscles of the skin, specialised nerve endings like the Pacinian corpuscles of skin or the specialised organs, the sense organs. |
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Parts of the Nervous System - Central Nervous System |
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It is made up of the brain and the spinal cord which is the continuation of the brain. Brain and spinal cord are surrounded by membranes called the meninges. There are three layers - outermost dura mater, middle arachnoid and the inner pia mater. The space between the arachnoid and pia mater is filled with the cerebrospinal fluid (CSF). It acts as a shock absorber. An infection of the meninges is called meningitis. |
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Parts of the Nervous System - Peripheral Nervous System |
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The peripheral nervous system is made up of nerves that connect the different parts of the body (peripheral tissues) to the central nervous system.; |
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Parts of the Nervous System - Autonomic Nervous System |
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They are the neurons that leave the ganglions and reach the smooth muscle/ gland. Their nerve cells are in the ganglions. |
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Reflex Action |
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In this type of reflex, the brain is not involved. The receptor is stimulated which is conducted to the spinal cord by the effector. The effector neuron from the spinal cord conducts a response to the muscle or the gland. This causes an immediate reaction. It does not involve any thinking or reasoning. |
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Endocrine System - Hormonal Control |
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Endocrine glands are those which are richly supplied with blood vessels and pour their secretions directly into the blood vessels. The secretions reach their target through blood. These glands are called the ductless glands as they do not have ducts. |
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Pituitary Gland |
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It is made up of three lobes - anterior, middle and posterior. They secrete hormones in response to the secretion of neurohormones by the hypothalamus. |
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Pineal, Thyroid and Parathyroid Glands |
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It is a butterfly-shaped, bilobed gland that is situated at the base of the larynx. The two lobes are joined by an isthmus. The hormone secreted is thyroxine. |
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Thymus and Pancreas |
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It is a gland that is prominent behind the breastbone in children. It secretes hormone called thymosin. Thymosin helps in the production of lymphocytes. |
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Adrenal and Gonads |
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The adrenal glands are present on top of the kidneys and appear cap-like on top of each kidney. Each adrenal gland has two layers - outer cortex and inner medulla. |
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Feedback Mechanism |
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It is a method of controlling the hormone production. In some cases the production of hormones is controlled by the nervous system. In other cases, the hormone itself acts as a control. |
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Summary |
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While the nervous system and endocrine system have their own features, they have a common method of communication. Both the systems release chemicals to communicate between cells. Together these two systems carry out a very complex process of maintaining a homeostatic (balanced) internal environment of an organism. |
