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The Nervous and Endocrine Systems Forms and Functions of Plants and Animals

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The Nervous and Endocrine Systems Forms and Functions of Plants and Animals MODULE - 2 Coordination and Control : The Nervous and Endocrine Systems Forms and Functions of Plants and animals 17 Notes COORDINATION AND CONTROL : THE NERVOUS AND ENDOCRINE SYSTEMS Every organism performs movements and a number of other tasks for its survival. Besides, several other actions are continuously occurring inside the body that need to be properly timed and coordinated. All this is the outcome of two organ systems – the nervous and the endocrine (hormonal) systems. OBJECTIVES After completing this lesson, you will be able to : z describe the functions of the nervous system and list its subdivisions; z list, draw and label the major parts of the human brain and spinal cord and explain their functions; z describe the nervous system of cockroach z explain the structure of a neuron, a nerve and describe the conduction of impulse through a nerve fibre and across the synapse; z define reflex action and draw the components of the reflex arc; z list various sensory receptors in human body and describe the structure and functioning of the sense organs–eye, ear, nose, tongue and skin; z distinguish between exocrine and endocrine glands; z list various endocrine glands and locate their position in human body; z identify properties of hormones and mention their nature and manner of functioning; z differentiate between hormones and pheromones; z name the various hormones secreted by pituitary, thyroid, parathyroid, thymus, adrenals, pancreas and reproductive organs in humans and mention their functions; z relate the hormonal imbalance with hormone related disorders in humans; z state the effects of over functioning (hyperactivity) and hypoactivity (underfunctioning) of pituitary and thyroid; z explain the feedback mechanism of hormonal control. 366 BIOLOGY Coordination and Control : The Nervous and Endocrine Systems MODULE - 2 Forms and Functions of 17.1 FUNCTIONS OF THE NERVOUS SYSTEM Plants and animals The major functions of the nervous system in humans are as follows: (i) It keeps us informed about the outside world through the sense organs. (ii) It enables us to remember, think and to reason out. (iii) It controls all voluntary muscular activities like running, speaking etc. (iv) It regulates several involuntary activities such as breathing, beating of the heart, movement of food through the food canal, etc. Notes Thus, the nervous system makes our body parts work together in proper coordination, as one single integrated unit. Some basic terms Before you learn about the various aspects of the nervous system, get familiar with the following related terms. Stimulus : an agent or a sudden change of the external or the internal environment that results in a change in the activities of the organism. Impulse : a wave of electrical disturbance that travels accross the nerve cell and its fibre. Response : a change in the activity of the organism caused due to stimulus. Receptors : The nerve cells which on receiving the stimulus, set up wave of impulses towards the central nervous system (brain and spinal cord). Effectors : muscles or glands, which on receiving the impulse from the brain or spinal cord contract or secrete substances. Nerve : A bundle of axons (nerve fibres) of separate neurons connecting the central nervous system with other parts of the body. Sensory (afferent) nerve or the cell : bringing the impulse from the receptor (sensory organ) to the main nervous system. Motor (efferent) nerve or the cell : Carrying the impulse from the main nervous system towards a muscle or a gland. 17.1.1 Nervous System in Animals Various activities of an animal’s body are controlled and coordinated through two systems viz. the nervous system and the endocrine system. We will discuss the nervous system of cockroach here. A detailed account of the nervous system in humans is given in your text book lesson 16: module 2: Book l. Recall that the nervous system basically consists of two parts: (i) Central nervous system (ii) Peripheral nervous system The nervous system of cockroach also follows the same basic plan and consists of: (i) Central nervous system (ii) Peripheral nervous system (iii) Sympathetic or visceral nervous system BIOLOGY 367 MODULE - 2 Coordination and Control : The Nervous and Endocrine Systems Forms and Functions of Plants and animals Central Nervous System It consists of brain or supra-oesophageal ganglion that lies above the oesophagus in the head. A sub-oesophageal ganglion lies below the oesophagus and is formed. The brain gives off a pair of short and stout circumoesophageal connectives that meet the sub-oesophageal ganglion. A double ventral nerve cord extends from the sub-oesophageal ganglion. It bears three thoracic and six abdominal ganglia (See figure below). Notes Peripheral Nervous System Brain Ventral It consists of nerves which are given off from the nerve cord ganglia so as to innervate all the parts of the body (See the figure). Segmental Sympathetic Nervous System ganglia It consists of frontal ganglion and a visceral ganglion. Various nerves are given are given off Nervous System of Cockroach from the visceral ganglion. (a) Central Nervous System (CNS), consisting of brain and spinal cord. It is the site of information processing (receiving information and responding to it). (b) Peripheral Nervous System ( PNS), consisting of all the nerves entering and leaving the brain and the spinal cord. Further division of these two components is shown in Fig. 17.1. Fig 17.1 The basic components of nervous system 368 BIOLOGY Coordination and Control : The Nervous and Endocrine Systems MODULE - 2 Forms and Functions of 17.4 NERVOUS SYSTEM OF HUMANS Plants and animals The central nervous system of humans includes a highly developed brains and spiral card (Fig. 17.1). Peripheral Nervous system is made of nervous as shown in Fig. 17.1. 17.4.1 The Brain The brain is a very delicate organ lodged inside the cranium of the skull (Fig.17.2a) Notes It is protected by three coverings, the meninges (meninx: membrane): an outer tough duramater (dura: tough; mater: mother), a thin delicate web-like middle arachnoid (arachne: spider), and the innermost highly vascular piamater (pia: tender) richly supplied with blood vessels. The space between the membranes is filled with a fluid called cerebrospinal fluid. There are cavities inside the brain, which are also filled with the same fluid. The brain consists of three main regions: (i) forebrain consisting of cerebrum and diencephalon, (ii) midbrain a small tubular part between the fore and the hindbrain, (iii) hindbrain consists of cerebellum, pons, and medulla oblongata. The individual parts of the brain are described below: (a) Cerebrum. This is the largest part of the brain, divided into two (the right and the left) parts called cerebral hemispheres. Their outer surface is highly convoluted with ridges and grooves. Each hemisphere is hollow internally and the walls have two (an inner and an outer) regions. The outer region (cerebral cortex) contains cell bodies of the nerve cells and being grayish in colour it is called gray matter. The inner region is composed of whitish axon fibres and is called the white matter. Corpus callosum is a sheet of cris-cross nerve fibres connecting the two cerebral hemispheres (Fig. 17.2b). Left side of the cerebrum controls the right side of the body and vice-versa. Cerebrum Skull Membranes Cerebellum Spinal Cord Vertebrae cut through Fig. 17.2 (a) Brain lodged inside cranium BIOLOGY 369 MODULE - 2 Coordination and Control : The Nervous and Endocrine Systems Forms and Functions of Plants and animals Cerebral Pineal Body Hemisphere Thalamus Notes Hypothalamus Pituitary Pons Mid Brain Medulla Cerebellum Oblongata Fig. 17.2 (b) brain in median section. The cerebral cortex has three main functions: (i) It controls and initiates voluntary muscle contractions. (ii) It receives and processes information form the sense organs, like eyes, ear, nose etc. (iii) It carries out mental activities of thinking, reasoning, planning, memorizing etc. (b) Diencephalon. This is the part of the forebrain lying below the cerebrum. It consists of the following two parts; 1. Thalamus. This is an egg shaped mass of gray matter, located in the centre below the cerebrum. It is the relay centre for sensory impulses (e.g. pain and pleasure) going to the cerebrum. 2. Hypothalamus. This is a region of the brain located below thalamus. It controls motivated behavior such as eating, drinking and sex. It controls the secretions of pituitary gland hanging below it. It also serves as the regulation centre of body temperature and body fluids (see lesson 17). (c) Cerebellum. The cerebellum is a smaller region of the brain located at the base and under the cerebrum. It has numerous furrows. It also has a cortex of gray matter. Its two main functions are. (i) to maintain the balance of the body, and (ii) to coordinate muscular activities. (d) Medulla oblongata. This is the last part of the brain, which is connected to the spinal cord. Its functions are as follows: (i) It is the cente for breathing, coughing, swallowing, etc. (ii) It controls heartbeat, the movement of alimentary canal and many other involuntary actions. 370 BIOLOGY Coordination and Control : The Nervous and Endocrine Systems MODULE - 2 Forms and Functions of In all, 12 pairs of nerves (cranial nerves) come out of the brain, some of these Plants and animals are sensory, some motor and some are of mixed type. 17.4.2 The Spinal cord The spinal cord extends form the medulla of the brain downward almost the whole length of the backbone. It is also wrapped in the same three meninges as the brain and the space between them contains the same cerebrospinal fluid. The arrangement Notes of the white and gray mater is reversed in it i.e. white matter is outside and the gray matter inside.
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