The Human Body - Nervous System PDF

## The Human Body - Nervous System **Learning Outcomes** By the end of the lesson, learners will be able to: * explain that in addition to nervous control, another control/coordination mechanism called hormonal control also exists in humans. **Connect** Label the parts of the human body marked...

## The Human Body - Nervous System **Learning Outcomes** By the end of the lesson, learners will be able to: * explain that in addition to nervous control, another control/coordination mechanism called hormonal control also exists in humans. **Connect** Label the parts of the human body marked in the adjacent diagram. Do you know, the part of the brain that you used to recall and write the labels is called cerebrum? **Introduction** In living organisms, a particular requirement of the body is fulfilled by the action of a number of interrelated organ systems. For example, in animals, the requirement of energy is fulfilled by the digestive, circulatory and respiratory systems. Food is digested by the action of various organs, glands and enzymes of the digestive system. The circulatory system then absorbs the digested food and transports it to various cells for oxidation. (The respiratory system supplies the oxygen necessary to oxidise the digested food in the cells and release energy.) ## The Nervous System **The Nervous System** The nervous system plays a role in nearly every aspect of our health and well-being. It guides everyday activities such as waking up; automatic activities such as breathing; and complex processes such as thinking, reading, remembering and feeling emotions. Now, imagine where you see yourself in a year, five years or ten years. Then, write a letter to your future self, outlining how you can keep your nervous system healthy and how that will help you achieve your goals. Your teacher can store the letters and mail them out once the right amount of time has passed! ### The Structure of the Nervous System ***The nervous system is composed of two parts:*** * **Central nervous system:** includes the brain and the spinal cord. * **Brain:** The brain is situated in the skull. It is well protected by the bones of the skull. The brain is covered by membranes called meninges. The space between the membranes of the brain is filled with a fluid known as the cerebrospinal fluid. It protects the brain from shocks and also gives nourishment to the brain. Meningitis is an infection of the meninges. * The brain is made up of three parts: * **Cerebrum:** It is the largest part of the brain. The surface of the cerebrum has ridges and furrows, which increase the surface area to accommodate more nerve cells. The cerebrum is made up of two hemispheres called the cerebral hemispheres. There is a deep furrow between the right and the left cerebral hemispheres. Internally, each cerebral hemisphere is divided into two portions. The cell bodies of all the neurons are concentrated in the outer portion. This portion is called the grey matter. The inner portion consists of axons and is called the white matter. * The cerebrum controls all voluntary movements. It also acts as the centre for mental activities such as memory, thinking and reasoning. The cerebrum is also responsible for the sensations of pain, touch, sight, taste and temperature. * **Cerebellum:** It is located at the base of the cerebrum and is of the shape of an egg. It also has two hemispheres. The cerebellum coordinates muscular movements and maintains the balance of the body. * **Medulla Oblongata:** It is also known as the brain stem. It emerges from the base of the brain and joins the brain to the spinal cord. The medulla oblongata controls activities such as breathing, heartbeat, sneezing and other involuntary functions. * **Peripheral nervous system** comprises the nerves which carry impulses to and from the central nervous system. There are two sets of nerves that make up the peripheral nervous system: * **Cranial nerves:** The nerves that arise directly from the brain and the brain stem are called cranial nerves. There are twelve pairs of cranial nerves. * **Olfactory nerves:** These carry impulses to the nose for the sense of smell. * **Optic nerves:** These carry impulses to the eyes for vision. * **Auditory nerves:** These carry impulses to the ears for hearing. * **Facial nerves:** These carry impulses to the muscles of the face for muscular coordination. * **Spinal Nerves:** The nerves that arise from the spinal cord and transmit nerve impulses between the spinal cord and the body are called spinal nerves. There are thirty-one pairs of spinal nerves arising from the spinal cord. Each pair of spinal nerve consists of a sensory nerve, which carries messages from the sense organs to the brain or the spinal cord and a motor nerve which carries messages from the brain or the spinal cord to the effectors. * **Autonomic nervous system:** The autonomic nervous system controls most of the internal mechanisms of our body which are beyond our conscious control. This system coordinates the smooth muscles, glands and heart muscles. It is divided into two systems- sympathetic nervous system and parasympathetic nervous system. These two systems control two different sets of responses and work opposite to each other. For example, sympathetic nerves dilate the pupil, while the parasympathetic nerves constrict it. ### The Spinal Cord The spinal cord is the continuation of the medulla oblongata. It is a tube-like structure and runs inside the vertebral column. A cross section of the spinal cord is given in Figure 5.4. It shows a small canal, called the central canal, in the centre. The central canal is surrounded by grey matter. The outer portion comprises the white matter. The major functions of the spinal cord are: * The spinal cord is concerned with reflex actions. * It conducts impulses from the muscles and skin to the brain. * It also conducts impulses from the brain to the muscles of the limbs and trunk. ## Neurons - The Basic Units of the Nervous System A neuron is the basic structural and functional unit of the nervous system. It is also called a nerve cell. The neuron is the pathway of an impulse. A neuron consists of a cell body called the cyton. A prominent nucleus is present in the cyton. From the cyton, many finger-like structures called dendrons extend. From the dendrons, fine fibre-like structures called dendrites originate. There is a long tail-like fibre known as axon. Some axons are covered with a myelin sheath, which is a layer of fatty insulating substance. The gap between two adjacent myelin sheath is called the node of Ranvier. The cell body contains cytoplasm and a nucleus. * **Sensory nerves:** They are made up of sensory neurons, which carry impulses from the sense organs to the brain or the spinal cord. Optic nerve is an example of sensory nerve. These nerves help us feel pain and other sensations. * **Motor nerves:** They are made up of motor neurons, which carry impulses from the brain and spinal cord to the muscles and glands. Nerves to salivary glands and the muscles of the eyeball are examples of motor nerves. These nerves control muscle contraction allowing movements such as walking, kicking and wiggling fingers. * **Mixed nerves:** They are made up of both sensory and motor neurons and transmit impulses from one neuron to another. The spinal nerves are good examples of mixed nerves. ## Important Terms * **Nerve impulse**: The electrical signal or pulse by which various messages are transferred inside the body. * **Stimulus**: The change in the external or internal environment of an organism, that arouses a specific reaction within the body of the organism is called stimulus. Stimulus could be sound, light, smell, pain or touch. Animals respond to stimulus in order to keep themselves in favourable conditions. * **Response**: Specific reaction occurring within the body of an organism as a result of the stimulus is called response. Animals that do not respond to stimuli do not survive long. * **Receptors**: Special cells that are present in the sense organs to detect the stimulus are called receptors. * **Effectors**: The cells or organs that show the response on receiving the nerve impulse from the brain or the spinal cord are called effectors. ## Coordination * **Coordination**: interaction of different parts of the body to fulfil a desired function * **Nerve impulse**: the electrical signal or pulse by which various messages are transferred inside the body.