Central Nervous System: The central nervous system controls the mental and physical activities of the human body and also helps maintain many aspects of homeostasis. The nervous system is made up of a complex system of cells called neurons in which they organize the division of labor so that the body works efficiently. Neurons are the cells that comprise the nervous system. These cells communicate the relationship between structure and function in living systems. Axons are a small threadlike extension of the neuron which allows the cell to transmit and recieve signals rapdily over distances. The organs in the central nervous system are the brain and the spinal cord. Along with the central nervous system is the peripheral nervous system which contains all the neurons in the body which aren't part of the brain or spinal cord. There are two kinds of neurons in the part of the nervous system: afferent and efferent. Afferent neurons are those that go towards the central nervous system and the efferent neurons are the ones that lead away from the central nervous system. Brain: The brain is the main part of the central nervous system. It is located in the head of the human. It consists of four main areas: the cerebrum, the diencephalon, the lower brain stem, and the cerebellum. The cerebrum is the largest portion of the brain. It's divided into hemispheres, which are connected by the corpus callosum. In addition to the two hemispheres, the cerebrum is divided into four lobes: frontal, parietal, temporal, and occipital. It's main function is to control the sensory and motor skills. It is responsible for the processing of visual images, hearing, taste, speech, body sensation, motor function, and intellectual function. The diencephalon contains importan relay centers for information entering and exiting brain. The upper relay center is called the thalamus, which directs incoming sensory signals to the proper region of the cerebral cortex. The lower relay center is called the hypothalamus. It is important in maintaing homestasis, and directly and indirectly controls much of the body's hormone production. The lymbic system is made up of the thalamus, the hypothalamus, and deeper parts of the cerebral cortex, and is important in dealing with emotion, memory, motivation and other complex feelings. The lower brain stem contains three divisions: the midbrain, the pons, and the medulla oblongata. The midbrain is important for visual and auditory information. The pons help with transmitting information betweem the cerebral hemispheres and those of the cerebellum. The medulla oblongata control varius homeostatic activities, such as heart rate and respiration. The reticular formation is a diffuse network of neurons. It helps control respiration and circulation and serves as a filtering system for incoming sensory signals. It separates important inormation from unimportant information. The cerebellum is just below the occipital lobe of the cerebrum. It is important in the coordination of muscle action. It receives sensory impulses from different organs throughout the body. The cerebellum sends nerve impulses down the spinal cord to stimulate muscle contraction. Spinal Cord: The spinal cord is made up nerve tissue, and runs through the spine. The outside part of the spinal chord is called white matter, made up mostly of axons. In the middle of the white matter lies the gray matter. This is the area that the peripheral nervous system stems from. Peripheral Nervous System The peripheral nervous system is composed of 12 pairs of crainial nerves and 31 pairs of spinal nerves. A nerve is a bundle of axons. Sensory division is when the sensory receptors receive information and send it through the interneurons to the central nervous system. Motor division allows the body to react to the sensory information. It contains two independent systems, the somatic nervous system and the autonomic nervous system. Somatic nervous system controls the movement of skeletal muscles. It can be used volunatarily of automatically. Reflexes are apart of this system. A special type of reflex is the spinal reflex, in which the brain is not involved. Autonomic nervous system is in charge of controlling the internal conditions of the body. Some of the main functions are controlling respiration, heart beat, and homeostatic activities. One major part of the autonomic nervous system is the sympathetic division which allows for the reaction to environmental stimuli. Another part is the parasympathetic division which controls the body under normal conditions. Transmission of Nerve Impulses When a signal moves along an axon, the movement is called an action potential. The stretcher of the neuron aids in the movement in action potentials. Dendrites are a specialized part of the cell which are located on the surface of the cell body. They are important in receiving action potentials from other neurons. The axon is a longer membrane-bound projection which transmits information away from the cell body. The end part of the axon is called the axon terminal. The myelin sheath is a protective lipid layer that surrounds the axon of most neurons. Schwann cells produce the myelin sheath. Neurons do not touch each other, instead they have a synaptic cleft, which exists between the axon of one neuron and the dendrite of another. Chemicals called neuro-transmitters are released into the synaptic cleft when electrical activity is present. Most iimportantly, the movement of action potentials occur with signaling activity of electrical activity within neurons and chemical flow between neurons. Neuron function: Electrical activity is necessary for neuron function. The difference in electrical charges between neurons and the extracellular fluid are is called a potential. There are two main types of potentials. First, resting potential is when there is little or no difference in electrical charge. This means that the neuron is neither sending nor recieving information. Second, action potential is when a dentrite cell is stimulated by an electric charge. Neurotransmitter Function: When an action potential reaches an axon terminal, a fusion occurs, releasing neurotransmitters into the synapitc cleft. Neurontransmitters are respnsioble for the exchange of nerve impules between neurons. If the fusion creates a large enough charge, a new action potential is generated, which continues the electrical signal. Sensory Systems: Sensory systems translate light, sound, temperature, and other environmental aspects into electrical charges and send them to the central nervous system where they are processed. The sensory systems contain many sensory receptors which are highly concentrated the sense organs: the eyes, ears, nose, mouth, and skin. The ear has two specific functions: hearing and maintaining balance. Sounds are processed through vibrations against a special membrane and then sent to the temporal lobe. The balance function of the ear is helped by the semicicrular canals and the hair cells in the inner ear. The eye recieves light and transmits action potentials to the occipital lobe of the brain to create images. The main processor in the eye is the retina, which is connected to the optic nerve. For taste and smell, the taste buds and olfactory receptors are the main communicators to the brain. The taste buds are mainly located on the tongue, although there are few in the throat and on the roof of the mouth. They pick up chemicals found in food and send the information to the parietal lobe of the brain. The olfactory recepticals are located deep in the nasal cavity and deal with the sense of smell. They process chemicals found in the air and send them to the brain and also to a limbic structure called the amygdala. Finally, the skin processes many other senses, such as touch, pressure, tension, and heat. There are also pain receptors located throughout the skin and internal body which transmit information of damaged tissue. The System Behind the Systems: The Nervous System interacts with every other system in the human body. The skeletal and muscular systems interact with the nervous system for every movement you make. The nervous system is accountable for voluntary and involuntary movements. Voluntary movements, such as swinging a bat or smiling, are controlled by nerve impulses from the brain that tell muscles when and how to move. Involuntary movements, such as breathing, are controlled by an automatic part of the brain. Reflexes are even different; some reflexes have nothing to do with the brain. A nerve is triggered, sending a signal to the spinal cord, motor neurons are set off and a reflex occurs. The skeletal system while containing and protecting the spinal cord also facilitates the muscles so they have something to pull against. This trifecta of the nervous, muscular, and skeletal system account for every movement of the human body. Multiple Sclerosis: Multiple Sclerosis, or MS, is an unpredictable disease that infects the central nervous system. Like many diseases and disorders of the central nervous system, MS can be completely devastating and destructive. However, it can also be very mild. Some patients can lose their ability to speak, write, or even walk. The disease can be caused by many different factors. MS interferes with the nerve impulses from the brain traveling to other parts of the body. Myelin is the fatty tissue covering the nerve, brain, and spinal cord cells assisting in fast message transmission. MS causes the body's T-cells to attack this myelin, hindering or stopping neuron messages resulting in slowed or completely lost functions. Gazeta Pacjenta