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Nervous System Steers, controls and watches over our bodily functions and processes WHY?– to protect us, to keep us alive, and to fit in with the environment It is divided into a central nervous system (brain and spinal cord) – and a peripheral nervous system (periphery nerves) The peripheral system collects information about the inner body and about the world around us via sensors, and delivers the messages from the central nervous system back to all parts of the body The sensors are our senses (conscious processes), as well as unconscious processes This information (signals inside the body) is either of a physical or chemical nature The information is carried by electric impulses on AFFERENT pathways in the peripheral nervous system to the central nervous system = this gives our brain a “screenshot“ This information is then matched to a „I need” or “it should be“ snapshot When differences are noticeable between these two snapshots, a plan is formed by the brain, then transmitted back out from the centre to the periphery by the EFFERENT pathways These pathways end in organs or muscles which must then react in order to change the situation and make it more desirable Somatic or animalistic System (Organism – Environment) the functions of the somatic nervous system are: o o o Conscious movement (supply the striated muscles with their innervation = orders to work Quick processing of information Conscious perception Autonomic or vegetative nervous system (Organism – internal organs) Is divided into a sympathetic subsection and a parasympathetic subsection: 1 PARASYMPATHETIC SYSTEM: conserves energy, and builds up reserves 2 SYMPATHETIC SYSTEM: mobilizes body systems during activity, „Fight or Flight“ reaction o o Both systems work hand in hand, to maintain a balance which provides the best conditions for the body (homeostasis) and to regulate organ functions dependant on the demands of the environment. AFFERENT chemical and physical information Central control (=brain) calculates a screenshot Muscle/Organ/ Adaption/Change Orders to bring about change given, if the screenshot is not ideal = EFFERENT Compares screenshot with an ideal situation Example: Skin temperature measures 30° Messages sent to brain „Here it is 30°“ = Afferent information Brain compares the information to its ideal of 22°, and has to react to the difference Brain’s plan: Open the capillaries = Vasodilatation, sent as Efferent information back to the skin Capillaries opened, more blood flows near the surface, warmth given off from the surface, body cools down, which is in turn monitored so as not to cool down too much. Brain receives new messages, “Here it is now 22°”, the balance is restored. One problem is that to constantly control so many structures, an incredible amount of information must be constantly sent to the brain. How does the brain sort through all this information to find out what is important to react to? Priorities must be laid down, and the most important priority is CHANGE. Therefore the body reacts to these changes. The most important of all change is damage, or even danger of damage being done. This causes an immediate red alert situation. The cells of the Nervous System (Neurons) In order to make the system run smoothly, there must be different types of cells for different functions within the system. First a message must be registered, then conveyed, and computed in the brain before the plan is then conveyed back to the specific part of the body. Sensory Cells Quelle: http://upload.wikimedia.org/wikipedia/commons/1/17/Structure_of_sensory_system_(4_models)_E.PNG All sensory cells have receptors of some sort, some more refined and specialized than others. Some react to any stimulus, others react only to certain stimuli. Having received this information, the cell then must convey its information to the nerve cell (Nucleus). Here the first processing takes place, and the message is either conveyed further, or ignored. Having reached the central nervous system, the message is then passed onto another (transmitter) cell, and conducted inside the spinal cord to the brain. Quelle: http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Neuron.svg/1280pxNeuron.svg.png The Axon is the „cable” along which an electric impulse can be sent. Because some neurons can be up to 1m long, the message needs to be carried as quickly as possible. This happens in the neurons that have a myelin sheath, built of other cells (Schwann cells), which wrap themselves around the cable, as a form of insulation. The electric impulse now travels not along the entire axon, but “springs” from one gap to another between the Schwann cells. This is called saltatorish movement. The afferent pathway consists of two neurons – one sends information from the periphery to the dorsal section of the spinal cord, the second neuron runs from here to the brain. The efferent pathway also consists of two neurons – one down the spinal cord to the required level of the spine, the second from the ventral section of the spinal cord to the effector tissue (muscle, organ or gland). The final connection between this second effector neuron (motor neuron) and the required muscle is called a motoric unit. Each motor unit has contact to many muscle fibres (= cells), and causes those fibres to contract when the impulse comes along the motor neuron’s (ὰ-Neuron) axon. Some muscles have larger motor units than other muscles. Muscles which must do fine tuning of movement (the eye muscles) have small motor units and innervate relatively few muscle fibres – as few as 3! (mostly Slow Twitch muscle fibres). Muscles which need to work quicker and more powerfully (Quick Twitch fibres) have large motor units – as many as 5000 – e.g. M. gastrocnemius (calf muscle), M. biceps brachii (arm flexor). The connections between the Neurons are called Synapses, and the gap is bridged by chemicals being sent from one cell to the next across this synapse. The Sympathetic system uses the chemicals Acetylcholin and Noradrenalin – the Parasympathetic system uses only Acetylcholin. Functions of the autonomous nervous system: Parasympathetic System– regeneration and building of resources for example: Blood pressure sinks Reduction of Heartbeat Reduction of breathing rate Increase of digestion Increase of saliva production Closing of the pupils Tendency to empty the bladder and bowels Sympathetic System – mobilization of resources for example: Increase of blood pressure Quickening of heartbeat Quickening of breathing rate Widening of the Bronchia (airtubes) Increased blood flow to the muscles Widening of the pupils Hairs stand on end More sweat production Reduction of bowel activity Increase of energy production Spinal Cord The spinal cord is made of nerve cells in a butterfly formation (grey matter) inside a circle made up of axons (white matter). Peripheral Nerves enter the Spinal Cord from all over the body, via the dorsal root. In the dorsal horn is a synaptic connection to the cell of the Central Nervous System, from where the information from the body or environment is directed to the brain to be controlled. After processing, the brain sends a return message (efferent pathway) back down the spinal cord, which then arrives at the ventral horn and is passed onto the efferent nerve via a sysnapsis. This efferent nerve then exits the Central Nervous System via the ventral root. Ventral and dorsal roots join after a very short distance to form the peripheral nerve. Therefore every peripheral nerve has afferent nerves, efferent nerves and vegetative nerves. Retrieved from - http://www.newhealthadvisor.com/Spinal-Cord-Cross-Section.html There are 31 pairs of spinal nerves: 8 cervical nerve pairs 12 thoracic nerve pairs 5 lumbar nerve pairs 5 sacral nerve pairs 1 coccygeal nerve pair These form the following Plexuses: Plexus cervicalis (C1-C4) Plexus brachialis (C5-Th1) Plexus lumbalis (Th12 – L4) Plexus sacralis (L5 – S4)