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An introduction to the Nervous system From: http://www.hiogolffitness.com/?p=262 The importance of the nervous system • Nervous systems reponse to stimuli (external or internal) by controling the actions of the body through electrochemical messages • Allows us to: detect light, odour, temperature or pressure… just to name a few What is the nervous system? • Elaborate communication system (>100 billion nerve cells in the brain alone!) • 2 main divisions (flow chart, p412): – central nervous system (CNS) • Brain and spinal cord • Coordinating system – peripheral nervous system (PNS) • Nerves that carry info between organs and CNS • Subdivided into somatic (skeletal muscle, bones and skin- relays info about environment) and autonomic (internal organs like the heart) Anatomy of a nerve cell • 2 types of cells – Glial: non-conducting cells important for structural support and metabolism – Neurons: functional units of the nervous system • Can be sensory- sense and relay info from the environment to CNS for processing (photoreceptors for light, chemoreceptors for chemicals etc…) and are located in clusters called ganglia • Or motor – relay information to the effectors (muscles, organs, glands) • Or Interneurons – link neurons in the body (integrate sensory and motor neurons) Motor neuron Sensory neuron From: http://www.dmacc.edu/instructors/rbwollaston/Chapter_8_Nervous_System.h tm From: http://www.daviddarling.info/encyclopedia/N/neuron.html Parts of the neurons • Dendrites: receive info from sensory receptors by conducting nerve impulses toward the cell body • Axon: projects nerve impulses from the cell body • Myelin sheath: covers many axons, insulates the neurons, preventing loss of charged ions from nerve cell. Formed by special glial cells called schwann cells. • Nodes of Ranvier: areas between sections of myelin sheath, nerve impulses jump from one node to another (speeding up process)… so nerve impulses are quicker in mylelinated axons. • Neurilemma: surrounds the axon and promotes regeneration of a damaged axon Neural circuits • Simplest nerve pathway is called a reflex arc • Occurs without brain coordination • 5 components: receptor, sensory neuron, interneuron, spinal cord, motor neuron and effector. From: http://www.biologie.uni-hamburg.de/b-online/library/cat-removed/u3aos22.html