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Download Physiolgy of the nervous system
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Physiology of the nervous system Structural classification The nervous system can be divided into: 1) Central nervous system (CNS), which includes, brain and spinal cord. 2) Peripheral nervous system (PNS), which includes, cerebral nerves (12 pairs) and spinal nerves (31 pairs). Functional classification This classification is concerned only with PNS or peripheral nervous system, which subdivided into: 1) Somatic (voluntary) nervous system, which controls the skeletal muscle 2) Autonomic (involuntary) nervous system, which controls smooth muscle - Central nervous system (CNS) is made up of 2 types of cells, 1) neuron (nerve cells) : dendrites, cell body and Axon it has 3 shapes, unipolar neuron, bipolar neuron and multipolar neuron. 2) supporting cells (Neuroglia) 1. Astrocyte - It has a swollen ends embracing neurons for protection. - It acts as a barrier between neurons and blood capillaries to prevent harmful substances to reach neurons. 2. Microglial cell - It phagocytes the debris like bacteria and dead cells. 3. Ependymal cell - It lines the cavities of skull and vertebral column to protect the brain and spinal cord. - It possesses cilia which circulate the cerebrospinal fluid which acts as a cushion fluid. 4. Oligodendrocyte - It wraps the nerve fibers to insulate. Reflex Arc - It consists of 5 elements: receptors – sensory (afferent) neurons – association neuron (integration center) – motor (efferent) neuron – effectors (muscle or gland). - Receptors receives sensation from sense organs, skin, eye, ear, taste buds in mouth, nose. - Sensory neuron carries the nerve impulses to CNS. - Association neuron integrates the coming nerve impulses to motor neuron. - Motor neuron carries the reaction as a nerve impulse to effectors. - ُEffector executes the reaction via muscle contraction or relaxation and gland secretion. What is the main functions of Neuron ? - Neuron has 2 main functions. 1. Irritability, ability to respond to stimulus (form of nerve impulses) 2. Conductivity, ability to transmit (propagation of nerve impulses), electrochemical transmission How the nerve impulse be made up? - Nerve impulse is made up by the conversion the nerve state from polarization (resting) state to depolarization (action) state. - neuron starts to increase the positivity inside by entering Na + ions inside. How the nerve impulse be propagated? Electrical transmission - Propagation of nerve impulse is executed by repeating the conversion from polarization to depolarization in the next site of nerve. - the previous site is returned to the resting state (polarization). - Conductivity or transmission is exerted electrically alongside neuron and chemically when nerve impulse transmit from neuron to another one. Chemical transmission (Synapsis) - Synapsis consists of 3 elements: presynaptic neuron – synaptic cleft – postsynaptic neuron - presynaptic neuron form neurotransmitter in vesicles. - vesicles fuse with cell membrane then open to release neurotransmitter in synaptic cleft. - neurotransmitter reacts with receptor on the cell membrane of postsynaptic neuron, which starts to form new nerve impulse.