Nervous System Essay

3013 words - 13 pages

Neuron (Greek.. Νεῦρον = fiber nerve) is the structural and functional unit of the nervous system, obtain to an important class of highly specialized cells , able to receive, absorb, process, transfer and respond information using electromagnetic signals (nerve impulses). Neuron as the basic unit of the nervous tissue was described in 1835 by Jan Evangelista Purkynije, the term neuron was established by Heinrich Wilhelm Waldeyer and the concept of neurons as the basic structural functional unit of the nervous system has been developed by Santiago Ramon y Cajal in the early 20th century. Y Cajal suggested that neurons are cells which communicate with one another (neuron doctrine). They ...view middle of the document...

We ca differ electrical Synapsises (contain GAP junction, which are mostly found in invertebrates and lower vertebrates , rarely in mammals, they are very fast but can not create complex stimuli) and chemical synapseses. A presynaptic neuron synthesize a single neurotransmitter (exceptions are very few neurons of the hypothalamus). Neurotransmitters are used in chemical synapses as messengers for the excitation transfer from one nerve cell to another cell (transmission) . Receptor proteins recognize each transmitter molecule wich binds specifically reversible to its spatial. In ionotropic receptor this affects the opening of ion channels in the membrane and allow for a short time ion currents and a change in the membrane potential. In metabotropic receptors neurotransmitter acts indirectly and needs the help of second messenger. Neurones are called depend on this neurotransmitter (by tryptophan hydroxylase from tryptophan synthesized Serotonin in serotonergic neurons, acetylcholine in cholinergic neurons , dopamine in dopaminergic neurons, glycine in glutamatergic neurons, gamma aminobutyric acid in GABAergic neurons) ans secretory neurons=neurons secreting highly active substances ( neurohormones ). Exitaatory synapses causes depolarization of the neuron , inhibitory synapses - the hyperpolarization of neuron. Neurons are divided into unipolar / pseudounipolarne (have only one extension, denedrit or axone, examples of unipolar neurons are embryonic neurons and primary sensory neurons ( olfactory and rods and cones of the retina) in adults, pseudounipolar neuron is a special type of bipolar neuron, near the soma dendrite and axon merge into a single projection (spinal ganglia and nerve ganglia of the brain) , dendraxon), bipolar (has two extension - dendrites and axons (in the spinal ganglia of vertebrates)) and multipolar (many dendrites and one axon, are located in the vertebrate CNS) . Neurons can also be divided by the length of the axon (Golgi I.typ - neurons with long neurites and Golgi II . type - the neurons with short neurites, their shape pyramidal cell, spindle cells and anterior horn cells). An important feature neurons is the presence of of excitable membrane. The ions can freely pass through the membrane and much faster through ion channels. ATPase pump helps to maintain ionic concentration against steady state. The nerve cells in an imbalance between the ions inside and outside the cell so the membrane creates membrane potential , making about -50 to -90 mV. The inner surface of the membrane carries a negative charge , the outer surface has a positive charge. Permeability of ion channels for each of the ions is significantly influenced by the concentration of intracellular Ca 2+. Nerve cell operation is fundamentally based on a voltage difference between the nerve cell's interior and exterior, referred to as membrane potential. The change in elektohimic balance causes entry of calcium ions into the presynaptic area ....

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