Nervous tissue part 1 (2).pdf

Nervous tissue Part 1 NERVOUS TISSUE The nervous system is divided anatomically into two subdivisions: Central nervous system the brain the spinal cord. Peripheral nervous system (cranial, spinal and autonomic nerves ) ,ganglia and nerve endings Histologically the nervous system is formed of 1. Nerv...

Nervous tissue Part 1 NERVOUS TISSUE The nervous system is divided anatomically into two subdivisions: Central nervous system the brain the spinal cord. Peripheral nervous system (cranial, spinal and autonomic nerves ) ,ganglia and nerve endings Histologically the nervous system is formed of 1. Nerve cells (neurons): the structural and functional units of nervous system. 2. Glial cells (neuroglia): supportive, nutritive and protective for nerve cells. Nerve cells (neurons Neurons are the structural and functional units of nervous system. Types of Neurons According to the number of processes, : 1.Unipolar & pseudo unipolar neurons. 2. Bipolar: From each pole of the usually oval cell arises one fiber; one of them acts as a dendrite and the other as an axon. Multipolar: This type is the most dominating type. From the cell body arise a number of dendrites which end in the vicinity of the cell and only one axon. Structure of Neuron Neurons are composed of three distinct parts: a cell body, an axon & dendrites. Neuronal Cell Body or perikaryon It is the part of neuron which contains the nucleus &cytoplasm. L.M: The nucleus is central large pale spherical with well defined nucleolus. Basophilic granules present in the cytoplasm of the cell body as well as in the dendrites. They are called Nissl granules (RER&ribosomes) no centrioles (as the Microtubules and neuron not divide). neurofilaments occupy the cytoplasmic matrix of the neuron in areas where there are no Nissl granules. Neurofilaments for support and microtubules are important in intracellular transport and also as a part of the cytoskeleton of the neuron. Function of neurons: The neurons are classified according to their functions to: Motor neurons: they transmit motor impulses from CNS to muscles (as anterior horn cells). Sensory neurons: they transmit sensory impulses from receptors to CNS (as posterior horn cells). Associative neurons (interneurons): they connect both motor and sensory neurons (at one side of the same level). The synapse Definition: It is the site of contact between two successive neurons. Components: There are three elements forming the synapse; 1-presynaptic element: the dilated part of the axon terminal or the end foot 2-The synaptic cleft 3- Postsynaptic element: part of the neuron which may be a dendrite, a cell body or an axon Types I- According to the nature of the postsynaptic element, there are: Axosomatic  axodendritic axoaxonic synapses when the end foot contacts a cell body, a dendrite or an axon respectively. Types II- According to the mode of impulse transport, there are: chemical synapses where the impulse is transported by chemical transmitters. electrical synapses where the impulse is transported through gap junctions between pre-and postsynaptic membranes