Tecido Nervoso

	Veterinary Histology UFF Department of Morphology - Biomedic Institute LaBEc - Laboratory of Cellular and Extracellular Biomorphology
	Veterinary Histology Atlas
			Versão em Português

Introduction

Nervous Tissue
General Characteristics • Originates from the neuroectoderm • Formed by highly specialized cells • Responsible for the mechanisms of internal regulation and coordination • Contains scarce extracellular matrix • Highly vascularised (high metabolic activity) • In the encephalon and spinal cord there are two different regions:
	Gray matter • Cell bodies of neurons • Glial cells • Neuron extensions
	White matter • Neuron extensions(myelinated) • Glial cells
Components I - Neurons Function: Reception, integration, conduction and transmission of nerve impulses. Constitution
	I - Cell Body • Central portion of the cell
	• Presents Nissl bodies (Are cisterns of RER and polyribosomes)
II - Dendrites • Numerous extensions • Receive the stimulations of the environment
	III - Axon • Single extension • Conduction of impulses • Transmit information from the neuron to other cells • Can be myelinic or amyelinic • Possesses many terminal buttons(region of synapses)
Classification According to morphology: • Unipolar: only one extension • Bipolar: two extensions(a dendrite and an axon) • Pseudounipolar: one extension that branches out • Multipolar: many dendrites and one axon According to function: • Afferent: Receive sensory impulses and conduct them to the CNS • Efferent: Originate from the CNS and Conduct their impulses to muscles, glands and other neurons • Interneurons: Completely situated in the CNS
II - Glial Cell Function • Protection • Metabolic support • Mechanical support of neurons Characteristics • Exceeds ten times the number of neurons • Don’t propagate nerve impulses Representatives: I - Astrocytes • Contribute in the energetic metabolism of neurons • Eliminate ions and residues of the neuron’s metabolism • Responsible for the maintenance of the blood-brain barrier II - Oligodendrocytes: Responsible for the production of the myelin sheath in the CNS III - Microglia: Act as phagocytes in the elimination of residues and damaged structures
	IV - Ependymal • Modified epithelial cells • Line the encephalic ventricles and the central canal of the spine
V - Schwann Cell • Responsible for the production of the myelin sheath in the PNS
Synapse and Transmission of Nerve Impulses Synapse: Sites where nerve impulses are transmitted from the presynaptic to the postsynaptic cell. Can be electrical or chemical Electrical: Allow the free movement of ions from one cell to the other Chemical: Use of neurotransmitters to diffuse themselves to the receptors in the postsynaptic membrane
Types of synaptic contact • Axodendritic: between axon and dendrite • Axosomatic: between axon and cell body • Axoaxonic : between axons • Dendrodendritic: between dendrites Neurotransmitters • Are signalizing molecules • Released by the presynaptic cell • Activate receptors of the postsynaptic membrane Myelin Sheath • Formed by oligodendrocytes in the CNS and Schwann cells in the PNS • Their function is to avoid the loss of the nerve impulse, turning it more efficient • Nodes of Ranvier are present (Interruptions of the myelin sheath along the axon)