Nerve tissue

Neuroneuronal nerve endings (synapses)

are specialized intercellular junctions ensuring conduction of excitation from one neuron to another

• There are principally such types of synapses as electrical and chemical synapses
• electrical synapses resemble a gap junction structure, while nerve impulses are conducted in both directions
• chemical synapses are asymmetric structures comprising both presynaptic and postsynaptic regions, which are separated by a synaptic cleft
• the presynaptic region contains vesicles with a neuromediator. This is the chemical substrate of nerve impulse conduction (produced in nerve cell bodies and brought to the axonal periphery via a fast axonal transport mechanism)
• the postsynaptic region is a part of neuronal plasma membrane (in dendrites usually) with a receptor to the neuromediator (with no synaptic vesicles)
• unilateral nerve impulse conduction via chemical synapses is provided by an interaction between mediators (released from presynaptic regions into synaptic clefts) and receptors of postsynaptic membrane

Glia

• is a totality of cells in the nerve tissue. It exerts accessory functions (sustentacular, limiting & separating, metabolic, synthetic, locomotive, protective function) to provide for vital activity of neurons
• the number of glial cells is much greater than the number of neurons
• the glia is classified into macroglia (astroglia, ependymal glia, oligodendroglia) and microglia (glial macrophages)