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)