Structure of neuron and classification

Histology of Nervous Tissue Two principal cell types Neurons—excitable cells that transmit electrical signals

Histology of Nervous Tissue Neuroglia (glial cells)—supporting cells: These are non excitable cells which support neurons. Smaller More in number

Astrocytes (CNS) Microglia (CNS) Ependymal cells (CNS) Oligodendrocytes (CNS) Satellite cells (PNS) Schwann cells (PNS

Astrocytes fibrous Most abundant, found in white matter Cling to neurons, synaptic endings, and capillaries Support and brace neurons Not much branched

Protoplasmic Astrocytes Found in gray matter Short thick processes Inner and outer glial limiting membrane

Help determine capillary permeability Guide migration of young neurons in embryo Serve as insulators and prevent axon terminals from influencing neighbouringneurons Control the chemical environment by taking up excess k Participate in replacement gliois

Finally, astrocytes are in direct communication with one another via gap junctions, forming a network through which information can flow from one point to another, reaching distant sites. For example, by means of gap junctions and the release of various cytokines, astrocytes can interact with oligodendrocytes to influence myelin turnover in both normal and abnormal conditions

Microglia Small, ovoid cells with thorny processes Migrate toward injured neurons Phagocytize microorganisms and neuronal debris Resemble tissue macrophages

Satellite Cells and Schwann Cells Surround neuron cell bodies in the PNS Schwann cells (neurolemmocytes) Surround peripheral nerve fibers and form myelin sheaths Vital to regeneration of damaged peripheral nerve fibers

Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber

Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers. Process of oligodendrocyte

Structural Classification of Neurons A. Number, length and mode of branching Three types: Multipolar—1 axon and several dendrites Most abundant Motor neurons and interneurons Bipolar—1 axon and 1 dendrite Rare, e.g., retinal neurons

Structural Classification of Neurons Unipolar (pseudounipolar)—single, short process that has two branches: Peripheral process—more distal branch, often associated with a sensory receptor Central process—branch entering the CNS

B.SIZE OF NEURON GOLGI TYPE 1 –Single long axon Tracts and motor cells of spinal cord, GOLGI TYPE 11-short axon with dendrites resembles star Cerebral and cerebellar cortex

Functional Classification of Neurons Three types: Sensory (afferent) Transmit impulses from sensory receptors toward the CNS Motor (efferent) Carry impulses from the CNS to effectors