Histology of Nervous Tissue PROF. DR. FAUZIAH OTHMAN DEPT OF HUMAN ANATOMY

Feature of nerves tissue Type of cell: neuron & neuroglia General feature of neuron Type of neuroglia: astrocyte, oligodendrocyte, ependymal cell, microglia Synapses Myelin – formation & function General structure of peripheral nerves Ganglia – dorsal root ganglia & autonomic ganglia

Nervous system divided into: Central nervous system (CNS) Brain and spinal cord Peripheral nervous system (PNS)  Cranial and spinal nerves – locate outside the CNS.

Morphology of typical neuron Neuron functional cell of the nervous tissue. Cell body or perikaryon - contains the nucleus – regulates the functioning of the neuron.  Numerous dendrites and a single axon.  Contains Nissl bodies in the cytoplasm  Axon hillock- no Nissl bodies Axon – cellular process (extension) – carries impulses away from the cell body. Dendrites – cellular process (extension) – carries impulses toward the cell body

2 types of cell i)Neurons (nerve cells) ii)Supporting cells Functions of neurons 1) specialized to receive stimuli and to conduct electrical impulses to other parts of the system. 2) Arranged as an integrated communications network, with several neurons in a chain-like fashion involved in sending impulses from one part of the system to another.

Neuron Classification Structural: Multipolar – most common type in CNS.  Include all motor neurons and interneurons of brain and spinal cord. Bipolar- not as common purely sensory.  Retina of eye, inner ear, olfactory epithelium in the upper region of nose. Unipolar (formerly known as pseudounipolar)  Sensory neurons found in numerous craniosacral ganglia of the spinal cord.

Comparison of Structural Classes of Neurons

Unipolar neuron Nucleus & nucleolus Cytoplasm fibrocytes Satellite cells Cytoplasm of neuron Myelinated axons

The supporting cells (neuroglia or glia): Astrocytes Oligodendrocytes Microglial cells Ependymal cells Schwann cells Satellite cells PNS CNS

Astrocytes Largest, most numerous, versatile, and highly branched glial cells They cling to neurons and cover capillaries Functionally, they: Support and brace neurons Anchor neurons to their nutrient supplies Guide migration of young neurons Control the chemical environment

Astrocytes

Microglia Microglia – smallest, ovoid cells with spiny processes - phagocytic cells that migrate through the CNS and remove foreign and degenerated material

Ependymal Cells Ependymal cells – squamous- to columnar- shaped cells They line the central cavities of the brain and spinal column

Oligodendrocytes Oligodendrocytes – branched cells that wrap CNS nerve fibers - Produce myelin in CNS

Schwann Cells and Satellite Cells Schwann cells (neurolemmocytes) – form myelin sheaths around peripheral axons Satellite cells surround neuron cell bodies with ganglia

Synapse The region where the terminals come close to another cell and transmit the impulse A junction that mediates information transfer from one neuron: To another neuron To an effector cell Presynaptic neuron – conducts impulses toward the synapse Postsynaptic neuron – transmits impulses away from the synapse

Myelin – formation & function Whitish, fatty (protein-lipid), segmented sheath around most long axons Its function: 1. Protection of the axon 2. Electrically insulating fibers from one another 3. Increasing the speed of nerve impulse transmission

2 types of neuroglia produce myelin CNS= Oligodendrocyte PNS= Schwann cells