2. Second lecture

3. Functions of neuroglea 1-Support. 2-Insulator. 3-Phagocytes (in pathological state by microglea). 4-Formation of myelin sheath in CNS by oligodendroglea. 5-Regulation of ionic environment of the neurone and thought to make up blood brain barrier (BBB) by astrocyte

4. Classification of neurons: I.Structural (histological) classification : Multipolar, bipolar, unipolar and pseudonipolar neurons. II. Functional (Physiological) classification : 1-Sensory 2-Motor or efferent neurons

5. Structure of neurons: They are formed of the cell body and cell processes A) The cell body (Soma): enlarged part of the neuron, which contains the nucleus. inside the CNS are usually collected into groups called nuclei or centers.

7. Structure of neurons: The cell bodies in the PNS usually collect to form ganglia. inside the CNS collected into groups called nuclei or centers. The cell bodies in the PNS usually collect to form ganglia.

8. Structure of neurons: The cell body is surrounded by the cell membrane and contains the following: - Nucleus - Neurofibrils - Microtubules and microfilaments - Nissl bodies - Endoplasmic reticulum - Golgi apparatus - Mitochondria - Ribosomes

9. Structure of neurons: B) The cell processes: 1- The dendrites. 2- The axon (axis cylinder).

10. Structure of neurons: The axon branches freely near its termination and makes junction with one of the following: Dendrites of cell body of another neuron forming a neuroneural junction or synapse. Muscle fibers to form a neuro-muscular junction. Secretory gland to form a neuro-epithelial junction. The axons are covered by two sheaths: 1- Myelin (medullary) sheath: 2- Cellular sheath (sheath of Schwann or neurilemma)

11. Structure of neurons: Myelin is a white, lipid rich substance (lipoprotein complex) which acts as an electric insulator. Myelin sheath envelops the axon except at its terminal endings. It is not a contineous layer, it is interrupted at intervals of about 0.1 to 1.0 mm by nodes of Ranvier. Through these nodes ions and water can undergo exchange with the surrounding tissues.. In the CNS, myelin sheaths are formed by oligodendrocytes - The axons in the PNS are surrounded by Schwann cells. - The outer layer of the Schwann cells is called the neurilemma. -Sheath of Schwann is essential for regreneration of the damaged nerve fibers which occurs only in the PNS. Schwann cells are absent in the CNS.