Second lectureSecond lecture

Functions of neuroglea1-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

Classification of neurons:

I. Structural (histological) classification :

Multipolar, bipolar, unipolar and pseudonipolar neurons.

II. Functional (Physiological) classification :

1-Sensory 2-Motor or efferent neurons

Structure of neuronsStructure 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.

Structure of neuronsStructure 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.

Structure of neuronsStructure 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

Structure of neuronsStructure of neurons::

• B) The cell processes:

• 1- The dendrites.

• 2- The axon (axis cylinder).

Structure of neuronsStructure 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)

Structure of neuronsStructure 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.