Nervous Tissues PDF

The Nervous Tissues Components of the nervous tissue The nervous tissue is composed of two kinds of cells: Nervous or nerve cells are the functional unit of the nervous tissue. They transmit nerve impulses. Neuroglia or glia or neurolgial cells are connective, supportive and n...

The Nervous Tissues Components of the nervous tissue The nervous tissue is composed of two kinds of cells: Nervous or nerve cells are the functional unit of the nervous tissue. They transmit nerve impulses. Neuroglia or glia or neurolgial cells are connective, supportive and nutritive but not excitable. Function of the nervous tissue The nervous system receives stimuli from outside or inside and transfers them toward highly specified central parts "brain and spinal cord" Location of the nervous system Anatomically, the nervous system is divided into: Central nervous system (CNS) which is represented by the brain and the spinal cord. Peripheral nervous system (PNS) which is represented by the nerve fibers and ganglia. The human nervous system is so far the most complex system in the human body and is formed by a network of more than (100 million) nerve cells (neurons), assisted by many more glial cells. Structurally, nerve tissue consists of two cell types:- ❑ Nerve cell or neurous: Which usually show numerous long processes ❑ Glial cells: Which have short processes support and protect neurons. Nerve cells or neurons ❑ They are responsible for the reception, transmission and processing of stimuli. Most neurons consist of two parts:- ❑ Cell body or perikaryon. ❑ Protoplasmic processes. A) Cell body or perikaryon. The cell body contain of the:- Nucleus: Cytoplasm: Neuro fibrils Nissl bodies Mitochondria Golgi Apparatus Centriole Pigment B) Protoplasmic processes Axon Dendrite  Axons The axons are the efferent process of the neuron, usually there is only one per neuron. The axon is larger and less branched. Nissl bodies are absent from the axon but neurotubules and mitochondria are present. Axons are often distinguished by their ensheathing layer of myelin. All axons originate from a short pyramid shaped region, the axon hillock that usually arises from the cell body. The plasma membrane of the axon is called the axonlemma. Axon is responsible in generating or conducting nerve impulses to other cells (nerve, muscle and gland cells) Axon may also receive information from other neurous.  Dendrites These are multiple elongated processes like the branches of a tree, which conduct the impulse into the neuron, they are afferent process. Nissl bodies and mitochondria are both present in the dendrites. The E/M shows that most dendrites contain neuro tubules. The surface of dendrite become rough because the contain gemmules.  Morphological classification of nerve cells Neurons are usually classified according on:- The number of their processes. The function. The length of the axon. Unipolar cells Bipolar neurons Pseudo- unipolar cells Multipolar cells B- Classification of nerve cells according on the function  Sensory neurons  Motor neurons a-Motor neuron b-Sensory neuron C- Classification of nerve cells according on the length of the axon  Golgi type I cells  Golgi type II cells  2.Glial cells. Although neurons are the principal cells of nervous tissue, Glial cell type Origin Location Main functions glial cells play an important Oligodendroc Neural Central Myelin production and yte tube nervous electric insulation supporting role in this tissue. system They can be classified according Schwann cell Neural Peripheral Myelin production and tube nerves electric insulation to their origin and function:- A strocyte Neural Central Structural support and Oligodendrocytes. tube nervous metabolic exchanges Schwann cells. system Ependymal Neural Central Lining cavities of central Astrocytes. cell tube nervous nervous system Ependymal cells. Microglia Bone system Central Macrophagic activity Microglia marrow nervous system