NERVOUS SYSTEM; TYPES OF NERVES TISSUE AND CELLS , CHARACTER

 The system is related with co-ordination of body activities through nerve impulse. Originated from ectodermal layer.

Nerve tissue are two type (ectodermal)

1. Nerve cell / Neurons - Highly specialised outgrowth of action potential.   

2. Neuroglia / neuroglial cells ( Neurogliar cells)- Schwan's cell ,oliga dendrocytes ( formation of myelin sheath ), microglial cells phagocytic , Astrocytes (Repairing cell of nervous tissue. The works of this type of cell is formation ,repairing.

Character :

-Relative response i.e. (Sensitivity) 
-Conduction of nerve impulse /stimuli transmission / (conductivity)
-Response production (excitability)
-Sensitivity + conductivity + excitability + irritability 
-Which of the following part of nervous system not originated from ectodermal layer? 
-Microglial cells is not originated from the ectodermal.
-In Insect ( arthropod ) better neural organization brain ring present : made up of ganglia In vertebrate, well developed neural organisation is present . 
-Neurons, nerves, nuclei, ganglia, nervous tissue like grey matter  are present .

Neuron / Nerve cell

The neuron divided into two parts .

1. Cyton / cell body / perikaryon / soma 

2. Nerve processes (neurites) Axon / Dendron 

Dendrons and axons are out growth of neuron to differentiate from other cells.

1. Cyton: 

It is irregular shapes structure due to outgrowth ,cytoplasm is neuroplasm.

 following structure are found in neuroplasm.

1. Nucleus : It is centrally located , 1-2 nucleolus is present.

After birth, centroid is absent or immature, so, power of division is neuron In embryonal neuron centriole is present so, power of division is present.

after birth repairing is possible due to astrocytes minimum or least regeneration is found in nervous tissue and highest in epithelial tissue.

2.Neurofibrils: These are found in complete neuron ( dendron+ cyton + axon ),These are microtubule or microfilament like structure. It is help in internal conduction of nerve impulse. external conduction is performed by neurotransmitter in chemical synapses and by gap junction electrical synapses.

3. Nissl's  granules: These are found in dendron and cyton only absent in axon, These are cluster of RER and free ribosome or these are iron containing  ribonucleoprotein. structural protein formation .It also help in least regeneration.  

  These granule help in identification of neuron from other common cells. 

these are stained by basic dye ; methyline blue 

Sometimes during injury fagtigness and by certain toxin nissl's granules convert in dust like particle and finally disappears and the process is known as chromatolysis.

4. Golgi bodies : Related to packaging of structural protein.

5. Mitochondria : found as energy source. In cytoplasm of axon only mitochondria is found as cell organelles. elongation is possible after birth thyroxine hormone is responsible for elongation of nerve and myelination.

6.Axon : It is single , longest , efferent fiber also known as nerve fiber, unbranched 

(terminal part is branched). cytoplasm = axoplasm , outer membrane =axolemma . function and structural part is axon. Axon arises from axon-hillock or trigger zone. 

Terminal part of the axon is Telodendria. Telodendria = small duct + synaptic node + synaptic vesicles +neurotransmitter.

Myelin sheath may be present or absent on neuron. If myelin sheath is present , then fiber are myelinated and modulated If myelin sheath is absent, then fiber are non-myelinated and non-modulated. 

2. Dendrite:

Small branch tree like, high branch provide more surface area to receive max stimuli, afferent fibers because it receive stimuli made up of two part.

1. Proxmial : towards or attached with cyton in this part neurofibrils and nissel granules .

2. Distal : Receptor plus to receive stimuli.