Structure of the nervous system

¤ Structure of the nervous tissue 

It is formed of two distinct cell types :

1\ Neurons Excitable cells initiate and transmit nerve impulses.

2\ Neuroglia cells Nonexcitable cells Support and protect the neurons.

¤ Neuron

*The neuron is the functional and structural unit of the central nervous system Characteristics of Neuron.

* Neurons have a high metabolic rate.

* Neurons have extreme longevity.

* Neurons typically are non-mitotic.

* Structure of neuron  :

1- Cell body (soma, perikaryon).

2- Dendrites Axon Cell body (soma, perikaryon).3- Cell membrane It is very thin.

4- Nucleus Large Regular round or oval(vesicular) Situated fairly centrally.

5- Cytoplasm.

6- Rough Endoplasmic Reticulum (RER) – Nissl’s bodies.

7- Golgi apparatus.

8- Mitochondria.

9- No centrioles Neurofibrils.

10- Glucogen Melanin pigments Lipofuscin granules, Fat droplets.

¤ Axon Single Uniform in diameter, Length of axons is variable:

* some reach up to 100 cm. Originate from a short pyramid-like structure called the axon hillock (Lacks Nissl’s granules).

* The plasma membrane of the axon is termed the axolemma.

*The cytoplasm of the axon is termed the axoplasm.

* Collaterals arise from the axon.

* Axon and collaterals end in fine processes called axon terminals.