Co-ordination - It is the process through which two or more organs interact and complement the functions of each other. Neuron - It is the functional and structural unit of nervous system. Therefore, the nervous system is also known as NEURAL SYSTEM. Neurons with longer projections are said to be the longest cells in our body. There are about 100 billion neurons and most of them exist in the brain. Some neurons have flask-shaped and are called Purkinje cells. They are found in the cerebellum of brain. Shortly after birth neurons do not develop. A neuron has two main parts viz.
a) Cell body or Cyton or Soma -
It may be up to 13.5 µm in diameter and may be irregular, oval, rounded, etc. Neuroplasm and neurolemma are its cytoplasm and cell membrane. A cyton consists of cell organelles like other cells. Besides, it also has neurofibrils, neurotubules and Nissls granules or bodies. Neurofibrils take part in transmission of impulse
Nissls granules or bodies are irregular masses of rough endoplasmic reticulum on which free ribosomes and polysomes are attached. Nissls granules probably synthesize protein for the cell. b) Cytoplasmic processes or neuritis –
They are of two types.
1. Dendrites or dendrons - They contain neurofibrils, neutubules and Nissls granules. They conduct nerve impulse towards the cell body and are called afferent processes (receiving processes). They may be one to several. 2. Axon or Axis - It is a single long process of uniform thickness. The part of cyton from where the axon arises is called Axon hillock and is the most sensitive part of a neuron. An axon does not have Nissls granules, golgi complex, ribosome, etc. So cyton supplies protein to axon. Its cell membrane and cytoplasm are known as axolemma and axoplasm respectively. Axon ends in a group of branches called terminal arborizations (axon terminals or telodendria). They have synaptic knob to form synapse where axon and dendrite...