Neuron or nerve cell is the basic structural unit of the nervous system. Like all other cells, the neuron has a cell membrane, cytoplasm and nucleus.
Axon
• Longest filament from the cell body.
• Carries impulses from the cell body to outside.
Axonite
• Branches of axon.
• Carries impulses to the synaptic knob.
Dendrite
• Branches of Dendron
. • Part that receives impulses from adjacent neuron.
Dendron
• Short filament from the cell body.
• Carries impulses from dendrites to the cell body.
Synaptic knob
• Tip of axonite
. • Secretes neurotransmitter.
Schwann cell
• Encircles the axon.
Axons of most of the neurons are repeatedly encircled by myelin, a membrane containing lipid. This is called myelin sheath.
Nerve is a group of axons. Myelin sheath in the nerves is formed of Schwann cells. Myelin sheath in the brain and the spinal cord is formed of specialized cells called oligodendrocytes. The myelin sheath has a shiny white colour. The part of the brain and the spinal cord where myelinated nerve cells are present in abundance is called white matter and the part where non-myelinated nerves cells are present is called grey matter.
The major functions of the myelin sheath are to provide nutrients and oxygen to the axon, accelerate impulses, act as an electric insulator and protect the axon from external shocks.