Ans.Nerve cell or Neuron
Nerve cell or neuron is the unit of the nervous system. The human nervous system consists of billions of neurons plus supporting (neuroglial) cells.
Function
Neurons are specialized cells that are able to conduct nerve impulses from' receptors to coordinators and from coordinators to effectors. In this way they communicate with each other and with other types of body cells.
Structure of Neuron
Neuron consists of following major components:
Cell body, dendrites, axons, Schwann cells, myelin sheath, and nodes of Ranvier.
The nucleus and most of the cytoplasm of a neuron is located in its cell body. Different processes extend out from the cell body. These are called dendrites and axons. Dendrites conduct impulses toward cell body and axons conduct impulses away from cell body.
Schwann cells are special neuralgia cells located at regular intervals along axons. In some neurons, Schwann cells secrete a fatty layer called myelin sheath, over axons. Between the areas of myelin on an axon, there are non-militated points, called the nodes of Ranvier.
Myelin sheath is an insulator so the membrane coated with the sheath does not
conduct nerve impulse. In such a neuron, impulses jump over the areas of myelin going from node to node. Such impulses are called saltatory ('jumping') impulses. This increases the speed of nerve impulse.
Cell body
Axon
Dendrites Nucleus Myelin sheath
Nodes of Ranviei Schwann cells
Directionof nerve impulse I
Nerve Growth Factor
Unlike ordinary cells mature neurons never divide. But a protein called nerve-growth-factor promotes the regeneration of broken nerve cells. The degenerating brain cells could be repaired, by using embryonic stem cells. Figure 12.2