How are axons and dendrites alike?
Neuron = the structural & functional unit of the nervous system also called a nerve cell.
Each neuron is composed of a cell body and many extensions from the cell body called neuron processes or nerve fibers.
The cell body is the central portion of neuron and contains the usual organelles, except centrioles including a nucleus, with a prominent nucleolus.
Neuron Processes/ Nerve Fibers are extensions from cell body.
There are two types:
- Dendrites : there may be as many as 1000 per neuron. They are short and branched and are the receptive portion of a neuron and carry impulses toward cell body.
- Axons : there is only one per neuron and they are a long and thin process and that carry impulses away from cell body.
They end in axonal terminals or synaptic knobs.
Axons in PNS are large axons are surrounded by a myelin sheath produced by many layers of Schwann Cells (a type neuroglial cell). We call these"myelinated nerve fibers".
Myelin is a lipoprotein. This provides insulation.
There are Interruptions in the myelin sheath between Schwann cells are called the Nodes of Ranvier. These allow the impulse to travel very rapidly by "skipping" from Node to Node
Small axons do not have a myelin sheath. and we call these "unmyelinated nerve fibers". However all axons (in PNS) are associated with Schwann cells.