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Neurons |
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| The human
brain is made up of 100 billion neurons. They vary greatly in size
depending on their location and job. The nerve cells in the brain are
interneurons. They have shorter axons are dendrites than motor neurons
and are arranged more circularly.
Motor Neurons: The cell body, one of three parts of the neuron, is about 5-15µ in diameter on average, but can be as large as 135µ, which is just barely visible. The body is similar to most cells and contains a nucleus and other organelles. It also has an arrangement of rough endoplasmic reticulum called chromatophilic substance or Nissl bodies. These Nissl bodies help grow and repair axons.
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| Axons
are long and thin cylindrical projections that join the cell body at a
bump called the axon hillock. The axon generally starts as one large
projection but can have branches known as axon collaterals. In the end,
the axon divides into many fine axon terminals. Throughout the axon,
there are mitochondria in its cytoplasm (axoplasm). The axon sends out
information to dendrites.
Dendrites are located at the opposite end of the cell body of the axon. Unlike the axon, dendrites are thin and branch off almost immediately into thinner, smaller, receptors. Dendrites pick up information and carry it to the cell body. They have Nissl bodies, mitochondria, and other organelles in their cytoplasm.
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