1. Neurons Vary in size and structure, but have common features:
Cell Body
Dendrites
Axon
Mature neurons do not divide, but neural stem cells can divide and form neurons or neuroglial cells.

2. 1. Cell Body
Contains normal cellular structures (golgi apparatus, mitochondria, cytoplasm, cell membrane, etc.)
Neurofibrils – fine threads that extend into the axon
Nissl bodies (chromatophilic substances)
Membranous sacs in the cytoplasm
Similar to rough ER
Ribosomes on Nissl bodies synthesize ______

3. 2. Dendrites Usually short and highly branched (dendr = ?)
The main receptive surfaces for receiving communication from axons of other neurons

4. 3. Axons
Arise from a slight elevation of the cell body, called the axonal hillock.
Conduct nerve impulses away from the cell body
Contains many mitochondria, microtubules, and neurofibrils
Originates as a single structure, but may have branches, especially at the end to interact with receptive surfaces of other cells

5. PNS Axons Enclosed in myelin sheaths composed of many Schwann cells
Myelin is a lipoprotein.
Neurilemma sheath surrounds the myelin sheath
Nodes of Ranvier – narrow gaps in the myelin sheath between the Schwann cells

6. Classification of Neurons
Classification based on Structural differences:
Bipolar neurons
Unipolar neurons
Multipolar neurons
Classification based on Functional differences:
Sensory neurons (afferent neurons)
Interneurons (association or internuncial neurons)
Motor neurons (efferent neurons)

7. Structural Differences
Sketch the neurons below. Notes on the next 3 slides:

8. Structural Differences, cont…..
Bipolar:
2 processes
Axon
Dendrite
Found in specialized parts of the eyes, nose, and ears

9. Structural Differences, cont…..
Unipolar:
1 process divides into 2 branches, which function as a single axon
1 branch (peripheral process) associated with dendrites
Other branch (central process) enters brain or spinal cord

10. Structural Differences, cont…..
Multipolar:
Many processes arising from cell body:
1 axon
Many dendrites
Most neurons whose cell bodies lie in the brain or spinal cord are multipolar.
Direction of impulse is ALWAYS from dendrites to axon.

11. Functional Differences
Sensory (afferent) neurons
From peripheral body parts to the brain or spinal cord
Have specialized receptor ends at the tips of their dendrites OR
Dendrites closely associated with receptor cells in the skin or sensory organs.
Most are unipolar, but some are bipolar.

12. Functional Differences, cont…..
Interneurons (association or internuncial neurons)
Lie entirely in the brain or spinal cord
Multipolar and link other neurons
Transmit impulses from one part of the brain or spinal cord to another
Motor (efferent) neurons
Multipolar
Carry nerve impulses from brain or spinal cord to effectors
Stimulate muscles or glands