1. Biology 322 Human Anatomy I
Cytology and Histology of the Nervous System

2. Brain
Spinal Cord
Central Nervous System (CNS) =
Peripheral Nervous System (PNS)
Nerves =

3. Recall:
Nervous system begins in trilaminar embryo as a “neural plate” of the ectoderm. This develops into a “neural groove” that closes over to form a “neural tube”

4. One end (caudal) of this neural tube thickens but stays tube-shaped to form the spinal cord.
The other (cephalic) end of this neural tube enlarges and folds to form the brain and its various divisions, which we will discuss later.

5. The cranial nerves and spinal nerves will form as outgrowths of this embryonic brain and spinal cord.

6. Recall: All organs are composed of, at most, four tissues
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
Nervous tissue: Excitable cells (neurons)
Nonexcitable (supporting) cells
Connective tissue: Meninges in central nervous system
Endoneurium
Perineurium in peripheral nervous system
Epineurium
Epithelium
found only in blood vessels
Muscle (smooth)

7. Cells of Nervous Tissue:
1) Excitable cells = Neurons
Carry electrical signals from one
place to another
Pass these signals to other cells
2) Nonexcitable cells
Glia in CNS
Satellite cells
Schwann cells
in PNS

8. 1) Excitable cells = Neurons
Carry electrical signals from one place to another
Pass these signals to other cells
Found in either central
nervous system, peripheral
nervous system, or may
have parts in both
Do not divide
Long-lived
High metabolic rates

9. 1) Neurons Classified by: Location

10. 2) Neurons Classified by: Shape
Bipolar
Multipolar
Unipolar or
Pseudo-unipolar

11. Dendrites
Axon Terminals
Axon Hillock
Axon
Telodendria
Cell Body

12. Exception to this classification: Unipolar or pseudo-unipolar neurons
Cell body
Single process
Dendrites
Axon branches
Telodendria and axon terminals

13. Cells of Nervous Tissue:
1) Excitable cells = Neurons
Carry electrical signals from one place to another
Pass these signals to other cells
2) Nonexcitable cells
Do not carry electrical information
Support, nourish, protect neurons
May divide

14. Non-excitable cells
In PNS:
Satellite cells surround
neuron cell bodies
Schwann cells surround
cell processes
In CNS:
Four types of Glia

15. Glia: 4 types in central nervous system
1) Astrocytes
2) Oligodendrocytes:
3) Microglia:
4) Ependyma:

16. Glia: 1) Astrocytes: Regulate environment around neurons
by controlling the passage of molecules into and
out of capillaries, and by absorbing or secreting
ions from/into extracellular matrix

17. Glia: 2) Oligodendrocytes: Produce myelin sheaths around
axons (and some dendrites) of neurons in C.N.S.

18. Glia: 3) Microglia: Phagocytic. Remove degenerating cells
and foreign debris from C.N.S.

19. Glia: 4) Ependyma: Line fluid-filled ventricles within C.N.S.

20. Non-excitable cells of Peripheral Nervous System
1) Satellite cells surround and protect neuron cell bodies
in P.N.S.
Satellite Cells

21. Non-excitable cells of Peripheral Nervous System
2) Schwann cells produce myelin sheaths which surround
axons (and some dendrites) in P.N.S.
Schwann Cells
Nodes of Ranvier

23. Pathology of the Nonexcitable Cells
Loss of oligodendrocytes causes multiple sclerosis and a group of diseases called leukodystrophies
Injury to astrocytes, usually from toxic substances, leads to cerebral edema and swelling of the brain
Injury to Schwann cells causes degeneration of the neuron processes and prevents their healing and regrowth. It is also responsible for Guillain-Barre syndrome

24. Pathology of the Nonexcitable Cells
Tumors can arise from all four types of glia, and these tend to grow rapidly and destroy nearby regions of the brain or spinal cord
Astrocytoma
Astrocytoma
Ependymoma
Tumors can also arise from satellite cells or Schwann cells, compressing and destroying the neurons they surround
Schwannoma