Nervous Tissue is found in the brain, spinal cord, and peripheral nerves. Nervous tissue is composed of two main cell types: neurons (nerve cells) and glial cells. Neurons transmit nerve messages. Glial cellsGlial cells are in direct contact with neurons and often surround them. Humans have about 100 billion neurons in their brain alone! While variable in size and shape. Pyramidal Neurons from the Central Nervous System (SEM x3,960). This image is copyright Dennis Kunkel at used with permission.

Neuron Smear Identification: Note distinctive shape of neuron, with long processes (dendrites, 5) extending out from main cell body. There are also numerous supporting glial cells, though only their small dark nuclei (4) are easily seen. Also see the nerve cross section below. Features to Know: The large, irregularly shaped cell body (3) contains a darker nucleus (2), which contains an even darker- staining nucleolus (1)

Diagram of multipolar neuron Neurons are the basic and functional cells of the nervous tissue. they are sensitive to certain types of changes in their surroundings and respond by transmitting nerve impulses along cellular extensions (nerve fibers) to other neurons or to muscles or glands.. Because neurons communicate with each other and with various body parts, they coordinate, regulate, and integrate many body functions. All neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body.Dendrites The cell body (perikaryon) contains the nucleus, mitochondria and other organelles typical of eukaryotic cells.cell body The axon conducts messages away from the cell body.axon

Neurons are individaul nerve cells. neuron (black arrows).

Type of neurons Unipolar: when they contain a single fiber, the axon, and no dendrites as seen in sensory ganglia. Bipolar: when there is one axon and one dendrite, as in the retina of the eye; Multipolar: when there are several dendrites and only one axon, as in the motor neuron

MOTOR NEURON : Note distinctive shape of neuron (multipolar). The cell body or perikaryon (A) is filled with Nissl bodies which are chromatophilic substances ; pick up the stain in this micrograph. The cell's axon can not be distinguished from its dendrites in the micrograph. B marks the axon and dendrite threads. The "C's" marks the neuroglia cells (dark spots) and the neurofibrils.

Thoracic spinal Cord - silver stain Neurofilaments: are aggregated into neurofibrils; which are part of the cytoskeleton of neurones is (like the reticular connective tissue fibers) argyrophilic, i.e. they "love" silver and can be stained by silver stains. Aside from the neurones and their processes, fine fibrils are visible in the neuropil. Many of the fibrils represent axons travelling in the grey and white matter of the spinal cord. Note the large cell, prominent nucleus and nucleolus.

the spinal cord/vertebrae model Hint: to distinguish the posterior from anterior side of the spinal cord, note that only the posterior horns of the gray matter extend to the edge of the spinal cord. 9. Dura Mater 10. Epidural Space 11. Subdural Space 12. Arachnoid Mater 13. Subarachnoid Space 24. Pia Mater 25. Anterior Median Fissure 28. Posterior Median Sulcus 30. Anterior Funiculus 31. Lateral Funiculus 32. Posterior Funiculus 35. Central Canal

Spinal Cord Model 1. Posterior Funiculus † 2. Lateral Funiculus † 3. Anterior Funiculus † 5. Posterior Horn * 6. Lateral Horn * 7. Anterior Horn * 8. Gray commissure * 9. Central Canal 10. Posterior Median Sulcus 14. Anterior Median Fissure 23. Dorsal Root 24. Dorsal Root Ganglion 25. Ventral Root 26. Spinal Nerve * Gray Matter † White Matter

The Spinal Cord

Key: Structures: 1. Posterior Median Sulcus 2. Gray Commissure 3. Central Canal 4. Anterior Median Fissure Gray Matter: 5. Posterior Horn 6. Lateral Horn 7. Anterior Horn White Matter: 8. Posterior Funiculus 9. Lateral Funiculus 10. Anterior Funiculus Optional Features (you will not need to find these on the slide): 11. Pia Mater 12. Subarachnoid Space 13. Dura & Arachnoid Maters

SPINAL CORD A" marks the central canal. "B" is the anterior medial fissure. The posterior medial sulcus is not seen in this preparation. C is the posterior horn composed of axons of the sensory neuron. D is the anterior horn composed of the cell bodies of motor neurons. C and D are gray matter. Outside the horns and the commissure that connects them is the white matter.

Thoracic spinal Cord - H&E, silver stain Try to identify neurones (primary dendrites, Nissl-bodies) and glial cell nuclei in the H&E stained section. Part of the cytoskeleton of neurones is (like the reticular connective tissue fibers) argyrophilic, i.e. they "love" silver and can be stained by silver stains. Aside from the neurones and their processes, fine fibrils are visible in the neuropil. Many of the fibrils represent axons travelling in the grey and white matter of the spinal cord.

The ventricles of the brain and the central canal of the spinal cord are lined with ependymal cells. The cells are often cilated and form a simple cuboidal or low columnar epithelium. The lack of tight junctions between ependymal cells allows a free exchange between cerebrospinal fluid and nervous tissue. Ependymal cells can specialise into tanycytes, which are rarely ciliated and have long basal processes. Tanycytes form the ventricular lining over the few CNS regions in which the blood-brain barrier is incomplete. They do form tight junctions and control the exchange of substances between these regions and surrounding nervous tissue or cerebrospinal fluid.

Spinal cord - center (4x objective lens) This low magnification view shows the central region of the spinal cord. The gray matter, which contains the cell bodies of neurons, is more darkly stained than the surrounding white matter, which contains axons and dendrites. Locate the central canal of the spinal cord, located in the center of the image. It is surrounded by a thin band of gray matter, called the gray comissure, which connects the larger masses of gray matter located in the left and right halves of the spinal cord. Lighter stained regions of white matter can be seen both above and below the gay commisure. In the lower center of the image is the ventral fissure of the spinal cord, which divides the ventral region of the cord into two halves. Stain = silver.

Multipolar (motor) neuron: from the anterior horn of the spinal cord.

Peripheral Nerves

Myelination of a peripheral axon Schwann cells form a sheath around one axon and surround this axon with several double layers (up to hundreds) of cell membrane. The myelin sheath formed by the Schwann cell insulates the axon, improves its ability to conduct and, thus, provides the basis for the fast saltatory transmission of impulses. Each Schwann cell forms a myelin segment, in which the cell nucleus is located approximately in the middle of the segment. The node of Ranvier is the place along the course of the axon where two myelin segments abut. Myelination of a peripheral axon Animation from Blue Histology, Copyright Lutz Slomianka Blue HistologyCopyright Lutz Slomianka (The image should be animated, if you watch patiently.) A Schwann cell is illustrated with brown cytoplasm. The blue oval is the Schwann cell's nucleus. Observe that as the growing Schwann cell spirals inward around the axon, it wraps its membrane into layers of myelin.Schwann cell

In peripheral nerves, myelin consists of Schwann cell membrane wrapped around and around an axon, while most of the Schwann cell cytoplasm lies alongside the axon. To visualize myelin formation: Imagine that a Schwann cell is a pillow with the pillowcase representing Schwann cell membrane and the stuffing representing Schwann cell nucleus and cytoplasm.Schwann cell Next imagine a broomstick (representing the axon) lying across one end of the pillow. Now roll the broomstick up in the pillow, wrapping the pillowcase tightly around and around the broomstick while squeezing the pillow-stuffing into one end. The tight wrappings of pillowcase now represent the myelin, while the remaining pillow with stuffing represents the Schwann cell body with nucleus and cytoplasm.

Teased nerve fibres Osmic acid- stained teased nerve fibres to demonstrate nodes of Ranvier.

Peripheral Nerve, rat - H&E In longitudinal H&E stained sections it is possible to identify the axon running in its myelin sheath, nodes of Ranvier and Schwann cell nuclei. Components of the connective tissue elements, which accompany the nerve, should be visible and identifiable in both longitudinal and transverse sections. H&E stained and transversely cut preparations give a good picture of the axon in the middle of a ring- like structure (sometimes fussy), which represents the remains of the myelin sheath. Due to their small size and the lack of a myelin sheath, type C fibres are very difficult to detect in either osmium or H&E stains..

Nerves or nerve trunks of peripheralnervous system are arranged in groups or bundles of fibers containing axons, dendrites, and their collaterals,bound together by connective tissue and invested with blood capillaries.

Peripheral Nerve cross section Identification: A similar basic arrangement as in muscles, with fibers (4) bundled into fascicles (1). Note that nerve fibers are much smaller than muscle fibers and instead of being uniformly red in color have a dark central axon (3), surrounded by white myelin (2). Individual nerve fibers, fascicles, and the entire nerve are each surrounded by connective tissue sheaths (5-7). Features to Know: connective tissue sheaths: endoneurium (5), perineurium (6), & epineurium (7); nerve fiber (4) composed of an axon (3) surrounded by myelin (2); fascicle (1).

A nerve fascicle at higher power Each myelinated axon appears as a dot surrounded by a clear space where the myelin has been removed during preparation of the histological section.

Part of a peripheral nerve treated with osmic acid which stains myelin black. Note the variable diameters of the myelinated axons.