Nervous Tissue

Your sketch should include large multipolar cells with a large, round nucleus and a prominent nucleolus. The cell bodies of these cells in the SLU section doesn’t demonstrate many features of the cytoplasm, but you can observe Nissl bodies in the Iowa slides. Cells can be diverse in shape because of their large shape and the 2-dimensional nature of histological sectioning.

You may not see the nucleus of each cell because they are so large, and the plane of section may have missed them.

The axon hillock and axon lack Nissl substance, so will stain lightly compared to the dendrites.

Glial cells are much smaller and much more numerous than the large, less abundant neurons.

These are axons. They appear different from one another because axons sectioned in cross section in white matter are traveling up to the brain and different spinal levels; axons sectioned transversely are traveling out.

In this preparation you can observe the pia mater as a layer of flat cells that lie directly on the surface of the spinal cord. The arachnoid mater is appreciable as a region superficial to the pia  with more sparse fibers and importantly, blood vessels. The dura mater is not present in these preparations.

Dorsal horn – sensory neurons – action potentials travel from PNS to CNS.

Ventral horn – motor neurons – action potentials travel from CNS to PNS.

Your pseudounipolar neuron should have a cell body with a short stem, and two axons projecting from it. Nuclei are round. Synapses do not occur in this ganglion

These are satellite glial cells.

Your multipolar neuron should be large and round, with large nuclei with prominent nucleoli, and an eccentrically placed nucleus. These cells are also surrounded by satellite glial cells.

These neurons can be found in between the longitudinal and circular layers of muscle in the ileum. The neurons here are multipolar.

Your sketch should include endoneurium, perineurium, and epineurium, as well as axons.

These nuclei belong to Schwann cells, which are thin, elongated cells with flattened, long nuclei.

They allow for increased conduction of action potentials (saltatory conduction).

Schwann Cells

Major dense lines and intraperiod lines.

Myelinated fibers conduct nerve impulses with greater speed because they insulate against loss of impulse. They also possess Nodes of Ranvier, which allow for saltatory conduction and even greater speeds.

This cross-section shows myelinated axons. Myelin stains dark brown in this preparation (i.e., with osmium tetroxide), while the nerve fiber itself is the clear part inside.

Whereas in connective tissue, fibrocyte nuclei are flatter and more sparse, in a peripheral nerve Schwann cell nuclei are oval-shaped and can be observed around clear-staining myelin sheaths. Threadlike axon fibers can be observed in the middle.

Connective tissue also stains intensely eosinophilic, and thick bundles of collagen fibers are abundant. Peripheral nerve staining is more uneven, with clear areas from myelin sheaths, and some eosinophilic areas with axons and Schwann cells.

It implies that it releases a great deal of neurotransmitter.

Oligodendrocytes are the myelin-forming cells in the CNS (as opposed to Schwann cells). They are small and heterochromatic (stain darkly).

Astrocytes provide physical and metabolic support for CNS neurons and form the blood-brain barrier. They are larger than oligodendrocytes and stain more lightly.

Microglia are the phagocytes of the CNS. They typically cannot be distinguished on routine preparations but instead require a macrophage-specific immunostain.

In the brain, neurons are larger, have a large nucleus with a prominent nucleolus, and are typically pyramidal in shape (and will have axons and dendrites projecting from them), allowing you to distinguish them from the smaller supporting cells.

Meissner’s corpuscles have unmyelinated nerve endings surrounded by Schwann cells in spiraling layers. They are receptors for low frequency stiumuli, located within dermal papillae. Their superficial location within the dermal papilla allows for the perception of light touch, as only a limited amount of displacement is required to activate it.

Pacinian corpuscles have several layers of concentric lamellae that require a more significant displacement of the surrounding tissues in order to activate the nerve fiber at the center, allowing them to perceive deep touch. They are also located deeper in the dermis (reticular layer) and in the hypodermis.