BIOLOGY 473 - Sensory Biology

Spring 2003

The transmission electron microscope (TEM) is used to reveal the cellular organization and microstructure of nervous tissue using retina as a model.

  (below, left) Transmission electron micrograph of the inner and outer rod segments from mouse retina. Rods contain light-sensitive pigments located on numerous membrane discs that are stacked like pancakes in the outer rod segments, while the inner segments are packed with mitochondria, a source of energy. Each cell is tightly adherent to its neighbors at the level of the outer limiting membrane, and the nuclei sit at the base of the cell.

(left) Shown here are several junctional complexes located in the outer plexiform layer, between the base of the rod cells and the bipolar/horizontal cell layer. The very dark features are known as synaptic ribbons, specialized structures unique to retinal tissue, where two or more cells are tightly apposed and communicate by means of changing electrical potentials. Many small, round organelles called synaptic vesicles cluster around the ribbons. These carry neurotransmitter substances.

(bottom of page) Myelinated nerve cell, and enlargement of the myelin sheath.