Part 5: Muscle and Nervous Tissues
Identification: Spindle-shaped (tapering at both ends) cells with a central nucleus packed tightly together (no gaps between cells); nuclei may not be visible. Cells lack striations and usually lack distinct borders, often appearing out of focus (blurry). Two views are shown. To find smooth muscle on the slide, look near the outer portion of the organ.
Features to Know: nuclei (if visible)
Where Located: mostly in the walls of hollow organs.
Function: involuntarily propels substances (e.g. food, urine) or objects (e.g. baby) along internal passageways.
Identification: note branching of muscle cells and faint striations. The darker bands across cells are intercalated disks.
Features to Know: nuclei (1), intercalated disk (2).
Where Located: wall of the heart (myocardium).
Function: involuntarily contracts to propel blood into circulation.
Identification: teased or l.s. section shows distinct, very long, parallel muscle fibers (cells). (Cells of cardiac muscle tissue are much smaller and branched.) Note the presence of distinct striations. Cells are multinucleated, the nuclei peripherally located (appearing to be located between the muscle fibers).
Features to Know: striations (1) composed of dark A-bands and light I-bands; nuclei (2) pushed to edge of fiber; sarcolemna (plasma membrane surrounding fiber).
Where Located: skeletal muscles.
Function: voluntary body movements.
Identification: you need to be able to identify features 1-4. The large, irregularly shaped cell body or soma(3) contains a large dark nucleus (2), inside of which is a smaller dark-stained structure called the nucleolus. There are also numerous supporting cells called glial cells or neuroglia, their nuclei clearly visible (4). Extending from the cell body (soma) are axons and dendrites (5).
Features to Know: The large, irregularly shaped cell body (3) contains a darker nucleus (2), which contains an even darker-staining nucleolus (1). There are also numerous supporting glial cells, though only their small dark nuclei (4) are easily seen.
Where Located: brain, spinal cord and nerves.
Function: neurons transmit electrical signals from sensory receptors to effectors (muscles and glands); glial cells (neuroglia) support, protect and insulate neurons.