Biology 241 – Lab
LAB #5
(5th/21 Lab Sessions for Fall Quarter, 2008)
TOPICS TO BE COVERED:
»A Discussion of the Classification Criteria for Muscle Tissue
»Microscopic examination of and drawing/labeling of the three sub-types of Muscle Tissue
DESIRED OUTCOMES:
After completing the activities described for this lab session, students should:
»Be able to recognize microscopically all three types of muscle tissue as characterized by
structural features such as cell shape, number of nuclei, presence/absence of striations and/or
intercalated discs. Look at both transverse sections and longitudinal sections.
»Have rendered drawings of the various muscle tissue sub-types along with proper labeling of
the unique and/or prominent features of each.
»Relate tissue sub-type structural characteristics to the specific functioning of that sub-type.
MATERIALS NEEDED:
»Blue Box of prepared microscope slides marked: HISTOLOGY SLIDE SERIES in Lab Bench drawer,
specifically Slide #17: Skeletal Muscle Tissue; Slide #18: Cardiac Muscle Tissue; Slide #19: Smooth
Muscle Tissue.
»Histology Drawing Sheets, pencils, eraser, Histology Drawings Assignment Guidelines for reference.
»Oversized 3-D model of Portion of a Skeletal Myofiber
»Set of 3-D Histology Models
»Wall Posters of Histomicrographs of Muscle Tissue
»Photographic Atlas, Ch. 3 and Figure 8.2
Activity #1: A Discussion of the Classification Criteria for Muscle Tissue
Muscle tissue consists of elongated cells called muscle fibers, or more concisely, myofibers. (In other
words, a myofiber = a muscle cell.) These cells are specialized to “generate force” (ie, contract) by using large amounts of ATP. As a result, the main functions of myofibers (and the many myofibers compartmentalized by important connective tissue “wrappings” and arranged systematically into muscle tissue) is to produce body movements,
move/store substances within the body, maintain posture and stabilize body positions, generate heat, and provide
protection.
The bases for classification of Muscle Tissue sub-types are (1) location; (2) structural features including
cell shape, number of nuclei per cell, and presence or absence of striations and intercalated discs; and (3) functional features such as type of innervation (voluntary or involuntary) and length of refractory period. Based
upon these three criteria, Muscle Tissue is classified into three sub-types: Skeletal Muscle Tissue, Cardiac
Muscle Tissue, and Smooth Muscle Tissue.
It is important to note that there are three connective tissue “wrappings” (or layers) associated with all
sub-types of muscle tissue. These three layers are all interconnected. They extend from the deep fascia to protect
and strengthen skeletal muscle tissue; and from superficial to deep to help compartmentalize and organize cardiac and smooth muscle tissue. The three layers are (from superficial to deep): epimysium, perimysium, and endomysium. Epimysium and perimysium are composed of dense, irregular C.T. Endomysium is composed of
areolar C.T. Epimysium (the outermost layer), encircles the entire muscle organ. Perimysium (the middle layer) surrounds groups of 10 – 100 (or more) myofibers organizing them into bundles called fascicles. (Whereas
Biology 241 – LAB #5 – continued
Page Two
myofibers are microscopic and not visible with the naked eye, muscle fascicles are quite large and ARE
macroscopically visible. In fact, it is the macroscopically visible fascicles that give muscle tissue its
characteristic “grain”; as evidenced by “playing with” a piece of cooked beef, chicken, pork, or fish: fascicles
are the “stringy structures” that result from teasing the meat apart: it tears along the fascicles. (If you look closely
enough, you can even see the tiny – but visible – bright white collagen fibers of the dense, irregular C.T. that comprises epiand perimysium!) Penetrating the interior of each fascicle, and separating individual myofibers from one another,
is the endomysium, a thin sheath of areolar C.T. that completely surrounds EACH and EVERY myofiber. The
“ends” of the sheaths of each of these C.T. “wrappings” all fuse together to form the proximal and distal tendons
of skeletal muscle organs (which serve as origin and insertion attachments to the periosteum of bones ) and the
encasements of cardiac and smooth muscular organs
Skeletal Muscle Tissue: is composed of large, long (up to 12–16”*) cylindrical myofibers with hundreds of
nuclei (referred to as multinucleated) pressed to the periphery of the cell just under the sarcolemma. The
myofibers do NOT branch; and they lie parallel to one another. These cells are also striated; that is they exhibit
a distinct banding pattern due to the repeating organization of internal contractile proteins (the myofilaments actin
and myosin) as they arrange into units called sarcomeres that line up end-to-end as myofibrils. Skeletal muscle
tissue may be stimulated to contract consciously and is therefore under voluntary control (aka it is innervated
by the Somatic Nervous System)
*Note: skeletal myofibers are the length of the muscle organ in which they are located; thus for oculus muscles this may be
only 3” but for the rectus femoris muscle it may be 16”. Also, the larger the muscle mass, the more numerous the
myofibers contained in any one fascicle. For an oculus muscle there may be as few as 2 – 5 myofibers per fascicle; but for
the rectus femoris muscle there will be 150 – 200 myofibers per fascicle.)
─
º
─
─
º
─
º
─
º
º
─
º
─
º
─
º
─
º
─
Cardiac Muscle Tissue: is composed of cylindrical, branching myofibers each with a single, centrallyplaced nucleus (referred to as uninucleated) that is, in turn, surrounded by a perinuclear region. Cardiac
myofibers (sometimes referred to as cardiocytes) are all interconnected one to the other, end-to-end, by transversely
oriented specialized thickenings of the adjacent sarcolemmas called intercalated discs which facilitate the
conduction of the stimulus of contraction to neighboring cells. (Intercalated discs contain both desmosomes and gap
junctions; the desmosomes strengthen the tissue and hold the myofibers together during their vigorous contractions while
the gap junctions provide a route for quick conduction of muscle action potentials throughout the heart.) Like skeletal
myofibers, cardiac myofibers are striated due to the strict arrangement of the contractile myofilaments (actin and myosin)
into sarcomeres aligned into myofibrils. Unlike the control of skeletal muscles, that of cardiac muscle is
involuntary (aka it is innervated by the Autonomic Nervous System). For example, when you exercise, autonomic
nerves increase the heart rate to deliver more blood to the active tissues; when you relax (or sleep), other
autonomic nerves lower the heart rate.
*Note: The terms “voluntary” and “involuntary” muscle control are used more for convenience than for description.
Skeletal muscle is said to be voluntary, yet you cannot stop your muscles from shivering when you are cold. Additionally,
once you voluntarily start a muscle contraction, the brain assumes control of the muscular activity. The heart muscle is
involuntary, yet some individual can train themselves through biofeedback to control their heart rate. It is just a convenient generality then to use the term “voluntary” for skeletal muscles and the term “involuntary” for cardiac and smooth
muscles.
─
º
─
º
─
º
─
º
─
º
─
º
─
º
─
º
─
º
─
Smooth Muscle Tissue (also called Visceral Muscle Tissue): is composed of uninucleated, fusiform (or “spindleshaped”) myofibers each with a single, centrally placed nucleus. (The term fusiform means the cell is thick in the
middle (where the nucleus is located) and tapered at the ends.) Smooth myofibers as so named because they lack
striations. That is, their contractile proteins (actin and myosin) are NOT arranged into sarcomeres and the actin
myofilaments attach to dense bodies scattered throughout the sarcoplasm and on the sarcolemma, not to Z-discs.
This muscle tissue sub-type usually occurs in double sheets of tissue organized at right angles; this arrangement
enables the tissue to shorten structures and reduce their diameter. Smooth muscle is under involuntary control.
Biology 241 – LAB #5 – continued
Page Three
Activity #2: Microscopic Examination, Drawing/Labeling of the three Muscle Tissue sub-types
For today’s lab session, you will examine Slides #17, #18, #19 with the goal being to recognize physical
features general to all three sub-types of muscle tissue, as well as those features that are unique to each subtype. Compare the appearance of the tissues in transverse as well as longitudinal sections. Draw and label the
significant microscopic structures of each.