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Lab 4: Shark Myology Lab Objectives 1. To gain an understanding of the muscular system of the shark. 2. To learn the insertions, origins, and actions of key muscles you study. 3. To study how the muscles of the shark act on the skeletal system to make it move. 4. To establish a foundation to which to compare the muscles of the cat. 5. To learn how the muscles of the shark are subdivided into functional groups. Material to Learn Shark musculature • Figures 3.17, 3.18, 3.19 • Associated text: pp. 40-­‐45 (supplementary) • OMIT: Figures 3.20, 3.21 • OMIT muscles/terms: labial pocket, dorsal interarcual muscles, lateral interarcual muscle. • OMIT: Origins, insertions, and actions of the muscles not listed in Table 1 of this document. Term List Levator palatoquadrati m. Structures Action Adductor mandibulae m. Linea alba Tendon Myomere Coracoarcual m. Raphe Myoseptum Coracobranchial m. Aponeurosis Pectoral abductor m. Coracohyoid m. Joint Pectoral adductor m. Coracomandibular m. Fulcrum Pelvic abductor m. Extend/Flex Cucullaris m. Pelvic adductor m. Abduct/Adduct Dorsal hyoid constrictor Raphe Dorsal superficial Elevate/Depress Spiracularis m. Protract/Retract constrictor m. Ventral hyoid constrictor Epaxial musculature Rotate Ventral longitudinal Epibranchial m. Constrict bundles Synergistic/ Horizontal skeletogenous Ventral superficial Antagonistic septum constrictor m. Hyomandibular n. Appendicular, Hypaxial musculature Branchiomeric, and Interhyoideus m. Hypobranchial Other Terms Intermandibularis m. musculature
Muscle f
iber Levator hyomandibulae Origin/Insertion m. General hint: muscles can be tough to ID. If you are having trouble, look through the pictures for that section of the animal and find the easiest one to identify. Then look for the relationship of your difficult muscle to the easy one. Background & Instructions This is the first lab of the course that requires involved dissection. Dissection is an art that requires a lot of patience, time, and practice to learn. Make sure that you put in the time that is necessary, but also make sure you are patient and do not just hack into structures. It is easy to destroy small and delicate structures without even realizing it. Before cutting, check to make sure that you need to cut. Use scissors in favor of a scalpel almost always. The scissors or forceps will often do the job more than adequately. Finally, if you are unsure of how to proceed, just ask. Shark skinning, and fin musculature Before cutting into the shark, examine its external anatomy again and identify the structures (Fig. 3.14 & 3.15). Then turn your attention to the posterodorsal surface of the animal. You will skin a portion of the body immediately dorsal to the pelvic fin. This is a great place to start because there are few features to make the skinning process complicated. Follow these steps to do the dissection: 1. Use chalk to draw the outline of the area you want to skin. If your shark is bent, it will be easier to skin the side that forms the outside of the bend. 2. Use your scalpel to make an incision following the line you have drawn. Hold the scalpel as you would a pencil and make a superficial cut. Err on the side of caution, making the cut too shallow and then retracing it, as opposed to cutting too deeply. Use continuous long cuts, don't make small incisions. The goal is to cut through the skin and underlying fascia, but to not cut into the muscle. Scalpels are extremely sharp, so be careful not to cut yourself or someone else. 3. Once you have traced the entire shape to be skinned, peel up the skin at the corners, deepening the cut as needed. Use the hemostat to grasp the corners and pull up the skin, being careful not to pry up the underlying muscle. 4. Skin part of the trunk and the entire dorsal and ventral sides of the fin. Since you are working in partners, make sure that both students get plenty of practice dissecting. As you skin on the body, you will run into difficulty near the lateral line. This is also the position of the horizontal skeletogenous septum, which is connective tissue that runs in a frontal plane from the lateral aspect of the vertebrae to the skin. It subdivides the trunk musculature into epaxial and hypaxial. As you skin the dorsal pelvic fin, you will notice a muscle that is more delicate than the epaxial and hypaxial ones, and that runs from the hypaxial muscles to the dorsal side of the fin. Also notice what the flexible ceratotrichia look and feel like in a wet specimen. As you skin the ventral side of the pelvic fin, you will notice a similar muscle running from the ventral trunk to the fin. These muscles are called extrinsic muscles because they connect the limb and the body. In contrast, intrinsic muscles run from some elements of the limb to other elements of the limb. The fin muscles are divided functionally into fin abductors and fin adductors (in Latin, ab means "away from" and ad means "towards"). If you have a male shark, you will find a sac-­‐like structure on the ventral side of the pelvic fin. This is the siphon, which the shark fills with water and uses to help rinse sperm down the groove in the clasper during insemination of the female. 1. Shark Dissection
Skin Flap 2 in Figure 3.16 and then enlarge the skinned area to extend more posteriorly. In the shark, the fascia between the skin and muscles is a tough, fibrous material. The fibers are arranged in layers and run diagonally to one another. The fibers are arranged in such a way that they maintain the body of a live shark, sleek and unwrinkled, decreasing drag while the animal swims through the water. Fascia also separates muscles. This fascia needs to be removed laboriously with curved forceps to reveal the muscles. Notice that you can see the direction of the muscle fibers for each muscle. This is a good way to distinguish muscles -­‐ often, their fibers run in different directions. Once the fascia is removed sufficiently to reveal all of the superficial muscles (those seen in Figures 3.17 and 3.18), muscles can be separated from one another, where possible. Each muscle should be separated so that you can follow the muscle fibers from one point of connection of a muscle to the other. Once muscles are completely cleaned in this way, deeper muscles can be dissected. To do this, some muscles have to be cut but should be cut in such a way so as to preserve them for viewing and studying. To get at the deeper muscles of the branchial region, the tip of a scalpel may need to be used to cut through one side of the m. intermadibularis. The cut should be made very superficially, allowing separation of the m. intermadibularis from the underlying m. interhyoideus. The cuts should then be repeated through the m. interhyoideus, allowing for both muscles to be reflected to reveal the deeper muscles (seen in Figure 3.19). Study the shark's muscles that you see in Figures 3.17, 3.18, and 3.19. 2. Muscle function and the musculoskeletal system As you learn the muscles of the shark and cat in the next few weeks, it is important to learn more than just the names of the muscles. All of these muscles have functions -­‐ they move parts of the skeleton -­‐ and an important skill is to learn how to elucidate this function. At the gross level, muscles are composed of muscle fibers, and as you remove the fascia from them, the fibers, and their direction will become clear. Finding fiber direction is important because when a muscle contracts, it does so parallel to the muscle fibers. This means that by noting muscle fiber direction, you know in what direction the muscle shortens. Muscles shorten along their fibers. As you dissect or examine each muscle, trace it to its attachment points. Following the muscle fibers along their length will lead you to the attachments. Muscles attach via tendons to bones, cartilage, other connective tissue, and even other muscles. A raphe is a sheet of connective tissue that runs perpendicular to a muscle and allows for muscle attachment. An aponeurosis is a sheet of connective that runs parallel to a muscle, forming a broad tendon. When a muscle contracts, it moves one part that it is attached to relative to the other. The part that moves is the muscle’s insertion, and the part that is stationary is the muscle’s origin. By knowing a muscle’s fiber direction, insertion and origin, you can determine its action. The action is simply a term for what the muscle does. Another helpful clue to a muscle’s function is that movement of skeletal components happens at joints. Therefore, to move the skeleton, muscles have to span a joint. This spanned joint is the fulcrum, or pivot point, of the movement. Muscles can move bones at joints in different ways, and this is partly dictated by the orientation of the muscle and partly by the structure of the joint. Specific terms are used to describe the actions of the muscles, or how the skeletal elements move. Common actions of muscles are to extend or flex a joint, abduct or adduct, elevate or depress, protract or retract, as well as rotate, and also constrict. As you study the muscles in lab, constantly think about insertion, origin, and action, using the terminology introduced here. For example, the lateral head of your triceps originates from the deltoid ridge of the humerus and it inserts on the olecranon process of the ulna (this is why we learned the small structures on the bones of the upper limb). It spans the elbow joint and moves your antebrachium (forearm) relative to your brachium (upper arm). Its muscle fibers run parallel to the long axis of your arm. Based on its location and the above information, you can deduce that when your triceps contracts, it straightens the elbow joint or, more correctly, extends the antebrachium. A useful tip for learning muscles is that in many (certainly not all) cases, the name of the muscle gives you information about its insertion, origin, or action. For example, the m. adductor mandibulae closes or adducts the lower jaw. The coracohyoid m. inserts on the basihyal (or hyoid) and is continuous with the coracoarcual m., which originates from the coracoid bar of the pectoral girdle. Finally, muscles can be synergistic or antagonistic in their actions. In the examples given in the previous paragraph, the coracohyoid and coracoarcual mm. are synergistic – their actions are the same or similar. In contrast, the coracomandibular and adductor mandibulae mm. are antagonistic: the former abducts Meckel’s cartilage while the latter adducts it. You should learn the name, origin, insertion, and action of each muscle that you study. This may seem daunting, and it is a lot of material. However, if you examine a muscle, you should be able to figure out its insertion, origin, and action. Knowing these three things can give important clues as to its name. Define each of the following terms with reference to what each type of muscle does at a joint: Extensor – Flexor -­ Abductor – Adductor – Levator – Depressor – Protractor – Retractor – Rotator – 3. Dividing the muscles of the shark The muscles that you are studying in the shark can be divided into basic functional groups. In the trunk, you have two muscle masses on each side that are involved in moving the trunk laterally during swimming. Dorsally is the epaxial musculature and ventrally is the hypaxial musculature. These two masses are separated by the horizontal skeletogenous septum which is a connective tissue sheet that runs laterally from the vertebral column to the dermis. The appendicular musculature is that associated with the fins. Anteriorly, the shark has branchiomeric musculature, or that associated with the gill arches including the jaws, specifically the branchial skeletal elements (ceratobranchials, epibranchials and pharyngobranchials). Finally, hypobranchial musculature is also associated with the gill arches, but ventrally. Attachments of this group tend to be to the basibranchials, ceratobranchials, ceratohyals, basihyal, and hypobranchial.
Looking at the epaxial musculature of the shark, what is the origin, insertion, and action of a myomere? What happens to the shark’s body when a series of myomeres contracts? How might they be used for swimming? From dissecting the fin musculature, explain how the shark moves its pectoral or pelvic fins up and down? Use appropriate anatomical terminology, including insertion, origin, and action. Fill out the following table as you study the shark's muscles. This table will help you to learn the muscles and their origins, insertions, and actions. Muscle Name
Origin
Pelvic/Pectoral adductor Ventral trunk Pelvic Fin musculature Lateral trunk musculature Pelvic Fin Chondrocranium Cucullaris Dorsal to constrictors Levator palatoquadrati Spiracularis Anterior to the spiracle Epibranchial of each branchial arch and scapular process of the pectoral girdle. Pass from Otic capsule to the upper jaw Anterior wall of spiracular valve Levator hyomandibulae Dorsal hyoid constrictor Posterior to the spiracle Between otic capsule and hyomandibular Compress pharyngeal pouches Lies between adductor mandibulae and 1st pharyngeal slit Raphe Extend between raphes assoc with each slit. Compress branchial region Extend between raphes assoc with each slit. Compress branchial region Lie between adductor mandibulae and 1st pharyngeal slit Ventral to levator palatoquadrati and levator mandibulae; posterior to angle of mouth Midventral Raphe Extend between upper and lower jaws Closes the mouth Fibers run posteromedially from mandibular Meckel’s cartilage toward the midline. Extends between the cartilages of the hyoid arch (ceratohyals) Extends between lower jaw and muscles posterior to it w/c attach to coracoid bar Inserts anteriorly to the basihyals Pelvic/Pectoral abductor Epibranchial Dorsal superficial branchial constrictor Ventral superficial branchial constrictor Ventral hyoid constrictor Adductor mandibulae Intermandibularis Interhyoideus Coracomandibuar Coracoarcual Coracohyoid Lying deep thru the intermandibularis. Exposed on reflection of the intermandibularis and interhyoideus Lie medially between the ventral superficial constrictors and anterior to hypaxial muscles Deep to the coracomandibular Insertion
Action
Lift or stabilize upper jaw In the table on the previous page, identify if each muscle is epaxial, hyaxial, appendicular, branchiomeric, or hypobranchial (you can simply use an abbreviation to do this in the margin). Under the headings below, write pairs or groups of muscles that are synergistic and pairs or groups of muscles that are antagonistic from the list in the table on the previous page. Synergistic Muscle Pairs Antagonistic Muscle Pairs