Lab 5: Myology of the Cat

Transcription

1 Lab 5: Myology of the Cat Objectives 1. To gain an understanding of the muscular system of the cat. 2. To learn the insertions, origins and actions of the muscles you study. 3. To study how the muscles of the cat act on the skeletal system to make it move. 4. To learn how the muscles of the cat are subdivided into functional groups. 5. To consider muscle homology and changes in function between the shark and the cat. Material to Learn Cat musculature Figures 7.27 to 7.30, 7.37 Tables 7.2, 7.4 (for only muscles listed in the term list) Associated text: pp OMIT: Figures 7.31 to 7.36, 7.38 OMIT: Table 7.3 OMIT muscles/terms: All hindlimb muscles, all salivary glands (these will be done during the digestive system lab, so keep them intact), muscles of the throat and neck not listed in the included figures. OMIT muscles: erector spinae m., iliocostalis m., longissimus dorsi m., multifidus m., semispinalis m., serratus dorsalis m., teres minor m. Term List Acromiodeltoid m. Acromiotrapezius m. Biceps brachii m. Brachialis m. Brachioradialis m. Clavobrachialis m. Clavotrapezius m. Cleidomastoid m. Coracobrachialis m. Digastric m. Epitrochlearis m. External intercostal m. External oblique aponeurosis External oblique m. Infraspinatus m. Internal oblique m. Latissimus dorsi m. Levator scapulae ventralis m. Linea alba Longissimus capitis Longus colli m. Lumbodorsal fascia Masseter m. Mylohyoid m. Pectoantebrachialis Pectoralis major m. Pectoralis minor m. Rectus abdominis m. Rhomboideus m. Rhomboideus capitis m. Scalenus m. Serratus ventralis m. Spinodeltoid m. Spinotrapezius m. Splenius m. Sternohyoid m. Sternomastoid m. Subscapularis m. Supraspinatus m. Temporalis m. Teres major m. Transversus abdominis m. Transversus costarum m. Triceps brachii m. Lateral head Long head Medial head Xiphihumeralis m. Background & Instructions Today you will begin dissecting the muscles of the cat, Since the cat is skinned, you are looking at the fat and fascia covering its muscles. Fascia must be laboriously removed. The

2 curve tipped forceps are the best tool for this. The scalpel is overly sharp and should not be used. The scissors can be used, but only to snip bits of fascia that aren t coming off the underlying muscle. Remove fascia from muscles until you clearly see the underlying muscle fibers. Clean muscle fibers completely (remove all fascia from muscles that you study). You will find that many of the muscles that you dissect in the cat are elongate. There are also multiple layers of muscles: superficial and deep. You will have to cut through and reflect superficial muscles to get a view of the deep muscles. To do this, first clean the superficial muscle entirely from origin to insertion. Then you can use the scissors to cut through the belly of the muscle, transversely to the muscle fiber direction. Make a clean cut, then fold back the two halves of the muscle to get at the structures underneath. Again, be diligent but patient you can t undo hasty cuts. A good rule of thumb is to never cut through a muscle until you see its origin, insertion, and can deduce its action. Dissecting instructions 1. First, decide on which side of the cat you will dissect the muscles and then stick with that side for the entire activity. This is imperative because it will allow you to more easily dissect the deep muscles and we will use the other side later in the course to dissect blood vessels. 2. Start by cleaning fascia and fat from muscles to reveal their muscle fibers. Use the curved forceps to do this. The easiest place to start is the ventral side - the abdomen (belly) and thorax (chest) (See figure 7.28). Use the bend of the forceps to pinch onto fascia and pull it off. Use the tips of the forceps to tear through fascia, but be careful not to snag and rip muscle. Also, note that there is a lot of fat that can be removed in the groin area, but be careful of the spermatic cords in males which run along the outside of the body wall towards the scrotum. 3. Starting with the ventral side of the thorax, you will find multiple overlapping sheet- like muscles: mm. xiphihumeralis, pectoralis minor, pectoralis major, pectoantebrachialis. Be careful not to tear through these muscles as you clean fascia; the m. xiphihumeralis is particularly thin and delicate. 4. A good sequence for study of the muscles is the thorax and abdomen (fig. 7.28), the back, shoulder and front limb (fig. 7.27), then move to the deep muscles (figs. 7.29, 7.30, and 7.37, in that order), and finally the superficial muscles of the neck (Fig. 7.28), for which you may need to skin more of the cat's head. Due to injection of latex into the blood vessels, you may find that one side of the throat is damaged. Choose the nicer side to dissect the muscles on - for the neck muscles the side doesn't have to match the side that you used for the rest of the muscles. 5. Do not worry that it takes a lot of work to uncover the muscles. As you remove fascia, watch for muscle fibers and muscle edges. Once you find an edge of a muscle, you can carefully use the forceps to separate the muscle from underlying muscles and tissues. Once you have a small separation, widen it along the length of the muscle. Work to separate the

3 muscle completely from its neighbors, so that when you are done, the muscle is attached at its origin and insertion only. At this point, you should also be able to see muscle fiber direction. 6. A useful tip is that if you get frustrated or progress slows in the area you are working, move to a different part of the cat and start dissecting there. Switching between areas moves the dissection forward while minimizing frustration. Also, dissecting in a nearby area can help to loosen up the muscles in the frustrating area, which may then seem easy when you return to it. Dividing the muscles of the cat Just like in the shark, the muscles of the cat can also be divided into functional groupings. Most easily, we can divide the cat s muscles into appendicular, trunk, and head & neck. For some muscles, it may seem ambiguous as to which grouping they belong to. The best way to determine this is to think about what a muscle moves. For example, the sternomastoid m. originates from the manubrium of the sternum and inserts on the mastoid process of the skull, so it is attached to both the head/neck and the trunk. However, since it moves the head, it belongs to the head & neck region. The appendicular muscles can be further subdivided into intrinsic and extrinsic. Intrinsic appendicular muscles are those that both originate and insert on the limb. Extrinsic appendicular muscles insert on the limb but originate from the body/trunk. Muscles in tetrapods are often divided into superficial and deep because this is how they are dissected. This division is one of convenience rather than function or evolutionary origin. Of the muscles that you have to learn over the next three weeks, list those that are appendicular, those that are trunk muscles and those that are head & neck muscles. Appendicular Trunk Head & Neck

4 Of the appendicular muscles that you listed in the previous question, divide them up into intrinsic and extrinsic appendicular muscles. Intrinsic Extrinsic 3. Muscle gross anatomy, attachment, and function Again, work on revealing the muscle fiber direction, then clean each muscle to insertion and origin and confirm its action. Origin, insertion, and action of muscles is already supplied in the lab manual in Tables 7.2 and 7.4. However, to learn the material well, it is important to do the dissection and confirm all of the information for yourself. The cat has more muscles than the shark and muscle fiber direction can differ very slightly between some muscles, leading to different actions - pay close attention to details! Pay closest attention to the front limb. The goal is to have a good functional understanding of the front limb. Review the postcranial osteology of the cat as needed, because all of the small structures you learned on the front limb bones are now important because muscles attach to them. Appreciate the homology between the cat and human muscles and osteology - when you study a muscle in the cat, you can try to contract the same muscle in your body to see what happens. Keep in mind that on an exam, you will be presented with a specimen with a muscle dissected on it. You will have to identify the muscle, its attachments, and its action. Also continue to think about sets of synergistic and antagonistic muscles.

5 Use the space below to write pairs or groups of muscles that are synergistic and those that are antagonistic. Synergistic Muscle Pairs Antagonistic Muscle Pairs 4. Muscle homology Just like other structures, muscles evolve, and over time a situation similar to what you have seen in the shark evolved into what you see in the cat. One thing that you have probably noticed is that, especially in the limbs, the cat has many more muscles than the shark. A common way that new muscles are able to evolve is through duplication: a single muscle splits in two that have the same action. Subsequently, natural selection can act on these two duplicates differently, leading to functionally distinct muscles. This is called differentiation. In many cases, the action remains similar, but not the same. For the branchiomeric muscles of the shark listed on the next page, try to work out the muscles in the cat that they are homologous to.

6 Muscle in the Shark Muscle in the Cat Function Adductor mandibulae Intermandibularis Coracohyoideus Cucularis Hypaxial myomeres Has the function changed in the homologous muscles? If so, how?