1. The Muscular System ANS 215 Anatomy & Physiology of Domesticated Animals

2. Primary Functions Movement Blood Ingesta/excreta Gametes/conceptus Support Generation of body heat

3. Calssifications Smooth No striations Individual cells are spindle shaped with centrally located nuclei Regulated by the autonomic nervous system Located in visceral structures Aggregates of myofilaments are composed of actin and myosin Filaments are not arranged in order

4. Smooth Muscle

5. Classifications Cardiac Found only in the heart Regulated by the autonomic nervous system Shows striations characterized by alternating white and dark bands Composed of elongated, branching cells with irregular contours at junctions with other cells

6. Classifications Cardiac Boundary area where cells meet is called intercalated disk This specialized structure facilitates transmission of nerve impulses Each cell has a nucleus (sometimes 2) that is centrally located

7. Cardiac Muscle

8. Classifications Skeletal Long bundles of cells – striated Multinucleated with nuclei at periphery of cells Innervated by spinal or cranial nerves Three types red or dark (highest myoglobin and mitochondria content) white or pale (lowest myoglobin and mitochondria content) intermediate (characteristics between white and red fibers)

9. Classifications Skeletal Skeletal muscle comprises majority of body muscle mass Skeletal muscle fiber can run the length of the muscle with which it is a part Skeletal muscle fibers do not branch or anastomose

10. Classifications Skeletal Often described according to type of movement performed Flexors – if they are located on the side of the limb towards which the joint decreases the joint angle Extensors – if they are located on the side of the limb towards which the joint increases the joint angle Adductors – if they pull a limb toward the median plane Abductors – if they pull a limb away from the median plane Sphincters – are arranged circularly to constrict body openings

11. Skeletal Muscle

12. Arrangement Function of muscles is to contract or shorten and thereby move an object Primary consideration for accomplishing this goal is arrangement Examples include: Sheets Sheets rolled into tubes Bundles Rings Cones Discrete cells or clusters of cells

13. Arrangement The effects of skeletal muscles (apart from sphincters) are noted some distance from their location This means the contraction must be transmitted One end must be anchored and the other attached directly to a tendon or moveable part Accordingly, anatomic description of a skeletal muscle sometimes refers to its origin and insertion

14. Arrangement

15. Skeletal Muscle Harnessing Harness for skeletal muscle fibers is composed of connective tissue elements Epimysium Perimysium Endomysium Continuous from the individual muscle fibers to the connective tissue structure to which it attaches and on which it exerts its contraction

16. Skeletal Muscle Harnessing Connective tissue elements of skeletal muscle are: Muscle fibers comprise a muscle bundle which are attached by their cell covering (sarcolema) to connective tissue division, endomysium The endomysium is continuous with the connective tissue that envelopes muscle bundles, the perimysium

17. Skeletal Muscle Harnessing The perimysium is continuous with the connective tissue that envelops the muscle (collection of bundles), the epimysium Then epimysium is continuous with the tendon or aponeurosis, which can travel some distance from its attachment

19. Microstructure of Skeletal Muscles Depending on diameter of the muscle fiber, there might be several hundred to several thousand myofibrils within one muscle Each myofibril has striations or banding Myofibrils are further broken into repetitive units (sarcomeres)

20. Microstructure of Skeletal Muscles Sarcomeres contain the protein myofilaments actin and myosin Give rise to striations by their arrangement Sarcomeres of a myofibril are in alignment with the sarcomeres of all the other myofibrils of the muscle fiber The Z line is located at each end of a sarcomere and is common to both sarcomeres that it separates

21. Microstructure of Skeletal Muscles Actin filaments project from the Z line into the sarcomeres that it separates Actin of two sarcomeres common to the same Z line comprise an I band

23. Microstructure of Skeletal Muscles The myosin filaments are centrally located within a sarcomere, coupled with the overlap of actin filaments provide for the dark banding (A band) There is a regular 2:1 ratio of actin to myosin

24. Sarcotubular System Skeletal muscle fibers contain a network of tubules known as the sarcotubular system Tubules are located within the muscle fiber, but outside the myofibrils

25. Sarcotubular System Two tubule sets Arranged transversely (right angles) to myofibrils Open to the outside of fibers contain extracellular fluid Found at boundary of A and I bands each sarcomere has two

27. Neuromuscular Junction Each skeletal muscle fiber is innervated by a motor neuron Axon terminal end bulb forms synapse with muscle fiber Release of Acetylcholine (Ach) causes depolarization One motor neuron innervates many muscle fibers Motor unit Motor unit ration of 1:150 means one nerve fiber supplies 150 muscle fibers Smaller ration increases precision

30. Scanning Electron Micrograph of Neuromuscular Junction

31. Skeletal Muscle Contraction Depolarization of muscle fibers Acetylcholine released into synapse Ca ++ facilitates release Parturient paresis occurs if not enough Ca ++ Opens ligand-coated Na + channels Causes a propagated action potential sarcolema T-tubule sarcoplasmic reticulum Cholinesterase destroys Ach

32. Skeletal Muscle Contraction Depolarization of muscle fibers Depolarization of sarcoplasmic reticulum causes Ca ++ release Ca ++ diffuses to myofibrils Ca ++ initiates contraction Ca ++ pumped back into sarcoplasmic reticulum active transport Ca ++ ATPase Pump