1. Muscles and Muscle Tissue Chapter 9

2. Overview of Muscle Tissue n There are three types of muscle tissue –Skeletal muscle –Cardiac muscle –Smooth muscle n These muscle tissues differ in the structure of their cells, their body location, their function, and the means by which they are activated to contract

3. Overview of Muscle Tissue n All muscle cells are elongated cells and are referred to as muscle fibers n Muscle contraction depends on two types of myofilaments, actin and myosin n All prefixes of myo or mys and sarco reference muscle

4. Skeletal Muscle Tissue n Skeletal muscle tissue appear as distinct muscle that attach to the skeletal system n It has obvious striations n It is voluntary muscle under conscious control

5. Cardiac Muscle Tissue n Cardiac muscle occur only in the heart n The muscle is striated but involuntary n Cardiac fibers are short, fat, branched and interconnected n Cardiac muscle cells are interlocked by intercalated discs and function as a single unit

6. Smooth Muscle Tissue n It is found in the walls of hollow organs such as the stomach, urinary bladder, and intestines n It has no striations n It is not subject to voluntary control

7. Differences in Contractions n Skeletal muscle can contract rapidly but tires easily and must be rested –Skeletal muscle contractions vary in force depending on use –Cardiac muscle contracts at a steady rate but can accelerate to cope with demand –Smooth muscle contracts in steady, sustained contractions and continues on tirelessly

8. Muscle Functions n Muscle performs four important functions in the body: –Producing movement –Maintaining posture –Stabilizing joints –Generating heat

9. Producing Movement n Movement results from muscle contraction n Skeletal muscle are responsible for all locomotion and manipulation n Allow to interact or react with your external environment n It controls eye movement, facial expression, circulation, and moves gas, liquids, and solids through organs

10. Maintaining Posture n Skeletal muscles are utilized constantly to maintain sitting, standing, and moving postures n Postural muscle develop to compensate for the never ending pull of gravity –Our developmental milestones as an infant are our initial victories over gravity n Curves of the spinal column are shaped by the interplay of skeletal muscle and gravity

11. Stabilizing Joints n Skeletal muscle provide the dynamic stability of joints n Many joints are poorly reinforced by ligaments and connective tissue n Many joints have noncomplementary surface which do not contribute to stability

12. Generating Heat n Muscles generate heat as they contract n The heat generated is vitally important to maintain normal body temperature n Skeletal muscle generates most of the heat because it represents 40% of body mass n Excess heat must released to maintain body temperature

13. Functional Characteristics n Excitability or irritability –It has the ability to respond to a stimulus n Contractility –It has the ability to shorten forcibly n Extensibility –Muscle fibers can be stretched n Elasticity –Resume its normal length after being shortened

14. Skeletal Muscle

15. Anatomy of a Skeletal Muscle n Each skeletal muscle is a discrete organ with thousands of fibers n Muscle fibers predominate the tissue but it contains, blood vessels, nerve fibers, and connective tissue

16. Connective Tissue Wrappings n Each muscle fiber is wrapped by fine sheath of areolar connnective called endomysium n Several fibers are gathered side by side into bundles called fascicles n Each fascicle is bound by collagen fiber layer called the perimysium

17. Connective Tissue Wrappings n Fascicles are bound by a dense fibrous connective tissue layer called the epimysium n The epimysium surrounds the entire muscle n External to the epimysium is the deep fascia that binds muscles into functional groups

18. Connective Tissue Wrappings n All the connective tissue layers are continuous with one another as well as with the tendons that join muscles to bone n When muscle fibers contract they pull these connective tissue sheaths which in turn transmit the force to the bone to be moved n Connective tissue supports each cell

19. Nerve and Blood Supply n Normal activity of skeletal muscle is totally dependent on its nerve and blood supply n Each skeletal muscle fiber is controlled by a nerve ending n Contracting muscle fibers use huge amounts of energy which requires a continuous supply of oxygen and nutrients n In general, each muscle is served by an artery and one or more veins

20. Attachments n Most muscles span joints and have at least two attachments n Origin –Attachment of a muscle that remains relatively fixed during muscular contraction –Generally a more proximal or axial location n Insertion –Attachment of a muscle that moves during muscular contraction –Generally a more distal or appendicular attachment

21. Attachments n Direct attachments have the epimysium attaching directly to the periosteum of the bone or perichondrium of a cartilage n Indirect attachments have the epimysium attaching to a tendon or an aponeurosis n Temporalis has both muscle attachments

22. The Motor Unit n Each muscle is served by at least one motor nerve which contains hundreds of motor neuron axons n As a nerve enters a muscle it branches into a number of axonal terminals, each of which forms a neuromuscular junction with a single nerve fiber n A motor neuron and all the muscle fibers it supplies is called a motor unit

23. The Motor Unit n When a motor neuron transmits an electrical impulse all the muscle fibers that it innervates respond by contracting n The average number of muscle fibers per unit is 150 but it ranges from 4 to several hundred

24. The Motor Unit n Muscles that exert very fine control have small motor units n Large muscles of locomotion and weight bearing have large motor units and as a consequence have less precise control

25. The Motor Unit n The muscle fibers in a unit are not clustered together but rather are spread throughout the entire muscle n Stimulation of a single unit causes a weak contraction of the entire muscle n This allows control of the intensity of the contraction

26. Smooth Muscles n Smooth muscle lacks the courser connective tissue seen in skeletal muscle n Small amounts of endomysium is found between smooth muscle fibers

27. Smooth Muscles n Smooth muscles are organized into sheets of closely apposed fibers n These sheets occur in the walls of all but the smallest blood vessels and in the walls of hollow organs of the respiratory, urinary digestive and reproductive tracts

28. Smooth Muscles n In most cases two sheets of muscles are present with their fibers aligned at right angle to each other n These forms the longitudinal (long axis) and circular (encircling) layer n These two layers squeeze the contents of the organ

29. End of Chapter Chapter 9