7. The Muscular System
Download as PPT, PDF5 likes1,805 views
The document discusses the muscular system. There are three types of muscle: skeletal, cardiac, and smooth muscle. Skeletal muscle is voluntary striated muscle that is attached to bones and controls movement. It has tendons, aponeuroses, and different types of muscle actions including prime movers, antagonists, synergists, and fixators. The document describes the anatomy and functions of muscles throughout the body including the head, neck, abdomen, limbs, and respiratory muscles. It also discusses the microscopic structure of muscle cells and how muscles contract through interactions between actin and myosin fibers.
7. The Muscular System
- 1. The Muscular System Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 2. Learning Objectives List the 3 types of muscles and describe the characteristics of each. Describe the structure and function of tendons, aponeuroses, and ligaments. Differentiate between prime mover, antagonist, syngergist, and fixator muscles. List the locations and actions of the muscles of the head and neck, abdomen, thoracic limb, pelvic limb, and the muscles of respiration. Describe the microscopic anatomy of skeletal, smooth, and cardiac muscle cells. List the components of a neuromuscular junction and describe the function of each. Describe the events that occur in muscle cells during muscle contraction and relaxation. Differentiate between visceral smooth muscle and multiunit smooth muscle Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 3. Muscle One of the four basic tissues of the body Made up of cells that can shorten or contract Three different types of muscle 1. skeletal muscle 2. cardiac muscle 3. smooth muscle Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 4. Skeletal Muscle Gross Anatomy Tendons: fibrous connective tissue bands Aponeuroses: sheets of fibrous connective tissue Origin: the more stable of a muscle's attachment sites Insertion: site that undergoes most of the movement when a muscle contracts Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 5. Muscle Actions Prime mover (agonist): a muscle or muscle group that directly produces a desired movement Antagonist: a muscle or muscle group that directly opposes the action of a prime mover Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 6. Muscle Actions Synergist: a muscle that contracts at the same time as a prime mover and assists it in carrying out its action Fixator: muscles that stabilize joints to allow other movements to take place Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 7. Muscle-Naming Conventions Action: e.g., flexor muscles; extensor muscles Shape: e.g., deltoid means “triangular shaped” Location: e.g., biceps brachii muscle is located in the brachial region Direction of fibers: e.g., rectus means “straight” Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 8. Muscle-Naming Conventions Number of heads or divisions: -cep means “head”; biceps brachii muscle has two heads Attachment sites: e.g., origin of the sternocephalicus muscle is the sternum and insertion is the back of the head Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 9. Cutaneous Muscles Thin, broad, superficial muscles Found in the fascia just beneath the skin Little or no attachment to bones Serve to twitch the skin Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 10. Head and Neck Muscles Functions Control facial expressions Enable mastication Move structures such as eyes and ears Support the head Allow the head and neck to flex, extend, and move laterally Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 11. Head and Neck Muscles Masseter muscle - closes the jaw Splenius and trapezius muscles - extend the head and neck Brachiocephalicus muscle - extends the head and neck; also pulls the front leg forward Sternocephalicus muscle - flexes the head and neck Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 12. Abdominal Muscles Functions Support the abdominal organs Help flex the back Participate in various functions that involve straining Play a role in respiration Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 13. Abdominal Muscles Arranged in layers External abdominal oblique muscle Internal abdominal oblique muscle Rectus abdominis muscle Transversus abdominis muscle Left and right parts of each muscle come together on the ventral midline at the linea alba Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 14. Thoracic Limb Muscles Superficial muscles of the shoulder region Latissimus dorsi muscle - flexes the shoulder Pectoral muscles - one superficial and one deep; adduct the front leg Deltoid muscle - abducts and flexes the shoulder joint Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 15. Thoracic Limb Muscles Brachial muscles Biceps brachii muscle - flexes the elbow joint Triceps brachii muscle - extends the elbow joint Carpal and digital muscles Extensor carpi radialis muscle - extends the carpus Deep digital flexor muscle - flexes the digit Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 16. Pelvic Limb Muscles Gluteal muscles - extensor muscles of the hip “Hamstring" muscle group - extend the hip joint; main flexors of the stifle joint Biceps femoris muscle Semimembranosus muscle Semitendinosus muscle Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 17. Pelvic Limb Muscles Quadriceps femoris muscle - main extensor muscle of the stifle joint Gastrocnemius muscle - extensor muscle of the hock Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 18. Muscles of respiration Function Increase and decrease the size of the thoracic cavity Inspiratory muscles • Diaphragm • External intercostal muscles Expiratory muscles • Internal intercostal muscles • Abdominal muscles Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 19. Skeletal Muscle Cells Very large Multinucleate Numerous myofibrils composed of actin and myosin Network of sarcoplasmic reticulum T tubules Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 20. Skeletal Muscle Cells A bands: thick myosin filaments I bands: thin actin filaments Dark line in the center of the I band is the Z line Disk that is the attachment site for the actin filaments Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 21. Skeletal Muscle Cells Sarcomere - basic contracting unit of skeletal muscle Area from one Z line to the next Z line Each myofibril is made up of many sarcomeres lined up end to end. Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 22. Neuromuscular Junction Nerves and muscles separated by the synaptic space Synaptic vesicles - sacs at the end of a nerve fiber; contain acetylcholine Acetylcholinesterase - enzyme in the synaptic space that removes acetylcholine Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 23. Motor Unit One nerve fiber and all the muscle fibers it innervates Muscles that make small, delicate movements have only a few muscle fibers per nerve fiber in each motor unit Large, powerful muscles may have a hundred or more muscle fibers per motor unit Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 24. Connective Tissue Layers Hold components of the muscle together Contain the blood vessels and nerve fibers that supply the muscle fibers Continuous with tendons or aponeuroses that connect muscle to bones or other muscles Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 25. Connective Tissue Layers Endomysium - composed of fine, reticular fibers; surrounds each muscle fiber Fascicles - groups of skeletal muscle fibers Perimysium - composed of reticular fibers and thick collagen fibers; surrounds fascicles Epimysium - fibrous layer composed of tough collagen fibers; surrounds groups of muscle fascicles Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 26. Initiation of Muscle Contraction & Relaxation Nerve impulse reaches the end bulb of the motor nerve fiber Acetylcholine is released into the synaptic space Acetylcholine molecules bind to receptors on the surface of the sarcolemma Impulse travels along the sarcolemma and through the T tubules to the interior of the cell Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 27. Initiation of Muscle Contraction & Relaxation Impulse reaches the sarcoplasmic reticulum Calcium ions (Ca++) are released into the sarcoplasm Ca++ diffuses into the myofibrils and starts the contraction process Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 28. Initiation of Muscle Contraction & Relaxation Sarcoplasmic reticulum begins pumping Ca++ back in again Ca++ is pulled out of the myofibrils Contraction stops, muscle returns to its original length Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 29. Mechanics of Muscle Contraction Relaxed muscle fibers have actin and myosin filaments that slightly overlap When stimulated to contract, crossbridges on myosin filaments slide back and forth Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 30. Mechanics of Muscle Contraction Actin filaments on both sides are pulled toward the center of the myosin filaments. This shortens the sarcomere. Shortening of all the end-to-end sarcomeres in a muscle fiber results in a muscle contraction. Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 31. Characteristics of Muscle Contraction All-or-nothing principle When stimulated, an individual muscle fiber either contracts completely or not at all. Nervous system controls the number of muscle fibers it stimulates for a particular movement Small, fine movements require only a few muscle fibers to contract. Larger, more powerful movements require contraction of many muscle fibers. Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 32. Muscle Contraction Three phases: 1. Latent phase - time between nerve stimulus and beginning of contraction (about 10 ms) 2. Contracting phase - lasts about 40 ms 3. Relaxation phase - lasts about 50 ms Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 33. Muscle Contraction Maximum contraction efficiency occurs if nerve impulses arrive about 0.1 second apart. Results in a series of complete muscle fiber twitches Careful timing of the nerve impulses to motor units of the muscle is needed to make muscle contract smoothly. Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 34. Chemistry of Muscle Contraction ATP provides energy to allow the sliding of the actin and myosin filaments Creatine phosphate converts ADP back to ATP Glucose and Oxygen - help produce ATP & CP Glucose stored in muscle as glycogen Oxygen stored as myoglobin Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 35. Chemistry of Muscle Contraction Anaerobic metabolism - used if oxygen need exceeds oxygen supply Results in lactic acid formation Lactic acid accumulation causes discomfort Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 36. Heat Production Muscle activity generates heat Panting or sweating - mechanisms to eliminate excess heat Shivering - spasmodic muscle contractions that increase heat production Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 37. Cardiac Muscle Small cells with single nucleus Intercalated disks: attachments between cardiac muscle cells Allow transmission of impulses from cell to cell for coordinated contraction of large groups of cells Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 38. Physiology of Cardiac Muscle Cardiac cells contract without any external stimulation Groups of cardiac muscle cells contract at the rate of the most rapid cell in the group Contractions are rapid and wavelike Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 39. Physiology of Cardiac Muscle Cardiac Conduction System Sinoatrial (SA) node Generates the impulse that starts each heartbeat Located in the wall of the right atrium Impulse follows a controlled path through the conduction system of the heart Structures in the system transmit, delay, and redirect Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 40. Nerve Supply Heart is innervated by nerves from both the sympathetic and parasympathetic systems Sympathetic fibers stimulate the heart to beat harder and faster as part of the "fight or flight response” Parasympathetic fibers inhibit cardiac function, causing the heart to beat more slowly and with less force Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 41. Smooth Muscle Gross Anatomy Two main forms Visceral smooth muscle Large sheets of cells in the walls of some hollow organs Multiunit smooth muscle Small, discrete groups of cells Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 42. Smooth Muscle Cells Small, spindle-shaped; single nucleus Actin and myosin filaments arranged as small contractile units that crisscross the cell Attached at both ends to "dense bodies" that correspond to the Z lines of skeletal muscle Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 43. Visceral Muscle Found in the walls of many internal organs (e.g., stomach, intestines, uterus, urinary bladder) Contracts in large, rhythmic waves Contracts without external stimulation Reacts to stretching by contracting more strongly Innervated by nerves from both the sympathetic and parasympathetic systems Sympathetic stimulation decreases activity; parasympathetic stimulation increases activity Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.
- 44. Multi-Unit Smooth Muscle Individual smooth muscle cells or small groups of cells Found where small, delicate contractions are needed (e.g., iris, walls of small blood vessels) Contraction requires autonomic nervous system impulse Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.