Chapter 12. Muscular System

Transcription

1 Chapter 12 Muscular System

2 What to Know What are the three types of muscle tissue? What are the functions of the muscular system? How are muscles named and what are the muscles of the human body? How are skeletal muscles and muscle fibers structured? How do skeletal muscles contract? How do skeletal muscle cells acquire ATP for contraction? What is rigor mortis? What are some common muscular disorders? What are some serious muscle diseases? How do the skeletal and muscular system help maintain homeostasis? How are these 2 systems related to other systems in maintaining homeostasis?

3 Review: 3 types of muscle tissue Smooth involuntary muscle found in hollow organs and vessels Cardiac involuntary muscle found in the heart Skeletal voluntary muscle that is attached to the skeleton

4 What are the functions of skeletal muscles? 1. Support the body by allowing us to stay upright 2. Allow for movement by attaching to the skeleton 3. Help maintain a constant body temperature 4. Assist in movement in the cardiovascular and lymphatic vessels 5. Protect internal organs and stabilize joints 1. Muscle Function

5 How are skeletal muscles arranged? Attachments: Tendon connective tissue that connects muscle to bone Origin attachment of a muscle on a stationary bone Insertion attachment of a muscle on a bone that moves Bones act as levers in working with skeletal muscles to produce movement Action: Antagonistic muscles that work in opposite pairsprime mover Synergistic muscles working in groups for a common action

6 An example of muscle arrangement

7 Skeletal Muscles Work in Pairs Origin of muscle: attachment of muscle to less moveable bone The biceps contracts and pulls the forearm up, flexing the arm. The relaxed triceps is stretched. (a) Flexion Insertion of muscle: attachment of muscle to more moveable bone Figure 6.1a

8 Skeletal Muscles Work in Pairs The triceps contracts and pulls the forearm down, extending the arm. The relaxed biceps is stretched. (b) Extension Figure 6.1b

9 Examples of how skeletal muscles are named Size the gluteus maximus is the largest buttock muscle Shape the deltoid is triangular (Greek letter delta is Δ) Location the frontalis overlies the frontal bone Direction of muscle fiber the rectus abdominus (rectus means straight) Attachment the brachioradialis is attached to the brachium (arm)and radius Number of attachments the biceps brachii has two attachments Action the extensor digitorum extends the digits

10 Muscles

11 Skeletal Muscles Triceps brachii Straightens arm at elbow Pectoralis major Flexes and rotates arm Serratus anterior Helps raise arm, draws shoulder blade forward; useful in pushing External oblique Assists in lateral twisting of body, compresses abdomen Rectus abdominis Compresses abdomen and chest, bends backbone Adductor longus Rotates thigh laterally, flexes thigh, draws thigh toward body Sartorius Bends lower leg at knee, bends and rotates thigh at hip Quadriceps femoris Flexes thigh at hips, extends leg at knee Tibialis anterior Flexes foot toward knee (a) Front view Figure 6.2a

12 Skeletal Muscles Biceps brachii Bends forearm at elbow, rotates hand Deltoid Raises arm Trapezius Raises, turns, and lowers the shoulder; turns head Latissimus dorsi Rotates and draws arm backwards (toward the body); helps in climbing Gluteus maximus Extends and rotates thigh when walking or climbing Hamstring group Draws thigh backward, bends knee Gastrocnemius Bends lower leg at knee, extends foot away from knee (b) Back view Figure 6.2b

13 Characteristics of Muscles All muscles are excitable, contractile, extensible, and elastic Excitable: respond to stimuli Contractile: shorten Extensible: stretch Elastic: return to their original length after being shortened or stretched

14 Muscle Fiber Arrangement

15 Muscle fibers/cells Terminology for cell structure The plasma membrane is called the sarcolemma The cytoplasm is called the sarcoplasm The SER of a muscle cell is called the sarcoplasmic reticulum (encases myofibrils contractile portions of the mm fibers) and stores calcium T tubules- unique feature of mm cell that penetrate the cell so they contact but do not fuse with expanded portions of the SR which store Ca 2+

16 Terminology For Structure Within A Whole Muscle Muscle fibers are arranged in bundles called fascicles Myofibrils are a bundle of myofilaments that run the length of a fiber Myofilaments are proteins (actin and myosin) that are arranged in repeating units Sarcomeres are the repeating units of actin and myosin found along a myofibril

17 Muscle Fiber Structure Figure 6.3

18 Muscle Arrangement Muscle Fasicles Muscle cell (fiber) Myofibrils» Myofilaments-myosin and actin

19 Visualizing muscle structure

20 Muscle Organization When skeletal muscles are viewed under a microscope, they have distinct bands called striations They are formed by the arrangement of myofibrils within the muscle cell Each myofibril contains groups of long myofilaments Each myofilament is composed of myosin (thick) and actin (thin) filaments Actin filaments are more numerous

21 Sarcomeres Sarcomeres are the contractile units of muscle The ends of each sarcomere are marked by dark protein bands called Z lines Within each sarcomere the actin and myosin filaments are arranged in a specific manner

22 Sacromeres Skeletal muscle consists of many bundles of muscle cells. A bundle of muscle cells is called a fascicle. A muscle cell consists of many myofibrils. (a) A section of a skeletal muscle The striped (striated) appearance of a skeletal muscle cell is due to the regular arrangement of myofilaments. (b) A light micrograph of a longitudinal view of skeletal muscle cells Figure 6.3a b

23 Sacromeres Z line One sarcomere (c) A diagram and electron micrograph of a myofibril Z line One sarcomere Z line Actin Myosin (d) A sarcomere, the contractile unit of a skeletal muscle, contains actin and myosin myofilaments. Figure 6.3c d

24 Made of two protein myofilaments Myosin: are the thick filaments shaped like a golf club Actin: are the thin filaments These filaments slide over one another during muscle contraction Rectangle shape of sarcomere changes into a square The sarcomere

25 The beginning of muscle contraction: The sliding filament model 1. Muscle Filament Arrangement 2. Nerve impulses travel down motor neurons to a neuromuscular junction 3. Acetylcholine (ACh) is released from the neurons and bind to the muscle fibers 4. This binding stimulates fibers causing calcium to be released from the sarcoplasmic reticulum

26 The beginning of muscle contraction

27 Muscle contraction continued 4. Released calcium combines with troponin, a molecule associated with actin 5. This causes the tropomyosin threads around actin to shift and expose myosin binding sites 6. Myosin heads bind to these sites forming cross-bridges 7. ADP and Pi that are already bound to the myosin heads are released and are used as energy to pull the actin filaments towards the center of the sarcomere. This is called the power stroke- contraction now occurs

28 Visualizing the role of calcium and myosin in muscle contraction

29 ATP Resting sarcomere- at the start of the cycle the myosin heads have split (or hydrolyzed ) ATP to ADP and Pi- This splitting of the ATP releases energy which causes the myosin heads to swivel and extend them towards the Z line- cocking the pistol

30 The Role of ATP Step 1: Cross-bridge attachment- myosin heads attach to an actin filament Step 2: Power Stroke- pulling the trigger ADP and Pi which were formed when ATP was hydrolyzed are released Step 3: Cross-bridge detachment- new ATP molecules bind to the myosin heads and are hydrolyzed causing them to disengage from the actin ATP is also needed to get the Ca 2+ back into the sacroplasmic reticulum

31 What role does ATP play in muscle contraction and rigor mortis? So ATP is needed to detach the myosin heads from actin After death muscle cells continue to produce ATP through fermentation and muscle cells can continue to contract When ATP runs out some myosin heads are still attached and cannot detach = rigor hrs. post mortem Body temperature and rigor mortis helps to estimate the time of death

32 Terms in whole muscle contraction Motor unit a nerve fiber (axon) branches (axon terminals) and all of the muscle fibers it stimulates about 150 cells /motor unit fine control: sm. # of cells (eye 1/23) gross control: lg # of cells( gastrocnemius 1/1000) All or none law- All the muscle fibers in a motor unit are stimulated at once (contract or not contract) Muscle twitch when a motor unit is stimulated a single contraction lasting a fraction of a second Summation an increase in muscle contraction until the maximal sustained contraction is reached Recruitment-AS nervous stimuli increases more motor units are activated Tetanus maximal sustained contraction Tone a continuous, partial contraction of alternate muscle fibers causing the muscle to look firm

33 Figure 6.7 (1 of 2)

34 How do we vary strength of contraction 1. Changing the number of muscle cells contracting at any given moment 2. Changing the force of the contraction in individual cells by altering the frequency of stimulation

35 Changing the number of muscle cells contracting at any given moment

36 Physiology of skeletal muscle contraction 40 ms 50 ms 5ms

37 Where are the fuel sources for muscle contraction? Stored in the muscle: Glycogen Fat In the blood: Glucose Fatty acids

38 12.3 Whole muscle contraction What are the sources of ATP for muscle contraction? Limited amounts of ATP are stored in muscle fibers Creatine phosphate pathway (CP) fastest way (1 step) to acquire ATP (inside the filaments)but only sustains a cell for 5 seconds; builds up when a muscle is resting Fermentation fast-acting, used if more than 5 s needed but results in lactate build up Cellular respiration (aerobic) not an immediate source of ATP but the best long term source

39 12.3 Whole muscle contraction Acquiring ATP for muscle contraction

40 Muscle fibers (myosin) come in two forms Fast-twitch fibers: - rely on CP and fermentation (anaerobic) - Designed for strength Light in color - Few mitochondria - Little or no myoglobin - Fewer blood vessels than slow-twitch Slow-twitch fibers: Rely on aerobic respiration Designed for endurance Dark in color Many mitochondria Myoglobin Many blood vessels

41 12.3 Whole muscle contraction Types of muscle fibers

42 Relative Distributions of Slow Twitch & Fact Twitch Myosin Isoforms (Type I & Type II) Type I (slow)/ Type II (fast) Average person 50% /50% Sprinter 20%/ 80% Marathoner 80%/ 20% Couch potato 40% /60% Spinal injury 4%/ 96%

43 Health focus: Benefits of exercise Increases muscle strength, endurance and flexibility Increases cardio-respiratory endurance HDL increases thus improving cardiovascular health Proportion of protein to fat increases favorably May prevent certain cancers : colon, breast, cervical, uterine and ovarian Improve density of bones thus decreasing the likelihood of osteoporosis Enhances mood and may relieve depression

44 Health focus: Exercise

45 Common muscle disorders Spasms sudden, involuntary muscle contractions that are usually painful Seizure multiple spasms of skeletal muscles Cramps strong, painful spasms often of the leg and foot *Strain stretching or tearing of a muscle *Sprain twisting of a joint involving muscles, ligaments, tendons, blood vessels and nerves Tendonitis inflammation of a tendon usually due to overuse (i.e. tennis elbow) Bursitis inflammation of a bursa usually from repetitive use or frequent pressure

46 Ankle sprains are usually caused by rolling the foot inwards

47 Muscular diseases Fibromyalgia chronic achy muscles that is not well understood Muscular dystrophy group of genetic disorders in which muscles progressively degenerate and weaken Myasthenia gravis autoimmune disorder that attacks ACh receptor and weakens muscles of the face, neck and extremities Amyotrophic lateral sclerosis (ALS) commonly known as Lou Gehrig s disease in which motor neurons degenerate and die leading to loss of voluntary muscle movement

48 Homeostasis: the skeletal and muscular systems Both systems are involved with movement that allows us to respond to stimuli, digestion of food, return of blood to the heart and moving air in and out of the lungs Both systems protect body parts Bones store and release calcium need for muscle contraction and nerve impulse conduction Blood cells are produced in the bone Muscles help maintain body temperature

49 How the skeletal and muscular systems interact with other body systems

50 Bioethical focus: Anabolic steroids? Anabolic steroids are a group of steroids that usually increase protein production Most common side effects are high blood pressure, jaundice, acne and great increased risk of cancer Abuse of these drugs may also cause impotence and shrinking of the testicles May lead to increased aggressiveness and violent mood swings Are they worth the risk? Should they be legal to use in athletics?

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52 The Muscular System The muscular system moves our body parts and maintains our posture Most skeletal muscles work in pairs Sacromeres are the contractile units of muscle The strength of muscle contraction depends on the number of motor units stimulated

53 The Muscular System Continued The strength of contraction increases if a muscle is stimulated before it has relaxed ATP for muscle contraction comes from many sources Slow-twitch and fast-twitch muscle cells differ in contraction speed and duration Aerobic exercise increases endurance; resistance exercise builds muscle