The Muscular System. P. Wilson Human Anatomy & Physiology 1

Transcription

1 The Muscular System P. Wilson Human Anatomy & Physiology 1

2 III. Introduction The 3 types of muscle are: 1. Skeletal (aka: striated, voluntary) 2. Smooth (aka: visceral, involuntary) 3. cardiac Kinds of Tissue Connective Muscle Nervous Blood P. Wilson Human Anatomy & Physiology 2

3 Structure of a Skeletal Muscle B. 1 through 3 1. A skeletal muscle is held in position by layers of fibrous connective tissue called fascia. 2. This tissue extends beyond the end of a skeletal muscle to form a cordlike tendon. 3. When this tissue extends beyond the muscle to form a sheet-like structure, it is called an aponeurosis. P. Wilson Human Anatomy & Physiology 3

4 III. Structure of a Skeletal Muscle 4. Fascicles are bundles of muscle fibers (cells) Thick (myosin) & thin (actin) fibers Myofibrils Muscle fiber (cell) Fascicle Muscle P. Wilson Human Anatomy & Physiology 4

5 III. Structure of a Skeletal Muscle A single muscle fiber (muscle cell) is a thin, elongated cylinder The cell membrane of a muscle fiber is called the sarcolemma The cytoplasm of a muscle fiber is called the sarcoplasm and it contains many nuclei, mitochondria, 7 other cellular structures; also in the sarcoplasm are many myofibrils that lie parallel to each other. Myofibrils are made up of bands of thick myosin fibers and thin actin fibers. P. Wilson Human Anatomy & Physiology 5

6 III. Structure of a Skeletal Muscle Describe the structure & function of a sarcomere. A sarcomere is a structural unit of a myofibril, consisting of a dark band (myosin fibers) and the nearer halves of the two adjacent pale bands (actin fibers). The striations of skeletal muscle are due to the structure of myofibril. P. Wilson Human Anatomy & Physiology 6

7 III. Structure of a Skeletal Muscle Describe the structure & function of a sarcomere. The structure of a sarcomere allows the actin & myosin filaments to slide with respect to each other when stimulated by the presence of ATP & Ca ++ ions. This is called the sliding filament mechanism The contraction of a muscle results from the simultaneous contraction of all of its sarcomeres P. Wilson Human Anatomy & Physiology 7

8 III. Structure of a Skeletal Muscle 3. The network of membranous channels in the cytoplasm/sarcoplasm of muscle fibers is the sarcoplasmic reticulum. A second set of channels is the transverse tubules which extend inward from the fiber s membrane. Each tubule opens to the outside of the fiber. 4. The sarcoplasmic reticulum and the transverse tubules activate the muscle contraction mechanism when the fiber is stimulated. P. Wilson Human Anatomy & Physiology 8

9 IV. Skeletal Muscle Contraction A. Describe the roles of actin & myosin in muscle contraction. Myosin filaments have cross bridges along their length Actin fibers have binding sites for myosin cross bridges The 2 proteins troponin & tropomyosin act together to expose the actin binding sites in response to an influx of Ca 2+ The myosin cross bridges bind to actin filaments, pulling on the actin filaments, causing the sarcomere to shorten (the Z lines are pulled closer together) P. Wilson Human Anatomy & Physiology 9

10 IV. Skeletal Muscle Contraction When a nerve impulse reaches the end of a motor neuron axon, vesicles in the neuron s cytoplasm release acetylcholine (neurotransmitter) into the synaptic cleft between the neuron & the motor end plate of the muscle The action of acetylcholine is halted by the enzyme acetylcholinesterase. P. Wilson Human Anatomy & Physiology 10

11 IV. Skeletal Muscle Contraction C.1. Describe the interaction between acetylcholine & Ca 2+ Acetylcholine stimulates a muscle impulse which passes in all directions over the surface of the muscle fiber, traveling to the sarcoplasmic reticulum & the transverse tubules P. Wilson Human Anatomy & Physiology 11

12 IV. Skeletal Muscle Contraction C.1. Describe the interaction between acetylcholine & Ca 2+ The SR & TT release Ca 2+ ions stimulating the 2 proteins troponin & tropomyosin to expose the binding sites on actin so that the myosin cross-bridges can bind to the actin filaments. P. Wilson Human Anatomy & Physiology 12

13 IV. Skeletal Muscle Contraction A cross bridge is formed when the projecting parts of the myosin filament can occupy a binding site on the actin filament and pull itself along the actin filament. Remember, this pulling causes the sarcomere to shorten. A muscle contraction occurs when all the sarcomeres shorten simultaneously P. Wilson Human Anatomy & Physiology 13

14 IV. Skeletal Muscle Contraction D. 1. ATP (adenosine triphosphate) stores energy in a high-energy chemical bond. When energy is needed for a muscle contraction, an ATP molecule releases energy and is degraded to an ADP (adenosine diphosphate) molecule. ATP Energy + ADP + P P. Wilson Human Anatomy & Physiology 14

15 IV. Skeletal Muscle Contraction Only small amounts of ATP are stored in a muscle so ATP must be regenerated in order for muscle contraction to continue. Creatine phosphate stores energy which can be used to recharge ADP into ATP: Creatine phosphate P. Wilson Human Anatomy & Physiology 15

16 IV. Skeletal Muscle Contraction Oxygen supply & cellular respiration Myoglobin is molecule synthesized in muscle cells that is capable of storing oxygen temporarily. Cellular respiration is an aerobic (requires oxygen) process that releases energy from glucose & forms ATP. In other words, oxygen is necessary for formation of ATP - muscle contraction requires ATP -so oxygen is necessary for muscle contraction. P. Wilson Human Anatomy & Physiology 16

17 IV. Skeletal Muscle Contraction Oxygen supply & cellular respiration In the absence of oxygen, a form of anaerobic respiration called lactic acid fermentation supplies the energy required for muscle contraction. This causes the build up of lactic acid AND as a result your muscles will owe an oxygen debt to the rest of your body. Oxygen debt equals the amount of oxygen required by liver cells to convert accumulated lactic acid into glucose, plus the amount of oxygen muscle cells need to restore ATP & creatine phosphate to their original concentrations. P. Wilson Human Anatomy & Physiology 17

18 IV. Skeletal Muscle Contraction E. Oxygen supply & cellular respiration??? How was lactic acid accumulated? During prolonged, strenuous exercise the muscles so not have sufficient oxygen to do aerobic respiration & must use anaerobic respiration to obtain energy. The anaerobic respiration causes an accumulation of lactic acid in muscles which diffuses into bloodstream & eventually reaches the liver. P. Wilson Human Anatomy & Physiology 18

19 IV. Skeletal Muscle Contraction F. Muscle Fatigue When a muscle is exercised strenuously for a prolonged period it may lose its ability to contract. Causes? Most likely an accumulation of lactic acid as a result of anaerobic respiration; could also be caused by An interruption in the muscle s blood supply, or A lack of acetylcholine in the motor neuron axons Less than half the energy released by cellular respiration is available for metabolic processes. The rest is lost as heat. P. Wilson Human Anatomy & Physiology 19

20 V. Muscular Responses A. 1. Threshold stimulus is the minimum strength needed for a stimulus to produce a muscle contraction. When a muscle fiber is exposed to a single stimulus of threshold strength it will contract once, then relax = twitch 2. All-or-nothing response means that when a muscle contracts, it contracts to its fullest extent; there is no such thing as a partial muscle contraction. P. Wilson Human Anatomy & Physiology 20

21 V. Muscular Responses A. 3. Summation: A muscle fiber receiving a series of stimuli of increasing frequency reaches a point when it is unable to relax completely and the force of individual twitches combine by the process of summation. If the sustained contraction lacks any relaxation, it is called a tetanic contraction. P. Wilson Human Anatomy & Physiology 21

22 V. Muscular Responses A. 4. Recruitment : as the stimulus intensity increases, the number of motor units responding to the stimulus increases (remember that a muscle fiber responds in an all-or-nothing manner). P. Wilson Human Anatomy & Physiology 22

23 V. Muscular Responses Fast-twitch fibers produce strong contractions but easily fatigued are activated during high-intensity exercise that requires strength (ex: weight lifting) Typical people are about 50-50; Olympic sprinters >80% fast twitch; Olympic marathoners >90% slow twitch Slow-twitch fibers are fatigue resistant are activated during lowintensity exercise when endurance is more important than strength (ex: swimming, running) P. Wilson Human Anatomy & Physiology 23

24 V. Muscular Responses Contractions: Sustained Contractions The result of both recruitment and summation produces sustained contractions of increasing strength. Sustained contractions of whole muscles produce the movement necessary to perform everyday functions. P. Wilson Human Anatomy & Physiology 24

25 V. Muscular Responses Contractions: Muscle Tone Muscle tone is a state of continuous partial contractions Even when the muscle is relaxed (appears to be at rest) some of its fibers are contracting. Keeps the muscle firm, healthy, & ready for use Muscle tone is important for maintaining posture. P. Wilson Human Anatomy & Physiology 25

26 V. Muscular Responses D. Contractions: Muscle Tone Loss of muscle tone (if motor neuron is damaged so muscle cannot be stimulated) The muscle becomes: paralyzed flaccid soft & flabby atrophied wastes away P. Wilson Human Anatomy & Physiology 26

27 VI. Smooth Muscles Compare Smooth & Skeletal Muscle Fibers The mechanisms of contractions are the same for both smooth & skeletal muscles. Both have actin & myosin fibers. But Smooth muscle fibers have a more random arrangement of the myosin & actin fibers so that smooth muscle lacks the striated appearance of skeletal muscle. Also, the sarcoplasmic reticulum of smooth muscle is less well-develop that that in skeletal muscle P. Wilson Human Anatomy & Physiology 27

28 VI. Smooth Muscles B. Types of Smooth Muscles Multi-unit Smooth Muscle muscle fibers are separate not organized in sheets Visceral Smooth Muscle muscle fibers are composed of sheets of spindleshaped cells in contact with each other P. Wilson Human Anatomy & Physiology 28

29 VI. Smooth Muscles B. Types of Smooth Muscles Multi-unit Smooth Muscle found in irises of eye and in the walls of blood vessels Visceral Smooth Muscle found in the walls of hollow organs (stomach, intestines, bladder, uterus, intestines) P. Wilson Human Anatomy & Physiology 29

30 VI. Smooth Muscles B. Types of Smooth Muscles Multi-unit Smooth Muscle typically contracts only in response to stimulation by motor nerve impulses or certain hormones Visceral Smooth Muscle Visceral muscle fibers can stimulate other visceral muscle fiber (self-exciting) also display rhythmicity a pattern of repeated contractions These 2 properties allow peristalsis to occur P. Wilson Human Anatomy & Physiology 30

31 Visceral Smooth Muscles & Peristalsis Self-excitation and rhythmicity are largely responsible for a wave-like motion called peristalsis that occurs in certain tubular organs like the intestines. Peristalsis helps force the contents of these organs along their lengths. P. Wilson Human Anatomy & Physiology 31

32 VI. Smooth Muscles: Smooth Muscle Contraction Skeletal muscles One neurotransmitter acetylcholine Smooth Muscles Two neurotransmitters acetylcholine and norepinephrine Each neurotransmitter can stimulate contractions in some muscles and inhibit contractions in others P. Wilson Human Anatomy & Physiology 32

33 VI. Smooth Muscles C.3. Compare Smooth & Skeletal Muscle Contractions Smooth muscle is slower to contract & relax than skeletal muscle Smooth muscle can maintain a forceful contraction longer than skeletal muscle Smooth muscle can change length without changing tautness this means smooth muscles in stomach & intestinal walls can stretch as these organs fill, yet maintain the pressure inside these organs P. Wilson Human Anatomy & Physiology 33

34 VII. Cardiac Muscle: Sarcoplasmic Reticulum The sarcoplasmic reticulum of cardiac muscle is distinctive in 2 ways: larger transverse tubules and less well-developed cisternae that store less calcium. The larger transverse tubules contain calcium obtained from outside the muscle fibers and release larger numbers of calcium ions. This results in a longer cardiac muscle twitch than found on skeletal muscle. P. Wilson Human Anatomy & Physiology 34

35 VII. Cardiac Muscle B. Opposing ends of cardiac muscle fibers are connected by intercalated discs which allow muscle impulses to pass freely so that they travel rapidly from cell-to-cell. C. When one portion of the cardiac muscle is stimulated, the impulse spreads to other fibers of the network and the whole network contracts as a unit (self-excitation & rhythmicity) Cardiac muscle is self-exciting & rhythmic so that it does not require stimulation outside the heart to produce regular periods of contraction & relaxation. P. Wilson Human Anatomy & Physiology 35

36 VIII. Skeletal Muscle Actions A. Muscle Attachments Each muscle has at least two points of attachment to bone: the origin and the insertion. The origin is the end of a skeletal muscle that is immovable (or relatively immovable) The insertion is the end of a skeletal muscle that is movable end. When a muscle contracts, its insertion is pulled toward its origin. P. Wilson Human Anatomy & Physiology 36

37 VIII. Skeletal Muscle Actions B. Muscle Movement The prime mover (aka agonist) is the muscle that provides most of the movement for a particular body movement A synergist is a muscle that contracts and assists the prime mover, making its action more effective. An antagonist is a muscle that can resist a prime mover s action and/or cause movement in the opposite direction. P. Wilson Human Anatomy & Physiology 37

38 VIII. Skeletal Muscle Actions B. Muscle Movement If an agonist and its antagonist contract simultaneously, the part they act upon remains rigid. Smooth body movements depend on antagonists relaxing and giving way to prime movers whenever the prime mover contracts. P. Wilson Human Anatomy & Physiology 38

39 Muscle Functions 1. producing movement- result of contraction 2. maintaining posture- via skeletal muscles overcoming gravity effects while sitting or standing 3. stabilizing joints- pull of skeletal muscles on bones 4. generating heat which is a by-product of muscle activity When ATP is used to provide energy for muscle contraction only about 25% contracts the muscle; the other 75% is released as heat P. Wilson Human Anatomy & Physiology 39

40 Five Golden Rules of Muscle Activity 1. Muscle crosses at least one joint (there are a few exceptions) 2. Bulk of the muscle lies proximal to the joint crossed 3. At least 2 attachments: 4. Only pull NEVER push 5. Insertion moves toward origin during contraction P. Wilson Human Anatomy & Physiology 40

41 Types of Muscle Contractions Isotonic same tone Myofilaments slide past each other so that the muscle contracts AND shortens Isometric same length Myofilaments try to slide past each other but cannot; tension in the muscle keeps increasing = muscle contracts without shortening. (pushing on a wall) P. Wilson Human Anatomy & Physiology 41

42 Skeletal Muscle Actions: Muscle Movement Flexion & Extension are terms that describe changes in the angle where two bones meet: Flexion decreases the angle where 2 bones meet Extension increases the angle where 2 bones meet P. Wilson Human Anatomy & Physiology 42

43 Effects of Exercise on Muscles Aerobic exercise results in stronger, more flexible muscles (NO INCREASE in SIZE) and in muscles with greater resistance to fatigue In other words endurance is increased Resistant Exercise (isometric) Results in an increase in muscle size due to an enlargement of muscle cells AND an increase in number of muscle filaments. P. Wilson Human Anatomy & Physiology 43

44 The name of a muscle: Muscle Names may indicate size &/or location: pectoralis major is located in the pectoral (chest) region and is of large size (minimus, minor, major, maximus); may indicate shape: deltiod is shaped like the Greek letter delta (a triangle); may indicate location & number of origins: biceps brachii has two heads (points of origin) and is located in the arm; external oblique is located near the outside with fibers that run obliquely (at an angle) P. Wilson Human Anatomy & Physiology 44

45 Know these muscles epicranius raises the eyebrow orbicularis oculi closes the eye (winks) orbicularis oris closes & protrudes lips (pucker up!) buccinator compresses cheek inward (whistling) zygomaticus raises corner of mouth (smile) platysma draws angle of mouth downward (frown) masseter closes jaw (chewing muscle) sternocleidomastoid pulls head toward chest (praying muscle) trapezius hyperextends the neck (stargazing muscle) and elevates the scapula (shrugs). P. Wilson Human Anatomy & Physiology 45

46 Know these muscles biceps brachii flexes forearm at elbow & has 2 origins triceps brachii extends forearm at elbow & has 3 origins gastrocnemius - plantar flexion of the foot Kicking Muscles glutes (gluteus maximus, g. minimus, & g. medius Hamstring group Quadriceps femoris group P. Wilson Human Anatomy & Physiology 46

47 Do you use more muscles to smile than to frown? "It takes one more muscle to smile than to frown, according to plastic surgeon David H. Song, MD, FACS, assistant professor at the University of Chicago Hospitals. Only Cecil's "The Straight Dope" got an expert (Dr. Song) to go through the motions. A genuine smile takes two muscles to crinkle the eyes, two to pull up the lip corners and nose, two to elevate the mouth angle, and two to pull the mouth corners sideways. Total smile: 12. On the other hand, a frown needs two muscles to pull down the lips and wrinkles in the lower face, three to furrow the brow, one to purse the lips, one to depress the lower lip, and two to pull the mouth corners down. Total frown: 11. A fake smile, however, only takes two muscles. We detect the fake because "the eyes aren't smiling." P. Wilson Human Anatomy & Physiology 47