MUSCULES OF THE BODY HOW THEY WORK

Transcription

1 MUSCULES OF THE BODY HOW THEY WORK

2 Muscles in the Body PROGRAM ANATOMY AND 2

3 Muscles in the Body There are 3 types of muscle tissue in the body: Skeletal Cardiac Smooth All three are specialized to their functions Here are is a video to help you understand the difference: Where are each types of muscle tissue found in the body? 3

4 Muscles in the Body Functions of Skeletal Muscles Produce movement Muscles contract, pulling bones at points of attachment Generate heat Muscle activity generates heat that maintains body temperature Stabilize the body Muscles hold joints in place and prevent dislocation and injury Maintain posture Muscles hold bones in place, allowing body to stand erect 4

5 Skeletal Muscle Histology Skeletal muscles form the flesh of the body. This is the stuff you massage When we eat meat, we are consuming the skeletal muscles of other animals. Each muscle is known as a muscle fiber These cylindrical muscle fibers are arranged parallel to each other The fibers are held in place by connective tissue, which surrounds individual fibers; bundles of muscle fibers and, finally, the entire muscle Three forms of connective tissue hold the muscle cells together: 1. Endomysium the connective tissue that surrounds individual muscle cells (glues adjacent muscle cells together) 2. Perimysium the connective that surrounds each fasciculus 3. Epimysium the connective tissue that surrounds the entire muscle. (The epimysium is different from the deep fascia-whereas the epimysium wraps each skeletal muscle individually, the deep fascia is a continuous sheet that covers the entire body) Fascicles are bundles of muscle fibers surrounded by additional connective tissue (perimysium) 5

6 Skeletal Muscle Histology The epimysium is continuous with a ropelike connective tissue called tendon or in some muscles, connective tissue sheet known as aponeurosis The fleshy part of the muscle that lies between the connective tissue that attaches it to both ends of the bone is known as the muscle belly 6

7 Skeletal Muscle Histology Skeletal Muscle Fibers Each fiber appears striated (light and dark bands) under a microscope The muscle fiber has many cell organelles The cytoplasm is known as the sarcoplasm and is enclosed in a membrane called the sarcolemma The skeletal muscle fiber is multinucleiated Embryonic muscle cells are called myoblasts Here s a video explaining the structure of muscle fibers. And another one. 7

8 Skeletal Muscle Histology Tubule Networks Muscle fiber has numerous tubes that run transversely into the sarcoplasm these are known as T-tubules Inside the sarcoplasm, the T-tubules encircle the myofibrils, which are long, cylindrical structures that extend the entire length of the muscle fiber Hundreds of myofibrils can be seen in each muscle fiber Each myofibril is actually a collection of specialized proteins called myofilaments The activity of myofilaments produces contraction and relaxation of the muscle 8

9 Skeletal Muscles Histology Tubule Networks There is another network of tubules in the sarcoplasm known as the sarcoplasmic reticulum (SR) This network is equivalent to the endoplasmic reticulum of other cells It surrounds individual myofibrils on each side of the T-tubules Close to the T-tubules, SR is enlarged to form an expanded chamber called the terminal cisternae SR contains a high amount of calcium ions that is required for muscle contractions Here s a video to summarize everything 9

10 Skeletal Muscles Histology Filaments Each myofibril is made up of myofilaments, which are regular arrangements of protein filaments Myofilaments, unlike the myofibrils, do not run the entire length of the muscle fiber nut are arranged in smaller sections called sarcomeres The sarcomere is the functional unit of the muscle, and its activity causes the muscle to contract Myofilaments consist of two types of protein: Actin Myosin 10

11 Skeletal Muscles Histology Filaments Because of size, actin is known as the thin filament Myosin is known as the thick filament The thin actin filaments are arranged in such a way that they can slide between the myosin filaments The actin filaments are held in place by protein fibers known as the Z line The myosin filaments are held in place by protein fibers known as the M line The width of the myofibril occupied by actin filaments is the I band The width of myofibril occupied by the myosin filaments is the A band The myosin and actin filaments do not overlap at the center of the A band the A band appears lights, and this is known as the H zone 11

12 Skeletal Muscles Histology Proteins Involved in Contraction The thin actin filament consists of three types of proteins that play a role in muscle contraction: Tropomyosin Troponin Actin molecules-binding sites Actin is interweaving strands of globular proteins, resembling two strings of pearls twisted together Each globular molecule has a site that has an affinity for myosin filaments These sites are covered by tropomyosin Troponin is located at regular intervals on the tropomyosin Troponin holds the tropomyosin in position 12

13 Skeletal Muscle Motor Unit Each muscle fiber is in contact with a nerve ending Skeletal muscle only contracts when stimulated by the communicating nerve The cell body of the nerve fiber is located in the spinal cord, brain stem, or brain (according to where the skeletal muscle is located and where it originated in the embryonic stage) The axons of these neurons extend from the cell bodies to individual muscle fibers in a muscle The axon, it branches, and all of the muscle fibers it supplies are known as a motor unit When a motor neuron is stimulated, all the muscle fibers that is supplies contract simultaneously 13

14 Skeletal Muscle Neuromuscular Junction The region where the nerve ending and the muscle fiber communicate is the neuromuscular junction Here, the nerve ending expands to form a synaptic knob The cytoplasm if the nerve ending has vesicles containing molecules of acetylcholine (ACh), a neurotransmitter A small gap, synaptic cleft, exists between the synaptic knob and the sarcolemma of the muscle fiber The portion of the sarcolemma directly under the synaptic knob is the motor endplate There are receptors that have an affinity for ACh and serve as ion channels that are regulated by ACh The connective tissue matrix in the synaptic cleft has acetylcholinesterase enzymes that can destroy ACh Here s a video explaining it 14

15 Skeletal Muscle Sliding Filament Theory The sliding filament theory mechanism explains the process of muscle contraction at the molecular level The process is initiated by impulses that travel down the nerve that innervates the muscle fibers The impulses result in changes in the neuromuscular junction, which causes the muscle to contract Here s a video about muscle contraction and sliding filament theory Sliding Filament Mechanism Step 1: ACh is released. Step 2: ACh receptors are activated. Step 3: Sodium is released into the sarcoplasm. Step 4: Calcium is released into the sarcoplasm. Step 5: Proteins are activated. Step 6: ATP is broken down to provide energy. Step 7: Calcium is pumped back into the sarcoplasm. 15

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17 More Videos About Muscle Contraction Video 1 Video 2 Video 3 17

18 Skeletal Muscle Muscle Contraction Muscle Twitch The contraction period is the duration of muscle contraction in response to a nerve impulse The relaxation period is the duration taken by the muscle to relax after a contraction The recording of the response of the muscle to a single nerve impulse is known as a muscle twitch For a short time after the first impulse arrives, the muscle is unable to respond to a second stimuli This period is known as the refractory period Latent Period The latent period is the short duration of time that elapses when a muscle responds to a single impulse before the muscle begins to shorten Tetanus A muscle that exhibits a sustained contraction is known as tetanization 18

19 Skeletal Muscle Muscle Fiber Organization Muscle fiber arrangement and direction are important in a muscle s tension direction of movement, and range of motion Five different fasicular arrangement patterns have been identified: Parallel Convergent/triangular Pennate Fusiform Circular 19

20 Skeletal Muscle Muscle Fiber Organization Parallel Parallel muscles have fibers that run parallel to each other along the long axis of the muscle Fusiform These muscles are almost parallel, ending in flat tendons Circular These have fibers that are arranged in a circle around an opening Triangular These muscles have a broad base but attach at a common site Pennate Shaped like feathers Unipennate have fascicles all on the same side of the tendon Bipennate muscles have fascicles on both sides Multipennates are arranged obliquely when the tendon branches 20

21 Muscles as fulcrums and levers A lever is a rigid structure that moves on a fixed point called a fulcrum In the body, the bone is the lever and the joint is the fulcrum Effort (or force) is provided by the contraction of the muscle The first-class lever has the fulcrum in the center and the effort and resistance are located on either side The second-class lever has the resistance in the middle Third-class levers have the effort applied in the center 21

22 Muscle Tone Muscle tone is defined as the resting tension in a muscle Muscle tone is also a result of the viscoelastic property of muscle Tone in a muscle stabilizes the position of bones and joints 22

23 Types of Muscle Contraction A twitch is a single contraction of one muscle cell. There is no such things as a partial contraction of a muscle cell. When a muscle cell is stimulated, it contracts to its fullest or not at all. When a cell receives a stimulus that is just barely strong enough to cause contraction, the cell will contract to its fullest. A stronger stimulus will not cause a stronger contraction. However, the strength of the contraction can vary according to temperature, ph, levels of oxygen, availability of nutrients, etc. Likewise, contraction is stronger when the muscle is allowed to warm up by performing preliminary exercises. 23

24 Skeletal Muscle Muscle Spindles and GTOs Muscle Spindles Muscle tone is maintained by the stimulation of muscle spindles scattered within the muscle They are located parallel to other muscle fibers Their length is altered as the whole muscle stretches or contracts 24

25 Golgi Tendon Organs Golgi tendon organs are located in the tendons They monitor muscle tension GTOs are sensory nerve endings that are wrapped around the collagen fibers of tendons When the muscle contracts, the stretch of the collagen fibers stimulates the GTO, which conveys impulses to interneurons located in the CNS Skeletal Muscle Muscle Spindles and GTOs 25

26 Types of Muscle Contraction Isotonic and Isometric Contractions Isotonic (iso = equal, tonus = tension) Muscle tension is constant while muscle length changes Used in walking and running Two types Concentric: muscle shortens Eccentric: muscle lengthens Isometric (iso = equal, metric = measure) Muscle length is constant while tension varies Example: trying to lift a weight that is too heavy to pick up 26 Here s a video explaining them all!

27 Energy for Skeletal Muscle Contraction Muscle requires energy for contraction to take place That energy is derived from ATP When energy is provided to the muscle without oxygen, this is known as anaerobic metabolism When oxygen is present, it is referred to as aerobic metabolism 27

28 Skeletal Muscles - Muscle Metabolism Muscle requires energy (ATP) to contract Two types of metabolism Aerobic: with oxygen (the process is called the Krebs Cycle or Citric Acid Cycle) Anaerobic: without oxygen (also known as Glycolysis) Demand for energy At rest: low demand for ATP; mitochondria produce surplus ATP Moderate activity: increased demand for ATP; oxygen supplied by blood is sufficient High activity: enormous demand for ATP; glycolysis must provide twothirds of energy needed When the production of pyruvic acid by glycolysis is faster than can be used by the mitochondria, it is converted into lactic acid Video 1 of Krebs Cycle Video 2 of Krebs Cycle Video of Anaerobic Respiration 28

29 Muscle Recovery and Fatigue Muscle Recovery During recovery, the body needs more oxygen than usual This oxygen is used for recovering ATP that was used during muscle contraction The amount of oxygen required to bring the muscle to its pre-exertion level is known as the oxygen debt Until the oxygen debt is repaid, the individual continues to breathe at a much faster rate and depth than normal Muscle Fatigue The muscle may find it difficult to contract, even when stimulated by the nerve This state is known as muscle fatigue The cause of fatigue is varied and depends on the type of activity (interruption to the chain of systems and structures responsible for contraction the CNS, PNS, NMJ, and muscle fiber) 29

30 Muscle Performance Types of Muscle Fibers Fast twitch Respond to stimulus in 0.01 second Large-diameter, huge reserves of glycogen, densely packed myofibrils, few mitochondria Rely largely on anaerobic metabolism Fatigue rapidly Provide speed and strength Used in sprinting Slow twitch Take three times longer to contract than fast twitch Smaller, extensive network of capillaries, numerous mitochondria Contain much myoglobin (red pigment) Rely more on aerobic metabolism Fatigue slowly Provide endurance Used in holding posture Intermediate Have properties of both slow and fast fibers Are pale and contain less myoglobin (like fast fibers) Have more endurance than fast fibers, due to more capillaries Proportion of fiber types Varies from muscle to muscle and person to person Determined genetically, but affected by conditioning 30

31 Summary of the Role of the CNS in Muscle Function Control Neural control mechanisms in CNS affect motor neurons in response to stimuli from internal/external environment Tracts descend from brain to affect spinal motor neurons Spinal motor neurons eventually stimulate muscle fibers Different parts of brain are responsible for different muscle function Neurons from cerebral cortex: discrete movements Neurons from other areas: posture and muscle tone Neurons from cerebellum: coordinate movement 31

32 Exercise and Its Effect on the Muscular System Physical training: Reduces body fat Increases fat-free body mass Improves temperature regulation Increases work capacity Increases sense of well-being Improves transport and use of oxygen Increases size and # of mitochondria and enzymes in muscle fibers Increases capacity to use fat and carbs for energy Increases endurance and physical capability Increases muscle size (hypertrophy) Increases muscle soreness, temporarily Muscles that are not used extensively reduce in size (atrophy) 32

33 Exercise and Its Effect on the Muscular System Cardiovascular adaptations with aerobic training resulting in improved oxygen delivery to muscle 33

34 Exercise and Its Effect on the Muscular System Respiratory Effects Breathing efficiency is improved Changes in respiratory muscles result in reduced use of oxygen for respiration Fatiguing effects of exercise on respiratory muscles is reduced Oxygen is freed for use by active muscles Respiratory rate is reduced during exercise Tidal volume is increased More time is available for oxygen extraction from inspired air 34

35 Exercise and Its Effect on the Muscular System Effects of Overtraining Athlete fails to adapt to training and normal performance deteriorates Athlete has difficulty recovering completely after a workout Symptoms Muscle soreness and stiffness Increased susceptibility to infection GI disturbances Sleep disturbances Loss of appetite Overuse injuries Fatigue Altered reproductive function Mood changes: apathy, depression, irritability 35

36 Exercise and Its Effect on the Muscular System Effects of Failure to Stretch or Warm Up A muscle stretched suddenly or too far results in tearing and bleeding Caused by not stretching and warming up adequately or cold weather Rest, ice, compression, and elevation (RICE) should be used to treat muscle tears Stretching and graded exercises should be started early Complete rest is not advisable in treating tears Stretching promotes correct orientation of collagen fibers 36

37 The Other Muscle Tissues: Cardiac and Smooth Muscle 37

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39 Cardiac Muscle Cardiac Muscle Present in walls of heart Propels blood from chambers Is branched and has intercalated disks that: Hold adjacent cells together Transmit force generated from muscle to muscle Allow many muscle fibers to contract together as if one Looks striated Because the heart must alter its force of contraction according to regional requirements Its contraction is not only regulated by nerves but also by hormones and ionic contents of the blood 39

40 Smooth Muscle Smooth Muscle Spindle-shaped, with no striations due to demand for speed and force of contraction Slower, longer-lasting contractions compared to other muscle tissue Is able to stretch and shorten to a greater extent and still maintain contractile function Has muscle tone Responds to changes in local environment and to hormones, ions, ph, temperature, and stretch Two types: single unit and multiunit 40

41 Muscle Terminology Origin: most stationary point of muscle attachment Insertion: more mobile point of muscle attachment Action: changes produced at joint by muscle contraction Agonist: main muscle producing a particular movement Antagonist: muscle that opposes action of agonist Synergist: muscle that assists agonist in movement Fixator: muscle that stabilizes origin of agonist 41

42 Muscle Terminology Contracture or rigor: muscle shortening Convulsion: abnormal uncoordinated tetanic contraction Cramp: painful muscle spasm Fasciculation: visible, involuntary muscle twitch Fibrillation: asynchronous contraction of fibers Hypertonia: increase in muscle tone Hypotonia: decrease in muscle tone Myalgia: pain originating in muscle 42

43 Muscle Terminology Myoma: tumor of muscle Myositis: inflammation of muscle Repetitive strain injury: muscle pain due to activity Rigidity: muscle spasm of agonists and antagonists Spasm: persistent contraction; can t release voluntarily Spasticity: spasm from excitability of stretch reflex Tic: involuntary spasmodic muscle twitch, usually in face Tremor: repetitive, involuntary, oscillatory movement 43