PHYSIOLOGY CHAPTER 9 MUSCLE TISSUE Fall 2016

Transcription

1 PHYSIOLOGY CHAPTER 9 MUSCLE TISSUE Fall Chapter 9 Muscles and Muscle Tissue Overview of Muscle Tissue types of muscle: are all prefixes for muscle Contractility all muscles cells can Smooth & skeletal muscle cells are also called 3 I. Muscle Tissue. a. Only in the. b. Makes up most of the heart. c. Involuntary - no control. d. - has vertical, perpendicular throughout the tissue. e. Cells are w/ 1 or 2. f. Cells are and interconnected by an so they can t. g. Volume vs. 2% in skeletal muscle (chapter 18) 4. Figure: 18.11a & b page: II. Muscle. A. Found in. B.. C. no stripes III. Skeletal Muscle Tissue A. Muscles are packages of muscle tissue wrapped in fascia (CT), connecting one bone to another B. Voluntary: conscious control C. D. 6 Table 9.3; page 309 (physio actin/myosin -?) 7 Skeletal Muscle Gross Anatomy Muscles (organs) made up of tissues A. primary tissue B. vessels. 1. Enter near muscle

2 . 2. Blood vessels when muscles & w/ muscle C. Individual muscles surrounded w/ that goes the muscle interior : ( ) outer layer of 2. : ( ) CT that surrounds bundles of muscle fibers called 3. : ( ) thin, whispy CT surrounds individual /cells All sheaths are w/ one another 9 Fig. 9.1 pg Figure: 9.1b; page Continuous fascia sheets connect w/ of bone. A. : Epimysium to bone. B. Fascia extends beyond muscle to form rope-like or, sheetlike, 12. Microanatomy of skeletal muscle Muscle /muscle Cytoplasm called A. Contains - stored form of Sarcomere B. Contains rod-like 1. Strands of - contractile (functional) unit of 14. Fig. 9.2a; page 280 a. contractile thick ( & thin ( ) b. filaments slide together over the shortening the

3 15. Fig. 9.2b; page Fig. 9.2c; page Fig. 9.2d; page Muscular System - Chapter 10 Interactions between multiple skeletal muscles. Roles of muscles A. Prime mover/ : muscle(s) responsible for a at a joint 19 B. : responsible for movement. 1. Needs to be when prime mover is contracting. 2. role with action. 3. Best to have strength C. :. 1. /smooth out motion. a. force. b. Reduce. c. supraspinatus (rotator cuff) 20 Sarcomere Smallest contractile unit (functional unit) of a muscle fiber The region of a myofibril between two successive Z discs Composed of thick and thin myofilaments made of contractile proteins 21 Features of a Sarcomere Thick filaments: run the entire length of an A band Thin filaments: run the length of the I band and partway into the A band Z disc: sheet of proteins that anchors the thin filaments and connects myofibrils to one another H zone: lighter mid region where filaments do not overlap M line: line of protein myomesin that holds adjacent thick filaments together

4 23 Structure of Thick Filament-myosin Myosin has 2 chains Myosin tails: 2 interwoven, heavy polypeptide chains Myosin heads: 2 smaller, light chains that act as cross bridges during muscle contraction Bind with the actin Binding sites for ATP ATPase enzymes 24 Structure of Thin Filament - actin Double strand of fibrous protein With subunits that the myosin heads attach to during contraction Tropomyosin and troponin: regulatory protein chains wrapped around the actin 26 Sarcoplasmic Reticulum (SR) Network of smooth endoplasmic reticulum that surrounds each myofibril Pairs of terminal cisternae form perpendicular cross channels Functions in the regulation of intracellular Ca 2+ levels 27T Tubules Continuous with the sarcolemma (muscle cell plasma membrane) Penetrate the cell s interior at each A band I band junction Associate with the paired terminal cisternae Cisternae are fluid filled with lots of Ca Triad Relationships T tubules conduct nerve impulses (action potentials) deep into the muscle fiber Impulses go to the cisternae where voltage gated channels open to release Ca++ into the myofibril 30Sliding Filament Model of Contraction actin over myosin In the relaxed state, thin and thick filaments overlap only slightly During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line

5 As H zones shorten and disappear, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens 31 32Requirements for Skeletal Muscle Contraction 1. Activation: neural stimulation at a neuromuscular junction 2. Excitation-contraction coupling: Generation and propagation of an action potential along the sarcolemma Final trigger: a brief rise in intracellular Ca 2+ levels 33Events at the Neuromuscular Junction Skeletal muscles are stimulated by motor neurons Axons of motor neurons travel from the central nervous system via peripheral nerves to skeletal muscles Each axon forms several branches as it enters a muscle Each axon has many terminal endings that forms a neuromuscular junction with a single muscle fiber 34 35Neuromuscular Junction Junction is in the middle of the fiber Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft Synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (ACh) Junctional folds of the sarcolemma contain ACh receptors 36Events at the Neuromuscular Junction Nerve impulse arrives at axon terminal ACh is released and binds with receptors on the sarcolemma Electrical events lead to the generation of an action potential 37 38Destruction of Acetylcholine ACh effects are quickly terminated by the enzyme acetylcholinesterase Prevents continued muscle fiber contraction in the absence of additional stimulation 39 Fig. 9.7a, pg. 285

6 40Events in Generation of an Action Potential 1. Local depolarization (end plate potential): ACh binding, opens chemically/ligand gated ion channels Simultaneous diffusion of Na + (inward) and K + (outward) More Na + diffuses, so the interior of the sarcolemma becomes less negative (mv potential) Local depolarization end plate potential 41Events in Generation of an Action Potential 2. Generation and propagation of an action potential: End plate potential spreads to adjacent membrane areas Voltage-gated Na + channels open Na + influx decreases the membrane voltage toward a critical threshold If threshold is reached, an action potential is generated 42Events in Generation of an Action Potential Local depolarization wave continues to spread, changing the permeability of the sarcolemma Voltage-regulated Na + channels open in the adjacent patch, causing it to depolarize to threshold 43Events in Generation of an Action Potential 3. Repolarization: Na + channels close and voltage-gated K + channels open K + efflux rapidly restores the resting polarity Fiber cannot be stimulated and is in a refractory period until repolarization is complete Ionic conditions of the resting state are restored by the Na + -K + pump

7 49Excitation-Contraction (E-C) Coupling Sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments (actin &myosin) Latent period: Time when E-C coupling events occur Time between AP initiation and the beginning of contraction 50Events of Excitation-Contraction (E-C) Coupling AP is propagated along sarcomere to T tubules Voltage-sensitive proteins stimulate Ca 2+ release from SR Ca 2+ is necessary for contraction Role of Calcium (Ca 2+ ) in Contraction At low intracellular Ca 2+ concentration: Tropomyosin blocks the active sites on actin Myosin heads cannot attach to actin Muscle fiber relaxes 60Role of Calcium (Ca 2+ ) in Contraction At higher intracellular Ca 2+ concentrations: Ca 2+ binds to troponin Troponin changes shape and moves tropomyosin away from active sites

8 Events of the cross bridge cycle occur When nervous stimulation ceases, Ca 2+ is pumped back into the SR and contraction ends 61Cross Bridge Cycle Continues as long as the Ca2+ signal and adequate ATP are present Cross bridge formation high-energy myosin head attaches to thin filament Working (power) stroke myosin head pivots and pulls thin filament toward M line 62Cross Bridge Cycle Cross bridge detachment ATP attaches to myosin head and the cross bridge detaches Cocking of the myosin head energy from hydrolysis of ATP cocks the myosin head into the high-energy state