Presentation is loading. Please wait.

Presentation is loading. Please wait.

Copyright © 2010 Pearson Education, Inc. Three Types of Muscle Tissue 1.Skeletal muscle tissue: Attached to bones and skin Striated Voluntary (i.e., conscious.

Similar presentations


Presentation on theme: "Copyright © 2010 Pearson Education, Inc. Three Types of Muscle Tissue 1.Skeletal muscle tissue: Attached to bones and skin Striated Voluntary (i.e., conscious."— Presentation transcript:

1

2 Copyright © 2010 Pearson Education, Inc. Three Types of Muscle Tissue 1.Skeletal muscle tissue: Attached to bones and skin Striated Voluntary (i.e., conscious control) Powerful Primary topic of this chapter

3 Copyright © 2010 Pearson Education, Inc. Three Types of Muscle Tissue 2.Cardiac muscle tissue: Only in the heart Striated Involuntary More details in Chapter 18

4 Copyright © 2010 Pearson Education, Inc. Three Types of Muscle Tissue 3.Smooth muscle tissue: In the walls of hollow organs, e.g., stomach, urinary bladder, and airways Not striated Involuntary

5 Copyright © 2010 Pearson Education, Inc. Table 9.3

6 Copyright © 2010 Pearson Education, Inc. Special Characteristics of Muscle Tissue Excitability (responsiveness or irritability): ability to receive and respond to stimuli Contractility: ability to shorten when stimulated Extensibility: ability to be stretched Elasticity: ability to recoil to resting length

7 Copyright © 2010 Pearson Education, Inc. Muscle Functions 1.Movement of bones or fluids (e.g., blood) 2.Maintaining posture and body position 3.Stabilizing joints 4.Heat generation (especially skeletal muscle)

8 Copyright © 2010 Pearson Education, Inc. Skeletal Muscle Each muscle is served by one artery, one nerve, and one or more veins

9 Copyright © 2010 Pearson Education, Inc. Skeletal Muscle Connective tissue sheaths of skeletal muscle: Epimysium: dense regular connective tissue surrounding entire muscle Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers) Endomysium: fine areolar connective tissue surrounding each muscle fiber

10 Copyright © 2010 Pearson Education, Inc. Figure 9.1 Bone Perimysium Endomysium (between individual muscle fibers) Muscle fiber Fascicle (wrapped by perimysium) Epimysium Tendon Epimysium Muscle fiber in middle of a fascicle Blood vessel Perimysium Endomysium Fascicle (a) (b)

11 Copyright © 2010 Pearson Education, Inc. Skeletal Muscle: Attachments Muscles attach: Directly—epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage Indirectly (more common) —connective tissue wrappings extend beyond the muscle as a ropelike tendon or sheetlike aponeurosis

12 Copyright © 2010 Pearson Education, Inc. Table 9.1

13 Copyright © 2010 Pearson Education, Inc. Microscopic Anatomy of a Skeletal Muscle Fiber Surrounded by sarcolemma (plasma membrane) Long (huge) cylindrical cells (up to 30 cm!!!) Multiple nuclei Many mitochondria (Why So Many?) Glycosomes (for glycogen storage) & myoglobin (for O 2 storage) Also contain myofibrils, sarcoplasmic reticulum, and T tubules

14 Copyright © 2010 Pearson Education, Inc. Myofibrils Densely packed, rodlike elements (100’s to 1000’s per muscle fiber) Makes up to 80% of muscle cell volume Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands

15 Copyright © 2010 Pearson Education, Inc. NucleusLight I bandDark A band Sarcolemma Mitochondrion (b) Diagram of part of a muscle fiber showing the myofibrils. One myofibril is extended afrom the cut end of the fiber. Myofibril

16 Copyright © 2010 Pearson Education, Inc. 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 responsible for muscle contraction

17 Copyright © 2010 Pearson Education, Inc. 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: coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another H zone: lighter mid-region on either side of the M line. Only seen in resting muscle fibers M line: Found in the center of the H zone, it is a line of protein myomesin (M for middle)

18 Copyright © 2010 Pearson Education, Inc. Figure 9.2c, d I band A band Sarcomere H zone Thin (actin) filament Thick (myosin) filament Z disc M line (c) Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere extends from one Z disc to the next. Z disc M line Sarcomere Thin (actin) filament Thick (myosin) filament Elastic (titin) filaments (d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments.

19 Copyright © 2010 Pearson Education, Inc. Thick Filament (Myosin) Composed of the protein myosin Myosin tails contain: 2 interwoven, heavy polypeptide chains Myosin heads contain: The “Business End” that act as cross bridges during contraction Binding sites for actin of thin filaments Binding sites for ATP ATPase enzymes (split ATP to generate energy)

20 Copyright © 2010 Pearson Education, Inc. Thin Filament (Actin) Composed mostly of protein actin Bears active sites for the cross-bridges (heads of myosin) during contraction Contains tropomyosin and troponin: regulatory proteins bound to actin Elastic filament (made of titan protein) allows muscle to spring back into place

21 Copyright © 2010 Pearson Education, Inc. Figure 9.3 Flexible hinge region Tail Tropomyosin TroponinActin Myosin head ATP- binding site Heads Active sites for myosin attachment Actin subunits Actin-binding sites Thick filament Each thick filament consists of many myosin molecules whose heads protrude at opposite ends of the filament. Thin filament A thin filament consists of two strands of actin subunits twisted into a helix plus two types of regulatory proteins (troponin and tropomyosin). Thin filament Thick filament In the center of the sarcomere, the thick filaments lack myosin heads. Myosin heads are present only in areas of myosin-actin overlap. Longitudinal section of filaments within one sarcomere of a myofibril Portion of a thick filament Portion of a thin filament Myosin molecule Actin subunits

22 Copyright © 2010 Pearson Education, Inc. Sarcoplasmic Reticulum (SR) Network of smooth endoplasmic reticulum surrounding each myofibril Pairs of terminal cisternae (reservoirs) form perpendicular cross channels Regulates calcium - stores and releases Ca+ for contraction (we’ll talk about Ca+ later)

23 Copyright © 2010 Pearson Education, Inc. T Tubules Continuous with the sarcolemma Penetrate the cell’s interior at each A band–I band junction Associate with the paired terminal cisternae to form triads that encircle each sarcomere ***NOTE: A skeletal muscle is very long. T- tubules allow the electrical stimulus and ECF to come in contact with deep regions which makes muscle reaction occur quicker

24 Copyright © 2010 Pearson Education, Inc. Figure 9.5 Myofibril Myofibrils Triad: Tubules of the SR Sarcolemma Mitochondria I band A band H zoneZ disc Part of a skeletal muscle fiber (cell) T tubule Terminal cisternae of the SR (2) M line

25 Copyright © 2010 Pearson Education, Inc. CHECK POINT!!!!! 1.) Which myofilaments have heads that form cross-bridges that are important during contraction? Thick filaments 2.) What surrounds the myofibril and regulates Ca+ needed for contraction? Sarcoplasmic Reticulum

26 Copyright © 2010 Pearson Education, Inc. You have 7 minutes from the time the bell rings…. If you don’t turn it in on time, you don’t get the credit! Briefly explain how actin and myosin work together in the sliding filament model Explain the major role of the sarcoplasmic reticulum (SR), especially the terminal cisternae. What key substance provides the final “go” signal for contraction? Hint: pg 282 What structure works close with the SR and forms a triad relationship?

27 Copyright © 2010 Pearson Education, Inc. Contraction The generation of force Shortening occurs when tension from the cross bridges on the thin filaments pulls the thin filament toward the M line ultimately contracting or shortening the muscle fiber

28 Copyright © 2010 Pearson Education, Inc. Sliding Filament Model of Contraction In the relaxed state, thin and thick filaments only overlap slightly During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line As H zones shorten and disappear, sarcomeres and muscle cells shorten, thus, the whole muscle shortens

29 Copyright © 2010 Pearson Education, Inc. Figure 9.6 I Fully relaxed sarcomere of a muscle fiber Fully contracted sarcomere of a muscle fiber I A ZZ H IIA ZZ 1 2 Sarcomere Contraction Animation

30 Copyright © 2010 Pearson Education, Inc. So now we know how a muscle fiber contracts…but what causes it to contract? 1.Activation: neural stimulation at a neuromuscular junction 2.Excitation-contraction coupling: Creation and increase of an action potential (electrical current) along the sarcolemma Final trigger: a brief rise in intracellular Ca + levels

31 Copyright © 2010 Pearson Education, Inc. Step One- The Activation Step: Takes place at the Neuromuscular Junction Skeletal muscles are stimulated by somatic motor neurons Axons of motor neurons travel from the central nervous system (brain or spinal cord) via nerves to skeletal muscles Each axon forms several branches as it enters a muscle Each axon ending forms a neuromuscular junction with a single muscle fiber

32 Copyright © 2010 Pearson Education, Inc. The axon of each motor neuron divides profusely and forms a neuromuscular junction at each muscle fiber

33 Copyright © 2010 Pearson Education, Inc. Figure 9.8 Nucleus Action potential (AP) Myelinated axon of motor neuron Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber Ca 2+ Axon terminal of motor neuron Synaptic vesicle containing ACh Mitochondrion Synaptic cleft Fusing synaptic vesicles 1 Action potential arrives at axon terminal of motor neuron. 2 Voltage-gated Ca 2+ channels open and Ca 2+ enters the axon terminal. Figure 9.8

34 Copyright © 2010 Pearson Education, Inc. Neuromuscular Junction Situated midway along the length of a muscle fiber Axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft Synaptic vesicles within the axon terminal contain the neurotransmitter acetylcholine (ACh) Junctional folds of the sarcolemma contain ACh receptors

35 Copyright © 2010 Pearson Education, Inc. Events at the Neuromuscular Junction Nerve impulse arrives at axon terminal Voltage sensitive Calcium channels open and release Calcium into the axon terminal Due to increased Calcium levels, ACh is released and binds with receptors on the sarcolemma which triggers electrical events These electrical events lead to the creation of an action potential (electrical current) which spreads down the sarcolemma

36 Copyright © 2010 Pearson Education, Inc. Destruction of Acetylcholine ACh effects are quickly stopped by the enzyme acetylcholinesterase which is located in the synaptic cleft Prevents continued muscle fiber contraction by breaking down Ach into basic “non-stimulating” components

37 Copyright © 2010 Pearson Education, Inc. Figure 9.8 Nucleus Action potential (AP) Myelinated axon of motor neuron Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber Ca 2+ Axon terminal of motor neuron Synaptic vesicle containing ACh Mitochondrion Synaptic cleft Junctional folds of sarcolemma Fusing synaptic vesicles ACh Sarcoplasm of muscle fiber Postsynaptic membrane ion channel opens; ions pass. Na + K+K+ Ach – Na + K+K+ Degraded ACh Acetyl- cholinesterase Postsynaptic membrane ion channel closed; ions cannot pass. 1 Action potential arrives at axon terminal of motor neuron. 2 Voltage-gated Ca 2+ channels open and Ca 2+ enters the axon terminal. 3 Ca 2+ entry causes some synaptic vesicles to release their contents (acetylcholine) by exocytosis. 4 Acetylcholine, a neurotransmitter, diffuses across the synaptic cleft and binds to receptors in the sarcolemma. 5 ACh binding opens ion channels that allow simultaneous passage of Na + into the muscle fiber and K + out of the muscle fiber. 6 ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase.

38 Copyright © 2010 Pearson Education, Inc. Figure 9.9 Na + Open Na + Channel Closed Na + Channel Closed K + Channel Open K + Channel Action potential Axon terminal Synaptic cleft ACh Sarcoplasm of muscle fiber K+K+ 2 Generation and propagation of the action potential (AP) 3 Repolarization 1 Local depolarization: generation of the end plate potential on the sarcolemma K+K+ K+K+ Na + K+K+ W a v e o f d e p o l a r i z a t i o n

39 Copyright © 2010 Pearson Education, Inc. Figure 9.9, step 2 Na + Open Na + Channel Closed K + Channel K+K+ Na + K+K+ Action potential Axon terminal Synaptic cleft ACh Sarcoplasm of muscle fiber K+K+ Generation and propagation of the action potential (AP) 1 Local depolarization: generation of the end plate potential on the sarcolemma 2 1 W a v e o f d e p o l a r i z a t i o n

40 Copyright © 2010 Pearson Education, Inc. Excitation-Contraction (E-C) Coupling Sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments Occurs during latent period: Time between AP initiation and the beginning of contraction

41 Copyright © 2010 Pearson Education, Inc. Events of Excitation-Contraction (E-C) Coupling AP is spread along sarcolemma to the T tubules Voltage-sensitive proteins stimulate the SR to release Ca+ Ca + is necessary for contraction

42 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 1 Axon terminal of motor neuron Muscle fiber Triad One sarcomere Synaptic cleft Setting the stage Sarcolemma Action potential is generated Terminal cisterna of SR ACh Ca 2+

43 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 2 Action potential is propagated along the sarcolemma and down the T tubules. Steps in E-C Coupling: Troponin Tropomyosin blocking active sites Myosin Actin Active sites exposed and ready for myosin binding Ca 2+ Terminal cisterna of SR Voltage-sensitive tubule protein T tubule Ca 2+ release channel Myosin cross bridge Ca 2+ Sarcolemma Calcium ions are released. Calcium binds to troponin and removes the blocking action of tropomyosin. Contraction begins The aftermath

44 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 3 Steps in E-C Coupling: Terminal cisterna of SR Voltage-sensitive tubule protein T tubule Ca 2+ release channel Ca 2+ Sarcolemma Action potential is propagated along the sarcolemma and down the T tubules. 1

45 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 4 Steps in E-C Coupling: Terminal cisterna of SR Voltage-sensitive tubule protein T tubule Ca 2+ release channel Ca 2+ Sarcolemma Action potential is propagated along the sarcolemma and down the T tubules. Calcium ions are released. 1 2

46 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 5 TroponinTropomyosin blocking active sites Myosin Actin Ca 2+ The aftermath

47 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 6 TroponinTropomyosin blocking active sites Myosin Actin Active sites exposed and ready for myosin binding Ca 2+ Calcium binds to troponin and removes the blocking action of tropomyosin. The aftermath 3

48 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 7 TroponinTropomyosin blocking active sites Myosin Actin Active sites exposed and ready for myosin binding Ca 2+ Myosin cross bridge Calcium binds to troponin and removes the blocking action of tropomyosin. Contraction begins The aftermath 3 4

49 Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 8 Action potential is propagated along the sarcolemma and down the T tubules. Steps in E-C Coupling: Troponin Tropomyosin blocking active sites Myosin Actin Active sites exposed and ready for myosin binding Ca 2+ Terminal cisterna of SR Voltage-sensitive tubule protein T tubule Ca 2+ release channel Myosin cross bridge Ca 2+ Sarcolemma Calcium ions are released. Calcium binds to troponin and removes the blocking action of tropomyosin. Contraction begins The aftermath

50 Copyright © 2010 Pearson Education, Inc. 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

51 Copyright © 2010 Pearson Education, Inc. Role of Calcium (Ca 2+ ) in Contraction At higher intracellular Ca + concentrations: Ca + binds to troponin Troponin changes shape and moves tropomyosin away from active sites Events of the cross bridge cycle occur When nervous stimulation stops, Ca + is pumped back into the SR and contraction ends

52 Copyright © 2010 Pearson Education, Inc. Cross Bridge Cycle Continues as long as the Ca+ signal and adequate ATP are present 1. Cross bridge formation—Energized myosin head attaches to actin on the thin filament forming a “cross bridge” 2. Working (power) stroke—ADP and Pi are released and the myosin head pivots and bends (low energy shape), pulling the thin filament toward M line

53 Copyright © 2010 Pearson Education, Inc. Cross Bridge Cycle 3. Cross bridge detachment—ATP attaches to myosin head weakening the link and the cross bridge detaches 4. “Cocking” of the myosin head—energy from hydrolysis of ATP back to ADP and Pi cocks the myosin head into the high-energy state

54 Copyright © 2010 Pearson Education, Inc. Figure Actin Cross bridge formation. Cocking of myosin head. The power (working) stroke. Cross bridge detachment. Ca 2+ Myosin cross bridge Thick filament Thin filament ADP Myosin PiPi ATP hydrolysis ATP 24 3 ADP PiPi PiPi

55 Copyright © 2010 Pearson Education, Inc. Figure 9.12, step 1 Actin Cross bridge formation. Ca 2+ Myosin cross bridge Thick filament Thin filament ADP Myosin PiPi 1

56 Copyright © 2010 Pearson Education, Inc. Figure 9.12, step 3 The power (working) stroke. ADP PiPi 2

57 Copyright © 2010 Pearson Education, Inc. Figure 9.12, step 4 Cross bridge detachment. ATP 3

58 Copyright © 2010 Pearson Education, Inc. Figure 9.12, step 5 Cocking of myosin head. ATP hydrolysis ADP PiPi 4

59 Copyright © 2010 Pearson Education, Inc. Figure Actin Cross bridge formation. Cocking of myosin head. The power (working) stroke. Cross bridge detachment. Ca 2+ Myosin cross bridge Thick filament Thin filament ADP Myosin PiPi ATP hydrolysis ATP 24 3 ADP PiPi PiPi Cross bridge animation

60 Copyright © 2010 Pearson Education, Inc.


Download ppt "Copyright © 2010 Pearson Education, Inc. Three Types of Muscle Tissue 1.Skeletal muscle tissue: Attached to bones and skin Striated Voluntary (i.e., conscious."

Similar presentations


Ads by Google