Muscular System 1

1. Muscular System 1 To be copied

2. Types of Muscle Tissue • 3 types: • Skeletal • striated & voluntary • Cardiac • striated & involuntary • Smooth • Smooth & involuntary

3. Skeletal Muscle Tissue • most attached to bone • striations: • see light & dark bands under microscope

4. Cardiac Muscle Tissue • found only in walls of heart chambers • heart has a pacemaker that initiates each contraction • called autorhymicity • controlled by hormones & neurotransmitters

5. Smooth Muscle Tissue • in walls of hollow organs • attached to hair follicles • some autorhythmic (wall of intestines) • regulated by ANS motor neuron& hormones

6. Functions of Muscular Tissue (#4) • 1. producing body movements • moving whole body or parts of body

7. Functions • 2. stabilizing body position • skeletal muscles stabilize joints & halp maintain body positions • postural muscles hold sustained contractions (holding head up all day)

8. Functions • 3. storing & moving substances w/in body • storing: accompanied by sustained contractions of ringlike bands of smooth muscle called sphincters (hold material in organ) • contraction/relaxation of smooth & cardiac muscle moves material thru bld vessels  heart  bld vessels

9. Functions • 4. generating heat • process called thermogenesis • most of heat generated by muscle contraction maintains normal body temp of 37°C • shivering: involuntary contraction of skeletal muscle increases heat production

10. Properties of Muscle Tissue (#4) • 1. electrical excitability • ability to respond to certain stimuli by producing electrical signals called action potentials • 2 main types stimuli: • autorhythmic electrical signals • chemical stimuli (neurotransmitters) released by neurons

11. Properties • 2. contractility • ability of muscle fibers to contract forcefully when stimulated by an action potential • muscle fiber shortens & pulls on whatever it is attached to • if force > resistance of object, movement occurs

12. Properties • 3. extensibility • ability of muscle tissue to stretch w/out being damaged • smooth muscle fibers are stretched every time your stomach or bladder is really full

13. Properties • 4. elasticity • ability of muscle tissue to return to original length & shape after contraction or extension

14. CT Components • fascia: sheet or broad band of fibrous CT that supports & surrounds muscles or other organs • 2 layers: superficial & deep

15. CT Components • 2. 3 layers of CT extend from deep fascia  deeper into muscle tissue • epimysium: outermost layer, encircles entire muscle • perimysium: surrounds groups of 10 – 100 muscle fibers = a fascicle • endomysium: surrounds individual muscle fibers

16. CT Components • 3. tendon: extension of epimysium, perimysium, & endomysium beyond muscle that attaches the skeletal muscle to another structure (bone or another muscle)

17. Muscle Histology Terms • hypertrophy: enlargement of existing muscle fibers • ex: muscle growth in newborn • hyperplasia: increase in # of muscle fibers • ex: growth hormone causes increase in #s from childhood  adult • fibrosis: replacement of muscle by fibrous scar tissue • satellite cells: stem cells in muscle tissue; limited capacity

18. Why Muscle Fibers are Multinucleated

19. Terms for Muscle Fiber Organelles • sarcolemma: plasma membrane • sarcoplasm: cytoplasm • myofibril: contractile organelles; thread-like structures; each extends length of muscle fiber

20. Terms for Muscle Fiber Organelles • T tubules: (transverse) invaginations of sarcolemma into sarcoplasma; increasing surface area • filled with interstitial fluid • ensures action potentials excites all parts of muscle fiber

21. Terms for Muscle Fiber Organelles • sarcoplasmic reticulum: (SR) endoplasmic reticulum that encircles individual myofibrils • dilated end sacs called terminal cistern • T tubule + 2 terminal cisterns = triad • in relaxed muscle fiber SR stores Ca++ • release of Ca++ triggers contraction

22. Muscle Proteins • 3 kinds proteins in myofibrils: • contractile proteins • myosin make up thick filaments, golf-club shape (myosin head) • actin thin filaments • regulatory proteins • tropomyosin &troponin: both in thin filaments • structural proteins • ~12 different ones function in alignment, stability, elasticity, & extensibility of myofibrils

23. Contraction Cycle Steps • ATP hydrolysis • ATP attached to myosin head • attachment of myosin head to actin to form cross bridges • power stroke • cross bridges rotate  center  slides thin filament past thick filament • detachment of myosin from actin • ATP binds to myosin head & cross bridges released

24. Neuromuscular Junction (NMJ) • somatic motor neurons innervate muscle fibers to contract

25. NMJ • synapse: functional junction between 2 neurons or between a neuron & an effector (muscle or gland); may be electrical or chemical • 1st side of synapse: end of axon of motor neuron called synaptic end bulb • then synaptic cleft (the space) • lastly, motor end plate: part of sarcolemma that has receptors for neurotransmitter acetylcholine (ACh)

27. Steps in Nerve Action Potential  Muscle Action Potential • 1. release of ACh • 2. activation of ACh receptors • 3. production of muscle action potential • 4. termination of ACh activity

28. Release of ACh • ACh stored in vesicles in synaptic end bulb • action potential travels down axon  reaches synaptic end bulb  induces exocytosis of neurotransmitter from synaptic vesicles • ACh diffuses across synaptic cleft toward motor end plate

29. Activation of ACh receptors • 2 molecules of ACh bind to ACh receptors embedded in sarcolemma opens ion channel  allows Na+ diffuse across membrane

31. Production of Muscle Action Potential • inflow Na+ makes inside of muscle fiber more + charged • this change in membrane potential triggers a muscle action potential  propagates along sarcolemma  T tubules • this causes SR to release Ca++  sarcoplasm  contraction

32. NMJ • @ midpoint of muscle fiber: • muscle action potential propagate  both ends of fiber • allows simultaneous activation & so contraction of all parts of muscle fiber

33. Curare • South American plant derivative • causes paralysis by binding to & blocking ACh receptors on motor end plates • curare-like drugs used in general anesthesia to relax skeletal muscles

34. Botulism • disease caused by Clostridium botulinum toxin that blocks exocytosis of synaptic vesicles so no ACh released so no muscle contraction • toxin one of most lethal chemicals known • causes death by paralyzing skeletal muscles: breathing stops when diaphragm & intercostal muscles stop contracting

35. Isotonic Contractions • “equal tension” • force of contraction developed by muscle remains almost constant while muscle changes its length • used for body movements & for moving objects • 2 types: • concentric isotonic contraction • eccentric isotonic contraction

36. Concentric Isotonic Contraction • when tension generated is enough to overcome resistance of object being moved …muscle shortens & pulls on another structure (tendon) ….producing movement that reduces angle at a joint

37. Eccentric Isotonic Contraction • tension exerted by the muscle resists movement of the load (whatever was lifted up) slowing the lengthening process

38. Isometric Contraction • tension generated by the muscle is < tension needed to overcome resistance of the object • muscle does not change its length

39. Cardiac Muscle Tissue • same arrangement actin/myosin: striations • muscle fibers branched • *intercalated discs: unique to cardiac muscle • autorhymicity alone: 75 bpm • remains contracted 10-15 x’s longer than skeletal muscle after 1 action potential • due to prolonged delivery of Ca++ (SR + interstitial fluid • larger & more #s of mitochondria

40. Smooth Muscle Tissue • +thick & thin filaments but no T tubules & less SR so no striations

41. Development of Muscle • from mesoderm • starts ~4 wks • cardiac muscle forms tubes  bends & folds to form heart

42. Medical Terminology • spasm: sudden involuntary contraction of a single muscle is a large group of muscles

43. Medical Terminology • tic: an involuntary twitching by muscles that are normally under voluntary control

44. Medical Terminology • tremor: rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement

45. Medical Terminology • fasiculation: involuntary, brief twitch that is visible under the skin; occurring irregularly & not ass’c with movement • seen in MS or ALS

46. Medical Terminology • fibrillation: spontaneous contraction of single muscle fiber that is not visible under skin but can be recorded by EMG (electromyograph) • signals destruction of motor neurons

47. Medical Terminology • muscle strain: tearing of muscle due to forceful impact + bleeding +pain • most often affect quadracepsfemoris • tx‘d RICE (rest, ice, compression ie a wrap, elevation)