The Muscular System

1. The Muscular System Chapter 6 (pages 161-200) http://www.healiohealth.com/Images/muscle-spasm.jpg

2. The Muscular System The muscular system provides for movement of the body and its parts, maintains posture, generates heat, and stabilizes joints. http://www.human-anatomy.com/human-anatomy/images/sh000-muscles.jpg

3. Objectives Throughout this chapter, we will cover the following topics: Overview of Muscle Tissues Microscopic Anatomy of Skeletal Muscle Skeletal Muscle Activity Muscle Movements, Types and Names Gross Anatomy of Skeletal Muscles Developmental Aspects of Skeletal Muscles

4. Muscles Muscle tissue makes up the muscles of the body, the majority of the heart, and the walls of hollow organs. Muscle makes up nearly half of the body’s mass. http://www.acantech.com/arnold/gif/arnyarm.jpg The Governator

5. Muscles The essential function of a muscle is contraction, or shortening. Muscles are responsible for all body movement.

6. Muscle Types There are three types of muscle tissue: Skeletal Cardiac Smooth

7. Similarities of Muscles All muscles are elongated Called muscle fibers All muscles contain myofilaments Give muscles the ability to contract

8. Skeletal Muscle Skeletal muscles are: cigar-shaped multinucleate cells Striated in appearance. Under conscious control (voluntary) Found in the skeletal muscles http://www.bishops.k12.nf.ca/science/biology/histology/images/striatedmuscle1.JPG http://www.mdtechacademy.org/web2002/cbeasley/gr/body1.gif

9. Cardiac Muscle Cardiac Muscle Tissue: Appears striated Made of branching cells with intercalated discs Controlled involuntarily by the brain. http://upload.wikimedia.org/wikipedia/commons/b/b7/Humhrt2.jpg

10. Smooth Muscle Smooth Muscle Tissue: Appears without striations. Has a spindle-shape with a single nucleus. Under involuntary control Found in the walls of hollow visceral organs.

11. Muscle Functions Muscle has four important functions: Producing movement Maintaining posture Stabilizing joints Generates heat http://www.freediettips.com/images/women-running.jpg

12. Producing Movement Almost all movements of body are due to muscle contraction. The activity of skeletal muscles are responsible for all locomotion and manipulation. Allows for quick reactions http://www.personal.psu.edu/users/n/a/nac5026/images/tyler%20hansbrough.jpg

13. Maintaining Posture The skeletal muscles work to maintain body posture. Function almost continuously against gravity.

14. Stabilizing Joints Muscle tendons are important for reinforcing and stabilizing joints

15. Generating Heat Heat is a by-product of muscle activity. ATP powers muscle contractions, but ¾ of energy is lost from heat. http://www.mtexpress.com/2003/03-01-08/03-01-08%20Polar%20Bear%20Club%20%201.jpg

16. Skeletal Muscle Anatomy The fibers are bundled together by connective tissue Provides strength Provides support to muscle http://www.mucslemag.com/images/illu_muscle_structure.jpg

17. Skeletal Muscle Anatomy Endomysium Encloses the individual muscle fibers. Perimysium Wraps several muscle fibers together in a fascicle. Epimysium Packages the many fascicles together covering the entire muscle. http://www.askfactmaster.com/images/en/thumb/f/f2/300px-Skeletal_muscle.jpg

18. Skeletal Muscle Anatomy Tendons Blended from the epimysium. If sheetlike, known as aponeuroses. Anchor muscle to bones. Provide durability and conserve space.

19. Microscopic Anatomy of Skeletal Muscle Multinucleated Nuclei pushed to the side to make room for myofibrils Sarcolemma Plasma membrane of muscle cells Striated Alternating Dark and Light Bands http://www.biology.eku.edu/RITCHISO/myofibril.jpg http://www.biology.eku.edu/RITCHISO/301notes3.htm

20. Microscopic Anatomy

21. Microscopic Anatomy Light (I) Band Area of Thin filiments Z-disc = dark area Dark (A) Band Area with both thin and thick filaments H-Zone = lighter area Z Line I A I H Zone

22. Microscopic Anatomy Myofibrils are chains of tiny contractile units called sarcomeres. Measured from Z Line to Z Line The placements of the myofilaments produces the banding pattern. Thick Filaments Thin Filaments http://www.cardiov.ox.ac.uk/images/people/sarcomere.jpg

23. Thick Filaments Myosin filaments Made of bundled molecules of myosin. Contain ATPase enzymes to generate power of contraction. Extend the entire length of dark A band Midparts are smooth Ends have myosin heads (cross bridges) http://webanatomy.net/anatomy/myosin.jpg

24. Thin Filaments Actin filaments are anchored to Z disc. Contains certain proteins that regulate when the mysosin binds with the actin. http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4b/graphics/C4b_actinFilaments.GIF

25. Sarcoplasmic Reticulum Specialized smooth endoplasmic reticulum Interconnecting tubules and sacs of SR surround each myofibril. Stores calcium to release it when the fiber is stimulated to contract.

26. 1 2 3 4 5 What is the name of the plasma membrane of a muscle cell?

27. Skeletal Muscle Activity I think that I should begin lifting my feet, so that I can get to my anatomy class on time. http://bioweb.wku.edu/courses/BIOL115/Wyatt/Neuro/Nervous_system4.gif http://online.morainevalley.edu/WebSupported/BIO112/muscle6.jpg http://www.csus.edu/indiv/w/wickelgren/psyc001/brain_areas2.JPG • To understand how we use our muscles, we must understand how they work. • Muscles have two special functional properties: • Irritability, allowing the muscle to react to stimuli • Contractility, allows the muscle to shorten generating movement. http://academic.wsc.edu/faculty/jatodd1/351/motor_unit.jpg

28. Irritability of Muscles http://academic.wsc.edu/faculty/jatodd1/351/motor_unit.jpg • Motor neurons stimulate the skeletal muscles through electrical stimulus. • A motor unit refers to: • Motor Neuron • All muscle cells connected to that neuron.

29. Irritability of Muscles http://faculty.southwest.tn.edu/rburkett/A&P1%20M11.jpg • Neuromuscular Junction • The axon of the neuron branches into several axonal terminals. • Forms a junction with the sarcolemma of the muscle cells. • Because the muscle and neuron never actually touch, this is called the synaptic cleft.

30. Irritability of Muscles http://www.uccs.edu/~rmelamed/MicroFall2002/Chapter%2018/Neuromuscular%20Junction.jpg • Generating an Action Potential • The brain sends signal down the neuron to tell the muscle to contract. • The impulse reaches the axonal terminal, releasing the neurotransmitter, Acetylcholine (ACh).

31. Irritability of Muscles http://www.protox.co.uk/images/synapse_post.jpg • Generating an Action Potential • ACh diffuses across the synaptic cleft. • Bonds to receptors on the sarcolemma, opening up Na+ channels. • As Na+ rushes into the cell, it creates a positive charge. • The positive charge creates an action potential down the muscle cell.

32. Irritability of Muscles http://programs.northlandcollege.edu/biology/AP1PowerPoint/AP1Muscle2_files/slide0133_image155.jpg • Generating an Action Potential • Once generated, the action potential is unstoppable. • Travels along the surface of the sarcolemma. • Results in a contraction. • To Return to the Resting State: • Potassium ions (K+) will diffuse out of the cell. • Sodium/Potassium Pump will actively transport the ions back to normal concentrations.

33. Contractility of Muscles • Sliding Filament Theory • The action potential releases calcium ions from the sarcoplasmic reticulum. • Causes the thick and thin filaments to slide past each other. • The thin filament is actin. • The thick filament is myosin. • Special proteins cover the actin filament to prevent binding when the cell is at rest.

34. Contractility of Muscles • Sliding Filament Theory • The Ca2+causes the special proteins to move, exposing the myosin binding sites. • The myosin head reaches up to bind to the actin filament. • The myosin head pivots to the inside of the cell. • ATP releases the myosin and recocks the head. • The action repeats, pulling the actin filament inward.

35. Contractility of Muscles • Sliding Filament Theory • The filaments never change length. • As they glide over each other, the sarcomere shortens. • Results in a contraction. • When the AP ends: • Ca2+ is reabsorbed into the SR storage area. • The special proteins return to their position, blocking the myosine binding site. • The muscle relaxes.

36. Muscle Contractions http://www.heavysports.com/emag/curtdennis/sebastianpics/Burnlock1.jpg http://online.morainevalley.edu/WebSupported/BIO112/muscle6.jpg • The All-or-None Principle • The muscle cell will contract completely when stimulated. • The individual cell will never partially contract. • Graded Response • Changes the strength of a contraction by different degrees of shortening. • Muscles are organs made of thousands of muscle cells.

37. Muscle Contractions • Changing the Frequency of Stimulation • A twitch is a brief jerky contraction. • The effects of successive stimulations sum together. • Contractions get stronger and smoother. • Fused Tetanus occurs when the frequency of the stimulus does not allow the muscle to relax.

38. Muscle Contractions • Changing the strength of the stimulus • The force of contraction depends on the number of motor units stimulated. • Few motor units produce small, controlled movements. • All motor units together produce the strongest contraction.

39. Muscle Contractions • Types of Contractions • Concentric contractions result in the shortening of the of the muscle. • Eccentric contractions result in the lengthening of the muscle in a smooth controlled manner. • Isometric contractions occur when the muscle is unable to shorten, muscle length stays the same.

40. Muscle Tone • When relaxed, some muscles fibers continue to contract. • Allows the muscle to remain healthy, firm, and ready for action. • Loss of Muscle Tone • When paralyzed, the muscle loses tone. • Muscle becomes flaccid and begins to atrophy.

41. Energy for Muscles http://users.unimi.it/~samaja/pictures/atp.gif • Because muscle contraction requires ATP, we must regenerate our amount of ATP. • Muscles generally store 4-6 seconds of ATP. • There are several strategies muscles use to replenish their ATP: • Creatine Phosphate • Anaerobic Glycolysis • Aerobic Repiration

42. Energy for Muscles • Creatine Phosphate • For a quick source of energy • Creatine phosphate turns ADP into ATP by inserting the last phosphate group on the end. • CP supplies are exhausted in 15-20 seconds.

43. Energy for Muscles • Anaerobic Glycolysis • Does not require oxygen • Breaks down glucose into pyruvic acid to produce ATP. • When oxygen is not available, produces lactic acid. • Provides 30-60 seconds worth of energy.

44. Energy for Muscles http://www.advantagecourt.com/images/aerobics4.jpg • Aerobic Respiration • Requires oxygen • Breaks down glucose and fats to produce ATP • Provides enough ATP to work for hours.

45. Energy for Muscles http://members.telering.at/photoart/sport/ironman.jpg • Muscle Fatigue • When a muscle is unable to contract even when stimulated. • Results from an Oxygen Debt • A person is unable to bring in enough oxygen to replenish the muscles. • Causes a person to breath deeply to repay the debt. • Lactic Acid Accumulation • Pumped onto the surface of the muscle • Causes a burning sensation and soreness the next day.

46. Muscle Types • Remember, a muscle is an organ of thousands of muscle fibers. • Not all muscle fibers are the same or perform similar functions. • The different types of muscle fibers are: • Fast Twitch (Type II) • Slow Twitch (Type I)

48. Fast Twitch White (Type IIb) http://www.bwgym.com/images/pic_plyometrics_lrg.jpg • Have the fastest response to stimulus with greatest force. • Quick to fatigue because of the low number of mitochondria. • Primarily used in activity with short spurts of energy. • Power lifts, sprints • 30-60 seconds • Require more recovery time to replenish ATP • Creatine and Anaerobic

49. Fast Twitch Red (Type IIa) • Have a medium response rate with a weaker force. • More resistant to fatigue and can work for longer periods of time. • 1 – 30 minutes • Requires less rest • Creatine, Anaerobic and some Aerobic.

50. Slow Twitch (Type 1) • Slowest response rate with long, low force production • Resistant to fatigue because it is filled with mitochondria. • Endurance, marathon • Greater than 30 minutes • Does not require rest to replenish ATP. • Aerobic Respiration