The Muscular System

1. The Muscular System Textbook Reference: chapter 6

2. Unit ___ Goals Describe the characteristics and function of skeletal muscle Differentiate between a muscle’s origin and its insertion Identify the microscopic anatomy of skeletal muscle Differentiate between different muscular contractions Define the 4 functional groups of muscles Describe how a muscle is stimulated to contract and the mechanism of muscle shortening Identify the major muscles of the human body

3. Muscles: the machines of the body • Skeletal Muscle Characteristics • Voluntary: move due to a conscious decision • Striated: striped in appearance • Multinucleate: Cells long; more nuclei • More mitochondria for energy production • 500+ muscles, 40-50% body weight

4. Skeletal Muscle Extras • Soft and fragile yet TOUGH • Exerts TREMENDOUS power • Power provided by bundles of muscle fibers wrapped in connective tissue • Connective tissue coverings allows for transmission of blood and nerves to muscles & provides support

5. Functional Characteristics of Skeletal Muscle • Produces movement: for locomotion, manipulation and responding to the external environment; also for expressing emotions • Maintaining posture: works continuously to fight downward pressure of gravity

6. Functional Characteristics of Skeletal Muscle • Stabilizing joints: muscle tendons stabilize and reinforce joints that have poor articulating surfaces • Generating heat: heat is a by-product of muscular activity; maintains normal body temperature

7. Skeletal Muscle Interactions • Muscles are arranged in the body to either work together or work in opposition of each other • Number 1 Rule of Muscle Activity: • MUSCLES ONLY PULL*** THEY NEVER PUSH! • In other words, muscle contractions are caused by SHORTENING of fibers

8. Insertion: the movable attachment of a muscle Examples: biceps tendon attachment to radial tuberosity Origin: the fixed, immovable point of attachment Examples: biceps tendon attachment to greater tubercle Skeletal Muscle Interactions A muscle contraction involves a muscle’s insertion moving toward its origin

9. Origins and Insertions

10. 4 Functional Groups of Skeletal Muscles • 1.) Agonists (prime movers): a muscle that provides the major force for providing a specific movement • Example: biceps brachii- prime mover of elbow flexion

11. 4 Functional Groups of Skeletal Muscles • 2.) Antagonists: muscles that oppose/reverse a movement; relaxed when the agonist is active; helps regulate action of agonist by providing resistance • Can also be agonists • Example: the triceps brachii is the antagonist to the biceps during elbow flexion

12. 4 Functional Groups of Skeletal Muscles • 3.) Synergists: “work together”; aids agonist by promoting the same movement or reducing unnecessary movements that might occur as the agonist contracts • Example: biceps brachii and brachioradialis in elbow flexion

13. 4 Functional Groups of Skeletal Muscles • 4.) Fixators: a synergist that immobilizes a bone or a muscle’s origin • Example: erector spinae (muscles for posture) • All types of muscles work together to provide smooth, coordinated and precise movements. • Any one muscle can be in any functional group, dependant on its action

14. Detailed Skeletal Muscle • Deep fascia: sheet/band of dense connective tissue covering muscles • Epimysium: connective tissue covering many fascicles, all bound together

15. Connective Wrappings of Skeletal Muscle

16. Fascicle: a bundle of fibers wrapped in perimysium Perimysium: connective tissue surrounding a bundle of muscle fibers Endomysium: connective tissue surrounding each muscle fiber Aponeuroses: sheetlike epimysia that connects muscle to each other and to cartilage/bone Detailed Skeletal Muscle

17. Detailed Skeletal Muscle • Tendon: cordlike band of epimysia connecting muscles to bones • Durable and able to cross bony projections • Small in diameter to fit in crowded joint spaces

18. Microscopic Anatomy of Skeletal Muscle • Muscle cell = muscle fiber • Sarcoplasm: cytoplasm of muscle fiber • Sarcolema: plasma membrane of muscle fiber • Sarcoplasmic reticulum: site of calcium storage used for contraction

19. Microscopic Anatomy

20. Microscopic Anatomy of Skeletal Muscle • Sarcomere: contractile units of myofibrils, aligned end-to-end • Myofibril: contractile proteins of muscle cells; lie parallel along length of fiber • Thin myofilaments: actin, tropomyosin and troponin • Thick myofilaments: myosin

21. Microscopic Anatomy of Skeletal Muscle • Z line: separates sarcomeres; where actin filaments attach • I band:light bands; where the actin filaments are aligned; extends to tips of myosin filaments • A band: where the myosin filaments are aligned • H Zone: less dense portion of A band where thin filaments don’t overlap thick filaments

22. Sarcomere

23. Nervous Stimulation of a Muscle Cell • Skeletal muscle cells possess unique abilities: • Excitability: can receive & respond to a stimulus • Contractility: they can shorten • Extensibility: lengthen or stretch • Elasticity: cells return to resting form after contracted or stretched • When a skeletal muscle contracts, it is told to do so by the nervous system

24. Nervous Stimulation of a Muscle Cell • Motor Neuron: nerve extending from spinal cord to muscle fiber • Motor Unit: one motor neuron and all the skeletal muscle cells it stimulates • Neuromuscular Junction: where the end of the nerve and the beginning of the muscle fiber meets • Synaptic cleft: space between nerve and muscle fiber • Motor end plate: highly folded sarcolema; lines synaptic cleft

25. Motor Unit

26. Nervous Stimulation of a Muscle Cell • Neurotransmitter: a chemical that carries a signal from the nerve to the muscle; continues the nervous stimulation • Synaptic Vesicles: sacs at motor end plate that holds ACh • Acetylcholine (ACh): the neurotransmitter specific to muscles • Action Potential: an electrical current that can cause a muscular contraction

27. Nervous Stimulation of a Muscle Cell • The nervous system sends a neural signal to the motor unit. This causes a release of ACh into the neuromuscular junction, where it binds to receptors on the muscle cell. This causes an action potential to run throughout the muscle cell, initiating a muscle contraction.

28. Synaptic Cleft

29. Graded Responses of Skeletal Muscle Contraction • A graded response: the degree of muscle shortening dependant on • 1. The speed of muscle stimulation • 2. The number of muscle cells stimulated

30. Speed of Stimulation • Muscle Twitch: a single, brief contraction caused by a mistake of the nervous system • Summing of Contractions: when nervous impulses are delivered to a muscle at a rapid rate so it can’t relax between impulses; the contractions are summed(added) to create a smooth, strong contraction • Tetanus: no relaxation between contractions; smooth and sustained

31. Number of Cells Stimulated • Small, weak contractions: few cells initiated • Large, strong contractions: all motor units are active and all muscle cells stimulated

32. Types of Skeletal Muscle Contractions • Isotonic: same tone or tension • Myofilaments slide, muscle shortens & movement occurs

33. Types of Skeletal Muscle Contractions • Isometric: same length • Muscles DO NOT shorten • Myosin myofilaments do not move, tension in the fibers build • Muscle tries to move but cannot

34. Energy for Muscle Contractions • There are 3 different energy systems in the body that provide for muscle contractions • Definitions: • Creatine Phosphate (CP): high energy molecule only in muscles which help replenish energy stores • Adenosine Triphoshate (ATP): energy source in the body • Glucose: blood sugar • Glycogen: storage form of blood sugar

35. Energy for Muscle Contractions • Lactic Acid: a byproduct of an anaerobic pathway; causes muscle burning • Aerobic: using oxygen during activity • Anaerobic: not using oxygen during activity

36. Energy Systems • There are 3 ways energy is utilized for muscular activity: • 1. ATP-PC/Rapid Recovery • Anaerobic, lasting no more than 20 seconds • ATP production rate is rapid • ATP stores broken down rapidly and resupplied by creatine phosphate (transfers a phosphate to ADP) • More creatine stored in muscles than ATP

37. Energy Systems • 2. Lactic Acid/Anaerobic • Breaks down glucose for energy without using oxygen • Muscles are working too fast for oxygen & glucose to be delivered by aerobic respiration • Results in build up of lactic acid in muscles: promotes muscle fatigue and soreness

38. Lactic Acid/Anaerobic Continued • Muscle fatigue: when a muscle is unable to contract even though it is still being stimulated. • Oxygen Debt: occurs during prolonged muscle activity; can’t get oxygen fast enough for the muscle’s needs; lactic acid builds up leading to fatigue; repaid by breathing deeply until the muscles receive enough oxygen to get rid of lactic acid and make more ATP and creatine phosphate

39. Energy Systems • 3. Aerobic Respiration • During light exercise, ATP stores are regenerated by using oxygen • Can last for hours if glucose supplies are present • Used in endurance activities

40. Types of Skeletal Muscle Fibers • There are 2 different kinds: • 1. Slow twitch • For endurance • Speed of contraction is slow • Uses aerobic respiration • Low glycogen stores-more fats used • Slow rate of fatigue

41. Types of skeletal muscle fibers • 2. Fast twitch • Explosive movements for short distances • Speed of contraction very fast • Some aerobic, some anaerobic fibers • High glycogen stores but fatigues quickly The distribution of muscle fibers is not complete until the teenage years. It varies between muscles, within muscles and between people.