The Muscular System

1. The Muscular System Anatomy & Physiology I Chapter 8

2. Types of Muscle • Smooth • Cardiac • Skeletal

3. Smooth Muscle • Makes up walls of hollow body organs (digestive tract, blood vessel wall), respiratory passageways, uterus, iris • Involuntary movement • Cell structure • Tapered ends • Single, central nucleus • No visible bands (striations) • Stimulated by nerve impulses, hormones, stretching

4. Cardiac Muscle • Makes up wall of heart • Involuntary movement • Cell structure • Branching interconnections • Single, central nucleus • Striated • Membranes are intercalated disks • Stimulated by electrical impulses, nervous stimuli, hormones

5. Skeletal Muscle • Attached to bones, muscles, or skin • Voluntary movement • Cell structure • Long and cylindrical • Multiple nuclei per cell • Heavily striated • Stimulated by nervous system • Number of individual skeletal muscles in the body: 600+

6. The Muscular System Skeletal muscle has three primary functions • Skeletal movement • Posture maintenance • muscles provided a steady partial contraction (muscle tone) of muscles of the thigh, abdomin, back, neck and shoulders • Heat generation • heat is a natural by-product of muscle cell metabolism

7. Structure of a Muscle • Muscle Fiber - one muscle cell • Fascicles - bundles of muscle fibers

8. Structure of a Muscle: Connective Tissue Components • Endomysium – deep layer of connective tissue surrounding indvidual muscle fibers • Perimysium – connective tissue surrounding each fascicle • Epimysium (deep fascia) – connective tissue sheath enclosing an entire muscle • the endomysium, perimysium and epimysium merge to form tendons • Tendon – the band of connective tissue that connect muscle to bone

9. Structure of a Skeletal Muscle Fiber Musclefiber Nucleus A band I band Z disc Mitochondria Openings intotransverse tubules Sarcoplasmicreticulum T riad: T erminal cisternae T ransverse tubule Sarcolemma Myofibrils Sarcoplasm Myofilaments

10. Structure Of A Skeletal Muscle • Structure of a muscle showing the tendon that attaches it to a bone. • Muscle tissue seen under a microscope. Portions of several fascicles are shown with connective tissue coverings. ZOOMING IN • What is the innermost layer of connective tissue in a muscle? • What layer of connective tissue surrounds a fascicle of muscle fibers?

11. Muscle Cells in Action • Motor unit is a single neuron and all the muscle fibers it • Skeletal muscle contraction requires stimulation by a neuron • Paralysis occurs when the damaged nervous system can’t get a signal to the muscles • Neuromuscular junction (NMJ) – the point of contact between a nerve fiber (axon) and a muscle fiber.

12. Neuromuscular Junction (NMJ) • Neurotransmitter – chemical released from neurons • Acetylcholine (Ach) is the neurotransmitter released at the NMJ • Synaptic cleft – tiny space between two cells involved in a synapse • Receptors – specialized structures (on the muscle cell membranes) that can be excited by a stimulus • Motor end plate – muscle cell membrane that contains receptors

13. Neuromuscular Junction (NMJ) • The branched end of a motor neuron makes contact with the membrane of a muscle fiber (cell). • Enlarged view of the NMJ showing release of neurotransmitter acetylcholine (Ach) into the synaptic cleft. • Acetylcholine attaches to receptors in the motor end plate, whose folds increase surface area. • Electron microscope photograph of the neuromuscular junction.

14. Properties of Muscle Tissue • Excitability (ability to respond to stimuli) • Action potential – spreading wave of electrical current • Contractility (ability to shorten when stimulated) • Actin – thin protein filament in muscle cells (light) • Myosin – thick protein filament in muscle cells (dark) • Striations result from the alternating bundles of actin (light) and myosin (dark) filaments • Crossbridge – attachment between myosin head and actin • Sarcomere – contracting subunit of skeletal muscle

15. Sliding Filament Mechanism of Skeletal Muscle Contraction • Muscle is relaxed and there is no contact between the actin and myosin filaments. • Cross-bridges form and the actin filaments are moved closer together as the muscle fiber contracts. • The cross-bridges return to their original position and attach to new sites to prepare for another pull on the actin filaments and further contraction.  ZOOMING IN • Do the actin or myosin filaments change in length as contraction proceeds?

16. The Role of Calcium Calcium • Is released when nerve fiber stimulates muscle cell • Attaches to proteins blocking receptor sites • Allows cross-bridges to form between actin and myosin • Returns to endoplasmic reticulum (ER), which is called “sarcoplasmic reticulum” in muscle cells.

17. Energy Sources Muscle contraction requires energy (ATP), oxidized in muscle cells from • Oxygen • Glucose or other usable nutrient Compounds in muscle cells that store oxygen, energy, or nutrients • Myoglobin – stores oxygen • Glycogen – stores glucose • Creatine phosphate – stores energy; can be used to make ATP

18. Oxygen Consumption • Aerobic glucose metabolism – cellular production of ATP in the presence of adequate oxygen • Anaerobic glucose metabolism – cellular production of ATP in the presence of low, inadequate oxygen • Inefficient production of ATP • Lactic acid accumulation • Oxygen debt – rapid breathing after exercise; replenishes oxygen stores; rid cells of lactic acid • Recovery oxygen consumption – the period after exercise when extra oxygen is needed

19. Effects of Exercise • Improved balance, joint flexibility • Increase in muscle size (hypertrophy) • Improvements in muscle tissue • Vasodilation • Strengthened heart muscle • Improved breathing and respiratory efficiency • Weight control • Stronger bones

20. Types of Muscle Contractions • Muscle Tone (Tonus) – the normal state of balanced tension or partial contraction while a muscle is in a passive state; constant state of readiness for action • Isotonic • No change in tension • Muscle length shortens • Movement • Isometric • Great increase in tension • Muscle length unchanged • No movement

21. Isometric and Isotonic Contractions Muscle develops tension but does not shorten Muscle shortens, tension remains constant Muscle lengthens while maintaining tension Movement Movement No movement (a) Isometric contraction (c) Isotonic eccentric contraction (b) Isotonic concentric contraction

22. The Mechanics of Muscle Movement Tendons attach muscles to bones • Origin—attached to more fixed part of skeleton • Insertion—attached to more moveable part of skeleton

23. Muscle Origins and Insertions • Origin • bony attachment at stationary end of muscle • Belly • thicker, middle region of muscle between origin and insertion • Insertion • bony attachment to mobile end of muscle Origins Origins Humerus Scapula Bellies Extensors: Flexors: Triceps brachii Biceps brachii Long head Brachialis Lateral head Insertion Radius Insertion Ulna

24. Muscles Work Together • action – the effects produced by a muscle • to produce or prevent movement • prime mover (agonist) - muscle that produces most of force during a joint action • synergist - muscle that aids the prime mover • stabilizes the nearby joint • modifies the direction of movement • antagonist - opposes the prime mover • preventing excessive movement and injury

25. Muscle Actions Across Elbow • prime mover - brachialis • synergist - biceps brachii • antagonist - triceps brachii Origins Origins Humerus Scapula Bellies Extensors: Flexors: Triceps brachii Biceps brachii Long head Brachialis Lateral head Insertion Radius Insertion Ulna

26. Skeletal Muscle Groups Characteristics for naming muscles (often combined) • Location • Size • Shape • Direction of fibers • Number of heads (attachment points) • Action

27. Superficial Muscles (anterior view) Associated structure is labeled in parentheses.

28. Superficial Muscles (posterior view) Associated structures are labeled in parentheses.

29. Muscles of the Head • Facial expression (orbicularis) muscles • Orbicularis oculi • Orbicularis oris • Levator palpebrae superioris • Buccinator • Mastication (chewing) muscles • Temporalis • Masseter • Intrinsic • Extrinsic

30. Muscles of the Head Associated structure is labeled in parentheses.   ZOOMING IN •Which of the muscles in this illustration is named for a bone it is near?

31. Muscles of the Neck • Are ribbonlike • Extend up, down, or obliquely • Extend in several layers in a complex manner • Most common is sternocleidomastoid

32. Muscles of the Upper Extremities • Position the shoulder • Move the arm • Move the forearm and hand

33. Muscles That Move the Shoulder and Arm • Trapezius • Latissimus dorsi • Pectoralis major • Serratus anterior • Deltoid • Rotator cuff • Supraspinatus • Infraspinatus • Teres minor • Subscapularis

34. Muscles That Move the Forearm and Hand • Brachialis • Biceps brachii • Brachioradialis • Triceps brachii • Flexor carpi • Extensor carpi • Flexor digitorum • Extensor digitorum

35. Muscles That Move The Forearm & Hand

36. Muscles of the Trunk • Breathing muscles • Abdominal muscles • Pelvic floor muscles • Deep back muscles

37. Muscles of Respiration • Diaphragm • Intercostal muscles

38. Muscles of Respiration Associated structures are also shown.

39. Muscles of the Abdomen and Pelvis • External oblique • Internal oblique • Transversus abdominis • Rectus abdominis • Levator ani

40. Muscles of the abdominal wall Surface tissue is removed on the right side to show deeper muscles. Associated structures are labeled in parentheses.

41. Muscles of the female perineum (pelvic floor) Associated structures are labeled in parentheses.

42. Deep Muscles of the Back • Erector spinae • Deeper muscles in the lumbar area

43. Muscles of the Lower Extremities • Among the longest and strongest in the body • Specialized for locomotion and balance

44. Muscles That Move the Thigh and Leg • Gluteus maximus • Gluteus medius • Iliopsoas • Adductors • Sartorius • Iliotibial (IT) tract • Hamstrings

45. Muscles of the Thigh Associated structures are labeled in parentheses.

46. Muscles That Move the Foot • Gastrocnemius • Achilles tendon • Soleus • Tibialis anterior • Peroneus longus • Flexor and extensor muscles

47. Muscles That Move The Foot Associated structures are labeled in parentheses

48. Effects of Aging on Muscles Beginning at about age 40 • Gradual loss of muscle cells • Loss of power • Tendency to flex hips and knees • Decrease in height

49. Muscular Disorders • Spasms • Colic • Seizure or convulsion • Cramps • Strains • Sprains • Atrophy

50. Diseases of Muscles • Muscular dystrophy • Myasthenia gravis • Myalgia • Myositis • Fibrositis • Fibromyositis • Fibromyalgia syndrome (FMS)