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  1. 1. Chapter 9 Muscular System PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 10 th edition , edited by S.C. Wache for Biol2064.01
  2. 2. You are responsible for the following figures and tables : Part I. Fine Structure and Function. Tab. 9.2 - Muscular System Function Fig. 9.1 - Muscular System Organs – Fig. 9.2 - 9.11 - Fine structure and function of muscles. Fig. 9.2 - Skeletal muscle organization. Fig. 9.4 – Myofibrils. Fig. 9.6 - Troponin, Tropomyosin, Actin and Myosin. Fig. 9.8 ­ NMJ, neuromuscular junction. Fig. 9.10 - Calcium from the SR binds troponin. Fig. 9.12 – ATP; creatine-phosphate. Fig. 9.13, 9.14 - Oxygen debt. Fig. 9.15 - Muscle twitches can be recorded. Fig. 9.16 - Different types of muscle contractions. See Glossary, p. 994. [see the table in the attached lecture handout]
  3. 3. You are responsible for the following figures and tables : Part II. Skeletal Muscle Identification. [see tables in the attached lecture handout ] Tab. 9.5 - Sternocleidomastoid Fig. 9.24 - Trapezius and Deltoid are named by their shape. Tab. 9.7 - Pectoralis major – Tab. 9.8 - Forearm muscles: Biceps brachii/agonist;Triceps brachii/antagonist. Tab. 9.10 - Muscle of the abdominal wall. Tab. 9.13 - Muscles that move the leg. Tab. 9.14 – Gastrocnemius.
  4. 4. Note: This chapter focuses on skeletal muscle fine structure and skeletal muscle identification. helps move substances through ducts or vessels (i.e. food, urine, semen, blood) walls of visceral hollow organs, irises of eyes, walls of blood vessels involuntary spindle shaped cells with one centrally located nucleus, lacking striations SMOOTH pump blood to lungs and body heart involuntary network of striated cells with a centrally located nucleus; are connected via intercalated discs CARDIAC move bones attached to bones voluntary long, thin, striated muscle fibers / cells with many nuclei SKELETAL FUNCTION LOCATION TYPE OF CONTROL STRUCTURE MUSCLE
  5. 5. Skeletal Muscle (Fig. 9.1) <ul><li>A muscle is composed of skeletal muscle tissue, nervous tissue, blood vessels, and connective tissue. </li></ul><ul><li>Individual muscles are held in place by fascia , dense connective tissue. </li></ul><ul><li>Tendons are extensions of the fascia that connect muscle to bone by intertwining with the fibers in the periosteum of the bone. </li></ul><ul><li>Aponeuroses are sheets of connective tissue that connect muscle to muscle . </li></ul>
  6. 6. <ul><li>Epimysium: connective tissue that surrounds a skeletal muscle. </li></ul><ul><li>Perimysium: connective tissue that extends inward from the epimysium and separates fascicles (bundles of muscle fibers also called muscle cells). </li></ul><ul><li>Endomysium: Connective tissue that separates muscle cells within a fascicle. </li></ul><ul><li>Each muscle cell contains many myofibrils . </li></ul>Skeletal Muscle Structure and Connective Tissue Coverings
  7. 7. Figure 9.2
  8. 8. Skeletal Muscle Fibers (Fig. 9.2) <ul><li>A muscle fiber is a multinucleated muscle cell that attaches to connective tissue. </li></ul><ul><li>Sarcolemma is the muscle cell membrane. </li></ul><ul><li>Sarcoplasm is the cytoplasm containing nuclei, mitochondria, and myofibrils. </li></ul><ul><li>Myofibrils are composed of protein filaments, predominantly myosin and actin. </li></ul>
  9. 9. Protein Filaments <ul><li>Myosin: Thick filament of twisted protein strands with globular ends called cross-bridges. </li></ul><ul><li>Actin: Thin filament protein which can be found in a complex with two other muscle proteins, tropomyosin and troponin . </li></ul><ul><li>The close association of these proteins makes muscle contraction possible. </li></ul><ul><li>Organization of these protein filaments leads to light and dark striations seen in skeletal muscle under the light microscope which denote each sarcomere . </li></ul>
  10. 10. Figure 9.6 Thin and Thick Filaments
  11. 11. Sarcomere Structure <ul><li>Striations form a repeating pattern along the </li></ul><ul><li>muscle fiber called sarcomeres. </li></ul><ul><li>Z Line – separates sarcomeres. </li></ul><ul><li>I bands (light bands) are composed of actin filaments attached to Z lines. </li></ul><ul><li>A bands (dark bands) are composed of myosin overlapping actin attached to Z lines by titin. </li></ul><ul><li>A central region ( H zone ) consists of myosin only with a thick line, the M line . </li></ul>
  12. 12. Figure 9.4
  13. 13. Intracellular Structure of Muscle <ul><li>Sarcoplasmic reticulum: network of membranous sacs surrounding myofibrils. </li></ul><ul><li>Transverse tubules (T-tubules) extend deep into the sarcoplasm and contain extracellular fluid. These transverse tubules allow a multinucleated muscle fiber to be stimulated simultaneously . </li></ul><ul><li>Cisternae: enlarged portions of the sarcoplasmic reticulum. </li></ul><ul><li>These three structures form a triad where the actin and myosin overlap. </li></ul>
  14. 14. Figure 9.7- Sarcoplasm content of a muscle cell = muscle fiber
  15. 15. <ul><li>Motor neuron axons join the skeletal </li></ul><ul><li>muscle at the neuromuscular junction . </li></ul><ul><li>Neurotransmitters are chemicals stored in vesicles of the motor neuron axon. Acetylcholine controls skeletal muscle contraction. </li></ul><ul><li>Motor end plate is a specialized region of the sarcolemma at the neuromuscular junction. </li></ul><ul><li>Synaptic cleft is a space between the neuron and the motor end plate. </li></ul><ul><li>A a motor unit consists of the motor neuron and the muscle fibers it controls. </li></ul>Events of Muscle Contraction
  16. 16. Figure 9.9 – Neuromuscular Junction
  17. 17. Figure 9.9
  18. 18. Molecular Events of Muscle Contraction <ul><li>Motor neuron axon releases acetylcholine. </li></ul><ul><li>Acetylcholine diffuses across synaptic cleft. </li></ul><ul><li>This stimulates the sarcolemma. The impulse travels over the muscle fiber surface and down the T-tubules to the sarcoplasmic reticulum (SR). </li></ul><ul><li>Calcium ions diffuse out of the SR into the sarcoplasm and bind to troponin. </li></ul><ul><li>Tropomyosin moves and exposes sites on actin filaments. </li></ul><ul><li>Actin and myosin form linkages. </li></ul><ul><li>Actin filaments are pulled inward by myosin cross-bridges ( sliding filament theory ). </li></ul><ul><li>Muscle fibers shorten as contraction occurs. </li></ul>
  19. 19. Figure 9.10 – a) resting relaxed muscle; b) excited contracted muscle. Note the change in the actin/ troponin/ tropomyosin complex by binding of Ca 2+
  20. 20. Figure 9.12 – Sliding filament theory explains how actin moves along myosin filament thereby causing the shortening of the muscle.
  21. 21. <ul><li>It explains how actin moves along myosin filament thereby causing the shortening or contraction of the muscle. </li></ul><ul><li>See Fig. 9.11 to envision the shortening of muscle in the course of actin sliding or walking alongside the myosin thick filament as it makes a bond with a myosin head, then breaks it, then remakes it with the next myosin head. </li></ul><ul><li>Imagine how tension and muscle strength increase as the muscle shortens . </li></ul>Sliding Filament Theory
  22. 22. Events of Muscle Relaxation <ul><li>Acetylcholine is degraded by the enzyme acetylcholine-esterase and the muscle is no longer stimulated. </li></ul><ul><li>Calcium ions are actively transported back into the SR . </li></ul><ul><li>Actin-myosin linkages break. </li></ul><ul><li>Troponin and tropomyosin cross-bridges reform. </li></ul><ul><li>Troponin and tropomyosin interaction inhibits the interaction between myosin and actin. </li></ul>
  23. 23. Energy Sources <ul><li>ATP , generated by cellular respiration, is enough for a brief contraction. </li></ul><ul><li>In the mitochondria, excess energy is stored as creatine phosphate. </li></ul><ul><li>Creatine Phosphate has a high energy phosphate bond that can regenerate ATP from ADP (ADP + P ATP). Creatinine is excreted in the urine. </li></ul><ul><li>It is generated by phosphokinase when there is excess ATP. </li></ul><ul><li>Muscles store excess glucose, needed for cellular respiration, in the form of glycogen in muscle tissue and liver . </li></ul>
  24. 24. Figure 9.12
  25. 25. Oxygen and Cellular Respiration <ul><li>Initially, oxygen is transported bound to blood hemoglobin inside RBC in the lung. </li></ul><ul><li>In muscle tissue, it is transferred to myoglobin , an oxygen binding protein found in muscle. </li></ul><ul><li>Glycolysis: early phase of metabolism that partially breaks down glucose and does not require oxygen (anaerobic phase). </li></ul><ul><li>Citric acid cycle: complete breakdown of glucose which requires oxygen (aerobic phase). </li></ul>
  26. 26. Oxygen Debt <ul><li>During strenuous exercise there may not be enough oxygen to maintain aerobic metabolism. </li></ul><ul><li>Anaerobic metabolism maintains ATP levels while lactic acid= lactate levels increase. </li></ul><ul><li>This causes muscle cramps . </li></ul><ul><li>Fig. 9.14 - Liver cells convert lactic acid to glucose using ATP energy. </li></ul><ul><li>Definition oxygen debt: It is the amount of oxygen needed for the liver to convert the accumulated lactic acid into glucose. </li></ul>
  27. 27. Muscle Fatigue <ul><li>Fatigue occurs when a muscle is exercised for a prolonged period and loses its ability to contract. </li></ul><ul><li>It is often due to lactic acid accumulation that lowers pH and prevents muscle fibers from responding. </li></ul><ul><li>It can also be caused by decreased blood flow, ion imbalances, and psychological causes. </li></ul><ul><li>Cramps can occur with fatigue: decreased electrolyte concentrations trigger uncontrolled stimulation . </li></ul><ul><li>Physically fit people make less lactic acid due to better circulation and increased oxygen carrying capacity. </li></ul><ul><li>Some muscle fibers are more likely to become fatigued. </li></ul>
  28. 28. Heat Production <ul><li>Heat is a by-product of cellular respiration. </li></ul><ul><li>Muscles are a major source of heat. </li></ul><ul><li>Blood transports heat throughout the body. </li></ul><ul><li>* Remember that one response of the body to a low body temperature is shivering or muscle contraction which results in raising body temperature (Chapter 1). </li></ul>
  29. 29. Types of Muscular Responses <ul><li>To get a muscle twitch, a threshold stimulus (= minimal </li></ul><ul><li>stimulus required to cause contraction) is required. A twitch is </li></ul><ul><li>the millisecond response of a muscle to a one stimulus. Phases </li></ul><ul><li>of a single muscle twitch: </li></ul><ul><li>Latent period is the time between stimulus and response. </li></ul><ul><li>Period of contraction is when the muscle pulls at its attachments. </li></ul><ul><li>Period of relaxation is when the muscle stretches to its former length. </li></ul><ul><li>Refractory period is a brief period when the muscle remains unresponsive. </li></ul><ul><li>All-or-none response: a muscle that does not reach threshold will not contract. Once threshold stimulus is reached, the muscle contracts completely. </li></ul>
  30. 30. Types of Muscular Responses Figure 9.17 – a) series of twitches; b) summation; c) tetanic contraction
  31. 31. Types of Muscular Responses <ul><li>A series of single twitches is the result of multiple stimuli, that are far apart allowing the muscle to relax in-between each stimulus. </li></ul><ul><li>Summation: each successive contraction increases to maximum. The staircase effect is due to a net increase in available calcium ions. </li></ul><ul><li>Summation is the process of combining twitches into a sustained contraction. </li></ul><ul><li>A tetanic contraction is a forceful sustained contraction. </li></ul><ul><li>A tetanus is a prolonged contraction of a muscle resulting from a series of motor impulses following one another too rapidly to permit intervening relaxation of the muscle. </li></ul>
  32. 32. Sustained Contraction Through Activation of Many Motor Units <ul><li>Definition motor unit: It is a motor neuron and the muscle fibers it controls. </li></ul><ul><li>Definition sustained contraction: Multiple motor unit summation or recruitment is an increase in the number of activated motor units leading to sustained contraction. </li></ul><ul><li>Muscle tone is a low level of sustained contractions in a muscle that appears at rest. </li></ul>
  33. 33. Further Differentiation of Muscle Contractions <ul><li>Isotonic: involve a change in length during contraction. </li></ul><ul><li>Concentric: occur when the muscle shortens. </li></ul><ul><li>Eccentric: occur when the muscle lengthens. </li></ul><ul><li>Isometric: do not involve a change in length. </li></ul>
  34. 34. Figure 9.17
  35. 35. Figure 9.17
  36. 36. Fast and Slow Muscle Fibers <ul><li>Slow-twitch (type I) fibers are oxidative and resistant to fatigue. They are called red fibers because they contain myoglobin. </li></ul><ul><li>Fast-twitch (type II a) are glycolytic and easily fatigue. They are called white fibers . </li></ul><ul><li>Fast-twitch (type II b) are intermediate fibers, oxidative and fatigue-resistant. </li></ul>
  37. 38. Cardiac Muscle (Heart) <ul><li>Cells have a single nucleus, sarcoplasmic reticulum, T tubules, and mitochondria. However, they are connected with each other by intercalated disks. </li></ul><ul><li>This connection allows cardiac muscle to act in unison, as a functional syncytium. </li></ul><ul><li>Note: A syncytium is a multinucleated cell. While cardiac muscle cells are not multinucleated, functionally they appear as if they are multinucleated. </li></ul><ul><li>Intercalated disks are gap junctions. </li></ul><ul><li>Cardiac muscle is involuntary in action and self-exciting with the help of a natural pacemaker called the sinoatrial node. It has rhythmicity. </li></ul>
  38. 39. Smooth Muscle (Glands, Vessels, and Organs) <ul><li>They lack striation and T- tubules. </li></ul><ul><li>Multiunit smooth muscle fibers function as separate units. </li></ul><ul><li>Single-unit smooth muscle (visceral smooth muscle) consists of sheets of cells joined by gap junctions. The fibers respond as a unit. The muscle displays rhythmicity. </li></ul>
  39. 40. Smooth Muscle Contraction <ul><li>In part, triggered by nerve impulses and release of calcium. </li></ul><ul><li>Uses ATP and actin-myosin reactions. </li></ul><ul><li>Smooth muscle lacks troponin and uses calmodulin to bind calcium ions. </li></ul><ul><li>Calcium diffuses in from extracellular fluid. </li></ul><ul><li>Norepinephrine or acetylcholine can function as a neurotransmitters. </li></ul><ul><li>Contraction can be affected by hormones . </li></ul><ul><li>Stretching can trigger contractions. </li></ul><ul><li>Smooth muscle is slower to contract and relax, but can forcefully contract longer with the same amount of energy expended. </li></ul><ul><li>Muscle fibers can change length without changing tautness. </li></ul>
  40. 41. <ul><li>Supplies of myoglobin, ATP, and creatine phosphate begin to decline by age 40 . Ultimately, this will lead to atrophy of muscle tissue. </li></ul><ul><li>Muscles shrink and become less elastic. </li></ul><ul><li>Muscles become smaller and capable of less forceful contraction. </li></ul><ul><li>By age 80 half of the muscle of young adulthood has atrophied. </li></ul><ul><li>Exercise can combat and delay these events. </li></ul>Life-Span Changes
  41. 42. Identification of Major Skeletal Muscles <ul><li>Focus will be on the following skeletal muscles: </li></ul><ul><li>Chest and abdominal wall muscles </li></ul><ul><li>Upper limb muscles </li></ul><ul><li>Lower limb muscles </li></ul><ul><li>Note: For arms and legs, identify the prime movers </li></ul><ul><li>of flexion and any synergists as well the </li></ul><ul><li>antagonist. </li></ul>
  42. 43. Skeletal Muscle Position and Function <ul><li>Positioning of skeletal muscles between bones: </li></ul><ul><li>Origin: immovable end of a joint </li></ul><ul><li>Insertion: movable end of a joint </li></ul><ul><li>Skeletal muscles work in groups: </li></ul><ul><li>Prime mover or Agonist: major muscle </li></ul><ul><li>involved in action </li></ul><ul><li>Synergists: assist the prime mover </li></ul><ul><li>Antagonists: resist the prime mover </li></ul>
  43. 44. <ul><li>Flexor carpi radialis </li></ul><ul><li>Extensor digitorum </li></ul><ul><li>Adductor longus </li></ul><ul><li>flexion </li></ul><ul><li>extension </li></ul><ul><li>adduction </li></ul><ul><li>Action of Muscle </li></ul><ul><li>Sternocleidomastoid =a thick superficial muscle on each side that arises by one head from the first segment of the sternum and by a second from the inner part of the clavicle, that inserts into the mastoid process and occipital bone, and that acts especially to bend, rotate, flex, and extend the head </li></ul><ul><li>2 origins = sternum, clavicle </li></ul><ul><li>insertion = mastoid process of the temporal bone behind the ear that is well developed and of somewhat conical form in adults but inconspicuous in children </li></ul><ul><li>Location of Origin and/or Insertion </li></ul><ul><li>Deltoid </li></ul><ul><li>Trapezius </li></ul><ul><li>Serratus anterior </li></ul><ul><li>Orbicularis oris </li></ul><ul><li>deltoid = triangle </li></ul><ul><li>trapezius = trapezoid </li></ul><ul><li>serratus = saw-toothed </li></ul><ul><li>orbicularis = circular </li></ul><ul><li>Shape </li></ul><ul><li>Biceps brachii </li></ul><ul><li>Triceps brachii </li></ul><ul><li>biceps = 2 origins </li></ul><ul><li>triceps = 3 origins </li></ul><ul><li>Number of Origins (Heads) </li></ul><ul><li>Gluteus maximus </li></ul><ul><li>Palmaris longus </li></ul><ul><li>Peroneus longus </li></ul><ul><li>maximus = largest </li></ul><ul><li>longus = longest </li></ul><ul><li>brevis = shortest </li></ul><ul><li>Relative Size </li></ul><ul><li>Frontalis </li></ul><ul><li>Tibialis Anterior </li></ul><ul><li>frontal bone </li></ul><ul><li>tibia </li></ul><ul><li>Location (bone or body part that a muscle covers) </li></ul><ul><li>Rectus abdominis </li></ul><ul><li>Transversus abdominis </li></ul><ul><li>External Oblique </li></ul><ul><li>rectus = parallel </li></ul><ul><li>transverse = perpendicular </li></ul><ul><li>oblique = at 45 o angle </li></ul><ul><li>Direction of fascicles relative to midline </li></ul><ul><li>EXAMPLES OF NAMES </li></ul><ul><li>VOCABULARY </li></ul><ul><li>SKELETAL MUSCLE NAMING </li></ul>
  44. 45. Muscles of Facial Expression closes eye circular muscle around eye Orbicularis oculi depresses mandible over lower jaw to neck Platysma compresses cheeks “trumpeter’s muscle” hollow of cheek Buccinator elevates corners of mouth (“smiling muscle”) muscle that connects zygomatic arch to corner of mouth Zygomaticus (*) Origin: zygomatic arch Insertion: orbicularis oris closes lips (“kissing muscle”) circular muscle around the mouth Orbicularis oris elevates eyebrow Covers cranium over forehead over occipital Epicranius Frontalis Occipitalis ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  45. 46. Muscle that moves the Head Muscles of Mastication elevates mandible convergent muscle over temporal bone Temporalis elevates mandible over lateral mandible Masseter Origin: Zygomatic Arch Insertion: Lateral Mandible ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE flexion of head toward chest (both contracted) rotation/abduction of head (as antagonists) Major neck muscle Sternocleidomastoid(*) Origin: sternoclavicular Insertion: mastoid process of temporal bone ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  46. 47. Muscles That Move the Head Fig.9.25- Sternocleidomastoid: pulls head to one side, flexes the neck
  47. 48. Muscles That Move the Head Fig. 9.23- Splenius capitis : rotates head, bends head, extends neck
  48. 49. Fig. 9.23 - Semispinalis: extends and bends head to one side, rotates head; Longissimus capitis: extends and rotates head.
  49. 50. Muscles that move the Pectoral Girdle scapula fixator Saw-toothed lateral thoracic muscle Serratus anterior scapula fixator Muscle deep to Pectoralis major Pectoralis minor elevates pectoral girdle (“shoulder shrug”) Trapezoid shaped muscle in posterior neck and upper back Trapezius (*) Origin: occipital bone & spines of C7-T12 Insertion: clavicle and acromion process of scapulae ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  50. 51. Muscles that move the Arm (Humerus) abduction of humerus Triangular shaped shoulder muscle Deltoid adduction of humerus Large, back muscle Latissimus dorsi flexes arm medially (pull arms forward and together) Large, convergent chest muscle Pectoralis major (*) Origin: clavicle, sternum, & costal cartilages of ribs 1-6 Insertion: Greater tubercle of humerus ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  51. 52. Muscles that move the Forearm (Radius and Ulna) extension of arm at elbow (antagonist) posterior upper arm muscle (three heads) Triceps brachii flexion of arm at elbow (synergist) lateral muscle between upper and forearm Brachioradialis flexion of arm at elbow (synergist) muscle beneath biceps brachii Brachialis flexion of arm at elbow (prime mover) fusiform, parallel, anterior upper arm muscle (2 origins) Biceps Brachii (*) Origin: Coracoid process Insertion: Radial tuberosity ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  52. 53. Figure 7.14
  53. 54. Muscles of the Forearm Fig. 9.29- Biceps brachii: flexes forearm, rotates hand; Brachialis, Brachioradialis: flexes forearm; Triceps brachii: extends forearm
  54. 55. Muscles of the Forearm Fig. 9.29- Supinator: rotates forearm laterally; Pronator teres: rotates forearm medially; Pronator quadratus: rotates forearm medially
  55. 56. Muscles that move Wrist, Hand, Fingers extension of wrist/fingers posterior forearm muscle Extensor digitorum flexion of wrist anterior forearm muscle located between two above Palmaris longus flexion of wrist anterior, medial forearm muscle Flexor carpi Ulnaris flexion of wrist anterior, lateral forearm muscle Flexor carpi Radialis ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  56. 57. Muscles that tense the Abdominal Wall tenses abdominal wall deep abdominal muscle; runs perpendicular to rectus abdominis Transversus abdominis tenses abdominal wall deep oblique abdominal muscle Internal Oblique tenses abdominal wall superficial/lateral oblique abdominal muscle External Oblique tenses abdominal wall strap like muscle from costal cartilages to ilium Rectus abdominis (*) Origin: pubic crest/symphysis Insertion: xiphoid process & costal cartilages of 5-7 th ribs ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  57. 58. Muscles that move the Thigh (Femur) adduction of femur medial thigh muscle Adductor Longus abduction of femur lateral hip muscle Gluteus Medius extension of hip at thigh (as in walking or climbing stairs) buttocks, largest muscle in body Gluteus Maximus (*) Origin: dorsal ilium, sacrum, coccyx Insertion: posterior femur ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  58. 59. Muscles that move the Tibia & Fibula flexion of leg at knee posterior thigh; hamstring Semimembranosus flexion of leg at knee posterior thigh; hamstring Semitendinosus flexion of leg at knee posterior thigh; hamstring Biceps femoris flexion of knee forward parallel strap-like muscle; crosses thigh Sartorius (*) Origin: iliac spine Insertion: medial tibia extension of leg at knee deep anterior thigh; quadriceps Vastus intermedius extension of leg at knee medial anterior thigh; quadriceps Vastus Medialis extension of leg at knee lateral anterior thigh; quadriceps Vastus lateralis extension of leg at knee anterior thigh; quadriceps Rectus femoris ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  59. 60. Muscles that move the Foot & Toes Note the location of the Calcaneal Tendon Fig 9.40, p324. plantar flexion (synergist) deep to gastrocnemius Soleus plantar flexion (prime mover) posterior lower leg (i.e. calf muscle); two origins Gastrocnemius (*) Origin: condyles of femur Insertion: calcaneus eversion lateral to fibula Peroneus longus dorsiflexion anterior to tibia Tibialis anterior ACTION LOCATION/ DESCRIPTION NAME OF MUSCLE
  60. 61. Life-Span Changes <ul><li>40’s: First signs of aging in the muscular system </li></ul><ul><li>80’s: Decline in motor neuron activity leads to muscle atrophy , diminished muscular strength, and slower reflexes </li></ul><ul><li>Exercise: Can help maintain a healthy muscular system (strength training and aerobics) </li></ul>