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2 Overview of Muscular SystemTypes of Muscle Tissue Under voluntary control Skeletal muscles The muscular system Under involuntary control Cardiac muscle Heart wall Smooth muscle Visceral organs

3 Skeletal Muscles Skeletal muscles attach to bones directly or indirectly Perform five functions Produce movement of skeleton Maintain posture and body position Support soft tissues Guard entrances and exits Maintain body temperature

4 Anatomy of Skeletal MusclesGross Anatomy: Connective tissue organization Epimysium Fibrous covering of whole muscle Perimysium Fibrous covering of fascicle Endomysium Fibrous covering of a single cell (a muscle fiber) Tendons (or aponeurosis)

5 Anatomy of Skeletal Muscles

6 Anatomy of Skeletal MusclesMicroanatomy of a Muscle Fiber: Sarcolemma Muscle cell membrane Sarcoplasm Muscle cell cytoplasm Sarcoplasmic reticulum (SR) Like smooth ER Transverse tubules (T tubules) Myofibrils (contraction organelle) Sarcomeres(repeating unit)

7 Anatomy of Skeletal MusclesSarcomere—Repeating structural unit of the myofibril Components of a sarcomere: Myofilaments Thin filaments (mostly actin) Thick filaments (mostly myosin) Z lines at each end Anchor for thin filaments

8 Organization of a Single Muscle Fiber

9 Myofibril Anatomy

10 Microcomponents of Skeletal Muscle

11 Changes During Contraction

12 Control of Muscle ContractionSteps in Neuromuscular Transmission: Motor neuron reaches action potential Acetylcholine release and binding Action potential in sarcolemma T tubule reaches action potential Calcium release from SR(Sarcoplasmic Reticulum)

13 Control of Muscle ContractionThe Neuromuscular Junction Synaptic terminal Acetylcholine release Motor end plate Acetylcholine receptors Acetylcholine binding Acetylcholinesterase Acetylcholine removal

14 Neuromuscular Junction

15 Action potential Axon Synaptic terminal Sarcolemma Vesicles AChArrival of an action potential at the synaptic terminal Axon Arriving action potential Synaptic terminal Sarcolemma Vesicles ACh Synaptic cleft AChE molecules ACh receptor site Muscle fiber Sarcolemma of motor end plate ACh binding at the motor and plate Appearance of an action potential in the sarcolemma Release of acetylcholine Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft. The binding of ACh to the receptors increases the membrane permeability to sodium ions. Sodium ions then rush into the cell. An action potential spreads across the surface of the sarcolemma. While this occurs, AChE removes the ACh. Action potential Na+ Na+ Na+

16 The Contraction ProcessActin active sites and myosin cross-bridges interact Thin filaments slide past thick filaments Cross-bridges undergo a cycle of movement Attach, pivot, detach, return Troponin-tropomyosin control interaction Prevent interaction at rest

17 Summary of Contraction Process

18 Control of Muscle ContractionKey Note: Skeletal muscle fibers shorten as thin filaments interact with thick filaments and sliding occurs. The trigger for contraction is the calcium ions released by the SR when the muscle fiber is stimulated by its motor neuron. Contraction is an active process; relaxation and the return to resting length is entirely passive.

19 Muscle Mechanics Some Basic Muscle Definitions:Muscle tension—The pulling force on the tendons that muscle cells generate when contracting Muscle twitch—A brief contraction-relaxation response to a single action potential

20 Twitch and Development of Tension

21 Muscle Mechanics The Frequency of Muscle Fiber Stimulation:Summation—Addition of twitch tension when a stimulus is applied before tension has completely relaxed Incomplete tetanus—Tension peaks and falls repeatedly and builds up beyond twitch tension Complete tetanus—Tension is steady (no relaxation phase) and largest if stimuli arrive at very high rates

22 The Effects of Repeated StimulationsMuscle Mechanics The Effects of Repeated Stimulations

23 Motor Units Motor Unit —A motor neuron and all the muscle cells it controls Recruitment—To increase muscle tension by activating more motor units Small motor units provide finer control Motor units are intermixed in the muscle to pull evenly on the tendon

24 Motor Units

25 Muscle Mechanics Key Note:All voluntary (intentional) movements involve the sustained, sub-tetanic contractions of skeletal muscle fibers organized into distinct motor units. The force generated can be increased by increasing the frequency of action potentials or by recruiting additional motor units.

26 Muscle Mechanics Muscle Tone—Tension in a “resting” muscle produced by a low level of spontaneous motor neuron activity. Distinct from resting tension produced by passive stretching. Function of muscle tone Stabilizes bones, joints Prevents atrophy (muscle wasting )

27 Types of Contractions Isotonic contraction Isometric contractionThe tension (load) on a muscle stays constant (iso = same, tonic = tension) during a movement. (Example: lifting a baby) Isometric contraction The length of a muscle stays constant (iso = same, metric = length) during a “contraction” (Example: holding a baby at arms length)

28 Muscle Elongation Muscle contracts actively Muscle elongates passivelyMuscles can only pull Muscles never push Muscle elongates passively Elastic forces Contraction of opposing muscles Effects of gravity

29 Energetics of Muscle ContractionATP and Creatine Phosphate Reserves: Muscle contraction consumes a lot of ATP ATP transfers energy directly to cycling cross-bridges and calcium pumping mechanisms CP stores energy and regenerates ATP CP transfers its energy to ADP reforming ATP Creatine phosphokinase (CPK) catalyzes rxn. ADP (2 “P”s) becomes ATP(3 “P”s) CP levels greatly exceed ATP levels

30 Energetics of Muscle ContractionATP Generation: Light activity Aerobic(O2) metabolism of fatty acids from blood stream Storage of glucose as glycogen in muscle tissue Moderate activity Breakdown of glycogen to produce glucose Glycolysis of glucose to generate ATP and pyruvate Peak activity Anerobic(no O2) breakdown of glucose Production of lactic acid(byproduct) Accumulation leads to soreness

31 Muscle Metabolism- Light

32 Muscle Metabolism- Moderate

33 Muscle Metabolism- Peak

34 Energetics of Muscle ContractionKey Note: Skeletal muscles at rest metabolize fatty acids and store glycogen. During light activity, muscles can generate ATP through the aerobic breakdown of carbohydrates, lipids, or amino acids. At peak levels of activity, most of the energy is provided by anaerobic reactions that generate lactic acid.

35 Energetics of Muscle ContractionMuscle Fatigue- When a muscle loses ability to contract due to a low pH (lactic acid buildup), low ATP levels, or other problems Recovery Period- Time after muscle activity that it takes to restore pre-exertion conditions Oxygen Debt- Amount of excess oxygen used during the recovery period

36 Muscle Performance Two Types of Skeletal Muscle Fibers: Fast fibersLarge diameter, abundant myofibrils, ample glycogen, scant mitochondria. Produce powerful, brief contractions Slow fibers Smaller diameter, rich capillary supply, many mitochondria, much myoglobin. Produce slow, steady contractions

37 Muscle Performance Physical Conditioning: Anaerobic enduranceTime over which a muscle can contract effectively under anerobic conditions. Hypertrophy Increase in muscle bulk. Can result from anerobic training. Aerobic endurance Time over which a muscle can contract supported by mitochondria.

38 Muscle Performance Key Note:What you don’t use, you lose. When motor units are inactive for days or weeks, muscle fibers break down their contractile proteins and grow smaller and weaker. If inactive for long periods, muscle fibers may be replaced by fibrous tissue.

39 Cardiac Muscle Cardiac Muscle Tissue: Small cells Single nucleus/cellAerobic metabolism Intercalated discs Long contraction time Self-exciting (automaticity) No tetanic contraction

40 Cardiac Muscle Tissue

41 Smooth Muscle Smooth Muscle Tissue: Nonstriated cells (no sarcomeres)Calcium control of contraction different from striated muscle Wide range of operating lengths Involuntary muscle Under hormonal or local control Contractions controlled by Pacesetter cells Motor neurons often unneeded

42 Smooth Muscle Tissue

43 Muscle Comparison

44 Anatomy of the Muscular System

45 Anatomy of the Muscular System

46 Origins, Insertions, and ActionsMuscle attachment that remains fixed Insertion Muscle attachment that moves Action What joint movement a muscle produces

47 Action Categories Primary Action Categories: Prime mover (agonist)Main muscle in an action Synergist Helper muscle in an action Antagonist Opposed muscle to an action

48 Muscle Terminology Names of muscles provide clues to location, orientation, or action Axial musculature—Muscles with origins on the axial skeleton that position and move head, spine, rib cage Appendicular musculature—Muscles that stabilize or move appendicular components

49 The Axial Muscles Four groups of axial muscles: Head and neck SpineTrunk Pelvic floor

50 Muscles of the Head and Neck

51 Muscles of the Jaw

52 Muscles of the Head and Neck

53 Muscles of the Anterior Neck

54 Anatomy of the Muscular SystemSelected Muscles of the Spine Splenius capitis Semispinalis capitis Erector spinae groups Spinalis Longissimus Iliocostalis

55 Muscles of the Spine

56 Axial Muscles of the TrunkThoracic region External intercostals Internal intercostals Diaphragm Abdominal region Rectus abdominis External oblique Internal oblique Transversus abdominis

57 Axial Muscles of the Trunk

58 Muscles of the Pelvic FloorPerineum: Sheets of muscle From sacrum and coccyx To pubis and ischium Pelvic organ support Control of material passing through urethra and anus

59 The Appendicular MusclesTwo functionally distinct groups: Muscles of the shoulder and upper limbs Muscles of the pelvic girdle and lower limbs

60 Selected Shoulder MusclesTrapezius Rhomboid Levator scapulae Serratus anterior Pectoralis minor

61 Muscles of the Shoulder

62 Muscles of the Shoulder

63 Muscles of the Upper ArmMuscles that Move the Arm: Deltoid Supraspinatus Subscapularis Teres major Infraspinatus Teres minor Pectoralis major Latissiumus dorsi

64 Muscles that Move the Arm

65 Muscles that Move the Arm

66 Muscles of the lower ArmMuscles That Move the Forearm: Biceps brachii Triceps brachii Brachialis Brachioradialis Pronators Supinator

67 Muscles of the Wrist Muscles That Move the Wrist Wrist flexorsFlexor carpi ulnaris Flexor carpi radialis Palmaris longus Wrist extensors Extensor carpi radialis Extensor carpi ulnaris

68 Muscles of the Forearm & Wrist

69 Muscle of the Pelvis and Lower LimbsThree functional groups Thigh movement Leg movement Ankle, foot, and toe movement

70 Muscles of the Thigh Muscles that Move the Thigh: Gluteal musclesThigh adductors Adductor magnus Adductor brevis Adductor longus Pectineus Gracilis Thigh flexors Iliopsoas (psoas major + iliacus)

71 Muscles That Move the Thigh

72 Muscles That Move the Thigh

73 Muscles of the Knee Flexors of the Knee: Biceps femorisSemimembranosus Semitendinosus Sartorius Popliteus Synergist muscle unlocks knee Extensors of the Knee: Quadriceps femoris group Rectus femoris Vastus lateralis Vastus intermedius Vastus medialis

74 Muscles That Move the Leg

75 Muscles that Move the FootPlantar flexion Gastrocnemius Soleus Eversion and plantar flexion Fibularis (peroneus) Dorsiflexion Tibialis anterior

76 Muscles That Move the Foot

77 Muscles That Move the Foot and Toes

78 Aging and the Muscular SystemAge-Related Reductions: Muscle size Muscle elasticity Muscle strength Exercise tolerance Injury recovery ability

79 END OF CHAPTER 7 NOTES!!!