Chapter 8: The Muscular System

Overview

Key Terms acetylcholine insertion spasm actin motor unit synapse agonist myalgia synergist antagonist myoglobin tendon bursitis myosin tonus contractility neuromuscular junction tropomyosin excitability neurotransmitter troponin fascicle origin glycogen sarcomere

Types of Muscle Learning Outcome Compare the three types of muscle tissue.

Types of Muscle

✓ Types of Muscle Checkpoint 8-1 What are the three types of muscle? 6

? Types of Muscle Pop Quiz 8.1 Which type of muscle tissue is striated and involuntary? Cardiac Intercalated Smooth Skeletal

? Types of Muscle Pop Quiz Answer 8.1 Which type of muscle tissue is striated and involuntary? Cardiac Intercalated Smooth Skeletal

The Muscular System Learning Outcomes Describe three functions of skeletal muscle. Explain how skeletal muscles contract. List compounds stored in muscle cells that are used to generate energy. Explain what happens in muscle cells contracting anaerobically. Cite the effects of exercise on muscles. Compare isotonic and isometric contractions.

The Muscular System Skeletal Muscle Has Three Primary Functions: Skeletal movement Posture maintenance Heat generation

The Muscular System Muscle Structure Fascicles Bundles of muscle cells (fibers) that make up a whole muscle Connective tissue Hold fascicles and whole muscle together Three layers Endomysium Perimysium Epimysium Tendons

Figure 8-1 Structure of a skeletal muscle. What is the innermost layer of connective tissue in a muscle? What layer of connective tissue surrounds a fascicle of muscle fibers? 12

The Muscular System Muscle Cells in Action Motor unit: A single neuron and all the muscle fibers it stimulates Small motor units used for fine movements Large motor units used for broad movements

The Muscular System Muscle Cells in Action Neuromuscular junction (NMJ): The point at which a nerve fiber contacts a muscle fiber A type of synapse NMJ anatomy Motor neuron Neurotransmitter (acetylcholine; ACh) Motor end plate (on muscle fiber) Contains acetylcholine receptors

The Muscular System Muscle Cells in Action NMJ allows motor neuron to stimulate muscle fiber to become electrically excited (action potential) Action potential stimulates muscle contraction Events at the NMJ Ach is released from motor neuron into synaptic cleft Ach diffuses across synaptic cleft towards motor end plate Ach binds to receptors on motor end plate and stimulates action potential

Figure 8-2 Nerve supply to a skeletal muscle and the NMJ.

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✓ The Muscular System Checkpoints 8-2 What are the three main functions of skeletal muscle? 8-3 What is the name of the special synapse in which a nerve cell makes contact with a muscle cell? 8-4 What neurotransmitter is involved in the stimulation of skeletal muscle cells? 18

? The Muscular System Pop Quiz 8.2 A single neuron and all the muscle fibers it stimulates comprise a(n): Motor end plate Motor unit Neuromuscular junction Synapse

? The Muscular System Pop Quiz Answer 8.2 A single neuron and all the muscle fibers it stimulates comprise a(n): Motor end plate Motor unit Neuromuscular junction Synapse

The Muscular System Muscle Cells in Action The sarcomere is the functional unit of contraction in the skeletal muscle fiber Sarcomere anatomy: Thick filaments (myosin) Thin filaments (actin) Regulatory proteins Troponin Tropomyosin

Figure 8-3 Detailed structure of a skeletal muscle cell. 22

The Muscular System Muscle Cells in Action Sarcomeres contract via the sliding filament mechanism: Myosin heads bind to actin, forming cross-bridges Using stored energy, myosin heads pull actin filaments together within the sarcomeres and the cell shortens New ATP is used to detach myosin heads and move them back into position for another “power stroke”

Figure 8-4 Sliding filament mechanism of skeletal muscle contraction. 24

The Muscular System Muscle Cells in Action Calcium regulates sarcomeric contraction within the muscle cell: Action potential from NMJ travels to sarcoplasmic reticulum (SR) SR releases calcium into cytoplasm Calcium shifts troponin and tropomyosin off of thin filament so that binding sites on actin are exposed Sliding filament mechanism now able to proceed Muscle relaxes when stimulation ends and calcium is pumped back into SR

Figure 8-5 Role of calcium in muscle contraction. 26

The Muscular System Summary of Events in a Muscle Contraction ACh is released from neuron ending into synaptic cleft at NMJ ACh binds to motor end plate and produces action potential Action potential travels to sarcoplasmic reticulum (SR) SR releases calcium into cytoplasm Calcium shifts troponin and tropomyosin so that binding sites on actin are exposed

The Muscular System Summary of Events in a Muscle Contraction (continued) Myosin heads bind to actin, forming cross-bridges Using stored energy, myosin heads pull actin filaments together within sarcomeres and cell shortens New ATP is used to detach myosin heads and move them back to position for another “power stroke” Muscle relaxes when stimulation ends and calcium is pumped back into SR

✓ The Muscular System Checkpoints 8-5 What are the two properties of muscle cells that are needed for response to a stimulus? 8-6 What filaments interact to produce muscle contraction? 8-7 What mineral is needed for interaction of the contractile filaments? 29

? The Muscular System Pop Quiz 8.3 The two filaments that form cross-bridges are Actin and troponin Tropomyosin and myosin Actin and myosin Troponin and tropomyosin

? The Muscular System Pop Quiz Answer 8.3 The two filaments that form cross-bridges are Actin and troponin Tropomyosin and myosin Actin and myosin Troponin and tropomyosin

The Muscular System Energy Sources Muscle contraction requires ATP Skeletal muscle prefers to produces ATP via aerobic metabolism, which requires Oxygen Glucose Storage compounds ensure an adequate supply of oxygen and glucose for aerobic ATP metabolism Myoglobin Glycogen

The Muscular System Energy Sources During strenuous activity, muscle cells use anaerobic ATP metabolism, which does not require ATP Breakdown of creatine phosphate Anaerobic glycolysis Lactic acid accumulation and oxygen debt Excess postexercise oxygen consumption After strenuous exercise, person takes in extra oxygen (via rapid breathing) to remove lactic acid and replenish energy stores

The Muscular System Effects of Exercise Improved balance, joint flexibility Increased muscle size (hypertrophy) Improved muscle tissue Vasodilation Strengthened heart muscle Improved breathing and respiratory efficiency Weight control Stronger bones

The Muscular System Types of Muscle Contractions Partial (muscle tone or tonus) Isotonic No change in tension Muscle length shortens Movement Isometric Great increase in tension Muscle length unchanged No movement

✓ The Muscular System Checkpoints 8-8 What compound is formed in oxidation of nutrients that supplies the energy for contraction? 8-9 What acid accumulates during anaerobic metabolism? 8-10 What are the two main types of muscle contraction? 36

? The Muscular System Pop Quiz 8.4 Which muscle cell compound stores oxygen? Creatine phosphate Glycogen Hemoglobin Myoglobin

? The Muscular System Pop Quiz Answer 8.4 Which muscle cell compound stores oxygen? Creatine phosphate Glycogen Hemoglobin Myoglobin

The Mechanics of Muscle Movement Learning Outcomes Explain how muscles work together to produce movement. Compare the workings of muscles and bones to lever systems.

The Mechanics of Muscle Movement Tendons attach muscles to bones. Origin: Attached to more fixed part of skeleton Insertion: Attached to more movable part of skeleton

Figure 8-6 Muscle attachments to bones. 41

The Mechanics of Muscle Movement Muscles Work Together Many muscles function in pairs Prime movers Antagonists Synergists

The Mechanics of Muscle Movement Levers and Body Mechanics Musculoskeletal system as a lever system Lever—bone Fulcrum—joint Force—applied by muscle Three classes of levers First class Second class Third class—most body systems

Figure 8-7 Levers. In a third-class lever system, where is the fulcrum with regard to the effort and the resistance? 44

The Mechanics of Muscle Movement ✓ The Mechanics of Muscle Movement Checkpoints 8-11 What are the names of the two attachment points of a muscle and how do they function? 8-12 What is the name of the muscle that produces a movement as compared with the muscle that produces an opposite movement? 8-13 Of the three classes of levers, which one represents the action of most muscles? 45

The Mechanics of Muscle Movement ? The Mechanics of Muscle Movement Pop Quiz 8.5 In anatomic lever systems, the fulcrum is the Bone Bursa Insertion Joint

The Mechanics of Muscle Movement ? The Mechanics of Muscle Movement Pop Quiz Answer 8.5 In anatomic lever systems, the fulcrum is the Bone Bursa Insertion Joint

Skeletal Muscle Groups Learning Outcomes Explain how muscles are named. Name some of the major muscles in each muscle group and describe the location and function of each.

Skeletal Muscle Groups Characteristics for Naming Muscles Characteristic Example Location Temporalis; near the skull’s temple Size Gluteus maximus; the largest Shape Serratus anterior; serrated edge Direction External oblique; runs obliquely Number of heads Biceps brachii; two heads Action Flexor digitorum; flexes toes

Figure 8-8 Superficial muscles, anterior view.

Figure 8-9 Superficial muscles, posterior view. 51

Skeletal Muscle Groups Muscles of the Head and Neck Name Location Function Orbicularis oculi Encircles eyelid Closes eye Levator palpebrae superioris Posterior orbit to upper eyelid Opens eye Orbicularis oris Encircles mouth Closes lips Buccinator Fleshy part of cheek Flattens cheek; helps in eating, whistling, and blowing wind instruments Temporalis Above and near ear Closes jaw Masseter At angle of jaw Sternocleidomastoid Along lateral neck, to mastoid process Flexes head; rotates head toward opposite side from muscle

Figure 8-10 Muscles of the head and neck. In a third-class lever system, where is the fulcrum with regard to the effort and the resistance? 53

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Skeletal Muscle Groups Muscles That Move the Shoulder and Arm Name Location Function Trapezius Posterior neck and upper back to clavicle and scapula Raises shoulder and pulls it back; superior portion extends and turns head Latissimus dorsi Middle and lower back, to humerus Extends and adducts arm Pectoralis major Superior, anterior chest, to humerus Flexes and adducts arm Serratus anterior Inferior to axilla on lateral chest Moves shoulder forward; aids in raising arms, punching, or reaching forward Deltoid Covers shoulder joint, to lateral humerus Abducts arm; flexes and extends arm

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Skeletal Muscle Groups Muscles That Move the Forearm and Hand Name Location Function Biceps brachii Anterior arm along humerus, to radius Flexes forearm; supinates forearm and hand Brachialis Deep to biceps brachii; inserts at anterior elbow joint Forceful flexor of forearm Brachioradialis Lateral forearm from distal end of humerus Flexes forearm Triceps brachii Posterior arm, to ulna Extends forearm

Skeletal Muscle Groups Muscles That Move the Forearm and Hand (continued) Name Location Function Flexor carpi group Anterior forearm, to hand Flexes hand Extensor carpi group Posterior forearm, to hand Extends hand Flexor digitorum group Anterior forearm to fingers Flexes fingers Extensor digitorum group Posterior forearm to fingers Extends fingers

Figure 8-11 Muscles that move the forearm and hand. What does carpi refer to in the names of muscles? Digitorum? 59

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Skeletal Muscle Groups Muscles of the Trunk Name Location Function Diaphragm Dome-shaped partition between thoracic and abdominal cavities Dome descends to enlarge thoracic cavity from top to bottom Intercostals Between ribs Elevate ribs and enlarge thoracic cavity Muscles of abdominal wall: External oblique Internal oblique Transversus abdominus Rectus abdominis Anterolateral abdominal wall Compress abdominal cavity and expel substances from the body; flex spinal column Levator ani Pelvic floor Aids defecation Erector spinae Group of deep vertical muscles between sacrum and skull Extends vertebral column to produce erect posture

Figure 8-12 Muscles of respiration. 62

Figure 8-13 Muscles of the abdominal wall. What does rectus mean? Oblique? 63

Figure 8-14 Muscles of the female perineum (pelvic floor). 64

Skeletal Muscle Groups Muscles That Move the Leg and Thigh Name Location Function Gluteus maximus Superficial buttock, to femur Extends thigh Gluteus medius Deep buttock, to femur Abducts thigh Iliopsoas Crosses anterior hip joint, to femur Flexes thigh Adductor group Medial thigh, to femur Adducts thigh Sartorius Crosses anterior thigh from ilium to medial tibia Flexes thigh and leg (to sit cross-legged) Gracilis Pubic bone to medial surface of tibia Adducts thigh at hip; flexes

Skeletal Muscle Groups Muscles That Move the Leg and Thigh (continued) Name Location Function Quadriceps femoris Rectus femoris Vastus medialis Vastus lateralis Vastus intermedius Anterior thigh, to tibia Extends leg Hamstring group Biceps femori Semimembranosus Semitendinosus Posterior thigh; ischium and femur to tibia and fibula Flexes leg at knee; extends and rotates thigh at hip

Figure 8-15 Muscles of the thigh. How many muscles make up the quadriceps femoris? 67

Skeletal Muscle Groups Muscles That Move the Foot Name Location Function Gastrocnemius Posterior leg, to calcaneus, inserting by the Achilles tendon Plantar flexes foot Soleus Posterior leg deep to gastrocnemius Tibialis anterior Anterior and lateral leg, to foot Dorsiflexes and inverts foot Fibularis longus Lateral leg, to foot Everts foot Flexor digitorum group Posterior leg and foot to inferior surface of phalanges Flexes toes Extensor digitorum group Anterior surface of leg bones to superior surface of phalanges Extends toes

Figure 8-16 Muscles that move the foot. On what bone does the Achilles tendon insert? 69

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Skeletal Muscle Groups ✓ Skeletal Muscle Groups Checkpoints 8-14 What muscle is most important in breathing? 8-15 What structural feature gives strength to the muscles of the abdominal wall? 71

Skeletal Muscle Groups ? Skeletal Muscle Groups Pop Quiz 8.6 An antagonist to the gastrocnemius is the Gracilis Sartorius Soleus Tibialis anterior

Skeletal Muscle Groups ? Skeletal Muscle Groups Pop Quiz Answer 8.6 An antagonist to the gastrocnemius is the Gracilis Sartorius Soleus Tibialis anterior

Effects of Aging on Muscles Learning Outcome Describe how muscles change with age.

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

Muscular Disorders Learning Outcome List the major muscular disorders.

Muscular Disorders Common Terms Used When Describing Muscular Disorders Spasms Colic Seizure Convulsion Cramps Atrophy

Muscular Disorders Muscle Injuries Strains Sprains

Muscular Disorders Diseases of Muscle Muscular dystrophy Myasthenia gravis Myalgia Myositis Fibrositis Fibromyositis Fibromyalgia syndrome (FMS)

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Muscular Disorders Disorders of Associated Structures Bursitis Bunions Tendinitis Shinsplints Carpal tunnel syndrome

Figure 8-17 Carpal tunnel syndrome. 82

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Case Study Learning Outcome Identify and locate the muscles involved in the tests carried out in the case study. 84

Case Study Muscles Involved in the Tests Carried Out in the Case Study Flexors of Right Upper Limb Flexors and Extensors of Right Lower Limb Biceps brachii Brachialis Brachioradialis forearm flexors Quadriceps femoris Hamstring group Tibialis anterior Gastrocnemius Soleus Foot/toe flexors Foot/toe extensors

Word Anatomy Learning Outcome 16. Show how word parts are used to build words related to the integumentary system. 86

Word Anatomy Word Part Meaning Example my/o muscle The endomysium is the deepest layer of connective tissue around muscle cells. sarc/o flesh A sarcomere is a contracting subunit of skeletal muscle. syn- with, together A synapse is a point of communication between a neuron and another cell brachi/o arm The biceps brachii and triceps brachii are in the arm. quadr/i four The quadriceps muscle group consists of four muscles. dys- disordered, difficult In muscular dystrophy, there is deterioration of muscles. sthen/o strength Myasthenia gravis is characterized by muscular fatigue (lack of strength).

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