Chapter 9: Muscular System

Types and Functions of Muscles Skeletal muscle Generally attached to bone and controlled by choice Cells are long/appear striped (striated) Smooth muscle Generally found in the walls of viscera Functions automatically Cardiac muscle Found only in heart Cells are long and branching

Types and Functions of Muscles (cont’d.) Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Copyright © 2007 by Saunders, an imprint of Elsevier Inc. Muscle Structure Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Whole Muscle Structure Belly: fleshy body of muscle between slender points of attachment Fascia: layers of tough connective tissue surrounding large skeletal muscles Epimysium: outermost layer of fascia Perimysium: surrounds small bundles of fibers (middle) Endomysium: surrounds individual muscle fibers (inner) Tendon: strong, cordlike fascia that extends toward and attaches to bone

Muscle Fiber Structure (Muscle cell) Sarcolemma: cell membrane of a muscle fiber Transverse tubules: points of cell membrane that penetrate deep into interior of muscle fiber Sarcoplasmic reticulum: specialized endoplasmic reticulum within muscle fiber Myofibrils: long cylindrical structures in each muscle fiber Sarcomeres: contractile units formed of proteins actin and myosin

Sliding Filament Theory Muscles contract because sarcomeres shorten Sarcomeres shorten because actin and myosin filaments slide past each other Myosin heads make contact with actin when stimulated Myosin heads rotate, pulling actin toward the center of the sarcomere and causing the actin to slide past myosin

Role of Calcium and ATP Contraction and relaxation of muscle: ATP allows the actin and myosin to interact in the presence of calcium Calcium: stored in sarcoplasmic reticulum, away from actin and myosin Muscle relaxation: calcium is stored in SR Muscle contraction: calcium is released from SR Muscle relaxation: calcium is pumped back into SR

Skeletal Muscles and Nerves Motor nerve: type of nerve that supplies skeletal muscle with stimulation Neuromuscular junction (NMJ): area where motor nerve meets muscle fibers

Muscle Contraction The electrical signal (nerve impulse) travels down the nerve to the terminal and causes the release of the neurotransmitter Ach (acetylcholine). The ACh diffuses across the neuromuscular junction and binds to the receptor sites. Stimulation of the receptor sites causes an electrical impulse to form in the muscle membrane. The electrical impulse travels along the muscle membrane and penetrates deep into the muscle through the T-tubular system

Muscle Contraction (cont’d.) 4. The electrical impulse stimulates the sarcoplasmic reticulum to release calcium into the sarcomere area. The calcium allows the actin, myosin, and ATP to interact, causing muscle contraction. This process continues as long as calcium is available to the actin and myosin. Muscle relaxation occurs when calcium is pumped back into the sarcoplasmic reticulum, away from the actin and myosin.

How Skeletal Muscles Are Named Characteristics of skeletal muscles: Size (ex: vastus= huge) Shape (ex: deltoid=triangular) Direction of fibers (transverse=across) Location (ex: pectoralis= chest) Number of origins (ex: biceps= 2) Identification of origin and insertion (ex: sternocleidomastoid) Muscle action (ex: flexor muscle=causes flexion) Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Muscles from Head to Toe Anterior view Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Muscles from Head to Toe (cont’d.) Posterior view Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Muscles of the Head & Neck Facial muscles Frontalis Orbicularis oculi Orbicularis oris Buccinator Zygomaticus Chewing muscles Temporalis Masseter Neck Muscles Sternocleidomastoid Trapezius

Muscles of the Trunk Muscles involved in breathing Intercostal muscles Diaphragm

Muscles of the Abdominal wall External oblique Internal oblique Transversus abdominis Rectus abdominis

Muscles That Move the Shoulder and Upper Arm Trapezius Serratus anterior Pectoralis major Latissimus dorsi Deltoid Rotator cuff muscles

Muscles That Move the Forearm and Hand Biceps brachii Triceps brachii Brachialis Brachioradialis

Muscles We Sit On Gluteus maximus Gluteus medius Gluteus minimus

Muscles That Move the Leg Quadriceps femoris (anterior thigh) Rectus femoris Vastus lateralis Vastus medialis Vastus intermedius Sartorius (Across thigh)

Muscles That Move the Leg Hamstrings (posterior thigh) Biceps femoris Semitendinosus Semimembranosus

Muscles That Move the Ankle and Foot Tibialis anterior Peroneus longus Gastrocnemius Soleus