© 2014 Pearson Education, Inc. Human Biology Concepts and Current Issues Seventh Edition Michael D. Johnson Lecture Presentations by Robert J. Sullivan Marist College 6 The Muscular System

© 2014 Pearson Education, Inc. Introduction to Muscles  Muscle tissue is found in every organ  Muscles participate in every activity that requires movement  Large proportion of body weight is muscle –40% of body weight in males –32% of body weight in females  Skeletal muscle: attaches to skeleton and provides strength and mobility  Cardiac muscle: exclusively in the heart  Smooth muscle: walls of digestive tract, blood vessels, uterus, ureters

© 2014 Pearson Education, Inc. Muscles Produce Movement or Generate Tension  Muscles may produce movement –Voluntary: conscious control over movement (picking up a pen) –Involuntary: unconscious control over movement (beating of heart, movement of intestines)  Muscles generate heat

© 2014 Pearson Education, Inc. The Fundamental Activity of Muscle Is Contraction  Excitable: contract in response to electrical or chemical stimuli  All muscle cells have one mechanism of action: –They contract (shorten), then relax (lengthen)

© 2014 Pearson Education, Inc. Pectoralis major Draws arm forward Serratus anterior Contributes to pushes Draws shoulder blade forward Biceps brachii Bends forearm at elbow Rectus abdominus Compresses abdomen External oblique Compresses abdomen Adductor longus Draws thigh toward body Sartorius Bends thigh at hip Quadriceps group striaghtens leg at knee Tibialis anterior Flexes foot toward knee Trapezius Lifts shoulder blade Braces shoulder Deltoid Raises arm Triceps brachi Straightens forearm at elbow Latissimus dorsi Draws arm backward Gluteus maximus Extends thigh Hamstring group Bends knee Gastrocnemius Bends foot away from knee Achilles tendon Connects gastrocnemius muscle to heel

© 2014 Pearson Education, Inc. Skeletal Muscles Cause Bones to Move  600 skeletal muscles  Synergistic muscles: work together to created the same movement  Antagonistic muscles: muscles that oppose each other  Many muscles attach to bones via tendons  Origin: end of muscle that attaches to relatively immovable bone  Insertion: end of muscle attached to relatively movable bone, action pulls insertion toward origin

© 2014 Pearson Education, Inc.

A Muscle Is Composed of Many Muscle Cells  Muscles –Group of muscle fibers with same origin, insertion, and function  Fasicles –Bundles of muscle fibers (cells) wrapped with connective tissue (fascia)  Muscle fibers (muscle cells) –Long, tube shaped –Vary in length from few mm to 30 cm –Multinucleate (many nuclei) –Packed with myofibrils, which are long cylindrical structures which contain proteins actin and myosin filaments

© 2014 Pearson Education, Inc. Figure 6.3 Muscle bundle (fascicle) surrounded by connective tissue (fascia) Whole muscle Single muscle cell (fiber) Tendon Bone

© 2014 Pearson Education, Inc. Figure 6.4 Muscle Cell (muscle fiber) Myofibril Nuclei Muscle cell A single muscle cell contains many myofibrils and has more than one nucleus. A photograph of portions of several skeletal muscle cells.

© 2014 Pearson Education, Inc. The Muscle Contractile Unit Is the Sarcomere  A myofibril is made of end to end sarcomeres:  A sarcomere: contractile unit made of: –Myosin: forms thick filaments –Actin: forms thin filaments  Z Lines: attachment points for sarcomeres  A sarcomere is a segment of myofibril extending from one Z line to the next  Arrangement of filaments gives rise to striated appearance of skeletal muscle

© 2014 Pearson Education, Inc. Figure 6.5 Myofibril Z-line Sarcomere Myosin Actin Thin filament (actin) Thick filament (myosin) A closer view of a section of a myofibril showing that it is composed of sarcomeres joined end to end at the Z-line. An electron micrograph cross section of a sarcomere in a region that contains both actin and myosin. Sarcomeres contain thin filaments of actin that attach to the Z-lines and thicker filaments of myosin a sarcomere..

© 2014 Pearson Education, Inc. Calcium Initiates the Sliding Filament Mechanism  Thick filaments: myosin  Thin filaments: actin  When skeletal muscle is stimulated by nerve, it will contract  Contraction: when thin filaments slide over thick filaments  Calcium must be present for contraction

© 2014 Pearson Education, Inc. Cardiac and Smooth Muscles Have Special Features  Involuntary  Able to contract entirely on their own in absence of nerve stimulation  Cardiac muscle cells –Have gap junctions allowing cells to electrically stimulate the next one  Smooth muscle cells joined by gap junctions allowing cells to activate each other  Cardiac and smooth muscle cells respond to stimulation from autonomic nervous system, which can modify the degree of contraction

© 2014 Pearson Education, Inc. Figure 6.12 Intercalated disc Cardiac muscle cell Adhesion junction Protein channel Gap junction Cell membranes of adjacent cells A closer view showing that intercalated discs are bridged by gap junctions that permit direct electrical connections between cells. A view of several adjacent cardiac muscle cells showing their blunt shape and the intercalated discs that join them together.

© 2014 Pearson Education, Inc. Speed and Sustainability of Contraction  Skeletal muscle: fastest  Cardiac muscle: moderate  Smooth muscle: –Very slow –Partially contracted all of the time –Almost never fatigues

© 2014 Pearson Education, Inc. Arrangement of Myosin and Actin Filaments  Cardiac muscle –Sarcomere arrangement of thick and thin filaments –Striated appearance  Smooth muscle –Filaments not arranged in sarcomeres –No striations

© 2014 Pearson Education, Inc. Cardiac muscle striated Smooth muscle Not striated

© 2014 Pearson Education, Inc. Diseases and Disorders of the Muscular System  Tetanus –Infection of deep wound by bacteria, Clostridium tetani –Bacteria produce tetanus toxin which causes muscles to contract forcefully –Death due to respiratory failure –Preventable by tetanus vaccine  Muscle cramps: often caused by dehydration and ion imbalances  Pulled muscles: result from overstretching of a muscle, fibers tear apart