The Muscular System

Skeletal Muscle Functions Produce movement Maintain posture Stabilize joints Generate heat

Characteristics of Muscles Skeletal and smooth muscle cells are elongated (muscle cell = muscle fiber) Contraction of muscles is due to the movement of microfilaments All muscles share some terminology –Prefixes myo and mys refer to “muscle” –Prefix sarco refers to “flesh”

Skeletal MuscleSmooth MuscleCardiac Muscle LocationAttached by tendons to bones Hollow internal organs Only in the heart Shape AppearanceMultinucleate and striated No striations and 1 nucleus Branched, striations, 1 nucleus Speed of Contraction Contracts quickly but tires Slow and steady (peristalsis) Slow (Pacemaker) Regulation of Contraction VoluntaryInvoluntary

SKELETAL MUSCLE

Smooth muscle around this artery allows the artery to regulate blood flow by shrinking and expanding. SMOOTH MUSCLE

CARDIAC MUSCLE

Structure and Organizational Level Muscle (organ) Hundreds to thousands of muscle cells, connective tissue wrappings, blood vessels and nerve fibers Fascicle (portion of muscle) Bundles of muscle cells segregated from the rest of the muscle by connective tissue Muscle Fiber (Cell)Elongated multinucleate cell with a striated appearance

Structure and Organizational Level Myofibril or Fibril Complex organelle composed of bundles of myofilaments SarcomereA segment of a myofibril The contractile part composed of myofilaments Myofilament of filament Contractile filaments composed of proteins Includes myosin and actin

Muscle Fascicle Muscle Fibers

Myofibril or fibril Sarcomere Myofilament or filament

Anatomy of Skeletal Muscle From internal to external: –Endomysium Connective tissue covering surrounding each individual muscle fiber

Anatomy of Skeletal Muscle Fassicle groups of muscle fibers together surrounded by connective tissue called perimysium

Anatomy of Skeletal Muscle Epimysium Connective tissue surrounding the whole muscle Epimysium surrounding quadriceps

Muscle Contraction Important Information to Remember: –Sarcomere—contractile unit of a muscle fiber –Organization of the sarcomere Myofilaments –Thick filaments = myosin filaments –Thin filaments = actin filaments – ucture/an/m5/s5/anm5s5_8.htmhttp:// ucture/an/m5/s5/anm5s5_8.htm

Myosin –Each molecule has a rod-like tail and two the heads –The heads link the thick and thin filaments together to form cross bridges Muscle Contraction

Sliding Filament Theory of Contraction –During contraction, the thin filaments slide past thick ones so that actin and myosin overlap –The myosin heads latch on to the binding sites on actin in the thin filaments and sliding begins –Cross bridges are formed and broken several times during contraction Act like ratchets to generate tension and sling the thin filaments towards the center of the sarcomere –When this happens, the sarcomere shortens and contraction occurs

Muscle Tone Relaxed muscles are almost always slightly contracted (partial contraction) Does not produce active movements –keeps muscles firm, healthy, and ready to respond to stimulation

Muscles and Body Movements Movement is attained due to a muscle moving an attached bone Muscles are attached to at least two points –Origin Attachment to a moveable bone –Insertion Attachment to an immovable bone

Muscles and Body Movements Prime Movers –Provides the major force for producing a movement Antagonists –Muscles that oppose or reverse a particular movement Synergists –Help prime movers by adding extra force and reducing unnecessary movements

Prime Movers and Antagonists

Finger flexor muscles cross both the wrist and finger joints but you can make a fist without bending your wrist because synergistic muscles stabilize the wrist

Flexion –Brings two bones closer together –Typical of hinge joints like knee and elbow Extension –Movement that increases the distance between 2 bones –Straightening a elbow or knee Muscles and Body Movements

Figure 6.13a

Figure 6.13b

Abduction –Movement of a limb away from the midline of the body Adduction –Movement of a limb toward the midline of the body Muscles and Body Movements

Figure 6.13d

Effect of Exercise on Muscles Exercise increases muscle size, strength, and endurance Muscle inactivity leads to muscle weakness and wasting (atrophy) –Types of Exercise Aerobic Resistance

Aerobic Exercise –Results in stronger, more flexible muscles with greater resistance to fatigue –Better body metabolism and improved digestion and coordination Effect of Exercise on Muscles

Resistance Exercise –Increases muscle size and strength –Increases size of muscle fibers instead of number of muscle fibers

Muscle Fatigue and Oxygen Deficit When a muscle is fatigued, it is unable to contract even with a stimulus Common cause for muscle fatigue is oxygen debt –Oxygen must be “repaid” to tissue to remove oxygen deficit –Oxygen is required to get rid of accumulated lactic acid Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

Homeostatic Imbalances Muscular Dystrophy (inherited muscle destroying diseases) –Duchenne Muscular Dystrophy Most common and serious form Inherited as a sex-linked recessive disease, so it is almost exclusively seen in males (1 in every 3500 births) Diagnosed between ages 2 and 7 Skeletal muscles weaken so movement becomes clumsy and falling is common Progresses from extremities upward, finally affecting the head and chest muscles and cardiac muscle of the heart Rarely live beyond their early 20s