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©2004 John Wiley & Sons, Inc. All rights reserved.
Chapter 8: The Muscular System
Anatomy and PhysiologyMr. Rhine
©2004 John Wiley & Sons, Inc. All rights reserved.
Types of Muscle Tissue
• The types of muscle are categorized by location, histology, and modes of control.
• There are three recognizable types of muscular tissue: SKELETAL, cardiac and smooth.
• Skeletal muscle tissue is primarily attached to the bones. It is striated and under voluntary control.
• Cardiac muscle is the principal muscle lining the walls of the heart. It is striated and involuntary (not under conscious control).
• Smooth muscle, also known as visceral muscle, is located in the major organs (viscera) and the walls of the blood vessels. It is non-striated and involuntary.
©2004 John Wiley & Sons, Inc. All rights reserved.
Function of Muscle Tissue
• Muscle tissue has five key functions. These include producing body movements, movement of substances within the body, stabilizing body positions, regulating organ volume, and generating heat.
• Producing body movements in function is related to walking or running. It is also finely tuned as in grasping a pen.
©2004 John Wiley & Sons, Inc. All rights reserved.
Function of Muscle Tissue
• Movement of substances within the body includes cardiac and smooth muscle.
• The cardiac muscle, through contraction, propels and moves the blood though the vessels of the body.
• Smooth muscle, through contraction, is involved in the movement of substances in the digestive, urinary and reproductive tracts.
©2004 John Wiley & Sons, Inc. All rights reserved.
Function of Muscle Tissue
• Stabilizing body position allows for proper posture during sitting and standing.
• Regulating organ volume involves the sustained contractions of ring-like bands of smooth muscles called sphincters which prevent outflow of contents of a hollow organ.
• Heat production arises from heat (energy) generated during contraction of muscle tissue.
©2004 John Wiley & Sons, Inc. All rights reserved.
Characteristics of Muscular Tissue
• Muscles are excitable — they are capable of receiving and responding to stimuli.
• Muscles exhibit contractibility — the ability to shorten and thicken.
• Muscles exhibit extensibility — the ability to be stretched.
• Muscles exhibit elasticity — the ability to return to their original shape after contraction or extension.
©2004 John Wiley & Sons, Inc. All rights reserved.
Skeletal Muscle Tissue
• Skeletal muscle tissue contains connective tissue components. The fasciae are sheets of fibrous connective tissue beneath the skin or around muscle and organs of the body.
Epimysium covers the entire muscle,
Perimysium covers the fascicules, and
Endomysium covers the individual muscle fibers.
•Extensions of connective tissue beyond the muscle cells include tendons, which attach muscle to bone or other muscles.
©2004 John Wiley & Sons, Inc. All rights reserved.
Skeletal Muscle Tissue
• Skeletal muscle tissue contains both nerve and blood supplies. Nerves convey impulses for muscular contractions. Blood provides the essential nutrients and oxygen while removing many of the metabolic wastes resulting from contraction.
• Histologically, skeletal muscle consists of fibers (cells) covered by a sarcolemma (plasma membrane). The fibers contain sarcoplasm, multiple nuclei, sarcoplasmic reticulum, and transverse tubules.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.01 Organization of Skeletal Muscle and its Connective Tissue Coverings
©2004 John Wiley & Sons, Inc. All rights reserved.
Skeletal Muscle Tissue
• Each muscle fiber contains smaller units called myofibrils that consist of thin and thick proteinaceous filaments.
• The filaments are compartmentalized into units of contraction called sarcomeres.
• The thin filaments are composed of actin, tropomyosin and troponin.
• The thick filaments are composed mostly of myosin and contain projecting myosin heads called cross-bridges that contain actin and ATP binding sites.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.02 Organization of Skeletal Muscle from Gross to Molecular Levels
©2004 John Wiley & Sons, Inc. All rights reserved.
Contraction and Relaxation of Skeletal Muscle
• The mechanics of muscle contraction follow the Sliding-Filament Theory.
• A motor neuron is responsible for transmitting the nerve impulse (action potential) to a skeletal muscle where it serves as the stimulus for contraction.
• The point at which the motor neuron and the muscle sarcolemma meet is referred to as the neuromuscular junction (NMJ).
©2004 John Wiley & Sons, Inc. All rights reserved.
Contraction and Relaxation of Skeletal Muscle
• A chemical neurotransmitter released at neuromuscular junctions in skeletal muscle is acetylcholine (Ach).
• The motor (efferent) neuron and all of the muscle fibers it stimulates form a motor unit.
• A single motor unit may affect as few as 10 or as many as 2000 muscle fibers
• The number of motor units that fire in a muscle at any one time is the basis for the variability in contraction.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.03 Detailed Structure of Filaments
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.04 Sliding-Filament Mechanism of Muscle Contraction
Contraction and Relaxation of Skeletal Muscle
• The mechanics of muscle contraction follow the Sliding-Filament Theory.
• A motor neuron is responsible for transmitting the nerve impulse (action potential) to a skeletal muscle where it serves as the stimulus for contraction.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.04 Sliding-Filament Mechanism of Muscle Contraction
Contraction and Relaxation of Skeletal Muscle
• The point at which the motor neuron and the muscle sarcolemma meet is referred to as the neuromuscular junction (NMJ).
• A chemical neurotransmitter released at neuromuscular junctions in skeletal muscle is acetylcholine (Ach).
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.05 Neuromuscular Junction
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.04 Sliding-Filament Mechanism of Muscle Contraction
Contraction and Relaxation of Skeletal Muscle
• The motor (efferent) neuron and all of the muscle fibers it stimulates form a motor unit.
• A single motor unit may affect as few as 10 or as many as 2000 muscle fibers
• The number of motor units that fire in a muscle at any one time is the basis for the variability in contraction.
©2004 John Wiley & Sons, Inc. All rights reserved.
Physiology of Contraction
• When a nerve impulse, or action potential, reaches the axon terminal, the synaptic vesicles in the axon terminal release ACh.
• The release of ACh ultimately initiates a muscle action potential in the muscle fiber sarcolemma.
• The muscle action potential travels into the transverse tubules and causes the sarcoplasmic reticulum to release stored calcium ions (Ca+) into the sarcoplasm.
• The released calcium combines with troponin which pulls on the tropomyosin filaments and changes their orientation. This exposes the myosin-binding sites on the thin filament.
• Splitting ATP with ATPase into ADP + phosphate releases energy which activates the myosin cross-bridges.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.06 The Contraction Cycle
Crossbridges being activated!
©2004 John Wiley & Sons, Inc. All rights reserved.
Physiology of Contraction• The activated cross-bridges attach to the thin
filament, and a change in the orientation of the cross-bridges occurs. This is called a power stroke.
• The power stroke results in the sliding of the thin filaments.
• Repeated detachment and reattachment of the cross-bridges results in the shortening (isotonic contraction) or increased tension without shortening (isometric contraction) of the muscle.
• The enzyme, acetylcholinesterase (AChE), in the neuromuscular junction, destroys acetylcholine and stops the generation of a muscle action potential.
• Calcium ions are then reabsorbed into the sarcoplasmic reticulum, exposing the troponin. This causes the cross-bridges to separate and the muscle fiber resumes its resting state, or relaxation.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.07 Summary of Events of Contraction and Relaxation
©2004 John Wiley & Sons, Inc. All rights reserved.
Energy for Contraction
• The immediate and direct source of energy for muscle contraction is ATP.
• Creatine phosphate and the metabolism of glycogen and fats are necessary for the continuous generation of ATP by muscle fibers.
• Creatine phosphate and ATP allow for initial contraction and short bursts of maximal contraction lasting up to fifteen seconds.
• The glycogen-lactic acid system provides energy via glycolysis. This is an anaerobic process which will allow thirty to forty seconds of maximum muscular contraction after the creatine phosphate supply is exhausted.
• An aerobic respiration and glycolysis are used for prolonged muscular contraction and will function efficiently as long as oxygen and nutrients are present in adequate amounts.
©2004 John Wiley & Sons, Inc. All rights reserved.
Muscle Fatigue and Oxygen Consumption
• Muscle fatigue is the inability of a muscle to contract forcefully after prolonged activity.
• Recovery oxygen uptake refers to the elevated use of oxygen after exercise.
©2004 John Wiley & Sons, Inc. All rights reserved.
Control of Muscle Tension
• Skeletal muscles are capable of producing several different types of contractions, depending upon the strength and frequency of stimulation.
• The various kinds of contractions are twitch, tetanus, isotonic, and isometric.
• A myogram is a record of muscular contraction shows the various phases involved in the various phases of muscular contraction.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.08 Myogram of a Twitch Contraction
The three major phases are the latent period, contraction period, and relaxation period.
©2004 John Wiley & Sons, Inc. All rights reserved.
Control of Muscle Tension
• The latent period is the time lapse between the action potential and the response of the muscle fibers.
• The contraction period is the time frame in which the muscle fibers are undergoing shortening.
• The relaxation period is that time frame when a muscle has temporarily lost its excitability.
• Skeletal muscles have short relaxation periods.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.09 Myograms Showings the Effects of Different Frequencies of Stimulation
A - Single Twich
B – Wave Summation
C – Unfused tetanus
D – Fused Tetanus
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.10 Histology of Smooth Muscle Tissue
©2004 John Wiley & Sons, Inc. All rights reserved.
Control of Muscle Tension
• There are three types of muscle fibers contained in skeletal muscles: slow oxidative (so), fast oxidative-glycolytic (fog), and fast glycolytic (FG).
• Skeletal muscles contain a mixture of the three types of muscle fibers.
• Slow oxidative fibers are resistant to fatigue and capable of prolonged contractions.
• Fast-oxidative glycolytic fibers contract and relax more quickly than so fibers, and have a moderately high resistance to fatigues.
• Fast glycolytic fibers fatigue quickly but generate the most powerful and rapid contractions in the body.
©2004 John Wiley & Sons, Inc. All rights reserved.
Cardiac Muscle
• Cardiac muscle is found only in the heart. It is striated and its action is involuntary.
• Muscle fibers branch freely, contain a single, centrally located nucleus, and are connected via gap junctions.
• Cardiac muscle cells are connected via intercalated discs which aid in the conduction of muscle action potentials by way of the gap junctions located at the discs.
• Cardiac muscle contracts and relaxes rapidly, continuously, and rhythmically.
• Cardiac muscle is Autorhythmic, it can contract without extrinsic stimulation and can remain contracted for sustained periods of time.
©2004 John Wiley & Sons, Inc. All rights reserved.
Smooth Muscle
• Smooth muscle is non-striated and involuntary. It is also referred to as visceral muscle.
• The smooth muscle fibers are elongated, tapered fibers with a single, centrally located nucleus. They contain actin and myosin myofilaments, but unlike skeletal muscle, the filaments are not arranged in an orderly fashion.
• Visceral (or single unit) smooth muscle, is found in the walls of the viscera as well as the walls of both small arteries and veins.
©2004 John Wiley & Sons, Inc. All rights reserved.
Smooth Muscle
• Multiunit smooth muscle is found in large blood vessels, large airways, and in the eyes. The muscle fibers operate singly, rather than as a unit.
• Compared to skeletal muscle, smooth muscle displays a longer duration of contraction and relaxation.
• Smooth muscle fibers respond to nerve impulses, hormones, and local chemical factors.
• Smooth muscle fibers are very extensible without developing tension.
©2004 John Wiley & Sons, Inc. All rights reserved.
Figure 8.11 Relationship of Skeletal Muscles to Bones
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Figure 8.12b Principal Superficial Skeletal Muscles, Posterior View
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Figure 8.12a Principal Superficial Skeletal Muscles, Anterior View
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Skeletal Muscles and Movement
• Skeletal muscles produce movements by exerting force on tendons, which in turn, pull bones or other structures, such as skin.
• Most muscles cross at least one joint and are attached to the articulating bones that form the joint. The bones serve as levers while the joints serve as fulcrums.
• When a muscle contracts, it draws a movable bone toward a stationary one.
• The origin is the point of attachment on the stationary bones, while the insertion is the point of attachment on movable bones.
©2004 John Wiley & Sons, Inc. All rights reserved.
Group Actions of Skeletal Muscle
• Most movements are coordinated by several skeletal muscles acting in groups rather than individually.
• Most skeletal muscles are arranged in opposing pairs at joints.
• The muscle that causes a desired movement is called the prime mover or agonist; the antagonist produces the opposite action.
• Most movements also involve muscles called synergists. These function to steady movements and to aid the agonist in functioning more efficiently.
• Muscles can also be fixators which stabilize the origin of the agonist so that it can operate more efficiently.
• Most muscles can act as agonists, antagonists, synergists, or fixators depending on the movement.
©2004 John Wiley & Sons, Inc. All rights reserved.
Naming Skeletal Muscles
• There are nearly 700 skeletal muscles. Their names are based on several characteristics. The muscle names may indicate the direction of muscle fibers or their size, shape, action, number of origins, or origin, and insertion points, or their location.
©2004 John Wiley & Sons, Inc. All rights reserved.
P r i n c i p a l S k e l e t a l M u s c l e s
FACIAL EXPRESSION
LOWER JAW EYEBALL MOVEMENT
occipitofrontal masseter superior rectus
zygomaticus major temporalis inferior rectus
buccinator lateral rectus
platysma medial rectus
orbicularis oculi superior oblique
inferior oblique
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Figure 8.13 Muscles of Facial Expression
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Figure 8.14a Muscles that Move the Mandible
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Figure 8.14b Muscles that Move the Mandible
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Figure 8.15 Extrinsic Muscles of the Eyeball
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Figure 8.16 Muscles of the Male Anterolateral Abdominal Wall
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P r i n c i p a l S k e l e t a l M u s c l e s
ANTERIOR ABDOMEN
BREATHING SHOULDER GIRDLE
rectus abdominis diaphragm subclavius
external obliquetransversus abdominis
external & internalpectoralis minor
rhomboideus majorpectoralis minor
internal oblique intercostals serratus anterior
trapezius
levator scapulae
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Figure 8.17 Muscles Used in Breathing
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Figure 8.18a-b Muscles that Move the Pectoral, Anterior View
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Figure 8.18c-d Muscles that Move the Pectoral, Posterior View
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Figure 8.19 Muscles that Move the Humerus
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Figure 8.20 Muscles that Move the Radius and Ulna
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P r i n c i p a l S k e l e t a l M u s c l e s
ARM MOVEMENT` FOREARM MOVEMENT
VERTEBRAL COLUMN
pectoralis major biceps brachii sternocleidomastoid
latissimus dorsi brachialis rectus abdominis
deltoid triceps brachii quadratus lumborum
subscapularis supinator sacrospinalis
supraspinatus pronator teres
infraspinatus
teres major
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Figure 8.21 Muscles that Move the Wrist, Hand, and Fingers
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Figure 8.22 Muscles that Move the Vertebral Column
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Figure 8.23 Muscles that Move the Femur
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THIGH MOVEMENT LOWER LEG MOVEMENT
psoas major adductor magnus
iliacus adductor longus
gluteus maximus pectineus
gluteus medius gracilis
gluteus minimus quadriceps femoris
tensor facia lata sartorius
adductor longus biceps femoris
adductor magnus semitendinosus
pectineus semimembranosus
P r i n c i p a l S k e l e t a l M u s c l e s
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Figure 8.24a-b Muscles that Move the Foot and Toes, Posterior Views
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Figure 8.24c-d Muscles that Move the Foot and Toes, Anterior and Right Lateral Views
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Exercise and Aging
• Muscle hypertrophy refers to an increase in the diameter of muscle fibers while muscle atrophy refers to a wasting away of muscle muscles.
• There is a progressive loss of skeletal muscle mass beginning at about 30 years of age.
• Endurance and strength training can retard these age-related changes.
©2004 John Wiley & Sons, Inc. All rights reserved.
Table 8.01 Summary of the Principal Features of Muscular Tissue
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Table 8.02a Characteristics Used to Name Skeletal Muscles
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Table 8.02b Characteristics Used to Name Skeletal Muscles