Muscular System PDF

MUSCULAR SYSTEM  KEY CONCEPTS Muscles generally function to allow movement, adjust posture, and produce body heat. The crucial properties of muscle tissue are its ability to contract, be excited by a stimulus, be stretched, and return to its original shape after st...

MUSCULAR SYSTEM  KEY CONCEPTS Muscles generally function to allow movement, adjust posture, and produce body heat. The crucial properties of muscle tissue are its ability to contract, be excited by a stimulus, be stretched, and return to its original shape after stretching or contracting. Skeletal muscles give the skeleton power to move, cardiac muscle is found only in the heart and its specialized anatomy and physiology give it a unique method of contracting and relaxing, smooth muscle is typically involved with involuntary rhythmic contraction of internal organs. Muscles and Muscle Tissue  Overview of Muscle Tissue There are three types of muscle tissue – Skeletal muscle – Cardiac muscle – Smooth muscle These muscle tissues differ in the structure of their cells, their body location, their function, and the means by which they are activated to contract  Overview of Muscle Tissue All muscle cells are elongated cells and are referred to as muscle fibers Muscle contraction depends on two types of myofilaments, actin and myosin All prefixes of myo or mys and sarco reference muscle  Skeletal Muscle Tissue Skeletal muscle tissue appear as distinct muscle that attach to the skeletal system It has obvious striations It is voluntary muscle under conscious control  Skeletal muscle cells run the full length of a muscle Line A show the width of one cell (fiber). Note the striations characteristics of this muscle type. These cells are multicellular, B marks one nucleus. Location: muscles associated with the skeleton  Cardiac Muscle Tissue Cardiac muscle occur only in the heart The muscle is striated but involuntary Cardiac fibers are short, fat, branched and interconnected Cardiac muscle cells are interlocked by intercalated discs and function as a single  Cardiac muscle cells branch, are striated, are uninucleate (B) and have intercalated discs (A). Locations: heart Function: involuntary, rhythmic  Smooth Muscle Tissue It is found in the walls of hollow organs such as the stomach, urinary bladder, and intestines It has no striations It is not subject to voluntary control  Smooth muscle cells are spindle shaped and uninucleate. (B). Locations: walls of hollow organs, i.e. stomach, intestine, uterus, ureter Functions: involuntary movement - i.e. churning of food, movement of urine from the kidney to the bladder, partuition Differences in Contractions Skeletal muscle can contract rapidly but tires easily and must be rested – Skeletal muscle contractions vary in force depending on use – Cardiac muscle contracts at a steady rate but can accelerate to cope with demand – Smooth muscle contracts in steady, sustained contractions and continues on tirelessly  Muscle Functions Muscle performs four important functions in the body: – Producing movement – Maintaining posture – Stabilizing joints – Generating heat  Producing Movement Movement results from muscle contraction Skeletal muscle are responsible for all locomotion and manipulation Allow to interact or react with your external environment It controls eye movement, facial expression, circulation, and moves gas, liquids, and solids through organs  Maintaining Posture Skeletal muscles are utilized constantly to maintain sitting, standing, and moving postures Postural muscle develop to compensate for the never ending pull of gravity – Our developmental milestones as an infant are our initial victories over gravity Curves of the spinal column are shaped by the interplay of skeletal muscle and gravity  Stabilizing Joints Skeletal muscle provide the dynamic stability of joints Many joints are poorly reinforced by ligaments and connective tissue Many joints have noncomplementary surface which do not contribute to stability  Generating Heat Muscles generate heat as they contract The heat generated is vitally important to maintain normal body temperature Skeletal muscle generates most of the heat because it represents 40% of body mass Excess heat must released to maintain body temperature  Functional Characteristics Excitability or irritability – It has the ability to respond to a stimulus Contractility – It has the ability to shorten forcibly Extensibility – Muscle fibers can be stretched Elasticity – Resume its normal length after being shortened Skeletal Muscle  Q&A Q: How much of a person’s body weight is taken up by skeletal muscle? male______ female_____ Choices: A. 30-40 B. 40-50 C. 20-30 D. 35-45 E. 25-35 Answer: for male: 40-50 for female: 30-40  Anatomy of a Skeletal Muscle Each skeletal muscle is a discrete organ with thousands of fibers Muscle fibers predominate the tissue but it contains, blood vessels, nerve fibers, and connective tissue  Connective Tissue Wrappings Each muscle fiber is wrapped by fine sheath of areolar connnective called endomysium Several fibers are gathered side by side into bundles called fascicles Each fascicle is bound by collagen fiber layer called the perimysium  Connective Tissue Wrappings Fascicles are bound by a dense fibrous connective tissue layer called the epimysium The epimysium surrounds the entire muscle External to the epimysium is the deep fascia that binds muscles into functional groups  Connective Tissue Wrappings All the connective tissue layers are continuous with one another as well as with the tendons that join muscles to bone When muscle fibers contract they pull these connective tissue sheaths which in turn transmit the force to the bone to be moved Connective tissue supports each cell  Q&A Q: What makes one muscle larger than another? A: Ordinarily, one muscle is larger than another because it contains more bundles of fibers. The largest muscle are found where large, forceful movements are common, such as in the back and legs. When a muscle is enlarged by exercise, the fibers increase in diameter, but the number of fibers remains the same  MICROSCOPIC ANATOMY MUSCLE FIBERS- individual specialized cells. MYOFILAMENTS- smaller fibers of the muscle fiber. MYOSIN- thick myofilament ACTIN- thin myofilament SARCOLEMMA- plasma membrane SARCOPLASM- cytoplasm SARCOPLASMIC RETICULUM- like the ER SARCOMERE- fundamental unit of muscle contraction.  MICROSCOPIC ANATOMY A BAND- dark bands of the skeletal muscle fibers. I BANDS- light bands of the skeletal muscle consisting only of actin myofilaments. Z LINES- dark lines that can be seen in the middle of the I BANDS. It is a network of protein fibers forming attachment site for actin myofilaments. H ZONE- a second light zone at the center of each sarcomere which consist only of myosin filament. MICROSCOPIC ANATOMY  Nerve and Blood Supply Normal activity of skeletal muscle is totally dependent on its nerve and blood supply Each skeletal muscle fiber is controlled by a nerve ending Contracting muscle fibers use huge amounts of energy which requires a continuous supply of oxygen and nutrients In general, each muscle is served by an artery and one or more veins  Attachments Most muscles span joints and have at least two attachments Origin – Attachment of a muscle that remains relatively fixed during muscular contraction – Generally a more proximal or axial location Insertion – Attachment of a muscle that moves during muscular contraction – Generally a more distal or appendicular attachment  Attachments Direct attachments have the epimysium attaching directly to the periosteum of the bone or perichondrium of a cartilage Indirect attachments have the epimysium attaching to a tendon or an aponeurosis Temporalis has both muscle attachments  The Motor Unit Each muscle is served by at least one motor nerve which contains hundreds of motor neuron axons As a nerve enters a muscle it branches into a number of axonal terminals, each of which forms a neuromuscular junction with a single nerve fiber A motor neuron and all the muscle fi bers it supplies is called a motor unit  The Motor Unit When a motor neuron transmits an electrical impulse all the muscle fibers that it innervates respond by contracting The average number of muscle fibers per unit is 150 but it ranges from 4 to several hundred  The Motor Unit Muscles that exert very fine control have small motor units Large muscles of locomotion and weight bearing have large motor units and as a consequence have less precise control  The Motor Unit The muscle fibers in a unit are not clustered together but rather are spread throughout the entire muscle Stimulation of a single unit causes a weak contraction of the entire muscle This allows control of the intensity of the contraction  Smooth Muscles Smooth muscle lacks the courser connective tissue seen in skeletal muscle Small amounts of endomysium is found between smooth muscle fibers  Smooth Muscles Smooth muscles are organized into sheets of closely apposed fibers These sheets occur in the walls of all but the smallest blood vessels and in the walls of hollow organs of the respiratory, urinary digestive and reproductive tracts  Smooth Muscles In most cases two sheets of muscles are present with their fibers aligned at right angle to each other These forms the longitudinal (long axis) and circular (encircling) layer These two layers squeeze the contents of the organ  Movement I). Movement along the Axis or Range of motion. A). Nonaxial Movement: B). Uniaxial Movement C). Biaxial Movement D). Multiaxial Movement II). Types of motion A). Gliding Movements One flat bone slides over another.  Muscular Movements FLEXION- bending motion in which angle between 2 bones is decreased. EXTENSION- straightening motion in which angle between 2 bones is increased. HYPEREXTENSION- Extension beyond straight position. DORSIFLEXION- flexion of foot and ankle joint PALMAR FLEXION- flexion of hand wrist PLANTAR FLEXION- extension of foot ankle B). Angular Movements Increase or decrease the angle between 2 bones 1). Flexion. Bending motion that decreases the angle of the joint bringing the 2 bones closer together. 2). Extension Movement that increases the angle between the 2 bones. 3.Hyperextension bending the head backward. 3). Dorsiflexion (of the foot) Lifting the foot up so that it points to the shin. 4). Plantar (of the foot) Pointing the foot down. 5). Abduction Raising an arm laterally or spreading the fingers. 6). Adduction Movement of the limb toward the body. 7). Circumduction Movement of a limb in a circle or cone shape. C). Rotation Turning of the bone along its own long axis. Only movement allowed between first 2 cervical vertebra D). Special Movements 1). Supination Movement of the radius around the ulna. palm faces up 2). Pronation Movement of the radius around the ulna. palm faces down 3). Inversion Sole of the foot turns medially 4). Eversion Sole of the foot turns laterally. 5). Protraction Nonangular anterior motion along the transverse plane. Jutting the jaw out 6. Retraction Nonangular posterior motion along the transverse plane. Pulling the jaw back. 7. Elevation Lifting a body part superiorly Shrugging shoulders closing the mouth. 8). Depression Moving a body part inferiorly Opening the mouth. 9). Opposition Movement of the thumb in relation to other digits. THE MAJOR MUSCLE S PHYSIOLOGY OF MUSCLE CONTRACTION  SLIDING –FILAMENT MODEL Muscle tissue contracts when the 2 kinds of myofilaments slide past each other, increasing the amount of overlap. In maximally contracted muscle, the myosin filaments are pulled inward the M line so that they actually overlap in the H zone. In partially contracted muscle, the myosin filaments of a sarcomere are separated by a relatively small space in the H zone In relaxed muscle, the distance between myosin filaments in the H zone is relatively large. Thus the length of the sarcomere can be seen to change with the degree of contraction.  EXCITATION- CONTRACTION COUPLING The molecular basis for muscle contraction Powered by the hydrolysis of ATP. A complete actin myofilament is made up not only of actin but also of the proteins, tropomyosin and troponin. These are arranged in thin, twisted strands. The myosin is composed of myosin molecules, which have oval-shaped “heads” and long “tails”  MUSCLE RELAXATION Acetylcholine is broken down by acetylcholinesterase. This breakdown prevents further stimulation of the muscle fiber by the motor neuron. Without the stimulation of an action potential, the Ca ions move away from the myofilaments and are actively transported to the sarcoplasmic reticulum by Ca-ATPase.  MUSCLE RELAXATION Without calcium, troponin and tropomyosin once again block the binding sites on the actin myofilaments, preventing myosin from forming cross bridges with actin. As the myosin & actin return to their original positions, the I bands become broader and the Z lines move farther apart.  TYPES OF MUSCLE CONTRACTION TWITCH momentary contraction of a muscle in response to a single stimulus such as electric current. TETANUS if a muscle receives repeated stimuli at a rapid rate, it cannot relax completely between contractions. The tension achieved under such conditions is greater than the tension of a single muscle twitch and is called summation of twitches. A more or less continuous contraction of muscle is called tetanus  CONTINUATION INCOMPLETE TETANUS This occurs when incomplete relaxations are still evident between contractions. COMPLETE TETANUS Occurs when the muscle is in a steady state of contraction with no relaxation at all between stimuli as in “lockjaw”  CONTINUATION TREPPE A type of contraction wherein a rested muscle receives repeated stimuli over a prolonged period, the first few contractions increase in strength so that the myogram starts out looking like an upward staircase. ISOTONIC & ISOMETRIC CONTRACTIONS ISOTONIC Muscle contracts by becoming shorter and thicker. Tension remains constant as movement takes place Example. Pulling a door. ISOMETRIC Muscles develop tension but remain the same length Example. Holding and open door.  Q&A Q: What causes “rigor mortis” A: 3 or 4 hrs after death, ATP in muscles breaks down and is not replaced. Thus, there is no ATP to release the cross bridges between the actin and myosin myofilaments. The myofilaments become locked in place, and the muscles become rigid. It is complete in about 12 hours. About 15 to 25 hrs later, the muscle proteins are destroyed by enzymes in the cells, the rigor mortis disappears.