Muscular System Skeletal Smooth Cardiac n Our body
Muscular System Skeletal, Smooth, & Cardiac
n Our body without muscles!!! AHHH!!
Muscles The term muscle? n “mus” of course is Latin and means little mouse. n The connection? ? ? n When flexing, muscles look like little mice scurrying beneath the skin…who knew? n
About our Muscles Almost half the body’s weight is muscle. n Muscles produce all movement in our body and allow for circulation. n Muscles are made of special tissues that can contract or shorten when they receive a signal from the brain. n
About our Muscles n Muscles are attached to bones by stretchy tissue called tendons. n When muscles contract, they pull on the tendons which pull on the bones and cause our limbs to move.
About our Muscles n Who can remember…what are three types of muscle tissue? n Skeletal n Cardiac n Smooth
Cardiac Muscle n n n Only in heart Involuntary Striated (like skeletal) Makes up wall of heart Pumps 5 liters of blood per minute Fibers branch and have single nucleus per cell n Function: pumping of the heart n
Cardiac Muscle
Smoothmuscle Muscle n Involuntary n Walls all hollow organs (except heart) n Regulates blood flow in arteries n Expels urine from urinary bladder n Regulates flow of air through lungs
Smooth Muscle
Skeletal Muscle Striated muscle n Made of muscle tissue, nervous tissue, blood, & connective tissues n Under voluntary control n All of these muscles attach to skeleton n
Skeletal Muscle
Characteristics of Muscles Tissue! n Muscle tissue is endowed with some special functional properties that enable it to perform its duties – Excitability (responsiveness) – Contractility – Extensibility – Elasticity
Function of Muscles! n Of course muscles perform 4 important functions – Produce Movement – Maintain Posture – Stabilizing Joints – Generating Heat!
About our Muscles n There are more than 640 muscles and they hardly ever work alone. n Muscles can get shorter and pull, but they can’t push
About our Muscles n Most muscles are arranged in opposing teams n 1 team pulls the body part 1 way and the other team pulls it back again n (Abduction and adduction)
Vocabulary Abduction- pulls away n Adduction- pulls toward you n Voluntary- can be controlled by thoughts in the brain n Involuntaryautomatically controlled by brain n
Skeletal Muscle: Nerve and Blood Supply Each muscle is served by one nerve, an artery, and one or more veins n Muscles are rich in arteries and veins to carry fuel and oxygen to the muscles and veins to carry waste products and carbon dioxide away. n Each skeletal muscle fiber is supplied with a nerve ending that controls contraction n
Skeletal Muscle Each muscle is a discrete organ composed of muscle tissue, blood vessels, nerve fibers, and connective tissue n Please familiarize yourself with the Table on pg 282…The Organizational level of skeletal muscles. n The Muscle (organ), Fascile (a portion of the muscle), Muscle fiber (cell), Myofibril or fibril (complex organelle), Sacromere (segment of a myofibril), and myofilament or filament. We will discuss this in more detail in a few slides. n
Skeletal Muscle
Skeletal Muscle
Skeletal Muscle In an intact muscle, the individual muscles fibers are wrapped and held together by several different connective tissue sheaths. n Together these connective tissue sheaths support each cell and reinforce the muscle as a whole, preventing the bulging muscles from bursting during exceptionally strong contractions. n
Skeletal Muscle n The three connective tissue sheaths are: – Endomysium – fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber – Perimysium – fibrous connective tissue that surrounds groups of muscle fibers called fascicles – Epimysium – an overcoat of dense regular connective tissue that surrounds the entire muscle
Skeletal Muscle n surrounds the entire muscle
Skeletal Muscle n An individual skeletal n This connective muscle is separated tissue surrounds from adjacent each muscle and muscles and held in may project beyond position by layers of the end of its muscle dense connective fibers to form a tissue called fascia. cordlike tendon.
Skeletal Muscle
Skeletal Muscle: Attachments n Most skeletal muscles span joints and are attached to bone in at least two places n When muscles contract the movable bone, the muscle’s insertion moves toward the immovable bone, the muscle’s origin.
Skeletal Muscle: Attachments n Muscles attach: – Directly – epimysium of the muscle is fused to the periosteum of a bone – Indirectly – connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis. – Of the two indirectly is much more common because of the durability of tendons.
Microscopic Anatomy of a Skeletal Muscle Fiber n This section can be very confusing…I am giving you a less detailed version. n Hope this helps I promise its much easier to understand.
Microscopic Anatomy of a Skeletal Muscle Fiber n One muscle fiber is an elongated multnucleate cell that has a banded appearance. n The muscle fiber (or cell) is composed of a Myofibrils (fibril).
Microscopic Anatomy of a Skeletal Muscle Fiber These Myofibrils occupy most of the volume of a cell and are composed of a number of thick and thin filaments. n The thick filaments are made of a protein known as myosin and the thin filaments of a protein called actin. n This arrangement of bands are called Sarcomere and it is this sacromere that is the contractile unit of the muscle cell or fiber n
Sarcomeres
Sarcomeres n Within the muscle cell are supporting structures to generate energy, the mitochondria and some fuel stores.
Sarcomeres n Within the muscle cell are supporting structures to generate energy, the mitochondria and some fuel stores.
Sacroplasmic Reticulum n There is also a network of channels within the muscle to transmit signals from the surface throughout the muscle called the sacroplasmic reticulum.
A little more detail on Myosin Filament n Thick filaments are composed of the protein myosin n Each myosin molecule has a rod-like tail and two globular heads – Tails – two interwoven, heavy polypeptide chains – Heads – two smaller, light polypeptide chains called cross bridges
A little more detail on Myosin Filament
A little more detail on the Thin Filaments Thin filaments are chiefly composed of the protein actin n The subunits contain the active sites to which myosin heads attach during contraction. n Tropomyosin and troponin found in the thin filaments are the molecular switches that control the interaction of actin and myosin during a muscle contraction. n
Ultrastructure of Myofilaments: Thin Filaments
How do Muscle actually contract? When you want to move, electrical impulses come from the brain, down through the spinal cord and are transmitted through the motor nerves to the muscles. n At the junction between the nerve end and the muscle (the motor end plate), chemical signals are released from the nerve endings. (acetylcholine). This binds to a key on the surface of the muscle (the receptor) n
How do Muscle actually contract? The binding of this chemical to the receptor causes calcium to enter the muscle cell, and this enable the troponin proteins to move the myosin up the actin molecule. n This causes the functional unit, the sarcomere, to shorten and when several of these shorten along the length of the fibre, the muscles as a whole contracts and shortens. n
How do Muscle actually contract? To release the bond between actin and myosin needs energy, to shorten the muscle further or to cause it to relax. n When the signal for contraction ends, the calcium is pumped back into the sacroplasmic reticulum and the muscle relaxes. n
Contraction of Skeletal Muscle Fibers The operation of most skeletal muscles involves the use of leverage and lever systems n The force exerted by a contracting muscle on an object is called muscle tension n The opposing force exerted on the muscle by the weight of the object to be moved is called the load. n
Contraction of Skeletal Muscle Fibers n Contraction of muscle fibers (cells) and muscles (organs) is similar n The two types of muscle contractions are: – Isometric contraction – increasing muscle tension (muscle does not shorten during contraction) – Isotonic contraction – decreasing muscle length (muscle shortens during contraction)
Isometric Contractions n Tension increases to the muscle’s capacity, but the muscle neither shortens nor lengthens n Occurs if the load is greater than the tension the muscle is able to develop
Isometric Contractions
Isotonic Contractions n In isotonic contractions, the muscle changes in length (decreasing the angle of the joint) and moves the load
Isotonic Contractions
Muscle Twitch n. A muscle twitch is the response of a muscle to a single, brief threshold stimulus n There are three phases to a muscle twitch – Latent period – Period of contraction – Period of relaxation
Phases of a Muscle Twitch Latent period – first few msec after stimulus; EC coupling taking place n Period of contraction – cross bridges form; muscle shortens n Period of relaxation – Ca 2+ reabsorbed; muscle tension goes to zero n
Treppe: The Staircase Effect n Staircase – increased contraction in response to multiple stimuli of the same strength n Contractions increase because: – There is increasing availability of Ca 2+ in the sarcoplasm – Muscle enzyme systems become more efficient because heat is increased as muscle contracts
Treppe: The Staircase Effect
Muscle Tone n Muscle tone: – Is the constant, slightly contracted state of all muscles, which does not produce active movements – Keeps the muscles firm, healthy, and ready to respond to stimulus n Spinal reflexes account for muscle tone by: – Activating one motor unit and then another – Responding to activation of stretch receptors in muscles and tendons
Muscle Metabolism: How do Muscles Get the Energy Needed for Contraction? ATP is the only source used directly for contractile activity. n Remember ATP’s produced in the Mitochondria. They are energy storing molecules…the energy is released when one of the phosphate bonds is broken then forming ADP. n Muscles can work in one of two environments…Aerobic and Anaerobic Exercise. n
Energy Sources for Contraction ATP supplies energy n ATP is necessary for contractions both muscle contraction and n Active muscles relaxation depend on cellular respiration for energy n
Aerobic Exercise As long as it has enough oxygen, a muscle cell will form ATP by aerobic reactions. n This is internal stores of ATP and can be supplemented by high energy phosphate compounds called Creatine Phospate (cp). n This can be for several hours in well conditioned adults. n
Anaerobic Exercise If the rate at which energy is demanded is high…generally when muscle contractile activity reaches 70% of maximum; then this is supplemented by contributions from anaerobic metabolism. n The immediate consequences include: – The production of lactic acid in the muscles which immediately breaks down to lactate and hydrogen ions. – Bulging muscles compress blood vessels. – Oxygen delivery is impaired n
Muscle Metabolism: Anaerobic Glycolysis n The lactic acid: – Diffuses into the bloodstream – Is picked up and used as fuel by the liver, kidneys, and heart – Is converted back into pyruvic acid by the liver
Muscle Fatigue Muscle fatigue – the muscle is in a state of physiological inability to contract n Muscle fatigue occurs when: n – ATP production fails to keep pace with ATP use – There is a relative deficit of ATP, causing contractures – Lactic acid accumulates in the muscle – Ionic imbalances are present
Muscle Fatigue n Intense exercise produces rapid muscle fatigue (with rapid recovery) n Na+-K+ pumps cannot restore ionic balances quickly enough n Low-intensity exercise produces slowdeveloping fatigue n SR is damaged and Ca 2+ regulation is disrupted
Oxygen Debt Oxygen debt – the extra amount of O 2 needed for the above restorative processes n This is why your muscles ache n Vigorous exercise causes dramatic changes in muscle chemistry n For a muscle to return to a resting state: n – – Oxygen reserves must be replenished Lactic acid must be converted to pyruvic acid Glycogen stores must be replaced ATP and CP reserves must be resynthesized
Heat Production During Muscle Activity n Only 40% of the energy released in muscle activity is useful as work n The remaining 60% is given off as heat n Dangerous heat levels are prevented by radiation of heat from the skin and sweating
Heat Production n Product of cellular respiration n Muscles act as heat source because muscle tissue represents such a large portion of the body
Effects of Aerobic Exercise n Aerobic exercise results in an increase of: – Muscle capillaries – Number of mitochondria – Myoglobin synthesis
Effects of Resistance Exercise n Resistance exercise (typically anaerobic) results in: – Muscle hypertrophy – Increased mitochondria, myofilaments, and glycogen stores
Muscle Fatigue n Fatigue and cramps Muscle loses its may occur together ability to contract n Cramps occur when n Causes: decreased intracellular fluid blood flow, ion triggers uncontrolled imbalances, stimulation of the physcological loss of muscle desire to exercise n
Muscle Fatigue n Usually due to accumulation of lactic acid n Athletes usually produce less lactic acid than nonathletes b/c of their ability to supply oxygen and nutrients to muscles
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