W4 Muscle Tissues & Muscular System PDF

MUSCULAR TISSUE PHC411 Gurmeet Kaur Surindar Singh (Level 7, FF1) Muscular Tissue ▪ Overview of Muscular Tissue ▪ Skeletal Muscle Tissue ▪ Contraction and Relaxation of Skeletal Muscle Fibers ▪ Muscle Metabolism ▪ Types of Skeletal Muscle Fibers ▪ Exer...

MUSCULAR TISSUE PHC411 Gurmeet Kaur Surindar Singh (Level 7, FF1) Muscular Tissue ▪ Overview of Muscular Tissue ▪ Skeletal Muscle Tissue ▪ Contraction and Relaxation of Skeletal Muscle Fibers ▪ Muscle Metabolism ▪ Types of Skeletal Muscle Fibers ▪ Exercise and Skeletal Muscle Tissue ▪ Cardiac Muscle Tissue ▪ Smooth Muscle Tissue Overview of Muscular Tissue ❑Types of Muscular Tissue The three types of muscular tissue: Skeletal Cardiac Smooth Overview of Muscular Tissue Skeletal Muscle Tissue So named because most skeletal muscles move bones of the skeleton Skeletal muscle tissue is striated: Alternating light and dark bands (striations) as seen when examined with a microscope Skeletal muscle tissue works mainly in a voluntary manner - Its activity can be consciously controlled Most skeletal muscles also are controlled subconsciously to some extent Ex: the diaphragm alternately contracts and relaxes without conscious control, posture maintaining muscle Overview of Muscular Tissue ❑Cardiac Muscle Tissue Found only in the walls of the heart Striated like skeletal muscle Action is involuntary Contraction and relaxation of the heart is not consciously controlled Contraction of the heart is initiated by a node of tissue called the “pacemaker” ❑ Smooth Muscle Tissue Located in the walls of hollow internal structures Blood vessels, airways, and most organs in the abdominopelvic cavity, also found in the skin, attached to hair follicles. Lacks the striations of skeletal and cardiac muscle tissue Usually involuntary Overview of Muscular Tissue Functions of Muscular Tissue ❑ Producing Body Movements Walking and running (integrated function of skeletal muscle, bones and joint) (skeletal muscle) ❑ Stabilizing Body Positions Posture (postural muscle contract continuously when awake) (skeletal muscle) ❑ Storage & moving Substances Within the Body Storage- sustained contraction of sphincters prevent outflow of content in hollow organ (food in the stomach and urine in the bladder) (smooth muscle) Movement- Heart muscle pumping blood, moving substances in the digestive tract (cardiac muscle, smooth muscle) ❑ Generating heat Contracting muscle produces heat - thermogenesis Shivering increases heat production - To maintain normal body temperature (skeletal muscle) Properties of Muscular Tissue ❑ Properties that enable muscle to function and contribute to homeostasis ❑ Electrical excitability Ability to respond to stimuli by producing electrical signals – action potentials/impulses. i.e. electrical signals from muscular tissue itself & chemical stimuli ❑ Contractility Ability to contract forcefully when stimulated by action potential ❑ Extensibility Ability to stretch without being damaged. Connective tissues limits the range of extensibility. ❑ Elasticity Ability to return to an original length and shape  Skeletal Muscle Tissue Connective Tissue Components-surrounds and protects muscular tissue ✓ Fascia Dense sheet or broad band of irregular connective tissue that supports and surrounds muscles and other organs of the body, ✓ Epimysium 3 layers of CT The outermost layer: collagen fiber (separate extend from fascia to muscle from surrounding tissues/organs). protect and ✓ Perimysium strengthen skeletal muscle Surrounds numerous bundles of fascicles Separates 10-100 muscle fibers into bundles called fascicles ✓ Endomysium Separates individual muscle fibers from one another ✓ Tendon is collagen fibers of all 3 layers CT come together to form tendon a cord that attach a muscle to a bone or a broad sheet called aponeurosis (connects different skeletal muscle). Muscle tissue, fascicles, Muscle fiber (cells), myofibril, filaments Skeletal Muscle Tissue  Skeletal Muscle Tissue ❑ Nerve and Blood Supply Neurons that stimulate skeletal muscle to contract are somatic motor neurons The axon of a somatic motor neuron typically branches many times Each branch extending to a different skeletal muscle fiber Each muscle fiber is in close contact with one or more capillaries – bring in oxygen and nutrients, remove heat and waste product of muscle metabolism Skeletal Muscle Tissue ❑ Microscopic Anatomy The number of skeletal muscle fibers is set before you are born Most of these cells last a lifetime Muscle growth occurs by hypertrophy An enlargement of existing muscle fibers Testosterone and human growth hormone stimulate hypertrophy Satellite cells retain the capacity to fuse with one another or with damaged muscle fibers to regenerate functional muscle fibers.  Skeletal Muscle Tissue ❑ Sarcolemma The plasma membrane of a muscle cell ❑ Transverse (T tubules) Tunnel in from the plasma membrane Muscle action potentials travel through the T tubules ❑ Sarcoplasm, the cytoplasm of a muscle fiber Sarcoplasm includes glycogen (containing many glucose molecules) used for synthesis of ATP and a red-colored protein called myoglobin which binds O2 Myoglobin releases oxygen when it is needed for ATP production Skeletal Muscle Tissue ❑ Myofibrils Thread like structures which have a contractile function ❑ Sarcoplasmic reticulum (SR) Membranous sacs which encircles each myofibril Stores calcium ions (Ca++) Release of Ca++ triggers muscle contraction ❑ Filaments Function in the contractile process Two types of filaments (Thick and Thin) There are two thin filaments for every thick filament ❑ Sarcomeres Compartments of arranged filaments Basic functional unit of a myofibril Muscle tissue, fascicles, Muscle fiber (cells), myofibril, filaments Skeletal Muscle Tissue During embryonic development, many myoblasts fuse to form one skeletal fiber. Once the fusion occurs the skeletal muscle fiber losses the ability to undergo cell division. Skeletal Muscle Tissue ❑ Sarcomere – basic functional unit of a myofibril ❑Z discs Separate one sarcomere from the next Thick and thin filaments overlap one another ❑ A band Darker middle part of the sarcomere Thick and thin filaments overlap ❑ I band Lighter, contains thin filaments but no thick filaments Z discs passes through the center of each I band ❑ H zone Center of each A band which contains thick but no thin filaments, includes the M line and the light regions on either sides of the M line. ❑ M line Supporting proteins that hold the thick filaments together in the H zone Contraction and Relaxation of Skeletal Muscle Skeletal Muscle Tissue Muscle Proteins ❑ Myofibrils are built from three kinds of proteins 1) Contractile proteins Generate force during contraction 2) Regulatory proteins Switch the contraction process on and off 3) Structural proteins Align the thick and thin filaments properly Provide elasticity and extensibility Link the myofibrils to the sarcolemma Skeletal Muscle Tissue 1) Contractile Proteins a) Myosin Main component of thick filaments Functions as a motor protein which can achieve motion Convert ATP to energy of motion Projections of each myosin molecule protrude outward (myosin head)  Contraction and Relaxation of Skeletal Muscle 1. Contractile Proteins b) Actin Main component of thin filaments Actin molecules provide a site where a myosin head can attach. 2. Regulatory proteins Tropomyosin and troponin are also part of the thin filament In relaxed muscle - Myosin is blocked from binding to actin by tropomyosin- Strands of tropomyosin cover the myosin-binding sites Troponin molecules held tropomyosin strands in place Calcium ion binding to troponin moves tropomyosin away from myosin- binding sites Allows muscle contraction to begin as myosin binds to actin Skeletal Muscle Tissue ❑ Structural Proteins Titin Stabilize the position of myosin – by connecting the Z disc and M line of the sarcomere. accounts for much of the elasticity and extensibility of myofibrils Dystrophin Links thin filaments to the sarcolemma Condition known as muscular dystrophy is due to mutated dystrophin gene – without the reinforcement of this protein, sarcolemma tears easily during muscle contraction, causing muscle fiber to rupture and die. Contraction and Relaxation of Skeletal Muscle ❑ The Sliding Filament Mechanism Myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere Progressively pulling the thin filaments toward the center of the sarcomere Z discs come closer together and the sarcomere shortens The length of the individual thick and thin filaments do not change Leading to shortening of the entire muscle  Z discs move closer I band gets shorter/smaller A band length does not change H zone disappears/shorter Contraction and Relaxation of Skeletal Muscle Contraction and Relaxation of Skeletal Muscle ❑ The Contraction Cycle The onset of contraction begins with the SR releasing Ca2+ into the muscle cell Ca2+ binds with troponin causing tropomyosin to move from the myosin-binding sites on actin. The binding sites are free, the contraction cycle begins. The contraction cycle consists of 4 steps 1) ATP hydrolysis Hydrolysis of ATP reorients and energizes the myosin head 2) Formation of cross-bridges Myosin head attaches to the myosin-binding site on actin 3) Power stroke During the power stroke the crossbridge rotates, sliding the filaments 4) Detachment of myosin from actin As the next ATP binds to the myosin head, the myosin head detaches from actin The contraction cycle repeats as long as ATP is available and the Ca++ level is sufficiently high Continuing cycles applies the force that shortens the sarcomere Contraction cycle Contraction and Relaxation of Skeletal Muscle ❑ Excitation–Contraction Coupling An increase in Ca++ concentration in the muscle starts contraction A decrease in Ca++ stops it Action potentials causes Ca++ to be released from the SR into the muscle cell Ca++ moves tropomyosin away from the myosin-binding sites on actin allowing cross-bridges to form The muscle cell membrane contains Ca++ pumps to return Ca++ back to the SR quickly Decreasing calcium ion levels As the Ca++ level in the cell drops, myosin-binding sites are covered and the muscle relaxes Contraction and Relaxation of Skeletal Muscle Rigor mortis Contraction and Relaxation of Skeletal Muscle ❑ The Neuromuscular Junction (NMJ) Motor neurons have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers Action potentials arise at the interface of the motor neuron and muscle fiber  The Neuromuscular Junction (NMJ) ❑ Synapse Where communication occurs between a somatic motor neuron and a muscle fiber ❑ Synaptic cleft Gap that separates the two cells ❑ Neurotransmitter Chemical released by the initial cell communicating with the second cell ❑ Synaptic vesicles Sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (ACh) ❑ Motor end plate The region of the muscle cell membrane opposite the synaptic end bulbs Contain acetylcholine receptors Contraction and Relaxation of Skeletal Muscle ❑ Nerve impulses elicit a muscle action potential in the following way 1) Release of acetylcholine Nerve impulse arriving at the synaptic end bulbs causes many synaptic vesicles to release ACh into the synaptic cleft 2) Activation of ACh receptors Binding of ACh to the receptor on the motor end plate opens an ion channel Allows flow of Na+ to the inside of the muscle cell 3) Production of muscle action potential The inflow of Na+ makes the inside of the muscle fiber more positively charged triggering a muscle action potential The muscle action potential then propagates to the SR to release its stored Ca++ 4) Termination of ACh activity ACh effects last only briefly because it is rapidly broken down by acetylcholinesterase (AChE) Summary of contraction and relaxation events of skeletal muscle fiber Contraction and Relaxation of Skeletal Muscle ❑ Botulinum toxin ▪ Produced by a bacterium Clostridium botulinum - Blocks exocytosis of ACh from synaptic vesicles ▪ May be found in improperly canned foods A tiny amount can cause death by paralyzing respiratory muscles ▪ First bacterial toxin to be used as a medicine (Botox®) Strabismus (crossed eyes) Blepharospasm (uncontrollable blinking) Spasms of the vocal cords that interfere with speech Cosmetic treatment to relax muscles that cause facial wrinkles Alleviate chronic back pain due to muscle spasms in the lumbar region ❑ Curare A plant poison used by South American Indians on arrows and blowgun darts Causes muscle paralysis by blocking ACh receptors inhibiting Na+ ion channels Derivatives of curare are used during surgery to relax skeletal muscles ❑ Anticholinesterase Slow actions of acetylcholinesterase and removal of ACh Can strengthen weak muscle contractions Ex: Neostigmine Treatment for myasthenia gravis – autoimmune disease that cause chronic progressive damage to the NMJ (destroy receptors of acetylcholine). Antidote for curare poisoning Terminate the effects of curare after surgery Muscle Metabolism ❑ Production of ATP in Muscle Fibers Important roles of ATP in muscle contraction: Power the contraction cycle: Bind to myosin head, energising it Responsible for disconnecting the myosin cross bridge at conclusion of power stroke. Pump Ca++ into the SR: Provides energy to calcium ion pumps on SR to transport back Ca++ into SR The ATP inside muscle fibers will power contraction for only a few seconds ATP must be produced by the muscle fiber after reserves are used up Muscle fibers have three ways to produce ATP 1) From creatine phosphate 2) By anaerobic cellular respiration 3) By aerobic cellular respiration Muscle Metabolism Muscle Metabolism ❑ Creatine Phosphate Muscle fiber relax - excess ATP is used to synthesize creatine phosphate - energy-rich molecule found in muscle fibers Relax - Creatine kinase catalyzes the transfer of one high energy phosphate from ATP to creatine to form creatine phosphate. Contract - Creatine phosphate transfers its high energy phosphate group to ADP regenerating new ATP catalyzed by creatine kinase Store of creatine phosphate and ATP provide enough energy for contraction for about 15 seconds First source of energy when muscle contract Muscle Metabolism ❑ Anaerobic Cellular Respiration Series of ATP producing reactions that do not require O2 Glucose is used to generate ATP when the supply of creatine phosphate is depleted derived from the blood and from glycogen stored in muscle fibers Glycolysis breaks down glucose into molecules of pyruvic acid and produces two molecules of ATP If sufficient O2 is present, pyruvic acid formed by glycolysis enters aerobic respiration pathways producing a large amount of ATP If O2 levels are low, anaerobic reactions convert pyruvic acid to lactic acid which is carried away by the blood Anaerobic respiration can provide enough energy for about 30-40 seconds of muscle activity Muscle ❑ Metabolism Aerobic Cellular Respiration O2 requiring reaction Pyruvic acid entering the mitochondria is completely oxidized generating ATP carbon dioxide Water Heat Although this reaction is slower than glycolysis, each molecule of glucose yields about 36 molecules of ATP Muscle tissue has two sources of oxygen 1) Oxygen from hemoglobin in the blood 2) Oxygen released by myoglobin in the muscle cell Myoglobin and hemoglobin are oxygen-binding proteins Aerobic respiration supplies ATP for prolonged activity Aerobic respiration provides more than 90% of the needed ATP in activities lasting for minutes to hours Control of Muscle Tension ❑ The tension or force of muscle cell contraction varies ❑ Maximum Tension (force) is dependent on i. The rate at which nerve impulses arrive ii. The amount of stretch before contraction iii. The nutrient and oxygen availability iv. The size of the motor unit (comprise of motor neuron and muscle fibers it stimulates; muscle that controls voice production have 2-3 muscle fiber per motor unit vs muscle in legs and arms have 2000- 3000 muscle fibers per motor unit) Muscle Metabolism ❑ Muscle Fatigue Inability of muscle to maintain force of contraction after prolonged activity Factors that contribute to muscle fatigue i. Inadequate release of calcium ions from the SR ii. Depletion of creatine phosphate iii. Insufficient oxygen iv. Depletion of glycogen and other nutrients v. Build-up of lactic acid and ADP vi. Failure of the motor neuron to release enough acetylcholine Muscle Metabolism ❑ Oxygen Consumption After Exercise After exercise, heavy breathing continues and oxygen consumption remains above the resting level ❑ Oxygen debt refers to The added oxygen that is taken into the body after exercise This added oxygen is used to restore muscle cells to the resting level in three ways 1) to convert lactic acid into glycogen (stored in liver) 2) to synthesize creatine phosphate and ATP 3) to replace the oxygen removed from myoglobin Types of Skeletal Muscle Fibers ❑ Muscle fibers vary in their content of myoglobin Red muscle fibers Have a high myoglobin content Appear darker (dark meat in chicken legs and thighs) Contain more mitochondria Supplied by more blood capillaries White muscle fibers Have a low content of myoglobin Appear lighter (white meat in chicken breasts) Types of Skeletal Muscle Fibers ❑ Muscle fibers contract at different speeds, and vary in how quickly they fatigue ❑ Muscle fibers are classified into three main types 1) Slow oxidative fibers 2) Fast oxidative-glycolytic fibers 3) Fast glycolytic fibers Types of Skeletal Muscle Fibers Higher the order, more stronger the muscle contraction Types of Skeletal Muscle Fibers ❑ Distribution and Recruitment of Different Types of Fibers Most muscles are a mixture of all three types of muscle fibers Proportions vary, depending on the action of the muscle, the person’s training regimen and genetic factors Postural muscles of the neck, back, and legs have a high proportion of SO fibers Muscles of the shoulders and arms have a high proportion of FG fibers Leg muscles have large numbers of both SO and FOG fibers Exercise and Skeletal Muscle Tissue ❑ Ratios of fast glycolytic and slow oxidative fibers are genetically determined Individuals with a higher proportion of FG fibers Excel in intense activity (weight lifting, sprinting) Individuals with higher percentages of SO fibers Excel in endurance activities (long-distance running) Exercise and Skeletal Muscle Tissue ❑ Various types of exercises can induce changes in muscle fibers Aerobic exercise transforms some FG fibers into FOG fibers Endurance exercises do not increase muscle mass Exercises that require short bursts of strength produce an increase in the size of FG fibers Muscle enlargement (hypertrophy) due to increased synthesis of thick and thin filaments Cardiac Muscle Tissue ❑ Principal tissue in the heart wall Intercalated discs connect the ends of cardiac muscle fibers to one another Allow muscle action potentials to spread from one cardiac muscle fiber to another Cardiac muscle tissue contracts when stimulated by its own autorhythmic muscle fibers Continuous, rhythmic activity is a major physiological difference between cardiac and skeletal muscle tissue Contractions lasts longer than a skeletal muscle twitch Have the same arrangement of actin and myosin as skeletal muscle fibers Mitochondria are large and numerous Depends on aerobic respiration to generate ATP Requires a constant supply of oxygen Able to use lactic acid produced by skeletal muscle fibers to make ATP Smooth Muscle Tissue Usually activated involuntarily Action potentials are spread through the fibers by gap junctions – visceral smooth muscle Fibers are stimulated by certain neurotransmitter, hormone, or autorhythmic signals Found in the Walls of arteries and veins Walls of hollow organs Walls of airways to the lungs Muscles that attach to hair follicles Muscles that adjust pupil diameter Muscles that adjust focus of the lens in the eye  Smooth Muscle Tissue Microscopic Anatomy of Smooth Muscle Contains both thick filaments and thin filaments Not arranged in orderly sarcomeres No regular pattern of overlap thus not striated Lack transverse tubules and contain only a small amount of stored Ca++ Filaments attach to dense bodies and stretch from one dense body to another Dense bodies Attached to thin filament Function in the same way as Z discs During contraction the filaments pull on the dense bodies causing a shortening of the muscle fiber Smooth Muscle Tissue One autonomic motor neuron Three autonomic motor neuron synapse with several visceral synapse with individual multiunit smooth muscle fibers and action smooth muscle fibers. Stimulation potential spread to neighboring of one multiunit fiber causes contraction fibers through gap junctions of that fiber only Smooth Muscle Tissue ❑ Physiology of Smooth Muscle Contraction lasts longer than skeletal muscle contraction Can both shorten and stretched to a great extend than other muscle types. Contractions are initiated by Ca++ flow from the interstitial fluid and SR. Contraction is delayed due to absence of transverse tubules, it takes longer time for Ca++ to reach the center of the fiber Ca++ move slowly out of the muscle fiber delaying relaxation Able to sustain long-term muscle tone Prolonged presence of Ca++ in the cell provides for a state of continued partial contraction Important in the: Gastrointestinal tract where a steady pressure is maintained on the contents of the tract In the walls of blood vessels which maintain a steady pressure on blood THE MUSCULAR SYSTEM  Muscle Attachment Sites: Origin & Insertion ❑ Skeletal muscles cause movements by exerting force on tendons, which pulls on bones or other structures. Origins from scapula Normally proximal ❑ Articulating bones usually do not move equally in response to contraction. the attachment of a tendon to the stationary bone is called the origin. the attachment of the muscle’s other tendon to the movable Normally distal bone is called the insertion. the action/s of a muscle are the main movements that occur during contraction (e.g., flexion or extension). Lever Systems ❑ A lever is a rigid structure that can move around a fixed point called a fulcrum. ❑ A lever is acted on at two different points by two different forces: the effort, which causes movement, and the load or resistance, which opposes movement. Types of levers Joints between atlas (first cervical Weight vertebrae) of skull and occipital Calf bone muscle Bicep brachii Body Weight of Ball of the weight Elbow arm and foot joint forearm ❑ There are 3 types of levers that differ on the positions of the fulcrum, effort, and load. First-class levers are not common: the fulcrum is between the effort and the load. Second-class levers are uncommon: the load is between the fulcrum and the effort. Third-class levers are common: the effort is between the fulcrum and the load. Effects of muscle fascicle arrangement ❑ All muscle fibers are parallel to one another within a single fascicle. ❑ Fascicles, however, form patterns with respect to the tendons. Parallel Fusiform Circular Triangular Pennate Effects of muscle fascicle arrangement ❑ Muscle fascicles have a compromise that they must make. They must compromise between power and range of motion. The longer the fibers in a muscle, the greater the range of motion it can produce. The power of a muscle depends not on length ( a short fiber can contract as forceful as long one) but on its total cross-sectional area – the more fiber per unit of cross-sectional area a muscle has, the more power it produce. Intramuscular injection Penetrates the skin and subcutaneous layer to enter the muscle Injected deep within the muscle to avoid injury (away from major veins and blood vessels). IM injections have faster delivery than oral medication but slower than intravenous infusions. Common sites 1. gluteus medius muscle of the buttock 2. lateral side of the thigh in the midportion of vastus lateralis muscle. 3. deltoid muscle of the shoulder