The Muscular System: Muscle Tissue PDF

THE MUSCULAR SYSTEM: MUSCLE TISSUE Integrated Biological Sciences – I DDS104 Dr. Jayaraj Ajman University 7-Oct-24 1 ...

THE MUSCULAR SYSTEM: MUSCLE TISSUE Integrated Biological Sciences – I DDS104 Dr. Jayaraj Ajman University 7-Oct-24 1  LEARNING OUTCOMES ▪ List the different types of muscles ▪ Describe the gross features of skeletal muscle ▪ Describe the microscopic features of skeletal muscle ▪ Describe the structure of neuromuscular junction ▪ Describe and molecular basis of contraction of skeletal muscle ▪ Define a motor unit ▪ Describe the muscle metabolism, fatigue and oxygen debt ▪ Describe the types of skeletal muscle fibers ▪ Define isometric and isotonic contraction Ajman University 7-Oct-24 2  Muscular Tissue Muscle Tissue Description Function Location Skeletal Consists of long cylindrical striated fibers ✓ Motion, posture, Usually attached to muscle tissue with peripherally located nuclei heat production, bones by tendons. Voluntary control protection Cardiac Consists of branched, striated fibers with ✓ Pumps blood to all Heart wall muscle tissue usually one centrally located nucleus parts of body Contain desmosomes and gap junctions Involuntary control Smooth Consists of spindle-shaped nonstriated ✓ Motion Iris of eyes muscle tissue fibers with centrally located nucleus ✓ Constriction of Walls of blood Contain gap junctions vessels and airways vessels, airways, Involuntary control ✓ Propulsion of foods stomach, intestines, ✓ Contraction of gallbladder, urinary urinary bladder bladder, and uterus Ajman University 7-Oct-24 3  Muscular Tissue Ajman University 7-Oct-24 4  Properties of Muscular Tissue Electrical excitability Is the ability of muscular tissue to respond to stimuli and trigger an action potentials Contractility Is the ability of muscular tissue to contract forcefully when stimulated Extensibility Is the ability of muscular tissue to stretch without being damaged Elasticity Is the ability of muscular tissue to return to its original length and shape after contraction Ajman University 7-Oct-24 5  Connective Tissue Components Fascia Is a dense sheet or broad band of irregular connective tissue Supports and surrounds muscles and other organs of the body Holds muscles with similar functions together ✓ Allows free movement of muscles ✓ Carries nerves, blood vessels, and lymphatic vessels ✓ Fills spaces between muscles Ajman University 7-Oct-24 6  Connective Tissue Components ❑ Three layers of connective tissue extend from the fascia Epimysium The outermost layer, Dense irregular connective tissue Encircle the entire muscle Perimysium Dense irregular connective tissue Endomysium Surrounds groups muscle fibers Thin sheath of areolar connective tissue Separating them into bundles Penetrating the interior of each fascicle called fascicles Separate individual muscle fibers from one another Ajman University 7-Oct-24 7  Connective Tissue Components Tendon Is as extension of all three connective tissue layers Cord of dense regular connective tissue Composed of parallel bundles of collagen fibers Attaches a muscle to the periosteum of a bone E.g. Calcaneal (Achilles) tendon - Gastrocnemius (calf) muscle Aponeurosis Connective tissue extend as a broad, flat layer of tendon E.g. Epicranial aponeurosis - Occipitofrontalis muscle Ajman University 7-Oct-24 8  Connective Tissue Components ❑ Tendon (synovial) sheaths Tendons of the wrist and ankle Enclosed by tubes of fibrous connective tissue Visceral layer The inner layer of a tendon sheath Is attached to the surface of the tendon Parietal layer The outer layer of a tendon sheath Is attached to bone ▪ Cavity between the visceral and parietal layers contains a film of synovial fluid ✓ Reduce friction as tendons slide back and forth Ajman University 7-Oct-24 9  Structure of Skeletal Muscle ▪ Muscles are attached to bones by tendons Ajman University 7-Oct-24 10  Structure of Muscle Fibre ❑ Muscle fibres ▪ Many long, thin, cylindrical cells that form each skeletal muscle ▪ Each muscle fibre Surrounded by sarcolemma Cytoplasm within in it is sarcoplasm Multinucleated Striated Made up of myofibrils Consist of cytoplasmic components Ajman University 7-Oct-24 11  Structure of Muscle Fibre ❑ Cytoplasmic components Large number of mitochondria Large amount of energy required for muscle contraction Sarcotubular system Elaborate and extensive endoplasmic reticulum ✓ Vital role in muscle excitation and contraction Ajman University 7-Oct-24 12  Sarcotubular System T-tubule Inward extension of sarcolemma Opens to exterior Contain ECF Run transverse to myofibrils Transmit action potential Sarcoplasmic reticulum Run parallel to myofibrils Terminate in terminal cisternae o Stores calcium ions Triads Two terminal cisternae abutting a t-tubule Ajman University 7-Oct-24 13  Myofibrils Thick filaments 16 nm in diameter 1–2 µm long Myosin filament Thin filaments 8 nm in diameter 1–2 µm long Actin filament ▪ Myofibrils show light and dark bands Ajman University 7-Oct-24 14  Components of the Sarcomere ❑ Sarcomere: Functional unit of contraction The portion of myofibril between two adjacent Z discs I bands: Light bands contain only actin filaments A bands: Dark bands contains myosin filaments and the ends of actin filaments Z discs: The ends of actin filaments are anchored in Z discs H zone: A narrow region in the center of each A band contains only thick filaments M line: A region in the center of the H zone that hold the thick filaments together Ajman University 7-Oct-24 15  Structure of Thick and Thin filaments Thick filament ▪ Contains about 300 myosin molecules ▪ Tails form the shaft of thick filament ▪ Heads project toward thin filaments Possess actin and ATP binding site Thin filaments ▪ Contain actin, troponin, tropomyosin o Actin Two intertwined helical chains form the primary structure of the thin filaments Possess myosin-binding site Ajman University 7-Oct-24 16  Structure of Thick and Thin filaments o Tropomyosin ▪ In relaxed muscle, Cover the myosin-binding sites on actin Myosin is blocked from binding to actin o Troponin During muscle contraction, Ca2+ bind to troponin Conformational changes occur Tropomyosin moves away from myosin-binding sites on actin Ajman University 7-Oct-24 17  Structure of Thick and Thin filaments Contractile proteins o Myosin o Actin ✓ Generate force during contraction Regulatory proteins o Troponin o Tropomyosin ✓ Help switch contraction on and off Ajman University 7-Oct-24 18  Neuromuscular Junction ▪ Somatic motor neurons stimulate muscle fibers to contract ▪ Neuromuscular junction (NMJ) Synapse between a somatic motor neuron and a skeletal muscle fiber ▪ Synaptic vesicle Contain neurotransmitter - Acetylcholine ▪ Motor end plate The region of the sarcolemma opposite to the synaptic end bulbs Consist of acetylcholine receptors Ajman University 7-Oct-24 19  Neuromuscular Junction ▪ A nerve impulse (nerve action potential) elicits a muscle action potential 1. Release of acetylcholine Arrival of the nerve impulse at the synaptic end bulbs Causes exocytosis synaptic vesicles and liberate Ach ACh diffuses across the synaptic cleft 2. Activation of ACh receptors Binding of ACh to the receptor on the motor end plate Opens Na+ channel and Inflow of Na+ 3. Production of muscle action potential Inflow of Na+ depolarizes the muscle fiber Triggers a muscle action potential 4. Termination of ACh activity ACh break down by acetylcholinesterase (AChE) Into acetyl and choline Ajman University 7-Oct-24 20  Neuromuscular Junction Ajman University 7-Oct-24 21  Ajman University 7-Oct-24 22  Contraction Cycle ▪ Action potential propagates along the sarcolemma into the T tubule system ▪ Release stored Ca2+ from sarcoplasmic reticulum into the sarcoplasm ▪ Ca2+ bind to troponin ▪ Tropomyosin moves away from the myosin binding sites on actin ▪ ATPase hydrolyzes ATP into ADP on myosin head ▪ Attachment of myosin to actin to form crossbridges ▪ Actin and myosin filaments slide alongside each other ▪ Power stroke leads to muscle fiber contraction ▪ At the end of the power stroke ▪ Crossbridge remains until it binds another molecule of ATP on the myosin head ▪ ATP binds to the ATP binding site the myosin head detaches from actin Ajman University 7-Oct-24 23  Excitation– Contraction Coupling Ajman University 7-Oct-24 24  Excitation– Contraction Coupling Ajman University 7-Oct-24 25  Myasthenia Gravis ❖ Myasthenia gravis ▪ Autoimmune disease ▪ Causes chronic, progressive damage of NMJ ▪ The immune system inappropriately produces antibodies ▪ That bind to and block ACh receptors o Initial symptoms include ▪ Weakness of the eye muscles Produce double vision ▪ Weakness of the throat muscles Produce difficulty in swallowing, chewing and talking Ajman University 7-Oct-24 26  Motor Units ▪ A motor unit consists of A somatic motor neuron plus all the skeletal muscle fibers it stimulates ▪ A single somatic motor neuron makes contact with an average of 150 skeletal muscle fibers And all of the muscle fibers in one motor unit contract in unison Ajman University 7-Oct-24 27  Muscle Metabolism and Exercise ❑ Muscle fibers have three ways to produce ATP ▪ Relaxed muscles use modest amount of ATP ▪ High level of activity use ATP at a rapid pace From creatine phosphate Relaxed muscle fibers don't use all produce ATP Excess ATP is used to synthesize creatine phosphate Enzyme creatine kinase catalyzes the reaction Form creatine phosphate and ADP ▪ This energy is sufficient for short bursts of activity E.g to run a 100-meter dash Ajman University 7-Oct-24 28  Muscle Metabolism and Exercise By anaerobic cellular respiration ▪ ATP-producing reactions that do not require oxygen ▪ Occurs when creatine phosphate depleted ▪ Glucose is catabolized to generate ATP ▪ Glycolysis breaks down glucose molecule to pyruvic acid ▪ Net gain of 2 molecules of ATP ▪ This energy is enough for 30 to 40 sec muscle activity ▪ E.g to run a 400-meter race Ajman University 7-Oct-24 29  Muscle Metabolism and Exercise By aerobic cellular respiration ATP-producing reactions require oxygen Occurs in mitochondria Pyruvic acid enters the mitochondria and oxidize And generate ATP, CO2, water, and heat ▪ Muscle tissue has two sources of O2: O2 from the blood O2 released by myoglobin ▪ Provide enough energy for muscular activities last more than 10 minutes Ajman University 7-Oct-24 30  Muscle Metabolism and Exercise ❑ Muscle Fatigue The inability of a muscle to maintain force of contraction after prolonged activity ▪ Causes of fatigue Energy consumption of muscle exceeds Neurotransmitters stored in presynaptic terminal is exhausted ❑ Heat production during muscle activity About 40% of the energy used during muscle contraction The rest is given off as heat to maintain body homeostasis Ajman University 7-Oct-24 31  Muscle Metabolism and Exercise Oxygen consumption after exercise Increases in breathing rate and blood flow Enhance oxygen delivery to muscle tissue ❖ Oxygen debt Refers to the added oxygen that is taken into the body after exercise ▪ Extra oxygen is used to restore metabolic conditions ✓ Convert lactic acid back into glycogen stores in the liver ✓ To resynthesize creatine phosphate and ATP in muscle fibers ✓ To replace the oxygen removed from myoglobin Ajman University 7-Oct-24 32  Fascicles and Muscle Shapes Fusiform muscles are thick in the middle and tapered at each end. Parallel muscles have a fairly uniform width and parallel fascicles. Some are elongated straps, and others are quadrilateral(four- sided) Triangular (convergent) muscles are fan- shaped broad at the origin and converging toward a narrower insertion.. Pennate muscles are feather-shaped. There are three types of pennate muscles: unipennate; bipennate; and multipennate Circular muscles (sphincters) form rings around certain body openings Ajman University 7-Oct-24 33  Functional Groups of Muscles ❑ The effect produced by a muscle, whether it is to produce or prevent a movement, is called its action Skeletal muscles function in groups whose combined actions produce the coordinated motion of a joint ▪ Classified into four categories according to their actions Ajman University 7-Oct-24 34  Functional Groups of Muscles Prime mover (agonist) Is the muscle that produces most of the force during a particular joint action Synergist Is a muscle that aids the prime mover Stabilize a joint and restrict the movements, or modify the direction of a movement so that the action of the prime mover is more coordinated and specific Antagonist Is a muscle that opposes the prime mover In some cases, it relaxes to give the prime Fixator Is a muscle that prevents a bone from moving Ajman University 7-Oct-24 35  Types of Skeletal Muscle Fibers Red muscle fibers High myoglobin content Appear darker More mitochondria Supplied by more blood capillaries White muscle fibers Low content of myoglobin Appear lighter Low mitochondria Comparatively less blood capillaries Ajman University 7-Oct-24 36  Types of Skeletal Muscle Fibers ▪ Classification based structural and functional characteristics Slow oxidative (SO) fibers Fast oxidative–glycolytic (FOG) fibers Fast glycolytic (FG) fibers Ajman University 7-Oct-24 37  Types of Skeletal Muscle Fibers CHARACTERISTICS SLOW OXIDATIVE FIBERS FAST OXIDATIVE FIBERS FAST GLYCOLYTIC FIBERS Color Red Red to pink White (pale) Fiber diameter Small Intermediate Large Mitochondria Many Many Few Capillaries Many Many Few Myoglobin content High High Low Glycogen stores Low Intermediate High Myosin ATPase activity Slow Fast Fast Speed of contraction Slow Fast Fast Pathway for ATP synthesis Aerobic Main: Aerobic Anaerobic glycolysis Minor: Anaerobic glycolysis Recruitment order First Second Third Rate of fatigue Slow - Very resistant to Intermediate- Moderately Fast - Fatigue quickly fatigue resistance to fatigue Activities best suited for Endurance-type activities- Walking and sprinting Short-term intense Running a marathon movements- Weight lifting Ajman University 7-Oct-24 38  Naming Skeletal Muscles ▪ Skeletal muscles are named according to a number of criteria Muscle location Some muscle names indicate the bone or body region with which the muscle is associated E.g. Temporalis muscle overlies the temporal bone Intercostal muscles run between the ribs Muscle shape Some muscles are named for their distinctive shapes E.g. Deltoid muscle is roughly triangular Ajman University 7-Oct-24 39  Naming Skeletal Muscles Direction of muscle fibers The names of some muscles reveal the direction in which their fibers (and fascicles) run in reference to some imaginary line, usually the midline of the body or the longitudinal axis of a limb bone E.g. Transversus abdominis (transverse muscle of the abdomen) Ajman University 7-Oct-24 40  Naming Skeletal Muscles Location of the attachments Some muscles are named according to their points of origin and insertion The origin is always named first E.g. Sternocleidomastoid muscle of the neck, Has a dual origin on the sternum(sterno) and clavicle (cleido), and it inserts on the mastoid process of the temporal bone Ajman University 7-Oct-24 41  Naming Skeletal Muscles Muscle size Terms such as maximus (largest), minimus (smallest), longus (long), and brevis (short) are often used in muscle names E.g. Gluteus maximus and gluteus minimus Number of origins When biceps, triceps, or quadriceps forms part of a muscle’s name, that means the muscle has two, three, or four origins, respectively. E.g. The biceps brachii muscle of the arm has two origins, or heads. Triceps brachii, Quadriceps femoris Ajman University 7-Oct-24 42  Naming Skeletal Muscles Muscle action Muscles are named for the movement they produce, such as flexor, extensor, or adductor E.g. Flexor carpi ulnaris and radialis Adductor longus, brings about thigh adduction Ajman University 7-Oct-24 43  Naming Skeletal Muscles ❖ Combining criteria Often, several criteria are combined in naming a muscle ▪ E.g. extensor carpi radialis longus tells us: 1. Muscle’s action (extensor) 2. What joint it acts on (carpi 5 wrist) 3. It location is close to the radius of the forearm (radialis) 4. It also hints at the size (longus) relative to other wrist extensor muscles Ajman University 7-Oct-24 44  Properties of Skeletal Muscle Muscle-twitch Contraction and relaxation of skeletal muscle in response to a single adequate stimulus (threshold) Duration of action potential: 1 to 5 ms Follow All-or-none Law An action potential either occurs completely or it does not occur at all Refractory period The period of time after an action potential begins during which an excitable cell cannot generate another action potential Ajman University 7-Oct-24 45  Muscle Response to Stimulus Strength Subthreshold stimuli Stimuli that produce no observable contractions Threshold stimulus Stimulus at which the first observable contraction occurs Supra-threshold stimulus Maximal stimulus that increases contractile force of muscle Point at which all the muscle’s motor units are recruited Ajman University 7-Oct-24 46  Properties of Skeletal Muscle Contractility Ability to contract when stimulated ▪ Isometric contraction Length of the muscle remains constant but tension of the muscle increases Eg: Holding a book steady using an outstretched arm ▪ Isotonic contraction Tension developed in the muscle remains constant but length of the muscle increases or decreases Body movements or moving objects Ajman University 7-Oct-24 47  Clinical Connections Muscular dystrophy Refers to a group of inherited muscle-destroying diseases Cause progressive degeneration of skeletal muscle fibers Most common form is Duchenne muscular dystrophy (DMD) Due the mutated gene is on the X chromosome Hypotonia Refers to decreased or lost muscle tone Such muscles are said to be flaccid Flaccid muscles are loose and appear flattened Nervous disorders and imbalance of electrolytes May result in flaccid paralysis Ajman University 7-Oct-24 48  Clinical Connections Myoma Hypertonia Refers to increased muscle tone Cause spasticity (continuously contracted) or rigidity Nervous disorders and imbalance of electrolytes May result in spastic paralysis Myalgia Myositis Pain in or associated with muscles Myoma A tumor consisting of muscle tissue Myositis Inflammation of muscle fibers Ajman University 7-Oct-24 49  Ajman University 7-Oct-24 50