Week 3 - Muscular System PDF

Week 3 Human Anatomy & Physiology - 1 (HMG380) MUSCULAR SYSTEM Dr. Merin Thomas [email protected] Office hours : Monday & Wednesday, 3:00pm to 5:00pm Tuesday & Thursday 1:00pm...

Week 3 Human Anatomy & Physiology - 1 (HMG380) MUSCULAR SYSTEM Dr. Merin Thomas [email protected] Office hours : Monday & Wednesday, 3:00pm to 5:00pm Tuesday & Thursday 1:00pm to 3:00pm  Learning Objectives Functions & Properties of muscle tissue Types of muscle tissues & their differences Structure of Muscle tissue Neuromuscular Junction Muscle metabolism How muscles produce movement Muscle nomenclature  Levels of Structural Organization - LEVEL 3 - TISSUE LEVEL Epithelial Tissue Connective Tissue Muscular Tissue Nervous Tissue Covers body surfaces, Connects, supports, and protects Contracts to make body lines hollow organs & body organs while distributing Carries information parts move & in the from one part of the cavities, and forms blood vessels to other tissues process generates heat glands. Loose Connective body to another Smooth Muscle through nerve Based on shape of Tissue impulses the cell 2 types of cells Dense Connective Tissue Skeletal Muscle Based on number Cardiac Muscle of layers of cells Special Connective Tissue Three parts: CNS, PNS, ANS  MUSCLE TISSUE - FUNCTION Contractile tissue which brings about movement. Muscular tissue has four key functions: 1. Producing body movements 2. Stabilizing body positions 3. Storing and moving substances within the body 4. Generating heat - Thermogenesis  MUSCLE TISSUE - PROPERTIES Muscular tissue has four special properties that enable it to function and contribute to homeostasis: 1. Excitability - the ability to respond to stimuli which maybe delivered from a motor neuron or a hormone. 2. Contractility - the ability of muscular tissue to contract forcefully when stimulated by a nerve impulse. 3. Extensibility - the ability of muscular tissue to stretch, within limits, without being damaged. Normally, smooth muscle is subject to the greatest amount of stretching. 4. Elasticity - is the ability of muscular tissue to return to its original length and shape after contraction or extension.  MUSCLE TISSUE - TYPES There are THREE types of muscles 1. Skeletal Muscle 2. Smooth Muscle 3. Cardiac Muscle  Location Type of movement Function Structure  SKELETAL MUSCLE - STRUCTURE Skeletal muscle contains connective tissue surrounding muscle fibers, and blood vessels and nerves. Muscles separated from skin by hypodermis which is is composed of areolar connective tissue and adipose. Fascia is a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body. Three layers of connective tissue extend from the fascia to protect and strengthen skeletal muscle. 1. Epimysium 2. Perimysium 3. Endomysium From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 308  SKELETAL MUSCLE - STRUCTURE All three layers are continuous with the connective tissue that attaches skeletal muscle to other structures, such as bone or another muscle. All three connective tissue layers may extend beyond the muscle fibers to form a rope/cord like tendon that attaches a muscle to the periosteum of a bone When the connective tissue elements extend as a broad, flat sheet, it is called an aponeurosis  SKELETAL MUSCLE - STRUCTURE Skeletal muscles are well supplied with nerves and blood vessels. The neurons that stimulate skeletal muscle to contract are somatic motor neurons. Each somatic motor neuron has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fiber. Blood capillaries are plentiful in muscular tissue; they bring in oxygen and nutrients and remove heat and the waste products of muscle metabolism.  SKELETAL MUSCLE - MICROSCOPIC STRUCTURE The most important component of a skeletal muscle - muscle fibers The diameter of a mature skeletal muscle fiber ranges from ~10 to 100 μm , with a typical length of about 10 cm. Each muscle fiber has 100 or more nuclei because it arises from the fusion of many myoblasts (developmental). These nuclei lie beneath the Sarcolemma, the plasma membrane of the muscle fibre. The cytoplasm of a muscle fiber is called as Sarcoplasm Sarcoplasm has small invaginations extending from surface towards centre called T-tubules (Transverse tubules) SKELETAL MUSCLE - MICROSCOPIC STRUCTURE  SKELETAL MUSCLE - MICROSCOPIC STRUCTURE Sarcoplasm Glycogen (for ATP synthesis) Myoglobin (protein found only in muscles; binds to oxygen). Mitochondria (Sarcosomes) lie in rows close to the contractile proteins so that ATP can be released when energy is needed Sarcoplasmic Reticulum (SR), fluid filled sacs similar to endoplasmic reticulum with dilated ends called Terminal Cisterns. Terminal cisterns push against T - tubules; Triad In relaxed muscle fibre SR stores Ca ions Release of Ca ions from terminal cisterns triggers muscle contraction. On high magnification, thread like structures seen - myofibrils - contractile organelles of skeletal muscle about 2 μm in diameter and extend the entire length of a muscle fiber. From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 311  SKELETAL MUSCLE - MICROSCOPIC STRUCTURE Sarcoplasm - Myofibrils Within myofibrils, thin filaments called myofilaments. Thin filaments are 8 nm in diameter and 1–2 μm long and composed of the protein actin Thick filaments are 16 nm in diameter and 1–2 μm long and composed of the protein myosin. Both are directly involved in contractile process. Myofilaments do not extend along entire length of the muscle fibre but are arranged in compartments - Sarcomere Basic functional unit of a myofibril Sarcomeres are separated by protein dense material called Z-discs From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 311  SKELETAL MUSCLE - MICROSCOPIC STRUCTURE Sarcoplasm ; Myofibrils; Sarcomere Sarcomere - Basic functional unit of a myofibril Sarcomeres are separated by protein dense material called Z-discs Dark A band - formed by thick filaments; ends have overlapping thick and thin filaments H band - region in the middle containing only thick filaments M line - Supporting proteins that hold the thick filaments together at the center of the H band Light I band - formed only by thin filaments Z disc lies in the middle of a light band Alternating light and dark bands create the striations hence called striated muscle (skeletal and cardiac) From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 312  Microscopic structure of skeletal muscle I BAND A BAND SARCOMERE Thick Filament Z Line M Line Thin Filament H BAND  SKELETAL MUSCLE - MICROSCOPIC STRUCTURE Sarcoplasm ; Myofibrils; Muscle Proteins Myofibrils are built from three kinds of proteins: 1. Contractile proteins, which generate force during contraction. Actin (Thin Filament) & Myosin(Thick Filament). Projecting myosin heads contain actin binding and ATP binding sites and are the motor proteins that power muscle contraction. 2. Regulatory proteins, which help switch the contraction process on and off. Tropomyosin & Troponin (Thin Filament) 3. Structural proteins, which keep the thick and thin filaments in the proper alignment, give the myofibril elasticity and extensibility, and link the myofibrils to the sarcolemma and extracellular matrix. Titin (links Z disc to M line and stabilizes thick filament), myomesin (forms M line), nebulin (anchors thin filaments to Z discs and regulates length of thin filaments during development), and dystrophin (links thin filaments to sarcolemma). CONTRACTION AND RELAXATION OF SKELETAL MUSCLE CONTRACTION AND RELAXATION OF SKELETAL MUSCLE  CONTRACTION AND RELAXATION OF SKELETAL MUSCLE The contraction cycle is the repeating sequence of events that causes sliding of the filaments: 1. Myosin ATPase hydrolyzes ATP and becomes energized 2. Myosin head attaches to actin, forming a crossbridge 3. The crossbridge generates force as it rotates toward the center of the sarcomere (power stroke); and 4. Binding of ATP to the myosin head detaches it from actin. The myosin head again hydrolyzes the ATP, returns to its original position, and binds to a new site on actin as the cycle continues. An increase in Ca2+ concentration in the sarcoplasm starts filament sliding; a decrease turns off the sliding process.  NEUROMUSCULAR JUNCTION Synapse: The site of transmission of electric nerve impulses between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector) The neuromuscular junction (NMJ) is a synaptic connection between the terminal end of a motor nerve and a muscle (skeletal/ smooth/ cardiac). It is the site for the transmission of action potential from nerve to the muscle. It is also a site for many diseases and a site of action for many pharmacological drugs  NEUROMUSCULAR JUNCTION The structure of NMJ can be divided into three main parts: 1. A presynaptic part (nerve terminal), 2. The postsynaptic part (motor endplate), and 3. An area between the nerve terminal and motor endplate (synaptic cleft).  NEUROMUSCULAR JUNCTION An electrical signal or action potential, arriving from the central nervous system, needs to cross the synaptic cleft. The neuromuscular junction accomplishes this by turning the electrical signal from the nervous system into a chemical signal that can be moved across the synaptic cleft. The chemical in this case is acetylcholine (ACh), an example of a neurotransmitter that allows neurons to communicate with other cells. ACh is stored inside the synaptic end bulb within membrane-enclosed sacs known as synaptic vesicles. As the electrical signal approaches the synaptic end bulb, it stimulates the inflow of calcium (Ca2+) by opening voltage-gated channels in the cell membrane of the neuron. The increase of Ca2+ within the cytosol of the synaptic end bulb causes the synaptic vesicles to move towards and fuse with the neuron’s cell membrane. Once fused, the synaptic vesicles release their contents – ACh – into the synaptic cleft.  NEUROMUSCULAR JUNCTION The ACh then moves across the synaptic cleft towards the motor end plate of the muscle fiber. The binding of two molecules of ACh to an acetylcholine receptor, opens the ion channel in the receptor and allows the influx of sodium (Na+) into the muscle fiber. It is this influx of Na+ that once again initiates an electrical impulse or action potential that travels outwards from the motor end plate towards both ends of the muscle fiber causing the muscle fiber to contract and shorten. From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p323  MUSCLE METABOLISM Skeletal muscle fibers often switch between a low level of activity, when they are relaxed and using only a modest amount of ATP, and a high level of activity, when they are contracting and using ATP at a rapid pace. ATP supplies the energy for all the work carried out by muscle cells.  MUSCLE METABOLISM Muscle fibers have three ways to produce ATP: 1. from creatine phosphate - Creatine is used by muscle cells to create creatine phosphate, a molecule that supplies the energy required for brief, intense exertion by 'donating' its phosphate to ADP, which results in the formation of ATP. 2. by anaerobic glycolysis - Anaerobic glycolysis serves as a means of energy production in cells that cannot produce adequate energy through oxidative phosphorylation. 3. by aerobic respiration – occurs in the presence of oxygen to produce energy. This energy lasts from a few minutes to several hours From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p326  HOW MUSCLES PRODUCE MOVEMENT Skeletal muscles that produce movements do so by exerting force on tendons, which in turn pull on bones or other structures (such as skin). Most muscles cross at least one joint and are usually attached to articulating bones that form the joint. When a skeletal muscle contracts, it moves one of the articulating bones ; the two articulating bones usually do not move equally in response to contraction. One bone remains stationary or near its original position, either because other muscles stabilize that bone by contracting and pulling it in the opposite direction or because its structure makes it less movable.  HOW MUSCLES PRODUCE MOVEMENT The attachment of a muscle’s tendon to the stationary bone is called the origin The attachment of the muscle’s other tendon to the movable bone is called the insertion. Origin is usually proximal and the insertion distal; the insertion is usually pulled toward the origin. The fleshy portion of the muscle between the tendons is called the belly (body) The actions of a muscle are the main movements that occur when the muscle contracts  HOW MUSCLES PRODUCE MOVEMENT Bones act as levers, and joints function as the fulcrums of these levers. 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. The effort is the force exerted by muscular contraction; the load is typically the weight of the body part that is moved or some resistance that the moving body part is trying to overcome. Motion occurs when the effort applied to the bone at the insertion exceeds the load From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 345  HOW MUSCLES PRODUCE MOVEMENT The relative distance between the fulcrum and load and the point at which the effort is applied determine whether a given lever operates at a mechanical advantage or a mechanical disadvantage. Levers are categorized into three types according to the positions of the fulcrum, the effort, and the load: 1. The fulcrum is between the effort and the load in first-class levers  HOW MUSCLES PRODUCE MOVEMENT 2. The load is between the fulcrum and the effort in second-class levers 3. The effort is between the fulcrum and the load in third- class levers HEAD & NECK DURING EXTENSION From The concise human body, by Parker,Steve, 2019,p 73 ©2023 VISIBLE BODY. FOOT / ANKLE ©2023 VISIBLE BODY. ELBOW JOINT ©2023 VISIBLE BODY.  HOW MUSCLES PRODUCE MOVEMENT - Effect of arrangement of muscle fascicles Skeletal muscle fibers within a muscle are arranged in bundles known as muscle fascicle. Within a muscle fascicle, all muscle fibers are parallel to one another. The muscle fascicles, however, may run one of five patterns with respect to the tendons: 1. parallel, 2. fusiform (spindle-shaped, narrow toward the ends and wide in the middle), 3. circular, 4. triangular, 5. pennate (shaped like a feather) – unipennate, bipennate, multipennate HOW MUSCLES PRODUCE MOVEMENT - Effect of arrangement of muscle fascicles  HOW MUSCLES PRODUCE MOVEMENT - Effect of arrangement of muscle fascicles Muscle fascicular arrangement affects a muscle’s power and range of motion. As a muscle fiber contracts, it shortens to about 70% of its resting length. The longer the fibers in a muscle, the greater the range of motion it can production. The power of a muscle depends not on length but on its total cross-sectional area, because a short fiber can contract as forcefully as a long one. So, the more fibers per unit of cross- sectional area a muscle has, the more power it can produce. Muscle fascicular arrangement often represents a compromise between power and range of motion.  HOW MUSCLES PRODUCE MOVEMENT - Coordination among muscles Movements often are the result of several skeletal muscles acting as a group. Most skeletal muscles are arranged in opposing (antagonistic) pairs at joints ; flexors– extensors, abductors–adductors etc. Of the opposing muscles, one muscle, called the prime mover or agonist, contracts to cause an action while the other muscle, the antagonist, stretches and yields to the effects of the prime mover. With an opposing pair of muscles, the roles of the prime mover and antagonist can switch for different movements. The antagonist and prime mover are usually located on opposite sides of the bone or joint. If a prime mover and its antagonist contract at the same time with equal force, there will be no movement.  HOW MUSCLES PRODUCE MOVEMENT - Coordination among muscles To prevent unwanted movements at intermediate joints or to otherwise aid the movement of the prime mover, muscles called synergists contract and stabilize the intermediate joints. Synergists are usually located close to the prime mover. Some muscles in a group also act as fixators, stabilizing the origin of the prime mover so that the prime mover can act more efficiently. Fixators steady the proximal end of a limb while movements occur at the distal end.  MUSCLE NOMENCLATURE The names of most of the skeletal muscles contain combinations of the word roots of their distinctive features such as the pattern of the muscle’s fascicles; the size, shape, action, number of origins, and location of the muscle; and the sites of origin and insertion of the muscle.  MUSCLE NOMENCLATURE - DIRECTION: Orientation of muscle fascicles relative to the body’s midline Name Meaning Example Rectus Parallel to the midline Rectus Abdominis Transverse Perpendicular to the midline Transverse Abdominis Oblique Diagonal to the midline External Abdominal Oblique From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 352 MUSCLE NOMENCLATURE - SIZE: Relative size of the muscle Name Meaning Example Maximus/Minimus Largest/Smallest Gluteus Maximus/Gluteus Minimus Longus/Brevis Long/Short Adductor Longus/Adductor Brevis Latissimus/Longissimus Widest/Longest Latissimus Dorsi/ Longissimus Capitis Major/Minor Larger/Smaller Pectoralis Major/Pectoralis Minor Vastus Huge Vastus Lateralis Magnus Large Adductor Magnus From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 352 MUSCLE NOMENCLATURE - SIZE: Relative size of the muscle  MUSCLE NOMENCLATURE - SHAPE: Relative shape of the muscle Name Meaning Example Deltoid Triangular Deltoid Trapezius Trapezoid Trapezius Serratus Saw-toothed Serratus anterior Rhomboid Diamond-shaped Rhomboid major Orbicularis Circular Orbicularis oculi Pectinate Comb like Pectineus piriformis Pear-shaped Piriformis Quadratus Square, four-sided Quadratus femoris Gracilis Slender Gracilis MUSCLE NOMENCLATURE - SHAPE: Relative shape of the muscle Deltoid Trapezius MUSCLE NOMENCLATURE - ACTION: principal action of the muscle Name Meaning Example Decreases/Increases Joint Flexor Carpi Radialis/ Extensor Carpi Flexor/Extensor angle Ulnaris Moves away from Abductor Pollicis Longus/Adductor abductor/adductor midline/Moves towards Longus midline Elevates body part/Depresses Levator Scapulae/Depressor Labii Levator/Depressor body part inferioris Turns palm anteriorly/ Turns Supinator/pronator Supinator/ Pronator Teres palm posteriorly Sphincter Decreases size of an opening External anal sphincter Tensor Makes body part rigid Tensor Fasciae Lata From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 352 MUSCLE NOMENCLATURE - NUMBER OF ORIGINS: Number of tendons of origin Name Meaning Example Biceps Two heads of Origin Biceps Brachii Triceps Three heads of Origin Triceps Brachii Quadriceps Four heads of Origin Quadriceps Femoris From Principles of Anatomy and Physiology, by Tortora, Gerard J. And Bryan H Derrickson, Wiley & Sons, 2020,p 352 MUSCLE NOMENCLATURE - LOCATION: Structure near which a muscle is found Temporalis: muscle near temporal bone. Sternocleidomastoid: originating on sternum and clavicle and inserting on mastoid process of temporal bone.  MUSCLES OF HEAD & NECK Sternocleidomastoid  MUSCLES OF THORAX & ABDOMEN Deltoid MUSCLES OF ABDOMEN & PELVIS  MUSCLES OF UPPER LIMB Anterior compartment of arm - Flexors Posterior compartment of arm - Extensors  MUSCLES OF UPPER LIMB Anterior compartment of Forearm - Flexors Posterior compartment of forearm - Extensors  MUSCLES OF UPPER LIMB Anterior compartment of Forearm - Flexors Posterior compartment of forearm - Extensors  MUSCLES OF LOWER LIMB Anterior compartment of Posterior thigh & leg - compartment of thigh Extensors & leg - Flexors  MUSCLES OF LOWER LIMB Anterior compartment of thigh & leg - Extensors Posterior compartment of thigh & leg - Flexors  Myasthenia gravis is an autoimmune disease that causes chronic, progressive damage of the neuromuscular junction. The immune system inappropriately produces antibodies that bind to and block some ACh receptors, thereby decreasing the number of functional ACh receptors at the motor end plates of skeletal muscle. The muscles of the face and neck are most often affected. Initial symptoms include weakness of the eye muscles, which may produce double vision, and weakness of the throat muscles that may produce difficulty in swallowing.  Muscular dystrophy refers to a group of inherited muscle destroying diseases that cause progressive degeneration of skeletal muscle fibers. The most common form of muscular dystrophy is Duchenne muscular dystrophy (DMD) X linked inheritance pattern. The disorder usually becomes apparent between the ages of 2 and 5, when parents notice the child falls often and has difficulty running, jumping, and hopping. In DMD, the gene that codes for the protein dystrophin is mutated, so little or no dystrophin is present in the sarcolemma. Without the reinforcing effect of dystrophin, the sarcolemma tears easily during muscle contraction, causing muscle fibers to rupture and die.  TOPICS FOR ILLUSTRATION DRAW A NEAT LABELLED DIAGRAM OF THE GIVEN TOPICS ON PLAIN A4 SIZE PAPER – FOLLOW RUBRICS COMPLETED DIAGRAMS TO BE SUBMITTED FOR CORRECTION ON 30.09.2024 – sections 22/66 & 33/77 (Mon/Wed) 08.10.2024 – sections 44/88 (Tue/Thurs) Microscopic structure of skeletal muscle  QUIZ 1 ❖ DATE : 16.09.2024 (Mon/Wed); 17.09.2024( Tue/Thurs) ❖ Duration : 15min; Written, on paper ❖ Max. Marks: 20 ❖ Weightage: 7.5% ❖ Portions: Week 1 to Week 3.1 (Introduction, Skeletal System, Muscular System -till Lecture 1)  REFERENCES Tortora, Gerard J. And Bryan H Derrickson. Principles of Anatomy and Physiology. John Wiley & Sons, 2020 Standring, Susan. Gray’s Anatomy E-Book. Elsevier Health Sciences, 2015. Parker, Steve. The Concise Human Body Book. 2019. Omar A, Marwaha K, Bollu PC. Physiology, Neuromuscular Junction. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan