W3 PPT- Physio- Bones, Joints and Muscular System PDF

Bones Primary Text: Fox, S. (2019). Human physiology (15th ed.) Tissue Structure Chapter 1, section 3 Fox Bone cell function, Chapter 19, section 6 © Stanbridge University 2023 Obje...

Bones Primary Text: Fox, S. (2019). Human physiology (15th ed.) Tissue Structure Chapter 1, section 3 Fox Bone cell function, Chapter 19, section 6 © Stanbridge University 2023 Objectives  List the functions of bone  Describe the structure of a flat bone and a long bone, naming all parts  Describe the structure of compact and spongy bone  List the locations and purpose of red and yellow bone marrow  Describe how a long bone grows in length and width  Describe bone remodeling  Understand Wolff’s Law and provide examples of it  List the various types of bone cells and describe their functions © Stanbridge University 2023 Functions of Bones  Support  Protection (ex. skull, spinal vertebrae, rib cage)  Movement  Mineral and growth factor storage  Blood cell formation (in red bone marrow of some bones)  Triglyceride storage (in bone cavities)  Hormone production (osteocalcin): helps regulate bone formation, protects against obesity, glucose intolerance and diabetes mellitus © Stanbridge University 2023 Bone Structure  Compact: external layer, appears smooth and solid  Also called lamellar bone or cortical bone  Spongy or Trabecular: internal layer; filled with red bone marrow (produces RBCs, WBCs, thrombocytes) or yellow bone marrow (stores fat) in living tissue © Stanbridge University 2023 Bone Structure  Organic components (bone cells and osteoid):  Made of soft components which allow bone to resist tension (stretch) and twisting  Cells: osteoblasts, osteocytes, osteoclasts, bone lining cells  Osteoid: 1/3 of the matrix, includes ground substance, and collagen fibers (both made by osteoblasts)  Inorganic components (mineral salts):  65% of bone mass  Consists of hard components which allow bone to resist compression  Hydroxyapatites (mineral salts, mainly calcium and phosphate)  Located in and around the collagen-fiber matrix © Stanbridge University 2023 Structure of Short, Irregular, and Flat Bones  Thin plates of spongy bone covered by compact bone  Compact bone covered by connective tissue membranes:  Periosteum covers outside of compact bone  Endosteum covers inside of compact bone  No shaft or epiphyses  Bone marrow between trabeculae, but no well- defined marrow cavity Marieb, 2019  Where these bones form moveable joints, hyaline cartilage covers surface © Stanbridge University 2023  Structure of Long Bones  Most long bones have the same structure:  Shaft (diaphysis)  Bone ends (epiphysis)  Membranes (periosteum and endosteum) Marieb, 2019 © Stanbridge University 2023 Long Bone Structure: Epiphysis  Outside: compact bone; periosteum lines the outside  Inside: spongy bone; endosteum lines the inside  Thin layer of hyaline cartilage covers joint surface, to cushion during movement and absorb stress Marieb, 2019 © Stanbridge University 2023 Long Bone Structure: Diaphysis  Thick compact bone surrounds medullary cavity or marrow cavity  In adults, cavity contains yellow marrow (fat) © Stanbridge University 2023 Marieb, 2019 Metaphysis or Epiphyseal Line  Where diaphysis and epiphysis meet  In adults, remnant of epiphyseal plate (disc of hyaline cartilage that grows during childhood to lengthen bone) © Stanbridge University 2023 Marieb, 2019  Red Marrow Cavities  Meaning: Contain red marrow or hematopoietic tissue (makes red blood cells)  Usually in trabecular cavities of spongy bone of long bones  In newborn infants: located in the medullary cavity of the diaphysis and all areas of spongy bone  In most adults: located in the femoral heads and humeral heads and in some flat bones (some skull bones, sternum, ribs, scapulae), clavicles, and irregular bones (coxal bones and vertebrae) © Stanbridge University 2023  Yellow Marrow Cavities  Meaning: Contains fat  Most of the marrow cavities of long bones in adults has become yellow marrow cavities  It goes from the diaphysis into a lot of the epiphysis of long bones in adults  Can change back into red marrow cavities due to demand for more red blood cells, like in significant anemia © Stanbridge University 2023 Membranes Periosteum Endosteum  Double layered membrane  Covers internal bone surfaces,  Covers external surface of entire bone lines trabeculae of spongy bone except joint surfaces and canals that pass through compact bone  Outer (fibrous) layer: dense irregular connective tissue  Contains the same cell types as in the inner (osteogenic) periosteal  Inner (osteogenic) layer: mainly layer osteogenic stem cells – makes all bony cells except osteoclasts  Some collagen fibers secure periosteum to bone  Periosteum also anchors tendons and ligaments with dense tissue © Stanbridge University 2023 Bone Cell Types  Osteogenic cells – stem cell; only cells that divide  Also called osteoprogenitor cells  Develop into osteoblasts  Osteoblasts – bone forming cells  “-blasts” = immature cell or tissue  Produce bone tissue  When surrounded by the bone matrix that they secrete, the become osteocytes © Stanbridge University 2023 Bone Cell Types  Osteocytes – mature osteoblasts “-cyte” = cell  Make up bone matrix Sense bone loading and weightlessness and communicate this to osteoblasts and osteoclasts for bone remodeling  Osteoclasts – bone destroying cells “-clast” = to break  Reabsorption © Stanbridge University 2023 Bone Cell Types Marieb, 2019 © Stanbridge University 2023 Compact (Lamellar) Bone  Osteon or Haversian System: structural unit of compact bone  Elongated cylinder parallel to bone axis  An osteon is a group of hollow matrix tubes, wrapping around each other like the rings in a tree trunk  Lamella (each matrix tube)  Canaliculi connect lacunae (small spaces between lamella) together  Central canal runs through the core of the osteon  AKA Haversian canal  perforating (Volkmann’s canals) connect blood and nerve supply of medullary cavity to the central canal © Stanbridge University 2023 Marieb, 2019 Compact (Lamellar) Bone: Osteon  Neighboring lamella have fibers that run in a different direction (for torsional stress)  Central canal: small blood vessels and nerve fibers  Volkmann’s canals: at right angles to long bone axis; connect blood and nerve supply from periosteum to central canals and medullary cavity © Stanbridge University 2023 Compact and Spongy Bone Marieb, 2019 © Stanbridge University 2023 Compact Bone: Osteon  Osteocytes are in lacunae (hollow areas) at junctions of lamellae  Canaliculi (small canals) connect lacunae to each other and to the central canal  Canaliculi connect osteocytes in a mature osteon together for communication, nutrient and waste transport  Cell to cell gap junctions also all provide nourishment © Stanbridge University 2023 Marieb, 2019 Spongy Bone  Trabeculae align along stress lines  Trabeculae are only a few cells thick with irregular lamellae arrangement  Nutrients diffuse through canaliculi from surrounding capillaries in endosteum Marieb, 2019 © Stanbridge University 2023 Growth in length of bones  Epiphyseal plates (growth plates) 1. Chondrocytes (cartilage cells) multiply 2. Outer margin of growth plates “ossify” 3. Bone grows longer 4. Growth stops when cartilage is all ossified © Stanbridge University 2023 Growth in length of long bone at epiphyseal plate © Stanbridge University 2023 Marieb, 2019 Growth in thickness of bones  “Appositional growth” (bone growth in diameter)  Osteoblasts in the periosteum lay down new bone matrix on the outer surface of the bone  Osteoclasts remove bone from under the inner layer (endosteum) of the diaphysis  Normally there is slightly more building up than breaking down which creates a thicker stronger bone but not too heavy Marieb, 2019 © Stanbridge University 2023  Compact bone is thickest where there is the most bending stress, usually midway down the diaphysis  Trabeculae of spongy bone lay down struts in response to compression  Where active muscles pull on bone, there are large bony projections  the dominant arm has thicker bones  Bones atrophy in people that are bedridden  A fetus has bones without features on it (no stresses placed on it yet) © Stanbridge University 2023  JOINTS Marieb, Elaine N. and Hoehn, Katja. Human Anatomy and Physiology, 11th Edition © Stanbridge University 2023 JOINTS Objectives  List the functional and structural classifications of joints and provide examples of each  List the 6 distinguishing features of synovial joints  List other associated features of some synovial joints © Stanbridge University 2023 Joints (Articulations)  Articulation  Site where two or more bones meet  Functions of joints  Give skeleton mobility  Hold skeleton together  Two classifications  Functional  Structural © Stanbridge University 2023 Functional Classification of Joints  Based on  Amount of movement joint allows  Three functional classifications: 1. Synarthroses—immovable joints 2. Amphiarthroses—slightly movable joints 3. Diarthroses—freely movable joints © Stanbridge University 2023 Functional Classification of Joints Synarthroses—immovable  “syn” = together; “arthro” = joint  Ex: sutures of the skull © Stanbridge University 2023 Functional Classification of Joints Amphiarthroses—slightly movable  “amphi” = both sides  Ex: Pubic symphysis and intervertebral joints © Stanbridge University 2023 https://www.frontrangeneurosurgery.com/blog/ Functional Classification of Joints Diarthroses—freely movable  “Dia” = throughout or completely  most joints of the body  exs.: hip, knee, shoulder Istockphoto.com © Stanbridge University 2023 Structural Classification of Joints  Based on  Material binding bones together  Presence/absence of joint cavity  Three structural classifications: 1. Fibrous joints 2. Cartilaginous joints 3. Synovial joints © Stanbridge University 2023 Structural Classification of Joints: Fibrous Joints  Connected by fibrous tissue  “Fixed" or “Immovable“ (do not move)  No joint cavity  Most are synarthrotic functionally  Sutures Marieb, 2019  Between bones of skull  Syndesmoses (slightly moveable)  Between long bones (radius, ulna)  Gomphosis  Between root of tooth and socket © Stanbridge University 2023  Marieb, 2019, Figure 8.1a Structural Classification: Fibrous joints. Fibrous Joints- Sutures Joint held together with very short, interconnecting fibers, and bone edges interlock. Found only in the skull  Rigid, interlocking joints  Immovable joints for protection of brain  Contain short connective Suture tissue fibers line Dense fibrous © Stanbridge University 2023 connective tissue Fibrous Joints- Joint held together by a ligament. Syndesmoses Fibrous tissue can vary in length, but is longer than in sutures  Bones connected by ligaments (bands of fibrous tissue)  Fiber length varies so movement varies, i.e.:  Little to no movement at distal tibiofibular joint Fibula  Large amount of movement at interosseous Tibia membrane connecting radius and ulna © Stanbridge University 2023 Ligament Marieb, 2019, Figure 8.1b Structural Classification: Fibrous joints  “Peg in socket” fibrous joint. Fibrous Joints- Periodontal ligament holds tooth in socket Gomphoses  Peg-in-socket joints of teeth in alveolar sockets Socket of  Fibrous connection is the periodontal alveolar process ligament Root of tooth © Stanbridge University 2023 Periodontal ligament Marieb, 2019, Figure 8.1c Structural Classification: Fibrous joints. Structural Classification: Cartilaginous Joints  Connected by cartilage  Slightly moveable  Form growth regions (epiphyseal line)  Synchondroses (hyaline cartilage)  Epiphyseal lines on long bones  Symphyses (fibrocartilage with hyaline cover) Marieb, 2019  Intervertebral discs © Stanbridge University 2023 Cartilaginous Joints-Synchondroses  Bar/plate of hyaline cartilage unites bones Bones united by hyaline cartilage Sternum (manubrium) Joint between first Epiphyseal rib and sternum plate (temporary (immovable) hyaline cartilage joint) Marieb, 2019, Figure 8.2a Structural Classification: Cartilaginous joints. © Stanbridge University 2023 Cartilaginous Joints- Symphyses  Fibrocartilage unites bone  All are amphiarthrotic functionally Body of vertebra Fibrocartilaginous intervertebral disc (sandwiched between hyaline cartilage) Pubic symphysis © Stanbridge University 2023 Marieb, 2019 Figure 8.2b Structural Classification: Cartilaginous joints. Structural Classification of Joints: Synovial Joints All are diarthrotic functionally Six Distinguishing Features 1. Articular cartilage: hyaline cartilage  Cushions, supports, reinforces, and resists compressive stress  Primarily found covering the ends of long bones 2. Joint (synovial) cavity  Small, fluid-filled “potential” space  Normally almost nonexistent space but can expand if fluid accumulates © Stanbridge Universitylike 2023 with inflammation Marieb, 2019 Synovial Joints 3. Articular (joint) capsule  Two layers 1. External Fibrous layer  Dense irregular connective tissue 2. Inner Synovial membrane  Loose connective tissue  Makes synovial fluid Marieb, 2019 © Stanbridge University 2023 Synovial Joints 4. Synovial fluid  Viscous, slippery filtrate of plasma and hyaluronic acid  Lubricates and nourishes articular cartilage  Contains phagocytic cells to remove microbes and debris Marieb, 2019 © Stanbridge University 2023 Synovial Joints 5. Reinforcing ligaments  Capsular  Thickened part of fibrous layer  Extracapsular  Outside the capsule  Intracapsular  Deep to capsule  Covered by synovial membrane © Stanbridge University 2023 Marieb, 2019 Synovial Joints 6. Nerves and blood vessels  Nerve fibers detect pain, monitor joint position and stretch  Capillary beds supply filtrate for synovial fluid © Stanbridge University 2023 Other Features of Some Synovial Joints  Fatty pads  Cushioning between fibrous layer and synovial membrane or bone  Articular discs (menisci)  Fibrocartilage separates articular surfaces to improve "fit" of bone ends, stabilize joint, and reduce wear and tear © Stanbridge University 2023 Structures Associated with Synovial Joints  Bursae  Sacs lined with synovial membrane  Contain synovial fluid  Reduce friction where ligaments, muscles, skin, tendons, or bones rub together  Tendon Sheaths  Elongated bursa wrapped completely around tendon subjected to friction © Stanbridge University 2023  Marieb, 2019, Figure 8.4a Bursae and tendon sheaths. Acromion of scapula Subacromial Joint cavity bursa containing synovial fluid Fibrous layer of articular capsule Articular cartilage Tendon sheath Synovial membrane Tendon of Fibrous long head layer of biceps brachii muscle Humerus © Stanbridge University 2023 Frontal section through the right shoulder joint  Bursa rolls Marieb, 2019, Figure 8.4b Bursae and tendon sheaths. and lessens friction Humerus head rolls medially as arm abducts Showing how a bursa eliminates friction where a ligament (or other structure) would rub against a bone © Stanbridge University 2023 Three Stabilizing Factors at Synovial Joints 1. Shapes of articular surfaces (minor role) 2. Ligament number and location (limited role) 3. Tendons that cross joint (most important)  Muscle tone keeps tendons taut  Extremely important in reinforcing shoulder and knee joints and arches of foot © Stanbridge University 2023 Synovial Joints: Range of Motion  Nonaxial—slipping movements only  Uniaxial—movement in one plane  Biaxial—movement in two planes  Multiaxial—movement in or around all three planes © Stanbridge University 2023 Movements at Synovial Joints  Shapes of joint surfaces  Define movements allowed  Determine classification of synovial joints  Six structural types of synovial joints: 1. Plane Joints 2. Hinge Joints 3. Pivot Joints 4. Condylar Joints 5. Saddle Joints 6. Ball-and-Socket Joints © Stanbridge University 2023 Plane joint Nonaxial movement Metacarpals Flat articular surfaces Gliding Carpals Examples: Intercarpal joints, intertarsal joints, joints between vertebral articular surfaces Marieb, 2019, The shapes of the joint surfaces define the types of movements that can occur at a synovial joint; they also determine the classification of synovial joints into six structural types. © Stanbridge University 2023 Hinge joint Uniaxial movement Humerus Medial/lateral axis Cylinder Trough Ulna Flexion and extension Examples: Elbow joints, interphalangeal joints Marieb, 2019, The shapes of the joint surfaces define the types of movements that can occur at a synovial joint; they also determine the classification of synovial joints into six structural types. © Stanbridge University 2023 Pivot joint Uniaxial movement Vertical axis Sleeve (bone and ligament) Ulna Axle (rounded bone) Radius Rotation Examples: Proximal radioulnar joints, atlantoaxial joint Marieb, 2019, The shapes of the joint surfaces define the types of movements that can occur at a synovial joint; they also determine the classification of synovial joints into six structural types. © Stanbridge University 2023  Condylar joint Biaxial movement Medial/ Anterior/ Phalanges lateral posterior axis axis Oval articular Metacarpals surfaces Flexion and Adduction and extension abduction Examples: Metacarpophalangeal (knuckle) joints, wrist joints Marieb, 2019, The shapes of the joint surfaces define the types of movements that can occur at a synovial joint; they also determine the classification of synovial joints into six structural types. © Stanbridge University 2023 Saddle joint Biaxial movement Medial/ Anterior/ lateral posterior axis axis Metacarpal  Articular surfaces are both concave Adduction and Flexion and and convex abduction extension Trapezium Example: Carpometacarpal joints of the thumbs Marieb, 2019, The shapes of the joint surfaces define the types of movements that can occur at a synovial joint; they also determine the classification of synovial joints into six structural types. © Stanbridge University 2023 Ball-and-socket joint Multiaxial movement Cup Medial/lateral Anterior/posterior Vertical axis (socket) axis axis Scapula Spherical head (ball) Humerus Flexion and extension Adduction and abduction Rotation Examples: Shoulder joints and hip joints Marieb, 2019, Figure 8.1f The shapes of the joint surfaces define the types of movements that can occur at a synovial joint; they also determine the classification of synovial joints into six structural types. © Stanbridge University 2023  The Muscular System Fox Chapter 12 © Stanbridge University 2023 59 Objectives  Understand and describe muscle structure, including skeletal and smooth muscles  Describe a skeletal muscle contraction (and relaxation) from excitation to the actual functional movement at a cellular and muscle belly level  Understand the relationship between stimulus and muscle tension as well as the size principle of recruitment  Describe various types of muscular contractions, length –tension relationships, and muscle fiber types  Understand energy sources for the muscle  List differences between skeletal, smooth, and cardiac muscle © Stanbridge University 2023 The Muscular System  VoluntaryMovement- walking, standing, sitting, being upright, balance, facial expression  Involuntary Muscle Action- Cardiovascular control, respiration, digestion, elimination, reflexes  Protection- through reflex, cover and surround viscera, support internal organs  Miscellaneous - produce heat, maintain temperature, provide shape to body © Stanbridge University 2023 61 Muscle Tissue Types of muscle tissue 1. Skeletal muscle: striated Voluntary 2. Cardiac muscle: striated Involuntary 3. Smooth muscle: non striated – no sarcomeres Involuntary © Stanbridge University 2023 62 Muscle Tissue Skeletal Muscle Cardiac Muscle Smooth (Visceral) Muscle © Stanbridge University 2023 Marieb, 2019  Skeletal Muscle Fox Chapter 12 © Stanbridge University 2023 Crash Course Anatomy Overview (https://youtu.be/Ktv-CaOt6UQ) © Stanbridge University 2023 Muscles of the Musculoskeletal System are “Skeletal Muscle” Tissue Skeletal muscle: striated/voluntary  Made of bundles of muscle fibers  Provide the force to move bones Marieb, 2019 © Stanbridge University 2023 66 Skeletal Muscle and Connective Tissue Sheaths © Stanbridge University 2023 Marieb, 2019 Structure of a Muscle  Myofilaments: (muscle version of microfilaments); myosin (thick) and actin (thin); contained in sarcomeres  Myofibrils: hundreds to thousands in muscle cells; parallel along muscle fiber length; contain sarcomeres; 80% of cellular volume  Muscle Fiber: muscle cell; also called myocyte  Fascicle: a bundle of muscle fibers  Muscle Body: a bundle of fascicles © Stanbridge University 2023 Muscle Fiber Structure © Stanbridge University 2023 Marieb, 2019 Connective Tissue Covering of Skeletal Muscle Muscle structures are held together by connective tissue coverings:  Epimysium: outer covering of a muscle  Epi = “upon”  Perimysium: covering that hold a fascicle together  Peri = “around”  Endomysium: covering of individual muscle fibers  Endo = “inside” © Stanbridge University 2023 Structure of a Skeletal Muscle Fiber and the Connective Tissue Coverings © Stanbridge University 2023 Marieb, 2019 Skeletal Muscle Cells  Myocytes = muscle fibers = muscle cell  “myo” = muscle; “cyte” = cell  Multinucleated  Diameter: 10-100um (10x size of average body cell)  Length: some 30cm in length Marieb, 2019 © Stanbridge University 2023 Skeletal Muscle Fibers  Sarcolemma: plasma membrane of a muscle cell  Sarcoplasm: cytoplasm of a muscle cell  Sarcoplasmic reticulum: smooth endoplasmic reticulum in muscle fibers  There are large amounts of stored glycogen (glycosomes and myoglobin: a red pigment that stores oxygen) © Stanbridge University 2023 The Muscular System  Muscle Attachments can be direct or indirect:  Direct is epimysium of a muscle fiber directly fuses to the periosteum of a bone or perichondrium of cartilage  Indirect is connective tissue wrappings extend beyond the muscle tissue itself into a tendon or aponeurosis © Stanbridge University 2023 74 The Muscular System  Tendons:  connects muscle to bone  cordlike extensions of connective tissue  inserts into bone that does most of the movement  Example: Achilles tendon  Aponeurosis: a broad, flat sheet of tendon that attaches skeletal muscles to other muscles or muscles to bones © Stanbridge University 2023 75 Skeletal muscle contractions  Contractility: ability to shorten, change shape, and thicken (muscle cells have this)  Excitability: ability to respond to external stimuli by changing their resting membrane potential (neurons and muscle cells have this) © Stanbridge University 2023 Motor Impulses to Muscles  Nerves that send signals to muscle fibers are called Motor Neurons  Motor neuron connects (innervates) to a group of muscle fibers  Motor nerve and the muscle fibers it innervates = Motor Unit  Neuromuscular junction: where a motor neuron contacts the skeletal muscle © Stanbridge University 2023 Neuromuscular Junction on a Skeletal Muscle Fiber Marieb, 2019 © Stanbridge University 2023 Neuromuscular Junction  Motor neuron releases a chemical called a neurotransmitter  In skeletal muscle the kind of neurotransmitter used is called acetylcholine [ACh]  When ACh lands on the receptors, a muscle contraction is triggered  This begins an electrical impulse called an action potential that calls the muscle into action © Stanbridge University 2023 Action Potential Generated at Neuromuscular Junction © Stanbridge University 2023 Marieb, 2019 Basic Understanding of energy  The ability to propagate electric signals allows nerve and muscle to be excitable and communicate with one another  All living cells maintain a separation of charge across the cell membrane that a net negative charge exists in the intracellular environment  This difference allows for potential electrical energy  Balanced between Na+ and K+  The potential across the cell is called the Resting Membrane Potential (RMP) © Stanbridge University 2023 Physiologic Responses  This difference results in cells being polarized  Polarity: having opposite properties, creating an attraction towards one another  Inside the cell has a negative concentration on ions  Outside has a positive concentration of ions  If chemical channels open, the rush of ions will occur to create equality  This is called: depolarization ©Stanbridge University 2023 Physiologic Responses : Electrophysiologic effects Repolarization is the process which returns the neuron cell into Depolarization is the process its resting potential after which initiates inflow of Na+ ions depolarization by stopping the into the cell and creates action inflow of Na+ ions into the cell potential in the neuron cell. and sending more K+ ions out of the neuron cell. Net Charge In depolarization, the neuron cell In repolarization, the neuron cell body has a positive charge. body has a negative charge www.differencebeetween.com ©Stanbridge University 2023  www.differencebeetween.com ©Stanbridge University 2023 Steps to Skeletal Muscle Excitation  Action potential arrives at the axon terminal of the motor neuron  Ca2+ channels open → Ca2+ enters the axon terminal  Ca2+ triggers ACh to be released from the neuron into the synaptic cleft (space)  ACh diffuses to receptors on the sarcolemma of the muscle cell  Opens channels on the sarcolemma → allows sodium ions (Na+) into the muscle fiber and potassium (K+) out © Stanbridge University 2023 Steps to Skeletal Muscle Excitation  More Na+ flows into the muscle cell, than K+ flows out of the muscle cell  This changes the charge inside of the cell at that area, changing the resting membrane potential  This process depolarizes the area (making that area more positive)  At a certain charge inside the cell → an action potential is triggered  the action potential spreads along the muscle cell membrane, resulting in the opening of other Na+ channels along the membrane  An action potential is propagated/spread in all directions along the membrane © Stanbridge University 2023  Action Potential: Depolarization Marieb, 2019 © Stanbridge University 2023 Repolarization  Occurs when there is a restoration of the original charge in the muscle cell and across the sarcolemma  This is caused by Na+ channels closing and K+ channels opening  K+ flows out of the cell, following it concentration gradient, which makes the inside of the cell more negative again © Stanbridge University 2023 Action Potential: Repolarization Marieb, 2019 © Stanbridge University 2023 Muscle Contraction in Sarcomere  Ca2+ is stored in the sarcoplasmic reticulum (SR)  Terminal cisterns are tubules of SR that surround each myofibril along with longitudinal tubules of SR; they are on each side of the T-tubule (sarcolemma protruding into cell)  When an action potential is triggered, electricity flowing through the cell triggers the SR to release Ca2+  Ca2+ allows the muscle to contract © Stanbridge University 2023 Sarcoplasmic Reticulum and T Tubules to Myofibrils of Skeletal Muscle Marieb, 2019 © Stanbridge University 2023 Muscle Excitation Marieb, 2019 © Stanbridge University 2023 Muscle Contraction  Contractile subunits inside a myocyte is called the Sarcomere  Sarcomere consists of myosin (thick) filaments with actin (thin) filaments (protein filaments) Marieb, 2019 © Stanbridge University 2023  Muscle Contraction  Globular heads on myosin attach to actin, linking the thick and thin filaments together, forming cross bridges  Cross bridge cycle animation (https://youtu.be/BVcgO4p88AA)  Calcium enables the cross-bridges to form  At rest, the two proteins block the site of attachment for the cross- bridges: Troponin and Tropomyosin  Calcium binds to troponin and Marieb, 2019 moves tropomyosin  The binding sites on actin are now open for myosin to bind to © Stanbridge University 2023 Muscle Contraction: Cross-Bridge Cycle  Once myosin binds to actin a cross-bridge forms  The myosin heads are energized with Adenosine diphosphate (ADP) and a phosphate group (P) bound to the side of it  Once ADP and P are released, the myosin head pivots and bends pulling actin filaments closer to each other © Stanbridge University 2023 Muscle Contraction: Cross-bridge cycle  Myosin heads will remain bound to actin  ATP attaches to the myosin head triggering it to release actin (cross-bridge breaks)  Myosin hydrolyzes ATP into ADP and P, this energy release cocks the myosin head back into its active state again (ready to bind to actin, if there is calcium present) © Stanbridge University 2023  Marieb, 2019 © Stanbridge University 2023 Sarcomere within a Muscle Fiber Marieb, 2019 © Stanbridge University 2023 Sliding Filament Theory Micrograph picture of a sarcomere at rest Marieb, 2019 © Stanbridge University 2023 Sliding Filament Theory: Micrograph of contracted sarcomere Marieb, 2019 © Stanbridge University 2023 Muscle Relaxation inside of the cell  After AP ends, tubule proteins return to original shape → close Ca2+ channels  Ca2+ levels in sarcoplasm reduce as Ca2+ is actively pumped back into the sarcoplasmic reticulum  Tropomyosin can block on actin again → myosin-actin interaction is inhibited → relaxation © Stanbridge University 2023  Muscle Contraction in Various Muscles  Muscles that have fine control, fingers and eyes, have smaller motor units (fewer muscle fibers innervated by a single motor neuron)  Large weight bearing muscles have large motor units (many muscle fibers innervated by a single motor unit)  Muscle fibers in each motor unit are spread throughout the muscle to provide a weak but uniform contraction throughout the muscle when a motor unit is stimulated  A muscle twitch is the response of a muscle to a single stimulation © Stanbridge University 2023  Relationship Between Stimulus Intensity and Muscle Tension Marieb, 2019  More motor units are recruited based upon the stimulus  Once a maximal stimulation is reached and allof the motor units are recruited for that muscle, it does not matter how much higher the stimulus is, there cannot be a greater muscle tension produced © Stanbridge University 2023  Size Principle of Recruitment Marieb, 2019  Motor units with the smallest muscle fibers are activated first because they are controlled by the smallest, most highly excitable motor neurons  Motor units with larger muscle fibers are recruited later and increase the strength of contraction © Stanbridge University 2023 Types of Muscle Contraction  Isometric:  The muscle does not shorten  The tension increases Pushing against a wall without movement occurring at a joint Marieb, 2019 © Stanbridge University 2023 Types of Muscle Contraction  Concentric:  The muscle shortens  Origin and insertion become closer together  Accelerating, often against gravity Ex. bend elbow with weight in hand, biceps brachii shortening Marieb, 2019 © Stanbridge University 2023 Types of Muscle Contraction  Eccentric:  Muscle generates force as it lengthens  Microscopically returning to normal resting position, from shortened  Decelerating, often with gravity, ex. lowering weight from elbow flexed to extended with gravity  About 50% more forceful than concentric contractions at the same load  More often cause delayed on-set muscle soreness © Stanbridge University 2023 Types of Muscle Contraction  Isotonic:  Concentric and eccentric  Can be a misleading term because most likely the amount of tension in a muscle is not consistent over the entire range (Lippert)  Resistance constant but velocity varies (Lippert) © Stanbridge University 2023 Muscle Tone  Skeletal muscles are almost always slightly contracted, even when relaxed  Due to spinal reflexes that first activate one group of motor units and then another in response to activated stretch receptors in muscles Ex. fingers slightly curled at rest; can be disrupted in patients with neurological impairment © Stanbridge University 2023 Length-Tension Relationship in Skeletal Muscles  Optimal length of a muscle fiber is the length it can generate maximal force  Within a sarcomere this occurs when overlap is over most of the thin (actin) filament length  Muscle generates maximum force when it is between 80- 120% of optimal resting length  Usually, joints prevent bone movements that would take a skeletal muscle beyond optimal range © Stanbridge University 2023 Length-Tension Relationship: during an isometric contraction Marieb, 2019 © Stanbridge University 2023 Skeletal Muscle Fiber Types  Slow oxidative fibers (slow twitch)  Fast oxidative fibers (fast twitch fibers, Type IIa)  Fast glycolytic fibers (fast twitch fibers, IIb, same as IIx/d) © Stanbridge University 2023 Muscle Fiber Type  Oxidative fibers: rely mostly on oxgen-using aerobic pathways for ATP generation  Glycolytic fibers: rely more on anaerobic glycolysis © Stanbridge University 2023 Muscle Fiber Type: Difference between Fast and Slow Fibers Speed of Contraction:  Speed of myosin ATPases split ATP  Pattern of electrical activity of motor neurons Contraction Duration:  Fiber type  How quickly Ca2+ moves from cytosol into the sarcoplasmic reticulum © Stanbridge University 2023 Energy Sources in Muscles  ATP is the primary source of energy  Cellular respiration  Myoglobin: stores extra oxygen in the muscle cell (similar to hemaglobin in the blood)  Glycogen: stored in myocytes as an extra source of glucose  Creatine Phosphate: acts as ATP when the myocyte has used up the ATP supply © Stanbridge University 2023 Energy Sources in Muscles  Muscles produce ATP in the presence of oxygen (aerobic exercise)  Jogging  When a muscle works harder than the available oxygen supply an oxygen debt is created  The muscle still can produce ATP from glucose alone (anaerobic exercise)  Sprinting © Stanbridge University 2023 Energy Sources in Muscles Anaerobic exercise  Less efficient than aerobic exercise  Produces lactic acid as a byproduct  Lactic acid causes a burning sensation in muscles during exercise  Lactic acid build up contributes to muscle soreness © Stanbridge University 2023  Smooth Muscle © Stanbridge University 2023 Smooth Muscle  In all hollow organs walls except the heart  Smooth muscle fibers are spindle-shaped cells of variable size, with one centrally located nucleus  Sheets of closely apposed fibers (except in smallest blood vessels), usually 2 sheets at right angles to each other © Stanbridge University 2023 Smooth Muscle Excitation  Instead of neuromuscular junctions, they have innervating nerve fibers from autonomic nervous system  Bulbous swellings called varicosities  Varicosities release NT into wide synaptic cleft (called diffuse junctions) © Stanbridge University 2023 Smooth Muscle Excitation  Sarcolemma has multiple caveolae that hold bits of extracellular fluid with lots of calcium  When those calcium channels open, rapid influx of calcium (most of calcium)  SR does release some calcium (most from extracellular space)  Contraction ends when cytoplasmic calcium is actively transported into SR and out of cell © Stanbridge University 2023 Smooth Muscle Myofilaments  Fewer thick filaments with myosin heads along entire length  No troponin complex in actin  Thick and thin filaments arranged diagonally so contraction is twisting  Non-contractile intermediate filaments resist tension, that attach to dense bodies, that harness pull generated, contributes to the synchronous contractions; transmits pulling to surrounding connective tissues © Stanbridge University 2023 Smooth Muscle Contractions  Takes 30 x longer to contract and relax than skeletal muscle  Can maintain contraction tension for prolonged periods of time  Using less than 1% of energy as skeletal muscle  Makes enough ATP through aerobic pathways for the demand, usually © Stanbridge University 2023 © Stanbridge University 2023 © Stanbridge University 2023 © Stanbridge University 2023  Assess Your Learning © Stanbridge University 2023