Anatomy Chapter 7/8

Energy Sources for Contraction

ATP! When a contraction starts, muscle fibers only have enough ATP for a short contraction, ATP must be generated by ADP and P. Creatine phosphate contains high energy phosphate bonds. When ATP is sufficient, mitochondria catalyzes the synthesis of creatine phosphate: stores excess energy in bonds. Creatine phosphate is 4-6 times more abundant in muscle fibers than ATP, but as ATP decomposes, P from CP can be transferred to ADP, making more. Active muscle fibers exhaust supply though, so you need cellular respiration. Glycolysis in cytosol anaerobic, but also complete breakdown of glucose occurs in mitochondria aerobically. Blood carries O2 from lungs- hemoglobin. Myoglobin is synthesized in myocytes, loosely combine with O2/store it. Oxygen debt - moderate activity is easy to supply, but strenuous activity makes muscles rely on anaerobic respiration to get energy. In anaerobic respiration, glucose molecules are broken down by glycolysis making pyruvic acid, which would enter the citric acid cycle if aerobic. However, it reacts to produce lactic acid, which dissociated creating lactate ion and H+. Lactate leaves by facilitated diffusion, and in liver is made into glucose. Whatever oxygen available is used to make ATP, but as lactate accumulates, you have oxygen debt. This equals the amount of oxygen that liver cells require to convert the accumulated lactate plus the amount needed to restore ATP and creatine phosphate. For muscle to return to resting state: Lactic acid MUST Be reconverted to pyruvic acid Glycogen stores replaced ATP and CP stores resynthesized Factor of age, size, fitness, health are all factors of O2 debt Increased exercise levels dec. O2 debt.: Metabolic capacity changes with training. High intensity exercise depends on glycolysis for ATP, a muscle so glycolytic enzymes and its capacity for glycolysis increases. More capillaries and mitochondria form, and so capacity increases. Heat Production Less ½ energy released in cellular respiration is transferred to ATP, and the rest is heat. MUscle is major source because muscle is large proportion of body mass. Blood transports this heat generated.

Sports Activities and Energy

Aerobic endurance - amount of time muscles can continue aerobic pathways Anaerobic threshold - pt. at which muscle converts to anaerobic pathways Short surges of power (weight lifting, sprinting, diving) - ATP and CP stores On and off activities (tennis, soccer) - anaerobic mechanism producing lactic acid Prolonged activities (marathon, jogging) - endurance vs. power - aerobic

Movements Allowed by Synovial Joints

Affected by muscle's origin and insertion on bone Can be described by axes around which body part moves, or by the planes of space along which movement occurs Articular ends covered in hyaline, and joint capsule holds bones together. Capsule has outer layer of dense connective and inner lining of synovial membrane secretes synovial fluid. Ligaments in fibrous layer. There may be menisci or bursae between tendons or bones and help glide between articulating surfaces of bones. Gliding movements - bones ares sliding over each other Simplest movement One bone surface is gliding over another similar surface (waving) Occurs at intercarpal and intertarsal joints, between vertebrae Angular movements - angle is increased or decreased b/w bones Flexion - decreases angle between two bones Usually occurs in sagittal plane Extension - increases angle between bones Can occur at same joints as flexion Hyperextension - beyond anatomical position Movements of Foot: Up and down movements at the ankle Dorsiflexion - up foot to shin Plantar flexion - down away from shin Abduction - Moving limb away from midline along frontal plane Adduction - Movement of limb toward midline along frontal plane Circumduction - Movement of limb to describe a cone in space; Circular movement at distal end of limb Rotational movements - when you turn your head: Turning a bone around its own long axis; May be directed toward midline or away from midline Special movement Inversion and eversion - eversion lateral and inversion medial foot Protraction and retraction - moving forward and back like your head on neck Elevation and depression - raising and lowering things like shoulders Opposition - Opposable thumbs Pronation and supination like palm up vs. down.

Bone Growth - 2 ways

Appositional - growth from outside - thicker Increase in thickness Balance between bone resorption on endosteal surface and bone deposition on periosteal surface Less resorption than deposition Creates thicker, stronger bones that are not too heavy Interstitial - growth from inside - longer Increase in length Similar to endochondral ossification Occurs primarily within epiphyseal cartilage abutting shaft Active division of chondrocytes which "pushes" epiphysis away from the diaphysis, causing bone to lengthen Older chondrocytes die and deteriorate, are replaced by calcified matrix

Features of Synovial Joints

Articular cartilage - covers the bone surfaces (ends) Joint (Synovial) Cavity - a space that contains synovial fluid Articular Capsule - a two layered capsule composed of loose connective tissue Synovial fluid - viscous, slipper friction resistant fluid Ligaments - connective tissue binding bone to bone

Skeletal Cartilages

Avascular Surrounded by membrane - perichondrium Contains chondrocytes encased in lacunae with a jelly like ground substance 3 major types Hyaline Cartilage - ends of most bones; costal cartilage; respiratory cartilage; external nose; larynx Elastic Cartilage - external ear (penna); epiglottis; lungs Fibrocartilage - vertebrae; symphysis pubis; knee

Skeletal Organization

Axial - bony and cartilaginous parts that support and protect organs of head, neck, and trunk Skull - made of 8 cranium and 14 facial bones, 6 middle ear bones. Hyoid - located in the neck between lower jaw and larynx - supports tongue and movements of jaw. Vertebral Column - many vertebrae and cartilaginous intervertebral discs near the distal end, you have sacrum (part of pelvis), and coccyx tailbone. Total 26. Thoracic Cage - protects organs - 12 parts of ribs, and sternum. Appendicular - consists of upper/lower limbs and bones that anchor to axial Pectoral Girdle - scapula, clavicle, and connects upper limbs. 4 total. Upper Limbs - humerus, radius, ulna, 8 carpals, 5 metacarpals, 14 phalanges. Pelvic Girdle - hip bones, sacrum, coccyx. Total 2. Lower Limbs - femur, tibia, fibula, patella, 7 tarsals, 5 metatarsals, 14 phalanges.

Blood Cell Formation (Hematopoiesis)

Begins in yolk sac (outside of embryo). Later, blood cells are manufactured in the liver and spleen, and later in bone marrow. Marrow is a soft, netlike mass of connective tissue within medullary cavities of long bones, irregular spaces of spongy bone, larger central canals of compact bone. Red and yellow. Red forms red blood cells (erythrocytes), white blood cells (leukocytes), and blood platelets. Color from oxygen carrying pigment hemoglobin. Yellow marrow stores fat, and replaces red marrow after infancy. Found in spongy bone of skull, ribs, sternum, clavicles, vertebrae, hip bones. Can become red marrow, then reverts back after deficiency is over.

Repair of fractures

Bone has been cracked or broken (caused by traumatic, spontaneous, or pathological fracture and by the nature of the break as greenstick, fissured, comminuted, transverse, oblique, or spiral) When a bone breaks, blood vessels in it rupture, periosteum tears, etc. Removal of bone fragments by osteoclasts New bone must be produced following reduction 4 stage process Hematoma formation by blood from broken vessels. The vessels in tissue dilate, swell and inflame. Developing blood vessels and osteoblasts rapidly divide in areas close to new blood vessels, building spongy bone. Granulation tissue develops and fibroblasts form a fibrocartilaginous callus formation. Phagocytic cells begin to remove the blood clot, and damage. Osteoclasts also appear and resorb bone fragments. Bony callus formation after cartilaginous callus breaks down, blood vessels and osteoblasts invade the area. Bone remodeling by osteoclasts

Skeletal Muscle Actions

Bones and muscles interact as levers: Rigid bar/rod, fulcrum/pivot on which bar turns Object moved against resistance Force that supplies energy for the movement of the bar Ex. Upper limb: Forearm bones rigid bar, elbow joint fulcrum, hand moved against resistance provided by the weight, and force is muscles on anterior side of arm like biceps brachii attached to radius. Straightens, forearm, elbow, and hand same, but triceps brachii on posterior side supplies force and attaches to ulna.

Muscle Types

Cardiac Only found in heart Striated, involuntary Contracts at a steady rate due to pacemaker - nerve tissue Neural controls can shift heart rate when necessary Skeletal Cover and attach to bones Observable striations (stripes) Voluntary - conscious choice Contracts rapidly, tires easily Adaptable in terms of amount of force necessary Smooth Found in walls of hollow visceral organs: ex. Stomach, intestines, uterus, bladder, blood vessels, etc. Forces fluids and other substances through internal body channels No striations, involuntary Slow sustained contractions P 218 and table 8.3 Similarities Cardiac and skeletal - striations Contraction depends on myofilaments Myo or mys - muscle Sarco - flesh

Skeletal Tissues*

Cartilage Bone Dense regular connective tissue Tendons - bone to muscle Ligaments - bone to bone Periosteum - membrane that surrounds every bone Each bone is an organ - contains epithelial, connective, and nerve tissue

Types of Synovial Joints

Classification based on shape of articular surfaces Plane - flat allowing sliding/twisting Hinge - convex to concave Pivot - cylinder with bone/ligament ring and you have rotation Condyloid/Ellipsoidal - oval condyle articulates with elliptical cavity and two plane move Saddle - concave or convex on two planes Ball-and-Socket - ball and cup shape providing free movement in all planes even rotation

Biology of Bone

Clasts from marrow Blasts from vessels Remove cartilage - brittle - oriented opposite diagonal, resisting torque.

Bone Remodeling

Combination of bone resorption and bone deposition In healthy adult skeleton, bone mass remains constant Not a uniform process - bones or areas of bones remodeled at different rates Coordinated by adjacent osteoblasts and osteoclasts Hormonal Regulation Calcitonin - stimulates calcium salt deposition in bones Parathyroid hormone - stimulates the bones to degrade and release calcium into the bone Storage of Inorganic Salts Extracellular matrix of bone tissue is rich in calcium salt, calcium phosphate. Low = parathyroid gland releases PTH stimulating osteoclasts to break down bone tissue and release. High = thyroid gland releases calcitonin stimulating storage of excess calcium. Stem Cells are used to help produce bone marrow and help treat disease. Mechanical Stress Muscle pull (tension applied to tendons) and gravity promote skeletal remodeling Wolff's Law - bone grows or remodels in response to forces placed on it Greater pull = greater deg. of remodeling Bones are loaded where weight bears down or muscles pull Remodeling Influences Subjected to both hormonal effects (testosterone, estrogen, HGH) and mechanical forces Hormones affect whether and when remodeling will occur in response to changing calcium levels (calcitonin and PTH) (vit. D) Mechanical stress determines where remodeling occurs

Connective Tissue Coverings (allows parts to move independently, and blood/nerve passage)

Dense connective fascia separates an skeletal muscle from adjacent. Fasca blends with epimysium, surrounds skeletal muscle. Perimysium extend inwards from epimysium and separate into fascicles Endomysium covers each muscle fiber within a fascicle. Tendon - project of muscle - intertwine with bone's periosteum, but sometimes fibrous sheets, aponeuroses, attach to bone, skin, or other muscle.

Bone Parts

Diaphysis Metaphysis w/ epiphyseal plate - until growth stops, in between is cartilage. Template from which bones form. Epiphysis

Classification of Joints

Fibrous - held together by dense connective fibrous tissue - no range of motion (synarthrotic) Bones are joined by fibrous tissue No joint cavity Types Sutures - seams between bones of the skull Bones are connected by a ligament - distal end of tibia and fibula Peg in a socket - teeth embedded in bone Cartilaginous - cartilage - small range of motion (amphiarthrotic) Joints with hyaline cartilage (as in the epiphyseal plate of the long bones) Joint that contain a pad of fibrocartilage - vertebrae Synovial - high range of motion (diarthrotic) and complex

Filament Structure and Arrangement

Filament Structure (of myofibril) Thick filaments - myosin Thin filaments - actin (troponin, tropomyosin) Filament Arrangement (of myofibril) Sarcomere: Contractile unit of myofibril A band: Region of the sarcomere where thick and thin filaments overlap (darker) I band: Region of sarcomere with only thin filaments (lighter) Z line: Protein strands perpendicular to thin filaments (brackets sarcomere)

Recording of a Muscle Contraction

Graded muscle responses Variations in FORCE of muscle contraction Contractions are relatively smooth and vary in strength as different demands are placed on them Grades in 2 ways: Changing frequency (speed) of stimulation Receiving multiple stimuli in rapid succession Second twitch stronger than first Muscle not completely relaxed from stimulus Contraction are summed - wave/temporal summation: A muscle fiber exposed to a series of stimuli of increasing frequency reaches a point when it is unable to completely relax before next stimulus in the series arrives, and the force of individual twitches combines by summation. At higher frequencies of stimulation, time relaxing is brief. Complete tetanic contraction where fiber can't relax at all. Tetanus-smooth, sustained contraction Muscle fatigue-due to prolonged summation Changing strength Recruitment: Delivering impulses of increasing voltage to muscle Stimulates more and more fibers Summation increases force of contraction of single fiber, but a whole muscle can generate more force if more fibers contract. A muscle fiber typically has a single motor end plate, but the axons of motor neurons are branches, enabling them to control many fibers. A motor neuron and the fibers it controls are a MOTOR UNIT. Motor neurons must be brought to different thresholds before impulse. Increase in the number of motor units activated during contraction is called recruitment. Threshold Stimulus - first observable muscle contraction: The certain strength of stimulation where a muscle fiber is responsive. Once reached, electrical impulse is generated and spread throughout the fiber, activating contraction. Maximal Stimulus - strongest stimulus that produces increased contractile force Involved more motor units Muscle tone Made with summation & recruitment. Even appearing at rest, muscle tone is a response to nervous stimulation that originates repeatedly from the spinal cord and stimulated only a few fibers at a time. Muscles always in slightly contracted state. Keeps muscles firm, healthy, read to respond - Maintain posture, stabilize joints, Isometric and isotonic contractions Muscle tension - force exerted by contracting muscle measured in grams Load - weight/reciprocal force exerted by object on muscle Types of contractions: Isotonic Muscle changes in length, moves load Tension remains constant through most of contractile period Muscle tension is greater than the resistance. The muscle shortens (concentric) or lengthens (eccentric), and movement occurs. Isometric Muscle neither shortens nor lengthens Tension increases, but the load is not moved Muscle tension is less than the resistance. Although tension is generated, the muscle does not sorten, and no movement occurs.

Speed of Contraction: Contractile response of a fiber to single impulse - twitch. Consists of a period of contraction, pulling force increases, followed by relaxation, pulling declines. Latent period where delay between stimulation and the beginning of contraction. MYOGRAM.

Isometric contraction speed varies in muscles Slow oxidative fibers (slow twitch) Slow myosin Produce most of their ATP by oxidative phosphorylation Small in diameter and generate less force Fast oxidative fibers High oxidative capacity Fast myosin Intermediate size and force generation Fast glycolytic fibers (fast twitch) Fast myosin High glycolytic capacity Fibers - largest and generate the most force

Types of Bones

Long Bones - bones that are longer than they are wide; femur, humerus, radius, ulna, tibia, fibula End has epiphysis (forms joint w/ another bone). Epiphysis nearest to trunk = proximal epiphysis, opposite = distal epiphysis. Outer surface of the articulating epiphysis is coated w/ hyaline → articular cart. The shaft of the bone = diaphysis. Periosteum encloses the bone, except for the articular cartilage on ends. Firmly attached, and the periosteal fibers are continuous with the connecting ligaments and tendons. Helps form and repair bone tissue. Bony projections, processes = sites where ligaments/tendons attach; grooves and openings form passageways for blood vessels and nerves; depression of one bone may articulate with a process of another. Wall of diaphysis = compact bone (cortical) - continuous extracellular matrix. Epiphysis = spongy bone (cancellous) - numerous branching bony plates, trabeculae, which reduce weight - thin layers of compact on the surface. Bony plates = highly developed in regions of epiphysis w/ compression. Compact bone in the diaphysis forms a tube with a hollow chamber - medullary cavity - continuous with spongy bone. A thin layer of cells called the endosteum lines the medullary cavity and spaces within spongy bone - specialized soft connective tissue called marrow fills them. Microscopic Structure: Osteocytes (bone cells) occupy lacunae (bony chambers) Lacunae w/in bony matrix of lamellae, which form concentric circles around central, Haversian, canals (containing blood ves., nerve fibers, surrounded by loose connective tissue, and blood nourishes bone cells) Osteocytes exchange substances with nearby cells through canaliculi Extracellular matrix of bone tissue = collagen, salts (ca + p) Entire system = osteon, and many osteons = compact bone. Central canals are longitudinal, and perforating, Volkmann's canals connect them (contain larger blood vessels and nerves by which smaller blood vessels and nerves in central canals communicate with the surface of the bone and medullary cavity). Short Bones - bones that are roughly cube shaped; wrist, tiny Flat Bones - thin, flattened and usually a bit curved; skull, ribs, clavicle, sternum, scapula Irregular Bones - complicated shapes that don't fit the other classes; vertebrae, facial bones Patella - only bone in body encased within a tendon - sesamoid

Nerve Supply - voluntary

Motor neurons - stimulate movement Synaptic cleft - interaction between nerve and muscle Neuromuscular junction - where interaction takes place Synaptic vesicles - release chemical signal between neuron and muscle cell

Microscopic Structure (muscle fiber/cell)

Multinucleated Sarcolemma - sheath enveloping cells and fibers Sarcoplasm - cytoplasm inside Sarcoplasmic reticulum Transverse tubule - run perpendicular to long axis of cells Thick filaments - myosin makes them up Thin filaments - actin, troponin, tropomyosin makes them up Hierarchy of Muscle Cellular level: Muscle fiber/Myocyte Myofibril Myofilament Sarcomere is what shortens within a muscle cell

Membrane Potentials (voltage difference across sarcolemma)

Muscle and nerve cells are the only ones that can change membrane potential (reversal) Resting membrane potential Inside of fiber-negative Outside of fiber-positive Action Potential Caused by nerve stimulation Brief reversal of charges across sarcolemma Inside of fiber becomes positive Outside of fiber becomes negative

Bone Structure

Network of osteocytes, fibers (collagen), and matrix of calcium salts Osteocytes - regulate deposition or removal of calcium from bone Fibers - flexibility Calcium salts - strength and rigidity

Neuromuscular Junction

Neurons that control effectors are called motor neurons. Stimulates muscle contract. Each skeletal fiber is functionally connected to axon of motor neuron that passes out from brain/spine. This connection is called a synapse, and neurons communicate with chemical signals, neurotransmitters. Synapse between motor neuron and muscle fiber is neuromuscular junction. Here, muscle fiber membrane is specialized to form a motor end place, where nuclei and mitochondria are abundant. Sarcolemma has indentations and is extensively folded, and end of motor neuron extends fine projections into them. Synaptic cleft separated membrane of neuron and membrane of muscle fiber. Cytoplasm at distal ends of motor neuron axons is rich in mitochondria and contains many tiny vesicles that store neurotransmitter molecules.

Origin and Insertion

One end of skeletal muscle attaches to relatively immovable or fixed part on one side of a movable joint, and other end attaches to a movable part on the other side of that joint, such that the muscle crosses the joint. Less movable end of the muscle is called its origin, and the movable end is insertion. When muscle contracts, insertion pulled to origin. Biceps brachii has 2 origins: scapula and radius Flexion and extension change angle Muscles move in groups. Agonist *prime mover* causes an action while an antagonist works against the action (relax). Synergists steady movement, and fixators stabilize origin of prime mover.

Bone Development and Growth

Ossification/osteogenesis Begins in first 2 mo. of prenatal life: Only have cartilage/connective when you first develop. At 2 months, formation of osteoid tissue. Intramembranous ossification Cells develop between sheets of connective tissue. Develop in fetus. Dense networks of blood vessels are contained within these connective tissues. Precursor cells → osteoblasts (from progenitor) Secrete matrix that form spongy bone tissue Become trapped within matrix and become osteocytes Reside in periosteum - membrane covering bone Compact bone laid down over spongy bones by cells within periosteum Flat bones of the skull, mandible, clavicles Endochondral ossification Bones from cartilage= hyaline Precursor cells → chondroblasts Cartilage → template for bone Blood vessel penetration Primary ossification center formed, then secondary ossification center distally Primary Ossification Perichondrium infiltrated with blood vessels - converted to periosteum after cells are differentiated, and encircles developing diaphysis Underlying cells specialize into osteoblasts Originates in center of diaphysis Condroblasts die → destruction of cartilage → caverns within template Spongy bone forms after blood vessels and osteoblasts from periosteum invade Osteoblasts in periosteum laying down compact bone Secondary Ossification Further penetration by blood vessels More cartilage destroyed → spongy bone replaces it Medullary cavity forms Diaphysis thickens with compact bone Epiphyseal plate formation: Cartilage of epi. plate = dividing cells. As they enlarge and extracellular matrix forms around, the plate thickens and lengthens bone. Ca+ build up, and as the bone calcifies, old cartilage dies. Bone growth and remodeling Bone resorbing cells, osteoclasts, break down calcified matrix. Multinucleated from marrow where white blood monocytes fuse. Secrete acid/lysosomal enzymes digest. After destroy, osteoblasts come. A long bone continues to lengthen while the cartilaginous cells of the epiphyseal plates are active. However once the ossification centers of diaphysis and epiphyses meet and the epiphyseal plates ossify, lengthening is no longer possible. Long bone thickens as compact bone deposited under periosteum. As it forms, osteoclasts erode other bone tissue on the inside = medullary cavity. The bone in the central regions of the epiphysis and diaphysis remains spongy and hyaline cartilage on the ends of the epiphysis persist throughout life as articular cartilage.

Homeostatic Imbalances

Osteomalacia - inadequate mineralization in adults Rickets - inadequate mineralization in children Osteoporosis - greater bone resorption than bone deposition Paget's disease - abnormal remodeling Calcium in blood is needed for muscle contraction, nerve cell function, blood clot, etc.

Gross Anatomy of a Bone

Periosteum - membrane covering bone Membrane of dense regular connective tissue Collagen fibers merge with those of tendons/ligaments attached to the bone Vascular Provides site for bone growth and repair: osteoblasts: Secrete/lay new matrix Gives bone nourishment: Blood vessels and nerves are present Transition from muscle to tendon - myotendinous junction. Diaphysis - center: Shaft of the long bone, constructed of compact bone - denser Epiphyses - towards the end of long bone, constructed with spongy bone, site of epiphyseal line (growth plate) Articular Cartilage - at the ends of bone

Muscle Functions

Producing movement Maintaining posture Stabilizing joints Generating heat - muscle contraction = body heat - shivering Functional Characteristics Excitability/irritability - being able to respond Contractibility Extensibility Elasticity

Muscle Metabolism

Provides energy for contraction Stored ATP Direct phosphorylation of ADP by creatine phosphate Anaerobic glycolysis and lactic acid formation Aerobic respiration Refer to POGIL NOTES ONLINE

Muscle Contraction (physiology)

Role of Myosin and Actin Myosin is composed of 2 twisted protein strands with heads projecting. Many of these molecules compose thick filament. Actin molecule is a globular structure with a binding site to which myosin heads can attach. Twist into helix, forming thin filament, and proteins troponin and tropomyosin are part of the thin filament. Fiber at rest Ca2+ stored in Sarcoplasmic Reticulum ATP bound to myosin filaments Thin filaments intact Stimulus Acetylcholine released in synaptic cleft from synaptic vesicles of motor neuron, which diffuses due to an impulse. This diffuses across the synaptic cleft, and binds to acetylcholine receptors in the muscle fiber membrane at the motor end plate, increasing membrane permeability to Na+. Generates action potential, and impulse passes through entire fiber. Sarcoplasmic reticulum stimulated to release Ca2+ (depolarized) and muscle cell depolarizes so reversal of membrane potential Action potential moves into Transverse tubule Contraction Cross bridge formation Action potential caused by depolarization → release of Ca2+ Ca2+ exposes myosin binding sites on actin as it binds to troponin; myosin heads bind to actin using ATP Movement (contraction/power stroke) Power stroke; filaments slide past one another - Myosin breaks down ATP to move cross bridges (heat released) (have ATPase). Then myosin is pulling actin and they slide. Cross bridge tilts due to another ATP Release 3rd ATP binds to myosin causing it to release actin and detachment of cross bridge Cross bridge reforms in new location nearer sarcomere's center Return to rest Atp is hydrolyzed and myosin heads return to resting position. If Ca2+ is returned to SR, muscle relaxes, but if available, cycle repeats and contraction continues. Acetylcholine inactivated by acetylcholinesterase Ca2+ returned to SR by ATP actively Original shape of thin filaments restored No binding sites available for myosin heads, as ATP breaks cross bridge, before decomposing. Thin filaments slide back to original position, muscle fiber relaxes As the sarcomere contracts, the Z lines decrease, and the width of the bands is decreasing. But the area where the thin and thick overlap is getting bigger.

Skeletal Muscle Fibers

Single cell that contracts responding to stimulation and then relaxes. Long, thin cylinder. Just beneath the cell membrane is sarcolemma, and sarcoplasm of fiber has many small nuclei and mitochondria, plus parallel myofibrils. Myofibrils are made up of thick filament myosin and thin actin. Create striations. Striations result from repeating sarcomeres, and myofibrils are sarcomeres joined end to end. 2 parts. I bands, thin filaments directly attaches to Z lines. A bands, thick filaments between regions where thick and thin filaments overlap. M line located down center, consisting of proteins helping hold thick filaments in place. Sarcomere is between 2 Z lines. Within sarcoplasm is a network of membranous channels surrounding each myofibril and runs parallel to it. Form sarcoplasmic reticulum. Another set of membranous channels called transverse tubules extend inward as invaginations from the fiber's membrane and passes all the way through the fiber. Thus, each one opens outside of the muscle fiber and contains extracellular fluid. Transverse tubule lies between cisternae near where thick and thin filaments overlap. Play a role in contraction after stimulation.

More on Other Muscles

Smooth Muscle Thick and thin filaments organized randomly, and SR not developed. 2 major types called multiunit and visceral. Multiunit smooth muscle, cells separate rather than sheets. Found in irises and in walls of blood vessels. Contracts responding to nerves/hormones. Visceral smooth muscle, sheets of spindle cells in close contact. Lines bladder, stomach, intestines, etc. Rhythmicity of contraction, and transmission of impulses responsible for wave peristalsis moving stuff. Contraction similar to skeletal. Include actin and myosin, triggered by membrane impulse and so on. Acetylcholine and norepinephrine stimulates and inhibits smooth muscle, and a number of hormones affect smooth muscle contraction and degree of response. Smooth muscle is slower to contract and relax, but maintains forceful contraction longer. Also can change length without tautness. Cardiac Muscle Only in heart, branched, striated, with 3D organization of filaments, amd SR with many mitochondria and system of LARGE transverse tubules. IE twitches last longer. Opposing ends of cells are called intercalated discs, which are junctions that allow impulses to pass freely and contract entire unit. Self-exciting, rhythmic contractions.

Muscle Fatigue

Strenuous for a long period may decrease ability to contract physiologically. Involve altered electrolyte levels within muscle cells, decreased ATP levels in muscle cells, etc. ATP production fails to keep up with ATP demand. No ATP available - contractures - Cramps come, possibly from extracellular fluid and motor neurons stimulating involuntary contract. Excessive lactic acid accumulation and ionic imbalances can also contribute

Function of Bones

Support - framework Protection from mechanical injury - physical barrier Movement - system of levers Mineral storage - calcium Blood cell formation - hematopoiesis - to make blood cells (in the red bone marrow)