MUSCULAR SYSTEM Mus little mouse Makes up nearly half the bodys mass Essential function: CONTRACTING & SHORTENING (unique characteristic Responsible for all body movements Machine of the body Other functions: Maintain posture, Stabilize joints & Generate heat

Muscle Types Skeletal and smooth muscle cells are elongated (muscle fibers) Myofilaments- muscle cell equivalent of microfilaments in cytoskeleton which controls the ability to shorten or contracts Mys- muscle Sarco- flesh Sarcoplasm- muscle cells of cytoplasm

1. Skeletal Muscles skeletal striated, coluntary Body Location: Attached to bones, some facial muscle & skin Cell Appearance: Single, Long. Cylindrical, Multinucleated with striations Connective Tissue components: Epimysium, Perymisium and Endomysium Regulation of contraction: Voluntary via NS controls Speed of Contraction: Slow to fast Rhythmic contraction: No Packaged in organs called Skeletal Muscles that attach the skeleton Cover our bony underpinnings Help form the much smoother contours of the body Largest of the muscle types (30 mm) Activated by reflexes (without willed command) Can contract rapidly and with great force but it tires easily and must rest soft and fragile like most cells but can exert tremendous power They dont rip apart because their fibers are bundled together by connective tissue which provides strength and support Endomysium- delicate connective tissue sheath the covers each muscle fiber Perimysium- courser fibrous membrane that wraps several muscle fibers Fascicle- Bundle of muscle fibers Epimysium- tougher overcoat that covers several fascicles/entire muscle (The epimysia can be tendon or aponeuroses) Tendons- strong cordlike that anchors muscles, provide durability and conserves space (small and pass over a joint);; tough collagenic fiber that can cross rough bony projections Aponeuroses- sheet-like that attach muscles indirectly to bones, cartilages or connective tissue coverings

2. Smooth Muscle- visceral, nonstriated, involuntary Body Location: Mostly walls of hollow visceral organs (Stomach, Bladder, Respiratory passageways Cell Appearance- Single, fusiform, uninucleated, no striations (spindle shaped) Connective Tissue Components: Endomysium Regulation of contraction: Involuntary; NS controls; hormones, chemicals, stretch Speed of contraction: Very slow Rhythmic Contraction: Yes in some Arranged in 2 layers: One running circularly and other longitudinally Sarcomeres- chain of tiny contractile units (segment of myofibrils) which are aligned end to end like boxcars in a train along length of myofibrils (Z disc to Z disc) Arrangement of even smaller structures (myofilaments) within sarcomeres that actually produces banding patters Myofilament- threadlike protein within our boxcar sarcomere Two kinds of Myofilaments:1. Thick filaments (Myosin)- made mostly of bundled myosins and contain ATPase enzymes(split ATP to generate the power for muscle contraction Extend the entire A band Midparts of it are smooth but their ends are studded with projections/myosin heads(called Cross bridges when they link thick and thin filaments together during contraction)2. Thin Filaments (Actin)- composed of contractile protein called actin plus some regulatory protein that play a role in allowing ore preventing binding of myosin heads to actin. Anchored to the Z disc I band includes parts of adjacent sarcomeres and ONLY thin filaments Do not extend into the middle of relaxed sarcomere and central region(H zone/Bare Zone) When contraction occurs, the thin filament slide toward each other into the center of sarcomere, these light zone disappear because actin and myosin overlap3. Sarcoplasmic Reticulum Muscle fiber organelles Specialized smooth ER Its tubules and sacs surround each myofibril like a crochet sweater in your arm Store calcium and to release it on demand when muscle fiber is stimulated to contract (Calcium- provides go signal for contraction)

Skeletal Muscle ActivityStimulation and Contraction of Single Skeletal Muscle Cell Special Functional Properties of muscle cells:1. Excitability Responsiveness/Irritability Ability to receive and respond to stimulus2. Contractility Ability to shorten(forcibly) when adequately stimulated Sets muscle apart from other tissues3. Extensibility Ability of muscle cells to be stretched4. Elasticity Ability to recoil and resume their resting length after being stretched

Nerve Stimulus and the Action Potential To contract skeletal muscle cells must be simulated by nerve impulses;; one motor neuron may stimulate a few muscle cells Motor unit- one neuron and the skeletal muscle cells it stimulates Neuromuscular Junction When a nerve fiber/axon(long threadlike extension of neuron) reaches the muscle it braches out into a number of Axon Terminals(each of which forms junctions with the sarcolemma of a diff muscle cell) Contain vesicles filled with Neurotransmitter

Attachment of myosin to cross bridges require Ca+2 Action Potential Pass deep into muscle cell along membranous tubules (T tubules) Stimulates the Sarcoplasmic Reticulum to release Ca2+ into the cytoplasm Ca2+ trigger the binding of the myosin and actin thus initiating the filament sliding When action potential ends, alcim is reabsorbed into SR storage areas Muscles relax and settle back to their original length The whole process take a few thousandths of a second Binding of ATP to the cross bridge- disconnects cross bridge from actin Hydrolysis of ATP- re-energizes and repositions the cross bridge

Contraction of a skeletal Muscle as a whole all or none phenomenon(muscle cell will contract to its fullest extent when its stimulated adequately; it never partially contracts) is applicable to individual muscles and NOT to the whole muscle Whole muscle reacts to stimuli with Graded Responses(different degrees of shortening) Graded Muscle Contractions can be produced in two ways:1. By changing the frequency of muscle stimulation2. Changing the number of muscle cells being stimulated

Muscle response to increasingly rapid stimulation Muscles do not operate with muscle twitches (single brief jerky contractions) In most types of muscle activity, nerve impulses are delivered to the muscle at very rapid rate (rapid that muscle does not get the chance to relax) Effects of successive contraction are summed together and the contractions get stronger and smoother Fused/Complete, Tetanus/Titanic Contraction State wherein muscle is stimulated so rapidly what no evidence of relaxation is seen and contractions are smooth and sustained;; Normal and desirable Unfused/Incomplete Tetanus More complete fusion of twitches that summing

Muscles Response to Stronger Stimuli Tetanus- produces stronger muscle contractions but its primary role is to produce smooth and prolonged muscle contractions Strength of contraction depends on how many of the cells are stimulated (few stimulated cells=weaker contraction) Strongest muscle contraction- all motor units are active and all the muscle cells are stimulated Muscle contractions can be slight or vigorous depending on what work has to be done

Providing energy for muscle contraction ATP molecules- their bonds are hydrolyzed when a muscle contracts;; only energy source of power muscle activity;;muscles store limited supplies (4-6 seconds)

Three pathway for ATP regeneration1. Direct phosphorylation of ADP by creatine phosphate Energy source: CP Oxygen use: NONE Products: 1 ATP per CP, creatine Duration of energy provision: 15 secondsTypes of Muscle Contractions Not all muscle shorten during contraction; common among them is Tension during contraction due to myofilaments1. Isotonic Contractions same tone or tension Familiar to most of us Myofilaments are successful in sliding movements, the muscle shortens and movement occurs Ex. Bending the knee, rotating the arms and smiling2. Isometric Contraction Muscles do not shorten same measurement or length Myosin filaments are spinning their wheels Tension in muscles keeps on increasing Myofilaments are trying to slide but muscle is pitted against an immovable object No movement Ex. Pushing a wall

Muscle Tone State of continuous contractions Result of different motor units stimulated in a systematic way Result: muscles remain firm, healthy and constantly ready for action

Effect of Exercise on Muscles Muscle Inactivity- due to loss of nerve supply, immobilization, etc. always leads to muscle weakness and wasting Muscles are not exceptions to use it or lose it Regular Exercise- increase muscle size, strength and endurance

Types of Exercise1. Aerobic/Endurance Aerobics class, jogging or biking Result in stronger, more flexible muscles with greater resistance to fatigue Blood supply to muscles increase, form more mitochondria and store more oxygen Makes overall metabolism more efficient Improves digestion(and elimination) Enhances neuromuscular coordination and makes skeleton stronger Hypertrophies(heart enlarges)- more blood is pumped out with each beat, fat deposits cleared from blood vessel wall and lungs before more efficient in gas exchange Does not cause the muscles to increase much in size2. Resistance/Isometric Bulging muscles of a body builder Pit the muscles against some immovable object Require very little time and little or no special equipment (push against the wall, standing) The key is forcing the muscles to contract with as much force as possible Increased muscle size and strength are due mainly to enlargement of individual muscle cells Amount of connective tissue also increases

Muscle. Movement and NamesFive Golden Rule of Skeletal Muscle Activity1. With a few exceptions, all skeletal muscles cross at least one point

4. Opposition In the palm of the hand, the saddle joint bet metacarpal 1 and carpals allows opposition of the thumb You move your thumb to touch the tips of other fingers on the same hand Makes the hand useful for grasping and manipulating things

Interactions of Muscles in the body Muscles can pull as the contract (cant push) Movements are the result of two or more muscles working together or against each other They arranges in such way that whatever one muscle can do, other muscles can reverse Prime Mover Has the major responsibility for causing a particular movement Antagonist Muscle that opposes or reverses a movement Can be a prime mover depending on movement Relaxed and stretched when prime mover is active Synergists Help Prime Movers by producing the same movement or by reducing undesirable movements Stabilizes joints moved by prime mover (kapag nagcontract kasi yung prime mover, maraming joints yung nagagalaw. Nasstabilize ng synergist yung movement ng joints na hindi naman talaga kailangan gumalaw) Fixator (specialized synergist) Hold a bone still or stabilize the origin of a prime mover so all the tension can be used to move the insertion bone Ex. Postural muscles of the vertebral column, muscles hat anchor the scapula to the thorax

Naming Skeletal Muscles1. Direction of muscle fibers Named in reference to some imaginary line (usually the midline if the body or the long axis of the bone) Rectus = straight (parallel the imaginary line) (ex. Rectus Femoris- straight muscle of femur) Oblique = Slant2. Relative size of the Muscle Maximus = largest Minimus = smallest Longus = long Ex. Gluteus Maximus largest muscle of gluteus3. Location of the muscle Named for the bone which they are associated Ex. Temporalis Muscles- temporal bones4. Number of Origins Bi, Tri, Quad Ex. Biceps, Triceps, Quadriceps5. Location of the muscles origin and insertion Named for their attachment sites Ex. Sternocleidomastoid- origin at sternum and clavicle and inserts on mastoid6. Shape of the muscle Deltoid = Triangular7. Action of the Muscle Flexor, extensor, adductor

Two layers alternately contract and relax, they change the shape and size of organs Housekeeping Activities: Moving food through digestive tract and emptying bowels and bladder Slow and sustained like steady heavy duty engine that lumbers tirelessly

Cardiac Muscle cardiac, striated, involuntary Body Location: Walls of heart Cell Appearance: Branching chains of cells, uninucleated, striations, intercalated discs Connective Tissue components: Endomysium attaches to the fibrous skeleton of heart Regulation of contraction: Involuntary, heart as pacemaker, NS controls, hormones Speed of contraction: Slow Rhythmic Contraction: Yes Endomysium- soft connective tissue that cushions cardiac fibers Arranged in spiral/figure 8-shaped bundles Contract smaller chambers, forcing blood out through arteries Intercalated discs- gap junction Circulates blood and maintain blood pressure

****The term muscular system ONLY applies to the skeletal muscles

Muscle Function Producing Movement Skeletal muscles are responsible for mobility of the body as a whole (locomotion and manipulation) Enable us to respond quickly to environment Allow us to express emotions through smiles and frowns Maintaining Posture and Body Position Function almost continuously. Making one tiny adjustment after another so that we maintain as erect or seated posture despite the never ending downward pull or gravity Stabilizing Joints Muscle tendons- important in reinforcing and stabilizing joints that have poorly fitting articulating surfaces (shoulder joint) Generating Heat Generated by product of muscle activity ATP- used to power muscle contraction \ and nearly 3-quarters escape as heat Skeletal Muscles 40% of body mass so its most responsible for generating heat Additional Functions Protect fragile internal organs by enclosure Smooth muscle forms valves to regulate the passage of substances through internal body openings, dilate and constrict the pupils of our eyes Activate arrector pili in skin

Microscopic Anatomy of Skeletal Muscle Sarcolemma(muscle husk)- cell membrane of muscle cells Myofibrils- pushes aside the nuclei and nearly fill cytoplasm Has alternating Light(I) bands and Dark(A) bands which gives stripped appearance Z disc- darker are with midline interruption in L band (actin is attached) H zone- lighter central area in A band M-line- center of H zone which contains protein rods that hold adjacent thick filaments together Acetylcholine/Ach- specific neurotransmitter of skeletal muscle;; diffuses across the synaptic cleft and attaches to receptors (membrane proteins) of the sarcolemma;; if enough Ach is released, Depolarization happens Synaptic Cleft- gap between nerve endings and muscle cells membrane(sarcolemma) which is filled with tissue(interstilial) fluid Muscle Depolarization- when the sarcolemma becomes temporarily more permeable to sodium ions which rush into the muscle cell and to potassium ions which diffuse out of the cell;; generates an electrical current called Action Potential

Events of neuromuscular junction Action potential reaches axon terminal of motor neuron Calcium(Ca2+) channels open and Ca2+ enters the axon terminal Ca2+ entry causes some synaptic vessels in the axon terminal to release their content (Ach) by exocytosis ACh diffuses across the synaptic cleft and binds receptors (membrane proteins) in sarcolemma (ACh receptor) ACh binds and channels open that allow passage of Na+ into and K+ out of the muscle fiber(More if enough Ach is released the sarcolemma becomes temporarily). More Na+ ions enter then K+ ions leave. Imbalance gives cell interior an excess of + ions which reverses the electrical conditions of the sarcolemma (Depolarization/Upset), which opens more channels that allow Na+ entry only and eventually leads to an action potential Action Potential- unstoppable;; it travels over the entire surface of the sarcolemma, conducting the electrical impulse from one end of the cell to another (results to muscle contraction) Ach effects are ended by its breakdown (Acetic Acid and Choline) in the synaptic cleft by the enzyme acetylcholinesterase (AchE). This produces one contraction only and prevent continued contractions. Muscle cell relaxes until the next round of Ach release

Events that return the cell to its resting state (Muscle Repolarization)sasrcolemma restores its permeability Diffusion of K+ ions out of the cell and the Operation of the sodium-potassium pump (active transport mechanism)

Mechanism of Muscle ContractionThe Sliding Filament Theory When muscle fibers are activated by NS, myosin heads attach to the binding sites of thin filaments and sliding begins Creates cross bridge which attaches and detaches (caused by power stroke) several times during a contraction, generating tension that helps to pull the thin filaments towards the center of the sarcomere While other myosin heads are moving, some myosin heads are always in contact with actin so that the thin filaments cannot slide back This walking of myosin cross bridges/heads during muscle shortening is like a centipedes gait. Some myosin heads(legs) are always in contact with actin (ground) so that thin filaments cannot slide backward in the cycle Myofilaments does not shorten, they simply side past one another

Also called Hydrolysis of Creatine Phosphate Creatine Phosphate- high energy molecule found in muscle fibers only and are easily exhausted Interaction between CP and ADP result in transfers of a high-energy phosphate group from CP to ADP thus regenerating more ATP in a fraction of a second

2. Aerobic Respiration Energy source: Glucose; Pyruvic Acid; Free fatty acids from adipose tissue; amino acids from protein catabolism Oxygen Use: Required Products: 32 ATP per glucose, Co2, H2O Duration of Energy provision: Hours Occurs in mitochondria 95% ATP used in muscle activity Oxidative Phosphorylation- series of metabolic pathways that use oxygen Slow and requires supply of oxygen and nutrient fuels

3. Anaerobic Glycolysis & Lactic Acid formation Energy source: Glucose Oxygen Use: NONE Products: 2 ATP per glucose, lactic acid Duration of energy provision: 30-40 seconds or slightly more Glycolysis- pathway of glucose breakdown;; anaerobic Occurs in cytosol Glucose is broken down to Pyruvic Acid and produces 2 ATPs Aerobic Pathway (with oxygen) Occurs in mitochondria Produce more ATP When muscle activity is intense or oxygen and glucose delivery is temporarily inadequate, Pyruvic acid is converted to Lactic Acid and goes through Anaerobic Glycolysis Anaerobic Glycolysis Produces only about 5% as much ATP from each molecule as aerobic respiration 2.5 times faster the aerobic Disadvantages: uses huge amounts of glucose for a small ATP harvest and accumulating lactic acid promotes muscle fatigue and muscle soreness (muscle cramps)

Muscle Fatigue When we exercise our muscles strenuously for a long time Unable to contract even though it is still being stimulated Without rest, it begins to tire and contracts more weakly until it ceases reacting and stops contracting Believed to be a result of Oxygen Deficit True Muscle fatigue: muscle quits entirely;; rarely occurs bec before this happens, we feel tires and stop working;; happens in marathon runners

Oxygen Deficit Person is not able to take in oxygen fast enough Depends on how good blood supply is When muscles lack oxygen: Lactic acid accumulates via anaerobic mechanism, muscles ATP supply starts to run low and ionic imbalance occurs Oxygen supply must be paid back whether fatigue occurs or not (rapid and deep breathing after to get rid of accumulated lactic acid2. Typically, the bulk of a skeletal muscle lies proximal to the joint crossed3. All skeletal muscles have at least 2 attachments (Origin and Insertion)4. Skeletal Muscles can only pull they can never push5. During contraction, a skeletal muscle insertion moves toward the origin

Points of Attachment:1. Origin attachment to the immovable of less movable bone2. Insertion attachment to the movable bone when muscle contracts, insertion moves toward origin* Some muscles have interchangeable origins and insertions.e.g. rectus femoris muscle* Body movement occurs when muscles contract across joints

Types of Body Movements1. Flexion On sagittal plane Decreases the angle of the joint and brings two bones together Typical of hinge joints(bending knee or elbow) Also common in ball and socket joints (bending forward at hip)2. Extension Movement the increases the angle between 2 bones Straightening the knee or elbow Hyperextension- if greater than 180 degrees3. Rotation Movement of a bone around longitudinal axis Ball and socket joints Describes movement of atlas around the dens of axis (shaking head no)4. Abduction Moving a limb away from midline Fanning movement of fingers or toe when they are spread5. Adduction Movement of limb away from body6. Circumduction Combination of flexion, extension, abduction and adduction Commonly seen in ball and socket joints like shoulder The proximal end of the limb is stationary and distal end moves in circles The limb as a whole outlines a cone

Special Movements1. Dorsiflexion and Plantar flexion Dorsiflexion- standing on heels (superior surface approaches the shin) (corresponds to extension of hand and wrist) Plantar flexion- pointing on toes (depressing the foot) (corresponds to flexion of hand)2. Inversion and Eversion Inversion- turn sole medially Eversion- turn sole laterally3. Supination and Pronation Refer to movement of the radius and ulna Supination- turning backward forearm rotates laterally that the palm faces anteriorly and the radius and ulna parallel Pronation- turning forward forearm rotates medially so that the palm faces posteriorly and brings radius across the ulna forming an x

Arrangement of Fascicles