muscular system.pdf

separates it from MUSCLES surrounding tissues MUSCLE TISSUE Connected to the deep ★ a primary tissue responsible for fascia contraction...

separates it from MUSCLES surrounding tissues MUSCLE TISSUE Connected to the deep ★ a primary tissue responsible for fascia contraction and movement surrounds individual fascicles (muscle fiber TYPES OF MUSCLE TISSUE bundles) move the body by pulling PERIMYSIUM SKELETAL MUSCLE Contains collagen fibers, on bones pumps blood through the elastic fibers, blood CARDIAC MUSCLE vessels and nerves cardiovascular system pushes fluids and solids surrounds individual SMOOTH MUSCLE through internal muscle cells (muscle passageways and organs fibers) and loosely interconnects them ENDOMYSIUM COMMON PROPERTIES Contains capillary networks, nerve fibers, 1. Excitability- responsiveness, ability to and myosatellite cells receive and respond to stimuli (stem cells) that repair 2. Contractility - ability of cells to shorten damage 3. Extensibility - ability of the muscle to stretch - The collagen fibers of the epimysium, 4. Elasticity - ability of the muscle to recoil perimysium, and endomysium come to its resting length together at ends of muscles to form - Tendons (bundles) - Aponeuroses (broad sheets) FUNCTIONS which - attach skeletal muscles to bones 1. Producing movement – pull on tendons to move bones 2. Maintaining posture and body position 3. Supporting soft tissues 4. Guarding body entrances and exits – such as those of the urinary and digestive tract 5. Maintaining body temperature – working muscle produce and release heat 6. Storing nutrients – source of proteins/amino acids SKELETAL MUSCLES SKELETAL MUSCLES ★ muscles of the body that are attached to bones ★ Contain: ○ Skeletal muscle tissue ○ Connective tissues Skeletal muscles have extensive ○ Blood vessels networks of blood vessels that ○ Nerves ○ Deliver oxygen and nutrients ○ Remove metabolic wastes Skeletal muscles contract only when 3 Layers of Connective Tissue stimulated by the central nervous system (CNS) layer of collagen fibers ○ Branches of neuronal axons EPIMYSIUM that surrounds the entire muscle and innervate (supply) individual muscle fibers  ○ Often called voluntary muscles ★ Quickly transmit electrical impulses ○ Some, like the diaphragm, work (action potentials) from the sarcolemma subconsciously into the cell interior to ensure a Skeletal muscle fibers (cells) are large, coordinated contraction of the entire cell multinucleate cells ○ Develop by fusion of embryonic Action potential cells called myoblasts ★ Propagated (spread) change in the ○ Also known as striated muscle membrane potential of an excitable cell cells due to the presence of ★ Initiated by a change in membrane visible striations permeability to sodium Due to the arrangement ★ Ex. muscle cell neuron of myofibrils (organized collections of contractile myofilaments) SARCOPLASMIC RETICULUM (SR) ★ a tubular network similar to the smooth endoplasmic reticulum ★ Surrounds each myofibril ★ Forms chambers (terminal cisternae) that attach to T tubules ★ 2 terminal cisternae + T tubule = triad ★ Specialized for the storage and release of calcium ions ○ Calcium ions are actively transported from the cytosol into the terminal cisternae SARCOLEMMA ★ the plasma membrane of a muscle fiber ★ Surrounds the sarcoplasm (cytoplasm of a muscle fiber) ★ Has a resting membrane potential ★ A change in the membrane potential initiates a contraction Membrane potential ★ mV (millivolts) ★ Electrical potential difference across MYOFIBRILS plasma membrane when cell is in a non-excited state ★ organized collections of myofilaments ★ Difference across a cell membrane that that are responsible for muscle results from an uneven distribution of of contraction positive and negative ions across the ★ Run along the entire length of the muscle membrane fiber MYOFILAMENTS TRANSVERSE TUBULES ★ bundles of contractile protein filaments ★ 2 TYPES: ★ T tubules ○ Thin filaments ★ narrow tubes continuous with the actin sarcolemma, which extend from the ○ Thick filaments surface of the muscle fiber deep into the Myosin sarcoplasm ★ Filled with extracellular fluid  SARCOMERES ★ repeating structural and functional units of a myofibril ★ Thin and thick filaments are organized in a specific way ★ Interactions between the filaments produce contraction ★ smallest contractile units of the muscle fiber ★ Each sarcomere contains: ○ Thin filaments ○ Thick filaments ○ Proteins that stabilize the position of the thin and thick filaments ○ Proteins that regulate the interactions between the thin and thick filaments A BANDS - dark bands / thick filaments vertical line in center of A band; contains proteins M LINE that stabilize the position of the thick filaments made only of thick H BAND filaments and extends on either side of the M line region where the thick and ZONE OF OVERLAP thin filaments overlap I BANDS - light bands / thin filaments bisect the I bands and mark the boundaries Z LINES between adjacent sarcomeres elastic protein which extends from the tips of thick filaments to the Z line TITIN Keeps filaments in proper alignment Aids in restoring resting sarcomere length - Extend from A band of one sarcomere to the A band of the next  THIN FILAMENTS Projects toward the F-actin nearest thin filament - Polymerized G-actin - Each thick filament has a core of titin that stretches from the M line to the Z twisted strand composed line of two rows of globular - Acts as a molecular spring to FILAMENTOUS G-actin molecules recoil and return the sarcomere ACTIN to its resting length G-actin - Monomeric form of actin Active sites - On G-actin bind to myosin holds the F-actin strands together NEBULIN gitna ng F-actin covers the active sites on SLIDING-FILAMENT THEORY G-actin and prevents TROPOMYOSIN actin–myosin interaction ★ During a contraction, the thin filaments slide toward the center of the sarcomere parang border (M line) alongside the thick filaments a globular protein that ○ H band and I bands narrow holds tropomyosin in ○ Zones of overlap widen place and binds to ○ Z lines move closer together calcium ions ○ The width of the A band remains constant TROPONIN parang tape In the presence of calcium ions, troponin moves tropomyosin off the actin active sites THICK FILAMENTS binds to other myosin molecules TAIL Tails point towards the M line made of two globular HEAD protein subunits  ★ the synapse between a motor neuron and a skeletal muscle fiber Synapse ★ Site of transmission ★ Where it takes place - Skeletal muscle will only contract if they are stimulated by motor neurons Motor neuron a. Both ends → center ★ What commands us to the change / b. Free end → fixed end move EXCITABLE MEMBRANES PARTS OF NMJ Synaptic cleft ★ Carriers of electrical signals ★ All cells maintain a negative resting AXON TERMINAL expanded end of the membrane potential axons of the motor ★ The resting membrane potential of neuron skeletal muscle cells is -85 mV (millivolts) the folded membrane of ★ Stimuli can change the local distribution MOTOR END PLATE the skeletal muscle fiber of ions across the plasma membrane and at the N M J therefore change the membrane narrow space between potential SYNAPTIC CLEFT the axon terminal and the motor end plate a chemical released DEPOLARIZATION from the axon ★ the membrane potential becomes less terminal into the negative due to influx (inflow) of sodium synaptic cleft Na ions Released when an NEUROTRANSMITTER HYPERPOLARIZATION action potential arrives ★ the membrane potential becomes more at the axon terminal negative due to outflow of potassium K ions The neurotransmitter at the NMJ is REPOLARIZATION acetylcholine (ACh) ★ return to the resting membrane potential after depolarization - ACh binds to and opens a chemically gated Na+ channel (ACh receptor - Neurons and muscle cells have membrane channel) on the motor end electrically excitable membranes and plate of the muscle fiber can produce electrical impulses called - Na+ enters cell and depolarizes action potentials that can propagate the motor end plate along the plasma membrane - An action potential is generated Electrical impulses ★ Generated when a stimulus causes rapid change in electrical charge NEUROMUSCULAR JUNCTION ★ NMJ ★ Synaptic connection between neuron and muscle cells  CONTRACTION CYCLE ★ series of molecular events that enable muscle contraction ★ Involves the formation of: ○ CROSS-BRIDGES the myosin heads bind to the active sites on actin ○ POWER STROKE the myosin head uses energy from A T P to pivot and pull on active towards the M line EXCITATION-CONTRACTION COUPLING - MYOSIN HEAD in resting phase is already energized ★ Sequence of events that converts action potentials in a muscle fiber to a contraction ★ the link between the generation of an action potential in the sarcolemma and the start of muscle contraction ★ The action potential travels down T tubules to triads ★ It then triggers the release of calcium ions from the S R ★ Calcium ions bind to troponin on thin filaments ★ Troponin changes position and moves tropomyosin off the active sites on actin 2. Calcium is binded w/ troponin para mamove ★ Contraction can begin si tropomyosin for the active site to be free  - The speed of shortening depends on the cycling rate (number of power strokes per second) RELAXATION The duration of a contraction depends on: ○ The period of stimulation at the N MJ ○ Presence of free calcium ions in the cytosol ○ Availability of A T P When the stimulus to contract ends: ○ ACh is broken down by Acetylcholinesterase (A C h E) ○ Calcium ions return to the S R via active transport. As a result: Calcium ions detach from troponin RESTING SARCOMERE Troponin returns to its original position The active sites on actin are covered by tropomyosin again RIGOR MORTIS ★ rigor - rigid ★ muscle stiffens after death resulting from a muscles being locked in a contracted position ★ ATP runs out: ○ ion pumps for active transport cease (come to an end) to CONTRACTING SARCOMERE function and calcium ions remain The entire cycle is repeated several times each second, as in the cytosol triggering a long as Ca2+ concentrations remain elevated and ATP sustained contraction reserves are sufficient. ○ cross-bridges cannot detach, so Calcium ion levels will remain elevated only as long as action the myosin heads remain potentials continue to pass along the T tubules and stimulate the terminal cisternae. attached to actin Once that stimulus is removed, the calcium channels in the SR close and calcium ion pumps pull Ca2+ from the cytosol and store it within the terminal cisternae. Troponin molecules then shift position, swinging the tropomyosin strands over the active sites and preventing further cross-bridge formation. Generation of muscle tension - When muscle cells contract, they produce tension (pull) - To produce movement, the tension must overcome the load (resistance) - At any given time, some myosin heads are undergoing a power stroke and some are being reactivated - The entire muscle shortens at the same rate - Because all sarcomeres contract together  TENSION Muscles in the body do not get stimulated just once, so twitches are Being stretched tight generated by electrical stimulation in a pull force generated by the muscle when laboratory it contracts Muscular contractions require many The amount of tension produced by an repeated stimuli individual muscle fiber depends on the: ○ Number of power strokes MYOGRAM performed ★ a graph showing tension development in ○ The resting length of the muscle muscle fibers fiber at time of stimulation (length-tension relationship) ○ The frequency (how often) of stimulation LENGTH-TENSION RELATIONSHIP ★ tension produced by a muscle fiber relates to the length of the sarcomeres ○ Tension by muscle fiber = length A myogram showing differences intension over time for a of sarcomeres twitch in the fibers from different ★ The number of power strokes performed skeletal muscles by cross-bridges depends on the amount of overlap between thick and thin filaments (zone of overlap) PHASES OF A TWITCH ○ No. of power strokes = amount the time it takes from the of overlap stimulation to moves ★ Maximum tension is produced when the LATENT PERIOD across the sarcolemma maximum number of cross-bridges is and for the S R to release formed at the optimal length of the calcium ions sarcomere, because more myosin heads tension increases as the can attach to actin muscle fiber is forming ★ If there is no zone of overlap, no tension CONTRACTION cross-bridges and the can be produced PHASE myosin heads do power ★ If the sarcomere is too short and cannot strokes shorten more, no tension can be tension decreases as produced even though the zone of cytosolic calcium overlap is large ion levels decrease, RELAXATION myosin-binding sites on PHASE actin are covered by tropomyosin, and cross-bridges detach The details of tension over time for a single twitch in a fiber of the gastrocnemius muscle. Notice the presence of a latent TWITCH period. It corresponds to the time need for the propagation of an action potential and the subsequent release of calcium ions by the sarcoplasmic reticulum a single stimulus-contraction-relaxation sequence Lasts 7–100 msec  TREPPE ○ INCOMPLETE TETANUS the muscle produces an increase in peak tension caused by near-maximum tension repeated stimulations which happen due to rapid cycles of after the end of each relaxation phase contraction and very brief Stimulus frequency 50/second continuous contraction Instead of allowing muscle to relax fully due to high stimulation between contractions, next stimulus frequency which arrives before muscle has completely eliminates the relaxation relaxes phase nerve sends signals so - Isang vibration would last 0.015 if 100 rapidly that the muscle vps doesn't have any time to relax between contractions. This leads to a smooth and steady contraction without any breaks. TETANUS Maximum tension - muscle stays contracted and doesn't relax because the nerve that controls it Disease sends signals very quickly. ○ Caused by the neurotoxin of the - Normally, muscles contract and relax in bacterium Clostridium tetani a rhythm, but if the signals come too ○ Results in sustained, powerful fast, the muscle can't keep up and stays muscle contractions and death in tense. 40-60% of cases  MUSCLE CONTRACTIONS ○ occurs until sufficient force is developed within the muscle to - The tension production by the entire move a load. skeletal muscle depends on the number ○ A maximum contraction is of stimulated muscle fibers generated when all the motor units are activated within a MOTOR UNIT muscle. ★ collective term ★ a motor neuron + all the muscle fibers it Tetanus controls ★ Fusion of contractions to produce a ★ May contain a few muscle fibers or continuous contraction thousands ★ All fibers in a motor unit contract at the same time ★ Smaller motor units allow for finer control of movement FASCICULATION ★ involuntary “muscle twitch” which is caused by the synchronous contraction of one motor unit The tension applied to the tendon remains fairly constant, even though individual motor units cycle between contraction and relaxation MUSCLE TONE ★ the resting tension of a skeletal muscle ★ Without causing movement, motor units actively: ○ Stabilize the positions of bones and joints ○ Maintain balance and posture RECRUITMENT ★ Elevated muscle tone increases resting energy consumption - increase in muscle tension due to the increase of active motor units - Aggressively involving more motor 2 TYPES OF MUSCLE CONTRACTIONS neurons to achieve smooth steady ISOTONIC cause the skeletal muscle tension (small muscles → large) CONTRACTIONS to change length - Produces smooth, steady increase in Muscle tension exceeds tension Isotonic Concentric the load (resistance) and - Maximum tension is achieved when all Contraction the muscle shortens motor units reach complete tetanus - Can be sustained for a very short time The speed of shortening depends on the size of the SUSTAINED CONTRACTIONS load ★ Produce less than maximum tension Isotonic Eccentric Peak muscle tension is less ★ Motor unit summation Contraction than the load and the ○ “relay” approach in which some muscle elongates due to motor units are contracting, and gravity or the contraction some are resting and recovering of another muscle ○ Successive stimuli are added together to produce a stronger muscle contraction the skeletal muscle ○ the recruitment of additional develops tension, but does motor units within a muscle to ISOMETRIC not change length develop more force. CONTRACTIONS The tension produced  never exceeds the load - A normal blood oxygen level - A normal blood p H - Interference with any of these factors reduces the efficiency of muscle contraction and cause premature fatigue ATP ★ Adenosine triphosphate ★ only energy source used directly for When stimulated, the tension rises, but the muscle length muscle contraction stays the same. ★ Contracting muscles use a lot of A T P ★ Muscles store A T P, but available stores Load INVERSELY RELATED to speed of are depleted within 4-6 seconds in contraction active muscles ○ The heavier the load, the slower ★ More A T P must be generated to sustain the contraction a contraction ○ The heavier the load, the longer it takes for the muscle to shorten AT REST and for movement to begin - skeletal muscle fibers produce more A T ○ For each muscle, an optimal P than needed combination of tension and speed exists for any given load ATP + creatine → ADP + creatine phosphate - A T P transfers energy (in the form of a phosphate) to creatine to create creatine phosphate (C P) Creatine ★ Chemical used to supply energy to muscles ★ Waste product that comes from digestion of proteins in food and the Muscle relaxation and the return to normal breakdown of of muscle tissue resting length ○ Return to resting length is a ADP + creatine phosphate → ATP + creatine passive process due to: - The energy in CP is then used to convert Elastic forces ADP back to ATP during a contraction tendons recoil and - Catalyzed by the enzyme creatine help return muscle kinase (C K) fibers to resting length - Energy store as C P is enough for about Opposing muscle 15 seconds of sustained contraction contractions can return a muscle to resting ATP is generated by: length quickly anaerobic (no oxygen Gravity needed) metabolism that assists opposing breaks down glucose to muscles in pyruvate in the cytosol returning muscles to their resting 2 ATP + 2 pyruvates / length glucose GLYCOLYSIS Glucose used in glycolysis come primarily ENERGY TO POWER CONTRACTIONS from glycogen stored in skeletal muscles - Normal muscle function requires: - Substantial intracellular (ATP) Important because: energy reserves Provides the substrates - A normal circulatory supply for aerobic catabolism in  the mitochondria Serves as a source of A T P production when oxygen supplies become low oxygen dependent process in which mitochondria use organic substrates (such as pyruvate) to produce A TP Primary A T P source of resting muscles Includes the citric acid AEROBIC cycle and electron METABOLISM transport chain 15 A T P molecules / pyruvate Resting muscles breaks down fatty acids from the circulation as an energy source Active muscles break down pyruvate from glycolysis Muscle metabolism and varying levels of activity RECOVERY PERIOD AT REST ○ Energy requirements are low and ★ the time required for muscles to return to oxygen availability is high pre-exertion conditions ○ Muscles metabolize (change digested food into energy) fatty CORI CYCLE acids and store glycogen and C ★ Lactate removal and recycling P ★ During exertion, lactate is transferred AT MODERATE ACTIVITY from muscles to the liver ○ A T P demand increases, oxygen ★ The liver converts lactate to pyruvate is still available ★ 70-80% of the pyruvate molecules are ○ Muscles generate A T P primarily then converted to glucose which returns through aerobic breakdown of to the muscle to help rebuild its glycogen glucose reserves AT PEAK ACTIVITY ○ Demand for A T P is very high OXYGEN DEBT and oxygen supply can not keep ★ Excess postexercise oxygen consumption up with the demand ★ EPOC ○ Muscle generate about ⅓ of A T ★ the amount of oxygen required to restore P via aerobic metabolism normal pre exertion conditions ○ The rest of the A T P comes from ★ After exercise or other exertion, the body glycolysis needs more oxygen than usual ○ Pyruvate that does not enter ★ Breathing rate and depth are increased mitochondria is converted to ★ Better fitness reduces the E P O C lactic acid duration ○ Hydrogen ions and lactic acid buildup resulting from anaerobic Heat production and loss metabolism can cause muscle ○ Active skeletal muscles produce fatigue heat ○ Muscles release up to 85% of the Lactic acid heat needed to maintain normal ★ produced when cells break down body temperature carbohydrates for energy ○ If they generate too much heat ★ LACTIC ACIDOSIS - hydrogen ions + as in peak activity, body lactic acid  temperature climb and heat loss at the skin accelerates RED MUSCLES ★ muscles dominated Hormones and muscle metabolism by slow fibers ○ Growth hormone and Are mid-sized testosterone stimulate protein INTERMEDIATE Little myoglobin synthesis and skeletal muscle FIBERS Slower to fatigue than enlargement fast fibers ○ Thyroid hormones elevate the rate of energy consumption in resting and active muscles ○ Epinephrine stimulates muscle metabolism, increases both the duration of stimulation and the force of contraction MUSCLE PERFORMANCE - Most human muscles contain a mixture FORCE of fiber types ★ the maximum amount of tension produced by a particular muscle MUSCLE HYPERTROPHY ENDURANCE ★ muscle growth from heavy training ★ the amount of time an activity can be ★ Increase in the diameter of muscle sustained fibers, the number of myofibrils, the number of mitochondria and the Force and endurance depend on: glycogen reserves - The type of muscle fibers ★ The number of muscle fibers does not - Physical conditioning change significantly, but they grow in size TYPES OF SKELETAL MUSCLE FIBERS MUSCLE ATROPHY Majority of skeletal muscle ★ reduction of muscle size, tone, and fibers power due to lack of activity ★ If moderate is reversible Contract quickly ★ If severe and muscle fibers die, they are Large diameter and not replaced many myofibrils Large glycogen reserves Few mitochondria FAST FIBERS CHANGES IN MUSCLE TISSUE AS WE AGE: Produce strong - Skeletal muscle fibers become smaller in contractions (high force), diameter but fatigue quickly (low - Skeletal muscles become less elastic endurance) - FIBROSIS – increase in fibrous connective tissue WHITE MUSCLES - Tolerance for exercise decreases ★ muscles dominated - Ability to recover from muscular injuries by fast fibers decreases Slower to contract - Number of satellite (stem) cells Small diameter decreases Numerous mitochondria High oxygen supply from MUSCLE FATIGUE extensive capillary ★ when muscles can no longer perform at a SLOW FIBERS network required level Contain myoglobin – red ★ CORRELATED W: pigment that binds oxygen ○ Depletion of metabolic reserves ○ Damage to the sarcolemma and Less force, but more sarcoplasmic reticulum endurance  ○ Decline in p H, which affects Removes carbon dioxide calcium ion binding and alters ○ RESPIRATORY SYSTEM enzyme activities Responds to the oxygen ○ Weariness due to low blood p H demand of muscles and pain ○ INTEGUMENTARY SYSTEM Disperses heat from Physical conditioning improves power and muscle activity endurance: ○ NERVOUS AND ENDOCRINE ANAEROBIC ENDURANCE SYSTEM ○ length of time muscle contraction Direct responses of all can be supported by stored A T P, systems C P and A T P produced by glycolysis ○ Conditioning improves muscle LEVERS power ○ Endurance is limited by: A T P and - Almost all skeletal muscles attach to C P available, glycogen available bones and the ability to tolerate lactate - Site of connection to a bone affects buildup and p H decrease force, speed, and range of movement ○ Fatigue onset is usually within 2 min of maximal activity LEVER ○ Involves fast fibers and ★ rigid structure that moves on a fixed stimulates hypertrophy point called FULCRUM (F) ○ Improved by frequent, brief, ★ moves when muscles provide a pressure intensive workouts called applied force (A F) to overcome a AEROBIC ENDURANCE load (L) ○ length of time muscle contraction ★ LEVERS - bones can be supported by A T P ★ FULCRUMS - joint produced by mitochondria ★ APPLIED FORCE -muscles ○ Does not stimulate muscle hypertrophy Levers can change the: ○ Requires blood supply to deliver - Direction of the A F nutrients and oxygen - Distance and speed produced by the A F ○ Training involves sustained, low - Effective strength of the A F levels of activity ○ Conditioning allows for prolonged activity 3 CLASSES OF LEVER the fulcrum lies between the applied force CROSS-TRAINING and the load ★ physical training using a combination of FIRST CLASS aerobic and anaerobic exercises LEVER Like a pry bar or crowbar Ex. extension of the neck and lifting the head EFFECTS OF TRAINING the load lies between the applied force and the Improvements in aerobic endurance fulcrum result from: ○ Alterations in the characteristics SECOND CLASS Like a wheelbarrow of muscle fibers – increase in the LEVER Small force can be used proportion of slow fibers to move a large weight ○ Improvements in cardiovascular Ex. ankle extension performance – better blood flow (plantar flexion) by calf and increased number of muscles capillaries the applied force is The muscular system is supported by between the load and other systems THIRD CLASS the fulcrum ○ CARDIOVASCULAR SYSTEM LEVER Delivers oxygen and Like a pair of tongs nutrients Most common lever in  the body Maximizes the speed and distance traveled at the expense of effective force Ex. elbow flexion by the biceps brachii FOR BETTER UNDERSTANDING: https://youtu.be/iezOKl3Uawc?si=6uNRvyYJPiU sKoHH