EXAM 4 STUDY GUIDEChapter 10 – Muscle Tissue & Skeletal Muscle- Muscle Facts- 40-50% of body weight is muscle- muscle gain is 2 times faster than muscle loss- smallest muscles are in ear, holding it (& ear drum) together- largest muscle: gluteus maximus, keeps us upright- strongest muscles: glutes, massester, tongue- muscles can only pull, no pushing it contracts, shortens- born with all muscle fibres you will ever have- skeletal muscle contractions are voluntary, except when cold somatic- skeletal = voluntary- heart muscle never gets tired, ~3billion beats in lifetime- Somatic Motor Neuron- Includes both sensory (to CNS) and motor neuron (to skeletal muscle)- Neurons that stimulate skeletal muscle fibers  Produce both reflexive and voluntary movements- ACh- Only one pathway- Effect of motor neuron is always excitation- Communication between motor neuron and a muscle fiber occurs at synapse- If motor neurons cease to stimulate a muscle = paralyzed, limp muscle that has nomuscle tone- Types of Muscles- Skeletal muscle tissue Striated Multinucleated Voluntary- Because it can be made to contract or relax by conscious control- Cardiac Striated  Uninucleated Involuntary Heart wall, pumps blood to all parts of body Natural pacemaker that initiates each contraction- authorhythmicity- Smooth Nonstriated Uninucleated Involuntary Located in the walls of hollow internal structures- Blood vessels, airways, and most organs in abdominopelvic cavity Function: motion- Muscle Function1. Produce body movements2. Stabilizing body positions3. Storing and moving substances within the bodya. Sphincters (smooth muscle) help prevent the outflow of the contents of a hollow organ; ex: temporary storage of food in the stomach or urine in the urinary bladderb. Cardiac muscle contractions of the heart pump blood through blood vessels of the bodyc. Smooth muscle contractions also move food and substancesi. Bile and enzymes through the GI tract, push gametes (sperm and oocytes) through the passageways of the reproductive system, and propel urine through the urinary system4. Generating heata. Thermogenesis = producing heatb. Heat used to maintain normal body temperaturec. Involuntary contractions of skeletal muscles = shivering = can increase rate of heat production- Properties of Muscular tissueo Electrical excitability Ability to respond to certain stimuli by producing electrical signals (actionpotential = impulses) Two stimuli triggers:- Electrical stimuli  autorhythmic = hearts pacemaker- Chemical stimuli  neurotransmitter released by neurons, hormones distributed by the blood, and local pH changeso Contractility Ability of muscular tissue to contract forcefully when stimulated by an action potential- Produce force by attempting to change shape- Shortening vs lengthening o Extensibility Ability of muscular tissue to stretch, within limits, without being damaged Smooth muscle has greatest amount of stretchingo Elasticity Ability of muscular tissue to return to its original length and shape after contraction or extension- Skeletal Muscle Hierarchy Skeletal muscle (muscle belly)  fascicles- Tendon and bone- Fascicleso Bundles of muscle fiber wrapped in perimysium Fascicles  muscle fibre (cell)- Capillaries and nerves Within muscle fibre  myofibrils- Contain sarcomere, thick and thin filaments Sarcolemma = plasma membrane of muscle cell Sarcoplasm = the cytoplasm of a muscle fiber Sarcomereo Basic functional units of a myofibril o Made up by z-disc o Actin attaches to sarcomereo M line is anchor for myosin Muscle Proteinso Contractile Proteins Myosin Actino Regulatory Proteinso Structural Proteins Thick Filamento Myosin is the main component  Functions as a motor protein in all 3 types of muscle tissue Binds to actino Thick filament apart of A band A band = overlapo Myosin molecule consist of a tail and two myosin headso Tails meet at M line Thin Filamento Anchored to Z discso Actin is main component each molecule is a myosin-binding site = where a myosin head can attach- binds to myosino Thin filament apart of I band I band = no overlapo consist of regulatory proteins troponin: protein that moves tropomyosin away from actin so it can bind to myosin- has bind site for Ca2+ ions tropomyosin: when skeletal muscle is relaxed, it covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin Contraction Cycle (driven by ATP)o ATP hydrolysis = myosin reoriented  Myosin heads hydrolize ATP and become reoriented and energizedo Attachment of myosin to actin to form cross-bridges Myosin binds to actino Power stroke Myosin cross-bridges rotate toward center of sarcomereo Detachment of myosin from actin = relaxation  As myosin heads bind to ATP, cross-bridges detach from actin Sliding Filamento Actin and myosin sliding past each other o Thin filaments move toward the M line of each sarcomere Rigor Mortiso Muscles locked in contraction o Begins 3-4 hours after death Lasts about 24 hourso Ca2+ ions leak out of the SR into the sarcoplasm and allow myosin heads to bind to actin ATP synthesis ceases shortly after breathing stops- Cross-bridges cannot detach from actin Neuromuscular Junction (NMJ)o the synapse between a somatic neuron and a skeletal muscle fibero muscle action potential arise hereo voltage gated channels open ACh (neurotransmitter) is released and goes across the synaptic cleft (small gap) Ach binds to Ach receptor on the motor end plate (muscle fiber part of NMJ)- Receptor opens channel- Targets are ligand-gated channels  opens and Na+ goes into muscle (excitatory period) Flow of Na+ in makes inside more positively charged = triggers actionpotential- Causes sarcoplasmic reticulum to release its stored Ca2+ into the sarcoplasm = muscle fiber contraction ACh lasts briefly bc it is broken down rapidly by acetylcholinesterase (AChE)- Breaks into acetyl and choline, products cannot activate the ACh receptoro Synaptic end bulbs: the neural part of the NMJ AP Transmissiono Motor neuron innervates surface fibers May innervate lots of muscle fiberso Firing in unison allows AP to get deeper into fibre Transverse Tubuleso Tiny invaginations of the sarcolemma Tunnel in from the surface toward the center of the fibero Allow AP to travel and excite all parts of the muscle fiber at the same time