2 Characteristics of Muscle Tissue Contractility- the ability to shorten and thickenExcitability – ability of muscle tissue to receive and respond to stimuliExtensibility – ability of the muscle to stretchElasticity – the ability of the muscle tissue to return to its original shape after contraction
3 3 Types of Muscle Tissue: Smooth – located in walls of hollow internal structures, non-striated, involuntarySkeletal – attached mostly to bone, striated, voluntaryCardiac – found in the heart, striated, involuntary
5 Skeletal Muscle Cells Muscle cell = muscle fiber Contains many nuclei and mitochondriaEach muscle fiber contains many myofibrils – threadlike protein filaments – 2 types:Myosin – thick filamentsActin – thin filamentsOrganization of these produces striations charac. of skeletal muscle tissue
6 Sarcomere Key Terms: actin (thin filaments) myosin (thick filaments) A band – dark band made up of thick filamentsM line – dark line in center of A bandI band – light band made up of thin filamentsZ line – mark boundary between sarcomeres
7 Sarcomere: the functional contractile unit of muscle
9 Sliding Filament Theory Myosin – protein strands with globular parts called cross-bridgesActin – protein strands with binding sites where myosin cross-bridges can attach; binding site protected by troponin and tropomyosinCa+ moves troponin and tropomyosin out of the way so cross bridges can bind.Cross-bridges (myosin) bind to actin and produce a powerstroke (myosin cross-bridges pull actin toward H zone)ATP releases the myosin. IT DOES NOT PRODUCE THE POWERSTROKECross-bridges release and attach to new binding site on actin, and whole process begins again; will continue as long as calcium and ATP are available
10 5 steps to muscle contraction Ca+ is released in large amountsCa+ moves troponin and tropmyosin out of way of myosin (so it can grab actin)Myosin grabs actin and pulls it in 1 stepATP causes myosin to release actinSteps 3 & 4 are repeated until;A. muscle can no longer contract any further.B. nerve impulse ends causing muscle relaxation.
11 3 Steps from nerves to muscles Nerve impulse comes from brain to activate muscleAt the end of the nerve Acetylcholine is released into gap between muscle and nerve (neuromuscular junction).Acetylcholine causes the release of Ca+
13 6 Steps of Muscle Relaxation Nerve impulse stopsAcetylcholine is no longer released at neuromuscular junctionCalcium ions are removedWithout Ca+ Troponin and tropomyosin go back to blocking myosin from grabbing actin.ATP causes linkage between myosin and actin to breakMuscle fibers relax
14 Rigor MortisWhen a person dies they release Ca+ causing their muscle to contract.This also causes the use of ATPHowever, the body is no longer producing ATP so the myosin cross bridges can not release.This causes the muscles to stay contracted and the body to feel stiff.
15 Energy Sources for Contraction ATP supplies the energy for muscle fiber contraction, which lasts only a few seconds. ATP must be regenerated continuously if the contraction is to continue.There are 3 pathways in which ATP is regenerated:1. Creatine phosphate, found in muscle fibers, stores energy that can be used to synthesize ATP from ADP and phosphate (uses no oxygen); runs out fast
16 Cont:2. Aerobic Respiration: glucose is broken down to supply ATP (oxygen is required).Yields 36 ATP3. Anaerobic Respiration – glucose is broken down not in the presence of OxygenThis yields 2 ATP.