Exercise Physiology Exam 2 Summer 2013 This one covers all of the muscles and all the endocrine Muscle Chapter 18 354 360 363 375 lab and lecture notes 1 Describe the three different types of human muscle fibers and their characteristics The three fiber types are type 1 2a and 2x They are also called Slow twitch type 1 and fast twitch type 2a and 2x and this refers to the speed of contraction of the fiber o When looked at in vitro the muscle was stimulated isometrically and this enabled the time to peak tension to be recorded Fast twitch fibers took 12 15 mmsec to reach peak tension and slow twitch took 50 70 mmsec So this shows that the difference is not big at all Type 1 fibers are considered the slow twitch fibers and rely on oxidative enzymes to supply energy They are rich in mitochondria and thus take a while to fatigue They are rich in capillaries and myoglobin which make sense to supply them with all the oxygen they need for oxidative metabolism These muscles are small compared to its fast twitch counterparts Type 2a is an intermediate of type 1 and type 2x It is a fast twitch fiber yet has some oxidative properties so it has a high amount of mitochondria Unlike type 1 it is larger less capillary density and less myoglobin This fiber is also called the fast oxidative fiber on Type 2x is the other end of the spectrum than type 1 It is very fast and very fatigable Relies mainly on glycogen and CP those immediate energy sources Its muscles are large have low capillaries myoglobin and mitochondria This is also called the fast glycolytic fiber Because of its glycolytic reliance it has a highly developed sacroplasmic reticulum 2 How are muscle fibers changed with training Fiber type doesn t change directly with training but fast twitch fibers can act like slow twitch and vice versa This occurs with training as muscles are highly adaptable so they will create more proteins and enzymes as needed 3 What is the role of calcium in muscle contraction Explain the sliding filament theory and how I m just combining question 3 4 and 5 since they are related Actually everything you need to muscles are fueled know about the muscle is in this question With muscles everything is in layers for example the outside covering of the muscle is called the epimysium Then the perimysium surrounds a group of muscle fibers which are packaged into bundles called fasicles and the endomysium surrounds an individual fiber Now that we got down to the fiber we look further at it and it contains repeating units called myofibrils The saromere is another name for the myofibril and it is the smallest contractile unit of the fiber and it repeats many times along the muscle and this gives origin to the striated patterns Looking at an individual sarcomere you will see proteins called the myofilaments These are the actin thin band and myosin thick band that you will hear so much about The sarcomere is separated into different segments depending on the presence of different myofilaments The I band meaning isotropic contains just actin and the A band meaning anisotropic contains both actin and myosin Now in the middle of the A band is the H zone which is just myosin Then further dissecting the H zone is the M line which is just proteins to keep the actin and myosin in the correct spatial arrangement during contraction Then the Z disks separate each sarcomere since the fiber is composed of hundreds to millions When a muscle contracts the individual myofibril or sarcomeres all work in unison to provide the necessary force and this is accomplished via the myosin and actin The myosin will pull the actin bands towards each other in a process known as excitation contraction coupling When this occurs the I band which was just actin will shorten as it slides together from the contraction The H zone which just composed of just myosin will disappear as it is covered from the overlap of the I Bands The A band will stay the same length throughtout the contraction process Now for the sliding filament theory Now to learn how the muscles actually contract So right now imagine two rows of sarcomeres just sitting at rest so there is no contracting going on and the muscle is not generating force The sliding filament theory is the theory of how a muscle contraction occurs Actin which is also called the thin filament is a globular protein The globes of actin wrap around each other to form a coil shape Each individual globe has a myosin binding site for the myosin head to attach to for the contraction but this is covered by a regulatory protein called trypomyosin Tm So the Tm wraps around the globe covering all of the myosin binding sites So how does myosin bind during contraction On every 7th globe there is another regulatory protein called troponin that is positioned on top of the Tm When Ca2 is present and binds to troponin it will literally pull the Tm out of the way exposing the binding sites for the myosin head And that is all you need to know about actin 6 How does nerve stimulation lead to contraction What is the role of calcium in this process The process of contraction starts with an action potential from a nerve and this propagates and depolarizes the sacroplasmic reticulum stores Ca 2 The action potential AP will travel down the neuron to the neuromuscular junction synapse to the muscle The AP causes the release of Acetylcholine to the neuromuscular junction which will then diffuse to the motor end plate causing chemical gated sodium channels to open thus creating an AP on the muscle Once this is done the AP will travel down a structure called the t tubule and it will spread the AP to the terminal cisterea which lie on each side of the t tubule The purpose of all this is to get the AP to the center of the muscle thus it travels down the t tubule The terminal cisterea will release Ca2 into the muscle and this binds on troponin on the actin Once it binds to troponin tropomyosin is signaled to move from the actin so the myosin head can bind Once attached the head pulls the filaments together This is called excitation contraction coupling The Z disks on the sarcomere are literally pulled closer together they contract and thus the I band will decrease size in length since being pulled together The H zone will disappear as it is covered via the sliding action Contraction will occur as long as the intramuscular concentration of calcium remains high as this is removing the typomyosin When the stimuli is over Ca2 is pumped back into
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