week9.pdf EXSC 223 001
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This 0 page Class Notes was uploaded by Chase Heffron on Sunday November 1, 2015. The Class Notes belongs to EXSC 223 001 at University of South Carolina taught by Thompson in Summer 2015. Since its upload, it has received 19 views. For similar materials see Anatomy and Physiology 1 in Physical Education at University of South Carolina.
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Date Created: 11/01/15
Week 9 Sarcomere is the part of muscle that changes length Sliding lament theory describes how this works thin laments slide over the thick laments The thick lament stays stationary Cross bridge cycling seen in week 8 notes A muscle cannot relax unless ATP is present Tropomyosin39s job is to cover up the myosin binding site on the actin There are 3 troponin molecules for every tropomyosin troponin I C and T that help uncover tropomyosin When a muscle contraction is triggered calcium is required Calcium binds to troponin C and changes the shape When troponin C changes its shape Troponin land troponin T change their shape The changing shape of the troponins pulls back the tropomyosin to uncover the myosin binding site on the actin With the site exposed a cross bridge will form Skeletal muscle does not contract on its own normally If it does that is called a cramp The central nervous system sends a neuron that forms a relationship with each muscle ber Neuron does not physically touch the skeletal muscle but it forms a relationship with it The button is the head on the neuron closest to each muscle ber Within the button of the neuron there are vesicles that store ACH Acetylcholine There are also calcium voltage dated channel on the button Across the synapse at the end of the button is the svnaptic cleft On the synaptic cleft there are ACH receptors On the membrane outside of the synaptic cleft there are sodium Na voltage gated channels Associated with the sodium voltage gated channels there are channels called potassium voltage dated channels Also on the membrane is the sodium potassium pump The outside of the cell is positive and the inside is negative The normal resting potential a cell is 90 millivolts In the button ACH docks onto the cell membrane of the neuron and is released as neurotransmitters into the synaptic cleft The goal is for the ACH to bind to the ACH receptor When the ACH receptor protein changes shape it allows sodium to move into the cell This starts to increase the membrane potential As sodium enters potassium leaves but more sodium enters than potassium leaves so the resting potential gets more positive Action potential a number of ACH receptors must be opened up for the cell to reach threshold 55 millivolt charge The sodium Voltage gated channels open at 55 When this happens there is a large in ux of sodium in the cell This is called depolarization When the membrane potential reaches 30 the sodium channels close At this point voltage gated potassium channels open which allows for potassium to leave the cell This is called repolarization Eventually the membrane potential drops below normal membrane potential this is called hyperpolarization After all this there is too much sodium in the cell and not enough potassium so the sodium potassium pump brings potassium back in the cell and takes sodium out Propagation When one action potential occurs this stimulates action potentials at all the other sodium pumps The positive charge inside the initial patch of sarcolemma changes the permeability of an adjacent patch thus opening Na voltage gating channels all throughout the sarcolemma and ttubules This is how calcium is released from SR When there are action potentials in the Ttubules they trigger the release of calcium in the SR A neuromuscularjunction is the button the sarcolemma and between them is the synaptic cleft Found on the button are calcium voltage gated channels They are also found on the sarcoplasmic reticulum bordering the cisternae The sarcolemma across the synapse contains Ach receptors Sodium voltage gated channels line the sarcolemma and ttubules There are also potassium gated channels that line up and down the sarcolemma and ttubules as well Sodium potassium pumps also line the sarcolemma Skeletal muscle sits and waits for a signal to do something It does not normally contract on its own Most of the time muscle contracts when a neuron tells it to When you activate a neuron you generate action potentials in a neuron There are action potentials that move down the length of the axon This is caused by a propagation of the opening of sodium channels Once the signal reaches the button the calcium channels open up and allow for calcium to move into the button This causes the vesicles containing ach to bind to cell membrane and release the ach neurotransmitters across the synapse Ach binds to the ach receptors This allows for the movement of sodium into the cell and potassium out of the cell Once the cell reaches threshold charge of 55 millivolts the sodium gated channels are triggered they open and allow sodium to cross the membrane At every sodium channel you have a depolarization This depolarization causes the membrane potential in a region of the muscle cell to rise That39s what triggers the next depolarization This is again called propagation These reactions propagate down into the Ttubule This rise in membrane potential then triggers the opening of other channels such as the calcium gated channels in the SR This allows for calcium to leave the SR and enter the cytosol This calcium that is released binds to troponin C which pushes the tropomyosin out of the binding site and allows for the myosin to bind to the actin and allows for cross bridge cycling How do we stop a muscle contraction We stop releasing neurotransmitters The ach can be taken back up into the button This is called reuptake The drug Prozac prevents this There an enzyme called Acetylcholinesterase that breaks down the neurotransmitter To stop muscular contraction Calcium must be pumped out of cell There is a pump that pumps calcium out cytosol into the SR This pump requires ATP so it takes energy for this to occur The Twitch a muscle twitch is when you give a muscle a single stimulus causing a contraction Twitches take a lot longer to occur 120 milliseconds about There are 3 phases the latent period period between stimulus and when tension occurs The period of contraction is when tension occurs Calcium is being released into the cell and many cross bridges are formed The relaxation period is when calcium is pumped out of the cell and the muscle relaxes