Human Anatomy and Physiology I
Human Anatomy and Physiology I BIOL 2010
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This 12 page Class Notes was uploaded by Floy Quitzon III on Wednesday September 23, 2015. The Class Notes belongs to BIOL 2010 at Middle Tennessee State University taught by Teresa Stegall-Faulk in Fall. Since its upload, it has received 16 views. For similar materials see /class/213210/biol-2010-middle-tennessee-state-university in Biology at Middle Tennessee State University.
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Date Created: 09/23/15
Biology 2010 rev Fall 11 1 Skeletal Muscle Chapters 10 Muscle Histology Three types of muscle 1 Skeletal muscle is striated and voluntary voluntary control by the somatic nervous system a body movements and posture b respiration assists in the control of elimination c body heat generation d glycogen storage 2 Cardiac muscle is striated and involuntary autonomic nervous system or ANS 3 Smooth muscle is not striated and involuntary ANS component of organs and blood vessels For all types of muscle to function properly amp efficiently they must possess the following 4 properties gt Contractility gt Excitability V Extensibility V Elasticity Gross Skeletal Muscle Structure and Function 1 Whole muscle structure a fascia dense connective tissue surrounding a muscle group b epimysium a fibrous sheath that surrounds the entire muscle c perimysium surrounds each fascicle d endomysium loose connective tissue that surrounds the muscle fibers within each fascicle Biology 2010 rev Fall 11 2 2 Muscle attachments to bone the connective tissue fibers of the perimysium epimysium and fascia are continuous with the connective tissue that attach muscles to bones a tendons b aponeurosis c retinaculum d origin and insertion sites Skeletal Muscle Histology 1 Skeletal muscle cell aka muscle fiber histology parallel fibers no branching a sarcolemma i transversetubulesT tubules b sarcoplasm cytoplasm ofa muscle cell i multinucleate amp many mitochondria ii lots of stored glycogen n sarcoplasmic reticulum specialized SER stores lots of Ca Biology 2010 rev Fall 11 3 d myofibrils contained within the sarcoplasm and lie parallel along the long axis of the muscle fiber i each myofibril is organized into 2 10000 repeating contractile units called sarcomeres the smallest contractile units of muscle fibers 1 sarcomere structure a Z disks b I bands c A bands i H zone ii M line d zone of overlap e Sliding Filament Theory 2 structural components of one sarcomere a thick filaments composed of myosin i myosin head 1 ATPase ii myosin tail Biology 2010 rev Fall 11 b thin filaments composed of actin Actin is composed of 4 proteins i F actin filaments composed of individual G actin proteins ii tropomyosin iii troponin 3 protein subunits 1 one attached to F actin 2 one attached to tropomyosin 3 one will bind to Ca 3 Accessory proteins found in sarcomeres a titin b dystrophin and linking proteins e triads composed of 2 terminal cisternae one transverse tubule T tubule Biology 2010 rev Fall 11 5 Control of Skeletal Muscle Fiber Activity Chapter 11 Contraction of skeletal muscles is controlled by the somatic division of the nervous system The somatic division innervates all skeletal muscles and is under voluntary control Motor Units 1 Components ofa one Motor Unit a One somatic motor neuron innervates several muscle fibers b One muscle is composed of several motor units 2 Components of neuromuscular junctions NMJ a synaptic knob ofa Somatic motor neuron also called the presynaptic membrane i neurotransmitter acetylcholine ACh is released from synaptic knob b synaptic cleft space between the presynaptic and postsynaptic membranes c motor end plate of sarcolemma also called the post synaptic membrane i ligand gated Na channels open when ACh binds to a receptor allowing an influx of Na at the motor end plate ii acetylcholinesterase ActionPotentialsandquot 39 39 39 Coupling Excitation is dependent upon the transmission of electrical signals called action potentials which travel along the axons of nerve cells to change the resting membrane potentials of muscle cells The change in resting membrane potentials elicits action potentials along the sarcolemma ofthe muscle cells leading to Contraction the mechanical interaction ofthe contractile proteins 1 Plasma membranes are polarized a Resting Membrane Potential RMP electrical charge difference between the ECF and ICF when the cell is quotat rest The RMP of skeletal muscle cell membranes is 90 mV Biology 2010 rev Fall 11 6 b Mechanisms by which the cell maintains RMP 2 How is an action potential propagated on the sarcolemma g 30 El 0 E E g 0 o quotD E E 40 Threshold Potential i a E 70 Resting Membrane Potential 90 RMP Tim e In sec a stimulation of the muscle fiber at the motor end plate produces a local potential to occur only at the motor end plate area ofthe sarcolemma i STEP 1 from RMP to threshold potential TP a ACh binds to and opens ligandgated Na channels on the motor end plate i Na influx causes a local potential at the motor end plate ii STEP 2 if TP about 40 mV is reached by stimulation at motor end plate voltage changes cause opening of voltagegated Na channels in the adjacent sarcolemma to produce an Action Potential 1 positions of voltage gated Na channel gates a activation gates b inactivation gates 2 at TP the Na channel activation gates open and allow a rapid influx of Na causing depolarization to about 30 mV Biology 2010 rev Fall 11 7 iii STEP 3 at 30 mV repolarization begins 1 voltage gated Na channel inactivation gates close activation gates remain open 2 voltage gated K channels open only 1 gate iv STEP 4 when repolarization returns to TP 40mV 1 voltage gated Na channels return to resting state activation gates closed inactivation gates open 2 K voltage gated channels begin closing and cause a brief period of hyperpolarization to about 95 mV 3 return to RMP both voltage gated Na and K channels are closed resting state v The All or None Response 2 Refractory periods a absolute refractory period the period of time between TP of depolarization to TP of repolarization i a stimulus of any strength absolutely cannot produce another AP b relative refractory period from threshold of repolarization to return to RMP i ifa stimulus is larger than normal it might produce another AP Biology 2010 rev Fall 11 8 ExcitationContraction Coupling When the electrical excitation the action potential propagation along the sarcolemma as outlined in the previous section reaches the t tubules of the triads the voltage change triggers the opening of Ca channels of the terminal cisternae and Ca is released into the sarcoplasm that surrounds the contractile proteins of the sarcomeres Calcium release initiates the shortening of the sarcomeres or 9h Zsical con traction Contraction 1 Excitation causes propagation of the AP throughout the sarcolemma through the T tubules a The release of Ca from the terminal cisternae into the sarcoplasm leads to contraction i Ca binds to troponin subunit ii Cross bridge formation 2 Pivoting of the activated myosin heads the POWER STROKE a Activated myosin head attached ADPPi releases stored energy and pivots toward the M line releases ADP Pi 3 Cross bridge detachment a new ATP binds to myosin head ATPADP Pi by ATPase causes the bond to break between the myosin head and the active site on F actin strand 4 Myosin reactivation a free myosin head with ADP Pi moves back to resting position RECOVERYSTROKE Biology 2010 rev Fall 11 9 5 Relaxation a SR actively transports Ca back into the terminal cisternae b as Ca levels in the sarcoplasm decline Ca detaches from troponin subunit tropomyosin returns to its original position covering the active sites 393 Q contractile proteins passively return to relaxed state ALL SARCOMERES WITHIN A MUSCLE FIBER CONTRACT amp RELAX IN UNISON Muscle Twitch a single cycle of contraction and relaxation of a muscle fiber produced by a single stimulus 3 phases 1 Latent phase produces internal tension 2 Contraction phase produces external tension 3 Relaxation phase Sarcomere length 8 lengthtension relationships The amount of tension and the force of contraction produced by a muscle depends on the amount of overlap present between actin and myosin at the time the electrical stimulus is received Biology 2010 rev Fall 11 10 Contraction Strength varies with stimulus intensity voltage and stimulus frequency how rapidly the stimulus is applied 1 Changes in intensity of voltage a Recruitment multiple motor unit summation 2 Changes in frequency that the voltage stimulus is applied a treppe b incomplete tetanus temporal or wave summation c complete tetanus Tension Production in order to apply enough tension force to lift or move a load several muscle twitches are needed The extracellular fibers of muscle cells endo peri epimysium and tendons are the structures that actually exert the force produced by muscle fibers on the load These fibers are also somewhat elastic so a single muscle twitch is not enough to transfer the tension to these structures Whole Muscle Activity When a single muscle fiber is stimulated to contract all of the sarcomeres in that fiber will contract and the fiber will always produce the same amount of tension When a whole muscle contracts it must be able to vary the strength of the contraction This graded response determines the strength or weakness of the contraction The amount oftension produced is determined by 1 the strength of the stimulus 2 thefrequency of stimulation amp 3 the number of muscle fibers stimulated Maintenance of muscle tone in posture depends upon motor units contracting out of phase with one another Types of Muscle Contractions 1 isometric muscle length does not change tension increases during contraction 2 isotonic tension is constant during contraction muscle length changes Biology 2010 rev Fall 11 11 Muscle Metabolism and Energetics ATP is the ultimate source of energy and comes from 3 sources 1 Immediate energy before the respiratory and cardiovascular systems can supply enough oxygen Muscle cells can convert ADP into ATP by borrowing high energy phosphates Pi from other molecules This is the phosphagen system a creatine phosphate 1 ADP creatine phosphate 9 creatine ATP Catalyzed by creatine phosphokinase b myokinase catalyzes 2 ADP 9 AMP ATP 2 Short term energy anaerobic respiration occurs when the phosphagen system is depleted i Glycolysis produces 2 ATP pyruvic acid which is converted to lactic acid 3 Long term energy aerobic respiration a One molecule of glucose produces 36 ATP water and C02 4 Muscle fatigue weakness and lack of contractility a duration of long term energy depends on glucose and glycogen stores oxygen supply and fluid and electrolyte depletion Biology 2010 rev Fall 11 5 12 Muscle Recovery a Repaying the Oxygen Debt b Restoring the phosphagen system c Oxidizing lactic acid Types of muscle fibers a slow oxidative fibers b fast glycolytic fibers
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