A&P1 CH10
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45 terms
Terms | Definitions |
|---|---|
 Three types of muscles | -skeletal -cardiac -smooth |
| Skeletal Muscle | -voluntary [conscious control] -striated [linear look, highly organized - under microscope] -attached to and cover bony surfaces -compared to the other types: contracts rapidly and forcefully, tire easily |
| Cardiac Muscle | -involuntary [no conscious control, controlled by autonomic system] -striated -compared to the other types: contracts at a steady rate but can go faster if necessary |
| Smooth Muscle | -involuntary -non-striated [not banded, smooth appearance] -in walls of hollow organs and vessels -compared to the other types: slow but sustained contractions |
| Functions of the Skeletal Muscle | -movement -maintain body posture -support soft tissue [ex: abdomen muscles support intestines, etc.] -guard openings [ex: mouth, urinary track, etc.] -maintain body temp [generate body heat that contributes to maintaining body heat... body muscles contract to burn off ATP and produce heat] |
| Anatomy of Skeletal Muscles: Muscle | Muscle: organ consisting of hundreds of muscle cells, connective tissue, blood vessels and nerve fibers Connective tissue associated with the muscle:-each muscle cell [fiber] is surrounded by a delicate layer of connective tissue called the endomysium -bundles of muscle fibers form fascicle, each fascicle is surrounded by perimysium -bundles of fascicles with nerve fibers and vessels form the muscle, the muslce is covered by the epimysium Tendons are formed when the collagen fibers of the endomysium and permysium become interwoven |
| Muscle Fiber Anatomy | -muscle fibers can be very large and very thin but long [some same length as structure] -muscle fibers are mulitnucleated -each fiber is a syncytium formed by the fusing of myoblasts |
| Muscle Fiber Anatomy: Cell Membrane | -is called the sarcolemma -small opening on the sarcolemma lead to transverse tubules [T-tubules]: small "pipes" leading from one cell side to the other, and act as rapid communication for the cell T-tubes: serve as rapid telegraph systems to conduct nerve stimuli deep into the muscle fiber |
| Muscle Fiber Anatomy: Cytoplasm | -is called the sarcoplasm: contains lots of glycogen [storage of glucose/energy - composed of polysaccharides] and myoglobin [red pigment, holds onto oxygen] -glucose and oxygen together = reproduction of ATP |
| Muscle Fiber Anatomy: Myofibrils | contractile element of the muscle fiber, bundles of myofilaments [the organelle of contraction - organelle inside cell that causes it to contract] |
| Muscle Fiber Anatomy: Sarcoplasmic reticulum | -form tubules that surround and run parallel to myofibrils -regulate intercellular levels of calcium ions -smooth ER: storage reservoir for calcium ions |
| Muscle Fiber Anatomy: Triad | -complex formed by the terminal cisternae of two sarcoplasmic reticulum and a T-tubule |
| Myofibril Anatomy | -the contractile element -are composed of linear arrangements of sarcomeres: repeating units containing protein arrangements [actin and myosin filaments] -striations of skeletal muscle tissue is evident to the repeating nature of the sarcomeres and the arrangement of the myofiliments |
| Sarcomere Anatomy | -one component of a myofibril -smallest functional unit of the muscle fiber, the contractile unit of the cell [composed of protein fibers] Contains: -"A" band: dark band, area with hick and thin filaments -"I" band: light band, area with thin filaments only -"H" zone: region within the A band where only thick filaments are present -"M" line: bisects A band, protein fibers secure the position of the thick filaments -"Z" line: boundaries of the sarcomere, point of attachment for thin filaments |
| Thick Filaments [Myofilaments] | -Myosin filaments [A band]: each myosin subunit consists of a tail and head -consists of 500 myosin molecules bundled together -made up of many protein subunits -each myosin molecule has myosin head [crossbridge can move, pivot, always located at the end] and rod-like tail [stationary, always located in the middle] |
| Thin Filaments [Myofilaments]: F actin | -actin filaments -twisted strands made up of hundreds of G actin molecules, each with active myosin binding site |
| Thin Filaments: Tropomyosin | -covers the active site on actin and prevents actin-myosin interaction |
| Thin Filaments: Troponin | -consists of 3 subunits, one binds to tropomyosin, one binds to G actin and one has a binding site for calcium [stabilizes and regulates position of tropomyosin relative to G actin molecular] |
| Neuromuscular Junction [NM] | intercellular junction between muscle fiber and motor neuron [neuron that controls a muscle cell] |
| Neuromuscular Junction: Synaptic Terminal | end of the nerve fiber |
| Neuromuscular Junction: Synaptic Cleft | narrow space between synaptic terminal and sarcolemma [between neuron and muscle fiber] |
| Neuromuscular Junction: Motor End Plate | surface of sarcolemma at neuromuscular junction, has receptors for chemical signals from neuron [region of sarcolemma associated with the synaptic terminal] |
| Action Potential | -sudden change in the membrane potential -result of movement of ions across the membrane, usually caused by the movement of Na+ into the cell -once initiated, AP spreads across the entire cell -depolarization or stimulation |
| Muscle Contraction Physiology | sliding filament theory: interaction of myosin and actin results in sliding of actin filaments over myosin filaments towards the M line |
| Muscle Contraction Steps | -Action potential arrives at synaptic terminal, causes change in TMP of nerve fiber a. Release of acetylcholine [Ach] from synaptic terminal b. Ach moves across the synaptic cleft and binds to receptors on the motor end plate c. Ach binding causes a change in sarcolemma permeability to sodium, influx of sodium causes an AP in the sarcolemma d. AP propagated across the sarcolemma and down the T-tubules e. Initial state a NMJ restored as acetylcholinestearase [AChe] removes Ach from receptors f. Excretion-contraction coupling: AO moves to triad causing sarcoplasmic reticulum [SR] to release calcium g. Calcium binds to troponin, troponin-tropomyocin comples changes shape exposing binding sites on actin h. Cross bridges [myosin heads] bind to actin i. Power stroke: stored energy in the cross bridge allows it to pivot towards the M line, pulling the actin filament towards the M line j. ATP binds the cross bridge causing it to release the actin and pivot away from the M line |
| Muscle Contraction Physiology | -as long as the calcium concentration is high and ATP supply is ample, the process will continue -relaxation: SR reabsorbs calcium, troponin releases calcium, actin-binding sites covered -lengthening of sarcomere requires external forces [gravity and opposing muscles] |
| Muscle Tension | -tension is the stress on a material produced by pull of force -in muscles, tension is equal to the number of cross-bridge attachments -a muscle fiber will produce the same tension at any given resulting length due to the al-or-none response of the stimulation of the muscle fiber -the stimulation is the arrival of an action potential at the sarcolemma -once the calcium is released from the SR, it cannot be captured quickly enough to prevent contraction -all triads within the fiber are affected by each AP -when considering the contraction at the level of the muscle, there is variation in the force and duration of a contraction |
| Tension produced at the organ level depends on: | -Variation in the frequency of stimulation [AP] -Variation in the number of muscle fibers stimulated |
| Variation in the number of muscle fibers stimulated | -motor unit: a motor neuron and all muscle fibers it innervates -when a motor neuron depolarizes to AP all muscle fibers of the motor unit will contract [all are effected at the same time] -motor unit size varies [few to hundreds] - between different muscles in the body which has differed motor units [ex: hand] -recruitment [increasing muscle tension by increasing the number of motor units stimulated] |
| Frequency of Stimulation | Twitch: single stimulus-contraction-relaxation cycle in a muscle fiber Myogram: graph on muscle tension over time during a twitch Myogram of a twitch |
| Myogram of a twitch can be divided into: | a. Lag [Latent] period: time when AP moves across the sarcolemma and calcium is released, no tension because the contraction has not begun b. Contractile phase: tension rises to a peak, cross-bridges are reacting with the actin c. Relaxation phase: cross-bridge detach, calcium levels are falling and muscle tension decreases |
| Frequency of Stimulation | -to accomplish anything, contraction must be sustained for longer than a twitch |
| Frequency of Stimulation: Wave Summation | second stimulus arrives before the fiber has relaxed, results in increased tension |
| Frequency of Stimulation: Tetany | -continuous muscle contraction -Incomplete: slight relaxation occurs between stimuli [peak muscle contraction with rapid cycles of contraction and relaxation] -Complete: relaxation phase is completely eliminated |
| Frequency of Stimulation: Treppe | stimuli of same strength produce increased tension |
| Muscle Metabolism | muscle contractions require many ATP -2500 used per second by each thick filament -a singe muscle fiber can contain 15 billion thick filaments |
| Muscle Energy in 3 forms | -ATP -Creatine phosphate [holds on to a phosphate molecule and passes it to ADP with turns it into ATP] -Glycogen [cells can burn the glucose from the glycogen to make ATP] |
| Relative storage amounts | -ATP stores are enough for about 6 seconds of contraction, ATP must be continuously regenerated by: interaction of ADP and CP -CP reserves provide enough energy for about 15 seconds of contraction -glycogen provides the fuel for ATP synthesis vis cellular respiration -ATP generation via aerobic respiration provides 95% of ATP demands of a resting muscle, requires oxygen, yield 36 ATP per molecule of glucose, more molecules of triglycerides -ATP generation vis anaerobic respiration is essentially glycolysis producing 2 molecules of pyruvate and a net yield of 2 ATP, pyruvate is converted to lactate in low oxygen conditions |
| Energy used by muscles at: | -in resting muscles: ATP produced from the breakdown of acids via cellular respiration [aerobic respiration], excess converted to CP -at low to moderate levels of activity: ATP is produced via anaerobic respiration, increase ATP demand -at peak levels of activity: 2/3 of ATP is produced via anaerobic respiration |
| Muscle Fatigue | occurs when muscles cannot contract despite continued stimulation, due to either exhaustion of energy reserves or build up of lactic acid |
| Recovery Period | -when conditions in the muscle fiber are returning to normal [homeostasis levels], primarily by oxygen reserves -oxygen deficit -aerobic respiration by liver to make ATP to convert lactate to pyruvate -aerobic respiration by muscles to restore ATP, CP and glycogen reserves -replenish normal oxygen concentration in blood and other tissues |
| Types of muscle fibers | -Fast fibers -Slow fibers -Intermediate fibers -percentage of fast v. slow fibers are genetically determined -proportion of intermediate fibers change with physical conditioning |
| Fast Fibers | -most common in the body -larger diameter and larger glycogen reserve -fatigue rapidly because of low numbers of mitochondria -produce fast, powerful contractions |
| Slow Fibers | -half the diameter of fast fibers -slow contractions [take about 3 times longer to contract] -specialized for aerobic respiration: many mitochondria large amounts of myoglobin extensive blood supply sometimes called red fibers [dark color] -capable of extended contraction |
| Intermediate Fibers | -sometimes considered a special type of fast fiber -fatigue faster than slow but slower than fast fibers -histologically similar to fast fibers -greater resistance to fatigue |
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