79 terms

AP 9 Muscular System Part 3 - Muscle Movement

chapter 9 Muscular system part 3 - muscle movements
Excitation-Contraction Coupling
Mechanism where an action potential causes muscle fiber cotraction; Involves: Sarcolemma, Transverse (T): invaginations of sarcolemma, Terminal cisternae, Sarcoplasmic reticulum:smooth ER, Triad: Ttubule, 2 adjacent terminal cisternae, Ca2+, Troponin
Actions Potentials & Muscle Contractions
4 steps
1st Step in Muscle Contraction
action potential produced at neuromuscular junction is propaged along the sarcolemma of skel. muscle. Depolarization spreads along membrane of T tubules into interior of muscle fiber
2nd Step in Muscle Contraction
depolarization of the T tubule causes gated Ca2+ channesl in the sarcoplasmic reticulum to open, resulting in increase in permeability of sarcoplasmic reticulum to Ca2+, especially in termina cisternae. Calcium ions then diffuse from sarcoplasmic reticulum into sarcoplasm surrounding myofibrils
3rd Step in Mucle Contraction
Calcium ions released from sarcoplasimic reticulum bind to troponin molecules of actin. Troponin molecules bound to G actin molecules are released, causing tropomyosin to move, and to expose active sites on G actin
4th Step in Muscle Contraction
Once active sites on G actin molecules are exposed, heads of myosin myofilaments bind to them to form cross-bridges. Movement of cross-bridges result in contraction
Cross Bridge Movement
1) Exposure of active sites, 2) Cross-bridge formation, 3) Power stroke, 4) cross-bridge releases, 5) Hydrolysis of ATP, 6) Recovery stroke, then back to #2 - how actin moves across myosin and contracts
Exposure to Active Sites
Before cross-bridges cycle. Ca2+ bind to troponins and the tropomyosins move, exposing active sites on actin myfilaments
Cross-Bridge Formation
the myosin heads bind to the exposed active site on the actin myofilaments to form cross-bridges and phosphates are released from mysoin heads
Power Stroke
energy stored in myosin heads is used to move the myosin heads (green arrow), causing the actin myofilaments to slide past the myosin myofilaments (purple arrow), and ADP molecules are released from myosin heads (black arrow)
Cross-Bridge Releases
an ATP molecule binds to each of the mysoin heads, causing them to detach from actin
Hydrolysis of ATP
the myosin ATPase portion of myosin heads split ATP into ADP and phosphate (P), which remain attached to the myosin heads
Recovery Stroke
the heads of myosin molecules return to their resting position (greenarrow) and energy is stored in the heads of the myosin molecules. If Ca2+ are still attached to troponins, cross-bridge formation and movement are repeated (return to step 2). This cycle occurs many times during muscle contraction. Not all cross-bridges form and release simultaneously
Cross-Bridge Movement (Cycling)
heads of myosin move at hinged region (cross-bridge). This forces actin to slide over surface of myosin. After cross-bridge movement, each myosin head releases from actin and returns to original position. Can then form another cross-bridge at different site on actin, followed by movement then release. During single contraction, occurs many times.
How many ATP needed for 1 Cross-Bridge Cycle?
1 ATP needed for each cycle of crossbridge formation, movement and release. Before myosin head binds to active site, it is in resting postion and ADP & phosphate are bound to head of myosin
Muscle Relaxation
Ca2+ moves back into sarcoplasmic reticulum by active transport (Requires energy) Ca2+ decreases in sarcoplasm and ions diffuse from troponin.Ca2+ moves away from troponin-tropomyosin complex; Complex re-establishes its position and blocks binding sites
Muscle Twitch
Muscle contraction in response to a stimulus that causes action potential in one or more fibers; Single, brief contraction and relaxation cycle in (1) muscle fiber; 3 Phases: Lag/Latent, Contraction, Relaxation
Lag Phase
time between application of stimulus to motor neuron and beginning of contraction
Contraction Phase
depolarization; time during which contraction occurs; increase to max in graph
Relaxation Phase
repolarization; time during which relaxation occurs; decrease from max in graph
Muscle Twitch Chart
Motor Units
single motor neuron and all muscle fibers innervated by it; an action potential in motor neuron generates action potential in each muscle fiber of its motor unit; not all motor units are identicle: may vary in terms of # of muscle fibers, their sensitivity to stimuli for contraction
Motor Unit Numbers
Different muscles contain diff # of muscle fibers; Large muscles preforming more powerful but less precise contractions have motor units with many fibers; Small muscles that make delicate movements contain motor units with few muscle fibers; ex -eye less than 10 fibers per unit, thigh several 100 per unit; few fibers give greater control
How is Force of Contraction Increased?
Summation & Recruitment; it takes greater force to lift 25 lb weight than feather
increasing force of contraction of muscle fibers within muscle; when muscle fiber demonstrates summation, usually because conditions w/in fiber have changed; ex when stimulated in rapid succession, contracts w/greater force each time (treppe)
increasing number of muscle fibers contracting
All-or-None Law for Muscle Fibers
contraction of equal force in response to each action potential; Sub-threshold stimulus, Threshold stimulus, Stronger than Threshold
Sub-Threshold Stimulus
stimulus not strong enough; no action potential; no contraction
Threshold Stimulus
stimulus strength increases until strong enough to produce action potential; contraction
Stronger than Threshold
action potential; contraction equal to that with threshold stimulus - once max motor units are recruited, does not matter how much more stimulus you use, can not get any more than max
Stimulus Strength & Motor Unit Response
strength of contraction is graded: ranges from weak to strong depending on stimulus strength; Multiple motor unit summation (submaximal, maximal, supermaximal)
Multiple Motor Unit Summation
relationship between increased stimulation strength and increased number of contracting motor units; force of contraction increases as more and more motor units are stimualted; A muscle has many motor units; Submaximal stimuli, Maximal Stimuli, Supramaximal Stimuli
Submaximal Stimuli
progressively stronger stimuli, produce actin potentials in axons of additional motor units
Maximal Stimuli
produces action potentials in axons of all motor units of muscle
Supramaximal Stimuli
greater stimulus than maximal; has not additional effect because all motor units are already recruited
Graded response; Occurs in muscle rested for prolonged period; When fiber stimulated (maximally at low frequency)in rapid succession, each fiber contraction is stronger than previous until all equal after few stimuli; Possible explanation: more and more Ca2+ remains in sarcoplasm and is not all taken up into the sarcoplasmic reticulum
Stimulus Frequency & Whole Muscle Contraction
As the frequency of action potentials increase, the frequency of contraction increases; Tetanus (Incomplete tetanus, Complete tetanus), Multiple-wave summation
as frequency of action potential increases, frequency of contraction increases until a period of sustained contraction is achieved
Incomplete Tetanus
muscle fibers partially relax between contraction
Complete Tetanus
No relaxation between contractions
Difference Between Trepee and Tetanus
Treppe - stimulus is maximal but delivered at low frequency; Tetanus - stimulus is at threshold but delivered at high frequency
Multiple-wave Summation
muscle tension increases as contraction frequencies increase
Muscle Length vs. Tension
Active tension; Stretched muscle; Crumpled muscle; Passive tension;Total tension
Active Tension
force applied to an object to be lifted when a muscle contracts; as length of muscle increases, its active tension also increases (to a point)
Passive Tension
tension applied to load when a muscle is stretched but not stimulated; similar to tension produced if musce replaced w/elastic band
Total Tension
sum of active plus passive tension
Stretched muscle
Not enough cross-bridging
Crumpled Muscle
myofilaments crumpled, cross-bridges can't contract; muscle damage and needs repair
Muscle Sarcomere Length
at the normal resting length of a muscle, the sarcomeres are also at an optimal length. The muscle produces maximum tension in response to a maximal stimulus at this length; Muscle length 1-3
Muscle Length 1
atrophy;the muscle is not stretched, and the tension produced when the muscle contracts is small because there is too much overlap between actin and myosin myofilaments. The myosin myofilaments run into the Z disks, and the actin myofilaments interfere with each other at the center of the sarcomere, reducing the number of cross-bridges that can form.
Muscle Length 2
healthy muscle; the muscle is optimally stretched, and the tension produced when the muscle contracts s maximal because there is optimal overlap of actin and myosin myofilaments, sot hte number of cross-bridges that can form is maximal
Muscle Length 3
damaged to point of bruising; the muscle is stretched severely, and the tension produced when the muscle contracts is small because there is little overlap between actin and mosin myofilaments, and few cross-bridges can form
Muscle Contractions
Isometric, Isotonic (concentric, eccentric), Muscle tone
Isometric Muscle Contraction
no change in length but tension increases; postural muscles of body
Isotonic Muscle Contraction
change in length but tension constant; ex - movements of upper limbs or fingers, as in waving or using computer keyboards; Concentric/Eccentric
Concentric Isotonic Muscle Contraction
overcomes opposing resistance and muscle shortens; ex - lifting loaded backpack from floor to table
Eccentric Isotonic Muscle Contraction
tension maintained but muscle lengthens; ex - person slowly lowers a heavy wieght
Muscle Tone
constant tension by muscles for long periods of time; responsible for keeping back and lower limbs straight, head upright, abdomen flat
Muscle Responses Chart
Muscle Fatigue
Decreased capacity to work and reduced efficiency of performance that normally follows a period of activity; 3 poss sites for fatigue: nervous system, muscles, NMJ; Types: psycological, muscular, synaptic
Psycological Muscle Fatigue
most common; involves central nervous system; muscles capable of functioning but person "perceives" that additional work is not poss; depends on emotional state of individual; ex - chronic pain and depression, tired athlete increases due to encouragement from crowd
Muscular Muscle Fatigue
2nd most common; occurs in muscle fibers; results from Ca2+ ion imbalance from ATP depletion; ex - fatigue in lower limbs of marathon runners or upper limbs of swimmers
Synaptic Muscle Fatigue
least common; occurs in NMJ due to lack of acetylcholine in synaptic vesicles due to amount released greater than amount synthesized
Physiologcial Contracture
state of fatigue where due to lack of ATP neither contraction nor relaxation can occur
Rigor Mortis
development of rigid muscles several hours after death; Ca2+ leaks into sarcoplasm and attaches to myosin heads and crossbridges form but to little ATP avail so bridges can not release. Rigor ends as tissues start to deteriorate
Energy Sources
ATP provides immediate energy for muscle contractions. Energy required to produce ATP comes from 3 sources: creatine phosphate, anaerobic respiration, aerobic respiration; Oxygen debt
Creatine Phosphate
during resting conditions, energy from aerobic resp is used to synthesise creatine phospate which accumulates in muscle fibers and stores energy to synthesize ATP
Anaerobic Respiration
occurs in absence of oxygen and results in breakdown of glucose to yield ATP and lactic acid; for each glucose metabolized, 2 ATP & 2 lactic acid produced; less effecient than aerobic but much faster; ex - short periods of intense exercise such as sprinting
Aerobic Respiration
requires oxygen and breaks down glucose to produce ATP, carbon dioxide and water; More efficient than anaerobic; produces up to 36 ATP for each glucose; uses fatty acids and amino acids as energy source; ex - long term exercise or long-distance running
Oxygen Debt
insufficient oxygen consumption relative to increased activity at onset of exercise; deficit must be repaid during and after exercise once oxygen consumption catches up with increased activity level; oxygen taken in by the body, above that required for resting meabolism after exercise (recovery oxygen consumption). ATP produced from anaerobic sources contributes
Slow & Fast Fibers
composition of muscle fibers can contain slightly different forms of myosin which cause them act differently; Slow-twitch and Fast-twitch
Slow-Twitch Oxydative (type 1 fibers)
contract more slowly, smaller in diameter, better blood supply, more mitochondria, more fatigue-resistant than fast twitch, large amount of myoglobin; respond relatively slowly to nervous stimulation; aerobic respiration; postural muscles, more in lower than upper limbs. Dark meat of chicken
Fast Twitch (type 2 fibers)
respond rapidly to nervous stimulation, contain myosin that can break down ATP more rapidly than that in Type 1, less blood supply, fewer and smaller mitochondria than slow twitch; anaerobic resp; lower limbs in sprinter, upper limbs of must people. Whit meat in chicken; Comes in oxidative and glycolytic forms
Distribution of Slow/Fast Twitch
most muscles have both but varies for each muscle; large postureal muscles contain more slow twitch, upper lims contain more fast-twitch
Effects of Exercise on Slow/Fast Twitch
change in size of muscle fibers; Hypertrophy, Atrophy
Hypertrophy of Muscle Fibers
increase in muscle size; increases in myofibrils, increase in nuclei due to fusion of satellite cells, increase in strength due to better coordination of muscles, increase in production of metabolic enzymes, better circulation, less restriction by fat
Atrophy of Muscle Fibers
decrease in muscle size; reversable except in severe situations where cells die
Muscle Fiber Type Chart
Heat Production
Exercise:metabolic rate and heat production increase; Post- exercise; metabolic rate stays high due to oxygen debt; Excess heat loss because of vasodialation and sweating; Shivering: uncoordinated contraction of muscle fibers resulting in shaking and heat production