Steps of MUSCLE FIBER CONTRACTION

How is the means of ATP supply used to distinguish muscle fibers. what are the characteristics of each type of muscle

Oxidative Fibers = Cellular respiration - extensive capillary network - lots of mitochondria - lots of myoglobin = red in color = *fatigue resistant* vs. Glycolytic Fibers = glycolysis - less of each of the above - white in color - have large glycogen stores -*fatigable*

Glycolysis What type of energy does this supply? How is the ATP obtained?

Short Term Energy Glucose either from the muscles glycogen stores or from the blood is broken down in the cytosol yielding 2 ATP and 2 Pyruvate

What happens to muscle naturally a we age Fibrosis

Starting in mid 30s decrease in muscle fiber number and diameter oxygen storage capacity decreases muscle strength and endurance decrease ability to recover decreases causes formation of scar tissue within muscles decreased cardiovascular ability decrease in the number of satellite cells decrease flexibility Fibrosis - the replacement of muscle mass by dense regular (fibrous) connective tissue

Oxygen Debt What is the oxygen used for?

The amount of oxygen that is required after strenuous exercise to restore the body to its pre-exercise conditions This debt is necessary to replace the oxygen on hemoglobin and myoglobin, replenish glycogen stores in muscles, replenish creatine phosphate and convert lactate back to glucose

Wave/Temporal Summation

The effect of a high frequency of muscle stimulation that causes the effect of each stimulation to be added to the combined effects of the previous stimulation Temporal = due to increased tempo

What determines Fast and Slow Twitch Muscle Fibers?

The genetic variant of ATPase which determines how fast ATP is split Fast twitch muscle are also shown to initiate contraction more quickly after initial stimulation due to an increase in the CA+ release from the SR and due to a fast rate of action potential propagation Fast twitch = faster contraction + shorter duration -generate more power and speed compared to slow twitch

Muscle Fatigue what is the most common cause of fatigue what are other 3 causes?

The inability or reduced ability to produce muscle tension most commonly caused by decreased glycogen stores 1. excitation at the neuromuscular junction -insufficient Ca+ or vesicles to allow for muscle stimulation by the motor neuron 2. excitation contraction coupling- change in Na/K ion concentration causing an inability for the fiver to conduct an action potential at the sarcolemma 3. cross bridge cycling - increased phosphate ion concentration in sarcoplasm which interferes with the release of Pi from myosin heads during cross bridge cycling *Basically anything that inhibits the release or availability of Ca+ ions will cause muscle fatigue* * ATP is not generally thought to be a factor in muscle fatigue*

What determines the means of ATP production for any given activity?

The intensity and duration

End-Plate Potential (EPP)

The minimum voltage change (or threshold) in the motor end plate that can trigger opening of voltage-gated channels in the sarcolemma to initiate an action potential

What allows for muscle relaxation How does this occur

The termination of nerve signaling to the muscle This causes: -no more ACh released -Ach receptors close - motor end plate and action potential cease -Ca+ channels in the SR close -Ca+ pumps return loose Ca+ to SR -Troponin of thin filament returns to its original shape = prevents actin/myosin cross-bridge formation -Muscles natural elasticity also helps it to return to its relaxed length

What are the 3 subtypes of muscle fibers + examples of each

Type 1 =Slow Oxidative (muscles that maintain posture = trunk and lower limb) Type 2a = Fast Oxidative (muscles for medium duration activity ex walking = lower leg muscles) Type 2b = Fast Glycolytic (short, intense activities = upper limbs)

Isotonic Contraction define two sub classes

When muscle contraction results in movement of the muscle. The tone in the muscle remains the same as the length changes ex. holding a baby or swinging a golf club 1. Concentric contraction = the shortening of a muscle (effort > load) vs 2. Eccentric contraction = the lengthening of muscle (load > effort)

Isometric Contraction

When the force generated by the muscle is not enough to overcome the load on the muscle and thus there is no movement of the muscle ex. pushing against a wall or attempting to lift a car

recruitment or multiple motor unit summation what does this concept mean in terms of the ways in which our muscles contract

as the intensity of a stimulation is increased so is the number of motor units that contract until you reach the point of maximum contraction the more motor units stimulated the stronger/ more powerful the contraction of the muscle in this way muscles can exhibit both the all or none law or varying degrees of contraction. This explains how our fingers can contract to lift a pencil or lift a heavy suitcase

What ultimately causes a muscle to contract/shorten

continued neural stimulation of the skeletal muscle causes levels of Ca+ in the sarcomere to remain high allowing cross-bridge cycling to continue

Hypertrophy Hyperplasia Atrophy

increase in muscle size due to increase in the number of mitochondria and glycogen reserves = improved ATP production increase in the number of muscle fibers. Relatively uncommon and limited decrease in muscle size, tone and power due to lack of activity. Is generally initially reversible but overtime dead muscle cells will be replaces by connective tissue which is an irreversible change

Cardiac Muscle Structure and Function what stimulates cardiac muscle?

individual cells arranged in thick, branched bundles that are typically shorter and thicker than skeletal muscle cells joined to adjacent cells via intercalated discs made of desmosome and gap junctions. up to 2 nuclei per cell with many mitochondria striated due to the presence of sarcomeres stimulated by autorhythmic pacemaker

Slow Oxidative Fibers (SO) (Type I)

small diameter slow acting ATPase slower, less powerful contractions can last longer due to aerobic cellular respiration appear dark red due to myoglobin endurance and posture muscles = trunk and lower limbs (ie erector spinae and calf muscles)

Resting Muscle Tone

the constant tension established on a muscles tendon by a small number of randomly contracting motor units contractions are not strong enough to cause movement of the muscle but does stabilize the the position of bones and joints decreases during sleep

Length-Tension Relationship What is it? What does it show?

the relationship between the amount of tension a muscle can generate and the overlap between its thick and thin filaments at the start of the initial contraction * a muscle generates a different amount of tension dependent upon its length at the time of contraction* represented by the length-tension curve which shows that a muscle that is at is normal resting length will generate the maximum contractile force vs a muscle that is already contracted (due to thick filaments being close to Z-discs ) or overly extended (due to a lack of overlap between filaments needed for cross-bridge formation) which will generate weaker forces

Muscle Tone

the resting tension in a muscle generated by involuntary nervous stimulation of the muscle. this is caused by a limited number of motor units being randomly stimulated to maintain the constant tension of the muscle without tiring out any of the individual units

Treppe

the stepwise increase in the strength of a muscle contraction due to an increased frequency of stimulation (even without an increase in the intensity of the stimulation)

What is the refractory period

the time it takes for depolarization and repolarization to take place this is significant because during this time, and until the RMP is returned to -90mV the muscle can not be restimulated

How much ATP is constantly stored in Skeletal muscle (ie for how long will it last) What are the 3 ways a muscle can supply ATP to meet its high energy demands?

very little ATP is stored in skeletal muscle at any given time. Only about enough for 5-6 seconds of contraction 1. Immediate = Phosphate Transfer 2. Short term= Glycolysis 3. Long term= Aerobic Cellular Respiration

Fast Glycolytic (FG) (Type II b)

*fast anaerobic fibers* *most common skeletal muscle fibers* largest in diameter fast ATPase short bursts of activity with maximum speed and power because ATP supplied via glycolysis white fibers due to no myoglobin Bis , Tris, Chest, Quads, etc

Fast Oxidative (FO) (Type II a)

*intermediate fibers * *least common type of fibers* faster acting ATPase faster more powerful contraction vs slow oxidative *fewer capillaries than slow oxi = slow oxygen delivery* light red or pink due to less myoglobin moderate exercise muscles = some leg muscles

Cross Bridge Cycling (5 steps)

1. Ca+ binds to troponin in thin (actin) filaments which causes the troponin-tropomyosin complex to move, uncovering the myosin binding sites on the actin filament 2. Myosin heads bind to the exposed myosin binding site on actin forming a *crossbridge* between actin and myosin 3. Pull =*power stroke* myosin pulls actin towards the center of the sarcomere (ADP and Pi are released) 4. Release = ATP binds to the ATP binding site of the myosin head which causes the release of the myosin from the binding site on the actin 5. ATP is split into ADP and Pi by ATPase providing energy to reset the myosin head either for relaxation or another stroke *process will repeat if Ca+ is still present*

Incomplete Tetany / Tetany

As a muscle approaches its maximum level of tension each subsequent stimulation adds less and less to the overall tension of the muscle = incomplete tetany until the muscle finally reaches its maximum tension and levels off regardless of the continued stimulation of the muscle = tetany Tetany is rarely reached naturally by the body unless you force your self to reach that point

How does Prolonged Exercise Effect Skeletal Muscle Endurance vs. Resistance

Endurance = synthesis of cellular structures needed for ATP production (mitochondria, glycolytic enzymes, etc) Resistance = Increase in contractile proteins (actin + myosin) = Increase in size = Hypertrophy

What is the preferred energy source for skeletal muscle? What is the major drawback/hindrance of this type of ATP production

Fatty Acids However, in order for fat to be used for ATP production oxygen must be constantly present which can be difficult during strenuous exercise

Muscle Tension Twitch Threshold Latent Period contraction period relaxation

Force generated when a skeletal muscle is stimulated to contract single brief period of contraction and then relaxation minimum voltage needed to generate a twitch in a muscle brief period between the stimulation and contraction= time needed for all of the steps of muscle excitation-contraction coupling time during which action of filaments shortening sarcomere occurs = muscle tension increase begins with the releasing of the cross bridges. muscle tension decreases and muscle returns to original length

What happens in terms of the H zone, I band, Z discs, and the thick and thin filaments during a muscle contraction What is this called?

H zone disappears I band narrows Z discs of one sarcomere moves closer to another filaments do not change in length, the thin filaments merely slide past the thick filaments Sliding Filament Theory

Phosphate Transfer What type of energy does this supply? How is the ATP obtained?

Immediate Energy High energy phosphate is transferred to phosphorylize ADP into ATP Via: myokinase = transfers a Pi from one ADP to another =ATP + AMP creatine kinase = transfers a Pi from creatine phosphate to ADP = ATP and creatine ... as ATP accumulates during times of rest this process is reversed so that Pi can be stored in creatine phosphate *These pathways do not require oxygen and can only yeild an extra 10-15 seconds worth of energy *

Aerobic Cellular Respiration What type of energy does this supply? How is the ATP obtained?

Long Term Energy The pyruvate from glycolysis is broken down in the mitochondria via the intermediate stage, citric acid cycle and finally the ETS/oxidative phosphorylation yielding 30 ATP *Requires Oxygen which is delivered through the blood via hemoglobin or through myoglobin within the muscle cells.*

Excitation-Contraction Coupling (3 steps)

1. Development of an end-plate potential (EPP) at the motor end-plate (ACh stimulates Na/K channels to open allowing Na to diffuse into cell and K out of cell) once enough Na is in cell the membrane potential changes from (-90mv to -65mv = the threshold) 2. EPP stimulates an action potential to be propagated along the sarcolemma and t-tubules =First Na channels open allowing Na to enter cell causing *depolarization* (changing the membrane potential to change from -65mv to +35mv) Depolarization continues rapidly down the length of the sarcolemma followed immediately by the opening of K channels allowing K to diffuse out of the cell causing *repolarization* which resets the membrane potential to -90mV 3. When the action potential reaches the T-tubules it triggers the opening of Ca channels in the terminal cristinae of the sarcoplasmic reticulum. This cause Ca+ to diffuse from the SA to the sarcoplasm where it "mingles" with the filaments of the myofibril

What are the three main steps of a skeletal muscle contraction and where does each take place

1. Excitation of a Skeletal Muscle Fiber -at the neuromuscular junction 2. Excitation-Contraction Coupling -at the Sarcolemma, T-Tubules and Sarcoplasmic Reticulum 3. Cross Bridge Cycling -at the Sarcomere

What are the ways in which skeletal muscle contractions differ.

1. Power = larger muscle = more myofibrils = more powerful contraction 2. Speed = slow vs fast twitch - this is determined by how fast ATPase splits ATP 3.

How are muscle types categorized

1. contraction generated 2. primary means used for supplying ATP

Excitation of a Skeletal muscle fiber (3 steps)

1. nerve signal travels down the axon of a motor neuron triggering the entry of Ca+ into the synaptic knob which binds to the proteins in teh synaptic vesicle membrane 2. Ca+ triggers synaptic vesicles to merge with synaptic knob and Ach is exocytosed into the synaptic cleft 3. Ach diffuses across the synaptic cleft in the motor end plate to bind with Ach receptors

Smooth Muscle structure functions in various systems

2% of body weight found in the walls of many organs in many body systems with varying functions depending on the system cardiovascular system - regulates blood pressure respiratory system - controls air flow in bronchioles digestive tract - moves food along GI tract urinary system - propel urine from kidney to bladder specialized functions ex iris of the eyes unlike most skeletal and cardiac muscle has the mitotic ability to regenerate and increase in overall thickness (ie hyperplasia)

How is the progression of ATP energy sources (by time) What is tricky about sustained aerobic activity and how does the body compensate for this?

5-6 seconds = available ATP and phosphate transfer up to 60 seconds = glycolysis 1 minute or longer = aerobic respiration extended bouts of intense exercise (which raise heart rate) are dependent on the bodies ability to supply the muscle with oxygen. As a person trains harder the body adapts becoming better at its oxygen delivery

When is energy (in the form of ATP ) required during muscle contraction and relaxation Why is this significant

ATP is needed to power Ca+ pumps throughout both contraction and relaxation if sufficient ATP is not available our muscles can not relax = cause of rigor mortis after death

What happens to a muscle when you increase the frequency of stimulation without increasing the intensity of each stimulation?

when there is a very low frequency and the muscle has time to contract and fully relax during the next contraction the strength of the contraction remains the same as the frequency of stimulation increase the muscle will have less and less time to relax and there will begin to be an insufficient amount of time for all of the Ca+ to be eliminated resulting in the formation of more and more cross bridges with each subsequent contraction thus creating a stronger contraction = Treppe. This increase in contraction causing in continual increase in the amount of heat generated which makes the molecular interactions within the muscle more efficient = warming up effect Once frequency peaks and the muscle is not given time to relax between contractions you end up adding the effect of each contraction onto that of the previous contractions = wave summation or temporal summation Once wave summation creates a situation where the muscle nears its maximum level of contraction the effect of each stimulation becomes less and less (although it is still combined with those previous) = incomplete tetany Finally once a muscle reaches its maximum tension = complete tetany each subsequent stimulation does not increase the tension any further and the muscle remains fully tense until it finally fatigues