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135 Cards in this Set
- Front
- Back
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Muscle tissue |
- skeletal, cardiac, smooth muscle tissue - voluntary vs involuntary - "myo" and "sarco" mean muscle |
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Special Characteristics of Muscle Tissue |
Excitability, Contractiility, extensibility, elasticity |
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Excitability |
Responsiveness) --> the ability to receive and respond to a stimulus eg: receive a chemical signal that says "contract" |
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Contractility |
the ability to shorten forcibly when stimulated
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Extensibility |
the ability to be stretched or extended - muscle cells shorten when contracting, my can lengthen considerably when relaxed |
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Elasticity |
the ability of a muscle cell to recoil and resume its resting length after being stretched |
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General Muscle Functions |
1. Movement 2. maintain body position 3. stabilize joints 4. generate heat 5. proteciton |
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Movement |
- smooth muscle moves fluids in hollow organs - skeletal muscle moves limbs |
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Maintain Body Position |
- maintains posture, head up (counter-acts the never-ending gravity pull) |
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. Stabilize Joints |
muscles pull on bones to cause movement, and stabilize joints in the process |
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Generate Heat |
- as your muscles contract, they generate heat ® helps maintain body temp |
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Protection |
skeletal muscles protect fragile internal organs by enclosing them |
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Viscera: |
The internal organs of the body, specifically those within the chest (as the heart or lungs) or abdomen (as the liver, pancreas or intestines). viscus (plural) |
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SKELETAL MUSCLE |
- this is the muscle that moves us around, moves our limbs - striated and voluntary - skeletal (and smooth muscle) are elongated = muscle fibers |
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SKELETAL MUSCLE nerves and blood |
every muscle has a nerve, an artery, and usually several veins. - nerve endings are required for skeletal muscle cell contraction (smooth and cardiac don't need it) |
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SKELETAL MUSCLE connective tissue sheaths |
- individual muscle fibers are wrapped in and held together by connective tissue sheaths - Fxn: to support muscle cells, and reinforce muscle as a whole (prevents them from bursting with strong contractions) - these sheaths are continuous with each other, and with tendons |
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epimysium |
epi=outside -->an overcoat of dense irregular connective tissue that surrounds the whole muscle |
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perimysium |
layer of fibrous connective tissue that surrounds the fascicles, fascicles are groups of muscle fibers in a muscle (see figure |
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endomysium |
("endo" = inner) --> areolar connective tissue that surrounds each individual muscle fiber |
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Muscle Fibers |
muscle cell --> an elongated, multinucleated cell, with a banded or striated appearance - very large cells (10-100mm) - cytoplasm = sarcoplasm - contains glycosomes (stores glycogen) and myoglobin (pigment that stores oxygen) - plasma membrane = sarcolemma |
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Myofibrils |
- rodlike contractile organelles that make up muscle fibers - densely packed - hundreds of myofibrils are in one muscle cell/fiber - composed of sarcomeres arranged end to end = contractile elements |
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myofibrils Why does it appear striated? |
- striations are basically a repeating series of dark and light bands - you can see them along a myofibril - dark bands = A bands - light bands = I bands - they are perfectly aligned, which makes the cells appear striated |
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Sarcomeres |
muscle segment - contractile element --> functional unit - each end contains an A band, and half of an I band - comprised of something even smaller, called myofilaments
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Myofilaments |
- actin and myosin-containing microfilaments (remember Ch 3!) ® remember they are proteins important in cell shape change and motility --> contractile proteins |
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3 types of microfilaments |
thick filaments, thin filaments, elastic filaments |
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Thick filaments |
myosin red, see myosin head, contain ATP binding sites |
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thin filaments |
actin blue, |
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tropomysin |
rod shaped protein that spiral around the actin core, and help stiffen and stabilize it |
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troponin |
globular complex, these components are important in contraction |
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elastic filament |
titin, giant protein, molecular spring, responsible for elasticity of muscle |
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Sarcoplasmic Reticulum |
- sophisticated smooth ER - interconnecting tubules encircle each myofibril - Fxn: stores calcium and releases it on demand (when a muscle contracts) |
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T Tubules |
- "T" = transverse (see figure 9.5) - Fxn: increase the surface area of a muscle fiber |
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Triads |
contain 2 terminal cisternae (ends of the SR), and 1 T Tubule |
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So what happens during contraction? |
- the thin filaments slide past the thick filaments, so that actin and myosin overlap to a greater degree - in a relaxed muscle fiber, they only overlap a little bit |
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3 things must happen for a skeletal muscle to contract: |
1. It must be activated = stimulated by a nerve ending, so that a change in membrane potential occurs 2. Next, it must generate an electrical current called an action potential (nerve impulse), along its sarcolemma 3. Finally, a rise in intracellular Ca2+ levels triggers the contraction |
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nerve cells |
neurons are responsible for muscle contraction --> they must be excited (excitable = respond to a stimulus) - muscle cells are also excitable, remember |
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Overall, the human body is electrically neutral. |
However, there are parts in which a particular charge predominantes. (some regions are positive, some are negative) |
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Potential energy is measured as |
a voltage (volts, V; millivolts, mV). |
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Voltage Potential |
or just potential) refers to the difference in charge between 2 points -->the greater the difference in charge, the higher the voltage |
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Current |
the flow of electrical charge from 1 point to another |
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Resistance |
the hindrance to charge flow provided by substances through which the current must past |
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high electrical resistance |
insulators |
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low resistance |
conductors |
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ohm's law |
current (I)= voltage(V)/resistance (R) the greater the voltage (potential difference), the greater the current |
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What does this have to do with a cell and a membrane? |
· These terms refer to the flow of ions across the cell membrane. · Remember from Ch 3, there is a slightly different number of positive and negative charged molecules on either side of the cell membrane --> thus, there is a "potential" across the membrane, and the membrane itself serves as "resistance" |
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Membrane potential |
is the difference in voltage (also called electrical potential) between the interior and exterior of a cell (Vinterior − Vexterior). |
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Ion channels |
allow the passage of ions eg: potassium channel only allows potassium to pass through the membrane - so when these ion channels open up, ions diffuse quickly, creating electrical currents and voltage changes across the membrane - |
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electrochemical gradient |
remember molecules diffuse along a concentration gradient --> |
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polarized |
in non-excited cells ("resting" neurons or muscle cells), the membrane potential is relatively stable --> resting potential. = |
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depolarization |
a reduction in membrane potential (relative to resting potential) = |
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hyperpolarization |
when the membrane potential increases = |
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Resting Membrane Potential |
polarization, depolarization, hyperpolarization |
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Remember the Sodium-Potassium Pump?
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low Na+ in the cytosol, but high Na+ extracellularly - high K+ in the cytosol, but low K+ extracellulary |
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Generating a resting membrane potential depends on: |
(a) differences in K+ and Na+ concentrations inside and outside cells - the concentrations of these ions are different on either side - Na+-K+ ATPases (pumps) maintain the concentration gradient
(b) differences in permeability of the plasma membrane to these ions - the permeability of these ions are different on either side
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the sodium-potassium pump helps to |
generate a cell's resting potential. |
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ELECTRICITY |
in the human body, our tissues are constantly responding to electrical stimuli, and they even transmit their own electrical stimuli |
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heart --> EKG (ECG) electrocardiogram |
monitors the heart |
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so cardiac muscle has the ability to transmit and respond to electrical stimuli |
and this causes the heart to beat - if there is an irregular electrical signal, the heartbeat is affected (arrhythmia --> heart beats too fast or too slow) |
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EEG: electroencephalogram |
other tissues: the brain and spinal cord has electrical activity: |
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remember excitability = the ability to respond to an electrical stimulus how does this happen? |
movement of ions across the plasma membrane generates a voltage, just like a battery. remember an ion is a charged particle. resting membrane potential = RMP Remember the rules of facilitated diffusion: if an ion is permeable, ie: K+, it will move from a high concentration to a low concentration --> inside to outside - Na+ moves outside to inside |
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Relative Permeabilities of these Ions: |
Ion Permeability (cell at rest; not contracting)
Sodium (Na+) not very permeable (most gates for sodium channels are closed) Potassium (K+) very permeable (most gates for potassium channels are open) Chloride not very permeable (most gates for chloride channels are closed) Protein Anions completely impermeable (cannot leave the cell bc they are so big) |
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different concentrations of these ions makes them want to move |
K+ can move lots Na+ a little (due to its permeability) (only a few gates are open) |
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Remember, this muscle is still at rest. |
as K+ leaves the cell, it carries + charge with it, leaving behind very negative proteins - the cell becomes more negative on the inside of the membrane (ICF) - the ECF becomes more positively charged - the difference in charge is separated by the plasma membrane |
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the voltage across of resting cell membrane |
-70mV = electrically polarized |
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How do we MAINTAIN the resting membrane potential? |
if K+ were to keep moving out, it would move till the concentrations are equal on both sides; polarity would be lost (ECF = ICF) - we have a special pump to keep this going --> brings the K+ back in the cell, and pushes the Na+ back out -->sodium potassium pump (active transport) |
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REVIEW Resting membrane potential (RMP) is |
-70mV and is characterized by opposite charges that are separated by a plasma membrane = polarized state - inner surface is more negative - potassium leaving the cell is balanced by the pump, which brings in 2 K+ for every 3 Na+ it pumps out - so a resting cell has more K+ on the ICF and more Na+ on the outside
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Action Potentials |
for example, when a muscle cell receives an electrical impulse - you will see that a muscle cell is always closely associated with a nerve ending - remember that electrical impulse from a nerve is created by movement of ions in and out of the cell |
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Action Potentials |
1. Electrical impulse of a nerve ending reaches a muscle cell (100mV hits the cell)
2. Na+ gates open up and sodium rushes into the cell - carries a more ++charge, making the ICF less negative - the membrane potential has changed and become less negative = depolarization
3. If the membrane potential reaches +30mV during depolarization, the threshold has been reached and an action potential is generated. 4. Na+ gates immediately and rapidly close |
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propagation |
action potentials are the only depolarizing wave that can travel across plasma membranes - this movement across the membrane is called |
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like a domino effect |
as each domino falls, or each Na+ gate opens, the next domino falls because of its proximity (and same for Na+ gates)
- for muscle cells, +30mV is the "magic" threshold number (different in the brain)
- as soon as the depolarizing wave hits +30mV, an action potential is transmitted. - there is always only one action potential (regardless if it hit +30mV or +100mV) --> all or none response
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4. Na+ gates immediately and rapidly close |
- this whole process occurs in milliseconds - depolarization is reversible |
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repolarization |
the action of closing the gates = repolarization ® the membrane is trying to get back to its orginal polarized state and prevent any re-entry of Na+ |
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- that can be difficult with all that Na+ inside the cell, and the gates closed, right |
the Na-K pump starts working again to restore the potential back to -70mV
- remember this happens in lightening speed----super fast, as I move my fingers |
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So when you move your muscles (contract), it's almost a constant state of depolarization and repolarization |
the cell has to be quickly repolarized, so it can receive a stimulus again, for the next muscle movement - many action potentials are generated |
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refractory period |
the period of time when the membrane repolarizes and is unable to accept another stimulus is called |
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HYPERPOLARIZATION |
more common in neurons - not so much in skeletal muscle (although it can occur in cardiac muscle) - occurs when the plasma membrane of the neuron is more negatively charged (like at -90mV) |
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How can hyperpolarization happen? |
if we open all the K+ gates, even more K+ would exit the cell, making the interior more negative - same with Cl- gates |
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What is the consequence of hyperpolarization |
- if a 100mV stimulus hits the cell, what will happen? - will an action potential be generated? - probably not (-90mV + 100mV = +10mV) - threshold is not hit, no action potential
Thus, hyperpolarization is a way to inhibit a neuron from responding to a common stimulus. |
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Why inhibit neurons? |
- it's a way to prevent unwanted body movement - ie: during a seizure, ALL neurons are responding. hyperpolarization can prevent that under normal conditions - Parkinson's disease is another example of the inability to regulate neurons ® unwanted muscle contraction |
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So what happens during contraction? |
- the thin filaments slide past the thick filaments, so that actin and myosin overlap to a greater degree - in a relaxed muscle fiber, they only overlap a little bit |
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2 important proteins bound to actin in thin filaments, required for contraction |
troponin and tropomysin |
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stores and releases Ca2+ on demand. |
SR (sarcoplasmic reticulum |
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neuromuscular junction |
the connection between an axon terminal and a muscle fiber --> the route of electrical stimulation of the muscle cell |
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nerve cells that activate skeletal muscle fibers are called |
motor neurons |
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axon |
long, octopus legs of a neuron |
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motor unit |
motor neuron + muscle fibers it innervates |
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neurotransmitter |
chemical messenger released by neurons (binds to receptors either on a neuron or effector cell) |
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synaptic cleft |
the axon and the muscle fiber are EXTREMELY close to each other, but they do NOT touch --> the space between them at the neuromuscular junction |
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3 things must happen for a skeletal muscle to contract |
1. The muscle fiber is activated = stimulated by a nerve ending, so that a change in membrane potential occurs 2. An action potential is generated, along its sarcolemma 3. A rise in intracellular Ca2+ levels triggers the contraction |
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1. The muscle fiber is activated = stimulated by a nerve ending, so that a change in membrane potential occurs |
when a nerve impulse reaches a neuromuscular junction, acetylcholine (ACh) is released by the motor neuron, and travels to the synaptic cleft
- ACh diffuses across the synaptic cleft, and binds to its receptor on the sarcolemma --> changes membrane permeability --> changes the membrane potential (ACh acts as a neurotransmitter)
--> triggers a series of electrical events on the sarcolemma |
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2 An action potential is generated, along its sarcolemma |
- occurs in response to ACh binding with its receptors
- ACh binds to its receptors on Na+ gates --> opens the gates
- there is an influx of Na+, making the membrane potential slightly less negative |
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How does Ca2+ promote muscle contraction? |
- when intracellular Ca2+ is low, muscles are relaxed - active sites on actin are physically blocked by tropomyosin (myosin can't bind)
- when Ca2+ levels rise, the ions bind to regulatory sites on troponin - confirmational change occurs (troponin changes shape) - now actin is free to bind to myosin |
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cross bridge formation |
attachment of a myosin head to an actin molecule results in |
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Where is the Ca2+ coming from? |
the SR |
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Mechanical Activity of a Muscle Contraction |
1. Power Stroke Mechanism 2. The Muscle Twitch This process is highly dependent on ATP. - sliding of thin filaments will happen as long as there is adequate Ca2+ ad adequate ATP |
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1. Power Stroke Mechanism |
myosin movement along actin filaments 1. ATP hydrolysis occurs, and myosin is tightly bound to actin 2. A phosphate molecule is released from myosin -->confirmational change occurs that PULLS against the actin 3. ADP is released, ATP binds, and myosin is released from actin 4. ATP hydrolysis within myosin causes it to bind actin again
….and the cycle is repeated -------> muscles contract |
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2. The Muscle Twitch |
the response of a motor unit to a single action potential is called the response of a muscle to a single threshold stimulus |
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myogram |
graphic recording of mechanical contractile activity produced by an apparatus that measures muscle contraction (the muscle is attached to an apparatus that produces a myogram |
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Every twitch myogram has 3 distinct phases |
1. Latent period 2. Period of contraction 3. Period of relaxation |
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1. Latent period |
- the first few milliseconds following a stimulation - no response is seen on a myogram |
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2. Period of contraction |
- lasts 10-100ms - when cross bridges are active |
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3. Period of relaxation |
- lasts 10-100ms - initiated by re-entry of Ca+ into the SR - muscle tension decreases to 0
· notice that the muscle contracts faster than it relaxes |
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3. Muscle response to changes in stimulation frequency |
wave summation, single muscle twitch, complete tetanus, Treppe, |
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Single muscle twitch |
A single stimulus is delivered. The muscle contracts and relaxes. |
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wave summation |
What if another stimulus is applied before the muscle relaxes completely --> more tension force results in an incomplete tetanus occurs at low stimulation frequency |
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complete tetanus |
At higher stimulation frequencies, there is no relaxation at all between stimuli |
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Treppe |
"staircase effect"
- the gradual increase in muscular contraction following rapidly repeated stimulation - staircase effect of successive increases in the extent of contractions following rapid, repeated stimulation of muscle - tension increases even though the stimulus strength and frequency remains constant - tension rises in stages, hence like steps in a staircase - due to a gradual increase in Ca2+ in the sarcoplasm, and the ion pumps can't recapture them in time between stimulations |
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What does treppe mean in the world of sports? |
Active muscles require decreasing degrees of succeeding stimuli to elicit maximal contractions. · Squats: the second set is often easier than the first: for the first, you weren't warmed up. by the second, you are already warmed up --> The contraction strength of a muscle increases, due to increased Ca2+ availability and enzyme efficiency during the warm-up. |
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4. Isotonic and Isometric Contractions |
There are 2 main categories of contractions: isotonic and isometric |
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Isotonic contractions |
muscle length changes and moves the load. Once enough tension has developed to move the load, the tension remains constant for the rest of the contractile period once the resistance is overcome, the muscle shortens, and the tension remains constant for the rest of the contraction |
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Concentric contractions |
when the muscle shortens ie: picking up a book; kicking a ball (most familiar) |
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Eccentric contractions |
when the muscle lengthens ie: what your calf muscles are doing when you walk up a steep hill - more forceful - tend to cause delayed muscle soreness (how do your calfs feel the day after a hike?) |
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Isometric contractions |
tension builds to a maximum, but the muscle doesn't shorten or lengthen
- occurs when a muscle attempts to move a load that is greater than the force that the muscle can develop
- muscle is attached to a weight that exceeds the muscle's peak tension developing capabilities - when stimulated, the tension increases, but the muscle does not shorten |
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Muscle Metabolism |
Obviously, we need energy for muscle contractions to occur. - ATP supplies energy for cross bridge movement - ATP is required for the Ca+ pump in the SR
Surprisingly, muscles store very small amounts of ATP. |
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How is ATP generated for skeletal muscle contraction? |
1. Creatine phosphate 2. Anaerobic Glycolysis and Lactic Acid formation 3. Aerobic respiration
(All body cells use Glycolysis and Aerobic respiration, not just muscle cells) |
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Direct phosphorylation of ADP by creatine phosphate |
ADP = adenosine diphosphate - recall: ADP + P --> ATP So we begin to exercise vigorously, and ATP is in high demand. · We quickly use up the ATP that was stored in the muscle (only good for 4-6 seconds) · Creatine phosphate (CP), which is stored in muscles, is called on - couples with ADP to instantly transfer a P and energy to form ATP
CP + ADP --> creatine + ATP (enzyme = creatine kinase)
- muscles store about 3X the amount of CP as ATP --> this will give you muscle power for about 16 seconds (100 meter dash) - reaction is reversible, so that CP is restored during periods of relaxation |
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2. Anaerobic Glycolysis and Lactic Acid Formation |
anaerobic pathway that converts glucose to lactic acid - it does not use oxygen (although O2 is present), so it's anaerobic
- when you run out of CP, the next thing the body will do is to break down glucose from the blood, or glycogen stored in the muscle |
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Glycolysis |
glucose is broken down into 2 pyruvic acid molecules, releasing |
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Pyruvic acid is converted to lactic acid. Advantages |
· fuels short spurts of vigorous exercise · produces ATP FAST (2.5 X faster than the aerobic pathway) · CP and glycolysis can support strenuous muscle activity for nearly a minute |
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Pyruvic acid is converted to lactic acid Disadvantages |
uses lots of glucose to yield a small amount of ATP -----> 60 seconds of muscle power · leftover lactic acid (accumulated lactic acid) can cause muscle soreness - when exercise stops, lactic acid will diffuse into the bloodstream - the liver can re-convert it into pyruvic acid |
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3. Aerobic Respiration |
95% of ATP used for muscle activity comes from this process - occurs in mitochondria - requires oxygen - involves a bunch of chemical reactions that yield ATP after about 30 min, fatty acids become the major energy source
--> yields about 32 ATP per glucose (sustains muscle power for hours)
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Muscle Fatigue |
the inability to contract even though the muscle is receiving a stimulus
- unclear why this happens - researchers believe it is a problem at the neuromuscular junction - ATP becomes unavailable |
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problems with ionic concentrations |
as action potentials are generated, K+ is lost, and the Na-K pump doesn't work --> membrane potential is disrupted --> Ca2+ is not released from SR |
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intense exercise in a short period of time contributes to muscle fatigue rapidly |
recovery is rapid |
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prolonged exercise leading to gradual muscle fatigue |
recovery takes several hours |
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Oxygen Debt/Deficit |
vigorous energy uses up a lot of oxygen, whether you are fatigued or not - oxygen reserves must be replenished |
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accumulated lactic acid in the muscle, and any leftover in the blood must be converted back to glucose by the liver (glycogen stores must be replaced) |
ATP reserves must be replaced - CP reserves must be replaced |
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oxygen debt |
the extra amount of oxygen that the body must take in to restore the body back to normal - the difference between the amt of oxygen needed for aerobic activity and the amount actually used |
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Muscle Hypertrophy (not a pathology) |
--> increase in muscle, due to exercise` |
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Muscle Spasm |
a sudden involuntary twitch in smooth or skeletal muscle - a cramp is a prolonged spasm, often occurring at night or during exercise - possibly due to chemical imbalance, and many other factors |
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Muscle Sprain |
pulled muscle - excessive exercise and possibly tearing a muscle due to overuse or abuse - becomes inflamed (myositis |
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Myopathy |
any disease of the muscle |
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Tetanus |
caused by Clostridium tetani --> the bacterium that causes tetanus this bacterium is all over the environment, but loves tissues with low oxygen (so a deep puncture wound, like a nail, is a good opportunity) this bacteria releases a powerful toxin that affects the central nervous system --> esp motor neurons (which control skeletal muscle contraction) - the toxin suppresses/inhibits motor neuron activity
- after exposure, in less than 2 weeks, symptoms occur: headache, muscle stiffness, difficulty swallowing
- severe tetanus has a 40-60% mortality rate. get the vaccine!!! |
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Muscular dystrophy |
muscle-destroying diseases - generally inherited - appear during childhood - muscle fibers atrophy and degenerate (decrease in muscle)
- most common = Duchenne muscular dystrophy (DMD) - females carry and transmit it, but it's expressed almost exclusively in males - affects all muscles…..imagine the effects - victims usually don't live past their 20's, commonly dying of respiratory failure |
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Fibromyositis |
"fibro" = fiber; "itis" = inflammation
= fibromyalgia
- chronic inflammation of a muscle or tendon - symptoms are very non-specific --> varying degrees of tenderness, fatigue, awakening from sleep |
