Chapter 12

T-tubules (______ tubules) is a deep invagination of the _____ into _____ -The invagination weaves around and between the ____

(transverse), sarcolemma (plasma membrane of skeletal muscle cell) into the cell's interior. -myofibrils

Cross bridge cycle step 5 5. Cocking of the myosin head -The ____ is hydrolyzed into ___ and ____ and ____ is released. -This energy is used by the ____. which reenters its _____ and the cycle begins again

-ATP, ADP and Pi, energy -myosin, high-energy state

Cross bridge cycle step 4 4. Unbinding of myosin and actin -When another ____ is put into the ____ on the myosin head, the myosin and actin ____. -this is why dead animals enter a state of constant muscle contraction called rigor mortis because ATP is not produced and actin cannot unbind so the muscles are locked in a state of contraction

-ATP, ATPase site, unbind

Motor unit= ____

-a somatic motor neuron together with all the muscle fibers it innervates

1. Contractile proteins: -responsible for _____ -include _______ (made up of ____ and ____)

-generating muscle's pulling force -thin and thick myofilaments (actin and myosin)

Cross bridge cycle step 2 2. Power stroke -the binding of the myosin to the actin causes the release of the ___ and ___ from the ____ on the myosin -the myosin head pivots towards ____ -Myosin then enters a ____

-inorganic phosphate (Pi) and ADP from the ATPase site -the middle of the sarcomere -low energy state

3 Types of skeletal muscle fibers 2. Fast oxidative-glycolytic (Type II-a) muscle fibers -contract ____ and use both ____ and ___ for ATP production -primarily used for activities such as ___ or ____ -myoglobin content, fatigue resistance, pinkish color, and fiber diameters lie between ____ and ___

-quickly, anaerobic and aerobic metabolic processes -walking or sprinting -slow oxidative muscle fibers and fast glycolytic muscle fibers

3 Types of skeletal muscle fibers 3. Fast glycolytic (Type IIb/IIx) muscle fibers -contract ____ and primarily produce ATP through ____ -fibers shorten ____, but have very _____ fatigue resistance -typically ____ due to low myoglobin content -these fibers are primarily used for activities that require ____ -Have the largest ____

-quickly, glycolysis -quickly, low -white (don't need oxygen to make ATP) -rapid bursts of power or intense movements that have short durations. diameters

Force Generation -uses the _____ model -the cross bridge cycle is how _____ -excitation-contraction coupling is how ____ -Muscle cell metabolism is how ____

-sliding filament -muscles generate force -muscle contractions are turned on and off -muscle cells proved ATP to drive the cross bridge cycle

Sliding filament model (electron microscope version) -Sarcomere= _____ -Z disc serves as the _____, and it also anchors the _____ on one end. the Z discs are histologically dark because they contain a lot of _____ -A band is the broad region that corresponds to the length of the ____. However ____ and ___ exist in the A band -I band is the area near the ______ where there are only ______ -H zone is the area in the _____ of the sarcomere where there are only ____ -M line is the _____ and is the "_____" of the sarcomere

-the fundamental repeating unit of striated muscle, delimited by the Z disks -border of the sarcomere, actin, actin filaments -myosin myofibrils, both actin and myosin exist -edge of the sarcomere, actin (lighter color) -middle, myosin -axis of myosin, midline

Available ATP supply 1. small store of ATP available at onset of muscle activity: ____-____ sec 2. Phosphorylation of ADP by creatine phosphate ___-____ sec 3. Anaerobic glycolysis: __-__ min 4. Oxidative phosphorylation of ADP in mitochondria: >___min

1. 5-10 sec 2. 40-60 sec 3. 1-3 4. 3min

Overview of Excitation-contraction coupling (6 steps)

1. Acetylcholine is released form the axon terminal of a motor neuron that binds to receptors on the motor end plate, causing an end-plate potential which triggers an action potential in the muscle cell. 2. The action potential travels along the sarcolemma and through the T-tubules triggering the release of calcium from the SR 3. Calcium binds to troponin, causing a conformational change in tropomyosin and myosin binding sites are exposed 4. Crossbridge cycle begins and muscle contracts 5. calcium is actively transported back into the SR 6. Tropomyosin blocks myosin binding sites and the muscle fiber relaxes

Events in Force Generation (3)

1. Excitation (motor axon delivers action potential to neuromuscular junction) 2. Excitation-Contraction Coupling Events (sarcolemma depolarized, calcium released, regulatory proteins move) 3. Contraction (actin and myosin interact and actin slides over myosin- sarcomere shortness)

Factors that affect cross bridge formation (3)

1. Frequency of stimulation 2. Fiber diameter 3. Fiber length

Sarcoplasm has 2 components that are not usually found in other cells 1. why? 2.

1. Glycogen muscle cells are highly metabolically active and require a constant energy input; glycogen stores replace glucose when it is needed 2. Myoglobin- red protein that binds to oxygen, found exclusively in muscle cells

Cross bridge cycle (5 steps)

1. Myosin binds to actin 2. Power stroke 3. rigor 4. Unbinding of myosin and actin 5. cocking of the myosin head

3 Classes of muscle

1. Skeletal 2. Smooth 3. Cardiac

2 factors that ermine the force generated by a whole muscle: 1. 2.

1. The force generated by individual muscle fibers depends on # of active cross bridges formed within the muscle fiber, more cross bridges, the greater the force 2. The number of muscle fibers that contract at the same time, muscles contract together in motor units. The more muscles that contract together at the same time, the more cross bridges are active, and the greater the force

3 Types of skeletal muscle fibers 1. Slow oxidative (Type 1) muscle fibers: -contract ____ and primarily produce ATP ___ -Although these fibers shorten slowly, they have _______ meaning they can continue to ______ and are used for ____ and for maintaining ____ *rely on ____, so they have a high content of ____ *also have very small _____

1. slowly, aerobically -high fatigue resistance, contract for a long time, endurance activities, posture *aerobic respiration, myoglobin (carries oxygen) and have a dark red color *diameters

3. Structural proteins two important structural proteins: 1. ____- helps _______ -is highly ___ which helps give the muscle the ability to _____ 2. _____- attaches the ____

1. titin -anchor the thick myosin filament to the Z-line at the end of the sarcomere -elastic, stretch and recoil 2. dystrophin - myofibrils to the sarcolemma at the end of the muscle cell

Hierarchy of skeletal muscle terms: 1.Skeletal muscles consist of many _____ 2. Fascicles are bundles of many skeletal ____ 3. Skeletal muscle fibers (skeletal myocytes) consist of many ____ 4. myofibrils are organelle that contain ____ 5. myofilaments include ____ and ____ filaments made of ___ and _____

1.fascicles 2.muscle fibers 3.myofibrils 4.myofilaments 5. thin and thick filaments, actin and myosin

Most skeletal muscles are connect to at least ____ by ____

2 bones, tendons (bands of connective tissue responsible for transmitting the force produced by the muscle to the bone)

Why is calcium important to muscle contraction? -Calcium is normally present in very small concentrations in the ____, so storing calcium in the SR allows the cell to _____

Because it triggers a muscle contraction by binding to troponin, which causes a conformational change in tropomyosin, uncovering the myosin binding sites on the actin heads. This allows actin and myosin to bind together, which begins a muscle contraction. -cytosol, regulate the cytosolic calcium levels to achieve the desired amount of muscle contraction

Cross bridge cycle step 1 1. Myosin binds to actin -Energized myosin has a very high affinity for actin, so the myosin heads bind to nearby actin. _____ is required for this step to proceed -This is known as the ______ state

Ca2+ -"energized"

During muscle contraction, the ____ and ___ shorten but the ____ does not

I band and H zone, A band does not

Thin filament is made of many ______ molecules strung together in a _____ like a _____. -Each of these actin "beads" has a ______ that interacts with ____ during muscle contraction.

actin molecules, double helix like a twisted pearl necklace. -myosin binding site, myosin

Excitation-Contraction Coupling= sequence of events that links an ____ to a ____ 1. signal to initiate a contraction begins with an ______ in the cortex of the brain 2. This motor neuron sends an action potential to the lower motor neuron whose soma is located in the ____ 3. Once activated, the lower motor neuron sends an action potential down an axon the leads to a _______ 4. The action potential results in a release of _____ from the motor neuron's axon terminal into the ____. This causes an extremely large, ______ in the sarcolemma called an _____ 5. The action potential travels across the entire sarcolemma and in the _______ it triggers a release of ____ from the ____, which is crucial to the cross bridge cycle *movemtns of calcium is crucial to contraction and relaxation of muscle fibers when a muscle cell is relaxed, there is very little _____ in the cytosol and so the binding between _____and ____ is minimal. This is because the SR actively pumps calcium from the cytosol into the SR. The SR also contains voltage gated calcium channels that are normally closed, but when an action potential travels through the T-tubules, they open and allow calcium to flow out and increase the calcium concentrations in the cytosol. If the frequency of action potentials is great enough, calcium doesn't have time to be reabsorbed by the SR and so it can continue to initiate the crossbidge cycle. 6. The links between the action potential reachingg the T-tubules and the SR releasing calcium are the _____ and ____ receptors *When an action potential reaches a DHP receptor, it undergoes a _____ that sends a signal to the ryanodine receptors causing their ____ 7. Calcium enters cytosol and cross bridge cycle can begin

action potential to a contraction 1. upper motor neuron 2. spinal cord 3. skeletal muscle 4. acetylcholine, sarcolemma. graded depolarization, end plate potential 5. T-tubules, calcium, sarcoplasmic reticulum *calcium, calcium and troponin 6. dihydropyridine (DHP) and ryanodine receptors *conformational change, calcium channels to open

Neuromuscular junction (NMJ) is the location of the interaction between an _____ and a ____ -As it approaches skeletal muscle fibers, a myelinated axon branches off into projections that end in _____ which release ____ via ___ -At the site of the synapse, the sarcolemma of the muscle fiber contains ______ that exist within the kinky borders of junctional folds in the sarcolemma -Junctional folds function to increase the ____ of the sarcolemma so that the sarcolemma can house more receptors for ______ -receptors located along junctional folds are ____

axon of a motor neuron and a muscle -axon terminals, acetylcholine (Ach), synaptic cleft -motor end plates -surface area, neurotransmitters -nicotinic cholinergic receptors

2. Regulatory Proteins- determine whether or not ______ -2 major regulatory proteins found on actin: 1.______- ______ 2._______- is a regulatory protein complex that attaches to ____. binding of ____ causes_____, exposing ____ and allows ____

contraction will occur 1. Tropomyosin - a long cord like protein molecules that covers many of actin monomers, blocking their myosin binding sites (and preventing binding and muscle contraction is impossible) 2. Troponin - attaches to tropomyosin, calcium to troponin causes conformational change in tropomyosin exposing myosin binding sites on actin, muscle contraction to proceed

Glycolytic fibers have a very high concentration of _______ so they are able to generate ATP rapidly through glycolysis. But because they do not contain many _____, they are less capable of generating ATP through oxidative phosphorylation

cytosolic glycolytic enzymes, mitochondria

Terminal cisternae are ______ -Terminal cisternae store ____ and release it in response to an action potential traveling down the T-tubule -A triad is formed by a _____ plus the ____

enlarged areas of the sarcoplasmic reticulum that lie adjacent to the T-tubule -calcium -T-tubule two adjacent terminal cistern

Muscles consist of many _____ (_____) of individual muscle cells (referred to as _____)

fascicles (bundles), muscle fibers

Recruitment= ____ *size principle states that _____ and vice versa

for contractions of grater strength, more motor units are recruited for contractions *larger motor units are controlled by larger motor neurons

Skeletal muscles are unique in the body; they are ____, with multiple _____, and compose roughly ____% of the human body

long, nuclei, compose roughly 80% of the human body

Sarcoplasmic Reticulum (SR)- is a weblike ______ located _____ and surrounds each ____ -main function= _____, which are released upon _____ **SR encircles the myofibrils like _____

membranous organelle, adjacent to the T-tubules, myofibril -storage of calcium ions, stimulation by electrical signals **fishnet pantyhose surrounds a leg

Oxidative fibers have numerous _____ and can generate ATP easily as oxidative phosphorylation

mitochondria (countered as low glycolytic capacity)

Load-velocity curve shows the relationship between the velocity of _____ and the ____ *velocity of shortening is higher when the load is ____

muscle shortening and size of the load *smaller

Thick filament is made of about 300 individual _____ -each myosin head has a site that binds to ____ and ____ site -myosin heads are called cross bridges because they bridge _______

myosin molecules (long, globular proteins that look like golf clubs with two heads instead of one) -myosin heads stick out of myosin filament and interact with actin during muscle contraction -actin and an ATPase site -the gap between actin and myosin during contraction

Skeletal myocytes have multiple _____ why?

nuclei because during development, stem cells fuse together end-to-end to form one large cell. Multiple nuclei are retained to maintain adequate control over the cell

Innervation ratio= ____

number of motor neurons per number of muscle fibers

Within plasma membrane, or sarcolemma there are several ______ surrounded by the ____

organelles surrounded by sarcoplasm (muscle cell's cytoplasm)

Skeletal muscles are _____ because they consist of multiple _____ including ____ and _____

organs, tissue types, skeletal muscle tissue and connective tissue

Muscle cells are surrounded by plasma membrane called _____ (only contains ____ and ____)

sarcolemma (phospholipids and proteins)

Thin and thick filaments overlap one another collectively and form a _____ which is the basic repeating unit of a ______

sarcomere, myofibril

Myofibrils are located throughout the _____ -Myofibrils are made up of 3 different classes of proteins: 1______ (____and___) 2. _____ (____and____) 3_______ (____and____)

sarcoplasm 1 Contractile proteins (actin and myosin) 2. regulatory proteins (tropomyosin and troponin) 3. Structural proteins (titian and dystrophin)

Sarcomere is the smallest, fundamental repeating unit of ____, located between two adjacent ____ disks

striated muscle, Z

Muscle fibers run _____ from ____ to ____

the length of the muscle cell from tendon to tendon

sliding filament model states that muscle contraction occurs when _____ (_____ is pulled toward midline) **myofilaments DO NOT____ however; ___

the myofilaments slide past each other (actin) **change in length during a muscle contraction; the muscle fiber itself becomes shorter because the myofilaments slide past one another towards the medial line of the sarcomere

Skeletal muscle fibers can be divided into 3 types based on how _____ and how ____ -Oxidative fibers primarily produce ATP ___ -Glycolytic fibers primarily produce ATP __ -Fast-twitch fibers contract ___ -slow twitch fibers contract ____

they manufacture energy (aerobic or anaerobic means) and how quickly they contract (slow or fast) -aerobically -anaerobically -quickly -slowly

Cross bridge cycle step 3 3. Rigor At this point in the cross bridge cycle, the actin and myosin are ______, a condition referred to as ____

tightly bound together, rigor