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Balliet SysPhys musc

NYCC System physiology Balliet Muscle Ch. 6 & 7

QuestionAnswer
major determinant of whole body activity muscle
determines the basal and active state metabolic rates muscle MASS
determines relative utilization of glucose and fatty acids as fuels muscle
predominant muscle type in body skeletal
three muscle types skeletal, cardiac, smooth
both of these muscle types are striated but which has mitochondria and nuclei centrally located cardiac (skeletal mito and nuclei are out by the endplates and scarcoplasmic reticulum)
function of skeletal muscle locomotin, heat, protein and gluconeogen reserve, MAIN DETERMINATE OF METABOLIC RATE
functional unit of muscle sarcomere
long multinucleated cells made of myofibrils are called myofibers
sarcomere goes from __line to __line. z-line to z-line
A band (anisotropic) Actin and Myosin
I band (isotropic) Actin only
H band (zone) Myosin
vowels have actin, consonants have myosin, and they are all in a band together I is Actin, H is Myosin and they are both in A band together.
M line is an assembly of Myosin
Z line is where Actin is ANCHORED
M line is for Myosin and Z line is where Actin is ? Anchored
sarcomere boundaries Z-line to Z-line
Nebulin is an accessory protein that extends from z-discs and attaches to actin (thin)
accessory protein that connects myosin to z-disk Titin
where is the sarcoplasmic reticulum and why? outside of cell because Ca+ needs to go out of cell because you can't violate the concentration gradient rule
extensions of the cell membrane that conduct electrical signals to center of myofibril T-tubules
accessory proteins for myosin and actin Nebulin (keeps actin straight) and Titin (bungees down myosin)
name for skeletal mm cell membrane sarcolemma
name for skeletal mm cell cytoplasm sarcoplasm
name for skeletal mm. cell endoplasmic reticulum sarcoplasmic reticulum
extracellular space outside of myofibril that stores Ca++ sarcoplasmic reticulum
Why does Ca++ have to be stored outside of the cell? because you can't violate the concentration gradient rule that Ca++ has to be stored outside - it is an EXTRACELLULAR ION
why is anything in a T-tubule considered to be OUTside of a cell? because a T-tubule can propagate an action potential - it conducts electrical signals to the center of the myofibril. It is not inside the cell membrane or it couldn't conduct electricity/action potential. T-tubules are the messengers.
During sarcomere/myofilament contraction, ____ must come in second, since it is extracellular. Ca++
describe A-band, I-band and H-band during contraction A (actin & myosin) stays the same, I (actin only) shortens, H (myosin only) practically disappears!
what is the involvement of A-bands, H-bands, I-bands, M-lines and Z-lines called? Sliding Filament model
Myosin composition composed of 2 Heavy chains and 4 Light chains
where is the globular head on myosin chains? at the 2 identical heavy chains
where are the 4 light chains on myosin 2 lights are attached to each heavy head
what makes up the globular head of myosin? 2 light chains and a little bit of 1 heavy chain
Where is ATP on myosin? globular head (2 lights and 1 heavy chain)
which filament controls skeletal muscle contraction? myosin (thick heavy muscle myosin)
which filament controls smooth muscle contraction? actin (thin smooth squeeze actin)
How is the body of myosin formed? tails bundle together -twist
Part of the body of myosin (from tails) forms the arms. The heads are made of? 2 light chains and one heavy chain
myosin arm and head is called crossbridge
myosin head and actin binding site crossbridge formation
Where is ATP? on myosin head light chain
Where is ATPase? on myosin head light chain, next to ATP and actin-binding site
gives energy to make and then break crossbridge formation ATPase on myosin head
_________ _______ contains ATPase myosin head
Describe the components of Actin in skeletal muscle F-actin, Tropomyosin, Troponin
The binding site for myosin is on the actin molecule - it is a _______________ monomer. G-actin
F-actin is 8nm in diameter (tiny!). What is it composed of? G-actin monomers with one molecule of ADP each
Where is F-actin anchored? at the Z-disk -via binding proteins
covers the binding sites for myosin when in its relaxed state Tropomyosin (the mother)
lines the grooves of the actin filament tropomyosin
stabilizes and stiffens the actin filament tropomyosin
covers the binding sites for myosin tropomyosin (the mother)
has a binding site for Ca++ in skeletal muscle troponin (the pool boy)
the pool boy distracts the mother so his best friend Myosin can get into bind on F-actin's sites Pool boy is Troponin, mother is TropoMyosin
attaches tropoMyosin to actin troponin
has 3 complexes of protein, each with a strong affinity for either actin, tropomyosin, or calcium troponin
describe the protein complexes of troponin (the pool boy) Troponin-I: actin binding, Troponin-T: tropoMyosin binding, Troponin-C: Ca++ binding
Need 2 ATP that breakdown to ____&_____. When these latter two are released, what happens? ATP to ADP & Phosphate. When ADP & Phosphate are released, the POWER STROKE happens and the muscle CONTRACTS. Then another ATP binds to release the myosin head from the actin binding site.
What prevents actin and myosin from interacting? tropoMYosin (the mother covering her daughter F-actin's binding sites by way of the devious pool boy Troponin)
In the presence of ________ and _______, pure actin and myosin bind instantly Mg+ and ATP
appearance of skeletal, smooth and cardiac muscle striated, smooth, striated
fiber arrangement of skeletal, smooth and cardiac muscle sarcomeres, oblique bundles, sarcomeres
how are smooth muscle fibers arranged oblique bundles
attached to bones; a few sphincters close off hollow organs skeletal muscle
forms the walls of hollow organs and tubes; some sphincters smooth muscle
heart muscle cardiac muscle
multinucleate; large, cylindrical fibers skeletal
uninucleate; small, spindle-shaped fibers smooth
uninucleate; shorter branching fibers cardiac
Has T-tubules and sarcoplasmic reticulum skeletal and smooth muscle
no t-tubules; sarcoplasmic reticulum reduced or absent smooth muscle
which kind of muscle does not have t-tubules? smooth
fiber proteins of smooth muscle actin, myosin, tropoMYosin
fiber proteins of skeletal muscle actin, myosin, tropomyosin, troponin (same as cardiac)
fiber proteins of cardiac muscle actin, myosin, tropomyosin, troponin (same as skeletal)
control of skeletal muscles Ca++ and troponin, fibers independent of one another
control of smooth muscle Ca++ and calmodulin (CaM), fibers electrically joined via GAP junctions (like cardiac)
control of cardiac muscle Ca++ and troponin, fibers electrically linked via GAP junctions (like smooth)
are skeletal muscle fibers independently controlled or electrically linked via GAP junctions? independent skeletal
contraction speed of each of the 3 types of muscle, from fastest to slowest: skeletal is fastest, cardiac is intermediate, smooth is slowwwwww
smooth is sloooooowwwwwww slowest contraction speed
is the contraction force of a single skeletal fiber twitch graded or not graded? not
THe contraction force of both smooth and cardiac single muscle fibers is GRADED (builds up, is not an all or none)
Skeletal muscle contraction requires ____ from a _______ neuron. Ach, motor
Acetylcholine from a motor neuron is required for the initiation of a skeletal muscle contraction.
What is required for the initiation of smooth muscle contraction? Stretch! Chemical signals. Can be autorhythmic.
What is required for the initiation of contraction of cardiac muscle? nothing - they are autorhythmic!
neural control of skeletal muscle? somatic motor neuron (from ventral horn)
neural control of smooth muscle? autonomic neurons
neural control of cardiac muscle? autonomic neurons
What is the hormonal influence of skeletal muscles? nothing.
Do hormones and paracrines influence smooth muscle? yes, many
What hormones influence the heart? Epinephrine!
muscles generate ________, _________ & heat. motion, force and heat
Cardiac and smooth muscles are controlled by (3) autonomic innervation, paracrines, hormones
autorhythmic muscles some smooth and all cardiac - means they contract spontaneously
allow action potentials to move rapidly into the interior of the muscle fiber (skeletal and cardiac) and release calcium from the sarcoplasmic reticulum t-tubules
from where does Ca++ get released in skeletal muscles? sarcoplasmic reticulum
what holds the thin actin filaments in position? Nebulin
what holds the thick myosin filaments in position? Titin
Myosin binds to actin, creating _________ formations between the thick and thin filaments. crossbridge
One sarcomere is composed of two z-disks and the filaments between them
A sarcomere (between two Z-disks), is divided into what bands? I, A, H, M
I-band actin/thin filaments only
A-band both actin and myosin overlap area
A-band is the area of overlap between actin and myosin. It runs the length of the ________ filament. thick/myosin
zone occupied by thick/myosin filaments only H-zone
attachment site for myosin M-line
attachment site for actin z-disk
largest protein in the body Titin, bungee-ing myosin back into place
regulatory skeletal muscle proteins tropomyosin and troponin
giant accessory proteins for skeletal muscle (skm) titin and nebulin
motor protein with the ability to create movement in skm. Myosin
allows myosin heads to swivel around their point of attachment hinge
in skm, 250 myosin molecules join to form a thick filament
a protein that makes up the thin filaments of skm fibers Actin [actum: to do]
One actin molecule is a _________ protein globular protein called G-protein
Many actin molecules polymerize to form chains or filaments called F-actin.
In skm, 2 _______polymers twist together like a double strand of beads, creating the thin filaments of the myofibril F-actin (made of polymerized G-actin proteins)
Each G-actin molecule has a ________-binding site. myosin
Each myosin head has one ______-binding site and one binding site for _____. actin, ATP
Forms when the myosin heads of thick filaments bind to actin in the thin filaments crossbridges
2 states of crossbridges: low force (relaxed muscles) and high force (contracting)
sarkos flesh (sarcomere is flesh + unit)
zwischen the German word for "between," hence z-disks are the ends of a sarcomere and have all the filaments between them
isotropic the lightest band is the I-band, reflecting light uniformly/isotropically, hence I-band for actin.
runs through the middle of each I-band of actin z-disk, so each half of an I-band belongs to a different sarcomere
darkest of the sarcomere's bands and encompasses the entire length of a thick filament. At the outer edges of this band, myosin and actin overlap. A-band (has both). The center is occupied by only myosin
anisotropic A-band has both myosin and actin so proteins in this region scatter light unevenly/anisotropically (not isotropically)
helles the German word for clear
central region of the A-band that contains only myosin and is clearly present. H-band (helles is Ger. word for clear- you can clearly see myosin)
the band represents proteins that form the attachment site for thick filaments, equivalent to the z-disk for thin filaments M-line [M is for 'mittel' in Ger. which means middle - so myosin is attached to the M line which divides each A-band in half/down the mittel)
A single _______ molecule stretches from z-disk to the neighboring M-line and is the largest known protein. Titin
Imagine one of these molecules as an 8-ft long piece very thick rope used to tie a ship to the wharf while a single actin molecule would be about the length and weight of an eyelash. Titin (myosin's accessory protein)
it's elasticity returns muscles to their resting length and it stabilizes contractile filaments of skm. Titin
an inelastic giant protein that lies alongside actin and attaches to the Z-disk, helping align actin in the sarcomere. Nebulin
what makes up a 'triad' of skm? One t-tubule and its flanking 2 terminal cisternae for Ca++ storage.
the membranes of t-tubules are continuous with the muscle fiber membrane (sarcolemma) which makes the t-tubules continuous with the extracellular fluid
t-tubules are continuous with both sarcolemma and extracellular fluid
rapidly move action potentials from the cell surface to the interior of a skm fiber. Without them, the only way an action potential would get to the center of the fiber is by diffusion of a + chg. through the cytosol and that would be very slow for a skm t-tubule
what two things are in the cytosol between the myofibrils and provide reserve energy and ATP glycogen (reserve E), mitochondria (ATP)
how do mitochondria provide ATP for muscle contraction? oxidative phosphorylation of mainly glucose
the force created by a contracting muscle muscle tension
the creation of a contraction (tension in a muscle) requires E from ____ ATP
the release of tension created by a contraction relaxation
events at the neuromuscular junction convert an _____ signal from a __________ motor neuron into an electrical signal in the muscle fiber. Ach, somatic motor neuron
the process in which muscle action potentials initiate calcium signals that in turn activate a contraction-relaxation cycle Excitation-Contraction coupling (E-C coupling)
E-C coupling muscle action potentials initiate Ca++ signals that in turn make a contraction-relaxation cycle
How is E-C coupling explained at the molecular level? sliding filament theory of contraction
In muscles, one contraction-relaxation cycle is called a muscle ________. twitch
band which stays the same length during muscle contraction A-band
how can a muscle create force without creating movement? the sliding fl theory because tension generated in a muscle is directly proportional to the number of high-force crossbridges between actin and myosin
tension in a muscle is directly proportional to the number of high-force _____________ between actin and myosin. crossbridges (# = tension)
provides the force that pushes the actin filament during contraction rotation of myosin crossbridges
What initiates the power stroke that causes myosin crossbridges to swivel and push actin ropes towards the center of the sarcomere? Ca++ signal!!!!
At the end of its power strokes, each myosin head releases actin then swivels back and binds to a new actin molecule, ready to start another contraction cycle.
Do all the myosin heads release at once? no, the fibers would slide back to their start
In the power stroke, what causes myosin heads to swivel? Myosin converts the chemical bond energy of ATP into the mechanical E of crossbridge motion.
Myosin is an _______, so it hydrolyzes ATP into ADP and Pi. ATPase
What is stored in the angle between the myosin head and arm, keeping it "cocked" and ready to rotate during the power stroke? the potential energy released when myosin hydrolyzed ATP into ADP + Pi. (Myosin IS an ATPase)
How does a Ca++ signal turn a muscle contraction on? troponin
tropos 'to turn'
what controls tropoMyosin position? troponin
In resting skeletal m., what partially covers actin's myosin-binding sites? tropoMyosin in its blocking or 'off' position
Can weak, low-force binding of myosin to actin still take place if tropoMyosin is blocking actin? yes, but cannot complete power stroke (like the safety on a gun)
What has to happen to tropoMyosin before contraction of skm can occur must be shifted to 'on' position that uncovers the actin myosin-binding site
What regulates the on/off position of tropoMyosin? troponin
When contraction of skm begins in response to Ca++ signal, what binds reversibly to Ca++? troponin-C
What pulls tropoMyosin completely away from actin's myosin-binding site? Calcium/troponin-C complex
The "on' position of tropoMyosin allows myosin heads to form strong, high-force crossbridge formations and carry out a power stroke, moving the actin filament
Contractile cycles repeat as long as the binding sites on actin are uncovered (tropoMyosin is in it's "on" position and Ca++ is bound to troponin-C)
What must happen for relaxation skm to occur? Ca++ concentrations in the cytosol must go down
By law of mass action, when levels of Ca++ decrease in the cytosol, Ca++ unbinds from troponin-C
In the absence of Ca++, troponin allows tropoMyosin to return to the 'off' position and cover actin's myosin-binding sites.
How does the skm return to its original length? during the brief relaxation phase, when actin and myosin are unbound, the filaments in the sarcomere slide back with the help of Titin (myosin) and elastic tissues
In the rigor state, the myosin head is bound to G-actin molecules of actin but there is no nucleotide (ADP or ATP)
Rigor state is brief. Then, ATP binds and myosin detaches.
what decreases the actin-binding affinity of myosin? ATP binding to it - myosin will release actin when ATP binds to its head
After ATP has bound to myosin and myosin detaches from actin, what provides the E for myosin head to rotate and reattach to actin? ATP hydrolysis! Myosin head closes around ATP, busts it into ADP and phosphate, and both ADP and Pi stay bound to myosin as the E released by the ATP hydrolysis rotates the head until it forms a new 90 deg. angle to the filament.
In the cocked, post-hydrolyzed ATP position of having ADP and a Pi attached to its head, myosin swivels with the released E and ? attaches to a new actin molecule 1-3 molecules away from where it started.
Now that myosin is on a new actin molecule, the newly formed crossbridge is weak and low force because? tropoMyosin is partially blocking the binding site.
In the rotated, cocked position, myosin has stored ___________ energy. potential
Most resting muscle fibers are in a state of cocked, prepared readiness, waiting for a ? Ca++ signal
the power stroke is also called crossbridge tilting
When does the actual power stroke begin? Ca++ signal comes in, binds to troponin-C and this pulls tropomyosin off binding sites on actin. THe strong, high-force bond happens when myosin releases it's phosphate. The release of the Pi allows the myosin head to swivel toward the M-line.
When myosin releases its Pi in the power stroke, what happens to the actin filament? The myosin head swings towards the M-line with the release of the Pi, dragging actin along with it.
Why is the power stroke also called crossbridge tilting? myosin head and hinge region was at 90 deg. but now at 45 deg.
At the beginning of the power stroke, myosin releases Pi
At the end of the power stroke, myosin releases ADP.
With ADP release at the end of the power stroke, myosin is again tightly bound to actin in the _______ state. rigor state
What will break the rigor state of myosin to actin and begin the E-C coupling again? the binding of a new ATP to myosin
combination of elec. and mechanical events in a muscle fiber E-C coupling (excitation-contraction coupling)
how many major events of E-C coupling? 4
1st E-C coupling event Ach is released from the somatic motor neuron
2nd E-C coupling event Ach initiates an action potential in the muscle fiber
3rd E-C coupling event The muscle action potential triggers Ca++ release from the sarcoplasmic reticulum
in E-C coupling, from where is Ca++ released in the 3rd major event? sarcoplasmic reticulum
4th E-C coupling event Ca++ combines with troponin-C and initiates contraction
When Ach released from somatic motor neuron binds to Ach receptor-channels on motor end plate of muscle fiber, the Ach receptor channels open to let in? Na+ and K+ come in and cross the membrane
When Na+ and K+ come in after the Ach receptor channels open in the motor end plate of a muscle fiber, Na+ influx _______ K+ efflux because the electrochemical driving force is greater for ___+. Na+ influx exceeds K+ because the driving force is greater for Na+ (more Na+ is going to come in than K+ going out at first)
Why does the membrane depolarize when Ach causes Ach channel receptors to open? Because the channel receptors let in Na+ and let K+ out, but more Na+ comes in than K+ goes out so membrane voltage goes from negative (resting) to positive (influenced by Na+ influx) and and end-plate action potential results!
EPP End Plate Potential created when more Na+ influxes vs. K+ effluxing out of cell, cell depolarizes (goes positive) and end plate potential fires.
do EPP's always reach threshold and fire? normally
At EPP, once more Na+ is coming in than K+ going out and the cell depolarizes, what happens to the action potential? it is conducted across the muscle fiber into the t-tubules by the sequential opening of voltage-gated Na+ channels
What is like a domino effect in a muscle action potential? after EPP, the ap travels to the t-tubules via the sequential or domino-effect of voltage gated Na+ channels flipping open BOOM BOOM BOOM ONE AFTER THE OTHER DOWN INTO THE T-TUBULE, PROPAGATING THE A.P. ACROSS THE MEMBRANE
Once the a.p. gets down in the t-tubule via domino-effect of opening Na+ channels, what does it run into? L-type calcium channel receptor called dihydorpyridine (DHP) receptor!
The a.p. goes down the t-tubule on the backs of opening Na+ channels, runs into the DHP receptor. What happens to the DHP receptor when the a.p. slams into it? It changes conformation and yanks the ryanodine receptor cap off the sarcoplasmic reticulum storage bin. Ca++ comes pouring out into the cytosol, flowing down towards an area of lesser concentration from the SR sardine can it's been holed up in.
The a.p. slams into a DHP in the t-tubule. The DHP changes shape, yanking RyR cap off the sarcoplasmic reticulum storage bin and Ca++ streams into the cytosol. Guess where it heads? To the area of lesser concentration - this would be the troponin-C receptors on the F-actin. You know what happens next! myosin hydrolyzes ATP to ADP & Pi, waits in the cocked position. Ca++ in, binds to troponin-C, tropomyosin shifts, then POWER STROKE!
Free cytolosolic Ca++ levels in a resting muscle are normally low but the release of Ca++ from SR when DHP yanks RyR cap off means Ca++ levels increase 100x with the _______________ action potential
How does the muscle fiber end the contraction? the Sarcoplasmic Reticulum pumps Ca+ back into it's lumen with a Ca+/ATPase.
Ca+/ATPase pump used to? pump cytosolic Ca++ back into the SR and stop muscle fiber contraction.
As the SR uses the Ca+/ATPase pump to get Ca++ back into it's storage bin (SR lumen), the levels of Ca++ in the cell drop. What happens? Ca++ releases from troponin-C, which then allows tropoMyosin to slide back into blocking actin's myosin-binding site. Crossbridges release and the muscle fiber relaxes.
The signal for muscle contraction is Ca++
Why isn't the action potential the signal for muscle contraction? Because Ca++ is required so Ca++ is the SIGNAL
the signal for muscle contraction is Ca++
Ca++ is an almost universal __________ messenger. second
The somatic motor neuron a.p. is followed by the skeletal muscle a.p., which is followed by a __________. contraction
A single contraction-relaxation cycle in a skeletal muscle fiber is called a twitch!
the delay representing the time for E-C coupling to take place when the muscle a.p. and the muscle tension develops. latent period
what it takes to evoke a single twitch in a muscle fiber a single action potential
where does muscle ATP come from? creatine kinase transferring Pi to ADP= ATP and fatty acids via beta-oxidation (requires Oxygen and makes acetyl-CoA)
experimental evidence suggests that muscle fatigue is the result of excitation-contraction failure in the muscle fiber, rather than in the neurons or neuromuscular transmission.
A new theory that sarcoplasmic Ca++ causes __________ fatigue.
What preceeds physiological fatigue? psychological fatigue (and acidosis)
______-twitch fibers pump Ca++ back into their Sarcoplasmic Reticulum more rapidly than _______-twitch fibers do. fast, slow. So fast twitch fibers have quicker twitches!
The tension a muscle fiber can generate is directly proportional to the number of _________ formed between the thick and thin filaments. crossbridges
In a muscle fiber, the tension developed during the twitch is a direct reflection of the ________ of the individual sarcomeres BEFORE contraction begins. length
Each sarcomere contracts with optimal force if it is at optimum ________ before the contraction begins. length (neither too long or too short)
Why is a very long sarcomere length unable to contract very well? because of so little overlap between the actin and myosin - not many crossbridges can form
sarcomere length is really a reflection of the __________ between thick and thin filaments. OVERLAP = sarcomere length
optimum force is generated in a twitch when the optimum number of overlaps between actin and myosin occurs in the sarcomere. If it's too short, what happens? overlap prevents crossbridge formation and the thick filaments run into the z-disks
The development of single-twitch tension in a muscle fiber depends on filament overlap and sarcomere length
Force of contraction increases with ________ of muscle twitches. SUMMATION
Not only does the optimum sarcomere length determine single-twitch tension, the force can be increased by raising the _________ at which muscle a.p.'s stimulate the fiber. frequency/rate
When a muscle fiber does not have time to relax between stimuli, a more forceful contraction results. What is this called? summation
If action potentials continue to stimulate a fiber repeatedly at short intervals (high frequency), what happens? no more relaxation but maximum stimulation called TETANUS
The basic unit of contraction in an intact skeletal muscle motor unit
the group of muscle fibers that function together and the somatic motor neuron that fires an action potential motor unit
Although one somatic motor neuron innervates multiple fibers, each muscle fiber is innervated by one single neuron.
fine motor skill muscle motor units motor unit contains only 3-5 muscle fibers, so small response allows fine gradations of movement
gross motor action muscle motor unit each motor unit may contain hundreds or 1000's of muscle fibers.
All muscle biers in a single motor unit are of the same ______ type. fiber (fast-twitch motor units and slow-twitch motor units)
In skeletal muscle, each motor unit contracts in an _____________manner. all-or-none manner.
contraction that moves a load isotonic contraction
contraction that creates force without movement isometric contraction
extension of a muscle when lengthening with a weight but still letting down slowly eccentric contraction (dumbell 'uncurl' part of a curl)
Once the elastic elements in a muscle have been stretched and the force generated by the sarcomeres equals the load, the muscle _________ and an ________ contraction results. shortens, isotonic {'teinein' means 'stretch' so think of tonic as a stretch receptor that finally says GO!]
what kinds of muscle are most important for maintaining homeostasis cardiac and smooth
Smooth muscle is noticeably different from skeletal muscle in the way it develops ________. tension (smooth m. relax and contract are much slower and uses less E and can maintain contraction for a long time)
Think of skeletal muscle as weasel and smooth muscle as an anaconda. Cardiac muscle is a hamster in a wheel. Okay, you come up with something.
Where is smooth muscle found? 6 types: vascular (blood vessel walls), GI, urinary, respiratory (airway passages), reproductive, ocular
contractile fibers of this kind of muscle are arranged in oblique bundles and may run in several directions smooth
what controls smooth muscle contractions hormones, paracrines, neurotransmitters (ie, Ach and NE)
Normal skeletal muscle responds to an action potential with a twitch, but smooth muscles may hyperpolarize, depolarize, depolarize without firing. Contract after an a.p., after a SUB-threshold graded potential, or WITHOUT ANY CHANGE IN MEMBRANE POTENTIAL AT ALL!
Skeletal muscles contract when Ach is released from a somatic motor neuron, and relax when stimulus stops, but smooth muscles must act as integrating centers. Why? because multiple neurotransmitters, hormones, paracrines can all hit it at once, inhibiting and causing contraction. Smooth muscle has to integrate overlapping regulatory pathways and respond correctly.
composed of small, spindle shaped cells with a single nucleus smooth muscle
when a neurotransmitter is controlling a smooth muscle, how does it get to the receptor? no specialized receptor regions on smooth muscle (like motor end plates)! The nt simply diffuses across the cell surface until it finds a receptor.
single-unit smooth muscle (unitary) is so called because the individual muscle cells contract AS A SINGLE UNIT
What is another name for single-unit smooth muscle? Visceral smooth muscle because it forms walls of viscera like blood vessels and intestines.
All the fibers of single-unit/visceral smooth muscle are electrically connected to each other. How does the signal spread? GAP junctions
Why aren't there any reserve units left to be recruited (as skeletal muscle does) to increase a contraction force in a smooth muscle? Because ALL fibers contract EVERY TIME together (nobody left out)in smooth muscle
What determines the force of contraction in smooth muscle? the amt of Ca++
The amount of ____ determines the FORCE of contraction in smooth muscle. Ca++ = Force of contraction in smooth muscle
Multi-unit smooth muscle cells consist of cells that are not linked ____________-- electronically
Because multi-unit smooth muscle cells are not linked electronically like single-unit cells (get it? these fire as a single unit), each individual multi-unit cell must be closely assoc. with an axon terminal or variscosity and stimulated independently
What is the advantage of multi-unit arrangement of smooth muscle cells? allows fine control of contractions through selective activation (they don't all contract at once like the gut muscles)
Where is multi-unit smooth muscle found? Iris and ciliary body of eye, vas deferens, uterus just prior to labor and delivery
Which has longer actin and myosin filaments, smooth or skeletal? smooth, and the myosin in smooth is different!
How is smooth muscle myosin different? the myosin ATPase activity is much SLOWER, decreasing the rate of crossbridge cycling and lengthening the contraction phase.
In addition to smooth muscle myosin ATPase having a much slower activity than in skeletal muscle, a small protein chain plays a regulatory role in controlling contraction and relaxation. What is it? Myosin light chain (gets phosphorilyzed by MLC kinase)
Actin is _____ plentiful than myosin in smooth muscle. more! Actin to myosin ratio is 10-15 to 1
Smooth muscle has tropoMyosin, like skeletal, but does not have troponin
Smooth muscle doesn't have __________ troponin
Smooth muscle doesn't have troponin and its sarcoplasmic reticulum is _____ in number. weak
How is Ca++ released from the SR in smooth muscle? IP3 receptor channel (Inositol triphosphate is a second messenger created in the phospholipase-C pathway)
Instead of DHP and Ryn using Ca++, smooth muscle's sarcoplasmic reticulum uses IP3 as a second messenger
What supplements the Ca++ storage function of smooth muscle SR since there is so little SR? CALVEOLAE
small vesicles that cluster close to the membrane of smooth muscle and help with the Ca++ storage function since smooth contains so little SR calveolae
is smooth muscle arranged in sarcomeres? no -ergo, no distinct banding patterns
Actin and myosin are arranged in long bundles that extend diagonally around the cell periphery, forming a lattice around the central ________ in smooth muscle cell. nucleus
the oblique arrangement of contractile elements of smooth muscle beneath the cell membrane causes the fibers to become _______ when they contract. globular (rather than simply shortening like skeletal fibers)
The long actin filaments of smooth muscle attach to ___________ of protein in the cytoplasm dense bodies
In smooth muscle, because there are fewer myosin, the entire myosin filament is covered with globular heads (skeletal myosin filaments don't have heads along the M-line)
What is the advantage of the continuous line of myosin heads in smooth muscle? allows actin to slide along the myosin for longer distances
Since actin can slide along the myosin for longer distances due to myosin being completely covered with globular heads, what can smooth muscle do? be stretched more while still maintaining absolute tension (ie, the bladder won't give)
The dense bodies that anchor smooth muscle actin are analogous to what structure in the sarcomere? Z-disk
What is similar about the signal to contract in both skeletal and smooth muscle? Both use Ca++
Where does the Ca++ signal come from in skeletal muscle? Sarcoplasmic reticulum after Ryn channel receptor opens due to DHP and is ALWAYS preceeded by an action potential
Where does Ca++ signal to contract come from in skeletal muscle? weak SR but more from extracellular fluid and an action potential is NOT required for Ca++ release.
Is an action potential required for Ca++ release in skeletal muscle? Smooth? Yes in skeletal, NO in smooth
In skeletal muscle the Ca++ acts upon _________ to initiate contraction troponin-C
In smooth muscle, there is no troponin-C so what happens to Ca++ signal? initates a cascade that ends with the phosphorylation of myosin
4th step of smooth mm contraction: Phosphorylation of myosin enhances myosin. ATPase activity results in contraction.
3rd step in smooth mm contraction: Ca++ binding to calmodulin is first step in cascade that ends in phosphorylation of myosin
2nd step in smooth mm contraction: Ca++ binds to Calmodulin, a binding protein found in the cytosol
1st step in smooth mm contraction: Increase in cytosolic Ca++ initiates contraction. Ca++ is released from the sarcoplasmic reticulum and also enters from the extracellular fluid (calveolae)
Smooth muscle contraction begins when cytosolic Ca++ increase
what makes cytosolic Ca++ concentrations increase in smooth muscle extracellular fluid Ca++ entry and release of Ca++ from SR
What happens to cytosolic Ca++ in smooth muscle after it enters from extracell fluid and from SR? It binds to calmodulin (CaM)
CaM calmodulin - the thing to which Ca++ binds in smooth muscle when it initially enters the smooth muscle cell
Why does Ca++ bind to CaM in smooth muscle cell? Why not troponin-C? It is obeying the law of mass action (concentration gradient). There is NO troponin-C, but just like Ca++ goes to t-C in skeletal because it is in an area of less concentration, so the same it goes to Calmodulin in smooth muscle cell.
Once Ca++ has bound to calmodulin in smooth muscle, what happens? The Ca++/Calmodulin complex then activates an enzyme called MYOSIN LIGHT CHAIN KINASE
what do kinases do? add phosphates to things
MLCK Myosin Light Chain Kinase
What binds to MLCK in the smooth muscle? Ca++/Calmodulin complex
What does MLCK do inside the smooth muscle cell once Ca++/calmodulin has bound to it? enhances ATPase activity by phosphorylating light protein chains (remember: myosin heads contain 4 light protein chains attached to an ATP)
MLCK phosphorylates? light protein chains near the myosin heads in smooth muscle (remember: there are A LOT of heads on the myosin in smooth muscle so it makes sense that there'd be someone to help phosphorylate with the ATPase - a buddy)
When myosin ________ activity is high in smooth muscle cell, actin binding and crossbridge cycling increase tension in the muscle ATPase
What happens when ATPase activity (and MLCK, too) is high in the smooth muscle cell? actin binding and crossbridge cycling creates TENSION in the muscle
As a result of myosin ATPase activity intensifying and subsequent actin binding and crossbridging, smooth muscle contraction is primarily controlled by? MYOSIN-linked regulatory processes, rather than troponin or tropoMyosin
phosphorylates light chains in myosin heads and increases myosin ATPase activity Myosin LIght Chain Kinase
In skeletal muscle relaxation, what happens? Ca++ is pumped back into the SR by Ca++/ATPase pumps and as Ca++ levels drop, Ca++ dissociates from troponin-C, tropoMyosin returns to "off" and myosin detaches when a new ATP arrives. Extra Ca++ is pumped out of cell by Ca+/Na+ ANTIPORTER.
In smooth muscle relaxation, what happens? Ca++ is pumped back into SR by Ca/ATPase pump and out of cell by Ca/Na antiporter, same as skeletal. Ca++ dissociates from CaM. No Ca/CaM, MLCK shuts down.
Not only does the dissociation of Ca++/Calmodulin cause MLCK to inactivate, but the myosin light chain is ____________ by the enzyme? dephosphorylated by myosin phosphatase
what does a phosphatase do? takes the phosphates off of things (de-phosphorylates)
myosin phosphatase dephosphorylates the light chains on the plentiful myosin heads in smooth muscle (counteracts the added phosphorylation activity of MLCK from earlier when contraction was happening)
what is working with MLCK? myosin ATPase
what works to restore the balance of DEphosphorylated myosin heads when smooth muscle cell needs to relax? myosin phosphatASE (comes in when Ca+/CaM dissociates from MLCK because Ca++ is being pumped back into SR by Ca++/ATPase and Ca++/Na+ antiporter to outside)
the removal of myosin's phosphate group decreases ______________ activity so the smooth muscle can relax myosin phosphatase
Does the dephosphorylation of myosin by myosin phosphatase and the inactivation of MLCK (after Ca/CaM dissociates) mean that smooth muscle will automatically relax? NO! Nothing is all or none with smooth muscle, remember? Dephosphorylated myosin might stay attached to actin for a period called the LATCH STATE.
this condition maintains tension in smooth muscle fiber without consuming ATP the LATCH STATE -when myosin is dephos'd but still stays attached to actin
the significant factor that allows smooth muscle to sustain a contraction without fatiguing the LATCH STATE (dephosphorylated myosin stays attached to actin)
Smooth muscle Ca++ comes from: SR and extracellular fluid
Variable amts of Ca++ enter a smooth muscle fiber cytosol, creating __________________ whose force varies according to the strength of the Ca++ signal. graded contractions
What determines the strength of contraction in smooth muscle? the strength of the Ca++ signal! (graded contractions)
The smooth muscle's intracellular Ca++ store sarcoplasmic reticulum
SR Ca++ release is mediated by IP3 activated receptor channel, which opens in response to signal transduction pathways that produce IP3
How is SR Ca++ release mediated in skeletal muscle? by ryanodine receptor that opens when an action potential slams into DHP receptor
How does a smooth muscle cell monitor and replenish its internal Ca++ (SR) store? store-operated Ca++ channels allow more Ca++ into the cell from the extracellular fluid
How does smooth muscle know when to let in extra Ca++ from outside (extracellular)? membrane channels whose openings are sensitive to stretch, depolarization or chemical signals
blood vessel smooth muscle cells contain _______________ that open when pressure or other force distorts the cell membrane STRETCH-ACTIVATED Ca++ channels in blood vessels
When contraction originates from a property of the muscle itself, as in stretch-activated Ca++ receptors in blood vessels allowing Ca++ in, the muscle is said to be myogenic
myogenic able to originate a contraction without a chemical signal, as in blood vessels with stretch-activated Ca++ channels that contract to maintain a constant tone
Eventually during a sustained stretch-activated Ca++ influx, the Ca++ channels will... close and the Ca++ will be pumped out of the cell so the muscle can RELAX
small invaginations of the sarcolemma of smooth muscle that concentrate Ca++ caveolae
Created by: hecutler