Final Review Deck - Lecture II - Muscle Figs Flashcards
What are skeletal muscle cells like?
very long while cardiac muscle cells are much shorter and stubbier and smooth muscle cells are tiny
What is the mechanism of contraction in skeletal muscle similar to?
cardiac muscle but different from smooth muscle
What does muscle have many bundles of?
muscle fibers
What is a bundle of muscle fibers called?
fascicle
What are these muscle fibers made up of?
they have an SR and t tubules which wrap around them
What is an A Band?
where the thick myosin filaments are - tend to be dark
What is an M line?
where the thick filaments come off of
What is a Z disk?
where the thin filaments come off
What is an H zone?
the centers of the A band where there are only myosin filaments no actin overlaps and they tend to disappear with contraction
What is the repeating unit of a muscle fiber and what does it consist of?
a sarcomere and it is made up of 1/2 a z disk the A band and H zone and the other 1/2 of a new z disk
What do nebulin, troponin, and tropomyosin do in thin filaments?
nebulin - helps stabilize actin
troponin - has a c complex binds calcium
tropomyosin - moves out of the way in calcium dependent reaction to let the myosin head bind to actin
Where are thick filaments located?
in the center of the sarcomere
What is a myosin molecule made of?
they are dimers of 2 identical subunits
What are the three regions of a myosin molecule?
the hinge, tail region, and myosin head
-myosin head binds to actin
How is the myosin head arranged around the thick filament?
it sticks out in a spiral array around the thick filament
What is the name of the model of muscle contraction?
the sliding filament mdel
What is the cross bridge cycle?
it is changes in the myosin head and the binding and unbinding of it to thin filaments
What is the first step of the cross bridge cycle?
-the myosin head has no ATP to second binding site and the myosin head has a 45 degree binding to actin and this state is the rigor state and that is because no sliding can occur due to this angle
What is a result of the 45 degree binding angle of myosin to actin in the rigor state?
the filaments cannot slide past each other - during rigor mortis in death atp is depleted so the myosin head is in this state
What is the second step of the cross bridge cycle?
the ATP binds to the myosin
What is the third step of the cross bridge cycle?
the ATP is hydrolyzed to ADP and Pi and this causes a conformational change of the myosin head and they shift to a 90 degree angle
What is the fourth step of the cross bridge cycle?
get weak binding to actin and this is binding to the actin monomer number 2 not number 1
What is the fifth step of the cross bridge cycle?
myosin looses affinity for inorganic phosphate and undergoes a power stroke and generates the force to cause the filaments to slide over one another
What is the sixth step of the crossbridge cycle?
the 45 degree angle conformation causes a loss of affinity for ADP and goes back to the rigor state
Where are motor nuclei located?
in the cross section of the spinal cord there is gray matter which has the cell bodies of motor nuclei in the ventral horn
What do the motor neurons in the ventral horn supply?
skeletal muscles
What are some characteristics of motor neurons that supply skeletal muscles?
have a large diameter and are heavily myelinated which are alpha motor neurons
How many muscles does an axon from the ventral horn supply?
one muscle and then it branches to supply many muscle fibers and makes an excitatory synapse called the NMJ
What is the nerve terminal known as at the NMJ?
it is the presynaptic terminal and it has branches in the plasma membrane or the plasma lamina of a muscle fiber that is called the sarcolemma
What is the role of the schwann cell at the motor nerve terminal?
the schwann cell myelinates the PNS axon and it covers the motor nerve terminal
Why is there folding in the postsynaptic membrane area?
it increases the surface area
Where are vesicles filled with ACh released at the presynaptic nerve terminal?
at the active zones which is where there are special proteins which help the vesicles release NT by exocytosis
What do you find at the postsynaptic folds directly under the presynaptic release sites?
-find a high concentration of nAChRs
What is found surrounding the muscle membrane that help the muscle fiber generate an AP down the length of the fiber?
sodium and potassium channels
What do the high density sodium channels at the bottom parts of the postsynaptic folds do?
act as current amplifiers to make sure there is a large enough depolarizing epsp to bring the muscle fiber to its threshold for an ap
How is the NMJ different from the CNS?
it is a strong synapse which will cause there to always be a postsynaptic AP paired with a presynaptic AP
What receptor binds the ACh and what happens when it binds?
a multiceptor receptor and it binds to ACh and when it binds a cation specific ion channels opens that has equal permeability to sodium and potassium - it is just permeable to monovalent cations the embryonic form is permeable to calcium as well
-the inward sodium current exceeds the outward current carried by potassium and produces a large epsp and sodium creates a greater driving force than the outward current carried by potassium because Vm = -80 and Ek = -90 and ENa is way out of bounds
Where does the AP start in a muscle fiber?
in the middle of it and spreads until it gets to the ends and will stop at the ends because they are attached to tendons (connective ligament which attaches muscles to bones)
What wraps around the muscle fibers?
t tubules so every sarcomere of a myofibril has a t tubule around it and the lumen of te t tubule is connected with the EC space
Where is there an increase of sodium channels in the sarcolemma?
around the t tubule so when the muscle depolairzes it is easier for the t tubules to depolarize by having the AP propagate passively into the interior of them
What wraps around the myofibril and what is the role of this?
the SR and it sequesters calcium and there are calcium ATPases and they can release calcium from the SR when they are activated and look at junction between t tubules
What is the triad junction and what is the purpose of the junction?
-it is an SR flanking both side of the t tubulke and they allow for communication between the dihydropyridine receptor in the membrane of the t tubule and the ryanodine receptor in the membrane of SR
What is another term for the calcium ATPases in the membrane of the SR and what is their role?
SERCA pumps
to sequester calcium from the cytosol into the the sarcoplasmic reticulum
What is the role of the dihydropyridine receptor in the lumen of the l type voltage gated calcium channel?
it does not function as a channel and the depolarization of the t tubule when it happens due to the AP propagating down the length of the t tubule due to the concentration of sodium channels at the ends of the t tubule causes a conformational change in the dihydropyridine receptor and it senses the depolarization and causes via a mechanical connection the release of calcium from the ryanodine receptor
What is the role of calcium biniding proteins in the sarcoplasm and what are these proteins?
These proteins in the sarcoplasm and the sequester calcium concentration and keep it low
-they are parvalbumin and calmodulin
What is the calcium binding protein in the lumen of the SR and what does it do?
calsequestrin
-keeps the free calcium concentration low so that calcium can continue to come in via the SERCA pump
How does calcium trigger contraction?
via troponin and moving tropmyosin out of the way
What are the subunits of actin and what do they make up?
G actin subunits and make up F actin filaments
What are the three parts of the troponin complex?
TnC, TnI, TnT
What is the role of TnC?
the calcium binding protein
What is the role of TnI?
binds to actin and shifts when TnC binds calcium
What is the role of TnT?
binds to tropomyocin
At what cytosolic calcium concentration is muscle relaxed and at what concentration is it not relaxed and is cycling?
10^-8M
>10^-7M
What causes tropomysoin to move to the side so that myosin can bind to actin?
rise in calcium cocentration when troponin C binds calcium
Are the forms of troponin in smooth cardiac and skeletal muscle the same?
no they are different forms; similar function and different form
What does cardiac troponin in the blood signal?
heart muscle damage - is used to differentiate between chest pain or angina and heart attack because in heart attack the heart muscle is damaged so cardiac troponin will be in the blood
What is contraction?
the generation of force in a muscle does not always mean shortening of the muscle because the cross bridge cycle generates only force
How can you figure out Lo or the length at which there is maximal force for a muscle?
fix muscle at various lengths and measure the force produced - in the laboratory take a muscle out of an animal ad put it in the chamber where it is perfused with saline and fix one end of the muscle and each end has a tendon and attach a force transducer which will measure the force generated by the muscle when you stimulate it while you keep the length constant
What is an isometric contraction?
the force generated by a muscle while you keep the length constant
If a muscle is very short why is there not much force generation?
the z disks run into each other
If a muscle is very long and stretched why is there not much force generation?
there is very little overlap between thick and thin filaments so can’t produce cross bridges
What does the starling curve illustrate?
the left hand side of the curve that as EDV increases the cardiac muscle is more stretched so more force is generated so have a greater CO
What is a concentric contraction?
when the muscle shortens
What is an eccentric contraction?
when the muscle lengthens
What does an isotonic contraction measure?
the force velocity relationship
-where you maintain constant force in the muscle and measure the change in length
How can you measure the isotonic contraction of muscle experimentally?
apply a fixed load to the muscle and measure the rate of change in length
-can attach a weight or load to a muscle and measure the rate of contraction based on the load attached
When measuring an isotonic contraction experimentally what is the scale used velocity wise to measure the shortening and lengthening of a muscle?
shortening of a muscle is positive velocity and lengthening of muscle is negative veloctiy
In an isotonic contraction experiment what is V0?
maximum velocity of shortening when no load is applied to the muscle
In an isotonic contraction experiment what is F0?
the maximum force developed by a muscle and when the velocity is zero because it opposes the load and is equal to it
What happens in an isotonic contraction experiment when the weight is to much?
cross bridges slip
What are the four properties used to classify muscles?
- whether ion channels in the sarcolemma allow action potentials (all or none twitch) or not (graded or tonic contraction)
- rate contraction during contraction related to the atpase activity of the myosin isoform (determines V0)
- number of calcium pumps in the SR determines rate of relaxation
- number of mitochondria and capillary density
What does the number of mitochondria and the capillary density of a muscle determine?
determines the capacity for oxidative phosphorylation and fatigue resistance
What does the number of calcium pumps in the SR determine?
the rate of relaxation for the muscle
What does the rate of cross bridge detachment during contraction and its relation to atpase activity of the myosin isoform determine?
Vo in an isotonic contraction
What does the rate of cross bridge detachment during contraction and its relation to atpase activity of the myosin isoform and the number of calcium pumps in the SR determine together?
twitch duration
What organisms have tonic muscle fibers?
all invertebrates and vertebrate classes but mammals
What is a type i muscle fiber activated by?
it is activated at low frequencies and continuously for a long period of time
What is a type iib/iix muscle fiber activated by?
activated at high frequency bursts with a quiet period in between
If you add up the APs during the day what motor units are much more active?
type I motor units
Are skeletal muscle neurogenic or myogenic?
neurogenic
What are some examples of type IIb muscles?
arms and legs
What are some examples of type i muscles since they do not generate alot of force but are active all the time?
they are the postural muscles
What muscle type is lower in contraction speed?
type I - which means their myosin atpase activity is lower
What muscle type has a longer decay time?
type i - it has less SR pumps for calcium
What muscle type is more likely to use oxidative metabolism and what do they have as a result?
type i - have more mitchondria, oxygen storgae molecules like myoglobin making them red in color, high density of capillaries
What does myoglobin (is a monomer has only one heme group) do?
has a higher affinity for oxygen than hemoglobin and strips it form hemoglobin and delivers it to muscles at very low oxygen levels
When do type I muscle fibers have APs?
after period of long hyperpolarization due to persistent opening of potassium channels
Does type iib have hyperpolarization?
no they have a shirt refractury period so they fire at a high frequnecy
Do type iib muscle fibers have more muscle fibers than type i in a unit and how many mitchondria do they have and what enzymes are most common in them and how many blood vessels and do they have myoglobin?
more muscle fibers
less mitchodnria
more glycolytic enzyme
less blood vessels
no myoglobin
How does compression of blood vessels cause muscle fatigue?
reduces perfusion
causes the applied pressure is greter than arterial bp
How does increase in extracellular potassium cause muscle fatigue?
depolarizes the fiber which inactivates sodium channels and causes attenutation in ap amplitude cause they come in the cell
Why does increasing intracellular phosphate cause muscle fatigue?
gretaer atp hydrolysis - binding site it can bind to which inhibits atp hydrolysis too
Why does increasing free Mg and decrease in Mg-ATP cause muscle fatigue?
gretaer atp hydrolysis - binding site it can bind to which inhibits atp hydrolysis too
How does depletion of glycogen cause muscle fatigue and in what two cells is glycogen found in?
-no more glucose reserve
-skeletal muscle cells and liver cells
What are reactive oxygen species and how do they cause muslce fatugue?
muscle contraction creates oxygen molecules with uneven valence electrons
How does elevated temperature cause muscle fatigue?
metabolism raises temperature
How does lowered pH cause muscle fatigue?
metabolism causes acidosis and affects the enzymes of muscle
What is the size principle and what does it describe?
-describes the order of recruitment for motor units in a muscle
-recruited in order from smallest to largest and get a graded increase in force as a result
What is a motor unit?
a motor neuron and all of its muscle fibers it innervates
What size motor units do low force units have?
small motor units
What size motor units do high force units have?
large motor units
What is the size of motor units innervating type i muscle fibers?
small
What is the size of motor units innervating type iib/x muscle fibers?
large
What is the input resistance?
V=IR
R = V/I
input resistance = change in membrane potential/current change
What motor neurons have a large input resistance?
small motor neurons - because the change in membrane potential is large
What motor neurons have a small input resistance?
large motor neurons - because the change in membrane potential is small
How much force to big motor neurons generate?
high force
How much force to small motor neurons generate?
small force
Is the motor neuron pool from one muscle to another different?
yes (all the motor neurons innervating one muscle)
What does the size principle increase two things?
the smoothness and the amount of force that can be created
What causes a smooth force?
the summation of motor units
How can you mimic the smooth force seen through the summation of motor units?
use tectanic stimulation to repeatedly stimulate one MN
In real life does a motor unit undergo tectanic stimulation?
no; but they do sum to get a small graded force
