musculatory system Flashcards
Three types of vertebrae muscle
Skeletal muscle
Cardiac
Smooth
Skeletal muscle - basic function
Voluntary movement
Most are connected to bones by tendons
Cardiac muscle - basic function
Heart muscles
Smooth muscles - basic function
Involuntary muscle
Controls blood flow
Movement of food through digestive tract
Skeletal muscles - detailed function / description
Very long muscles
Have multiple nuclei
Shapes and sizes are central to their function
Huge cells develop by the fusion of smaller cells into long fibers
how do skeletal muscle fibers form
Myoblasts fuse to form a skeletal muscle fiber
Satellite cells are
a type of stem cells that are intermingled into your muscle
If you damage your muscle these will repair it
Going to gym and your muscles get bigger
You aren’t getting more muscle cells but you are increasing the diameter of the fibers of the cells you have
How muscles generate force
Muscles shorten
musscle cells contract to generate force
Skeletal muscle consists of
a bundle of long fibers, each a single cell, running along the length of the muscle (muscle fiber)
A muscle fiber is a bundle of
smaller subcellular myofibrils arranged longitudinally
One big membrane around it
One single muscle fiber(in the bundle) will be filled with a subcellular array called
myofibers
The myofibrils are
bundles of organized contractile protein molecules called sarcomeres
Arrays of protein molecules that generate a contractile force
what interaction in the sarcomeres shorten muscles
interaction of myosin and actin
Muscle fiber cell contraction relies on the interaction between
thin filaments, composed mainly of the proteins actin, and thick filaments, staggered arrays of myosin
\Bundles of Myosin interact with bundles of actin
Force is generated when the sarcomeres
contract
Actin filaments(thin) are anchored to ___
Z-line\
and myosin tug on these thin filaments moving the Z-disks closer
How does myosin pull the z-lines together?
Each myosin has a long tail region and a globular head region
The head of a myosin molecule binds to an actin filament, forming a cross-bridge and pulling the thin filament toward the center of the sarcomere
The sliding filament model\
One sarcomere will get shorter and since all the saromeres are glued together each sarcomere will pull the fibers together and shorter and force can be generated
Hydrolysis of ATP causes myosin head to go through a configuration change
how does this happen
Myosin head binds to ATP (low-energy configuration/bent)
When myosin has ATP bound to it it will not associate with actin
Enzymes catalyze the hydrolysis of ATP to ADP +Pi (high-energy configuration)
Hydrolysis of ATP causes change in myosin configuration
Atp hydrolysis allows what two thngs to bind
myosin bind to actin and form a cross-bridge
Binding of myosin release
ADP + Pi
what movement officially causes our muscle to contract
While myosin is bound to actin, it moves back into original configuration causing our muscles to contract
After ADP + Pi is released and myosin is still attached to actin, what occurs
a new ATP can bind to the myosin and it releases the myosin from the actin (small nudge/movement)
Many cycles required to contract muscle
what determines the strength of contraction of a muscle
There are millions of myosin molecules in each muscle fiber
Many or all of the myosin molecules work together to generate force when needed
The number of myosin molecules activated determines the strength of the contraction
what regulatoru components allow you to control your muscle
Troponin and tropomyosin
do troponin and tropomyosin generate any force
no
What prevents actin and myosin from interacting
tropomyosin
When u aren’t using the muscle the tropomyosin sits where myosin wants to bind
troponin is regulated by Ca2+ in what way
Ca2+ binds to troponin
Causing the tropomyosin to move out
Exposes myosin binding sites
Calcium binding allows interaction of myosin and actin
A low concentration of Ca2+ means that o
only some of the troponin will have bound Ca2+
Generate a weak contractile force
A higher concentration of Ca2+ means that
more of the troponin will have bound Ca2+
Generate a stronger contractile force
the degree of contraction is changed by
Adjusting the amount of calcium
Motor neuron talks to a muscle at
the neuromuscular junction
Where does Ca2+ come from?
Sarcoplasmic reticulum is a series of internal sacss within the muscle fiber
Muscle cells store calcium in these sacs
An internal membrane enclosed compartment
Calcium can be selectively released from the SR into the cytoplasm where it will bind to troponin
what does action potentials propogating through muscle fibers result in
muscle contraction
describe the general steps of the beginning of muscle contraction via action potentials
what sets off the action potential
- Starts with arrival of the action potential at the motor nerve terminus
- All of our motor neurons release acetylcholine when an action potential arrives → when brain tells muscle to contract
Acetylcholines allow sodium into the cell, depolarizes it, set off action potential → action potential move through surface of cell
Muscle fibers are big and have only one neuromuscular junction per fiber, per cell, the goal is to activate contraction throughout fiber. To accomplish this the action potential
spreads in the fiber membrane
One action potential down a motor neuron will always set off an action potential in the muscle cell
why
Already made decision to contract muscle so it will happen
Transverse tubules
extensions of the plasma membrane that extend into the cell
The action potential moves down the T tubules
what happens once action potential reaches the T tubules
since the T tubules are close to the SR, the
Arrival of the action potential in the T tubules is sensed by the sarcoplasmic reticulum and Ca2+ channels are opened
Ca2+ rushes out of the SR into the cytoplasm where it binds to troponin and moves tropomyosin out of the way which initiates contraction
Contraction must also be turned off
how is this done
ATP uses the Ca2+ pump and activates it and causes it to pump Ca2+ against its concentration gradient back into the SR
As the Ca2+ moves back into the SR, the tropomyosin now blocks myosin binding site on actin again and the muscle fiber relaxes
Which is true?
As cytoplasmic (myoplasmic) Ca2+ increases, more actin binding sites are blocked by tropomyosin
Ca2+ and ATP both bind actin
The ATPase activity of myosin means that it makes ATP
Myofibrils are found inside the sarcoplasmic reticulum
ADP is released from myosin when it binds actin
: (e) ADP is released from myosin when it binds actin
How we control strength of muscle contraction → muscle tension
Two mechanisms by which the nervous system produces graded contractions
Not all fibers within a muscle are activated for a contraction
It depends upon the desired strength of the contraction
Individual fibers can also adjust their strength too, to be activated to varying degrees by varying the amount of Ca2+ released
Motor unit
Each motor neuron makes contact with multiple muscle fibers
Each muscle fiber has only one neuromuscular junction but one motor neuron makes muscle neuromuscular junctions with multiple fibers
Motor neuron and all the muscle fibers it controls
How do differing motor units determine strength of contraction
Our muscles contain a mix of large and small motor units
Muscles that do large strenuous tasks like those in our legs and back have mostly large motor units
Fine motor control like in our fingers requires many small motor units
Depending on task, the big vs small motor units that are used are different
This process of which motor units get activated is called
recruitment or recruited
Motor unit recruitment
Recruitment is the process by which more and more motor neurons are activated in order to meet the required task
As recruitment proceeds and large motor units are activated, the force developed by a muscle increases
Start with little motor units → activate larger and more if we aren’t accomplishing task and so on and so forth → get more contraction and strength
A single motor unit…
Consists of many motor neurons but only a single muscle fiber
Are all of the same size
When faced with a task you always recruit the largest motor units first
The cell bodies of motor neurons are in the muscles they control
None of these is correct
(E) none of these is correct
(d) the cell bodies of motor neurons are in your spinal cord and it sends an axon out to the muscle and you have one motor neuron controlling multiple muscle fibers
Second way that you regulate strength
within a motor unit control how strongly we tell each fiber to contract (turn on motor unit high or low)
A twitch
Results from
a single action potential in a motor neuron
In a twitch only a few troponin bind Ca2+
Only some of the actin and myosin go through cross-bridging cycles
Only a small amount of tension is generated in the muscle
Change how much cross-bridging occurs by changing
amount of Ca2+ is in the area
Tension increases as
the series of action potentials(frequency) increases
The nervous system dictates that strength of contraction in each fiber
Via
frequency of action potentials it sends down the motor neuron
One action potential gives us a little contraction
The amount of calcium released into the cytoplasm is not enough for every troponin to be bound to them → only some possible cross-bridges take place
If action potentials are closer together in time the twitches sum up and the tension increases
One action potential occurs and calcium is pumped out of SR while atpase is also working to put calcium back into SR
If second action potential occurs before calcium pump can pump all the calcium back to SR what can occur
the calcium concentration adds up and more can bind to troponin
Occurs because Ca2+ pumps cannot pump the released Ca2+ pumps cant pump the released Ca2+ back into the sarcoplasmic reticulum from before the next action potential arrives
Increases cross-bridging
Tetanus
- A state of smooth and sustained contraction produced when the rate of stimulation is so high that muscle fibers cannot relax between stimuli
- Once you have every troponin with a calcium bound to it you won’t be able to get more cross-bridging and tension is at its max
If ca2+ is released faster from their channels on the sarcoplasmic reticulum faster then
the ca2+ pump can send it back into the sarcoplasmic reticulum, then the force of contraction will increase
When you need more strength:
Use
larger motor units but also send more action potentials so that you can contract more strongly
Not all skeletal muscle fibers are the same
One of the ways they differ is
how they generate ATP
How do we get ATP from muscle cells?
Muscles have three systems for obtaining ATP
Immediate system
Glycolytic system
Oxidative system
Immediate system for obtaining atp
creating phosphate (anaerobic)
Uses creatine-phosphate which can rapidly generate ATP
Only enough for a few short bursts of energy
Glycolytic system
(anaerobic)
Metabolizes carbohydrates to pyruvate and lactic acid
Get 2 atp
Oxidative system
(aerobic) → require oxygen
Metabolizes carbohydrates and fatty acids to H2O and CO2
Get about 26 or 28 atp
When you are exercising you can’t deliver enough oxygen to meet the needs of your muscles
Why you can only run at full speed for a short time
Limited by lack of oxygen
Muscles become fatigued → lactic acid build up
solution for muscle fatigue
For short intense contractions muscles use Creatine-P and Glycolysis for ATP synthesis (not enough oxygen for oxidative phosphorylation)
The anaerobic or glycolytic ATP generation
Anaerobic ATP generation causes lactic acid buildup which fatigues your muscles (glycolysis) → eventually have to stop
Pant to get oxygen back → oxidative phosphorylation to catch-up
Lactic acid goes back to pyruvate and then goes to oxidative phosphorylation
Happens when you exceed limits of circulatory system to deliver oxygen to _
slow oxidative muscle fibers
(contraction speed, major atp source, rate of fatigue, mitochondria, muoglobin content)
slow contraction speed
aerobic respiration
slow rate of fatigue
many mitochondria
high myoglobin content (red muscle)
fast oxidative muscle fibers
contraction speed is fast
major atp source is aerobic respiration
intermediate rate of fatigue
many mitochondria
high myoglobin content
fast glycolytic muscle fibers
fast contraction speed
major atp source is glycolysis
fast rate of fatigue
few mitochondria
low myoglobin content (white muscle)
Myoglobin draws oxygen to muscle cell from
interstitial fluid
In a muscle we will have motor units that are slow twitch and fast twitch
what is the difference in structure
Fast twitch motor units are bigger
Used for big strenuous actions
Fast-twitch vs Slow-twitch fibers
Fast twitch
Enable brief, rapid, powerful contractions
Fast-twitch fibers can be either glycolytic or oxidative
Slow-twitch
Contract more slowly but sustain longer contractions
Slow fibers have less sarcoplasmic reticulum than fast fibers and pump ca2+ more slowly
All slow-twitch fibers are oxidative
Q: during an aerobic exercise
a.Your muscles fatigue quickly due to lactic acid build up
b.Your muscles generate ATP via oxidative phosphorylation
c.The use of oxygen by your muscles does not exceed supply
d.Your muscles switch from using atp to power cross-bridging to using lactic acid
e.More than one of these is correct
(E) b and c are correct
Cardiac muscle
Found only in the heart
Has sarcomeres
Consists of Striated cells that are electrically connected by intercalated disks
Only one nucleus per cell
Electrically connected via gap junctions
Have action potentials that are conducted through gap junctions
Cardiac muscle can generate action potential without
neural input
smooth muscle
Cardiac and smooth muscle cells are arranged in sheets
Cells in the sheets are in electrical contact via
gap junctions
gap junctions allow for
action potential in one cell can spread to all others in the sheet
Synchronize contractions
Smooth muscle
Not muscle you think about to move
Simplest muscle cells structurally
Found mainly in walls of hollow organs such as those of the circulatory, digestive, and reproductive systems
Contractions are relatively slow and may be initiated by the muscle themselves
Relatively weak
Contractions may also be caused by stimulation from neurons in the autonomic nervous system
smooth muscles lack striations becausr
the actin and myosin are not regularly arrayed
Calcium ions enter the cytosol through the plasma membrane
They don’t have a sarcoplasmic reticulum
Interacting network that contracts the whole cell
