Skeletal muscle Flashcards
What is a sarcolemma?
Plasmalemma for muscle cells
What is a sarcomere?
The functional unit of a muscle cell; from one I band to another
What is the sarcoplasmic reticulum?
Where Ca is stored
What is the transverse tubules (T tubules)?
The connection between the outside of a muscle fiber to the outside. Allows for the conduction of electrical signals
What is a muscle fiber?
Synonymous with muscle cell
What is a myofibril?
Cylindrical structure made up of an end-to-end chain of repeating unit, the sarcomeres
What is titin?
The protein that hold the thick filaments to the Z disk
What is dystrophin?
The protein in myofibrils that attached an actin filament to a transmembrane protein
(This is the causitive agent of Duchanne’s muscluar dystrophy)
What is a ryanodine receptor?
The DHP channel located in the Triad
What are DHP receptors?
1
Which is the actin filament (thin or thick)?
Thin
Which is the thick filament?
Myosin
What is the Z-disc made of?
1
What are cross-bridges?
1
What is the sliding filament theory of muscle contraction?
The fact that the thick filaments slide across the thin filaments
What is the role of ATP in muscle contraction?
Detaches the myosin from the actin active site
this is the reason for rigormortis
What is the role of Ca in muscle contraction?
binds to the TnC, moving the actin complex, and allowing the myosin head to attach to the actin filament
Which type of muscle is striated?
skeletal
Which type of muscle have intercalated discs, and many branches?
Cardiac
Which type of muscles have a centrally located nucleus?
Smooth
What type of connections do intercalated discs have?
Electrical and mechanical (d/t pores)
Which type of muscles have multiunit connections to each cell?
Smooth
Smooth muscle cells that have a unitary innervation have what connection between cells? Why?
Gap junctions for transmission between cells
What is the layer of CT around a bunch of fasiculi?
Epimysium
What is the CT layer around a single fasicle?
Perimysium
What is the CT layer around an individual muscle fiber?
Endomysium
What are the dominant organelle in muscle cells?
Mito
What is the sarcoplasma?
The cytosol for muscle cells
What is inside T tubules?
Extracellular fluid
What are the components of a triad? What is the importance of this?
Sarcolemmas x2 + transverse tubule
allows for conduction of signals from ECF to myofibrils
What is the etiology of Duchenne’s muscular dystrophy?
An almost total lack of dystrophin
What is the etiology of Becker’s muscular dystrophy?
Mutated, but still somewhat functional dystrophin
Which part of the mrosin protein actually attach to the actin?
Heads
What is tropomyosin?
The protein that covers the active sites on the actin?
What are the proteins that form the troponin complex?
Tnt
TnC
TnI
What do the troponins bind?
TnT- tropomyosin
TnC- Ca
TnI-actin
What is the chemical changes that allow a detached myosin head to attach to the actin?
Loss of phosphate from head (NOT from ATP)
What is the consequence of ADP being released from the myosin head?
Nothing much (look at slide)
How far do muscle fibers extend?
The length of the muscle
What are the two components to the sarcolemma?
Plasma membrane
Transverse tubules
What is the outer coat of a sarcolemma made of?
A thin layer of collagen
What is the area that is between two Z discs?
sarcomere
What are the two attachments of a titin protein molecule?
Z line
Myosin thick filaments
What is the sarcotubular system?
The system of transverse tubules and sarcoplasmic reticulum
What is the function of the sarcoplasmic system?
Transmits action potential throughout the cell,
What is the function of the sarcoplasmic reticulum?
Stores Ca until signalled by a depolarization to release it into the cytosol
How does dystrophin add strength to muscles?
connecting fibrils to the ECM
What are the two types of striated muscle?
Skeletal and cardiac
What is the only type of muscle that is not striated?
Smooth
What is the component of the I band? (the light band)
Actin
What is the component of the H band?
Myosin
What are the components of the A band?
Where myosin and actin overlap + H band
Which type of muscles are connected by gap junctions?
Cardiac and smooth muscles–in the intercalated discs for cardiac muscles
What are the two kinds of smooth muscle?
Multiunit and Unitary
Where are nuclei found in skeletal muscle cells?
At the periphery
What is the unit of muscle that contains just thick and thin filaments?
Myofibril
What are bunches of myofibrils called?
Muscle fibers
What are bunches of muscle fibers called?
Fascicles
What is the M line?
The central line in the sarcomere
What is the cause of familiar dilated cardiomyopathy?
Titin mutation
What is the cause of hereditary myopathy with early respiratory failure?
Titin mutation
What is the mode of inheritance for Duchenne’s muscular dystrophy?
X-linked recessive
What is the cause of the limb-girdle dystrophies?
mutations of genes coding for other components of the dystrophin-glycoprotein complex and other muscle proteins
What are the components of myosin?
Head (S1 chain)
Hinge region of heavy chains
Tail region of heavy chains
What is tropomyosin, and what is its role in muscle contraction?
The rope like protein that surrounds actin, and blocks the active site until Ca binds
What happens to myosin’s affinity for actin when ATP binds?
Falls
If all cross-bridges in the muscle have ATP bound to them muscle is (contracted or relaxed)?
Relaxed
What happens to the myosin head when the bound ATP dephosphorylates?
Cocks the myosin head into alignment with actin binding site
What must occur to the actin/tropomyosin complex before the ADP-myosin complex can bind?
Ca has to bind to troponin and move tropomyosin out of the way
What triggers the power stroke of the myosin head?
Release of the pyrophosphate
What happens after the myosin head binds to the active site on the actin filament?
ADP is lost (but myosin stays on)
What causes the myosin head to become detached from the actin after ADP has left?
ATP binding
What is the cause of rigor mortis?
Lack of ATP to free myosin from actin
What happens to the I line as a muscle contracts?
Get smaller/disappears
What happens to the A band of the sarcomere as a muscle contracts?
Stays constant
What happens to the H band of the sarcomere as a muscle contracts?
Gets smaller
How does a muscle cell relax?
ATP will help pump out Ca, as well as detach myposin heads from actin
A neuromuscular junction is a “safe” synapse. What does this mean?
only one action potential in pre-junctional neuron is necessary to cause an action potential in muscle cell.
What type of synapse innervates muscle cells?
The motor plate
How does the action potential spread through a muscle cell (through what structure)?
Through T tubules
What is the neurotransmitter used at motor plates at the neuromuscular junction?
Acetylcholine
What does acetylcholine bind to? What does this cause?
Acetylcholine receptor, which causes K to go out slightly, but Na to rush in a ton
In the triad, where is the action potential? Where is Ca stored?
Action potential is an element of the T tubule
Ca is stored in the sarcoplasmic reticulum
What are the voltage gated channels in the T tubules that open to allow Ca to rush in?
L-type (DHP) channels
When the DHC (L-type) channels open, what does this cause in turn?
The Ca channels on the sarcoplasmic reticulum side to open
The Ca++- release channels on the sarcoplasmic reticulum are also called what?
ryanodine receptors.
What are the proteins that enable the sarcoplasmic reticulum to pump Ca against its gradient?
Calsequestrin and Calreticulin
What are the three ways that Ca is pumped out of the cytosol of muscle cells?
Pumped into sarcoplasmic reticulum by ATP pumps
Pumped out via Ca pumps
Antiport with Na
What is the purpose of phosphocreatine?
High energy molecule that can regenerate ATP from ADP in times when ATP demand exceeds supply
What is the breakdown product of creatine?
Creatinine
What is the other source of energy for working muscle besides creatine?
Glycogen
What is a motor unit?
A small group of nerves with the muscles they innervate
What is a motor neuron pool?
All of the motor units that collectively innervate an entire muscle
Muscle that need very fine motor control (such as the eyes) have what type of motor units? (very small or very large)
Very small
How do muscles achieve graded contraction? (2 ways)
Increase/decrease the number of motor units at any one time
Summation effect of action potential -> Ca released before taken back up
True or false: There is a very short delay between end of AP and development of muscle tension
True
Continuous state of full activation of muscle is called what?
tetany or tetanization
What prevents the heart from reaching tetany?
Longer action potential (d/t [Ca])
True of false: an action potential in motor neuron will cause AP in all the muscle fibers of that motor unit
True
What is isometric contraction?
When a muscle does not shorten during the contraction
What is isotonic contraction?
When a muscle does shorten during a contraction but the tension on the muscle remains constant.
When using muscles normally, what type of contraction is being used: isotonic or isometric?
Both
When is the most tension present in a sarcomere?
When all the myosin heads are attached to an actin filament
What causes the decrease in tension as sarcomeres shorten to their ends?
Abutment of the actin filaments
When looking at a curve of passive vs total tension, what is the active tension?
The difference between the two curves
