Lecture 6+7: Muscle Physiology Flashcards
steps in neuromuscular transmission?
- AP at neuromuscular junction
- Ca+ release
- myosin and actin interaction
- muscle contraction
- Ca+ removed
- Relaxation
the neuromuscular junction is what type of synapse?
Chemical
opening of ACh receptors results in what?
end plate potential (EPP)
each vesicle release of ACh causes a miniature _____
miniature EPP
what effect does end plate potential cause
EPP depolarizes the membrane and initiates APs
the summation of multiple miniature EPPs produces an _____
EPP
EPP is a _______ localized to the motor end plate
EPP is a GRADED POTENTIAL
what does EPP magnitude depend on
the amount of and duration of ACh at the end plate
what factors affect the magnitude of the EPP
- voltage gated Ca+ channel function
- amount of ACh released
- rate of ACh breakdown
- Ach receptor agonists and antagonists
site of Calcium storage inside the muscle
Sarcoplasmic reticulum (SR)
- Ca is released for contraction
what does tropomyosin (Tm) do
tropomyosin inhibits the binding of myosin to actin
what does Troponin (Tn) do
Troponin is a Calcium sensitive molecular switch
— the presence of Ca causes troponin to interact with tropomyosin and make binding sites for the myosin heads available
what is the role of calcium in the regulation of myosin binding to actin
Ca binding to troponin complex allows for the repositioning of the tropomyosin filament, this repositioning exposes the mysoin binding sites on actin molecules
The sliding of actin along the myosin filament results in the _____ of the sarcomere
shortening (contraction)
what are the steps in neuromuscular transmission?
- An AP arrives in the presynaptic motorneuron axon terminal
- opening of voltage-gated Ca+ channels & entry of Ca into axon terminal
- release of ACh from synaptic vesicles into the synaptic cleft
- ACh diffuses into sarcolemma
- ACh binds to its receptors on the motor end plate within the sarcolemma, increasing the conductance of the motor plate for Na and K, resulting in an EPP
- Depolarization of the muscle membrane adjacent to the motor end plate reaches threshold & opens voltage-gated channels that initiate an AP on the sarcolemma
- degradation of acetylcholine by acetylcholinesterase (AChE)
what is a myosin molecule (thick filament) composed of
two proteins twisted together forming a tail with two heads (cross-bridge)
A single thick filament consists of many myosin molecules
what is an actin (thin filament) in a sarcomere composed of
3 types of proteins: actin, tropomyosin, troponin
the power stroke of myosin results in filament sliding and muscle _____
contraction
what is the role of Ca in muscle contraction?
- AP arrives at axon terminal of motorneuron
- opening of voltage gated Ca channels and entry of Ca into axon terminal
- release of ACh into synaptic cleft - Upon activation, Ca is released for contraction
- membrane depolarization opens L-type Ca channels - Mechanical coupling b/w L-type Ca channel and the Ca release channel causes Ca release channels to open
- Ca leaves the SR via the Ca releasing channel and activated troponin
- Ca binding to troponin complex causes the physical repositioning of the tropomyosin filament, which exposes the myosin binding site on actin molecules
what removes Ca from the ICF back into the SR and why does this happen
the sarcoplasmic reticulum Ca+ ATPase (SERCA pump)
this occurs for the purpose of relaxation / to prepare for the next contraction
how is Ca removed from ICF to the ECF
by sarcolemmal Ca+ ATPase and a Ca/Na exchanger
the Ca/Na exchanger is an example of 2ndary active transport because….
it uses the gradient for Na to
an action potential travels through the entire sarcolemma and into the ______
transverse (T) tubules
when Ca is released into muscle fiber, it causes a ______ of the T-tubules
depolarization
