Muscle Pt 2 (S.M contraction initiation/termination) Flashcards
what are the 2 types of motor neurons?
- upper motor neuron = primary motor cotex –> spinal cord
- alpha (lower) motor neuron = spinal cord –> muscle fibers
the neurotransmuscular junction refers to . . .
area where motor neuron makes synaptic contact with muscle fiber
The AP created by one motor neurons will cause a rxn ______ on all of its connected fibers
spontaneousy
alpha motor neurons are _____ with ___ diameters that creat fast AP
mylenated with large diameters
what is a nuerodegenerative motor neron disease? Ex?
its a death of a lower (somtimes upper) motor neuron due to disuse that results in loss of muscle control
“if you dont use it = you loose it”
What are the 3 components of the neuromuscular junction:
- Presynaptic motor neuron filled with synaptic vesicles
- The synaptic cleft
- Postsynaptic membrane of the skeletal muscle fiber
T?F Input can either be inhibitory/excitatory in skeletal muscle.
false = only ever excitatory
How does nueral transmission stop at the neurmuscular junction?
remaining Acetyl CoA in synaptic cleft will either diffuse away or be broken down by the enzyme acetylcholineresyerase into aceate & choline. choline returns to motor neuron for reuse by choline acetyltransferases to make acetylcholone
What does autoimmune mean?
your body makes antibodies to ACho receptors and block them, making the synapse to be ineffecient due to decrease in receptors & therefore AP = leads to loss in muscle movement (Ex. myasthenia gravis)
AP propogate from the sarcolemma (cell membrane) into the muscle fiber via ___________ network
transverse (T-tubule) network
the T-tubules penetrate into the muscle fiber and wrap around each ____ at the __ & __ band
wrap around myofribril at A & I bands
AP propogation down the T-tuble triggers __ release from the ____
Ca+ release from the sarcoplasmic reticulum
The ultimate intracellular signal required to trigger contrcation in ALL muscle types is ___
an increase in intracellular Ca+ (wether gained from extracelllar spaace or internal release (SR))
excitation-contraction coupling refers to . . .
the process by which electrical excitation of the surface membrane tiggers an increase of Ca+ in muscle
excitation-contraction coupling refers to . . .
the process by which electrical excitation of the surface membrane tiggers an increase of Ca+ in muscle
T-tubules are neighbeired by x2 __ (specialized region of SR) to form a ____
terminal cisternea to form a triad
T/F T-tubules bring Ca+ into interior of muscle fiber
False - T-tubules bring AP into interia
How is an AP initiated in a muscle?
- Somatic motor nuerons release ACho at neuromuscular junction
- Net entry of Na+ via ACho receptors on the motor end plate starts the muscle AP
Where are DHP & RyR receptors located? what are they?
DHP = L-type Ca+ voltage channel = on sarcolemma
RyR = Ca+ release channel = on sarcoplasmic reticulum
In some muscles, this receptors are mechanically linked (not in all though, ex. cardiac)
What alters the conformatino of the DHP receptor? What is the result?
AP recieved from T-tuble (depolarization) –> structural change in receptor –> pulls opens the RyR = which results in Ca entering cytoplasm {skeletal}
For the muscle types in which these receptors arn’t linked (cardiac), the RyR receptor can also be activated by Ca+ induced Ca+ releae (this is not a big factor in skeletal)
The increase in intracellular Ca+, triggers _____ by removing the ___ of cross bridge cycling
triggers contraction y removing the inhibition of cross brdige cycling
What terminates muscle contraction requires . . .
removal of Ca+ –> which will lead to the myosin binding sites on actin to be covered by tropomyosin
stoping AP won’t stop contraction, only once there is no excess Ca+ in the intracellular space to alow for cross-bridge cycling will contraction stop
What are x2 intracellular Ca+ removal options?
- Ca+ leaves to extracellular space via Na-Ca exchanger or Ca+ pump (doens’t happen often)
- Ca+ is reuptaken into SR via SeRCA pump (Main destination)
High Ca+ in SR blocks the SERCA pump to stop more intake
Calsequestrin & calreticulin store Ca inside SR to allow for more CA uptake
When Ca+ is removed, the ___ shifts to once again cover the ___
torpomyosin shifts to cover myosin binding sites
What is Rigor Mortis
when the cross bridge cycleing remain in a latched state (due to Ca+ leake that binds to troponin), with your body unable to make more ATP to release myosin head from actin
development of rigid muscle, hours after death
