Synaptic transmission and contraction coupling Flashcards
what are gap junctions used for
transmission of an electrical signal from one cell to the next
found in the heart and the eye
Synaptic transmission: Chemical
utilization of a neurotransmitter
can be excitatory or inhibitory
the presynaptic cell can signal one or many postysynaptic cells
postsynaptic cell can receive signals from one or many presynaptic cells
How many signals does a postsynaptic cell recieve?
it recieves one signal from only one presynaptic axon
If a patient presents with flaccid paralysis what might be one way this is caused
lack pf uptake of Ca2+ through the ionic gated channels of the presynaptic cell
What is the percentage of choline that gets reuptook after AChE breaks ACh down
about 50 percent
thats why if a AChE inhibitor is used, inittially there is contraction but after time there is no choline to be re uptaked so thre is paralysis of that muscle due to lack of ACh production
what happens to the threshold if the AChR of the post synaptic cell are stuck open
it will eventally increase because they will be open for so long that eventually there is not gonna be enough receptors to fly open to get more influx of Na+
this is also because they are already so depolarized
What happens once the signal travels down the T tubules
the AP causes the DHP receptor to physically alter its state of the Ryanodine receptors (occurs in skeletal tissue, in cardiac it is the release of Ca+) (RyRs) causing the Ca++ channel to open
Ryanodine receptors of SR to open
Ca++ diffuses to troponin component of actin and bind which causes the tropomyosin to pull off the binding sites of actin so that myosin can bind actin
What could lead the body to have increase temperature after anestesia
the ryanodine receptors inabillity to close
or constant activation of dihydropyridine receptor which activates the RyR and release of Ca++
process of contraction with the myosin and actin
1) in the rigor state tight binding of the myosin with the ADP bound
2) ATP binds the myosin and the myosin releases the actin
3) the ATPase activity of the myosin hydrolyzes the ATP this makes the myosin head swing and bind weakly to the actin
4) then the pi is released causing the power stroke causing the myosin to pull the actin
5) then the ADP is released and the myosin still stays bound in the rigor state
Relaxation
at the termination of the AP the SR begins sequestering the Ca++ via the Ca++/ATPase pump
removal of the Ca++ causes the binding sites to again be covered
myosin is no longer able to complete its cycle of pulling of actin
Force of contraction
two factors: the strating length of the sarcomere
the optimal force is found to be generated near the middle of length extremes
2nd is how rapidly the fiber is stimulated by the nerve or frequency
overlap of twitches such that complete relaxation is not achieved between them is referred to as tetanus and that increases the force
Types of contraction deal with the type of innervation as well
a neuron that innervates more fibers will generate an increased force
more glycolytic fibers will generate a greater force but fatigue quicker
and more motor neurons and their units will generate a greater force this is called recruitment
