Chapter 7-NMJ Flashcards
What is the motor eng plate?
the nerve fiber branches and invaginates into the surface of the muscle fiber, but lies outside the muscle fiber plasma membrane. It is insulated from surrounding fluid by Schwann Cells.
What is the synaptic trough/gutter?
invaginated membrane between axon terminal and muscle fiber membrane
What are the subneural clefts?
folds of muscle fiber membrane which increases surface area for synaptic transmitter action
What is the fxn of acetlchoniesterase?
a) Breaks down ACh that remains the synaptic cleft, otherwise the ACh would continuously stimulate the ACh receptors.
How is ach synthesized?
ACh is synthesized in the cytoplasm of the terminal. Mitochondria provide the ATP for synthesis.
How is Ach packaged?
vesicles are formed by the Golgi in the cell body of neuron and are transported, via axoplasm, down the core of the axon to the NMJ. ACh is synthesized in the cytosol of the nerve fiber terminal and is immediately transported into the vesicle
How is Ach secreted?
On the inside surface of the neural membrane are linear dense bars which are associated with voltage-gated calcium channels. When an action potential reaches the terminal it opens the Ca channels allowing Ca to enter the cell from the cleft. The Ca causes the ACh containing vesicle to fuse with membrane and release ACh into the cleft.
What happens when Ach binds to its receptor?
a) When ACh binds to the ACh receptors on the post synaptic membrane it opens them, this allows positive ions (Na, K, Ca) to flow through the channel because the channel has negative charge in the pore. Chloride is not allowed to move through the channel.
b) Na flows into the cell while K flows out. More Na flows into the cell then K out because the charge of the membrane within the cell is negative. The negative potential pulls Na in and prevents K from flowing out.
i) More Na flowing in creates local positive potential charge inside the muscle fiber membrane called End Plate Potential.
What is an end plate potential?
a) End Plate Potential: More Na flowing into the muscle fiber creates local positive potential charge inside the muscle fiber membrane. This increase in membrane potential allows for more Na channels to open allowing Na to enter, which initiates another action potential
What is the RMP of SkM?
i) Resting membrane potential: about –80 to –90 millivolts in skeletal fibers—the same as in large myelinated nerve fibers.
What is the duration of an AP on SkM?
1 to 5 milliseconds in skeletal muscle—about five times as long as in large myelinated nerves.
What is the velocity of conduction of an AP?
3 to 5 m/sec—about 1/13 the velocity of conduction in the large myelinated nerve fibers that excite skeletal muscle.
What is excitation-contraction coupling?
The T tubule action potentials cause release of calcium ions inside the muscle fiber in the immediate vicinity of the myofibrils, and these calcium ions then cause contraction.
What is the calcium pulse?
the time [Ca] is high in the muscle fiber causing contraction. It is longest in heart muscle
