^^Images for my project can be found here.
There are many intricacies we do not think about when contracting a muscle. Firing a muscle is not just a thought, it takes place through many steps. In relation to how complex activating a muscle is, is similar to how an airport works, both inside and out. My project further explains how a neuromuscular junction excitation is similar to how an airport works and overall just hopefully give everyone another way to envision what is happening.
To begin, when you want to fire a muscle you first have to have the idea. The junction consists of the points of contact between axon terminals of a motor neuron and the motor endplate of a skeletal muscle fiber. Nerve Impulses (action potentials) travel from the brain/spinal cord to trigger muscles. Then there are seven consecutive steps that occur in order to fire the muscle altogether.
Step one: an action potential travels down a motor neuron and excites a skeletal muscle fiber.
Step two: voltage-gated calcium channels open and calcium ions diffuse into the terminal.
Step three: calcium ion entry causes synaptic vesicles to release acetylcholine via exocytosis.
Step four: acetylcholine diffuses across the synaptic cleft and binds to acetylcholine receptors which contain ligand-gated cation channels. The ligand-gated channels open.
Step five: sodium ions enter the muscle fiber and potassium ions exit the muscle fiber.
Step six: once the membrane potential reaches the threshold value an action potential travels along the sarcolemma.
Step seven: neural transmission to a muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Acetylcholine diffuses from the synapse. Acetylcholine is broken down by the enzyme acetylcholinesterase to acidic acid and choline is transported to the axon terminal for the resynthesis of acetylcholine.
After all of these steps are complete, a muscle can contract. A correlation can be made between this process and how an airport works. This brochure includes the differences between the body and how it is connected, on the inside right-hand page. To better understand each step, you must read one step on the inside and compare it to the step on the back. Each sentence is paralleled to the next to better understand both standpoints. Similar to step one above, we can see that an action potential travels down a motor neuron and excites a skeletal muscle fiber. In this case, an action potential is an airplane, a motor neuron is a flight route, and a skeletal muscle fiber is an airport.
Step two explains how voltage-gated calcium channels open and calcium ions diffuse into the terminal. In this instance, the voltage-gated calcium channels are the jet bridge walkways, and the calcium ions themselves are the gate agents flowing into the terminal. The following steps are the same.
An airport and neuromuscular junction both have many steps, either to firing a muscle or getting a plane off the ground. Similarly, they both occur in many places: all over the body or all over the world. They are constantly being used simultaneously in many locations.