Muscle Physiology!!!

Now that we’ve covered bones, let’s move onto muscles and how they work. I will be focusing on the physiology. To try to explain this clearly, we’re going to go through a set of steps that cause the muscle to contract.

First there is a neuron. This neuron transmits neurotransmitters, which are hormones that cause chemical reactions. They release the neurotransmitters when the dendrites receive a signal and shoot it down the axon and to the synaptic bulb. In the bulb, the neurotransmitters are floating around in synaptic vesicles. They are then released through the pre-synaptic membrane into the synapse. In our case now, the synapse is located between the neuron and a muscle fiber.

Once the neurotransmitters are released in to the synapse, they vibrate until they attach to their neurotransmitter specific receptors which are located on the sarcolemma (cell membrane of the muscle fiber). In our case, the neurotransmitter to activate a muscle fiber is acetylcholine. Once acetylcholine binds to the muscle fiber, sodium specific channels open. Sodium rushes into the interior of the muscle fiber. Once its threshold is reached, the sodium gates close. Then potassium gates open and potassium rushes out of the muscle fiber into the synapse. This causes an action potential which activates the muscle fiber. This signal travels along the muscle fiber cause sodium voltage gates channels to open and this action repeats down the sides of the muscle fiber with a wave of voltage.

For the muscle to makes it’s movements, there is a presence of calcium. In the muscle fibers, there is a t-tubule system which takes this wave of voltage and charges the sarcoplasmic reticulum. This open the calcium channels and allows calcium to rush out. This causes thick and thin filaments, myosin and actin, respectively, to be shifted to make a movement. This happens because the actin and the myosin are very close together. There are myosin heads located on the myosin. The myosin heads bind to a receptor on a thin filament and shoot ATP which drives the thin filaments forward. The myosin heads, when driven forward, pop out of the receptor and latch onto another one. This repeats as the heads move down a line, causing a contraction.



Picture taken from: http://en.wikipedia.org/wiki/Myofibril