Muscle Contraction/Excitation

Muscle Contraction & Excitation Muscle excitation takes place when there is a synaptic transmission and induction of an impulse. There are six steps that take place during muscle excitation. (1)The action potential travels down the somatic motor neuron axon reaching the synaptic bulb causing calcium ions to flow into the synaptic bulb. (2)The increase of calcium in the synaptic bulb causes the synaptic vesicles to undergo exocytosis. (Exocytosis a process that allows large molecule to leave the cell without actually passing through the plasma membrane) It then spits out the contents which is Acetylcholine (ACh) (3) ACh is then released into the synaptic cleft. (4)ACh diffuse across the cleft and binds with the receptors on the motor end plate, known as sarcolemma which is a muscle fiber that mirrors the synaptic bulb. (5)ACh grabs onto the receptor causing Na+ to enter the muscle fiber. This also allows K+ to exit the muscle fiber which causes depolarization and the production of an action potential.
Muscle contraction takes place when the fibers pull on the endomysium which pulls on the perimysium which then pulls of the epimysium to cause the contraction to take place. There are seven steps involved in the physiology of muscle contraction. (1)First an action potential comes down the somatic motor neuron axon and stimulates an action potential on the sarcolemma of the muscle fiber (cell). (2)Then the action potential travels down the T tubules and (3) stimulates the sarcoplasmic reticulum to release calcium into the sarcoplasm. (4)Calcium then binds with the tropomyosin and moves it out of the way exposing the binding sites on the actin. (5)The binding sites are now free for the myosin to attach to them. (6)When the myosin attaches to the actin it forms a cross bridge. At this point we burn an ATP in order for the myosin to grab an actin. (7)The myosin then pulls on actin causing contraction. This is called the “power stroke”. In order for myosin to