What are the detailed steps for a muscle contraction?in as much detail

Expert Answers
dano7744 eNotes educator| Certified Educator

It depends on which muscle you are asking about. You have skeletal muscles which are under voluntary control and you have cardiac muscle that is under involuntary control.

When skeletal muscles contract you have a conscious thought to move (contract) them. For example, when sitting at your desk you decide to get up and walk outside. Skeletal muscle would enable you to do this. Several things must happen. Your brain (the thought) tells your body to get up. The muscles that allow you to do this must contract. A motor neuron sends chemical messengers to your skeletal muscles. These are called neurotransmitters. The neurotransmitter for skeletal muscle is acetylcholine. This chemical crosses synapses from one nerve to the next. This sets in motion a series of events that make you move. You need sufficient amounts of anions--charged particles like sodium,potassium,magnesium, and calcium to further propagate the muscular contraction (movement). These anions move into and out of the skeletal muscles which create an electrical potential that moves the muscles.

If the muscle is the heart, you do not have to have a conscious thought to make your heart beat. The myocardium is innervated by the vagus nerve (10th cranial nerve). Some of the same anions must be present in the correct amounts to make the heart beat, especially calcium and potassium.

charles85 | Student

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(a)Muscle contraction is starting from central nervous system, by brain or spinal cord.

(b)A motor neuron in the spinal cord is activated, and an action potential passes outward in a ventral root of the spinal cord.

(c)The axon branches to supply a number of muscle fibers called a motor unit, and the action potential is conveyed to a motor end plate on each muscle fiber.

(d) At the motor end plate, the action potential causes the release of packets or quanta of acetylcholine into the synaptic clefts on the surface of the muscle fiber.

(e) Acetylcholine causes the electrical resting potential under the motor end plate to change, and this then initiates an action potential which passes in both directions along the surface of the muscle fiber.

(f)At the opening of each transverse tubule onto the muscle fiber surface, the action potential spreads inside the muscle fiber.

(g)At each point where a transverse tubule touches part of the sarcoplasmic reticulum, it causes the sarcoplasmic reticulum to release Ca++ ions.

(h)The calcium ions result in movement of troponin and tropomyosin on their thin filaments, and this enables the myosin molecule heads to "grab and swivel" their way along the thin filament. This is the driving force of muscle contraction.