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  • Hey Tracy, has anyone ever taught you about muscle contraction?
  • Let's go through the steps together. I think I know some about the subject.
  • First, muscle contraction begins by nerve impulses in the central nervous system. The impulse is sent by what is called the motor neuron to the motor end plate (also known as axon terminal).
  • Yeah and then when that happens the neuromuscular junction (NMJ) is where the motor unit (the motor neuron and muscle) meet. In time, the neuromuscular junction is depolarized in context with Na+.
  • Oh don't forget there is a gap at the NMJ, called the synaptic cleft! This fills with a neurotransmitter - Acetylcholine (ACh).
  • Exactly, so ACh triggers the receptors of the muscle fibers called sarcolemma to accept the Na+. As the ACh attaches to the sarcolemma, it becomes temprorarily more permeable to Na+ and K+. When the balance of Na+ and K+ is restored, the NMJ is repolarized.
  • So,after ACh is used it is then dissolved by an enzyme called acteylcholinesterase?
  • Yes! Afterwards, an increase of Na+ creates an action potential.
  • Oh okay, so at the NMJ mitochondria produce ATP and release energy for the muscle to contract. ATP is made from ADP +P (Creatine phosphate).
  • Then the action potential triggers the release of Ca+.
  • And this causes the myosin heads to move the actin filaments across and move the sarcomere unit together to form a contraction.
  • Finally, remove the contraction Ca+ is absorbed and actin slides back muscle relaxes.
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