Stimulation and Contraction of Single Skeletal Muscle Cells Elliett baca Period 5

overview Muscle cells perform the way they do due to special functional properties 1. Excitability, the ability to receive and respond to a stimulus 2. Contractility, the ability to shrink when stimulated 3. Extensibility is the ability of muscle cells to be stretched 4. Elasticity is the ability to pull back and return to its default position

Structure In order to contract, muscles cells must be stimulated by signals from the nervous system Depending on the muscle and its function, one motor neuron can stimulate a couple to hundreds of muscle cells One neuron and all the skeletal muscle cells it stimulates are a motor unit Long extensions of the neuron (axons or nerve fibers) extend to the muscle and divides into axon terminals Creates neuromuscular junctions, junctions formed with the sarcolemma of another muscle cell The location where the signals are exchanged from the nervous system to the muscle cells

Once the axon receives a nerve impulse, a chemical called neurotransmitter is discharged Specifically, acetylcholine (ACh) is released to activate muscle cells Acetylcholine is then diffused into the synaptic cleft and adheres to receptors If there is enough ACh, the sarcolemma becomes more absorbent and may allow sodium ions to enter the muscle cells and potassium ions which leave the cell. More sodium ions enter the cell than potassium ions leave, which creates an overflow of positive ions in the muscles The cell then creates more passageways for the sodium ions to enter only Action potential, an electrical current, then allows more potassium ions to enter in order to balance it out again, results in the contraction of the muscle cell Meanwhile the action potential is happening, ACh is separated to create acetic acid and choline by enzymes in the sarcolemma

Continued… Action potential, an electrical current, then allows more potassium ions to enter in order to balance it out again, results in the contraction of the muscle cell Meanwhile the action potential is happening, ACh is separated to create acetic acid and choline by enzymes in the sarcolemma Continuous contractions of muscle cells are prevented because a single nerve impulse generates a single contraction

The sliding filament theory When myosin heads that project from thick filaments attach to the thin filaments, they begin sliding Thin filaments are unable to slide back because the myosin heads are always touching the actin The sliding continues during contraction Calcium ions are necessary to activate the sliding between myosin and actin Within the cell, action potentials trigger the sarcoplasmic reticulum to allow calcium ions enter the cytoplasm Once the action potential finishes, the calcium ions are absorbed back into the sarcoplasmic reticulum and the muscle relaxes back to its default length

Question #1 What are special functional properties of muscle cells? A. Conductivity B. Aggressiveness C. Intractability D. Excitability

Question #2 What part of the sarcomere does not shorten during contraction? A. H Zone B. A Band C. I Band D. None of the above

Question #3 How do calcium ions contribute to the sliding filament theory? A. It prevents the sliding between myosin and actin B. It activates the sliding between myosin and actin C. It activates the sliding between the sarcoplasmic reticulum and cytoplasm D. allows the muscle to relax when released into the cytoplasm

bibliography “Essentials of Human Anatomy & Physiology, 9th Edition.” Essentials of Human Anatomy & Physiology, 9th Edition, Benjamin Cummings, n.d. Web. 11 Dec, 2016. Krans, Jacob L. "The Sliding Filament Theory of Muscle Contraction." Nature.com. Macmillan Publishers, 2014. Lewis, Ricki. "ELearning." Life | eLearning. McGraw-Hill Global Education Holdings, LLC., 2016.