The central (brain) and peripheral (spinal cord, etc.) nervous system: Stretch receptors (what are these? Find the definition!) Example: doctor hits your knee with a hammer A reflex arc: the most simple circuit ? input and output Motor neuron anatomy: Myelin sheaths are crucial for a fast response What is the basis for neural signals? They are charged Sodium-Potassium Pump (see animation) Energy compared to a water turbine Death means that there?s no energy to pump ions anymore Energy release requires energy production Another Basic Principle: Protein change configurations due to changes in their external electrostatic environment (e.g. Na-K pumps, Na, K voltage gated channels, enzymes) Like charges repel, opposite charges attract Nerve Cross-section: What is a nerve impulse? (see animation) How and why do action potentials move along nerves? Voltage gated channels allow them to move down the axon MUSCLE STRUCTURE AND FUNCTION 11/14/08 Outline of Today?s Material: A. Macro to micro muscular structure/organization 1) Muscle opposition: figure 49.27 2) Macro to molecular structure: figures 49. 28 , 49.29 , 49.30 3) Muscle cell twists in structure, function: 49.31 B) Structure-function connections 1) Calcium and molecular exposure: figure 49.31 2) The molecular contraction cycle: animation, 49.32, 49.33 3) Controlling muscle power: twitch vs. tetanus: figure 49.35 C) Neuro-muscular anatomy: Motor units: figure 49.34 D) Contraction in two dimensions: only in lecture E) What your book doesn't show you 1) Muscles and molecules in three dimensions: only in lecture 2) Contraction in three dimensions: only in lecture Effects of Pesticide Exposure A long cell Myofibrils are the actual contracting part of the muscle Black and white part derived from electron micrographs Two key parts Z-line: anchor for the elements, flat plate Actin filaments: thin Myacin: thick filaments Interact with each other to cause the muscle to contract Actin looks like a twisted string of pearls with a hot spot on each pearl Contraction Sequence: Actin and myosin are spaced out b. The gap has closed some - The actin is pulled together because the myosin is grabbing and pulling it c. The gap has closed completely Myosin : Two daffodil bouquets with the stems overlapping and the blooms to the left and right . ?Hot spot? has electrostatic properties. ?Rowers? pull in opposite directions. How do we turn the process on and off? Calcium binding to the sites allows myosin binding sites to expose so the muscle can contract. Calcium comes from the sarcoplasmic reticulum. The Nerve Impulse: Calcium takes the place of Sodium in maintaining the voltage (polarization) of the muscle cell Calcium storage/release causes the muscle contraction Voltage gated channels for calcium. T-tubule: communication system with the interior. Causes stored Ca+ ions to be released. Must have ATP to maintain ion pumps, sequester calcium, to make muscles contract. The muscle uses a lot of energy. What happens to the muscle electrically? Many signals sent tetanus Engaging more and more muscle fibers Muscles are attached to tendons which are attached to bones Blood vessels cause the swelling during weight training, circulation is improved, not actual muscle mass. Electron micrograph of muscle cross-section: The most compact arrangement you can possibly have, actin reaching out in six directions.
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