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Biol 273L final notes.docx

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Bruce Wolff

Biol 273L Notes Practice equation calculations Lab 1 Nerve cell job to sustain a difference in electrical charges between the cytoplasm and the surrounding extracellular fluid. Resting membrane potential is due to the cell being more permeable to certain ions that others. K+ are high inside, and Na+ are higher outside. Na cannot diffuse in, but K can, creating a positive change on the outside surface of the cell = RMP. A charge difference can travel as a wave to the cell surface as a graded potential or action potential. This enables the neurons to transmit sensory info to the SC and brain and send signals to effector organs. Ussing chamber –permeable to Na and K, impermeable to Cl and I. Cations pass through the artificial membrane down their concentration gradient  difference in charge. Nernst equation*** Activity coefficient = measure of how independently ions behave when dissolved. Small at low concentrations and high at high conc. Activity = conc * activity coefficient Procedure: make different concentrations of KCl, add 60mL to chambers filling at same time for pressure is equal, and allow air bubbles to flow in at a rate of 5-10 per sec. place electrodes into the chambers  set to a certain mV. Turn the multimeter off after each reading Lab 2 Specialized receptors in the muscle respond to the stretching of the tendon attached to the muscle, then send signals to motor neurons through a single synapse. The muscle fibers depolarize and twitch (contract) in response to the incoming impulse from the motor neuron through a single synapse. The fibers depolarize and twitch (contract) in response to the incoming impulse from the motor neuron. The sensory receptors convey info about muscle length, tension, and pressure to the CNS. These receptors are called muscle spindles. They are arranged in parallel with muscle fibers, and the spindles are stretched when the muscle is stretched by an external force. Therefore, these receptors play a significant role in developing antigravity reflexes and maintaining muscle tone. Muscle spindles contain a small bundle of intrafusal fibers which do not contribute to the overall tension of the muscle, but regulate the excitability of the sensory afferent spindle nerves by innervated gamma motor neurons. Majority of the muscle consists of extrafusal fibers, which are innervated by alpha motor neurons and responsible for developing muscle tension. When a muscle is stretched, this excitation of its muscle spindles causes a reflex contraction
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