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BIO 20B Lecture 10

by: Ku'u Tai

BIO 20B Lecture 10 BIOE 20B

Ku'u Tai

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These notes cover the tail end of action potential for the nervous system and the beginning of the muscular system.
Developmt & Physiol
Class Notes
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This 3 page Class Notes was uploaded by Ku'u Tai on Thursday February 11, 2016. The Class Notes belongs to BIOE 20B at University of California - Santa Cruz taught by Dunkin,R.C. in Winter 2016. Since its upload, it has received 19 views. For similar materials see Developmt & Physiol in Biology at University of California - Santa Cruz.


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Date Created: 02/11/16
BIO 20B WEEK 6 LECTURE 10 NOTES Action Potential & Muscular System TEST YOURSELF 1 What is the relationship between a graded potential and an action potential? 2 What is the threshold? 3 Why is an action potential all or none - can you explain in terms of what is happening to the voltage gate channels? 4 An action potential is an example of a positive feedback loop - can you explain why? THE CHANGE IS PROPAGATED DOWN THE NEURON IN A FAST, SELF-PROPAGATING WAY Hyperpolarization (undershoot phase) = refractory period  During this period Na+ inactivation gates remain closed  This period is known as the absolute refractory period o Because another action potential cannot fire o Sets the maximum rate at which a neuron can fire  Because the gate is closed, another AP cannot be generated for 1-2 ms  The refractory period sets a maximum frequency for which action potential can be generated o Think a toilet needs to refill before next flush CONDUCTION OF ACTION POTENTIALS 1 AP's must travel in one direction and their strength not diminish across the length 2 AP's regenerate themselves along the axon 3 Zone of hyperpolarization directly behind AP prevents AP from spreading backwards SPEED OF AP's 1 Neuron size: a Larger neurons will conduct the AP faster 2 Myelin sheaths also increase the speed of action potentials in vertebrates NODE OF RANVIER  In between the myelin-encased Schwann cells Saltatory conduction - leaping along the Neuron speeding up the signal AP's jump from node to node MULTIPLE SCLEROSIS The patient's own body destroys myelin as if it were a foreign substance impairing function of myelinated neurons controlling movement speech, memory, and emotion. WHEN ACTION POTENTIAL ARRIVES AT THE OTHER END OF NEURON, T WILL RESULT IN RELEASE OR INHIBITION OF NEUROTRANSMITERS How does the information in a cation potential get transmitted to other cells? 1 Neuron to Neuron a Electrical synapses are gap junction which allow the electrical current to be propagated to the next neuron 2 Neuron to neuron OR to other cell a Chemical synapses are areas where neurotransmitters are released from synaptic vesicles in response to the action potential b Neurotransmitters are released from vesicles via exocytosis into the synaptic cleft. They then bind to receptors on the postsynaptic cell. Chemical synapses Postsynaptic synapses can be either: 1 Excitatory: cause postsynaptic cell to depolarize 2 Inhibitory: cause postsynaptic cells to hyperpolarize Contributes to major complexity of nervous system ***NEED TO KNOW: Acetylcholine Dopamine GABA GABA AND THE GABA RECEPTOR  GABA is a neurotransmitter that has an inhibitory effect on neurons  When GABA attaches to its receptor on the postsynaptic membrane, it allows Cl- ions to pass into the neuron  This hyperpolarizes the postsynaptic neuron to inhibit transmission of an impulse ALCOHOL AND THE GABA RECEPTOR  When alcohol enters the brain, it binds to GABA receptors and amplifies the hyperpolarization effect of GABA  The neuron activity is further diminished  This accounts for some of the sedative effects of alcohol LOCOMOTION AND THE MUSCULAR-SKELETAL SYSTEM HOW DO MUSCLES MOVE BONES  Muscle is a grouping of cells (muscle fibers)  Ligaments link bones to bones or bones to cartilage  Tendons link bones to skeletal muscle  Skeletal muscle fibers increase in size during growth but under normal condition no new fibers are formed o Increase in size NOT quantity SLIDING FILAMENT THEORY OF CONTRATION  Muscle shortens when it contracts and this causes movement of the skeletal system How do muscles shorten? Sliding Filament Theory  Muscles are composed of a series of smaller and smaller unis  A single muscle is composed of muscle fibers (cells)  Muscle fibers are single cells with multiple nuclei  Each muscle fiber (muscle cell) is composed of smaller units called myofibrils  Myofibrils are composed of two kinds of filaments: 1. Thick filaments i. Composed of the protein myosin 2 Thin filaments i. Composed of two strands of actin protein and a regulatory strand of protein coiled together Muscle Muscle Fibers (cells) Myofibrils Thick Myosin protein strand filaments Thin 2 actin protein strands; 1 regulatory protein strand all filaments coiled together The functional unit of the muscle is the sarcomere.


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