Week 6 - Functional Anatomy and Pathophysiology I: Lecture Notes
Week 6 - Functional Anatomy and Pathophysiology I: Lecture Notes PHCL 2600
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This 4 page Class Notes was uploaded by Audrey Hernandez on Sunday October 2, 2016. The Class Notes belongs to PHCL 2600 at University of Toledo taught by Dr. Frederick Williams in Fall 2016. Since its upload, it has received 6 views. For similar materials see Human Anatomy and Pathophysiology in Biology at University of Toledo.
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Date Created: 10/02/16
Functional Anatomy and Pathophysiology I Dr. Frederick E. Williams Week 6 Lecture Notes Propagation continued ❖ Continuous propagation ➢ Happens over a short distance ➢ Progresses down the axon slowly step by step ❖ Saltatory propagation ➢ Action potentials will leap from node to node as the myelin sheath has some resistance to depolarization ■ Each node undergoes depolarization process ➢ Saltatory conduction ■ Channels tend to be more condensed around the nodes of ranvier than the myelinated segments of the axon ❖ Workings of local anesthetics ➢ Lidocaine ■ Prevents the opening of sodium channels so that no ion influx can take place ● No depolarization occurs ● No action potentials are created ● No signals are sent to “feel” the pain ❖ Factors of speed for propagation ➢ The amount of myelination that has occurred ■ The more myelin sheath there is, the faster the action potential can jump from node to node ➢ Diameter of the axon ■ The larger the diameter, the quicker the the propagation can occur ➢ Temperature ■ Speed will decrease as temperature is lowered Neurotransmission ❖ Types of synapses ➢ Presynaptic ■ Sends the signals ■ Contains vesicles containing neurotransmitters ➢ Postsynaptic ■ Receives signals ■ Has receptors to bind vesicle to chemical ligands ➢ Electrical synapses Functional Anatomy and Pathophysiology I Dr. Frederick E. Williams Week 6 Lecture Notes ■ Conducts directly between two cells at gap junctions ➢ Chemical synapses ■ Information is relayed by chemical neurotransmitter ■ Released through the synapse gap ■ Types ● Axodendritic synapse ◆ Axon terminal comes close to the dendrites of the postsynaptic neuron ● Axosomatic synapse ◆ Axon terminal comes close to the soma (cell body) of the postsynaptic neuron ● Axoaxonic synapse ◆ Axon terminal comes close to the axon of the postsynaptic neuron ■ Form of transmission ● What is a neurotransmitter? ◆ A substance that has been created within the neuron and is released when the neuron reaches the depolarization threshold ➢ Kinds of neurotransmitters created ■ Neuropeptides ● Originate from the soma of the neuron and packaged to transport to the axon terminals ■ Smaller molecules ● Originate from the axon and are package into vesicles at the axon terminals ◆ Responds only to the influx or absence of calcium ions and goes into an inactivated state one released from the neuron ◆ Must contribute to the physiological responses of the postsynaptic neuron ● Possible pathways for a neurotransmitter ◆ In order to not overload or over stimulate the postsynaptic neuron with chemical input, neurotransmitters can… ➢ Reach the intended neuron receptors and interact with them ➢ Exit the synapse gap due to diffusion and go off to a second location to be broken down Functional Anatomy and Pathophysiology I Dr. Frederick E. Williams Week 6 Lecture Notes ➢ Can “bounce back” and be taken up again to be reused or recycled ● Impact of the neurotransmitters ◆ Response is heavily dependent on the type of ligand sent out, the receptor that ligand interacts with as well as the kinds of channels that are associated with the process ◆ Can either be inhibitory and decrease the chance of an action potential being created, or excitatory and increase the chance of an action potential being created ● About neurotransmitter receptors ◆ Types ➢ Ionotropic receptors ■ Work insanely fast and is made of generally 4-5 subunits ■ Has a channel for the four main ions (potassium, sodium, chloride, and calcium) ➢ Metabotropic receptors ■ Works much slower due to its longer mechanism ● The ligand-gated receptor is not the ion channel, there are two separate proteins ● Receptor is hooked up to a G-protein which will send a signal to an effector protein which will then send a signal to the designated ion channel ■ Direct with ion channels ● G-proteins acts directly on the ion channel to open or close it ■ Indirect with ion channels ● G-protein acts indirectly by acting on an effector protein that sends a secondary signal that then acts on the ion channel ❖ Potential in the postsynaptic ➢ Summation ■ The postsynaptic neuron receives many different signals from the multiple surrounding presynaptic neurons around it Functional Anatomy and Pathophysiology I Dr. Frederick E. Williams Week 6 Lecture Notes ● Must summize the total input to determine whether it should send out an action potential or not ◆ Summarizes by adding all graded potentials together and the sum of them together determines the action taken ■ Excitatory postsynaptic potential - (EPSP) ● Increases the likelihood of an action potential being propagated ● Creates slight depolarization ■ Inhibitory postsynaptic potential - (IPSP) ● Decreases the likelihood of an action potential being propagated ● Creates slight hyperpolarization ■ Graded potential ● Created in a local environment in the soma or dendrites ● Dies out but can vary in amplitudes ■ Action potential ● Travels longer distances down the axon ● Is propagated through the cell but has the same amplitude
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