PS263 Week 3 Notes.docx - Week 3 Notes January 15th 17th...

This preview shows page 1 - 3 out of 11 pages.

Week 3 Notes – January 15 th , 17 th , 19 th 2018 Response Specificity Look at image in the PowerPoint (Textbook 3.1) Instructions o Make a neuron that only responds to light moving in one direction Diagram information o Neuron (purple) attached to 4 sensory neurons (with their somas in the middle) o (+) are the excitatory synapses o The neuron fires when the light hits the retina Light going from yellow red o The light causes the yellow (1 st ) neuron to fire (EPSP) Little bump in action potential – moves down the membrane o The light moves down and activates the green (2 nd ) neuron (EPSP) This happens just as the other depolarization occurs Maybe still not enough action potential – moves down the membrane o The light moves down and activates the blue (3 rd ) neuron EPSP may be enough to reach threshold Light going from red yellow (opposite direction) o Problem with the blue neuron firing is that when it goes downwards towards the axon, the red neuron has already fired, and therefore is going through the refractory period, so the EPSP dies off Therefore, the neuron can only go in one direction The circuit only responds to light moving down and not upwards Rate of Firing Most neurons have a spontaneous firing rate o Fire with no external stimulation o At a constant rate (more or less) Once a second, twice a second etc Synapses are not only on/off o Can fire at different rates – maximum 10,000 times a second o Rate of firing can be part of the message IPSPs can decrease the rate of firing EPSPs can increase the rate of firing Synapses Where the action is! Connections between neurons o Presynaptic neuron end of axon (axon terminal) o Postsynaptic neuron dendrite (dendritic spine) or soma Require a different form of communication
o Chemical (not electrical) An action potential is usually electric but when it reaches the neuron, it changes to chemical Structure of the Synapse Pre-and postsynaptic cells do not touch Presynaptic neuron has a terminal bulb/button at the axon’s end Communication across the gap Presynaptic cell releases chemicals (neurotransmitters) that affect the postsynaptic cell The Importance of Glia Almost all synapses are wrapped in astrocyte (a type of glia cell) processes (tentacles) o Cyte = cell o Astro = shaped like a star o Astrocyte Cells shaped like stars Overview of Synaptic Transmission 1. Neurotransmitters Synthesized o Neurons have to make its neurotransmitters 2. Action Potential Arrives o Presynaptic neuron has an action potential (comes from the top) and moves down the membrane 3. Voltage-gated Ca+ channels open; Ca+ enters o Another kind of ion channel (Calcium – which is usually closed and is voltage- gated meaning a change in voltage causes it to open or close) opens o Since there is a lot more calcium outside the neuron than there is inside, it rushes in and gets stored in vesicles (membrane sacs to store neurotransmitters) 4.

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture