BMS 300 1st Edition Lecture 21 Outline of Last Lecture I. Action Potential Propagation -in membrane lacking v-gated channels 1. concept of decrementing potential -in membrane with v-gated channels but no myelination 1. concept of the regenerating potential-in membrane with v-gated channels clustered at nodes of Ranvier 1. concept of conduction II. From generation potential to action potential in a sensory neuron -DNA as molecules of life 1. stores information about RNA structures 2. RNA structure stores information about protein structure III. The generation potential -opening stretch-activated channels -amplitude of the potential is proportional to the strength of the stimulus-reaching threshold -propagating the potential Outline of Current Lecture IV. From generator potential to action potential to chemical synapsesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-generating action potential in the trigger zone1. the generating potential >voltage gated channels -frequency coding 1. transmission of information by all or nothing invariant signals >bout duration >frequency within a bout -delivery to the next neuron >the chemical synapsesV. Why a chemical synapse-some history of the concept VI. Structure of a synapse -presynaptic element >neurotransmitter -synaptic clapt -post synaptic >the ligand-gated channels as receptorsCurrent LectureStretch activated channels-input region of a sensory neuron -stretch receptor -if we draw out the whole neuron it is primary sensory afferent Primary sensory afferent-carrying information towards the nervous system -there will be spinal cord on the outside which is part of the central nervous system-these neurons have a neuronal cell body in a structure known as the dorsal root ganglia-when there is a stretch on the neuron the channels will open and allow sodium to comeinto the neuron -we will see that the sodium influx depolarizes the membrane so it -each time we open one of these stretch activated channels we let a little positive chargein so it depolarizes the neuron -the number (amplitude) of the generator potential is proportional to the strength of thestimulus >the amount of stretch put on the membrane determines the amount of depolarization that occurs in this neuron -the generator potential is the potential that is generated from these stretch activated channels (prequel to the opening of the v-gated channels) -these are enriched for voltage gated channels -out beyond the input region there are voltage gated sodium channels -they are clustered at the trigger zoneregion of the membrane where we have clustered v-gated channels 1. we pull on the membrane 2. sodium comes in and provides depolarization 3. depolarization moved membrane potential to the threshold 4. the sodium comes in the v-gated channels and then shoots an action potential to the central nervous system -there are v-gated potassium channels as well responsible for the repolarization **how we carry signals along long distances -there is almost never only one action potential fired at one time -if the generator potential reaches above threshold we can fire an action potential whichcreates a “series of action potentials”-the interval between these is variable -action potential interval may vary between about 10 millisecond to 100 millisecond maybe longer**remember that each one of the action potentials is the same as every other oneFrequency Coding of Action Potentials -is from the duration of the bout in combination with the frequency of the action potentials-we are beginning to see that we can take these all or nothing signals and depending on how many we can propagate the information into the central nervous system and this can then be transferred to the next cell Chemical synapse-the site for interneuron communication -a man named Sherrington created a term called synapse: to clasp or hold>there must be a chemical that transmits information from one cell to the next -a man named Langley also worked with Sherrington >interested in nicotine >nicotine causes muscle to contract >asked a simple question: does nicotine effect a muscle fiber uniformly >took a mouse and dissected until he had a single muscle fiber -beaker with a solution of nicotine -dipped a camels hairbrush that only had one filament in it -then brought it to the muscle fiber and carefully dabbed it along the fiber-he found there was a region in the middle of the fiber where the muscle contracted-the muscle fiber is sensitive to nicotine at a restricted site -the site where it was sensitive was the neuromuscular junction (endplate)-the next man that tried to help solve this issue was named Ottoloeu who took out frog hearts with a vagus nerve attached to it, which stimulates and slows the heart beat -he did this again in a second beaker and transported a little amount of the fluid from the first one and put it in the second one-the “stuff” that slows the heart is “vagus stuff” acetylcholine **determined that there is chemical synaptic intervention Structure of the Synapse -they see two cells that come close together but with a gap in between -the top is the presynaptic element which sends information to the bottom cell which is the postsynaptic element-the space in between the two is the synaptic clapt -the presynaptic element contains structures called synaptic vesicles -then later found that there is a voltage gated calcium channel on the presynaptic element -the vesicles tended to be nestled right next to the v-gated calcium channels-on the postsynaptic side there are neurotransmitter receptors that are released from the presynaptic