5a Neural Conduction What is the action potential what channels does it depend on and how do changes in those channels result in the action potential s 3 phases Refractory period absolute VS relative Action Potential is a quick increase and decrease in membrane potential Conducted down the axon starting at the soma and travels down the Nodes of Ranvier It depends on voltage gated channels Rising phase threshold is reached sodium channels open and sodium enters and further depolarizes the neuron Potassium channels open and potassium exits Sodium channels inactivate Repolarization Falling Phase Sodium channels inactivate Potassium continues to exit and potassium channels start to close Afterhyperpolarization Undershoot Phase Potassium channels don t close completely until neuron is hyperpolarized Local change in channels that makes neuron less likely to fire an action potential Absolute immediately after the AP it is impossible to initiate another AP because the sodium channels are inactivated Relative more input is needed than usual to initiate another AP because potassium channels are still open so any incoming charge can leak out Number of action potentials triggered Can be increased or decreased depending on the strength of input to a neuron The more excitatory input that is given to a cell the faster the rate of APs Model that describes how action potentials in neurons are initiated Used giant squid axon and received the 1963 Nobel Prize Rate code Hodgkin Huxley model What is exocytosis and how does it work 5b Synaptic Transmission What does it mean that the neuron is said to be polarized Across what voltage range would a neuron be hyperpolarized Depolarized How can synapses be categorized Synapses can be categorized by postsynaptic cell type site on neuron where synapse occurs and form in which the message is sent from the pre to the postsynaptic neuron There are 4 types of synapsed axo dendritic axo somatic axo axonic and dendro dendritic The process by which neurotransmitter is released from vesicles into the synaptic cleft It s triggered by a large influx of calcium in the terminal button as a result of voltage gated calcium channels opening and allowing calcium to enter the neuron What are the two main types of neurotransmitter receptors How do they differ Ligand gated channel ionotropic receptor Neurotransmitter activates channels that allow ions to pass the membrane Effects are immediate G Protein coupled receptor Metabotropic receptor Neurotransmitter action at receptor changes protein signaling inside neurons a G protein inside the postsynaptic neuron induces the changes Effects How can drugs interfere with neurotransmission Why is syanpse clearance important How does it occur are indirect they go through the G Protein synthesizes a second messenger in the neuron Effects are slower and often longer lasting It is important to clear out the synapse so that it s ready for the next round of neurotransmission This allows rate coding and prevents desensitization to the receptor Agonist drugs increase or mimic the activity of the neurotransmitter They can stop synaptic clearance allowing more of the neurotransmitter to be in the synapse for longer Antidepressants inhibit the protein that stops serotonin allowing more serotonin to linger in the system Antagonists inhibit the effects of a neurotransmitter and prevent the synapse from binding or activating They may take the shape of the neurotransmitter just to trick the body but not actually activate anything They can prevent exocytosis Know the classes of neurotransmitters and the features of each class and which neurotransmitters fall into each group Small and Conventional Dopamine Epinephrine Serotonin etc Amino Acids fast acting Glutamate excitatory and GABA inhibitory Monoamines Made from a single amino acid They are synthesized from each other so they can use the expression of enzymes to differentiate which monoamine is produced in a given neuron Acetylcholine autonomic and somatic nervous system Motor neurons synapse onto muscle fiber Neuromuscular junctions Unconventional Neurotransmitters that use retrograde transmission Are released from the postsynapse to act at the presynapse Neuropeptides large proteins like hormones opioids etc Endogenous naturally occurring in the body Exogenous not endogenous Receptors on the presynaptic cells Action at autoreceptors usually prevents subsequent neurotransmitter release Electrical communication of neurons occurs through gap junctions Ions can directly flow from one cell to another to activate neurons simultaneously 1 NT molecules are synthesized under the influence of enzymes 2 NT molecules are stored in vesicles 3 NT molecules that leak from the vesicles are destroyed by enzymes 4 AP s cause vesicles to fuse with the presynaptic membrane and release their NT molecules into the synapse 5 Released NT molecules bind with autoreceptors and inhibit subsequent NT release 6 Released NT molecules bind to postsynaptic receptors Endogenous VS exogenous Autoreceptor Gap junction Neurotransmitter system 7 Released NT molecules are deactivated by either reuptake or being destroyed by enzymes 6 Neurodevelopment What embryonic tissues form the central and peripheral nervous systems The three swelling at the anterior end of the neural tube become what structures of the brain Notochord future backbone mesoderm Future central nervous system ectoderm The 3 swellings become the forebrain midbrain and the hindbrain Prefrontal cortex What part of the brain develops for the longest amount of time as in 20ish years What are the steps that we outlined in brain development In particular what happens during differentiation Natal Neurodevelopment fertilization zygote cell division and differentiation Differentiation Totipotency Pluripotency Multipotency Unipotency Understand Sperry s experiment and what it taught us about the role of chemical gradients in axon guidance the chemoaffinity hypothesis Sperry s experiment tested what guides one axon to the place that it needs to go For instance eye neurons going to the areas of the brain that get visual information He realized the parts of the retins go to specific corresponding parts in the brain He rotated the retina took out the retina and cut the axons to see whether they regrow back properly They always regrow back to the corresponding colors Yellow retina will always go to the yellow tectum Chemoaxiffinity Hypothesis Yellow is always going to be
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