Biological Basis of Psychology
Biological Basis of Psychology
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Date Created: 04/19/14
Electrostatic pressure forces Cl out more negative on inside Cl channels are open at rest so no resistance to them crossing the membrane Polarizing the membrane of a neuron When neurotransmitters are released from the axon terminal of the presynaptic neuron and diffuse across the synapse connecting with receptors in the dendrite of the postsynaptic neuron they can change the voltage or electrical potential of the postsynaptic neuron postsynaptic potential or PSP Excitatory postsynaptic potentials or EPSPs some PSPs can make the inside of the cell more positive relative to the outside 9 depolarization movement of positive charge inside or negative charge outside Inhibitory postsynaptic potentials or IPSPs Some PSPs can make the inside of the cell more negative relative to the outside 9 hyperpolarization movement of positive charge outside or negative charge inside PSPs are graded their size depends upon the intensity of the stimulus that elicited them Things that effect this 0 The amount of neurotransmitters released 0 The number of receptors activated PSPs degrade as they travel along the dendrite or cell body Spatial Summation The integration of PSPs arriving at different parts of the neuron Scenario 4 presynaptic neurons synapsing on a postsynaptic neuron Neurons A and B activate excitatory receptors EPSP Neurons C and D activate inhibitory receptors IPSP What happens when neurons A and C fire simultaneously Temporal Summation The integration of PSPs arriving at different times Scenario 2 presynaptic neurons synapsing on a postsynaptic neuron Neurons A activates excitatory receptors EPSP and fires rapidly Neurons B activated inhibitory receptors IPSP and fires rapidly Review of EPSPs and IPSPs The size type and effect of PSPs small changes in voltage across the membrane depend upon several factors 0 Frequency of firing and neurotransmitter release from the presynaptic neuron o Number and identity of presynaptic neurons firing at the same time on a postsynaptic neuron o The neurotransmitter receptor combination Number of a particular type of receptor on the postsynaptic neuron 0 Distance of receptors from the axon hillock which is the area where the cell body becomes the axon O The starting site of an action potential Axon hillock initial segment High in voltage gated Na channels Highly sensitive to ionic ux Where the action potential is generated The ionic basis of the action potential Action potential a massive momentary 1 msec reversal of the membrane potential From 70 mV to 50 mV NOT GRADED IT39S ALL OR NONE Propagated down the entire axon Action potentials are generated when depolarization reaches a particular threshold of excitation a depolarization of about 5 to 20 mV around the axon hillock The depolarization is a change in voltage that open voltage gated Na channels in the area of the axon hillock 9Na comes rushing in making the membrane potential depolarize all the way up to 50 mV rising phase then overshoot All or none property either it fires at its full amplitude or it doesn39t fire at all The ionic basis of the Action Potential The in ux of Na Na moving into the neuron activates additional K gates to open allowing K to ow out The in ux of Na is so large that the ef ux moving out of K does not alter the effect of Na on the membrane potential rising phase When the neuronal membrane becomes very depolarized about 50 mV the Na channels close Voltage gated channels have thresholds for opening as well as closing K continues to leave the neuron 9 repolarization because you39re losing positive charge from the inside of the cell falling phase Unlike Na channels K channels are slow to close 9 keep spitting out K dropping the membrane potential below the resting membrane potential 9 hyperpolarization undershoot When the neuronal membrane is hyperpolarized below resting membrane potential the neuron is now that much further away from the threshold of AP now you39re at 90 mV instead of 70 mV so you need EPSPS to raise the potential by 40 mV instead of 20 mV The period of time when the neuron is hyperpolarized is called the Refractory Period Absolutely Refractory Period time when it is impossible to fire another AP Relative Refractory Period time when it is possible to fire another AP but only if you apply greater than normal stimulation When the neuronal membrane is hyperpolarized ie below resting membrane potential the neuron is now that much further away from the threshold of AP now you39re at 90 mV instead of 70 mV so you need EPSPs to raise the potential by 40 mV instead of 20 mV The period of time when the neuron is hyperpolarized is call the Refractory Period Keeps the AP travelling in one direction Allows the rate of neural firing to be related to the intensity of the stimulation Mediation of the Action Potential by VoltageGated Sodium Channels 1 5 Open K channels create the resting potential Na want to enter K want to exit Some Na channels are open depolarizing the cell to threshold At threshold additional voltage gated Na channels open causing a rapid change in polarity Na channels are inactivated gated K channels open repolarizing then hyperpolarizing All gated channels close The cell returns to its resting potential Propagation of the Action Potential Once generated at the axon hillock the action potential travels without degrading down the length of the axon When an action potential is generated in one area of the axon it alters the membrane potential in the adjacent area 9 triggering the threshold for activation of Na channels there and the massive depolarization happens again in the adjacent area of the axon The action potential does not degrade because there are so many sodium channels covering the axon right up to the terminal boutons Disorder affecting myelination Multiple Sclerosis MS An auto immune disease that is characterized by the degeneration of myelin resulting in neuronal death and the formation of plaques in brain and sprinal cord Disruption in fast saltatory conductance sometimes loss of conductance altogether Results in weakness paralysis or spasms impaired coordination visual problems etc 417 The synthesis transport amp storage of Neurotransmitters Neurotransmitters a chemical gas or hormone that is synthesized in and released from a neuron Large neurotransmitters ex peptides and hormones are synthesized in the cell body and then transported down the axon to the terminal Small neurotransmitters ex amino acids monoamines acetylcholine and gases are synthesized in the terminals In the terminal most neurotransmitters are stored in membranes called vesicles Release of a neurotransmitter Neurotransmission 1 2 4 Action potential travels down the axon of the presynaptic neuron The depolarization of the membrane in the terminals activates voltage gated calcium channels 9 Ca2 enters Ca2 turns on machinery to stimulate vesicles to move to the Active zone the site where vesicles dock prior to neurotransmitter release The membrane of the vesicles fuses joins with the cell membrane in the active zone and neurotransmitters are released into the synaptic cleft Exocytosis Ca2 turns on machinery to stimulate vesicles to move to the active zone the site where vesicles dock prior to neurotransmitter release The membrane of the vesicles fuses the cell membrane in the active zone and neurotransmitters are released into the synaptic cleft Small molecule neurotransmitters are released in pulses every time calci9um enters the neuron because of an action potential Large molecular neurotransmitters are only released when there are high rates of action potentials and calcium levels rise substantially in the terminal Receptors ust as a particular key can open different doors a molecule of the correct shape called a ligand can fit into a particular receptor protein and activate or block the channel Ionotropic receptors directly control ion channels when they receive a particular neurotransmitter Metabotropic receptor receive particular transmitters but do not directly control ion channels Instead they activate molecules known as G proteins These G proteins can then activate neighboring ion channels when released Autoreceptors a metabotropic receptor that is located in the presynaptic membrane They tell the axon terminal how much neurotransmitter has been released and they regulate calcium channels and the machinery involved in exocytosis Normal behavior depends upon precise neurotransmission autoreceptors ensure that neurotransmitter levels do not get too high Ending Neurotransmission 1 3 Reuptake transporters in the terminals or on the dendrites take the neurotransmitter back inside the neuron to be re packaged or degraded Enzymatic degradation enzymes found in the synaptic cleft break down the neurotransmitter after it is released Diffusion neurotransmitters simply move our of the synaptic cleft There are 7 Processes in Neurotransmitter Action Neurotransmitters Neuropeptides large molecules that more resemble proteins 0 Over 100 different peptide neurotransmitters in the brain 0 Endorphins pain and pleasure 0 Slower signaling than the small molecule neurotransmitters 0 Broken down by degradative enzymes in synaptic cleft Amino Acids small molecule neurotransmitter 0 Building blocks of proteins 0 Glutamate glycine aspartate From food excitatory o GABA made from glutamate in neurons and astrocytes inhibitory 0 Found in the majority of fast acting directing synapses 0 Use re uptake mechanisms Soluble Gas small molecule neurotransmitter o Nitric oxide and carbon monoxide 0 Made in the cell body and diffuse across the membrane not released in vesicles 0 Believed to play a role in retrograde signaling signaling from postsynaptic neuron to presynaptic neuron 0 Very short lived broken down inside cells quickly by enzymes Acetylcholine Ach small molecule neurotransmitter Monoamines small molecule neurotransmitter 0 Made from a single amino acid hence their name 0 More diffuse effects than amino acid neurotransmitters 0 Monoamine neurons have highly branched axons Neurotransmitters Cholinergic Pathways Cholinergic cells in the basal forebrain Neurotransmitters Serotonergic Pathways Drug Effects Agonist Antagonists The endogenous ligand is a naturally occurring molecule such as a neurotransmitter that binds and activates the receptor Some drugs resemble the endogenous ligand and affect the receptor in the same way Both endogenous and exogenous ligands are known as agonists Other molecules antagonists bind the receptor but fail to activate it they block agonists Other agonist effects facilitate 0 Drug increases the synthesis of neurotransmitters 0 Drug increases the release of neurotransmitters at the terminal 0 Drug blocks reuptake Agonist examples 0 Morphine which binds to endorphin receptors and mimics the action of endorphins 0 Cocaine which is a serotonin norepinephrine dopamine reuptake inhibitor Other antagonist effects prevent 0 Drug blocks the synthesis of neurotransmitters 0 Drug activates autoreceptors and inhibits neurotransmitter release Antagonist examples 0 Naloxone which binds to endorphin receptors and blocks the action of endorphins o Antihistamine which blocks the synthesis of histamine
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