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What about communication between neurons?. Some terms……. presynaptic ending – portion of the axon conveying information to the next neuron. Some terms……. presynaptic ending – the portion of the axon that is conveying information to the next neuron synapse or synaptic cleft
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Some terms……. • presynaptic ending – • portion of the axon conveying information to the next neuron
Some terms……. • presynaptic ending – • the portion of the axon that is conveying information to the next neuron • synapse or synaptic cleft • the space between neurons where communication occurs
Some terms……. • presynaptic ending – • the portion of the axon that is conveying information to the next neuron • synapse or synaptic cleft • the space between neurons where communication occurs • postsynaptic membrane • the portion of the neuron (usually dendrite) that receives information
Some terms……. • presynaptic ending – • the portion of the axon that is conveying information to the next neuron • synapse or synaptic cleft • the space between neurons where communication occurs • postsynaptic membrane • the portion of the neuron (usually dendrite) that receives information • pre and postsynaptic receptors • proteins in both the presynaptic and postsynaptic ending that allow for information to be transferred
synaptic vesicles --small enclosed membranes that contain neurotransmitter - found in presynaptic ending • neurotransmitter – substance in vesicles that are released in synapse and convey info to the next neuron
Presynaptic ending synapse Postsynaptic ending
What happens at level of synapse? • AP reaches presynaptic ending- • Ca+2 channels in presynaptic ending open and Ca+2 enters
Why are Ca+2 ions important? Ca+2 entry into the presynaptic ending critical for neurotransmitter release
postsynaptic receptors • protein embedded in membrane • mechanism for neurotransmitter to influence postsynaptic activity by binding to receptor
Summary • NT binds to postsynaptic receptors and causes small local changes in electrical potential (depolarizations or hyperpolarizations)- • Called graded potentials
Graded Potentials • increase or decrease the likelihood of the neuron receiving info to generate an action potential • graded potentials that increase the likelihood of an action potential are called EPSPs (excitatory postsynaptic potentials)
Graded Potentials • increase or decrease the likelihood of the neuron receiving info to generate an action potential • graded potentials that increase the likelihood of an action potential are called EPSPs (excitatory postsynaptic potentials) • graded potentials that decrease the likelihood of an action potential are called IPSPs (inhibitory postsynaptic potentials)
How does the neurotransmitter cause EPSPs and IPSPs? • NT binding to postsynaptic receptors cause local ion channels to open • chemically dependent ion channels • (in contrast with electrically dependent ion channels in the axon)
How does the neurotransmitter cause EPSPs and IPSPs? • postsynaptic receptors open ion channels – • ion channels in postsynaptic membrane (that we need to worry about) include Na+, Cl- and K+
Two kinds of Graded Potentials • EPSPs – excitatory postsynaptic potentials • - increase the likelihood of an AP • - opening of • IPSPs – inhibitory postsynaptic potentials • decrease the likelihood of an AP • - opening of
How do graded potentials result in an action potential? • graded potentials are summed at axon hillock and……if the sum is a great enough depolarization….
action potential or spike
Graded potentials vs action potentials • Graded Potentials and AP differ in a number of ways • AP – occurs at the axon • GP – occurs anywhere the neuron receives info from another neuron (usually dendrite although NOT ALWAYS) • action potentials are “all or none” graded potentials decrease over space and time • Graded potentials are localized – has impact in limited region; AP travels down the axon
Graded vs Action Potentials • Graded potentials can either increase or decrease the likelihood of an action potential
So what about these NT? • Postsynaptic receptor and NT – think about a lock and key!
Neurotransmitter represents a key Receptor represents the lock
2 ways that neurotransmitter exert these effects • directly opening the ion channel • occurs and terminates very quickly
2 ways that neurotransmitter exert these effects • directly opening the ion channel • occurs and terminates very quickly • more indirect • ultimately opens ion channel via stimulating a chemical reaction • takes longer but lasts longer
2 main ways for getting the neurotransmitter out of the synapse 1. reuptake - most common • protein on presynaptic ending transports it back into the neuron that released it • Means of recycling NT • saving energy (neurons have to synthesize or produce their own NT) • a common way for drugs to alter normal communication
Examples of reuptake inhibitors cocaine, amphetamine, methylphenidate (Ritalin) – block reuptake of a number of NT – particularly dopamine (reward) many of the newer antidepressants are SSRIs (selective serotonin reuptake inhibitors)
enzyme degradation • enzyme - speeds up a reaction • ex. acetylcholine (ACh)is a neurotransmitter is broken down by acetylcholinesterase (AChE) • For ACh – this is done in the synapse
Neurotransmitters • probably 100s of “putative” neurotransmitters – more being discovered all the time • role that the novel NTs play still being determined
Some classic NT • acetylcholine (ACh) –
Some classic NT acetylcholine (ACh) – found in CNS and PNS • receptor subtypes – • nicotinic and muscarinic
Some classic NTs acetylcholine (ACh) – found in CNS and PNS • receptor subtypes – • nicotinic and muscarinic • nicotinic receptors – muscles • acetylcholine also important for various behaviors including learning and memory alzheimers disease, REM sleep, among other things…
Neurotransmitters (cont) • Monoamines • dopamine (DA) important for reward circuits schizophrenia and Parkinsons disease
Neurotransmitters (cont) • Monoamines • dopamine (DA) • norepinephrine (NE) important for arousal altered activity implicated in depression