PSYCH261 Chapter Notes -Monoamine Oxidase, Nitric Oxide, Exocytosis

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PSYCH&261&*&Physiological&Psychology&
&
Module&3.2:&Chemical&Events&at&the&Synapse!
!
Charles&Sherrington!identified!many!properties!of!the!synapse!
Knew!that!synaptic!transmission!was!slower!than!transmission!along!an!axon&
Thought!that!it!was!due!to!electrical!activity,!when!in!reality,!many!synapses!rely!on!
chemical!processes&
&
T.R.&Elliott!(1905)!discovered!that!applying!adrenaline!directly!to!the!heart,!stomach,!and!pupils!
produces!the!same!effects!as!the!sympathetic!nervous!system!
Therefore,!sympathetic!nerves!stimulate!muscles!by!releasing!adrenaline!or!a!similar!
chemical!
!
Otto&Loewi:!discovered!that!nerves!send!messages!by!releasing!chemicals!
Decreased!one!frog’s!heart!rate!by!stimulating!vagus!nerve!
Collected!fluid!from!first!heart,!transferred!it!to!a!second!frog’s!heart!which!decreased!heart!
rate!as!well!
!
Sequence!of!Chemical!Events!at!a!Synapse!
Neuron!synthesizes!neurotransmitters!in!axon!terminals!and!neuropeptides!in!cell!body!
(soma)!
Action!potentials!travel!down!the!axon,!opening!calcium!channels!and!causing!Ca2+!to!enter!
the!cell!
Calcium!releases!neurotransmitters!into!the!synaptic&cleft!between!the!presynaptic!and!
postsynaptic!neurons!
Neurotransmitter!diffuses!across!the!cleft,!attaches!to!receptors,!and!opens!ion!channels!
o Depolarization!or!hyperpolarization!occurs!
Neurotransmitters!separate!from!receptors!
o Either!recycled!by!the!presynaptic!neuron!or!diffuse!away!
Some!postsynaptic!cells!send!reverse!messages!to!control!further!release!of!
neurotransmitters!by!presynaptic!cells!
!
Types!of!Neurotransmitters!
Neurotransmitters:!chemicals!released!by!a!neuron!at!a!synapse!that!affect!another!neuron!
Amino&acids:!acids!containing!an!amine!(NH2)!group!
o Form!building!blocks!of!neurotransmitters;!obtained!from!proteins!in!diet!
Monoamines:!chemicals!formed!by!changing!certain!amino!acids!
Acetylcholine:!similar!to!an!amino!acid,!but!has!N(CH3)3!instead!of!NH2!
Neuropeptides:!chains!of!amino!acids!
Purines:!adenosine,!guanine!and!their!derivatives!
Gases!
o Nitric&oxide!(NO)!diffuses!across!and!is!very!reactive/unstable;!dilates!blood!
vessels,!increasing!blood!flow!to!that!brain!area!
!
Storage!of!Neurotransmitters!
Most!neurotransmitters!are!synthesized!in!the!presynaptic!terminal,!where!they!are!stored!
in!vesicles!
Neurons!that!release!serotonin,!dopamine,!or!norepinephrine!contain!monoamine&oxidase&
(MAO)!that!breaks!these!down!into!inactive!chemicals!
!
Release!and!Diffusion!of!Neurotransmitters!
Calcium!entry!into!the!presynaptic!terminal!causes!neurotransmitter!release!through!
exocytosis!
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Diffuses!across!synaptic!cleft!to!postsynaptic!membrane!receptors!
o Takes!0.01!ms!
Most!neurons!release!a!combination!of!two!or!more!neurotransmitters!
o Combination!makes!the!neuron’s!message!more!complex!
o May!receive!and!respond!to!many!neurotransmitters!at!different!synapses!
!
The!effect!of!a!neurotransmitter!depends!on!the!receptor!on!the!postsynaptic!cell.!
Ionotropic&effect:!when!the!neurotransmitter!attaches!to!the!receptor,!it!opens!a!
transmitterXgated!or!ligandXgated!channel!
o Begin!quickly!and!last!short!periods!of!time!
o Most!of!the!brain’s!excitatory!ionotropic!synapses!use!glutamate!or!acetylcholine!
o Inhibitory!synapses!use!GABA,!which!opens!chlorine!channels!
o Used!in!vision!and!hearing!
Metabotropic&effect:!initiate!a!sequence!of!metabolic!reactions!that!are!slower!and!longer!
lasting!than!ionotropic!effects!
o Use!many!neurotransmitters,!including!dopamine,!norepinephrine,!serotonin,!
glutamate,!GABA!
o G*protein&coupled&receptors!activate!second&messenger!system!that!may!open!or!
close!ion!channels!
o Used!in!taste,!smell,!pain,!arousal,!pleasure,!attention,!emotion!
!
Neuropeptides!are!often!referred!to!as!neuromodulators!
Synthesized!in!the!cell!body!and!then!transported!to!other!parts!of!the!cell!
Released!mainly!by!dendrites,!soma,!sides!of!axon!
Release!requires!repeated!stimulation!
Substantial!amounts!released!infrequently!
Diffuse!widely,!affecting!many!neurons!in!their!region!of!the!brain!
o Neurotransmitters!generally!don’t!do!this!
o Exception:!neurogliaform&cell!releases!large!amounts!of!GABA!at!once,!producing!
widespread!inhibition!
Many!exert!longXlasting!effects,!such!as!altering!gene!activity!
Important!for!hunger,!thirst,!intense!pain,!other!longXterm!behaviour/experience!changes!
!
Hormone:&chemical!that!is!secreted!by!cells!in!one!part!of!the!body!and!conveyed!by!the!blood!to!
influence!other!cells&
Useful!for!coordinating!longXlasting!changes!in!the!body!
Released!from!the!endocrine&gland&
Protein!hormones!and!peptide!hormones!attach!to!membrane!receptors!and!activate!second!
messenger!systems!
Hormones!secreted!by!the!brain!control!secretion!of!many!other!hormones!
Pituitary&gland:!attached!to!hypothalamus,!releases!hormones!
o Posterior&pituitary!releases!oxytocin!and!vasopressin!into!blood!
o Anterior&pituitary!synthesizes!6!hormones!
o Releasing&hormones!flow!through!blood!to!anterior!pituitary!where!they!stimulate!
or!inhibit!release!of!many!hormones:!
! ACTH,!TSH,!prolactin,!somatotropin,!gonadotropins,!FSH,!LH!
o Hypothalamus!maintains!constant!level!of!hormones!in!the!blood!by!negative&
feedback&system&
!
Inactivation!and!Reuptake!of!Neurotransmitters!
Acetylcholine!is!broken!down!by!acetylcholinesterase!into!acetate!and!choline!
o Choline!diffuses!back!into!presynaptic!neuron,!where!it!is!recycled!
Sertatonin!and!catecholamines!detach!from!receptor!
o Reuptake!through!transporter&proteins!
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Document Summary

Psych 261 - physiological psychology. Module 3. 2: chemical events at the synapse. Some postsynaptic cells send reverse messages to control further release of neurotransmitters by presynaptic cells. The effect of a neurotransmitter depends on the receptor on the postsynaptic cell. Neuropeptides are often referred to as neuromodulators. Important for hunger, thirst, intense pain, other long- term behaviour/experience changes. Acth, tsh, prolactin, somatotropin, gonadotropins, fsh, lh: hypothalamus maintains constant level of hormones in the blood by negative. Sertatonin and catecholamines detach from receptor: reuptake through transporter proteins feedback system. Negative feedback from postsynaptic cell: autoreceptors respond to the released transmitter by inhibiting further synthesis and release, located on presynaptic terminals. Some postsynaptic neurons release chemicals that travel to the presynaptic terminal and inhibit further neurotransmitter release: ex. Opiate drugs: derived from or chemically similar to the opium poppy. Includes morphine, heroin, methadone: relax people, decrease attention, and decrease pain sensitivity.

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