Transcript N. Synapse & Neurotransmitter

Supplemental instruction
Additional review
•Neural synapse
•Neurotransmitters
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Designed by Pyeongsug Kim ©2010 [email protected]
Synapse
- The location where a neuron passes its signal to its target cell
Target cell =usually another neuron, a muscle cell, or a gland cell
-A synapse includes…
Axon terminals of the presynaptic cell
Dendrites of the postsynaptic cell or muscle cell or gland cell.
Synaptic cleft
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A : Neuron (Presynaptic)
B : Neuron or cells (Postsynaptic)
C: Neurotransmitter(NT)
C
1. Mitochondria 2. Synaptic vesicle
3. Autoreceptor 4. Synaptic cleft
5. NT receptor
6. Calcium Channel
7. release NT by___________
exocytosis
8. NT re-uptake pump
Chemical Synapse!
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Synaptic
Transmission
1.Action potentials reach
at the axon terminal.
2.VG-Ca2+ channels
open.
3. Ca2+ activates calmodulin.
4. Calmodulin activates a
protein kinase.
5. Protein kinase promote
fusion and exocytosis of
vesicles.
The presynaptic neuron uses neurotransmitters(NT) to send
the signal across the synaptic cleft.
The NTs diffuse across the cleft to the dendrites of the
postsynaptic cell.
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Picture from http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A570&rendertype=figure&id=A576
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In the postnaptic cell……..
-NTs bind receptor proteins on
the dendrites.
 Cause ion channels open.
If the channel is for Na+
Na+ (enter/ get out of ) the cell.
(EPSP/ IPSP) will occur
If the channel is for K+
K+ (enter/ get out of ) the cell.
(EPSP/ IPSP) will occur
If the channel is for ClCl- (enter/ get out of ) the cell.
(EPSP/ IPSP) will occur
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EPSP
IPSP
-Exitatoy Postsynaptic Potential
from one exposure to neurotransmitter
-The region of positive charge inside
the neuron or negative charge out of
the neuron.
-promote an action potential in the
axon.
-Inhibitory Postsynaptic Potential
from one exposure to neurotransmitter
-The region of negative charge inside
the neuron or positive charge out of
the neuron.
-inhibit an action potential in the axon.
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EPSP? IPSP?
IPSP
IPSP
EPSP
EPSP
+ charge? –charge?
In? Out?
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EPSPs and IPSPs summate.
 if membrane potential in postsynaptic cell reaches
threshold at the axon hillock, a new AP is generated.
 if not, no AP occur.
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Neurotranmitters
1) Acetylcholine
-Choline
Some CNS neurons(excitatory)
Many PNS motor neurons (either excitatory or inhibitory)
-Cholinergic neurons: use acetylcholine as NT
-Somatic neuron
:synapses on skeletal muscle
:large EPSPs - stimulates muscles to contract
-Preganglionic neuron in both Symp. & ParaSymp.
-Postganglionic ParaSymp.
-Curare blocks ACh action
-Cholinergic receptors in the postsynaptic cells
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-Cholinergic receptors
Nicotinic
- skeletal muscle fibers, autonomic ganglia
- Directly bind to channel (Na+ in; followed by K+ out)
EPSP!
Muscarinic
- binds smooth and cardiac muscle; glands
- G-protein; open indirectly adjacent channel (K+ out)
 IPSP!
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Monoamines act through second messenger.
- dopamine
- norepinephrine
- serotonin
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Neurotranmitters(monoamines)
1) Norepinephrine
- catecholamines
- works both CNS and PNS
-fight-or-flight response
-postganglionic Sym.
stimulate cardiac muscle,
cardiac muscle, some glands
Picture from: Dr. Wright Bio6 slide http://www.thecausewayretreat.com/blog/2009/06/fight-or-flight-response/
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Neurotranmitters(Monoamines)
2) Dopamine
- Monoamines
-Nigrostriatal dopamine system
:originates in the substantia nigra
:involved in motor control.
disease
:Degeneration of this system causes Parkinson's
________________
L-DOPA and MAO inhibitors
- Mesolimbic dopamine system
:involved in behavior and emotional reward
:Most addictions activate this system
schizophrenia
Overactivity contributes to _____________
anti-dopamine drugs!
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Neurotranmitters (Monoamines)
3) Serotonin
- Involved in regulation of mood, behavior, appetite
and
cerebral circulation
- SSRIs (serotonin-specific reuptake inhibitors)
- as antidepressants
- Prozac, Zoloft
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Enteric nervous system (ENS)
-efferent nervous system (PNS)
-directly controls the gastrointestinal system
-May be considered ANS(Autonomic nervous system)
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Glutamic acid
-the most common neurotransmitter in the brain
-always excitatory
-Receptors that increase the flow of positive ions by opening ionchannels
eg) NMDA(or NMDAR) receptor & AMPA receptors
 LTP (Long-Term Potentiation) ~ crucial to some forms of learning &
memory.
-concentrated in the cerebral cortex (hippocampus, amygdala, & basal
ganglia
-When Mg2+ block the NMDA channel, AMPA allows Na+ in.
 AMPA cause depolarization enough to expel Mg2+.
 Na+ & Ca2+ in through NMDA.
 EPSP!!!
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Glycine
-makes the post-synaptic membrane more permeable to Cl- ion.
 Hyperpolarization! (IPSP)
-Spinal cord, Brain stem
-GlyR (Glycine receptor)
-Glycine-gated chloride channels
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Tryptophan(serotonin)
-Found in both CNS & PNS (enteric nervous system)
-regulation of mood, appetite, sleep, muscle contraction, and some cognitive
functions including memory and learning.
-the serotonin in the brain is independently synthesized from
tryptophan transported across the blood-brain barrier.
-Raphe nuclei
-5-HT receptors
~ EPSP or IPSP
~G protein-coupled receptors, cAMP(2nd messenger)
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Arginine (nitric oxide)
-does not bind to surface receptors
-readily diffuses across cell membranes
-increase cGMP(2nd messenger)
-Parasymphethetic neurons
Enteric nervous system(ENS)
-Relaxation of smooth muscle
(=inhibition of smooth muscle contraction)
-vasodilation
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Designed by Pyeongsug Kim, ©2010 www.science-i.com