NS 1 - PT 2 Flashcards
Name the 2 types of synapses
Chemical and electrical synapses
Explain electrical synapses
Characterised by gap junction with ion channels that connect the cytoplasm of adjacent cells
Function of gap junctions
Allow free movement of ions from the cytoplasm of one cell to the next
Function of electrical sunapses
Allow bidirectional transmission of impulses
Explain chemical synapses
Characterised by the secretion of a neurotransmitter
Which type of synapse is abundant in the CNS
Chemical neurotransmitter
How many known neurotransmitters are there?
More than 50
Membrane of the presynaptic terminal is called the_______________
Presynaptic membrane
Which ion channel is abundant in the presynaptic membrane?
Voltage-gated calcium channels
Explain synaptic transmission
AP depolarises the presynaptic membrane open the calcium channels and allow influx of calcium ions into the terminal.
Calcium influx cause transmitter vesicles in the presynaptic terminal to release their neurotransmitter into the synaptic cleft
What guides and promotes vesicle fusion with the cell membrane?
SNARE proteins
Synaptobrevin
*SNAP-25
*Syntaxin
*Synaptotagmin – Ca2+ sensing
Target for neurotoxins: Botulinum toxins
Chemical synapses transmit signals bidirectionally - true or false
f. they transmit in one direction from presynaptic neuron to postsynaptic neuron
What is the target site of neurotransmitters?
Receptors in the postsynaptic membrane
What is the action of neurotransmitter in the postsynaptic neuron?
Excitation, inhibition, or modify sensitivity
Types of postsynaptic membrane receptors
Ionotropic receptors and metabotropic receptors
Explain the mechanisms of postsynaptic excitation
Opening of sodium channels allows influx of positive electrical charges to flow to the interior of the postsynaptic cell
Decrease of chloride or potassium channels or both. Increased expression of excitatory membrane receptors or decreased expression of inhibitory membrane receptors
What membrane mechanisms receptors cause inhibition? (3)
Opening of chloride channels on the postsynaptic membrane
Increased efflux of potassium ions out of the neuron
Increased expression of inhibitory synaptic receptors, or decreased expression of excitatory receptors
What are neurotransmitters?
Endogenous chemicals in the brain that enable signalling across a chemical synapse
3 functions of neurotransmitters
Carry and modulate signals between neurons or other cell types
Act on a variety of targets to elicit biological functions
Cause electrophysiological changes in the postsynaptic cell (Excitation by depolarization or inhibition by hyperpolarization)
Explain synthesis and transport of neuropeptides
Neuropeptides are
synthesized in the cell
body and pre-loaded
into vesicles which are
delivered to the axon
terminal by axonal
transport.
Which types of receptors does glutamate act on?
Glutamate acts on both ionotropic and metabotropic receptors
How are glutamate receptors named? give examples
Glutamate receptors named after synthetic agonists that activate them.
* AMPA (amino-methylisoxazole propionic acid)
* Kainite
* NMDA (N-methyl-D-aspartate)
Repetitive activation of the NMDA receptor leads to what?
Long term potentiation
Influx of calcium ions leads to activation of ____________________ enzymes
Ca2+ dependent enzymes
Action of calcium dependent enzymes once activated
They modify the structure and number of synaptic contacts in the target cell
Action of anaesthetic drug ketamine on NMDA channel
▪ Anaesthetic drug ketamine blocks the NMDA channel, also blocks memory
formation
Which glial cell is responsible for taking up glutamate?
Astrocye
_______________ converts glutamate to glutamine
Glutamine synthase
Where is glutamine transported?
Into the nerve terminal
What happens to the glutamine once in the nerve terminal?
n the nerve terminal glutamine converted to glutamate
by glutaminase.
5. Glutamate returned to a synaptic vesicle
Explain the process of glutamate reuptake and resynthesis
- Glutamate is taken up by an astrocyte.
- Glutamate is converted to glutamine by glutamine
synthetase. - Glutamine is transported back into the nerve terminal.
- In the nerve terminal glutamine converted to glutamate
by glutaminase. - Glutamate returned to a synaptic vesicle.
Full name of GABA
Gamma-aminobutyric acid
Name the 2 major types of GABA receptors
ionotropic and metabotropic.
what happens when GABA receptors are activated?
▪ Activation of GABA receptors - channel pores opens and Cl− ions influx from the
synaptic cleft to the cytosol – Hyperpolarisation
What receptors are activated when sedative hypnotic agents are administered?
Activation of GABA receptors
Examples of sedative hypnotic agents
barbiturates, benzodiazepines and alcohol
What is useful for the Rx of seizures? Why?
Barbiturates and benzodiazepines.
They are Anticonvulsant
What drugs are GABA receptor antagonist?
Bicuculline. It is therefore a convulsant
Picrotoxin
Which glial cell takes up GABA?
Astrocyte
Explain GABA reuptake and resynthesis (5)
- GABA is converted to glutamate by GABA transaminase.
- Glutamate is converted to glutamine by glutamine synthetase.
- Glutamine is transported back into the nerve terminal and converted to glutamate by glutaminase.
- Glutamate is converted to GABA by glutamate decarboxylase.
- GABA returned to a synaptic vesicle
What neurotransmitter plays a role in learning and memory?
Acetylcholine
What causes onset of Alzheimer’s disease?
Degeneration of cholinergic neurons is associated with the onset of Alzheimer disease
_________ is the main neurotransmitter in the NMJ
ACh
▪ Ionotropic ACh receptors are called ______________.
▪ Metabotropic ACh receptors are called __________.
nicotinic.
muscarinic
Explain ACh synthesis (4)
▪ Choline from the extracellular fluid is sent to the nerve ending.
▪ Choline is acetylated by acetyl coenzyme A (acetyl CoA) released by mitochondria
and the reaction catalysed by choline acetyltransferase (ChAT).
▪ Synthesized ACh molecules are taken up by synaptic vesicles.
▪ Released ACh binds with its receptor
Explain ACh degradation (2)
Acetylcholinesterase (AChE) hydrolyses the transmitter.
▪ The choline is transported back into the cytosol
Explain recycling of ACh (3)
Formation of a fresh molecule of ACh is mediated by the transferase, en route to a
synaptic vesicle.
▪ Acetate is transported into the cytosol.
▪ Mitochondria use the acetic acid to produce fresh acetyl CoA
Examples of catecholamines
dopamine, norepinephrine, and epinephrine
Catecholamines are derived from which amino acid?
Tyrosine
Which catecholamine is associated with Parkinsons disease, drug addiction and schizophrenia?
Dopamine
What is the classic feature of Parkinson disease?
Degeneration of neurons in the substantia nigra
Explain catecholamine degradation
▪ Catecholamines molecules within the synaptic cleft are broken down by catechol Omethyltransferase (COMT).
▪ Surplus catecholamines molecules in the cytosol are degraded by mitochondriaderived monoamine oxidase (MAO) enzyme
Another name for serotonin
5-HT (5-hydroxytryptamine)
Serotonin is implicated in which conditions?
Serotonin is implicated in depression, insomnia, anxiety disorders.
Serotonin is derived from which amino acid?
Tryptophan
Tryptophan is converted to_________________ by the __________________ enzyme
5-hydroxytryptophan
tryptophan
hydroxylase.
5-hydroxytryptophan is converted to _____________________ by the _________________ enzyme
serotonin
5-hydroxytrytophan
decarboxylase.
What returns serotonin to the cytosol?
Serotonin reuptake transporter
What degrades serotonin?
monoamine oxidase (MAO).
Name 2 antidepressants
SSRI:
Selective Serotonin Reuptake Inhibitor
▪ MOA:
Monoamine oxidase A inhibitors
