Lecture 5 Flashcards
What is synaptic transmission?
Transfers information at a synapse
- named by Charles Sherrington
What’s the direction of information transfer?
Neuron to target cell
- Presynaptic neuron to postsynaptic neuron
What are the 2 types of synapses?
Electrical and Chemical Synapses
What are gap junctions made of?
connexin proteins formed by 6 connexins
What are cells electrically coupled?
flow of ions from cytoplasm of one cell to the cytoplasm of another cell
How do electrical synapses differ from chemical ones?
- bidirectional
- fast transmission (postsynaptic potentials)
- multiple PSPs occur at the same time to excite a neuron (cause action potential)
What are the 5 synaptic arrangements in the CNS?
- axodendritic: axon to dendrite
- axosomatic: axon to cell body
- axoaxonic: axon to axon
- axospinous: axon to dendritic spine
- dendrodenritic: dendrite to dendrite
What is Gray’s type I morphology?
asymmetrical, excitatory synapses
- Glutamate neurotransmitterW
What is Gray’s type II morphology?
symmetrical, inhibitory synapses
- GABA or glycine neurotransmitter
What’s the purpose of the neuromuscular junction?
studies of this established the principles of synaptic transmission
What is the neuromuscular junction made of?
junctional folds with numerous neurotransmitter receptors
How do chemical synaptic transmissions work?
1) Neurotransmitter synthesis
2) Load neurotransmitter into synaptic vesicles
3) Vesicles fuse to presynaptic terminal
4) neurotransmitter spills into synaptic cleft
5) Binds to postsynaptic receptors
6) Biochemical/electrical response elicited in postsynaptic cell
7) removal of neurotransmitter from synaptic cleft
What are the 3 groups of neurotransmitters with an example?
Amino acids: small organic molecules - vesicle (GABA)
Amines: small organic molecules - vesicles (dopamine)
Peptides: short amino acid chains - secretory granules (dynorphin)
What are secretory granules made of?
peptide neurotransmitter at the soma by the rough ER (golgi apparatus pathway)
- sent to presynaptic sites by microtubule transport
What do synaptic vesicles require?
Neurotransmitter synthesizing enzyme and vesicular neurotransmitter transport protein
What is docking of synaptic vesicles mediated by?
v-SNARES and t-SNARES proteins
What causes exocytosis?
Increase in intracellular calcium
Ca++ binds to calcium sensor proteins (Synaptotagmin) and alters conformation of SNARE complexes, triggering vesicle membrane incorporation into presynaptic membrane
Neurotransmitter released into cleft
Vesicle membrane recovered by endocytosis
What are examples of neurotransmitter receptors?
Transmitter-gated ion channels
Metabotropic Receptors
G-protein coupled receptors
Contrasts EPSP and IPSP.
EPSP = Excitatory Post-Synaptic Potential
- transient postsynaptic membrane depolarization caused by presynaptic release of neurotransmitter
- EPSPs added together to produce significant, postsynaptic depolarization
- Threshold can be reached to fire action potential after integration
IPSP = Inhibitory Post-Synaptic Potential
- Transient hyperpolarization of postsynaptic membrane potential caused by presynaptic release of neurotransmitter
What causes generation of an EPSP?
Neurotransmitter (usually glutamate) and Glutamate ion channels like AMPA, NMDA
How do you quantitatively measure EPSPs?
Synaptic vesicles: elementary units of synaptic transmission
Quantum: invisible unit
Quantal analysis: used to determine number of vesicles that release during neurotransmission
What are some important dendritic properties?
Many have voltage gated channels
They contribute to more complex integrative properties
Membrane depolarization falls off exponentially with increasing distance along a dendrite
How do different EPSP summations affect the graph?
Spatial summation = high peak on action potential
Temporal summation = little bumps upwards
What’s the point of EPSP summation?
allows for neurons to perform sophisticated computations
How do excitatory and inhibitory synapses differ?
They bind different neurotransmitters, allowing different ions to pass through channels
When will IPSP have hyperpolarizing effect?
when membrane potential is less negative than -65 mV
What is shunting inhibition?
Synapse inhibits current flow from soma to axon hillock
What are autoreceptors?
Presynaptic receptors sensitive to the neurotransmitter released by the presynaptic terminal
What is the function of autoreceptors?
Safety valve
- common effect is inhibition of neurotransmitter release
What are the possible fates of synaptic released neurotransmitters?
- diffusion of transmitter molecules away from the synapse
- reuptake: neurotransmitter re-enteres presynaptic axon terminal (requires plasma membrane transport proteins)
- uptake by nearby glia cells AKA astrocytes (requires plasma membrane transport proteins)
- enzymatic degradation
What is neuropharmacology?
study of effect of drugs on the nervous system
What are receptor antagonists?
inhibitors of neurotransmitter receptors
ex. curane
What are receptor agonists?
mimic actions of naturally occurring neurotransmitters
ex. nicotine
How does drug addiction work molecularly?
destroys brain reward circuits
