Chapter 4 - Synaptic Transmission Flashcards
Define electrical synapse
Ion channels connect cytoplasm of pre- and post-synaptic cells
Define chemical synapse
Neurons are separated by synaptic cleft
Briefly explain the chemical synapse. SIMPLY
AP leads to real ease of neurotransmitters that diffuse across the synaptic cleft.
Neurotransmitter interacts with receptors on postsynaptic cell causing either depolarization or hyperpolarization
What is a gal junction?
A gap junction is the channel at the electrical synapse comprised of 2 connexons with 6 connexins each
What contains neurotransmitters?
Synaptic vesicles
What are the three types of synapses?
- axodendritic
- axosomatic
- axoaxonic
What is another way of differentiating synapses (not axoaxonal,…)?
The symmetry of the membranes :
- asymmetrical membranes (Gray’s Type 1) —> round vesicles —> excitatory
- symmetrical membranes (Gray’s type 2)
—> flattened vesicles—> inhibitory
What the different types of neurotransmitters?
Give one example per nt.
- Amino acids : glutamate, GABA, glycine
- Amines : acetylcholine (ACh)
- Peptides (molecule of different amino acids) : dynorphin
Where and how are large peptides formed?
1) large peptides are formed in the ribosomes in the rough endoplasmic reticulum.
2) Thé Golgi apparatus folds the newly formed, PRECURSOR, peptide
3) The active peptide neurotransmitter is packaged into secretory granules for transport and ease
What déterminâtes the effect of a specific chemical messenger on the postsynaptic cell?c
The action of the messenger depends on the properties of the receptor with which the transmitter binds.
It DOES NOT depend on the chemical nature of the neurotransmitter.
Ex : there is nicotonic ACh and muscarinic ACh. The difference is the type of receptor
What do the agonist and antagonist do respectively?
Agonist : mimics the effect of the neurotransmitter
Antagonist : blocks the effect of the neurotransmitter
What is the motor unit?
The motor neuron and muscle cell it inervates
Explain the neuromuscular junction ( how the neurotransmitter actually reaches the other side and everything…)
The synaptic vesicles lead the neurotransmitter to synaptic cleft.
Then the nt reach the postsynaptic receptors.
This leads to the channels opening and releasing potassium and intaking sodium ions.
This leads to depolarization of postsynaptic.
The depolarization opens voltage-gated sodium channels.
This leads to Na+ inflow (positive feedback after)
This all embodies the AP
Explain the 9 steps of chemical transmission
1) transmitter is synthesized and stored in vesicles
2) An action potential invades the presynaptic terminal
3) Depolarization of the presynaptic terminal causes opening of voltage-gated Ca2+ channels
4) Influx of Calcium causes vesicles to bind with presynaptic membrane
5) Transmitter is released in synaptic cleft via exocytosis
6) Transmitter binds to receptor molecule in postsynaptic membrane
7) This causes opening or closing of postsynaptic channels
8) Postsynaptic current causes excitatory or inhibitory postsynaptic potential that changes the excitability of postsynaptic cell
9) Retrieval of vesicular membrane from plasma membrane (Reuptake)
What are the two types of proteins involved with the binding of vesicles to membrane? What are their roles?
- SNARE proteins : bring two membrane close together
—> synaptobrevin (vesicle membrane)
—> syntaxin and SNAP-25 (in plasma membrane) - Calcium binding protein :
—> synaptotagmin (in vesicles membrane, binds calcium)
The reversal potential for the GABA-A receptor is -65mV. When patch clamping a
GABA-A receptor, which way will ions flow through the ion channel if the
membrane potential is -60mV when GABA is applied to the bath?
Cl- will grow in.
What are the mechanisms involved in the recovery and degradation of the neurotransmitter?
- Reuptake: neurotransmitter re-renters the pre-synaptic axon terminal.
- diffusion: away from the synapse
- enzymatic destruction (inside cytosol, or in synaptic cleft)
ex: AChE cleaves ACh to inactive state
What are the two gating mechanisms at chemical synapses?
1) Direct gating (or Ligand-gated ion channels):
- receptor = effector
- Ionotropic receptors
2) Indirect gating (G-protein-coupled receptors):
- receptor protein that binds transmitter is distinct from the ion channel
- effects of transmitter binding receptor are coupled to an effector protein by a set of G-proteins
- receptor =/ effector
- Metabotropic receptors
On what does the effect of opening an ionotropic channel depend?
It depends on the type of ion.
ex: flow of Chloride would be into the cell, as this ion is negatively charged and would want to bring the Vm down to the E(Cl)
This would make it less likely for the cell to fire an AP (as it is further from threshold potential)
What is an inhibitory synapse?
IPSP —> flow of ions makes it harder to reach threshold
REVIEW REVERSAL POTENTIAL!
Review
What are the forms that the effector of the metabotropic receptor can take?
- G-gated ion channel
- enzyme (créâtes second messenger)
What are the characteristics of metabotropic receptors?
- metabotropic receptors that use second messengers act too slowly to fire an AP
- they influence the efficacy of direct gating channels (ionotropic channels)
- these channels are called neuromodulatory
- neurotransmitters that hind metabotropic receptors are called neuromodulators
What are a receptor’s two major functions?
1) recognize and bind transmitter
2) activate effector proteins
