Neurotransmitters, Synaptic Transmission-Lecture 11 Exam 2 Flashcards
Synapse
The tiny gap across which a nerve cell, or neuron, can send an impulse to another neuron
Electrical Synapses
Pass an electrical signal from
one cell to another through gap
junctions
Chemical Synapses
Use neurotransmitters to carry information from one cell to the next cell
Most Common Neurotransmitter(s) Used in the Nervous System
-Glutamate (amino aciid)
-GABA (amino acid)
-Glycine(amino acid)
-Seratonin (amine)
-Dopamine (amine)
-Norepinephrine (amine)
-Epinephrine (amine)
Acetylcholine (ACh) Synthesis
-Acetyl CoA and choline combine to make Ach
-Packaged into vesicles
Acetylcholine (ACh) Receptors
-Nicotinic Receptor
-Muscarinic Receptor
Acetylcholine (ACh) Termination/Inactivation Mechanism (s)
-Degraded by
acetylcholinesterase (AChE)
in the synaptic cleft
-Choline is transported back
into the presynaptic neuron
-Acetate diffuses away
Structures Involved in a Typical Chemical Synapse
-Presynaptic Terminal
-Synaptic Cleft
-Postsynaptic Membrane equipped with Neurotransmitter Receptors
-Synaptic Vesicles with Neurotransmitters
Synaptic Transmission
- Action potential reaches the presynaptic axon terminal and depolarizes it
- Voltage-gated Ca++ channels open and Ca++ enters the neuron from the ECF
- Ca++ entry causes exocytosis of vesicles containing NT
- NTs diffuse across the synaptic cleft and bind to and activate receptors on
the postsynaptic cell - NT binding initiates a response in the postsynaptic cell
Ways Neurotransmitter Activity at a Synapse can be Terminated/Inactivated
-Reuptake by the neuron that released it
-Uptake by neighboring glial cells
-Enzymes degrade or inactivate NT
-Diffuse away from the synapse
The Excitatory Neurotransmitter(s) that can Lead to an EPSP
Glutamate
What ion channel(s), when opened, can lead to an EPSP?
Na+ channels-> influx of Na+
How will the membrane potential of a postsynaptic neuron change during an EPSP?
Depolarization
The inhibitory neurotransmitter(s) that can lead to an IPSP
GABA or Glycine
What ion channel(s), when opened, can lead to an IPSP?
-K+ channels-> efflux of K+
-Cl- channels-> influx of Cl-
How will the membrane potential of a postsynaptic neuron changes during an IPSP?
Hyperpolarization
How can depolarization (EPSP) of a postsynaptic neuron can initiate an action potential by the processes of Temporal Summation?
Multiple subthreshold EPSPs from one neuron occur close enough in time to combine to reach threshold and trigger an AP
How can depolarization (EPSP) of a postsynaptic neuron can initiate an action potential by the processes of Spatial Summation?
Subthreshold EPSPs, from
multiple neurons, occur simultaneously at different points and combine to reach threshold and trigger an AP
How is an action potential initiated in a postsynaptic neuron?
- Postsynaptic neuron at rest (-70 mV)
- Excitatory NT (glutamate) is released from presynaptic neuron(s) and binds to receptors on the postsynaptic neuron, opens ligand-gated Na+ channels
- EPSP begins (membrane potential increase/becomes more positive/depolarizes due to the influx of Na+)
- EPSPs continue, charge summates (spatially and/or temporally) until the potential at the axon hillock reaches -55 mV (threshold)
- Voltage-gated Na+ channels open at axon hillock
- Action potential begins in postsynaptic neuron and travels down the axon to the axon terminal
Summation
The combination of excitatory and inhibitory signals that may or may not reach threshold to trigger an action potential
Summation of EPSPs
-EPSPs can add together to produce a significant postsynaptic depolarization
-If the summed EPSPs reach threshold (−55 mV) in a postsynaptic neuron, an action potential begins
Hyperpolarized neurons are _____ to produce an action potential
less likely
