C11 15-19 Flashcards
Synapse
A junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell .
Axodendritic
synapse between axon endings of a neuron to dendrites of another
Axosomatic
synapse between axon endings of a neuron to soma of another
Presynaptic Cells
Neuron conducting impulses towards the synapse
Postsynaptic Cells
Neuron conducting impulses away from the synapse
Synaptic cleft
Fluid filled space that separates presynaptic/postsynaptic cells (chemical synapses)
Chemical synapses
Structure: synaptic cleft/vesicles, ps receptor,
Synaptic delay .3 .5 ms
Common
Unidirectional
Size varies - amount of neurotransmitters
Neurotransmitters
How are neurotransmitter effects terminated?
Degradation by enzymes associated with the postsynaptic cell membrane or in the synaptic cleft, Reuptake by astrocytes or the presynaptic terminal, diffusion away from the synapse
Synaptic delay
The time required for a neurotransmitter to be released, diffuse across the synaptic cleft and bind to receptors. It is the slowest step of neural transmission.
Postsynaptic potential
A graded potential in the postsynaptic neuron (caused by the presynaptic neuron releasing a neurotransmitter that crosses the synaptic cleft and binds to receptors on the postynaptic neuron)
EPSP
What does this stand for?
What is it?
How does it happen?
- Excitatory Postsynaptic Potential
- Local GP depolarization event that occurs at excitatory postsynaptic membranes and function to help trigger an AP distally at the axon hillock.
- excitatory neurotransmitter opens Na+ channels (actually cation which allow flow of both K+ and Na+, but Na+ gradient is steeper) and depolarizes the membrane.
IPSP
What does this stand for?
What is it?
How does it happen?
- Inhibitory Postsynaptic Potential
- GP that reduces a postsynaptic membranes ability to generate an AP.
- inhibitory neurotransmitter opens either K+ or Cl- channels and hyperpolarizes the membrane.
6 steps in chemical synapse
- AP arrives at axon terminal 2. Volt-gated Ca2+ channels open, Ca2+ enters axon terminal 3. Ca2+ entry causes syanaptic vesicles to release neurotranmitters by exocytosis 4. Neurotransmitter diffuses across SC and binds to specific receptors on the postsynaptic membrane. 5. binding of neurotransmitters opens ion channels creating GP. 6. Neurotransmitter effects are terminated.
What step? Action potential arrives at axon terminal
1 Neurotransmission at a chemical synapse begins with the arrival of an action potential at the presynaptic axon terminal
What step? Voltage gated Ca2+ channels open and Ca2+ enters the axon terminal
2 Depolarization of the membrane by the action potential opens not only Na+ channels but voltage gated Ca2+ as well. During the brief time the Ca2+ are open, Ca2+ floods down its electrochemical gradient from the extracellular fluid into the terminal.
What step? Ca2+ entry causes synaptic vesicles to release neurotransmitters by exocytosis
3 The surge of Ca2+ into the axon terminal acts as a messenger. A Ca2+ sensing protein binds Ca2+ and interacts with SNARE proteins that control membrane fusion. As a result, synaptic vessels fuse with the axon membrane and empty their contents by exocytosis. Ca2+ is then removed from the terminal (taken up by mitochondria or ejected by Ca2+ pump)
What step? Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.
4
What step? Binding neurotransmitter opens ion channels, creating graded potentials.
5 The receptor changes the 3D shape of the protein channel and opens it. Often Ligand channels. May also be inhibitory.
What step? Neurotransmitter effects are terminated.
6 As long as the neurotransmitter is bound to the receptor, it continues to affect the membrane permeability. It must be terminated (reuptake/degradation/diffusion)
- Describe how synaptic events are integrated..
Events are integrated by temporal and spatial summation of both IPSPs and EPSPs. The axon hillock keeps a tally of both - their potential reflects the sum of incoming neural info.
- Describe how synaptic events are modified.
By synaptic potentiation, presynaptic inhibition and neuromodulation.
- -Synaptic potentiation increases the excitability of the postsynaptic neuron
- -presynaptic inhibition decreases the excitatory stimulation of the postsynaptic neuron
- -Neuromodulation affects the strength of synaptic transmission.
Synaptic potentiation
- A learning process that increases the efficiency of neurotransmission along a particular pathway.
- Repeated or continuous use of a synapse enhances the presynaptic neuron to produce larger than expected EPSPs.
- i.e. Signals being sent repeatedly along a circuit, circuit lead to the circuit being modified to be more efficient/useful (more receptors, more axon terminals, more neurotransmitters), changes in neuron.
Presynaptic Inhibition
Occurs when the release of excitatory neurotransmitter by one neuron is inhibited the activity of another neuron.
The result is that less neurotransmitter is released and bound forming smaller EPSPs.
What are neuromodulators, how does neuromodulation work?
- -Neuromodulators are chemical messengers released by a neuron that do not directly cause EPSPs or IPSPs, but instead affect the strength of synaptic transmission.
- -Neuromods may act presynaptically to influence synthesis/release/degradation or reuptake of a neurotransmitter OR they may act postsynaptically by altering the sensitivity of the postsynaptic membrane to neurotransmitters.
Ca2+ plays a role in?
Nerve conduction, blood clotting, muscle contraction, hormonal mechanism, co-factor in enzymatic reactions
Electrical synapse
Gap junctions, fast, rare, bidirectional, same signal size, ions (NA+, K+)
