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Bio 350, Exam 2
Question | Answer |
---|---|
What's a Synapse? | Point at which one neuron connects to another |
What are the two types of synapses? | Chemical and electrical |
What's plasticity? | It's crucial to memory and the higher brain functions. |
Four types of CNS synapses based on connection? | 1. Axodendratic (attaches to dendrite) 2. Axosomatic (attaches to soma) 3. Axoaxonic (attaches to axon) 4. Dendrodenditic (dendrites form synapses) |
Differences between Gray's type 1 & 2 synapses? | Grays's type 1 has a thicker pre-synaptic membrane, while Gray's type 2 has a similar membrane thickness on both the pre- and post-synaptic sides. |
Benefits of elexctrical transmission? | 1. Either chemical or electrical 2. Electrical synx |
Action potential? | Caused by depolarization of the membrane beyond threshold Short term change in the electrical potential such that the inside of the membrane becomes positive with respect to outside. |
Seven key events of action potential? | 1. Threshold 2. Rising Phase 3. Overshoot 4. Falling Phase 5. Undershoot 6. Absolute Refractory Period 7. Relative Refractory Period |
1. Threshold? | Membrane potential at which enough voltage-gated sodium channels open so that the relative ionic permeability of the membrane favors sodium over potassium. |
2. Rising Phase? | When inside of the membrane has a negative electrical potential, there is a large driving force on Na+. Na+ rush into the cell through the open Na+ channels = membrane rapidly depolarizes. |
3. Overshoot? | The membrane potential goes close to ENa which is > zero mV The point at which the membrane potential becomes positive. |
4. Falling Phase? | Voltage gated Na+ channels inactivate. The voltage gated K+ channels open. K+ rush out = of the cell potential becomes negative again. |
5. Undershoot? | Open voltage gated K+ channels increase potassium permeability. Relative Na+ permeability is low. Membrane potential goes to EK; hyper polarization relative to the resting membrane potential, until the voltage gated potassium channels close again |
6. Absolute Refractory Period? | Membrane is strongly polarized = Na+ channels inactivate. They cannot be activated until the membrane potential goes -ve to de- inactivate the channels |
7. Relative Refractory Period? | The membrane potential stays hyperpolarized until the voltage gated potassium channels close = more depolarizing current is required to bring the potential to threshold. |
Orthodromic conduction? | Action Potential travels only in one direction does not turn back on itself. |
Refractory Periods? | Refractory periods are times when it is either impossible or more difficult than normal to generate a second action potential. |
Absolute Refractory Period? | During this period the voltage gated channels responsible for the action potential have not reset and therefore, do not respond to stimulation. |
Relative Refactory Period? | The membrane potential stays hyperpolarized until the voltage gated potassium channels close more depolarizing current is required to bring the potential to threshold. |
Excitability? | Excitability varies among neurons, as they vary in the type and # of voltage-gated channels. Also, consider spontaneous firing, accelerating/deaccelerating train of potentials, secondary messengers, and desensitation. |