Lecture 17: Neurotransmission Flashcards
Unmyelinated axon
continuous conduction
AP’s occur at one spot on membrane and stimulate adjacent regions
Local Current
movement of positive ions into center of axon during unmyelinated AP propagation (positive starts outside and moves into center during AP)
Absolute Refractory Period
some local currents move in reverse direction because are is still in absolute refractory period. This prevents APs from reversing in direction. Allows them to only go forward cause we desensitize the area of the axon cause its still in refractory period. Cant restimulate the membrane
The absolute refractory period is a time during which a nerve cell (neuron) cannot send another signal (action potential) right after it has already sent one. This happens because the channels that allow the action potential to flow (sodium channels) are temporarily “shut down” after being used.
This period helps prevent the action potential from moving backward along the neuron because the section of the neuron that just fired is in this “resting” phase and can’t fire again immediately. So, the signal can only move forward along the neuron, not backward.
Myelinated Axon
Saltatory conduction - AP conducted from one node of ranvier to another. Local current flows between nodes of ranvier. Voltage gated Na+ channels are concentrated at the nodes, allows to have large and fast change in membrane potential because we can open many channels at once. Allows local currents to jump from one node of ranvier to another.
Why does saltatory conduction use less ATP?
instead of depolarizing the entire region, we only depolarize little regions at the node of ranvier. Makes everything much faster in the way we move the electrical signals. More energy efficient.
3 Factors that affect propagation speed:
- Axon Diameter
- Amount of Myelination
- Temperature
3 Nerve Fiber Types:
- Type A - large diameter, myelinated, conduct at 15-120m/s. Fastest. Motor neurons supplying skeletal and most sensory neurons.
- Type B - medium diameter, lightly myelinated, conduct at 3-15m/s, part of ANS. Smooth muscle, cardiac muscle, glands
- Type C - small diameter, unmyelinated, conduct at 2m/s or less, part of ANS, slow processes like digestion
synapse
the junction between cells that allow them to communicate with one another
2 types of synapses
1.Electrical - cardiac and smooth muscle, not nervous system
- Chemical - neurons
Electrical synapse
AP’s move away from connexons (where AP start). Take advantage of absolute refractory period and cannot go backwards
-important for coordinated contractions (cardiac muscle, smooth muscle)
chemical synapse (5 steps)
- AP’s arriving at presynaptic terminal cause voltage gated Ca2+ channels to open
- Ca2+ diffuses into the cell and stimulates exocytosis of the synaptic vesicles, which releases neurotransmitter molecules
- Neurotransmitter molecules diffuse from the presynaptic terminal across synaptic cleft
- Neurotransmitter molecules combine with their receptor sites and cause ligand gated Na+ channels to open.
- Na+ diffuses into the cell and causes depolarization (in postsynaptic membrane) - if we can get large enough graded potential occurring in region of postsynaptic membrane, then we can generate AP in next neuron
3 ways to remove neurotransmitter from synaptic cleft
1.diffusion
2. enzymatic degradation
3. uptake by neurons or glial cells
How does Prozac work and what is is?
Serotonin reuptake inhibitor - blocks the reuptake of serotonin. Inhibitor of the reuptake pump. allows serotonin to stay in the synaptic cleft longer than normal. Stimulating post synaptic membrane for extended period of time. Helps reduce depressive symptoms.
2 postsynaptic potentials
Excitatory postsynaptic potential -
Inhibitory postsynaptic potential
spatial summation
diff axons come to the same cell body and release neurotransmitter independently of each other. Add independent graded potentials that come from diff neurons
