BMS 108 Ch. 7 Nervous System Part 2 Flashcards
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Does an AP ever vary in amplitude?
No, it’s always +30mV
Action Potentials are _____________, once threshold is reached, there is no going back!
All-or-nothing
If AP can’t increase amplitude, how does it increase intensity?
by increasing frequency of APs
What is a refractory period?
A period following an action potential, where another action potential cannot be produced.
What are the two types of refractory periods?
Absolute and relative refractory periods
What is absolute refractory period? Why?
membrane cannot produce another AP; Na+ ion channels are inactivated (plugged)
What is a relative refractory period? Why?
Takes a much stronger stimulus to fire another AP (unlikely to happen); Some Na+ channels are inactivated and many VG K+ channels are still open.
AP uses _______ ________ to travel down an axon.
cable properties
If membrane potential is subthreshold, current leaks out as it travels through the cytoplasm, down the axon. What is this model called?
leaky hose model
Resistance ___________ as axon diameter ___________.
decreases; increases
Describe the conduction of an unmyelinated axon.
- After axon hillock reaches threshold and fires AP, its Na+ influx depolarizes ADJACENT regions to threshold.
- Which generates a new AP (processes propagates down the axon)
- Refractory period causes the AP to travel one direction only
- Conduction is relatively slow
Describe the conduction in a myelinated axon.
- Ions can’t flow across myelinated membrane (no leaky hose; increases efficiency and speed by controlling ion direction)
- APs occur ONLY at Nodes of Ranvier (VG Na+ channels only open at Nodes of Ranvier)
- Current from AP at 1 node can depolarize next node to threshold (fast because APs skip from node to node
How do neurons communicate?
Synaptic transmission
What is a synapse?
A functional connection between a neuron (presynaptic) and another cell (postsynaptic).
What are the two types of synapses?
Chemical and electrical
What chemical do chemical synapses use to communicate?
neurotransmitters
Where are you likely to find electrical synapses?
in gap junctions (heart, smooth muscle)
How does an electrical synapse work?
Depolarization flows from one cell to another through channels called gap junctions.
The _______ ______ separates the _________ ________ (aka axon terminal) of presynaptic to postsynaptic cell.
synaptic cleft; terminal bouton
Neurotransmitters are inside ______ _______.
synaptic vesicles
Vesicles fuse with the terminal bouton’s membrane, releasing neurotransmitters by _____________.
exocytosis
What ion is the trigger for exocytosis of neurotransmitter?
Ca++
How does Ca++ come into the terminal bouton?
Via voltage-gated Ca++ channels
An action potential is required for _________ __________.
neurotransmitter release
Why do APs travel dow to the terminal bouton?
- to depolarize the bouton
- which opens the voltage-gated Ca++ channels
- Ca++ travels into the bouton down its concentration gradient
- Ca++ triggers exocytosis of neurotransmitter
What determines the frequency of an AP?
Refractory period
Neurotransmitter diffuses across the synaptic cleft and binds to ________ on the postsynaptic membrane (dendrites).
receptors (proteins)
These postsynaptic protein receptors are often chemically regulated, ________ _______ ion channels.
Ligand-gated