Ch 48 pt B Flashcards
(51 cards)
Action potential sequence (4)
1) Begins with graded potential depolarizes to threshold potential (-50mV)
2) Voltage-gated Na channels open triggering action potential
3) Na+ rapidly diffuses into the cell causing the characteristic spike
4) Inactivation- gate in Na channel swing shuts once membrane is polarized
What are voltage gated K channels opened by?
threshold potential but 1 msec later than Na Channels
When does the membrane become negative again
When the K+ leaves
membrane hyperpolarizes
What happens when K+ channels close
The resting membrane potential is restored
What are the 2 types of refractory periods?
1) absolute refractory period
2) relative refractory period
When does the Absolute refractory period occur?
When the Na+ Gate is closed and become unresponsive
What does the absolute refractory period do? (2)
1) Places limits on the frequency of action potentials
2) Also ensures action potential doesn’t move backward
When does the relative refractory period occur?
while K+ channels still open
What happens during the relative refractory period?
Membrane hyperpolarizes
What is the difference between the absolute refractory period and the relative refractory period?
Absolute refractory period is completely unresponsive to stimulus
Relative refractory period may respond to stimulus if graded potential is big enough
What does speed of info depend on (2)
1) Axon diameter
2) Myelination
How does axon diameter effect speed?
Broad axons provide less resistance and action potential moves faster
How does myelination affect speed? (2)
1) Faster than unmyelinated
2) Saltatory conduction- action potential seems to jump from node to node
What are the parts of synapses? (3)
Presynaptic (send signals) synaptic cleft and postynaptic cell (receives signal)
What are the 2 types of synapses?
Electrical: electric charge flows through junction
Chemical: neurotransmitter acts as signal
Describe the Chemical Synapse process (6)
1) Presynaptic nerve cells contains vesicles of neurotransmitter
2) Exocytosis releases neurotransmitter into synaptic cleft
3) Neurotransmitters diffuse across cleft
4) Binds to channels or receptors in postsynaptic cell membrane
5) Binding of neurotransmitter changes membrane potential of postsynaptic cell
6) signal ends when neurotransmitters are broken down by enzymes or taken back by presynaptic cell
What are the 2 types of changes in postsynaptic potential?
1) excitatory postsynaptic potential
2) inhibitory postsynaptic potential
What is Excitatory postsynaptic potential (EPSP)? (2)
1) Brings membrane closer to threshold potential
2) Sodium Channels opening
What is Inhibitory postsynaptic potential (IPSP)? (2)
1) Takes membrane farther from threshold potential
2) Opening of chlorine channels Cl enters the cells
What causes the synaptic signal to end?
When neurotransmitter broken down by enzymes or taken back into presynaptic cell for reuse
A single EPSP is usually too small to trigger what?
Action potential in a postsynaptic neuron
What is Summation?
combination of multiple individual postsynaptic potentials
If two EPSP are produced in rapid succession called
Temporal summation
What is temporal summation?
2 EPSP’s produced in rapid succession on the same synapse
