Ch 48 pt B Flashcards
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
EPSP produced nearly simultaneously by different synapses on the same postsynaptic neuron
Spatial summation
What is spatial summation?
2 EPSP’s produced nearly simultaneously by different synapses on 1 postsynaptic neuron
Combination of EPSP through spatial and temporal summation can trigger?
Action potential
What counters EPSP
IPSP (through summation)
The sum of EPSP’s and IPSP’s determine whether _______ reaches threshold to generate action potential at the _______?
stimulus; axon hillock
After ____, a chemical synapse returns to resting state
response
Where are neurotransmitter molecules cleared from
Synaptic cleft
What causes severe effects that can lead to death
The inhibition of the enzyme that breaks down the neurotransmitter controlling skeletal muslces
What is the gas that inhibits enzymes from breaking down neurotransmitters?
nerve gas (sarin)
Explain how Metabotropic differs from Ionotropic
in Metabotropic, neurotransmitters activate signal transduction pathways
in Ionotropic, Neurotransmitters bind directly to gated channel
An advantage of metabotropic signaling is
Many channels can be opened or closed
What are the 5 types of neurotransmitters?
1) acetylcholine
2) amino acids
3) biogenic amines
4) neuropeptides
5) gases
What is acetylcholine involved in? (3)
1) muscle stimulation
2) memory
3) learning
What inhibits acetylcholine? (2)
sarin and botulism
What are the 3 types of amino acids
1) glutamate
2) glycine
3) Gamma-aminobutyric acid (GABA)
What does glutamate function as?
amino acid neurotransmitter in vertebrates and invertebrates
What is the function of glycine?
acts at inhibitory synapses in the CNS outside of the brain
What is the function of Gamma-aminobutyric acid?
neurotransmitter at most inhibitory synapses in brain
What are the 4 types of biogenic amines?
1) norepinephrine
2) epinephrine
3) dopamine
4) serotonin
What is the function of most biogenic amines?
central role in # of nervous system disorders
ex) Parkinson’s disease: lack of dopamine in brain
What makes up neuropeptides?
short chains of amino acids
What are the 2 types of neuropeptides? What is their function?
substance P and endorphins
both affect pain reception
What inhibits substance P and endorphins?
opiates: used as pain killers
What are the 2 gases?
1) NO
2) CO
What are the characteristics of NO? (3)
1) local regulator in PNS
2) synthesized on demand
3) broken down within a few seconds of production
What are the characteristics of CO? (2)
1) can be deadly
2) vertebrate body synthesizes in small amounts to be used as neurotransmitters
what are orphan receptors?
receptors that have been identified but their ligands not found/discovered yet
