Exam #3 Chapter 11- part 2 Flashcards
what are action potentials caused by?
graded potentials
what causes ion differences?
the membrane
what does neuron and muscles cells use the ion differences to produce?
action potential
what do graded potentials go up and down from?
diffusion across the membrane
what will happen if certain molecules bind to ligand-gated sodium channels?
it will produce a depolarization (graded potential)
what happens if graded potentials summat to (or past) the threshold in the initial segment?
an action potential will occur in the initial segment (all-or-none principle)
what can graded potentials do before diffusing away?
persist for a while
what is the difference in length of action and graded potentials?
graded potentials are long, action potentials are only 1-2 milliseconds long and a graded potential can be added together
where do action potentials occur?
in the initial segment in the axon
where do graded potential occur?
cell bodies and dendrites but can diffuse far enough that they reach the initial segment (axon)
what is an action potential for the membrane?
a quick change
what is a depolarization phase followed by?
a repolarization phase and afterpotential
what is the depolarization phase?
when the membrane potential moves away from the resting state and becomes more positive
what is the afterpotential?
when the plasma membrane becomes hyperpolarized after repolarization
what is the repolarization phase?
when the membrane potential returns toward the resting state and becomes more negative
what encourages action potentials?
graded depolarizations
what discourages action potentials?
graded hyperpolarizations
what will a graded depolarization to or past the threshold do?
open voltage-regulated sodium channels producing the depolarization and action potential
what do voltage-regulated sodium channels have?
two gates operated independently
what are the three possibilities for the voltage-regulated sodium channels?
1) closed but CAN open (inactivation gate open and activation gate closed)
2) open- (both gates open)
3) closed and CANNOT open (inactivation gate closed and activation gate open)
what does a graded potential do to the membrane?
depolarizes it to the threshold
what are the gates when a graded potential is below the threshold?
sodium channels are closed but can open
what are the gates when a graded potential is at the threshold?
the sodium channels are open
what are the gates when a graded potential is at +30mV?
the sodium inactivation gates close and voltage-gated potassium channels open producing the repolarization
what are the gates when a graded potential is in repolarization?
the sodium-voltage gated channel activation gates close and then the inactivation gates open
what happens to the potassium voltage-regulated channels when at -70mV
they close
what dose the closing of the potassium regulated channels when at -70mV allow for?
the membrane polarization to exceed -70mV (afterpotential)
after the afterpotential of the potassium voltage regulated channel exceeding -70mV what occurs?
the membrane potential returns to -70mV
what happens to the small amount of sodium ions that came into the potassium voltage channel?
it is quickly pumped out
where does the all-or-none principle occur?
in the initial segment
what needs to occur in order for an action potential to occur?
needs to reach the threshold
between the time that the sodium channels open until the sodium channels are returned to configuration before a depolarization what occurs?
the initial segment will NOT respond to any graded potential to generate another action potential (absolute refractory period)
between the return of the sodium channels to the configuration before depolarization until the return to the resting membrane potential what occurs?
another action potential can be generated by a larger stimulus than the original one (relative refractory period)
what will a larger stimulus past the threshold generate?
a series of action potential (up to a limit) and higher frequency of action potentials is interpreted as a stronger signal
what do action potentials propagate from?
the initial segment to the axon terminals
`what will happen with an unmyelinated axon?
the depolarization of one section during the depolarization phase will depolarize the next section to the threshold.
what will happen with a myelinated axon?
the depolarization of one node depolarizes the next node to the threshold, propagating the action potential down the axon in saltatory conduction
what influences the propagation speed of action potentials? (3) (PTD)
1) the presence of myelin
2) the thickness of myelin
3) the diameter of the axon
what are the characteristics of type A fibers? (3) (TLF)
1) thick myelin
2) large axon
3) fastest
what are the characteristics of type B fibers? (3) (TMS)
1) thin myelin
2) medium axon)
3) slower than Type A but faster than Type C
what are the characteristics of type C fibers? (3) (NTS)
1) no myelin
2) thin axon
3) slowest
what happens at the synapse?
information from one neuron (the presynaptic cell) is transmitted to another neuron or an effector cell (postsynaptic cell)
how many synapses does the average neuron have?
about 5000
how many synapses do certain neurons have in the cerebellum?
up to 200,000
are electrical synapses rare or common?
rare
how are cells connected in electrical synapses?
by gap junction
in electrical synapses what is an action potential in the presynaptic cell aways generate ?
an action potential in the postsynaptic cell (2 cells behave as one making it fast)
what are the most common synapses between neurons?
chemical synapses
in chemical synapses what occurs to the action potential in the presynaptic cell?
it MAY generate an action potential in the postsynaptic cell (allows information processing) (slower)
in chemical synapses what is the presynaptic termainal separated from?
the postsynaptic membrane
what is the presynaptic terminal separated from the post synaptic membrane by in chemical synapses?
a synaptic cleft
what are synaptic clefts usually filled with?
synaptic vesicles containing a neurotransmitter
in chemical synapses when an action potential in the presynaptic axon opens what happens?
voltage-gated calcium channels and the calcium causes synaptic vesicles to fuse with the presynaptic axon membrane
what happens when synaptic vesicles fuse with the presynaptic axon membrane in chemical synapses?
the neurotransmitter is dumped into the synaptic cleft
after the neurotransmitter is dumped into the synaptic cleft in chemical synapses what does the neurotransmitter usually do?
bind to a ligand-gated ion channel that produces a graded depolarization or hyperpolarization
when neurotransmitters bind to ligand-gated channels in chemical synapses and produce a grade depolarization or hyperpolarization, what does that depend on?
the ion that crosses the membrane and receptor
what happens to neurotransmitter in chemical synapses?
either enzymatically degraded, taken up by the presynaptic terminal or diffuses out of the synapse
what are the neurotransmitters in chemical synapses usually?
ligand-gated channels to which only specific molecules can bind
what does the effect of a neurotransmitter in chemical synapses on a postynaptic membrane depend on?
the nature of the neurotransmimtter receptor and what ion crosses the membrane
what is an example that the neurotransmitter AcH would be used for?
myasthenia gravis
what is an example that the neurotransmitter serotonin would be used for?
antidepressant therapy and hallucinogens
what are some transitters that fall into the category of biogenic amines?
1) serotonin
2) dopamine
3) norepinephrine
what is an example that the neurotransmitter dopamine would be used for?
drug addiction and parkinson disease
what is an example that the neurotransmitter norepinephrine would be used for
ADHD and amphetamines
what neurotransmitters fall into the category of amino acids? (3) (GGG)
1) gamma-amino butyric acid (GABA)
2) Glycine
3) glutamate
what is an example that the neurotransmitter GABA would be used for? (3) (BBA)
1) barbiturates
2) benzodiazepines (anti-anxiety drugs)
3) alcohol dependence
what is an example that the neurotransmitter glycine would be used for?
strychnine poisoning
what is an example that the neurotransmitter glutamate would be used for?
stroke and excitotoxicity
what have many substances been identified as?
neurotransmittesr
what do some neurons release?
more than one neurotransmitter
what are neuromodulators?
neurotransmitters released by neurons that affect synaptic activity at distant synapses
what do some drugs affect?
synaptic activity
what do axoaxonic synapses do?
either reduce or increase the amount of neurotransmitters released
what is it called when axoaxonic synapses reduce the amount of neurotransmitters released?
presynaptic inhibition
what is it called when axoaxonic synapses increase the amount of neurotransmitters released?
presynaptic facilitation
what is a graded depolarization in a postsynaptic neuron called?
excitatory postsynaptic potential (EPSP)
what is true of EPSP?
the neuron is close to firing
what neurotransmitter falls into the category of purines?
adenosine
what is an example that the neurotransmit adenosine is used for?
neuroprotective agent and caffeine
what is a neurotransmitter that falls under the category neuropeptides?
endorphins
what is an example of what the neurotransmitter neuropeptides (endorphins) are used for?
pain therapy and opiates
what is a neurotransmitter that falls into the category of gases?
nitric oxide
what is an example that the neurotransmitter nitric oxide is used for?
stroke damage and treatment for erectile dysfunction
what is a graded hyperpolarization in a postsynaptic neuron called?
an inhibitory postsynaptic potential (IPSP)
what is true of IPSP?
the neurons is further from firing
is a single EPSP large enough to depolarize the initial segment to or past the threshold?
no
even though a single EPSP isn’t large to depolarize the initial segment to or past the threshold what does it do?
persist for a period of time
what has to happen to ESPS and IPSP in order for an action potential to be produced?
the EPSP and IPSP are added together in time and the neuron does nothing until the membrane at the initial segment is depolarized to or past the theshold
what are two ways that EPSPs can be added together?
1) spatial summation
2) temporal summation
where do EPSPs and IPSPs ocur?
on the dendrite
how does spatial summation occur?
by 2 or more neurons
how does temporal summation occur?
by one neuron
with thousands of neuron synapses on a neuron what are neural pathways?
complex
what type of pathways exist?
serial and parallel
what are some of the circuits that there are evidence of? (4) (CDRP)
1) convergent pathways
2) diverging pathways
3) reverberating circuits
4) parallel after-discharge circuits
what does convergent pathways allow?
IPSPs and EPSPs to affect an output. multiple neurons converge upon and synapse with a smaller number of neurons
what does diverging pathways do?
enlarge the effect of a signal
what does reverberating circuits do?
produce a series of action potentials
what does parallel after-discharge circuits have?
complex functions
what type of pathway does divergent pathways create?
parallel pathways
what does the reverberating circuit cause?
complete tetanus
what type of circuit is parellel-discharge circuit?
serial
