Nerve Communication Flashcards
How do nerves communicate?
Communicate w/ one another by electrical signals
What are the different types of communication?
Graded potential
-short distance communication
Action potential
-long distance communication
-nerve action potential (impulse)What do the production of graded & action potentials depend on?
Resting membrane potential
Presence of specific ion channels
Why does resting membrane potential exist?
Consists of 5 facts
- more negative ions inside cell membrane
- more positive ions out cell membrane
- difference in charge causes electrical potential
- measured in millivolts(mV)
- normal resting potential is -70mV
- membrane said to be “polarized”
- NA-K pump stabilizes resting membrane potential
- 3 NA ions out, 2 K into cell
- difference in charge causes electrical potential
Role of ion channels?
What is this called? Definition?
Main path for current to flow across membrane
Called electrochemical gradient
-ion movement from high to low concentration
Changes in membrane potential produce how many types of signals? What are they? What do they consist of?
2 types Graded potentials -incoming signals -occur over short distances Action potentials -long distance signals of axon
What does nerve communication involve? (3 things)
Graded potentials
Action potentials
Synapse
Graded potentials
What is it? Location? What does it do? Description of distance?
Small changes in membrane potential
-either more polarized- inside more negative OR less polarized- inside less negative
Most occur in dendrites & cell bodies
Short distances- few millimeters
Initiates action potentials in axon
Graded potentials
What does graded mean?
Depends on?
“Graded” means amplitude of electrical signal varies
- depends on strength of stimulus
- # of ligand-gated or mechanical gated channels open
How do ions move?
Ions move using ‘gates’ (proteins) in cell membrane
Leak channel
Channel
-randomly open & close
Ligand-gated channel
Chemical stimulus opens the channel
Opens w/ neurotransmitters
(Muscle contraction)
Mechanically gated channel
Mechanical stimulus opens the channel
-open w/ response to deformation of receptor (touch, pressure, sound)
(This is involving graded potentials)
Voltage-gated channel
Change in membrane potential opens the channel
-opens w/ change in membrane potential
Action potential
Where propagated?
Propagated along axon
Only in excitable membranes- neurons & muscle cells
Brief reversal of membrane potential & return to resting state
Long distance neuron communication
Do not decrease w/ distance
Use voltage gated ion channels (NA/K pump)
What is a comparison for an action potential propagated along the axon?
The domino effect - not all at once, 1 part at a time
Generation of action potential. 4 states
Resting state
Depolarization
Repolarization
Hyperpolarization
Resting state
Type of channels? What do they do? Mv at this stage?
Voltage gated channels open (NA & K)
-70 mV membrane potential
Depolarization
What is it?
What must happen for this to occur?
Channels?
Membrane potential becomes less negative reaching zero
-must reach threshold (-55mV)
- “all or none” principle (like muscle contraction)
NA channels open
Repolarization
Channels?
What happens?
Na channels close, k channels open
Membrane potential restored to resting state (-70 mV)
Hyperpolarization
Channels?
Some k channels open, Na channels reset.
Factors affecting speed of axon potential what are they? (3)
Amount of myelination
Axon diameter
Temperature
Amount of myelination
More rapid when myelinated
Axon diameter
Larger diameter -> faster propagation
Less resistance to flow
Temperature
Cooler temp -> lower speeds
Synaptic transmission is where? Definition?
Synapse - junction btwn neurons that action potential travels through
(Btwn 2 neurons bulb to dendrites)
what are the two neurons in the synapse? function?
presynaptic neuron- sends signals (bulb)
postsynaptic neuron- receives signal (dendrites)
what are the 2 types of synapse?
electrical synapses chemical synapses (muscle contraction, neurotransmitters)
describe electrical synapses
location? what happens? how? examples?
btwn 2 close neurons held together by GAP JUNCTIONS
ionic current flows by passive transport through gap junctions
current flows in both directions
fast transmission (instantaneous)
EX) areas of brain for eye movements, emotions, & memory
description of chemical synapse
job? location?
convert electrical signals (action potential) to chemical signals (neurotransmitter)
uses neurotransmitters across a synapse
neurotransmitters (4)
acetylcholine
norepinephrine & dopamine
serotonin
histamine
acetylcholine
muscles
norepinephrine & dopamine
“fell good”
fits depression, anxiety, make happy!
serotonin
sleep, regulating mood
histamine
wakefulness, appetite control
mediates inflammation, vasodilation (asthema, dialate bronchial tubes)
what part of the neuron when excited causes a generation of an action potential?
axon
where are electrical synapses made?
GAP JUNCTIONS
are electrical synapses excitatory or inhibitory?
excitatory
what is an advantage of electrical synapses over chemical synapses?
electrical synapses is FAST transmission (instantaneous). it also goes to a group instead of only 1
where are chemical synapses made?
synaptic cleft
what type of molecule is used to carry the chemical signal?
neurotransmitter
at a chemical synapse, neuronal membranes are separated by a gap called the ______
synaptic cleft
the calcium inside the synaptic knob initiates ______
release of neurotransmitter (or initiates the synapse)
what type of behavior are electrical synapses associated with?
areas of brain for eye movements, emotions, and memory
what are the steps in the process of a chemical synapse btwn neurons?
1) axon potential arrives at axon terminal
2) Na+ channels open & depolarization causes Ca2+ channels to open
3) Calcium causes synaptic vesicles to fuse w/ neuron membrane, dumping neurotransmitter into synapse
4) Neurotransmitter binds receptor, receptor opens
5) Na+ enters postsynaptic neuron & depolarizes cell, causing action potential (once ACh is released in there)
(SAME AS NMJ)
the neuron conducting an action potential toward the synapses is called the __________ neuron
presynaptic
the axon terminal of the presynaptic neuron contains membrane sacs called _________ which are filled with _______
synaptic VESICLES
neurotransmitters
polarized means
unequal charge across the membrane
when a cell membrane is polarized, the inside is ______ charged with respect to the outside
negative
the polarization of a cell membrane is due to _______
the sodium/potassium pump
_____ is the major intracellular positive ion and ________ are the major extracellular cation
potassium (K+)
Sodium (Na+)
the measured value of resting potential is
-70 mV
at resting membrane potential, sodium channels are _____ but when threshold is reached, sodium channels _____
open
open
the measured value of threshold is
-55 mV
What happens during the absolute refractory period?
voltage gated Na channel activation gates are open then
voltage gated K channels are open & Na channels are inactivating
(hill of depolarization & repolarization)
Whats happens during the relative refractory period?
voltage gated K channels are still open; Na channels are in resting state
(hyperpolarization to the start of resting)
explain the graph dealing with sodium (Na) & potassium (k)
resting- pump maintains Na Sodium outside and K Potassium inside
Depolarization- Na (Sodium) in!
Repolarization- K (Potassium) out!
1st part of hyperpolarization still going down- K (Potassium) out overshoot
2nd part going up- pump
resting- pump maintains Na (Sodium) outside & K (Potassium) inside
what happens to the channels when the different ions move? give all situations on graph
Na? K? Pump?
Na (sodium) in = Na channels open, K channels close
K (potassium) out = K channels open, Na close
Pump= 3 Na (sodium) pumped out, 2 K pumped in
what would happen is we didn’t have Na or K?
No nerve conduction!
what channels are involved in resting membrane potential? What happens to them?
voltage gated Na channels and voltage gated K channels are closed!
what causes depolarization to threshold?
STIMULUS
electrical signals cannot do what? what do we use?
cannot jump across gap, so we use chemical signals!
whats a neuron?
basic unit of information processing & building block of the brain
it’s an excitable cell the receives a stimuli & either sends the signal on, or not
what ion is the high concentration outside the neuron?
sodium Na ions
what ion is in high concentration inside the neuron?
K potassium ions
what specialized protein exists in the neural cell membrane?
channels
what is the function of channels?
form pores in the membrane that are selectively permeable to particular ions
under resting conditions which ion leaks more, sodium leaking inward or potassium leaking outward?
potassium leaking outward
result of the leaks makes the outside of the cells charged ___ and the inside of the cell charged __. the cell is said to be what?
positive, negative
polarized
since sodium is in high concentration outside the cell, what happens if the sodium channel opens in the membrane? which way does the sodium move?
into the neuron
when the sodium moves in, the neuron is momentarily what? this is called?
positive
depolarized
the switch in membrane potential (when the inside is postive from sodium entering) is the what?
action potential
speed of an action potential is relate to?
size of the axon
what type of axon results in fast transmission rates?
big axons
what substance allows for rapid action potential?
myelin
where does the action potential take place on a myelinated neuron?
nodes of ranvier
what does the myelin sheath allow action potentials to do?
allows action potential to jump from 1 node to another, greatly increasing the rate of transmission
multiple sclerosis
demyelinating disease that affects bundles of axons in the brain, spinal cord, and optic nerve, leading to lack of co-ordination muscle control (and difficulties with speech and vision). this proves that w/o myelin sheath, we cannot function.
