Action potential - Part I Flashcards
Which type of ion channels do neurons generally have in their cellular membrane?
- Ligand Gated Ion Channels
- Voltage Gated Ion Channels
- Modality Gated Ion Channels
- Leaking Ion Channels
What are Ligand Gated Ion Channels?
- Synaptic/Receptor Potential
- MOST COMMON at synapse
- Where neuron communicates with its target
What are Voltage Gated Ion Channels?
- Action Potential
- When Voltage changes on the cell membrane opens this channel, initiates action potential
- MOST IMPORTANT!
What are Modality Gated Ion Channels?
- Receptor Potential
- Examples: Touch, Mechanic Stretch, Initiates receptor potential
What are Leaking Ion Channels?
- K+ to maintain the rest membrane potential
-NOT fast
-Leaks Slowly - Higher Concentration out
Which type of ion channel is most common?
ligand-gated ion channels
Which type of ion channel is most important?
voltage-gated ion channels
Which type of ion channel initiates AP?
Voltage gated
What is a synapse?
communicating unit, axon and target structures
What releases neurotransmitters?
Axonal terminal
What causes the neurotransmitters to be released?
depolarization
What are the three parts of a neuron?
- cell body
- dendrites
- axons
What is within the cell body/soma?
all cellular organs, including the nucleus
Why is the nucleus different?
terminally differentiated cell, nucleus condensed = no replication anymore
What is the function of the neuron cell body/soma?
- synthesizing functions
- reception and summation of receptor or synaptic potentials
What are the functions of the mitochondria of the axon?
- conduction of AP
- active transportation
What is the specialized region of the mitochondria for? Where are they?
- initation of AP
- located in hillock around soma and trigger zone around the receptor endings
Where are the two types of neurons with NO axon located?
retina
How many axons do most neurons have?
1
What is the function of mitochondria?
energy!
- transports different molecules in the axon
How do we type neurons?
number of dendrites
- unipolar
- bipolar
- pseudopolar
- pseudounipolar
What are multipolar neurons?
- more dendrites, different poles, 1 axon
What are bipolar neurons?
1st order neuron in retina to conduct signals
- axon on both sides
What are unipolar neurons?
- doesnt have other dendrites
- 1 axon, exists in limted areas of cerebellum
- common in animals/ lower level life forms
What are the two types of pseudounipolar neurons?
- central processes (1 part)
- peripheral processes (mostly)
What do pseudounipolar neurons need?
golgi apparatus and mitochondria
- golgi apparatus synthesized by cell body
- mitochondria for energy
What are two ways molecules are transported in the neurons?
- Railway
- Active transportation
What is required for railway transportation of molecules in neurons?
- tubulins: elongating to the plus direction (have polarity)
Which way can railway transport molecules in neurons?
- either way in dendrites, only to the terminal in axon
- dendrites fast, axons slower
- go from negative to positive in terminal
What is required for anterograde trasportation?
kinesin
- negative to positive, interacts with 2 railways
What is required for retrograde transportation?
dynein
- positive to negative, nucleus to cell body
What are other functions of kinesin and dynein for active transportation?
cargo!
What are the components of the bilayer phospholipids?
- hydrophilic head: likes water, abundant water molecules around the head
- hydrophobic tail: repels water
- contains cholesterol to stabilize, other proteins pierce or attach on either side to form channels
What kind of permeability does the neuron cellular membrane have?
selectively permeable
- things cannot cross in and out freely
What is the water channel in the neuron cellular membrane?
aquaporin
- if increase in osmotic pressure, such as with salty food, water inside needs out
What are the ion channels in the neuron cellular membrane?
subtypes of receptors, leaking or gated
What are the ion pumps on the neuron cellular membrane?
Na+/k+ pump
What does the Na+/K+ pump depend on?
ATP
What is the ratio for the NA+/K+ pump?
3 Na+ out, 2 K+ in
What are the roles of other molecules in the neuron cellular membrane?
transporters, receptors, etc
What is osmotic potential?
unbalanced particles
What is electric potential?
unbalanced charges
What is polarity of neuron cellular membrane?
inside negative
What is the rest membrane potential of a neuron?
~-90 to -40 mV
What happens with an increase in rest membane potential?
depolarization
- bigger than 40
What happens with a decrease in rest membane potential?
hyperpolarization
- -90 - -120 mV
When do voltage gated ion channels open?
above the threshold
- otherwise closed
- all sodium ions flow in based on osmotic potential
-“black friday”
What is the ligand and receptor with ligand-gated ion channels?
neurotransmitter as ligand, ion channel as receptor
- Na+ ions flow in = more = induces depolarization = increases membrane potential
Where are most modality gated ion channels found?
a receptor on receptor ions
How do modality-gated ion channels open?
with heat, stretch, light, etc
What happen with leaking channels?
K+ freely crosses the membrane
- SLOW, maintains stability of rest membrane potential
What are the stimuli that change the receptor potential?
- Duration
- Intensity
What are the types of duration with receptor potential?
- fast adaptation
- slow adaptation (getting used to stinky smells)
What is the intensity of receptor potentials measured in?
amplitude
- higher with stronger stimuli
What kind of potential are synaptic potentials ALWAYS?
short-duration
What is the intensity of synaptic potential measured in?
amplitude
What is the duration of an action potential?
SHORTEST DURATION (~1ms)
Is the amplitude fixed for specific neurons with action potentials?
YES
What is the intensity of an action potential measured using?
Frequency
Which proteins over see the anterograde and retrograde transportation in the axons?
anterograde: kinesin
retrograde: dynein
What happens to the membrane potential with hyperpolatization?
decreased
What happens to the membrane potential with depolarization?
increased
What happen if the membrane potential is above the threshold?
action potential
What happens to the frequency with a stronger stimuli?
higher frequency
- induces more AP
What are the 5 phases of initiation of an action potential?
- resting potential -70mV
- slow depolarization >-70mV , < -55 mV
- Fast depolarization >-55 mV, threshold = AP
- Repolarization: decrease until to -70mV
- hyperpolarization: below threshold
What happens during fast depolarization?
- Voltage-gated sodium ion channels open
- ACTION POTENTIAL
What channel threshold is reached during repolarization?
K+ voltage-gated ion channel threshold
- K+ out
Na+ voltage-gated ion channel threshold
- Na+ in
What happens during the absolute refractory period?
- No or not enough voltage-gated sodium channels to reopen
- UNIDIRECTIONAL CONDUCTION (one direction, not backwards)
What happens during the relative refractory period?
- some voltage-gated sodium channels to reopen
- higher stimuli intensity will open channels to allow Na+ to slowly get in and initiate another AP
What does the sodium potassium pump do?
maintian Na+ and K+ gradients
What is the ratio of sodium to potassium with the pump per 1 ATP?
3 Na+ out, 2 K+ in
What is the sodium potassium pump dependent on?
ATP!
- 20-40% of the energy consumed by the brain
What happens with passive conduction with distance?
decreases
What causes bidirectional conduction?
if stimulated in the middle of axons
What is active conduction?
- reinitiating action potentials
- unidirectional (due to absolute refractory period)
What is the amplitude with active conduction?
fixed! above the threshold
If a neuron with a rest membrane potential of -70mV and a threshold of -55mV receives the following synaptic stimuli, will it be able to initiate an action potential?
a. -3mV; b. +22mV; c. -7mV; d. +14mV; e. +25mV
Yes, membrane potential changes to -19mV, above the threshold, initiating an action potential
Explain why the action potential can ONLY be conducted unidirectional?
Absolute refractory phase: no voltage-gated sodium channels available
