lecture 4- excitability 2 Flashcards
list 3 main functions of action potential
1- amplifies incoming stimuli (incoming stimuli can be weak, need to be amplified)
2- transmits information rapidly across long distances in the body (nerve impulses traveling along nervous system)
3- initiates & regulates effector responses (usually a muscle contraction)
define action potential
the discharge of potential energy on the membrane
remember conductance of membrane comes from…
and capacitance comes from…
conductance comes from active transport of sodium pump
capacitance comes from differential permeability (depletes inside of positive charge)
mechanism of action potential is also based on the ___ and ___ of sodium and potassium ion channels
structure and function
what determines whether sodium and potassium channels are open or closed?
voltage/charge on membrane
describe the mechanics behind the sodium channels activation/deactivation
the channels have a voltage sensor, when voltage changes- activate gate opens
- an incoming stimulus pushes voltage sensors upward and causes activation gate to swing open- allows sodium to diffuse through the channel down its concentration gradient
- as soon as that happens, change in shape of protein begins to automatically swing inactivation gate closed, so the ball&chain channel closes
- after some time, it will reset and be ready to respond to another stimulus
for the sodium channel, movement of electrical charge is called the ____
accumulation of what kind of charge and where?
__polarizes the membrane
sodium current
positive charge on inside of membrane- makes inside less negative
depolarizes
describe the mechanics behind the potassium channels activation/deactivation
slightly different structure than sodium, but same principle
- voltage sensor is more like a paddle- when voltage changes, paddle flips up and opens the channel, allowing K+ to diffuse out
- when the paddle flips up like this, it pushes against lipids, this hydrophobic interaction closes the gate again
for the potassium channel, movement of electrical charge is called the ___
accumulation of what kind of charge and where?
__polarizes the membrane
potassium current
outwardly directed, takes positive charge away from inside of membrane, makes it more negative
hyperpolarizes
sodium __polarizes the membrane
depolarizes
potassium __polarizes the membrane
hyperpolarizes
what organism has been used to study action potentials?
the giant axons of squid
when studying action potentials, can manipulate charge on membrane by turning on stimulator
- describe what happens when you give a -10 mV electrical shock
start off at -70 mV (resting) –> when you give a nerve a stimulus, giving it an electric chock
- giving a -10 shock causes membrane to go from -70 to -80 –> becomes more polarized (hyperpolarized) –> opens potassium current, K+ leaves, membrane becomes more negative (when u turn stimulator off, goes back to -70)
- this is a passive local response (passive b/c membrane potential changes in proportion to stimulus, local b/cit is transient- only lasts as long as stimulator is turned on)
when studying action potentials, can manipulate charge on membrane by turning on stimulator
- describe what happens when you give a -20 mV electric shock
goes from -70 to -90
- passive local response, larger stimulus opens more potassium channels, causing more K+ to leave membrane, leaving it more negative (hyperpolarized)
when studying action potentials, can manipulate charge on membrane by turning on stimulator
- describe what happens when you give a +10 mV electrical shock
goes from -70 to -60 –> membrane becomes more positive, depolarized –> activates sodium channels, increases inward sodium current
- passive local response
what is the threshold stimulus required on the membrane to cause an action potential
+15 mV (-70 –> -55) –> action potential
an action potential is generated at __ voltage, which holds this value
threshold voltage
+15 mV
threshold is the minimum ___ needed to elicit a ___
strength stimulus
physiological response