nerve impulse + action potential Flashcards
define nerve impulse
the electrical message that is transmitted down the axon of a neuron
define resting potential
state of the neuron prior to the sending of a nerve impulse
define electrical gradient
the difference in electrical charge inside and out of cell > membrane maintains
define electrical polarization
the difference in electrical charge of two locations
describe the membrane and what it allows to pass-through
selectively permeable = allowing some chemicals to pass more freely than others
- sodium, potassium calcium, and chloride pass-through
- sodium channels = closed
- potassium channels = partially closed
define sodium-potassium pump
a protein complex that continually pumps three sodium ions out of cells while drawing two potassium ions into the cells
- helps maintain the electrical gradient
what is action potential?
rapid depolarization of the neuron
- stimulation of the neuron past the threshold of excitation triggers it
list the steps of action potential
- depolarisation
- repolarization
- refractory period
describe the first step of action potential
depolarisation = sudden increase in membrane potential
- when a neuron is stimulated, some sodium channels are opened
- sodium ions move in and intracellular fluid becomes less negative which increases the potential difference
- if the potential difference increases to -55mV, voltage-gated sodium channels open, and sodium ions rush in
- the inward movement of sodium is too great to be balanced by outward movement of potassium, making inside more positive
- orignal polarity increases to +40mv = depolarised membrane
describe the second step of action potential
repolarisation
- sodium channels close which stops the influx of sodium ions
- simultaneously, potassium channels open, increasing K flow out of the cell
- this makes the inside more negative and decreases membrane potential and the membrane is repolarised
describe the third step of action potential
refractory period
- once sodium channels have opened they quickly become inactivated - unresponsive to stimulus
f- or a brief period, the membrane won’t undergo another action potential
- lasts form -55mV to -70mV
define hyperpolarization
increase the polariazation
define depolarization
refers to decreasing the polarization to zero
define the threshold of excitement
any stimulation beyond a certain level and results in massive depolarisation, reaches -55V
what are voltage-activated channels
membrane channels whore permeability depends upon the voltage difference across the membrane
- sodium channels
what is the all or none law?
states that the amplitude & velocity of an action potential are independent of the intensity of the stimulus
define the refractory period
after action potential where the neuron resists another action potential
define the absolute refractory period
first part
- membrane cannot produce an action potential
define the relative refractory period
2nd part
- needs stronger stimulus to trigger an action potential
what is the state of sodium and potassium channels when the membrane is at rest
sodium channels are closed
potassium channels are partially closed allowing slow passage of sodium
how does action potential work to carry a message
occurs in one section of membrane and triggers an AP in adjacent membrane and continues along length of neuron
how does conduction of nerve impulse occur along unmyelinated fibres
- AP travels along the whole length of the membrane, moving away from the stimulation point
- impulse is prevented from going back by a refractory period
how does conduction of a nerve impulse occur along myelinated fibres
- ions cannot flow between inside and outside of the membrane
- AP jumps from one node of Ranvier to the next via saltatory conduction
- allows nerve impulse to travel much faster
