3B: Nervous system Flashcards
Miguel Velazquez (24 cards)
what is graded potential?
a change in the membrane potential, that is decremental (decreases as distance from area of stimulation increases)
why does the degree of depolarisation lessen w distance?
- cytosol offers resistance to ion movement
- sodium (Na+) ions entering cell move back out through the membrane through sodium leak channels
what is an excitatory postsynaptic potential?
EPSP: graded depolarisation
what is and inhibitory postsynaptic potential?
IPSP: graded hyperpolarisation
what does opening of Na+ (or Ca2+) channels result in?
EPSP
what does opening of K+ (or Cl-) channels result in?
IPSP
what is the strength of the depolarisation stimulus in a graded potential determined by?
how much charge enters the cell
-> how many gated sodium channels are open
what is a subthreshold graded potential?
a graded potential that decreases in strength as it travels through the body so much, that it is below the threshold when it reaches the “trigger zone” and thus cannot initiate an action potential
what is a suprathreshold graded potential?
a graded potential that is still above the threshold by the time it reaches the trigger zone, generating an action potential
what is the summation of graded potentials?
adding up of graded potentials to generate a signal strong enough to create an action potential
what is a temporal summation?
repeated stimulation of one presynaptic terminal
what is a divergent neural circuit?
one neuron sends info to several neurons
what is a convergent neural citcuit?
many neurons influence a single neuron
what is a neural circuit that is parallel after-discharge?
a signal diverges into multiple parallel pathways, then converges onto a single neuron
what is a reverberating neural circuit?
signal creates a self sustaining loop of neural activity
what is spatial summation?
many excitatory neurons fire graded potentials simultaneously at many presynaptic terminals
-> an action potential is generated
how can graded potentials cancel each other out?
if some excitatory neurons fire graded potentials, these can be reduced to a signal below the threshold for an action potential, by inhibitory neurons
does an action potential decrease in strength as it travels along an axon?
no, as it becomes self propagating
explain the all-or-none principle of action potential initiation
- a depolarisation that is at the threshold elicits same action potential as one far above it
- the strength of the depolarisation has no effect on the amplitude of the action potential, as long as it is at minimum at the threshold
what is the absolute refractory period?
period of 1-2 ms after an action potential has been generated in which no stimulus can trigger another action potential
- prevents the action potential from travelling backward, ensuring one way travel from cell body to axon terminal
what is a relative refractory period?
period of 5-15 ms, when a second action potential can only be generated by a larger-than-normal stimulus
what is continuous propagation of an action potential?
action potentials travel along an axon by continuous propagation in un myelinated axons, taking approx. 1m/s
what is saltatory propagation of an action potential?
action potentials “jump” from one node of ranvier to another, bypassing the myelinated internodes
what is a node of ranvier?
the unmyelinated section of a myelinated axon
