Nerve Cells and Neuron Potentials 2 Flashcards
Electrical signals in neurons result in …
membrane potential changes
Electrical signals are due to …
gated channels (voltage, ligand, mechanically gated)
Describe gated channels.
- open or close in response to stimuli
- affect movement of ions
- ion movement = electrical signal
What are the 2 types of electrical signals?
- graded potentials
- action potentials
Graded potentials are (small/large) and communicate over (short/long) distances.
- small
- short
Action potentials are (small/large) and communicate over (short/long) distances.
- large
- long
Describe graded potentials.
- initiated by a stimulus
- small change in membrane potential
- magnitude varies (graded)
- spread by electronic conduction
- are decremental (magnitude decays as it spreads)
- communicate over short distances
What is the purpose of graded potentials?
determine whether an action potential will occur
What is the threshold?
level of depolarization necessary to elicit action potential
Excitatory is …
depolarization
Inhibitory is …
hyperpolarization
What is temporal summation?
same stimulus repeated close together in time
What is spatial summation?
different stimuli that overlap in time
Describe action potentials?
- rapid, large depolarization of membrane
- used for communication
- travel from cell body –> axons –> axon terminal
What can generate action potentials?
excitable membranes
What are the phases of an action potential?
- depolarization
- repolarization
- hyperpolarization
What happens to trigger depolarization?
Na+ channels open
What happens to trigger repolarization?
K+ channels open
Name 2 threshold triggers (depolarization).
- graded potentials bring membrane to threshold
- rapid opening of Na+ channels
What parts of the neuron are responsible for graded potentials?
- dendrites
- cell body
- receptors
Rapid opening of Na+ channels means …
- slow closing of Na+ channels
- slow opening of K+ channels
Why does the action potential not reach the equilibrium potential of sodium?
- K+ channels opening
- Na+ channels closing
What happens during repolarization?
- Na+ channels closed
- K+ channels opened
What happens during hyperpolarization?
- K+ channels remain beyond -70 mV
- membrane potential gets close to the equilibrium potential of potassium
What restores resting potential?
Na+/K+ pump
What are the 2 gates associated with voltage-gated sodium channels?
- activation gate
- inactivation gate
Describe the activation gate.
- voltage dependent
- opens at threshold and depolarization
- positive feedback
Describe the inactivation gate.
- voltage and time dependent
- opens during depolarization
- closes during repolarization
Describe voltage-gated potassium channels.
- one gate
- voltage/time dependent
- negative feedback: restores resting membrane potential, prepares the neuron for another AP
What is the refractory period? What are the 2 categories?
- follows an action potential
- decreased excitability
- absolute and relative
Describe the absolute refractory period.
- all of depolarization + most repolarization phase
- second action potential cannot be generated
- Na+ gates are inactivated
Describe the relative refractory period.
- spans the last part of the repolarization phase and hyperpolarization
- second action potential can be generated with a stronger stimulus
- some Na+ gates are closed; some are inactivated
What kind of stimulus can generate an AP during the absolute refractory period?
no stimulus of any strength can
What kind of stimulus can generate an AP during the early parts of relative refractory period?
a much stronger stimulus than normal
What kind of stimulus can generate an AP during the late parts of relative refractory period?
a stimulus a little stronger than normal
What is the all or none principle in reference to threshold stimulus?
- threshold depolarization = AP
- sub threshold depolarization = no AP
- suprathreshold depolarization = AP
What are 3 consequences of refractory periods?
- all or none principle
- frequency: greater frequency of AP for greater stimuli
- unidirectional propagation of action potentials
What 3 factors affect propagation?
- refractory period (unidirectional)
- axon diameter
- myelination
Describe how axon diameter affects propagation.
- larger: less resistance, faster
- smaller: more resistance, slower
Describe how myelination affects propagation?
- saltatory conduction
- faster propagation
Mechanisms of action potential conduction depends on the presence or absence of _______.
myelin
What are the 2 effects of graded potentials/APs?
- dissipate Na+ and K+ concentration gradients
- the Na+/K+ pump prevents dissipation
