topic 5: membrane excitability 2 Flashcards
(24 cards)
What are graded potentials?
Signals that travel over short distances and lose strength the further they travel through the cell
Graded potentials vary in magnitude and can be positive or negative, depending on ion movement.
What determines the magnitude of graded potentials?
Depends on:
* Whether ions are entering or leaving the neuron
* Charge of ion (Ca2+, K+, Cl-, Na+)
What initiates graded potentials?
Normally occur following a stimulus activating receptors on the end of the neuron
How do neurotransmitters affect graded potentials?
They act on receptors to make the cell more or less excitable
What are excitatory postsynaptic potentials (EPSPs)?
Depolarizing graded potentials that increase the likelihood of an action potential
What are inhibitory postsynaptic potentials (IPSPs)?
Hyperpolarizing graded potentials that decrease the likelihood of an action potential
What is the threshold for triggering an action potential?
Greater than -55mV at the trigger zone
What is membrane potential?
Potential inside cell membrane relative to fluid just outside; it is negative under resting conditions and becomes positive during an action potential
What primarily determines the resting membrane potential?
Concentration of K+ and the cell’s permeability to K+, Na+, Cl-
What happens during depolarization?
Na+ ions enter the neuron, causing the cell to become more positive
What happens during hyperpolarization?
K+ ions leave the neuron, making the inside of the neuron more negative
What are the types of ion channels?
- Mechanically gated ion channels
- Chemically gated ion channels
- Voltage-gated ion channels
What are the three phases of an action potential?
- Depolarization - rising phase
- Repolarization - falling phase
- Restoration - after hyperpolarization phase
What triggers the opening of Na+ channels during an action potential?
A depolarizing stimulus, normally as a result of an EPSP
What is the role of the Na+/K+ pump?
Restores resting ion balance by moving Na+ out and K+ into the neuron
What is the refractory period?
Period after an action potential during which another action potential cannot be produced
What is the significance of the nodes of Ranvier?
They allow positive charge to travel between unmyelinated sections of the axon
What is exocytosis in neurotransmitter release?
Process where neurotransmitters are released from vesicles in the axon terminal
What happens when neurotransmitters bind to receptors?
They can create rapid/short acting responses by directly opening ion channels
What is the function of glutamate?
Excitatory neurotransmitter important for learning and memory, can produce EPSP
What is the function of GABA?
Inhibitory neurotransmitter that decreases activity in neurons and produces IPSP
What is temporal summation?
Occurs when two graded potentials overlap in terms of effect at the trigger zone
What is spatial summation?
Occurs when several stimuli arrive at the same time from different neurons
What happens to neurotransmitters after release?
They need to be broken down and recollected by the neuron or removed from the synapse
