Lecture 17 - Nervous Systems 2 Flashcards
Resting potential (3)
Membrane potential when neuron is not firing, inside of membrane is more electronegative, outside of membrane is defined as 0 mV
The resting potential is determined by several transmembrane proteins: (4)
- Potassium (K+) leak channels
- Sodium ion (Na+) voltage-gated channels
- Potassium (K+) voltage-gated channels
- Proton pumps
Potassium (K+) leak channel
Allows K+ to leak across cell membrane
Sodium ion voltage-gated channel (3)
Open or closed depending on difference in electric charge across cell membrane (membrane potential), when closed Na+ cannot cross neuron’s membrane, when open Na+ can cross the neuron’s membrane
Potassium (K+) voltage-gated channels
Open or closed depending on difference in electric charge across cell membrane (membrane potential)
Proton pump
Causes inside of neuron to become more electronegative
Why is the inside more electronegative? (5)
Na+ voltage-gated channels are closed or K+ voltage-gated channels are closed, proton pump trades 3 Na+ positively charged ions for 2 K+, leading to fewer positive charges on the inside of the neuron, therefore causing the inside to be more electronegative, K+ can cross leaky channels and the concentration gradient favors a net export of K+
Equilibrium gradient of K
When the electrochemical gradient favors a net import of K+ but at the resting potential there is no net movement of K+
Action potential
A rapid change in electrical potential across a cell membrane
Threshold potential (2)
Membrane potenital that will trigger an action potential, at this threshold the Na+ voltage gated channels open and phase I (depolarization) begins
Depolarization phase
After reaching the threshold potential, phase 1 (aka depolarization phase) begins, in which Na+ ions rush in causing a decrease in electronegativity
Repolarization phase (3)
Phase 2 (aka repolarization phase) in which Na+ voltage-gated channels close, K+ voltage gated channels open, and K+ moves out of cell via K+ voltage-gated channels and K+ leaking ion channels
Hyperpolarization phase (3)
After phase II ends and the membrane potential drops to resting potential, the hyperpolarization phase begins. Due to loss of K+, the membrane potential becomes slightly more negative than the resting potential. K+ voltage gated ion channels flip between open and closed before finally closing.
Propagation of action potentials along a neuron (3)
- Na+ enters axon, where it attracts negative charges and repels positive charges
- Neighboring membranes depolarize, causing the inside to become more electropositive. The threshold potential is reached.
- This causes an action potential in the neighboring membrane, causing the Na+ voltage gated ion channels to open. Na+ depolarizes the membrane
Propagation of action potentials along a neuron pt 2 (3)
“upstream” action potentials cause “downstream” membranes to depolarize, the action potential is propagated along the axon from “upstream” to “downstream”, “upstream” Na+ voltage gated channels need to reset before they can fire again
Triggering an action potential
The trigger comes from another neuron
Synapse
The interface between the two neurons
Synaptic cleft
The space between the two communicating nerve cells
Neurotransmitter
A molecule that transmits a signal between two neurons or a neuron and an effector cell
Presynaptic neuron
The neuron that releases neurostransmitters
Postsynaptic neuron
The neuron that receives neurotransmitters
Excitatory neurotransmitter (3)
Makes the postsynaptic neuron more likely to produce an action potential, excitatory neuropeptides bind to receptors in the postsynaptic neuron causing the opening of + ion channels, + ions then rush into postsynaptic neuron
Inhibitory neurotransmitter
Makes the postsynaptic neuron less likely to produce an action potential, ethanol mimics the inhibitory neurotransmitter GABA
