Flashcards in Chapter 3 Neurophysiology Deck (22)
What are Ions
electrically charged molecules
How do Ions contribute to the polarization of neurons?
A resting neuron is polarized.
Electrical charge is:
Positive on the outside =Potassium k+()
Negative on the inside = Sodium (Na+)
Resting potential of Membrane = an electrical difference across the membrane
-50 to -80
determined by inserting the electrode into the axon.(axon is more negative than the outside)
Sodium -potassium pump
A specialized membrane protein that helps pump 3 sodium ions (Na+) out and 2 K+ in
proteins that span the cell membrane & allow ions to pass.
Selective permeability to potassium ions (k+)
The can enter or leave the cell freely
2 opposing forces that drive K+ ions in & out cells?
Diffusion = The movement of ions from an area of higher concentration to an area of lower concentration.
Electrostatic Pressure = causes ions to flow towards oppositely charged areas.
electrical charge that balances two opposing forces acting on K+
Electrical signals sent through the axon
Action Potential Threshold
Brief, large change in membrane potential
Membrane potential becomes positive
Depolarization vs Hyper-polarization
Depolar = decrease in membrane potential (interior of the cell becomes less negative) grader response up to a point.
Hyper = increase in membrane potential, (interior of the cell becomes more negative.) Produces a graded response.
"All-or-none" property of action potential
The neuron fires at full amplitude or not at all.
Ionic Mechanisms that cause an action potential?
Voltage-Gated Na+ channels open:
Until the membrane potential reaches +40mv
As cell becomes positive,
Voltage-gated K+ channels open
K+moves out of cell
Resting potential is restored
What is a refractory period?
Temporarily unresponsive or inactivated
Absolute refractory phase vs. Relative refractory phase.
Absolute = the neuron is insensitive to further stimulation.
Relative = Only strong stimulation can produce an action potential
The speed of propagation of action potential along the axon (axon diameter & myelination cause it to vary)
Axons that show the fastest conduction velocity
Myelin = a fatty insulator around an axon, (formed by glial cells) that boosts the speed.
Satatory Conduction & Nodes of Ranvier
Action potential that jumps from one node of Ranvier to next. (form of conduction that is characteristic of myelinated.)
Nodes of Ranvier = small gap in the insulating myelin sheath
1) Action potential reaches the end of an axon
2) Calcium (Ca2+) ion channels open & Ca2+ enter cell.
3) Synaptic vesicles move to the release site on the presynaptic membrane
4) Neurotransmitter binds to receptors on postsynaptic membrane
5) Changes the membrane potential of the postsynaptic cell.
What are the 2 types of Postsynaptic Potentials that change membrane potential?
Excitatory Postsynaptic potential (EPSP) = small local depolarization (Na+) Sodium channels open
Inhibitory postsynaptic potential (IPSP) = a small local hyperpolarization (Cl-) choloride channels open
What are 2 ways the synaptic transmission is Halted?
Degradiation = rapid breakdown and inactiviation of transmitter by an enzyme.
Reuptake = transmitter is absorbed back into the presynaptic axon terminal
(Transmitter = special receptors that bring the transmitter back inside.)