CH3: Neurophysiology Flashcards
neurophysiology
the study of the life processes of neurons
ion
an atom or molecule that has acquired an electrical charge by gaining or longs one or more electrons
anion
a negatively charged ion, such as a protein or a chloride
cation
a positively charged ion, such as a potassium or sodium ion
intercellular fluid
the watery solution found within cells
extracellular fluid
the fluid in the spaces between cells
cell membrane
the lipid bilayer that ensheathes a cell
resting potential
the difference in electrical potential across the membrane of a nerve cell at rest
millivolt (mV)
a thousandth of a volt
ion channel
a pore in the cell membrane that permits the passage of certain ions through the membrane when the channels are open
potassium ions (K+)
a potassium atom that carries a positive charge
sodium ions (Na+)
a sodium atom that carries a positive charge
selective permeability
the property of a membrane that allows some substances to pass through, but not others
what are the 2 forces driving the movement of ions into and out of a neuron?
diffusion and electrical pressure
diffusion
the spontaneous spread of molecules from an area of high concentration to an area of low concentration until a uniform concentration is achieved
electrical pressure
the propensity of charged molecules or ions to move toward areas with the opposite charge
what are the functions of the sodium-potassium pump?
the pump is semipermeable and its function is pump 3 sodium (Na+) ions out of the cell for every 2 potassium (K+) ions pumped in. the pump is selectively permeable to K+ but not Na+ ions.
equilibrium potential
the point at which the movement of ions across the cell membrane is balanced, as the electrostatic pressure pulling ions in one direction is offset by the diffusion force pushing them in the opposite direction
axon hillock
the cone-shaped area on the cell body from which the axon originates
hyperpolarization
an increase in membrane potential (the inside of the neuron become even more negative or farther from zero)
depolarization
a decrease in membrane potential (the inside of the neuron becomes less negative or closer to zero)
local potential
an electrical potential that is initiated by stimulation at a specific site, which is a graded response that spreads passively across the cell membrane, decreasing in strength with time and distance
threshold
the stimulus intensity that is just adequate to trigger an action potential in an axon
action potential
also called spike. a rapid reversal of the membrane potential that momentarily makes the inside of the membrane positive with respect to the outside
all-or-none property
referring to the fact that the size (amplitude) of the action potential is independent of the size of the stimulus
voltage-gated Na+ channel
a Na+-selective channel that opens or closes in response to changes in the voltage of the local membrane potential. it mediates the action potential
refractory
temporarily unresponsive or inactivated
absolute refractory phase
a brief period immediately following the production of an action potential, no amount of stimulation can induce another action potential, because the voltage-gated Na+ channels can’t respond
relative refractory phase
during which only strong stimulation, well beyond the threshold, can produce another action potential
what are the steps from resting potential to action potential?
- open potassium K+ channels and closed sodium Na+ channel create the resting potential.
- closed K+ channel, any depolarizing force will bring the membrane potential closer to the threshold; sufficient depolarization of the axon results in an action potential.
- at the threshold, voltage-gated Na+ open, causing a rapid change of polarity - the action potential; positive polarization.
- Na+ channels are inactivated; gated K+ channels open, repolarizing and even hyperpolarizing the cell (afterpotential.
- all gated channels are closed. the cell returns to its resting potential.
afterpotential
the positive or negative change in membrane potential that may follow an action potential
how are action potentials propagated across the axon?
an action potential is regenerated along the length of the axon.
a) continuous conduction along unmyelinated axon; the inrush of Na+ ions depolarizes the neighboring region of the axon, opening Na+ channels there. the successive opening of neighboring Na+ channels continues down every branch of the axon.
b) rapid saltatory conduction along myelinated axon; Na+ channels open, generating an action potential. myelin channels the depolarization down the axon interior. depolarization spread within the axon very rapidly, like electricity through a wire. the depolarized Na+ channels open, re-creating the action potential at the new node… and so on, hopping down the nodes in saltatory conduction
myelin
a fatty insulation around an axon, formed by glial cells. this sheath boosts the speed at which action potentials are conducted
node of Ranvier
a gap between successive segments of the myelin sheath where the axon membrane is exposed
saltatory conduction
the form of conduction that is characteristic of myelinated axons, in which the action potential jumps from one node of Ranvier to the next
multiple sclerosis (MS)
a disorder characterized by the widespread degeneration of myelin
neurotransmitter
the chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons
presynaptic
located on the “transmitting” side of a synapse
postsynaptic
postsynaptic to the region of a synapse that receives and responds to the neurotransmitter
postsynaptic potential
a local potential that is initiated by stimulation at a synapse, which can vary in amplitude, and spreads passively across the cell membrane, decreasing in strength with time and distance
excitatory postsynaptic potential (EPSP)
a depolarizing potential in postsynaptic neuron that is normally caused by synaptic excitation. EPSPs increase the probability that the postsynaptic neuron will fire an action potential
inhibitory postsynaptic potential (IPSP)
a hyperpolarizing potential in the postsynaptic neuron. IPSPs decrease the probability that the postsynaptic neuron will fire an action potential
what ions are responsible for postsynaptic EPSPs and IPSPs?
EPSPs, when Na+ channels open;
IPSPs, when Cl- channels open
chloride ion (Cl-)
a chlorine atom that carries a negative charge
spatial summation
the summation of postsynaptic potentials that read the axon hillock from different locations across the cell body. if this summation reaches the threshold, an action potential is triggered.
ex: if 3 EPSPs arrive at three different parts of the dendrite, that may be enough to push the postsynaptic cell to the threshold, triggering an action potential. any IPSPs that might arrive would counteract the EPSPs
temporal summation
the summation of postsynaptic potentials that reach the axon hillock at different times. the closer in time the potentials occur, the more complete the summation is.
ex. even a single synapse may push the postsynaptic cell to the threshold if many action potentials arrive in quick succession; providing overlapping EPSPs.
summarize the chemical synaptic transmission.
- action potential arrives at the presynaptic axon terminal.
- voltage-gated calcium channels in the membrane of the axon terminal open, and calcium ions (Ca2+) enter the axon terminal.
- Ca2+ causes synaptic vesicles filled with neurotransmitter to fuse with the presynaptic membrane and rupture, releasing the transmitter molecules into the synaptic cleft.
- some transmitter molecules bind to special receptor molecules in the postsynaptic membrane, leading -directly or indirectly- to the opening of ion channels in the postsynaptic membrane. the resulting flow of ions creates a local EPSP or IPSP in the postsynaptic neuron.
- the IPSPs and EPSPs in the postsynaptic cell spread toward the axon hillock.
- synaptic transmission is rapidly stopped, so the message is brief and accurately reflects the activity of the presynaptic cell.
- synaptic transmitter may also activate presynaptic receptors, resulting in a decrease in transmitter release
calcium ions (Ca2+)
a calcium atom that carries a double positive
synaptic delay
the brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential
acetylcholine (ACh)
a neurotransmitter that is produced and released by parasympathetic postganglionic neurons, by motoneurons, and by neurons throughout the brain
ligand
a substance that binds to receptor molecules, such as a neurotransmitter or drug that binds postsynaptic receptors
agonist
a substance that mimics or potentiates the actions of a transmitter or other signaling molecule
antagonist
a substance that blocks or attenuates the actions of a transmitter or other signaling molecule
degradation
the chemical breakdown of a neurotransmitter into inactive metabolites
Reuptake
the process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, thus stopping synaptic activity
transporter
a specialized membrane component that returns transmitter molecules to the presynaptic neuron for reuse
what would happen if calcium channels were blocked in the presynaptic neuron?
the neurotransmitter in the synaptic vesicles would not diffuse across the synaptic cleft
