Chapter 4 Flashcards
Symptoms of Epilepsy
Aura: a “feeling” or sensation
Abnormal movements
loss of consciousness
Electrical Stimulation
passing an electrical current from the uninsulated tip of an electrode onto a nerve produces behavior–> muscle contractoin
Voltmeter
device that measures the flow and the strength of electrical voltage by recording the difference in electrical potential between two bodies
Electroencephalogram (EEG)
can detect fluctuations in voltmeter recordings by placing electrodes on the skull
North Atlantic Squid
has “giant” axons–millimeter in diameter
Oscilloscope
device that serves as a sensitive voltmeter by registering the flow of electrons to measure voltage
Microelectrode
microscopic insulated wire or a salt-water filled glass tube of which the uninsulated tip is used to stimulate or record from neurons
Na
Sodium; positively charged
K
potassium; positively charged
Cl
chloride; negatively charged
A
protein molecules; negatively charged
Cations
positively charged ions
anions
negatively charged ions
Diffusion
movement of ions from an area of higher concentration to an area of lower concentration through random motion
Concentration Gradient
differences in concentration of a substance among regions of a container that allow the substance to diffuse from an area of higher concentration to an area of lower concentration
Voltage Gradient
difference in charge between two regions that allows a flow of current if the two regions are connected
Efflux
outward flow
influx
inward flow
Resting potential
store of potential energy in a membrane; -70mV
Ions in intracellular fluid
K+ and A-
Ions in the extracellular fluid
Na+ and Cl-
Maintaining Resting Potential
- membrane is mostly impermeable, leaving A- inside
- Ungated K+ and Cl- channels allow ions to pass freely, but gates keep Na+ out
- Na+ -K+ pump extrude Na+ from inside and inject K+
A-
large protein anions; manufactured inside cells; too large to leave; alone sufficient to produce a transmembrane voltage or resting potential
How do cells balance A-?
K+ cross through channels; 20:1 inside to outside to balance the A- charge; K+ gets drawn out because of the concentration gradient; not enough K+ can enter to balance it
Outside the cell
Na+ is gated outside
Sodium-Potassium Pump
protein molecule embedded in the cell membrane that escorts out Na+ ions that leak into the cell; exchange three intercellular Na+ for two K+ ions
Cl-
move in an out of the cell freely; contribute little to resting potential;
Graded Potentials
small voltage fluctuations that are restricted to the vicinity on the axon where ion concentration change
Hyperpolarization
increases in electrical charge across a membrane, usually due to the inward flow of Cl- or Na+ or the outward flow of K+ ions; ex. -73 mV
Depolarization
decrease in electrical charge across a membrane, usually due to the inward flow of sodium ions; ex. -65 mV
Where does hyperpolarization/depolarization take place?
soma (cell-body) and dendrites; these areas contain channels that can open and close
Potassium Channels
for a membrane to become hyperpolarized, outside must become more positive–> efflux of K+. there is resistance to outward flow of K+–> reduce resistance for hyperpolarization
Chloride Channels
hyperpolarization–> influx of Cl-. Can pass through, but more remain outside. Thus, decreased resistance to Cl- can result in brief increases of Cl- inside
Sodium Channels
depolarization–> influx of Na+ by opening of normally gated Na+ channels
Action Potential
large, brief reversal in the polarity of an axon; summed current changes of inflow of Na+ and outflow of K+
Threshold Potential
voltage on a neural membrane at which an action potential is triggered by the opening of Na+ and K+ voltage-sensitive channels; about -50 mV relative to extracellular surroundings
Voltage Sensitive Channels
closed during resting potential; open briefly when the threshold voltage is met
How voltage sensitive channels work
- Na+ and K+ have a threshold voltage of -50 mV–> channels open if this is met
- Na+ open first because they are more sensitive
- Na+ have two gates: once membrane depolarizes to +30 one gate closes
- K+ open more slowly but stay open longer–> efflux reverses depolarization caused by Na+ influx
Absolutely Refractory
State of an axon in the repolarizing period during which a new action potential cannot be excited because gate 2 of Na, which is not voltage sensitive, is closed
Relatively Refractory
state of an axon in the later phase of an action potential during which increased electrical current is required to produce another action potential; K+ channels are still open
of Na+ gates
2
of K+ gates
1
During resting potential
gate 1 of Na+ is closed with gate 2 open–>threshold–>gate 1 opens and gate 2 quickly closes. When BOTH are open and when 2 is closed–> absolutely refractory
When a membrane is hyperpolarizing it is….
relatively refractory
Nerve Impulse
propagation of an action potential on the membrane of an axon
Refectory periods prevent…
action potentials from reversing direction on an axon
Largest human axons
30 micrometers wide and thus are not quick to transmit information
Glial Cells
speed up nerve impulses by forming meyling
Schwann Cells
Glial cells in the PNS; form meylin
Oligodendroglia
Glial cells in CNS; form meyling
Node of Ranvier
part of axon not covered by meylin; action potential occurring at one node can trigger the opening of voltage-sensitive gates at an adjacent node
Saltatory Conduction
propagation of an action potential at successive nodes of ranvier
Excitatory Postsynaptic Potentials (EPSPs)
reduce the charge of the membrane toward the threshold level and increase the probability that an action potential will result
Inhibitory Postsynaptic Potentials (IPSPs)
increase the charge of the membrane away from the threshold level and decrease the probability that an action potential will result
EPSPs
open Na+ channels and allow an influx of Na+ ions
IPSPs
open K+ channels, allow for an efflux of K+ ions OR the opening of Cl- channels and the influx of Cl-
Temporal Summation
graded potentials that occur at approximately the same time on a membrane are summed
Spatial Summation
graded potentials that occur at approximately the same location and time on a membrane are summed
Will a cell fire?
membrane indicates the summed influences of multiple inputs (temporal and spatial summation). Neuron analyzes inputs before determining what to do–> decision made at the axon hillock
Axon Hillock
region that initiates the action potential; inputs close are more influential than those further away
To produce an action potential
summed graded potentials must depolarize the membrane at the axon hillock to -50 mV
Hippocampus
can produce additional action potentials (depolarizing potentials) when the cell would typically be refractory
Back Propagation
movement of an action potential from the axon hillock into the dendritic field; signals that the neuron is sending an action potential over the axon and may influence learning
Stretch Sensitive Channel
Ion channel on a tactile sensory neuron that activates in response to stretching of the membrane, initiating a nerve impulse
End Plate
on a muscle, the receptor-ion complex that is activated by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron
Transmitter-sensitive Channels
receptor complex that has both a receptor site for a chemical and a pore through which ions can flow
