ch 12.4 - Flashcards
resting membrane potential
membrane potential of an unstimulated resting cell
3 important concepts regarding the membrane potential:
- The extracellular fluid (ECF) and intracellular fluid (cytosol) differ greatly in ionic composition.
-ecf has high concentrations of sodium and chloride ions , whereas the cytosol has high concentrations of potassium ions + negatively charged proteins. - cells have selectively permeable membranes
- membrane permeability varies by ion
current
movement of charges to eliminate a potential difference
resistance
measure of how much the membrane restricts ion movement
electrochemical gradient
the sum of the chemical and electrical forces acting on that ion across the plasma membrane
chemical gradient
passive movement of ions across the plasma membrane driven by their concentration gradient
electrical gradient
passive movement of ions due to charge differences
equilibrium potential
membrane potential which there is no net movement of a particular ion across the cell membrane
sodium potassium exchange pump
powered by atp
moves 3 sodium (Na) ions out of the cell + 2 potassium (K) ions into the cell per atp
gated ion channels
open and close in response to stimuli
chemically gated ion channels
open when they bind specific chemicals or ligands
voltage gated ion channels
open or close in response to changes in the membrane potential
mechanically gated ion channels
open or close in response to physical distortion of membrane
graded potentials
temporary localized change in the resting membrane potential
- can cause depolarizatio and hyperpolarization
repolarization
returning to normal resting membrane potential after depolarization
action potentials
large depolarization that once initiated, affects the entire excitable membrane
threshold
membrane potential at which an action potential begins
all or none principle
an action potential is either triggered or not
steps of action potentials
- depolarization to threshold
- rapid depolarization
- repolarization
- hyperpolarization
refractory period
a period during which the membrane will not respond normally to additional depolarizing stimuli
propagation
series of steps that move the action potential along the axon
continuous propagation
occurs in unmyelinated axon
saltatory propagation
-occurs in myelianted axons
3 groups of axons
type a fibers
type b fibers
type c fibers
synapse
a specialized site where the neuron communicates with another cell
types of synapses
electrical
chemical
electrical synapses
signal transmitted via direct physical contact between cells
chemical synapses
signal transmitted across a gap using a chemical signal (neurotransmitter)
- most common type of synapse
types of chemical synapses
axoaxonic
axosomatic
axodendritic
neuromuscular junction
neuroglandular junction
neurotransmitters
chemical messengers contained within synaptic vesicles in the axon terminal of the presynaptic cell
neurotransmitter function
alters the membrane potential of the other neuron
cholinergic synapses
releases acetylcholine
synaptic delay
a delay between the arrival of the action postsynaptic membrane
synaptic fatigue
response of the synapse weakens due to insufficient neurotransmitter until the neurotransmitter has been replenished
types of neurotransmitters
excitatory: caused depolarization of postsynaptic membrane + promote generation of action potentials
inhibitory: causes hyperpolarization of the postsynaptic membranes and suppresses generation of action potentials
biogenic amines
-norepinephrine (excitatory)
-dopamine ( inhibitory or excitatory effects)
- serotonin
amino acids
glutamate
glycine
gamma-aminobutyric acid (GABA)
neuropeptides
small peptide chains synthesized and released by the axon terminal
neuromodulator
compound released by a neuron that alters the other neuron’s response to specific neurotransmitters
opioids
relieve pain and bind to the same receptors as opium and morphine
classes of opioids in CNS
enkephalins
endorphins
dynorphins
disolved gases
nitric oxide
carbon monoxide
ionotropic effect
a direct effect on the membrane potential by opening and closing chemically gated ion channels
postsynaptic potential
graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter
excitatory postsynaptic potential
graded depolarization of postsynaptic membrane
inhibitory postsynaptic potential
graded hyperpolarization of postsynaptic membrane
summation
integrates the effect of all incoming graded potentials
temporal summatio
summation of rapid, repeated stimuli at a single synapse
spatial summation
summation of simultaneous stimuli that arrive at multiple synapses
facilitation
bringing the membrane potential of the initial segment closer to threshold
presynaptic inhibition
decrease in the rate of neurotransmitter release at the presynaptic membrane
presynaptic facilitation
increase in the rate of neurotransmitter release at the presynaptic membrane
depolarization is also known as
rising phase
repolarization is also known as
falling phase
