Nervous System Physiology Flashcards
What is resting potential
the transmembrane potential or a resting cell
how is resting potential established
with Na/K pumps, they pump sodium in and potassium out against their concentration gradient
what is equilibrium potential
the transmembrane potential when there is no net movement of a particular ion across the cell membrane
the equilibrium potential of K = -90mv, Na = 66mv. what is the resting potential of a neuron and why
it is -70 mv. its much closer to the potential of K because the membrane is much more permeable to K than Na
What are the characteristics of the sodium potassium pump
it is powered by ATP
it carries 3 Na+ out, and 2 K+ in
it balances passive forces of diffusion
it maintains the resting potential of -70 mv
what causes membrane potential to change
temporary changes in membrane permeability caused by the opening or closing of specific membrane channels
What are the two types of channels that affect transmembrane potential
passive (leak) channels - always open - permeability changes with conditions active (gated) channels. - open and close due to stimuli - at resting potential most are closed
What are the three types of gated channels
chemically gated
voltage gated
mechanically gated
what are chemically gated channels
channels found on the cell body and dendrites that open with chemicals (ACh)
what are voltage gated channels
channels found in axons, skeletal muscle, sarcolemma, and cardiac muscle that are characteristic of an excitable membrane. they open and close due to changes of the transmembrane potential
what are mechanically gated channels
channels found in sensory receptors of touch, pressure, and vibration that respond to distortion of the membrane
what is a graded potential
a temporary and local change in resting potential caused by a stimulus. the larger the stimulus, the larger the change in resting potential
what is depolarization
a shift in transmembrane potential toward 0 mv, caused by a stimuli that causes movement of Na+ through a channel. it depolarizes the nearby plasma membrane
what is repolarization
when the depolarizing stimuli is removed, the resting potential of the membrane moves back to -70 mv
what is hyperpolarization
when the resting potential moves away (lower) from -70 mv (example = -80 mv)
What is an action potential
an electrical impulse produced by graded potentials that propogates along surface of axons to the synapse
what initiates an action potential
graded potentials that are large enought (10-15 mv) at the axon hillock to depolarize it to threshold (-60 to -55 mv) (this is the potential at which sodium voltage gated channels open)
what is the all or none principle of action potentials
action potentials don’t vary in strength, if threshold is reached the action potential is the same no matter the strength of the graded potential. if threshold isn’t reached there is no action potential
what are the four steps of an action potential
- depolarization to threshold
- activation of Na+ voltage gated channels
- inactivation of Na+ voltage gated channels and activation of K+ voltage gated channels
- return to normal permeability
what happens at -60 mv
voltage gated Na+ channels open, sodium rushes into the cytoplasm, inner membrane changes from - to +, causing rapid depolarization
What happens at +30 mv
voltage gated Na+ channels close (inactivation gate)
voltage gated K+ channels open
repolarization begins
when do voltage gated K+ channels begin, and finish closing
they begin to close at -70 mv, and finish closing at -90 mv. at this point the membrane is hyperpolarized, but it returns to normal and the action potential is over
what is needed for the Na/K pump to work
ATP
what is the refractory period
the time period that starts at the beginning of an action potential and ends when it returns to resting potential during which the membrane will not respond normally to additional stimuli
what are the two refractory periods
absolute = sodium channels are open or inactivated and no action potential can occur relative = membrane potential is close to normal, and a very large stimulus can cause an action potential
what is propagation of an action potential
the movement of an action potential generated in the axon hillock along the entire length of the axon
what are the two types of action potential propagation, and what determines which kind will occur
continuous propagation (unmyelinated) saltatory propagation (myelinated)
which is faster and why saltatory or continuous propagation
saltatory, because it essentially skips over the myelinated segements and occurs in the nodes of ranvier
what happens to the propagation speed if you have a large diameter axon
the larger the diameter, the faster the propagation due to less resistance
what are the three different groups of axons
Type A, Type B, Type C
what are type A axon fibers
large, myelinated, high speed axons that carry rapid information to/from the CNS (touch, balance, position, motor impulses)
what are type B axon fibers
medium, myelinated, medium speed axons that carry intermediate signals like sensory information and peripheral effectors
what are type C fibers
small, unmyelinated slow speed axons that carry slower information like involuntary muscle and gland controls
What are the three parts of a synapse
presynaptic neuron
synaptic cleft
postsynaptic neuron
what are the two types of synapses
electrical (direct physical contact between cells)
chemical (signal transmitted across a gap by neurotransmitters)
what are the two types of neurotransmitters
excitatory (cause depolarization and promote action potentials)
inhibitory (cause hyperpolarization and inhibit action potentials)
is ACh an excitatory or inhibitory neurotransmitter
it can be both, which one it is is determined by the receptor, not the neurotransmitter (usually excitatory, but inhibitory at cadiac neuromuscular junctions)
what does AChE do
breaks down the ACh in the synaptic cleft, in order to stop the ACh from activating postsynaptic receptors
what is the synaptic delay
the signals stops at a synapse for .3 mseconds, so fewer synapses = quicker response (reflexes sometimes only have 1)
what is synaptic fatigue
when the neurotransmitter can’t be recycled fast enough to meet the demands of intense stimuli
what are some important neurotransmitters
Norepinephrine
dopamine
seratonin
GABA
what are neuromodulators
chemicals similar to neurotransmitters, but have slow, long lasting effects.
What are the three ways that neurotransmitters and neuromodulators actually affect postsynaptic cells
direct effects on membrane channels
via G proteins (work through second messengers - adenylate cyclase and cAMP, cAMP opens channels)
via intracellular enzymes
(some other enzyme opens channels)
What are EPSPs and IPSPs
they are postsynaptic potentials
EPSP = excitatory (depolarization)
IPSP = inhibitory (hyperpolarization)
what is summation
when multiple EPSPs are added together so that threshold can be reached
what is temporal and spatial summation
temporal summation is when one presynaptic neuron sends multiple, quick EPSPs that are added together until they reach threshold
spatial summation is when multiple presynaptic neurons send EPSPs at the same time, then they are added together and they reach threshold
what is the effect of hormones and neruromodulators on the activity of neurotransmitters
they can affect the sensitivity to neurotransmitters and thus shift the balance of EPSPs and IPSPs
what is presynaptic facilitation
when there is a synapse that sends EPSPs and causes Na gates to open more on another neuron just before that neurons synapse so that it sends more neurotransmittors
what is presynaptic inhibition
when there is a synapse that sends IPSPs and causes Na gates to close on another neuron just before the synapse of that neuron so that less Na comes in, and less neurotransmitters are sent
