neurophysiology Flashcards
what generates action potencials?
neruons
when do action potencials occur?
when ions flow down electrochemical gradients
what do electrochemical gradients result in?
membrane potencial
what is a membrane potencial
charge difference across cell membrane
measured in volts
voltage represents potencial energy resulting from seperation of oppositely charged particles
what is resting membrane potencial?
70mv
what does polarized mean?
neurons at rest are relative more negative inside then than outside (cells are polarized)
what are the 2 main factors for resting potencial?
na and k exchange pump moves 3na in for 2 k out
leakage of ions varies
what are the different types of ion channels?
leak channels- always open allow passive diffusion of ions
gated channels- open or close in responce to different stimulii
i. ligand-open or close when bind to specific molecules
i. mechanically gated- open or close in responce to membrane distortion
i. voltage gated- open or close in responce to changes in membrane potencial particular voltage
what is an action potencial?
reversal in membrane potencial propagated along the length of the excitable cell neruron or muscle cells
describe action potencial?
stimulas opens voltage gated na plus channels
action potencial propagated along axon of neuron as more voltage gated channels open
resting potencial is restored when na gates close and voltage gated k open
what is resting potencial?
=-70mv
inside of cell is negative relative to inside of cell (polarized)
what is depolarization?
to 30mv
stimulas causes depolarization and volatage gated na channels open = na enflux= more na gates open= action potencial propgated as icf becomes more negative
what is repolarization?
at +30mv na channels close and voltage gated k channels open icf becomes more negative
what is hyperpolarization?
k+ efflux continues and icf becomes even more negative = k gates close at 90mv
why do the na/k. channels keep working
keeps working to restore ion channels
when is an action potencial intiated
if stimulas is strong to move the membrane potencial up to specific threshold
what is a threshold voltage?
membrane potencial to which a membrane must be depolarized to intiate an action potencial
at threshold voltage gated channel open and na rushes in cell (depolarization)
must depolarize to at least 60mv
what is a graded potencial?
temporary localized changes in membrane potencial
decline with distance to stimulas
vary with stimulas strength
sum of all graded potencial in cell body may intiate an action potencial if they exceed threshold
what are the refractory periods?
period during which neruon does not respond normally to a threshold stimulas
why? membrane must return to resting potencial
what are the two refractory periods?
absolute- neuron unresponsible to a new stimulas
relative- neuron has reduced responsiveness to stimulas
what determines the speed of condcution of velocity
axon diameter- large diameter increased velocity =less resistent to current flow
myelin sheath- lipid sheath around axon
myselin sheath=increased velocity
why = salitory conduction
only need to open na channels at nodes
what are the three axon classifications?
type a- large diameter
target skeletal muscles, relay sensory info from body surface
type b- intermediate diameter
pain temp from body surface
type c- small diameter unmyselintaed
target smooth muscle of internal muscles
how is an action transmitted to other cells?
synapse
what is a synapse?
site of communication between neuron and target cells
neuron- neuron
neruon- muscle
neuron- gland
describe synapse
presynatpic cells goes towards target cell synapses then action potencial goes to postganglionic cells
types of synapses?
electrical- very rare
a.p spreads to postsynaptic cells by ion flow through gap junctions formed by proteins called connexins
chemical- a.p spreads to postsynaptic cell by neurotransmitter
what are neurotransmitters?
chemicals released from presynaptic cell that diffuses across synapse
binds to receptors
may be exitaoty and inhibitory
what are the two classifications of neurotransmitters?
epsp- n.t causes depolarization in post synaptic cell
ipsp- n.t causes hyperpolarization in postsynaptic cell (supresses action potencial) =more negative
what is summation two types?
temporal- number of epsps arriving in a given
spatial- total number or epsps and ipsps from diff axons
how long action potencials continues in post synaptic cell depends on?
speed of which neurons are deactivited and destroyed by enzymes in synapse
and reabsorbed/recycled = reuptake (endocytosis by presynapic cell)
what are the mechanisms of action of neurotransmitters?
direct action- nt opens or closes ion channels
indirect action- nt acts through receptor to alter cellular metabolism and or gene expression
definition of summation?
process of which determines or not an action potencial will be generated by temporal or spatial summation
temporal- epsps
inhibitory- ipsps and epsps
