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describe divisons of the nervous systems? CNS and PNS

brain and spinal chord to go afferent and efferent divisions. Afferent has sensory and visceral, efferent has somatic and autonomic. somatic is motor neurons onto skeletal muslces, autonomic is sympa and para sympa onto smooth muscle, cardiac, exocrine, endocrine. both skeletal muscles and the other ones are "effector organs:


whats a neuron?

dendrites soma axon axon terminal


whats rmp?

electical actiity to perform roles. -70 mv for a cell.
exitable cells. harness change to do a role.
negative inside because of potassium and sodium gradient. right up against the membrane.


what does electrical activity require?

1. selectively permeable membrane
2. differential distribution across the membrane of ions. (potassium high in, sodium high out)


what is facilitated diffusion?

passive in which paricles go through a channel (cause they can't cross lipid bilayer)


whats the distribution of na and k ions?

na, 15mM inside, 150mM outside
k, 150mM inside, 5mM outside


whats the ATPase?

sodium potassium pump
- pumps 3na out and 2k in! always. maintains gradient.


whats equilibrium potential?

the voltage it would move the membrane to if permeability increased. concentration and electrical gradient at equliibrium. done with nernst equation.


what is relative ionic permabilitY?

some are more leaky than others, more permable or conductance. more permeabiliyt, greater the ions influence on membrane voltage. k is 50x more permeable than na.


how to depolarize membrane? (same w hyperpolarize only the opposite)

make k less permeable (relatively!! - so increase na permeability by a lot)
change gradient of na or k (theoretically)


whats an action potential?

all or nothing event, when threshold is reached. depolarization, repolarization, hyperpolarization (kchannesl still open). incrased na+ permeablity at voltage gated channels.
regenerative event: ap will be initiated in more distant part of the cell.
subthreshold: no ap
suprathreshold: same ap regardless


whats a graded potential?

Generator potentials or EPSPs, larger stim, greater GP (graded)


describe the gating of voltage gated ion channels:

na: activation (fast) and inactivation gate (slow) .
k: activation gate only.

depolarization increases the probability that gates are open/closed.

for na, if either gate is closed, it will not conduct


whats the ap threshold positive feeedback loop?

event triggers depolarization which leads to more gates opening leading to more depolarization (influx of na) (decrease membrane potential)


look on slides for inactivation gate chennels

do it


why is there a recovery period?

to let na channels recover, can't fire new action potentials (absolute vs relative refractory periods) this is so that it can't reverbareate back and ap travels one way


what ion is better at conducting

na because it goes down its concentration and electrical gradient


electrotonus + decay

how electrical events propegate, charge enters ion channels, it will travel axially along resistive pathways of axon. (water in a hose)
charge spreads out ajacently (passive spread, not regenerated, its just gonna happen)
electotonic decay: leaks out as depolarization moves from original site


whats length constant

lamda, determined with axial and membrane resistance. (only so far a passive electrical event can happen)
constant: how far it will gobefore its reduced to 1/3 of its length.
kirchoffs law (move across resistances paths all ofthem)
incrase diameter of axon, decrease Ra


whats active propegation?

regeneration of the ap via na voltage gated channels
- some is faster if its more important info


what influences rate of ap firing?

diameter (less resistance
myelin -50x faster (oligodendrocytes -multiple segments, schwann (pns)) that is a capacitor (condunctive plates with an insulator) the thicker the myelin the reduces membrane capacitance.


what is a capacitor?

takes time to change membrane charges on the surface, Vm gradually changes as capaacitor changes, but if capacitor is reduced, Vm can change more quickly.


whats saltatory conduction?

node of ranvier sodium channels, ap propegate fast in between them (passively), Rm is increased so longer lamda (not as much leak) and actively regenerated at nodes cause capacitance is greater/longer/slows down here. return path of electricity


whats synaptic transmission

chemical signal. ap propegation to synaptic button, activates voltage gated calcium channels, which cause vesicles to go to membrane and exocytosis, nt binds to receptors, opens ion channels (synaptic current) to deoplarizel/hyperpolarize.


whats synaptic current?

ion movement through the pore in postsynaptic cell


whats PSP

postsynaptic potential produced by synaptic current. EPSPs and IPSPs. temporally and spatially summed. single epsp won't bring to threshold, frequency is important and so is multiple axons.


whats a neurotransmitter gated ion channel

allow 1 ion at a time in and out (na and k)


EPSPs + glutamate:

ampa and nmda receptors. na and k ions through the open pore. (move towards equilibrium potentials) EPSP has equilibrium potential of 0mV.

ampa dominates here, nmda is for structural changes longer term (Mg etc.)



keep from reaching threshold. algebraically sum.
allows cl through with is -70 mv. same as RMP in some cells. membrane "clamped" at -70 no depolarization.


describe the nmj

reliable, rapid transmission. specialized synaptic ontact between alpha mn and muscle cell. forms a unit. this happens on a single fibre, but ap can hae multiple branches and simultaneously excite each muscle fiber within a unit. all units form a motor unit POOL.
motor unit: one axon mulitple branches
motor unit pool; multiple axons.