(06) Intro to Neurons Flashcards
three major general components of the nervous system
sensory - monitor environmental / internal events
integrative - process / store info
motor - generate responses
neurons communicate via what types of signals?
electrical (dendrites, cell body, axon)
chemical (synapses)
name the main features and functions of neurons
dendrites - receive electrical input
cell body - passively conducts electrical input
axon - propagate action potentials
axon terminals - release chemical signals
what are synaptic potentials?
when e-signals travel through DENDRITES
what are action potentials?
when e-signals travel through axon / axon terminals
where are Purkinje cells found?
briefly describe them
in the cerebellum
(multipolar, has tons of branched dendrites and branched axon terminals)
where are pyramidal cells found?
in the cerebral cortex
also multipolar
define membrane potential
voltage across cell membrane
it is generally more negative WITHIN A CELL
range of voltage within a cell
-100 to +50 mV
define resting membrane potential
what is its value?
the voltage at rest (absence of synaptic / action potentials)
usually between -50 and -70 mV, typically -65mV
so cytosol has potential 50-70mV LOWER than the extracellular fluid
How is RMP maintained?
without something to maintain ionic differences, RMP would dissipate
Sodium-potassium pumps = Na+ K+ ATPase prevent this
how can RMP be measured?
using intracellular microelectrodes
patch-clamp pipettes - cell membrane sucked into pipette, forms electrical seal. measure ions flowing through a particular channel
define “excitable tissue”
in response to stimulus, muscle fibres / neurons can suddenly respond with a transient change of potential = action potential
general cause of e-potential diff
a result of a separation of charge
general cause of e-potential diff
a result of a separation of charge
more -ve charges inside cell compared w/ xtracell fluid
what two main factors cause a separation of charge?
unequal conc of ions resulting in electrochemical gradients
unequal permeability of cell membrane to ions
describe concentrations of K+ and Na+ inside and outside of the cell
K+ higher INSIDE (100mM vs 5mM)
Na+ higher OUTSIDE (150mM vs 15mM)
how are concentration gradients maintained?
by sodium-potassium pumps
ratio 3 Na+ out, 2 K+ in
hence net negative
what is the permeability of K+ and Na+ at rest
P(K+) / P(Na+) = 40/1 at rest
due to conc grad, there is steady diffusion of K+ out and Na+ into cell
what determines the permeability of ions across membrane
Leak channels
non-gated
open at rest, allows for diffusion of ions
types of gated channels
voltage-gated
ligand-gated
mechanically-gated
closed at rest
what two types of ion channels in cell membrane affect permeability (P)?
Non-gated channels (leak) open at rest
gated channels closed at rest
what equation can be used to calculate eq potential for each individual ion contributing to RMP?
the Nernst eqn
E(ion) = 2.3 x RT/zF x log [ion]outside/[ion]inside
where z= charge of specific ion
R, F constants
T = abs temp
what does E(ion) represent in the Nernst eqn?
equilibrium potential
the point at which electrical and conc forces are equal for a given ion
balances ion’s conc grad so no net ionic current would flow if the membrane was permeable to that ion
what type of cell has only K+ leak channels, and what does this mean for the RMp?
Glia cells
so RMP = equilib pot = -80mV
can use Nernst
How does the permeability of a cell membrane to an ion affect the RMP?
greater permeability, ion shifts the RMP closer to its own Equilibrium potential
eg. E(K+) = -80mV, E(Na+) = +60mV
middle is -10mV
BUT in neuron, K+ greater P, so RMP between -10 and -80mV
what two factors does the Goldman eqn take into consideration?
the conc grad AND relative permeability
same as Nernst, but multiplies conc of each ion by P, relative permeability (use P(K+)=40 and P(Na+)=1)
define electrogenic transport
leads to translocation of net charge across membrane
