(06) Intro to Neurons

Question 1

three major general components of the nervous system

Answer 1

sensory - monitor environmental / internal events
integrative - process / store info
motor - generate responses

Question 2

neurons communicate via what types of signals?

Answer 2

electrical (dendrites, cell body, axon)
chemical (synapses)

Question 3

name the main features and functions of neurons

Answer 3

dendrites - receive electrical input
cell body - passively conducts electrical input
axon - propagate action potentials
axon terminals - release chemical signals

Question 4

what are synaptic potentials?

Answer 4

when e-signals travel through DENDRITES

Question 5

what are action potentials?

Answer 5

when e-signals travel through axon / axon terminals

Question 6

where are Purkinje cells found?
briefly describe them

Answer 6

in the cerebellum
(multipolar, has tons of branched dendrites and branched axon terminals)

Question 7

where are pyramidal cells found?

Answer 7

in the cerebral cortex
also multipolar

Question 8

define membrane potential

Answer 8

voltage across cell membrane
it is generally more negative WITHIN A CELL

Question 9

range of voltage within a cell

Answer 9

-100 to +50 mV

Question 10

define resting membrane potential
what is its value?

Answer 10

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

Question 11

How is RMP maintained?

Answer 11

without something to maintain ionic differences, RMP would dissipate
Sodium-potassium pumps = Na+ K+ ATPase prevent this

Question 12

how can RMP be measured?

Answer 12

using intracellular microelectrodes
patch-clamp pipettes - cell membrane sucked into pipette, forms electrical seal. measure ions flowing through a particular channel

Question 13

define “excitable tissue”

Answer 13

in response to stimulus, muscle fibres / neurons can suddenly respond with a transient change of potential = action potential

Question 14

general cause of e-potential diff

Answer 14

a result of a separation of charge

Question 15

general cause of e-potential diff

Answer 15

a result of a separation of charge
more -ve charges inside cell compared w/ xtracell fluid

Question 16

what two main factors cause a separation of charge?

Answer 16

unequal conc of ions resulting in electrochemical gradients
unequal permeability of cell membrane to ions

Question 17

describe concentrations of K+ and Na+ inside and outside of the cell

Answer 17

K+ higher INSIDE (100mM vs 5mM)
Na+ higher OUTSIDE (150mM vs 15mM)

Question 18

how are concentration gradients maintained?

Answer 18

by sodium-potassium pumps
ratio 3 Na+ out, 2 K+ in
hence net negative

Question 19

what is the permeability of K+ and Na+ at rest

Answer 19

P(K+) / P(Na+) = 40/1 at rest

due to conc grad, there is steady diffusion of K+ out and Na+ into cell

Question 20

what determines the permeability of ions across membrane

Answer 20

Leak channels
non-gated
open at rest, allows for diffusion of ions

Question 21

types of gated channels

Answer 21

voltage-gated
ligand-gated
mechanically-gated

closed at rest

Question 22

what two types of ion channels in cell membrane affect permeability (P)?

Answer 22

Non-gated channels (leak) open at rest
gated channels closed at rest

Question 23

what equation can be used to calculate eq potential for each individual ion contributing to RMP?

Answer 23

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

Question 24

what does E(ion) represent in the Nernst eqn?

Answer 24

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

Question 25

what type of cell has only K+ leak channels, and what does this mean for the RMp?

Answer 25

Glia cells
so RMP = equilib pot = -80mV
can use Nernst

Question 26

How does the permeability of a cell membrane to an ion affect the RMP?

Answer 26

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

Question 27

what two factors does the Goldman eqn take into consideration?

Answer 27

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)

Question 28

define electrogenic transport

Answer 28

leads to translocation of net charge across membrane