Nervous System, Neurons, and Membrane Potential

CNS

brain

spinal cord

CN II (optic nerve)

neural retina

basic unit of CNS

neurons

support cell of CNS

glia cells

PNS

nerves and ganglia outside of CNS

• sensory division: afferent nerve fibers

• motor division: efferent nerve fibers

  • somatic nervous system: voluntary

  • autonomic nervous system: involuntary

afferent nerve fibers

• signals from tissues and organs TO the CN

efferent nerve fibers

• signals FROM the CNS to organs

basic elements of axon

• dendrites

• cell body

• axon hillock

• axon terminal

dendrites

receive signals (inputs) via synapses

has neurotransmitter receptors in the plasma membrane

***sensory neurons in skin fo not have dendrites, but instead receptors for physical stimuli**

axon function

• carry neural signals

• microtuble

• transport lipids, proteins, polypeptide, mitochondria, synaptis vesciles in the cell body to the axon terminal (anterograde)

• key proteins: dynein, kinesin 1 and kinesin 2

concentration gradients of 4 major species

1. extracellular fluid

• Na+: 150 mM

• K+: 5mM

• Cl-: 110 mM

• Ca2+: 1 mM

2. intracellular fluid: 

• Na+: 15 mM

• K+: 150 mM

• Cl-: 7 mM

• Ca2+: 0.0001 mM

these ions are not permeable to membrane, will always need a chnanel/pump

resting membrane potential

membrane is non-permeable to ions, no traffic

electroneutrality on each side

E= -90 mV (equilibrium)

Ohm’s equation

V=RI

V= electromotive force (volts)

I= ion current (amps)

R= resistance, channel openned/closed (ohms)

conductance (G)= conductance (Siemens) is 1/R

conductance (G)

1/R

high value if channels opened

low value if channels closed

electroneutrality

ECF and ICF have equal concentration of ions

what is the E value for resting potential?

E= -90 mV to -70 mV

K+ channel opens

• create transitory electrical current

• K+ from ICF flows outward

• net flux is electrical current (in amps)

Ik+ = Gk+(Em-Ek+)

Em-E = driving force

the direction is (+)

compare G value of species at rest

Gk > Gcl > Gna > Gca

Nernst Equation

• calculate electrochemical equilibrium potential for an ion

E= (RT/z)ln(ion outcside/ion inside)

R= 8.314 JK-1mol-1

T= absolute temp (K=C+273.15)

F= 98485 Cmol^-1

z= valence of ion

what is standard body temperature?

37*C

chord equation

don’t have remember the equation, just the logic

does not take into account of temperature

goldman-hodgkin-Katz equation

When membrane is permeable to several different ions, the resting membrane potential depends on permeability, charge, and concentrations of all the ions and temperature. 

P_ion in the GHK equation is relative conductance of that ion.

P_{ion in GHK equation =} G_ion/G_total

_{it iss the product of the Nernst and chord equations}

neuronal organization of retina

1. photoreceptors (outer nuclear layer): receive input and make synapses w bipolar cells

2. bipolar (inner nuclear layer): receives input from photoreceptors and makes synapses w retinal ganglion cells

3. retinal ganglion cells (retinal ganglion cell layer): receive input from bipolar and send it to the brain for vision processing

hyperpolarizing

more negative than resting potential

depolarizing

more positive than resting potential

repolarizing

a change toward resting potential, from more positive or more negative potential

signaling

fluctuation of the membrane potential round its resting state

flux

net flux = electrical current (amps)

direction of electric current

defined by the direction in which the (+) charge moves (inward or outward)

the driving force

when the membrane potential to at an x current away from an ion steady state, that ion will move in a direction that will compensate the difference → generate a current