EXAM 3- AP (LECTURE 14)

Ion channels

• always active transports// uses ATP

• goes against conc. gradient

Which is voltage-gates channels?

Leak channels

Voltage gate

change in response to membrane potential

Ligand gate

change in response to chemical messenger w membrane receptor nearby

• may be intracellular or extracellular

Mechanosensative gate

respond to stretch or deformation

Voltage gate: Na+ channel- gate

• active & inactive gate (have to be opened to work)

Voltage gate: Na+ channel- configurations (3)

• closed but able to open

• open (activated)

• closed but incapable of open (inactive)

voltage gate: ion channels- gate

• one gate (2 states: open + closed)

Channel & Pump Distribute - Everywhere

• (plasma membrane over whole neuron)

• Na+/K+ ATPase

• Na+ leak channels

• K+ leak channels

Channel & Pump Distribute - Localized

• Receptive segment (dendrites & cell body)

  • Chemically-gated (Na & K, Cl-, K)

• Initial segment (axon hillock)

  • Voltage-gated (only for Na and K)

• Conductive segment (axon)

  • Voltage gated (same w initial)

• Transmissive segment (axon terminal)

  • voltage gates Ca2+ channels

  • Ca2+ pumps

Ion movement- chemical gradient

• Diff. in number of ions bwt 2 areas

  • ions passive diffuse from high to low conc. areas

Ion movement- electrical gradient

• difference in charge bwt 2 areas

• can be diff. # of charges, or opposite charges

  • ions move towards area of opposite charge

Electrochemical gradient

both Ion movements move together- opposes one another

Membrane potential (Vm)

difference in charges across plasma membrane (form of potential energy)

• requires energy

All cells have

membrane potentials (serves as electrical signals)

voltmeter (mV)

measure difference in charge (voltage) across plasma membrane & cell’s ability to work

Voltmeter- Reference

Electrode outside

Voltmeter- Record

Electrode inserted

Voltmeter- negative

inside cell has negative relative to outside

Factors responsible for membrane potentials

• permeability

• unequal distribution of key ions in ICF & ECF

Na+/K+ ATPase- what goes in and out?

• Move K+ into cell

• Na+ move out of cell

• steep concentration gradient for each ion

K+ potential

• lots of leak channels

• steep gradient to move OUT of cell

  • movement stops when equal inside and outside

A- pump

• membrane impermeable to A-

• attract cations INTO cell

• negative charge inside

  • K+ leaves down conc. gradient

Na+ potential

• VERY few leak channels

• steep gradient to move INSIDE of cell

  • movement stops when equal inside and outside

Cl- potential

attract cations OUT of cell

The greater the permeability

• membraine of cells more permeable to K+ than Na+

the greater chance for equilibrium

Na+ & K+ leakage produces

resting membrane potential

Membrane Electrical States

• polarized

• depolarized

• hyper-polarization

• repolarization

Membrane Electrical States

• Electrical signals produced by change in ion across membrane

• Inward flow of positive ions _____

→ depolarization (less negative)

Membrane Electrical States

• Electrical signals produced by change in ion across membrane

• Outward flow of positive ions _______

→ hyper-polarization (more negative)

Changes of membrane potential results to?

electrical signals

• result from: change or alter of ion conc. on 2 sides

2 kinds potential change- which is short and long signals

• Graded potentials → short-distance signals

• Action potentials → long-distance signals

Graded potential- causes what?

chemically-gated ion channels to open in receptive segments of excitable membrane

• common: Na+ gated channels → depolarize

Graded potential decrease in intensity with

distance traveled

• localized stimulations; the rest of membrane @ resting potential

• temporary depolarized (active area)

• difference in potential → charges move more passively

• loss in intensity due to resistance to current

Graded potential- live long or short

• short

  • last only when opened until local current stops

Action potential

All or None law

• Either excitable membrane respond to triggers w mac actin potential or does not do anything at all

• must reach a threshold to open gates

Action potential

at initial segment & propagated along conductive segment to transmissive segment

Action potential- large changes in membrane potentials _?__

reverses (inside of cell becomes more positive than outside)

Postsynaptic response is what potential

graded potential

postsynaptic response- where is the mediated graded response at?

in post-synaptic neuron (dependent on NT amount)

2 types: Excitatory & Inhibitory

excitatory post-synaptic potential (EPSP)

• neurotransmitter binds to receptors which opens chemically gated cation channel

  • more Na+ move INTO cell

    • K+ move OUT of cell

  • depolarization

  • brings potential closer to threshold

• Na+ dies as move closer to axon hillock

Inhibitory post-synaptic potential (IPSP)

• Neurotransmitter binds receptors which opens channels for either K+ or Cl-

  • either Cl- move in

    • K+ move out

  • hyper-polarization

  • brings potential further to threshold

• K+ or Cl- dies as move closer to axon hillock

EPSP end result

local graded potential closer to threshold

IPSP

membrane potential further from threshold

Threshold- temporal summation

success fire of single presynaptic neuron

Threshold- spatial summation

simultaneous fire of more than 1 action potential from different synaptic input

Summation cacellation

• Simultaneous activation of EPSP & IPSP so sum of magnitudes cancel each other