Voltage/Current Clamps

what is the current and voltage in this image

yellow → VOLTAGE

Red → CURRENT (the stimulus signal causing the spike in voltage).

What is the point of voltage clmp. What is overall goal

Voltage clamp used to → measure voltage to → detect conductance to → assess channel activity

During downstroke of voltage, what is happening and what are words to describe it? Which channel is active

Depolarization happening at down stroke.

early, inward (negative b/c sodium), Fast, Transient, voltage-dependent current.

Happens because of SODIUM INFLUX VIA SODIUM VOLTAGE CHANNEL

During UPSTROKE of voltage, what is happening, what are words to descrvibe it? Which channel is active.

Repolarization happens at upsroke

Late, outward (positive b/c potassium), slow, lono

Happens because POTASSIUM INFLUX VIA POTASSIUM VOLTAGE CHANNEL

Inhibitors of sodium and potassium voltage channel?

sodium —> ttx

Potassium → TTA

What type of current whtn positive charge flows into the cell or out of the cell?

Positive INTO cell → INWARD current (NEGATIVE)

Positive OUT OF cell → OUTWARD current (POSITIVE)

What can be deterined from the Current driving force equation?

Ix= Gx (Vm - Ex)

^ Can determine …

• Which channel open/closed

• channel behavior

• Ions involved

What can you do to determine inos leaving/entering cell

Labeling in radioactivity and using a special microscope

What is general process of how neurons are firing and communcating with each other with AP and Graded potentials

AP are depolarizing pre-synaptically → Travels down the axon (output) to the dendrites (input) -? Calcium influx

w/ Calcium influx, ——→ release Glutamate → EPSP → Depolarizes

OR

w/ Valvium influx ——→ release GABA → IPSP → Hyperpolarizes

What is an Active circuit’s electrical properties

Components of it ENGAGING IN ACTIONS that amplify, alter, or control signals

• REQUIRE ENERGY (could be generated by the component itself)

What are examples of Active circuit components

Power sources (batteres), switches (channels), amplifiers, Inverters

what is a passive circuit’s electrical properties?

Passice respones that do NOT amplify, alter or Control signlas

• DO NOT require external or energy

DO NOT generate energy or power but MAY dieupt.store.or release or distribute energy

What are examples of passive circuit components? Physiological examples?

Capacitors, Resistors

Myelin, Membrane, LEAK Channels

Why are ost channels active and passive

They are switches (which are active). Can be passive when open, active when closed

• Active and passive b/c of ability to open/close

What is capacitance? What is the main capacitor we know about and why

Ability to store charge (Farads)

• INSIDE → INSULATORS

  • OUTSIDE → CONDUCTORS

Lipid bilayer → Capacitor

What are the equations for capacitance

What does it mean?

Changes in Area and distance = change in capacitance, and thus change in voltage

write out relationships regading area and distance for capacitance and thus voltage

INC Area → INC Capacitance → DEC Voltage

(area=amnt of membrane you have)

INC Distance → DEC Capacitance → INC Voltage

specific capacitance equation and actual capacitance?

Equation for conductance? what is it

G = 1/R

• Inverse of resistance. Permits flow of current (seimen, S)

What are the 2 types of SPECIFIC resistance and what does each mean?

Membrane resistivity (Rm) → resistance to current flow through/across membrane

Internal (axial) resistivity (Ri) → resistance to current dlow DOWN or ALONG interior of neuron

What are the 2 types of ACTUAL resistance and what does each mean (the ones we actually use). Equation for each?

Membrane resistance (rm) → ACTUAL overall resistance to current flow Through/across membrane

Internal (axial) resistance (ri) → ACTUAL resistance to curretn flow DOWN the INTERIOR of neuron/axon

equation for membrane resistance

equation for internal resistance

where does capacitance in membrane come from (two)

Membrane itself

Channels

What happens with increase in axon radius.

how does more cytoplasmic elements affect resistance

more organelles → more membrane resistance

What is used to describe decay of graded potential because of distance. What is it and what does it mean

LAMBDA (length constant). Distance required for voltage signal to decay 37% of it’s maximum valuel

lambda equation?

What is used to describe decaryof graded potential because of time? What is it and what does it mean?

TAU (time constant) . Time required for voltage signal to decay 37% of maximum valueW

What is the equaion for tau

How does change in capacitance affect tau?

How does change in membrane resistance affect lambda?

What equaions describe dacay of voltage beacause of distance (lambda) and time)

Differences between Proximal and Distal dendrites?

• distance from body?

  • Amnt of membrane → How that affects tau or lambda)? Which better for summation

• How many EPSP are good for it and why?

Why does unmyelinated axons taje a long time and are slow?

each part of axons has to go through full entire AP (depol, repol, hyperpol)

What does myelin allow the AP to do?

Allows AP to jump between the myelin hitting the nodes of ranvier (saltatory conduction)W

What happens in the myelin? how does it help?

Graded potentials. Helps travel between nodes faster. At the edge of a node it helps the graded potential reach threshold faster

What are the two relationships that having myelination around a point in the axon do? (lambda and tau) For tau what is unique for the contradictory actions

myelin → increase membrane resistance → means that tau would go up
^TRUE, BUTTTT there is a MUCH MUCH MUCH greater decrease in capacitance, so tau actually doesn’t go up it goes DOWNNNNN


myeling → increase distance b/n inside and outside → decrease in capacitance → decrease in tau → decrease time to charge/discharge (WHOLE POINT OF MYELIN)

myelin → increase membrane resistance → increase lambda → signal can travel further without degrading

Why do graded potentials in myelin depolarize fast?

DEC tau (dec time)

How does having no myelin affect relation ship of time neede for chargin/dischargin

Draw out map of membrane and sodium channels and potassium channels in relation to physics like circuits