BME 207 Midterm 1 Review (Lec 1-5)

action potential

caused by movement by ions through the axon membrane

ion - definition and two types

charged particle (cation and an ion)

find v(t) in following circuit

check answer

for any voltage remaining across the capacitor, the energy would

continue to flow into the resistor and be dissipated as heat

series connection

current stays the same

mesh analysis results in direct calculation of

currents

at the end of the day, a capacitor is nothing but a

disconnection

the flow of electrons from source to capacitor is nothing but - describe change in current from beginning to end

electric current - begins at maximum, and after a certain time the current will become zero

when a voltage is suddenly applied across a capacitor, what happens

electrons immediately shift from source to capacitor - accumulation of charge in the capacitor starts instantly

why are metals good conductors

electrons in outer orbits of metals are not tightly bound to atoms (thus called "free electrons") and serve as charge carriers

rule two for solving norton and thevenin circuits

find r(eq), which is equal to r(n) and r(th)

supernode

formed by enclosing a voltage source connected between two nonreference (annodes

current flows from

high v to low v

in resting membrane potential, what is the charge of the intracellular and extracellular membrane

intra is neg, extra is pos

nodal analysis uses

kcl

mesh analysis uses

kvl

a current is described by its

magnitude and direction

bioelectricity

movement of ions through bio-objects

circuit

network of electrical components that contains at least one closed path

removing a current source

no current flow, but a voltage can appear across a terminal - replace with open circuit (treat like a disconnection)

removing a voltage source

no voltage drop, but current can flow - replace with a short circuit (treat it like a wire)

nodal analysis results in direct calculation of

nodal voltages

practical voltage sources have

non-zero internal resistance

resistivity formula (units)

ohm meter

lethal current

one amp

a simple capacitor consists of

parallel plates on which the charge separation causes an internal electric field (storing energy)

voltage

potential difference due to sep of charges

depolarization

process during the action potential when sodium is rushing into the cell causing the interior to become more positive

charge - definition and two types

property of particles (coloumbs) - proton and electron

independent current source

provides a current that is completely independent of the voltage across it

independent voltage source

provides a terminal voltage that is completely independent of the current through it

current - formula, definition, and units

rate at which charge is flowing (amperes or 1/coloumbs)

power definition (units)

rate of energy transfer (work done) - units (watts or joules/sec)

conductance (units)

reciprocal of resistance (siemens - s)

in a general rc circuit, how do you combine multiple resistors

reduce to an eq resistor from the c's pov

norton theorem (draw!)

replacing everything except the load with a norton current source in parallel with a resistor

thevenin theorem (draw!)

replacing everything except the load with a thevenin voltage source in series with a resistor

superposition

response in a linear circuit having more than one independent source can be obtained by adding the responses caused by the sep independent sources acting alone

repolarization

return of the cell to resting state, caused by reentry of potassium into the cell while sodium exits the cell

rule one for solving norton circuits

set i(norton) equal to i(sc) - disconnect r(load) and define i(short circuit)

rule one for solving thevenin circuits

set v(th) equal to v(oc) - disconnect r(load) and define v(open circuit)

conductivity formula (units)

siemens/meter

kcl

sum of the currents entering/exiting any node is zero

kvl

sum of voltages around any closed path is zero

as the voltage developed across the capacitor approaches the supply voltage, what happens

the rate of charge accumulation in the capacitor decreases

time constant is the time at which

the voltage has dropped to 37% of the initial value

by the equivalent source theorem, what can you conclude about r(norton) and r(thevenin)

they're equal

explain "not so fast" for a capacitor - draw two graphs

this is what the capacitor essentially says to the source voltage - tries to decrease the time it takes for the voltage to build up vs

how many mv lower is the cell interior as compared to the extracellular environment

70

when an increasing dc voltage is applied to a discharged capacitor, the capacitor draws what is called

a charging current and charges up to build up stored electric energy

a mesh is defined as

a loop that does not contain any other loops within it

node

a point at which two or more elements have a common connection (hint: every element has a node at each of its ends)

define an rc circuit

an electric circuit composed of resistors and capacitors driven by a voltage or current source

insulators have

tightly bound electrons

the duration in which current changes in the capacitor is known as

transient period

describe the electric field inside a capacitor

uniform, pointing from positive to negative

capacitance equation (include units)

units: farad (F)

resting membrane potential/resting voltage

voltage across cell membrane

as the charge accumulating in the capacitor increases, what increases

voltage developed across the capacitor

two configurations that represent a practical source

voltage source in series with resistor or current source in parallel with resistor

parallel connection

voltage stays the same

under what conditions will there be no more flow of charge from the source to the capacitor

when source voltage equals the voltage developed across the capacitor

when do you use a super node

when there is both a current and voltage source - helps to determine diff in voltages within chosen super node, since you know current flows from high to low v

damaged capacitor

when there is current that flows through the air gap in the capacitor - in a normal capacitor, think of positive build up on one end and negative on the other equal to current flowing from "positive to negative"

is a step function seen with or w/o a capacitor

without

ideal voltage sources have

zero resistance