Exam #1

Question 1

Factors that affect rate of diffusion - remember diffusion is movement of particles from high to low concentration

Answer 1

1. concentration difference
2. electrical potential - aka charge difference
   - remember that movement occurs to equalize the charge across the membrane
3. pressure difference - higher pressure results in increased energy available to cause net movement from high to low pressure

Question 2

Osmosis

Answer 2

PASSIVE transport of fluid across a membrane from an area of lower solute concentration into an area of higher solute concentration (less fluid comparatively)

*AKA water moves down it’s concentration gradient

Question 3

Osmotic pressure

Answer 3

difference in solute concentration across the membrane creates osmotic pressure difference (osmosis occurs)

• isotonic = no water flow
• hypotonic = low solute - fluid will rush into cell
• hypertonic = high solute - fluid out of cell (given to help with dehydration)

Question 4

Facilitated diffusion

Answer 4

molecules move along electrochemical concentration gradient (down concentration gradient) attached to “carrier” protein molecule that facilitates its passage
-no energy is required bc it does NOT move against it’s electrochemical gradient

Question 5

Primary ACTIVE Transport

-what is an example?

Answer 5

molecules ARE moved/pumped against (UPHILL) a concentration gradient

• example is Na+,K+, ATPase pump
• MUST HAVE ATP to do this

Question 6

What is the Na+,K+, ATPase pump and how does it work?

• plays an important role in?
• requires how much energy?
• ATPase does what?

Answer 6

• It is a carrier protein located on the plasma membrane of ALL cells
• Na/K ATPase = enzyme that converts ATP to ADP to release energy
• Plays important role in regulating osmotic balance by maintaining Na and K balance, preventing cells from swelling and bursting
• Requires 1-2/3 of cells energy
• Also important in establishing negative electrical voltage inside the cells which is the basis for nerve function

Question 7

With the Na/K pump - what is pumped out and what is pumped in?

Answer 7

3 Na+ are pumped out, and 2 K+ are pumped in

Question 8

Ca2+ ATPase function and what is it? where is it located?

Answer 8

uses primary active transport

• present on the cell membrane and the sarcoplasmic reticulum
• MAINTAINS LOW CYTOSOLIC Ca2+ concentration

Question 9

H+ ATPase
where is it found?
what does it do?

Answer 9

uses primary active transport

• found in parietal cells of gastric glands (HCl secretion) and intercalated cells of renal tubules (controls blood pH)
• concentrates H+ ions up to 1 million-fold

Question 10

Secondary active transport

how is transport driven? how is it created?

Answer 10

• secondary active transport is driven by energy stored in the concentration gradient of another molecule (Na+)
• created originally by primary active transport (INDIRECT USE OF ENERGY)

Question 11

Secondary active transport co-transport - This is indirect use of energy

Answer 11

co-transport (co-porters): substance is transported in the same direction as the “driver” ion

• example Na+ and bicarb into cell- remember this is what stops being driven into the cell during metabolic acidosis. Assuming this makes bicarb more available to balance the low pH
• other examples = Na+ & AA into the cell; Na+ and glucose into the cell

Question 12

Secondary active transport counter-transport

Answer 12

anti-porters = substance is transported in the OPPOSITE direction as the “driver” ion (Na+)

examples: Na driven inside and H driven out; Na driven in and Ca driven out, Na+/HCO3- in and Cl-/H+ to outside of cell

Question 13

How do cardiac glycosides increase cardiac contractility?

Answer 13

By inhibiting the Na/K pump, this causes Na+ to stay inside the cell and reduces the sodium gradient - this means that Na and Ca2+ can not be exchanged thereby keeping more calcium inside the cell and increasing cardiac contractility

Question 14

Remember that facilitated diffusion does not use…

Answer 14

ENERGY

Question 15

Ungated ion channels - allow ions through depending on what?

Answer 15

size, shape, distribution of charge, etc.

Question 16

Gated ion channel - 2 types and explain

Answer 16

voltage dependent gated ion channels - voltage depends on Na+ channels

chemically gated channels - only open/close whether specific substance has attached. Ex. nicotinic ACh receptor channels

Question 17

The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane

Answer 17

Nernst potential (or equilibrium potential of that ion)

Question 18

the chemical and electrical driving forces acting on an ion are equal and opposite, and no further net diffusion occurs

Answer 18

Electrochemical equilibrium

Question 19

The resting membrane potential is established by…

Answer 19

by the diffusion potentials that result from concentration differences of permeable ions

-each permeable ion will attempt to drive the membrane towards its equilibrium potential, and ions with the highest permeabilities, or conductance, will make the greatest contributions (aka K+)

Question 20

The electrical potential that counters net diffusion of K+ is called the…

Answer 20

K+ equilibrium potential

Question 21

The potassium Nernst potential (aka the equilibrium potential) would be what? if the membrane were only permeable to K+?

Answer 21

Ek = -94mV

Question 22

The sodium Nernst potential if the membrane were only permeable to Na+ would be

Answer 22

Ena = +61mV

Question 23

Vm =

what is it normally?

Answer 23

resting membrane potential

normally -70 to -90 mV

Question 24

What calculate Vm when more than one ion is involved and what is the take home message?

Answer 24

Goldman-Hodgkin-Katz equation
-Take home message is the resting membrane potential is closest to the equilibrium potential for the ion with the highest permeability

Question 25

Action potential rely on what type of ion channels?

Answer 25

voltage-gated ion channels -ion channels that are activated by changes in the electrical membrane potential near the channel. The membrane potential alters the conformation of the channel proteins, regulating their opening and closing

Question 26

Membrane potential at which occurrence of the AP is inevitable

Answer 26

threshold potential

Question 27

portion of the AP where the membrane potential is positive (cell interior is positive)

Answer 27

OVERSHOOT

Question 28

also called the hyerpolarizing after-potential, the portion of the AP following repolarization where the membrane potential is actually more negative than at rest

Answer 28

UNDERSHOOT

Question 29

Flow of positive charge into the cell | -example: Na+ flows into the cell during the ______ of the AP

Answer 29

inward current; during the upstroke of the action potential

Question 30

Flow of positive charge out of the cell is called? example? creates what kind of stroke?

Answer 30

outward current - these currents hyperpolarize the membrane potential - ex. flow of K+ out of the cell during the repolarization phase of the AP, creating a downward stroke

Question 31

When action potential occurs what happens to let sodium inside. Change in membrane potential causes these channels to open...

Answer 31

voltage gated channels open to let Na+ in, then AP reached and they close -- then K+ moves out and causes hyperpolarization b/c stay open slightly longer

Question 32

At rest the inactivation gate is _______ and the activation gate is ________

Answer 32

inactivation gate is open; activation gate is closed

Question 33

during the upstroke of the AP, both gates are ______

Answer 33

both gates are open and Na+ flows into the cell down its electrochemical potential gradient

Question 34

During the repolarization period, the inactivation gate is ______ and the activation gate is ________

Answer 34

inactivation gate is closed; activation gate is open

Question 35

Myelination - what is it, and what does it do?

Answer 35

myelin is a lipid substance that decreases ion flow through the membrane - allows the nerve signal to be transmitted quickly and efficiently

Question 36

What interrupts the the myelin sheath every 1-3mm? And what is it's function

Answer 36

node of Ranvier - this is the only place on the nerve cell where action potentials can occur (Na channels are concentrated here!) - allows for increased velocity of nerve transmission - allows for energy conservation for the axon

Question 37

Remember the difference b/w gap junction and chemical synapse?

Answer 37

gap junctions are electrical synapses that allow current to flow from one excitable cell directly through space b/w cells - a gap junction connects the cytoplasm of two cells (connection is direct b/w the presynaptic neuron and the postsynaptic neuron) a neuromuscular junction is a chemical synapse - there is a gap b/w the pre and postsynaptic cell - uses neurotransmitters to transmit information across the cleft

Question 38

What occurs at a chemical synapse

Answer 38

1- AP reaches axon terminal and depolarizes membrane 2- voltage-gated ca channels open and calcium comes into cell 3- ca influx triggers synaptic vesicles to release neurotransmitters 4- neurotransmitters bind to postsynaptic cell and elicit AP (Na+ rushes in)

Question 39

change in membrane potential can be _____ or _____

Answer 39

excitatory - meaning that depolarization occurs | inhibitory - meaning that hyperpolarization occurs of the postsynaptic cell

Question 40

specialized synapse b/w a motoneuron and a muscle fiber

Answer 40

occurs at a structure on the m. fiber called the motor end plate. this is also the same as the neuromuscular junction (usually only one per fiber) action potential can apparently travel in both directions

Question 41

motor end plate = ______ = ________

Answer 41

neuromuscular junction, chemical synapse

Question 42

what neurotransmitters are released from motoneurons and to what do they bind on muscle cells

Answer 42

ACh and they bind nicotinic receptors which open Na/K channels and result in an AP in the muscle tissue

Question 43

how is ACh degraded and what happens to it?

Answer 43

it is degraded by Acetylcholine esterase and (AChE) into acetate and choline --> choline is taken back up by the presynaptic terminal of the motoneuron on a Na choline co-transporter (Na and choline go into the cell at the same time) --> rem. counter transport would be opposite

Question 44

Opening of nicotinic ACh receptor channels produces an __________ which will normally initiate an AP in the local spread of current is sufficient to open voltage sodium channels How is this process terminated?

Answer 44

end plate potential -this process is terminated by AChE b/c this makes ACh less available at the motor end plate or chemical synapse or neuromuscular junction

Question 45

Drug effects on the end plate potential - inhibitors

Answer 45

curariform drugs (d-turbocurarine) - block nicotinic ACh channels by competing for ACh binding sites; reduces amplitude of end plate potential therefore, no AP botulinum toxin - decrease the release of ACh from nerve terminals - insufficient stimulus to initiate AP

Question 46

Curariform drugs (D-turbocurarine)

Answer 46

blocks nicotinic ACh channels by competing for ACh binding sites this reduces amplitude of end plate potential - therefore, no AP -generally used in anesthesia - m. relax - can cause paralysis and death in maximal doses

Question 47

botulinum toxin

Answer 47

decreases release of ACh from the nerve terminal (motoneuron terminal) insufficient stimulus to initiate an AP - no skeletal m. contraction can cause respiratory failure and death

Question 48

Stimulants - Drug effect on end plate potential

Answer 48

ACh-like drugs (methacholine, carbachol, nicotine) - bind and activate nicotinic ACh receptors - not destroyed by AChE b/c it's not ACh - so there is a prolonged effect Anti-AChE (neostigmine, physostigmine, diisopropyl fluorophosphate or "nerve gas") - inactivate AChE - prolong effect of ACh - these drugs can be used in myasthenia gravis to prolong effect of ACh since there is a decrease in nicotinic receptors