Midterm 1 - Neurotransmission

Question 1

Membrane Potential

Answer 1

Electrical charge across a membrane. The difference between the inside and the outside.

Question 2

Resting Potential

Answer 2

The membrane potential when the axon is neither being excited nor inhibited.

• 70 mV

Question 3

Depolarization

Answer 3

• Towards 0
• A rise in the membrane potential from the normal resting potential.
• EPSP

Question 4

Hyperpolarization

Answer 4

• In the negative direction
• A decrease in the membrane potential relative to the resting potential.
• IPSP

Question 5

Action Potential

Answer 5

A brief electrical impulse that’s responsible for the conduction of information down an axon.

AKA, “spike,” “the neuron fires”

Question 6

Critical Firing Level

Answer 6

• The threshold of excitation.
• The value of the membrane potential that must be reached in order to produce an action potential.
• Change = +15 mV (-55 mV)

Question 7

Where Do EPSPs and IPSPs Occur?

Answer 7

Dendrite

Question 8

How long is an AP?

Answer 8

1 mSec

Question 9

Summation

Answer 9

When 2 EPSPs build on each other.

2 Types.

Question 10

2 Types of Summation

Answer 10

1. Temporal - Same neuron sends a signal 2x in a row in a very short time period.
2. Spatial - When 2 different neurons send a NT to a neuron at about the same time.

Question 11

Does Summation Apply to IPSPs?

Answer 11

NO.

2 IPSPs building on each other don’t yield a reverse spike - the most that happens is that the membrane potential just drops to a certain level and stays there.

Question 12

Concentrations of Ions In and Out of Cell At Rest

Answer 12

• More sodium (Na+) outside than inside
• More potassium (K+) inside than outside
• More chloride (Cl-) outside than inside
• More calcium (Ca2+) outside than inside

Question 13

Resting Membrane Potential

(Visual)

Answer 13

Question 14

Action Potential Graph

Answer 14

Question 15

Driving Forces on an Ion

(2)

Answer 15

1. Diffusional Force - An ion will want to go from an area of high concentration to an area of low concentration.
2. Electrostatic Force - Opposites attract.

Question 16

Which Ion Has The Largest Driving Force Acting On It?

Answer 16

Na+

(Both diffusional and electrostatic forces want to push it inside)

Question 17

Driving Force on Cl- inside Cell?

Answer 17

Because it’s negative, it wants to leave the cell to go to the positive environment (electrostatic force)

Question 18

Driving Force on K+ inside Cell

Answer 18

Because K+ is in high concentration on the inside, the diffusional force wants to push it out of the cell.

Question 19

Driving Force on Na+ Inside Cell

Answer 19

Na+ is happy where it is b/c the inside of the cell is negative and it’s positive.

Question 20

Driving Force on Cl- Outside of Cell

Answer 20

Diffusional force wants to push inside because it is in higher concentration outside.

Question 21

Driving force on K+ Outside Cell?

Answer 21

Electrostatic force wants to push it in to a negative environment because it’s positive (opposites attract).

Question 22

Diffusional Force on Sodium Outside The Cell?

Answer 22

Both the diffusional force and the electrostatic force want to push Na+ into the cell b/c

• There is less concentration of it inside the cell (diffusional force)
• It is positive and is attracted to a negative environment (electrostatic force)

Question 23

Equilibrium Potential

&

Equation

Answer 23

At some point, an ion will reach a balance where the driving force is zero (the diffusional and electrostatic forces are balanced).

Nernst Equation (need to know concentration of ion inside and outside of cell)

E(Na+) = +45 mV

E(K+) = - 80 mV

Question 24

Driving Force on Na+?

Answer 24

• -70 at rest
• EP = +40
• Therefore, 110 mV of driving force on Na+ (diffusional + electrostatic)

Na+ will rush in until the diffusional and electrostatic forces balance (driving force = 0). Once its EP is reached, Na+ channels will close.

***All the K+ will leave the cell until it reaches it’s equilibrium potential of -80mV.

Question 25

Permeability of Membrane to K+ vs Na+

Answer 25

* Very permeable to K+ (leak channels), therefore resting membrane potential is closer to K+ equilibrium potential * Whereas the membrane is not permeable to Na+ unless the ion channels are open.

Question 26

Na+, K+ Pump

Answer 26

Carries 3 Na+ out for every 2 K+ back in Ensures that Na+ remains in greatest concentration in extracellular fluid despite both the forces of diffusion and electrostatic pressure.

Question 27

All-or-None Law

Answer 27

* An action potential is always the same value (e.g., +45). * It either fires or it doesn't. * The only thing that changes is the frequency of firing.

Question 28

Rate Law

Answer 28

* An action potential can vary in frequency * Ex. The difference between a small pain and a big pain is the frequency with which a neuron fires.

Question 29

Where do neurons synapse?

Answer 29

Dendritic Spine

Question 30

How Is A Message Conveyed From The Dendrite Down the Axon?

Answer 30

* If there are more EPSPs than IPSPs at the initial segment/axon hillock, there will be an AP and the neuron will fire. * As AP sweeps down axon and if at NOR the critical firing level is reached, the spike will happen again (nothing happens in the internode space). * At the end, there are Ca2+ voltage gated channels and if they open, the NT will be released. NOT Saltatory Conduction but rather a WAVE OF DEPOLARIZATION. Na+ will leak out as goes along but so long as the charge is +15mV at NOR, the AP will be re-propagated.

Question 31

Speed of Neurocommunication

Answer 31

Avg. = 120 meters/second

Question 32

What travels faster to brain: Messages About Temperature or Messages About Pain?

Answer 32

Temperature. Pain fibers are small and unmyelinated, whereas temperature axons are myelinated and wider around.

Question 33

To Make An Axon Faster ...

Answer 33

1. Myelinate (provides insulation, AKA decreases resistance) 2. Make axon giant (the larger it is around, the less resistance = more current)

Question 34

Ohm's Law

Answer 34

Cable Properties * Speed of transmission down an axon. * Decrease resistance by insulating with myelin and making axon bigger * Voltage = Current (Amps) x Resistance (Ohm)

Question 35

Multiple Sclerosis

Answer 35

Disease of demyelination. Because myelin is lost, there's a loss of voltage and a lack of re-propagation at the subsequent NOR.

Question 36

Picture of Forces and Concentrations of Ions Inside and Outside of Cell @ Rest

Answer 36