Chapter 3 and 4 - Nerve Activity

Question 1

The cell membrane is made up of…

Answer 1

Mostly water

Question 2

Phospholipids

Answer 2

The molecules that make up the cell membrane

Question 3

Phospholipid Bilayer

Answer 3

Hydrophilic heads (will dissolve in water)

Hydrophobic tails

Question 4

Protein Chain

Answer 4

Dna (transcription ->) RNA (translation ->) Amino Acid Chain (folding ->) Protein

Question 5

Amino Acid

Answer 5

Basic building block of protein
- 20 different kinds (human)
- Vary on the ‘R’ group

Question 6

R Groups

Answer 6

Can have hydrophilic or hydrophobic properties

Lead to different structure when left alone in the cellular environment

Protein folding

Question 7

The Cell Membrane

Answer 7

Semipermeable Phospholipid Bilayer

Causes difference in electrical charge between, inside and outside of cell

Question 8

Ionic Basis of the Resting Potential

Answer 8

Ions, charged particles, are unevenly distributed

4 Ions Contributing:
- Sodium (Na+)
- Chloride (Cl-)
- Potassium (K+)
- Negatively charged proteins
(synthesized within the neuron)
(found primarily within the neuron)

Question 9

What 4 factors influence the resting potential and the unequal ion distribution?

Answer 9

Two factors are homogenizing (distribute ions equally)

Two factors counteract the homogenization
(contribute to uneven distribution)

Question 10

Random Motion

Answer 10

Particles move down their concentration gradient

Contributing to even distribution.

Question 11

Electrostatic Pressure

Answer 11

Like forces repel, opposites attract

Contributing to even distribution.

Question 12

Selective Permeability

Answer 12

Ions move in and out through ion-specific channels

K+ and Cl- pass readily

Little movement of Na+

Negatively charged proteins don’t move at all, trapped inside

To calculate the equilibrium of one ion -> Nerst equation

All relevant ions -> Goldman equation

Contributing to uneven distribution.

Question 13

Sodium-Potassium Pump

Answer 13

Moves 3 Na+ out for every 2K+ in

Active process – much of the energy consumed by the brain (asleep or awake) goes toward maintenance of these ionic differences across the membrane

Contributing to uneven distribution.

Question 14

Membrane Potential

Answer 14

The end result of all of these forces is that we have a resting membrane potential – the difference in charge between the inside and outside of a cell – of -70mv

Question 15

Neurons in action

Answer 15

Neuron at rest -> resting membrane potential
- Homeostatic balance of ions
- -70mv

Neuron in action -> action potential (AP)
- Ions in flux
- Changing potentials depending on stage

Question 16

The Action Potential

Answer 16

All-or-none:

• if threshold is reached the neuron “fires” and AP occurs
• If threshold not reached – no AP
• Through APs - message can be transmitted from one neuron to another

When threshold is reached, voltage activated ion channels are opened

Question 17

When summation = threshold of excitation
(-55mV)…

Answer 17

When summation = threshold of excitation
(-55mV), voltage-activated Na+ channels
open and sodium rushes in

Question 18

Voltage Gated Sodium Channel

Answer 18

Immediate response when threshold is reached

Allows near full permeability to sodium

Question 19

The Ionic Basis of Action Potentials

Answer 19

Remember, all forces were acting to move Na+ into the cell

And now permeability isn’t an issue

Membrane potential moves from -70 to +50mV

Question 20

The Action Potential - Steps

Answer 20

Rising Phase:
- Na+ in, K+ out
- Potassium channels open
- Sodium channels open

Repolarization:
- Sodium channels close

Hyperpolarization
- Potassium channels start to close

Rising phase (Depolarization):
Na+ moves membrane potential from -70 to +50mV

End of rising phase:
After about 1 millisec, Na+ channels close

Repolarization:
Concentration gradient and change in charge leads to efflux of K+

Hyperpolaization: Channels close slowly - K+ efflux leads to membrane potential <-70mV40

Question 21

Depolarization in one location leads to…

Answer 21

An increase in membrane potential in an adjacent location

• This opens voltage gated sodium channels along the next part of the membrane
• This propagates the action potential

Question 22

Refractory Periods

Answer 22

Prevent the backwards movement of APs and limit the rate of firing (to 1000 times/sec!)

ABSOLUTE → impossible to initiate another action potential

RELATIVE → harder to initiate another action potential

Refractory periods occur because of the ion channel properties, and ion concentrations

Overshoot:
Membrane potential is below the resting potential
Greater jump is required to reach threshold

Question 23

Conduction in Myelinated Axons: Saltatory Conduction

Answer 23

Passive conduction along each myelin segment to next node of Ranvier

New action potential generated at each node

Faster conduction than in unmyelinated
axons -Saltatory conduction