Week 2-Neurophysiology

Question 1

Types of electrical signals

Answer 1

1. Action potentials
2. Synaptic potentials
3. Generator potentials

Question 2

Resting state

Answer 2

Membrane has electrical charge due to charges particles (ions) on either side

Inside usually about -65mV

Question 3

Membrane potential (Vm)

Answer 3

Difference in electrical charge across the membrane

Question 4

Resting membrane potential (Vr)

Answer 4

Membrane potential of neuron not conducting or signaling

Question 5

Hyperpolarization

Answer 5

Increase in potential

-makes inside MORE NEGATIVE

Question 6

Depolarization

Answer 6

Decrease in potential

Making inside MORE POSITIVE

Question 7

Voltage

Answer 7

Membrane electrical potential (Vm)

Question 8

Current

Answer 8

Follows flow of ions

Question 9

Cation

Answer 9

Positively charged ion

Question 10

Anion

Answer 10

Negatively charged ion

Question 11

Intrinsic proteins

Answer 11

Attached to membrane

-can span whole bilayer or only a portion

Question 12

Extrinsic proteins

Answer 12

Not attached to membrane

Question 13

Waters of hydration

Answer 13

Electrostatically bound water molecules to ions

-ions carrying water–>cannot pass hydrophobic membrane

Question 14

Gated ion channels

Answer 14

• Conduct ions (provide hold to cross membrane)
• select for specific ions
• open and close depending on various stimuli

Question 15

Gated ions open/close stimuli

Answer 15

1. Electrical (Vm)
2. Mechanical
3. Chemical (presence of certain molecules)

Question 16

Mechanisms for opening/closing of channels

Answer 16

1. One point of lumen closes
2. Lumen wall itself closes
3. Attached particularly may swing into lumen to block it

Question 17

Ligand gated

Answer 17

When ligand binds, causes signal cascade

Question 18

Phosphorylation gating

Answer 18

ATP phosphorylation opens channel

Question 19

Voltage gated

Answer 19

Change in membrane potential opens channel

Question 20

Pressure/stretch gating

Answer 20

Cytoskeleton causes channel to stretch open

Question 21

Non-gated/passive channels

Answer 21

“Leaky”

• flick open randomly and continuously
• select for specific ions
• found over entire neuronal membrane

Question 22

Ion size varies (K+ vs Na+)

Answer 22

Na+: smaller, with larger hydration shell

K+: larger, with smaller hydration shell

Question 23

Selectivity filter of non-gated/passive channels

Answer 23

Forms weak and brief bond to ion passing through

Question 24

Na+ passive channel mechanism

Answer 24

K+ simply too big to pass through

Question 25

K+ passive channel mechanism

Answer 25

Na+ cannot pass through because not fully stabilized (Na+ only binds to 2 water molecules) -->K+ binds to 4 water molecules

Question 26

Saturation

Answer 26

Flow of ions through channel causes saturation due to quick bonding in lumen

Question 27

Channel structure

Answer 27

Made of at least 4 alpha helical structures - different proteins - copies of same proteins - one protein complex with 4 parts

Question 28

Kinetics of ion flow depends on...

Answer 28

1. Size of ion 2. Channel characteristics 3. Electrochemical force (electrostatic or concentration gradient) 4. Permeability of membrane

Question 29

ion pumps

Answer 29

maintain concentration gradients - must undergo conformational change - must use energy (ATP) to transport against electrochemical gradient * Active Transport

Question 30

desensitization

Answer 30

refractory state when exposure to agonist is prolonged

Question 31

inactivation

Answer 31

Voltage gates enter refractory period - closed, cannot be opened by positive voltages * membrane potential must return to VR before recovering

Question 32

Equilibrium potential (Ex)

Answer 32

value of Vm when concentration gradient and electrostatic are at balance -->no more net flow of ions

Question 33

Equilibrium potential of K+, Na+, Cl-

Answer 33

``` EK+ = -75mV ENa+ = +55mV ECl- = -65 mV ```

Question 34

Nernst equation does NOT predict VR because

Answer 34

1. does not assume multiple forces are acting on it 2. assumes only 1 ion is free to pass through membrane 3. assumes equilibrium has been reached

Question 35

Na+/K+ ATPase pump

Answer 35

- corrects passive channels leaking ions - intrinsic enzyme - changes conformation 1. open to inside of cell, binds 3 Na+ 2. ATP phosphorylates 3. releases Na+ outside - picks up 2 K+ 4. dephosphorylates 5. releases 2 K+ inside

Question 36

Synaptic potentials

Answer 36

Changes in VR in one neuron as consequence of another neuron firing

Question 37

PSP (post synaptic potential) & properties

Answer 37

The neuron receiving the signal from another 1. they are GRADED (vary with intensity of stimulus) 2. They can be SUMMATED

Question 38

EPSP

Answer 38

PSP causes depolarization in neuron

Question 39

IPSP

Answer 39

PSP causes hyperpolarization in neuron

Question 40

Capacitor + resistor

Answer 40

provides delay | -electricity will first flow to the capacitor, then to the resistor

Question 41

Time constant (tau)

Answer 41

Time it takes for change in Vm to reach 63% of its final value of change *longer the time constant = longer duration of PSP ex: tau = 1 msec --> multiple small PSP tau = 10 msec --> temporal summation of PSP until it reaches threshold and fires

Question 42

Temporal summation

Answer 42

process whereby one PSP sums with another PSP -1 input

Question 43

Axon hillock

Answer 43

where decision to fire occurs | -distance a PSP must travel

Question 44

Length constant (lambda)

Answer 44

*current delays over distance site on membrane where Vm has delayed to 37% its initial change *larger lambda = further PSP can travel & have an impact on axon hillock

Question 45

Spatial summation

Answer 45

process whereby PSP's generated at different sites on the neuron reach the hillock at the same time and Summate *can be multiple inputs

Question 46

Passive properties affect speed of AP (slow it)

Answer 46

1. cytoplasmic resistance | 2. membrane capacitance

Question 47

2 properties to make AP faster

Answer 47

1. increase neuron diameter (decrease resistance) | 2. myelinate axon surface (next available hole is farther)

Question 48

nodes of ranvier

Answer 48

breaks in myelin sheaths-->places for AP to regenerate