NEUROPHYSIOLOGY OF NEURAL SIGNALS

Question 1

Membrane potential

Answer 1

The electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell.

Question 2

What are the 2 basic electric potentials that axons have?

Answer 2

1. Resting membrane potential: The membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials.
2. Action potential: The brief electrical impulse that provides the basis for conduction of information along an axon.
   Action potential is the same all the time no big no small it’s a ALL OR NONE

Question 3

the resting potential

Answer 3

When we insert our electrode into the axon, we get a straight line
(usually –60,-70)

Question 4

How the membrane potential can change?

Answer 4

a. Hyperpolarization: An increase in the membrane potential of a cell, relative to the normal resting potential. drive it further away from zero)

Larger the hyperpolarization stimuli the larger the response the farther down it’ll go

b. Depolarization: Reduction (toward zero) of the membrane potential of a cell from its normal resting potential.Only depolarization causes action potential

Question 5

Threshold of excitation

Answer 5

: The value of the membrane potential that must be reached to produce an action potential.
change that has to occur in order to trigger an action potential)
Once the response reached the threshold a series of events causes an action potential (very strong depolarizing spike that not only drives response toward 0 but overshoots it)(changing the inside and outside cell charge temporarily)

Question 6

What are the values of Resting potential, Threshold ≈Action Potential

Answer 6

1. Resting potential ≈ -70 mV
2. Threshold ≈ -55 mV

Action Potential ≈ +40 mV and Hyperpolarization ≈ -90 mV

Takes approximately 2 msec!

Question 7

Diffusion gradient

Answer 7

Movement of molecules from a region of high

concentration to regions of low concentration.

  (e.g. sugar dissolving in water)

Question 8

Electrostatic gradient

Answer 8

Molecules can carry charge (ions)

Cations (+ charge)
Anions (- charge)
Move towards areas of unlike charge

-THERE IS A GRADIENT BC OPPOSITES ATTRACT-

Question 9

Dynamic equilibrium

Answer 9

Gradients can balance one another.

Question 10

Intracellular fluid

Answer 10

The fluid contained within a cell

Question 11

Extracellular fluid

Answer 11

Body fluids located outside the cell.

Question 12

membrane equilibrium

Answer 12

certain ions inside and outside the cell

Question 13

dynamic equilibrium

Answer 13

dynamic equilibrium maintained by sodium-potassium pump.

• Mechanical pump that exchanges sodium for K+, brings sodium out K= back inside
• Ex of an active transport- against concentration gradient
• electrostatic pressure and diffusion work to get Na+ inside the cell.

the sodium-potassium pump pushes it outside again to maintain equilibrium.

Question 14

What happens inside of the cell? membrane equ’

Answer 14

The ones labeled A- are large proteins that can’t leave the cell and contribute to making inside the cell more negative

K+ diffuses from inside to outside (high to low concentration) the electrostatic pressure pushes it inside because K is + charged (the 2 forces are reaching equ bc they are opposing each other) , K+ can generally free flow in and out bc the 2 pressures are in equ

Question 15

What happens outside of the cell? membrane equ’

Answer 15

Cl is negative so the electrostatic pressure pushes it outside and the diffusion gradient is pushing it inside bc there’s more outside than inside (dynamic equ= the 2 forces are working against each other keeping things balanced)

Na; more outside then inside so diffusion pushes it inside and electrostatic pressure is also pushing it inside the cell bc sodium is + so its being attracted to the more negative inside

But sodium can’t pass thru the lipid layer and it needs to wait for a sodium channel to open, which is the start of an action potential

Question 16

Describe the sodium-potassium pump

Answer 16

• A- ions & K+ ions have higher concentration inside axon relative to outside…
• Cl- ions & Na+ ions are more concentrated outside the axon
• Na+ channels are ordinarily closed to prevent entry of Na+
• Na+/K+ pump exchanges 3 Na+ for 2 K+. The high concentration of extracellular Na+ is due to this pump. 10x as much Na+ is outside the cell as inside, contributing to the membrane’s RP of -70
• K+ is free to ENTER & LEAVE the cell but Na+ CANNOT reenter once pumped out

Question 17

Describe how an action potential occurs

Answer 17

As soon as you make membrane potential more positive (cross threshold), sodium channels open sodium rushes in (everything is trying to push sodium into cell), large spike of action potential is a result of sodium being positive, temporarily making inside of the cell more + than outside, once you reach peak there is a refractory period when Na channels temporarily close, and K+ channel opens and rushes out which drive inside of the cell more negative and get to hyperpolarization, when K+ channels close sodium potassium pump starts exchanging to restore resting membrane potential (AT REST INSIDE IS MORE – BUT DURING ACTION POTENTIAL OUTSIDE IS MORE-)

• Every neuron has a resting charge or resting potential (-70 mv)
• Maintained by sodium potassium pump- continually pumping Na+ out and K+ in
• When an ion channel opens Na+ rushes into the cell and K+ goes out changing the potential
• With enough stimulation of this kind the resting potential passes a threshold (-55 mv) and the cell fires
• Thise reverses the polarity of the cell for a brief period- known as the cells action potential
• This is all generated at the axon hillock
• Sodium channels only open briefly and then cannot open for some period of time (absolute refractory period)

Question 18

What do pufferfish contain?

Answer 18

tetrodotoxin – sodium channel blocker prevents action potentials and the person suffocates

Question 19

Laws of conduction

Answer 19

all-or-none – once triggered an action potential can’t be stopped.

variable information, representing the strength of a response to a stimulus (or the strength of a command to act), is conveyed by firing rate.(strong stimulus= very fast firing rate)

Question 20

How does an action potential propagate along the axon?

Answer 20

• Axon Hillock - where the action potential begins.
• Terminal Buttons - the end point for the action potential.
• Action potential flows toward the terminal.
  (does not reverse direction because area where the action potential came from is still in refractory.)

Question 21

Describe the conduction of action potentials in unmyelinated axons

Answer 21

Sodium channels are available to be open all the way down the axon

Action potential happening, Na comes in then refractory period neighboring area start to depolarize etc and move down the end feet

Question 22

Describe the Conduction of action potentials in myelinated neurons

Answer 22

• faster, cheaper

• Nodes of Ranvier have sodium channels that can be opened but the axon that have myelin, the myelin covers those potential channel openings
• Na + channels open up generating an action potential at the nodes of Ranvier
• The action potential propagates passively through the myelinated axon and when it reaches another node another action potential is triggered and continues from node to node as fast at 150 m/s up to 15 times faster than an unmyelinated axon

Described as jumping from node of Ranvier to node of Ranvier

Question 23

cable properties

Answer 23

signal degrades as it travels along the axon

A stimulus will weaken over time as it passively travels over the axon

Question 24

Saltatory conduction

Answer 24

Conduction of action potentials by myelinated axons. The action potential appears to jump from one Node of Ranvier to the next.

rejuvenated at the nodes of Ranvier- signal is strong enough even though its passively making its way through the myelinated axon that it can rise above the threshold and trigger a new action potential

Question 25

What are the advantages of myelin?

Answer 25

conservation of energy & speed of conduction

Question 26

How are the nodes of ranvier spaced?

Answer 26

Spacing of the nodes is optimized according to axon length and diameter.

Question 27

What causes demyelination? And what does it result in

Answer 27

Multiple Sclerosis- less white matter areas
degeneration of myelin sheaths (plaques) or breakdown of myelin bc of Phagocytosis – macrophages gone wild – immune system glitch or
Apoptosis – programmed cell death

Question 28

What are consequences of demyelination?

Answer 28

affects transmission of nerve impulse (myelin is perfectly spaced so signals can travel from node of Ranvier to node of Ranvier and be regenerated but degeneration because of MS causes much more noise to the system, traveling like an unmyelinated axon but even more disturbing)

Question 29

What are the symptoms of MS?

Answer 29

Different symptoms that depend on area affected

visual disturbances (particularly colour vision or tunnel vision)

nystagmus- (twitching of the eyes)

loss of sensation

loss of motor control

Question 30

What is Multiple Sclerosis?

Answer 30

autoimmune disease of the CNS

Question 31

synaptic cleft

Answer 31

between the presynaptic membrane and postsynaptic membrane

Question 32

post-synaptic potentials

Answer 32

the released neurotransmitter leads to post-synaptic potentials hyperpolarization or depolarization, make it harder or easier for the neighboring neuron to reach threshold ) that alter the firing rate of the receiving neuron (decrease or increase chance of neuron firing).- can be excitatory or inhibitory

Question 33

Neurotransmitters

Answer 33

chemical substance released from the end of a neuron during the propagation of a nerve impulse; it relays information from one neuron to another.
has to be released bc of an action potential happening)

Question 34

Neuromodulators

Answer 34

secreted in larger amounts and diffuse further (composed of peptides).

Question 35

Hormones

Answer 35

produced in endocrine glands – released into extracellular fluid to be taken up by specific target cells.’

Question 36

How do neurotransmitters bind to receptors?

Answer 36

only specific neurotransmitters will bind with specific receptor sites – like a key in a lock.

Only specific neurotransmitters will bind with the post-synaptic membrane.(will open a channel or keep it close, depolarize or hyperpolarize the stimulus)

Question 37

ligand

Answer 37

chemical that attaches to a binding site
neurotransmitters are naturally produced ligands
neurotoxins are also ligands and various drugs have their effect in the same manner – artificially produced ligands (e.g., LSD).

Question 38

Axodendritic

Answer 38

synapse on the dendrite of the neuron

Question 39

Axosomatic

Answer 39

on the soma

-terminal button is connecting to some

Question 40

Axoaxonic

Answer 40

on the axon

- terminal button forming a connection with the terminal button of another neuron

Question 41

Receptors

Answer 41

neurotransmitter specific postsynaptic receptors

open to allow ions to flow into the postsynaptic neuron

Question 42

What are the 2 main types of receptors?

Answer 42

ionotropic

Metabotropic

Question 43

Ionotropic receptors

Answer 43

receptor site has its own ion channel.
contain sodium channels.
fast acting and short lasting.

Question 44

Metabotropic receptors

Answer 44

• indirect method.
• molecules bind with receptors
• located nearby G-proteins.
• G-proteins in turn activate an ion channel.
• slower to begin and longer lasting.
• G-proteins can also activate second messengers – enzymes that in turn activate an ion channel.

Question 45

Excitatory or inhibitory post-synaptic potentials

Answer 45

once neurotransmitters are bound to the post synaptic membrane the electrical charge is now altered in the receiving neuron.

the change in the electric charge can be more positive than the resting potential (excitatory) or more negative than the resting potential (inhibitory).

Question 46

Describe the characteristics of a post-synaptic potentials

Answer 46

determined by the ion channel opened by the neurotransmitter and not the transmitter itself.

graded – the potential dissipates with distance traveled. (changes in membrane potential that vary in size, as opposed to being all-or-none, the variable-strength signals that can be transmitted over short distances whereas action potentials are large depolarizations that can be transmitted over long distances.)

smaller in magnitude than action potentials.

action potentials are always excitatory – post-synaptic potentials can be either excitatory or inhibitory

Question 47

excitatory PSP

Answer 47

typically related to sodium ion channels (rush of Na+ into the cell makes it more positively charged).

Question 48

inhibitory PSP

Answer 48

typically related to potassium ion channels (extra K+ maintained inside cell by sodium-potassium pump leaks out making the cell more negatively charged).

• cl channels open making it more negative
  action of Cl– channels depends on the state of the receiving neuron

–if depolarised Cl– will bring the cell back to a resting state

Question 49

reuptake

Answer 49

rapid removal of neurotransmitter from the synaptic cleft.

Question 50

SSRIs

Answer 50

(selective seratonin reuptake inhibitors – e.g, Prozac) prolong the PSP by inhibiting reuptake.

Question 51

Summation of post- synaptic potentials

Answer 51

whether the PSP leads to the excitation or inhibition of the neuron depends on the combined effects of many PSPs.

Question 52

Spatial integration

Answer 52

: equal excitatory and inhibitory input will cause no change

Question 53

Temporal integration

Answer 53

ripples can combine to make bigger ripples
both subthreshold EPSPs occurred at the same time, however, they could sum, or add up, to bring the membrane potential to threshold.

Question 54

Autoreceptors

Answer 54

respond to neurotransmitters they produce.

regulate synthesis and release of other transmitters.

metabotropic

usually inhibitory – may control amount of neurotransmitter released

Question 55

Why do you need to know all this?

Answer 55

different disease processes involve different aspects of the basic electrochemical transmission of neural information.

Parkinson’s Disease – dopamine deficiency.

Multiple Sclerosis – affects the myelin sheath of white matter.

Epilepsy – abnormal electrical stimulation.

Alzheimer’s Disease – neurofibrillary tangles may affect the transport of neurotransmitters.

Question 56

Describe the direction of travel of AP

Answer 56

a. In response to a signal, the soma end of the axon becomes depolarized
b. The depolarization spreads down the axon. Meanwhile, the first part of the membrane repolarizes. Because Na+ channels are inactivated & additional K+ channels have opened the membrane cannot depolarize again
c. The AP continues to travel down the axon

Question 57

What would an image of a patients brain with Multiple Sclerosis look like?

Answer 57

less white matter areas

Question 58

Name 3 neurochemicals

Answer 58

1. Neurotransmitters
2. Hormones
3. Neuromodulators

Question 59

Describe how the signal goes from from electrical to chemical

Answer 59

• electrical charge causes calcium channels to open on the terminal button which causes calcium to come into the cell which causes the vesicles filled with neurotransmitters to bind to the presynaptic membrane and release the neurotransmitter into the cleft
• axon terminal contains synaptic vesicles
• Vesicles release neurotransmitters across synaptic cleft
• Neurotransmitter binds to receptors on post synaptic membrane- basis for - neural
• the released neurotransmitter leads to post-synaptic potentials