Midterm 2: Chapter 4

Question 1

Descartes proposed that (3)

what flow+what control+example

Answer 1

• through cerebrospinal fluid flowing through nerve tubes
• the nonmaterial mind controls body mechanics
• reasoned that when the fire burns the man’s toe, it stretches the skin, which tugs on a nerve tube leading to the brain. In response to the tug, a valve in a brain ventricle opens, and cerebral
  spinal fluid (CSF) flows down the tube, filling the leg muscles and causing them to contract and pull the toe back from the fire.

Question 2

Electricity

Answer 2

the flow of electrons from a body that contains a higher charge (more electrons) to a body that contains a lower charge (fewer electrons)

Question 3

electrical potential

Answer 3

the ability to do work using stored electrical energy

Question 4

electrical stimulation

Answer 4

passing an electrical current from the uninsulated tip of an electrode onto a nerve to produce behavior—a muscular contraction

Question 5

voltmeter

Answer 5

a device that measures the flow and the strength of electrical voltage by recording the difference in electrical potential between two bodies

Question 6

Information flow in the nervous system, is much too slow to be

Answer 6

flow of electricity (based on electrons)

Question 7

Loligo is not a giant squid. But its axons are giant and……. beacause…..

Answer 7

is formed by the fusion of many
smaller axons. Because larger axons send messages faster than smaller
axons do, these giant axons allow the squid to jet-propel away from
predators

Question 8

oscilloscope

Answer 8

a voltmeter with a screen sensitive
enough to display the minuscule electrical signals emanating from a
nerve or neuron over time to visualize and measure electrical signals as they change.

Question 9

Microelectrodes (2)

What is it+ what can it do

Answer 9

an electrode small enough to place on or in an axon—can deliver electrical current to a single neuron as well
as record from it.

Question 10

The tip of a microelectrode placed on an axon provides an

Answer 10

extracellular measure of the electrical current from a tiny part of the axon

Question 11

The tip of one electrode can be placed on the surface of the axon, and the tip of a second electrode can be inserted into the axon. This technique can be
used to measure

Answer 11

voltage across the cell membrane

Question 12

Three factors influence the movement of anions and cations into and out of cells:

Answer 12

diffusion,
concentration gradient, and voltage gradient

Question 13

diffusion (4)

What it is+energy+results from+results in

Answer 13

• molecules spread out from a point of high concentration
• no additional energy
• results from the random motion of molecules as they move and bounce off one another to gradually disperse in a solution
• results in a dynamic equilibrium, with a relatively equal number of molecules everywhere in the solution.

Question 14

Concentration gradient

Answer 14

describes the relative abundance of a substance in a space

Question 15

voltage gradient aka concentration gradient of ions

Answer 15

the difference in charge between two regions

Question 16

When salt is dissolved in water, the diffusion of its ions can be described either as

Answer 16

movement down a concentration gradient (for sodium and chloride ions) or movement down a voltage gradient (for the positive and negative charges)

Question 17

Explain this picture in terms of concentration gradient and voltage gradient

Answer 17

In the left side of the container, there is no longer a gradient for either sodium or chloride ions because they occur everywhere with the same relative abundance. There are no gradients for these ions on the other side of the container either because the solid membrane prevents the ions from entering that side. But there are concentration and voltage gradients for both sodium and chloride ions across the membrane—that is, from the salty side to the freshwater side. The left side of the container is more positively charged because some chloride ions have migrated, leaving a preponderance of positive (Na ) charges. The right side of the container is more negatively charged because some chloride ions have entered that chamber, where none were before. The charge is highest on the surface of the semipermeable membrane, the area at which positive and negative ions accumulate.

Question 18

Electrical activity in neurons

Answer 18

the movement of specific ions through channels across neuronal membranes.

Question 19

resting potential

Answer 19

the inside of the membrane at rest is −70 mV relative to the extracellular side

Question 20

Four charged particles take part in producing the resting potential

Answer 20

ions of sodium (Na ), potassium (K ), chloride (Cl ), and large negatively charged protein molecules (A-)

Question 21

Charged particles are distributed unequally across the axon’s membrane, with more—- in the intracellular fluid and more —- in the extracellular fluid.

Answer 21

• protein anions and potassium ions
• sodium and chloride ions

Question 22

Three features contribute to the cell membrane’s resting charge

Answer 22

1. Because the membrane is relatively impermeable to large molecules, the negatively charged proteins (A ) remain inside the cell.
2. Ungated potassium and chloride channels allow potassium (K ) and chloride (Cl ) ions to pass more freely, but gates on sodium channels keep out positively charged sodium ions (Na ).
3. Na−K pumps extrude Na from the intracellular fluid and inject K.

Question 23

Inside the cell and talk about the negative charge+ components (3)

Answer 23

• Large protein anions are manufactured inside cells. No membrane channels are large enough to allow these proteins to leave the cell, and their negative charge alone is sufficient to produce transmembrane voltage, or a resting potential.
• Potassium ions cross the cell membrane through open potassium channels. With this high concentration of potassium ions inside the cell, however, the potassium concentration gradient across the membrane limits the number of potassium ions entering the cell.
• Because the internal concentration of potassium ions is much higher than the external potassium concentration, potassium ions are drawn out of the cell by the potassium concentration gradient

Question 24

Outside the cell componets+ talk about how its makes -70mV RP (3)

Answer 24

• The equilibrium of the potassium voltage and concentration gradients results in some potassium ions remaining outside the cell. It is necessary to have only a few positively charged potassium ions outside the cell to maintain a negative charge inside the cell.
• Sodium ions are kept out to the extent that about 10 times as many sodium ions reside on the outside of the axon membrane as on its inside. Sufficient sodium ions could leak into the cell to neutralize its membrane potential. When sodium ions do leak into the neuron, they are immediately escorted out again by the action of a sodium potassium pump. The difference in sodium concentrations also contributes to the membrane’s resting potential.
• Unlike sodium ions, chloride ions move in and out of the cell through open channels in the membrane. The equilibrium point, at which the chloride’s concentration gradient equals its voltage gradient, is approximately the same as the membrane’s resting potential, so chloride ions ordinarily contribute little to the resting potential.

Question 25

Graded potentials

Answer 25

small voltage fluctuations across the cell membrane

Question 26

Hyperpolarization is due to the

Answer 26

efflux of K+ making extracellular side more positive

Question 27

Depolarization is due to

Answer 27

an influx of Na+ through Na+ channels

Question 28

Hyperpolarization and depolarization typically take place on the—– because—-

Answer 28

• soma (cell body) membrane and on neuronal dendrites
• These areas contain gated channels that can open and close, thereby changing the membrane potential

Question 29

Three channels underlie graded potentials:

Answer 29

• Potassium channels
• Chloride channel
• Sodium channels

Question 30

Potassium channels in hyperpolarization

Answer 30

For the membrane to become hyperpolarized, its extracellular side must become more positive, which can be accomplished with an outward movement, or efflux, of potassium ions. But if potassium channels are ordinarily open, how can the efflux of potassium ions increase? Apparently, even though potassium channels are open, some resistance to the outward flow of potassium ions remains. Reducing this resistance enables hyperpolarization.

Question 31

Chloride channels in hyperpolarization

Answer 31

The membrane can also become hyperpolarized if an influx of chloride ions occurs. Even though chloride ions can pass through the membrane, more ions remain on the outside than on the inside, so a decreased resistance to Cl flow can result in brief increases of Cl inside the cell.

Question 32

Sodium channel and depolarization

Answer 32

Depolarization can be produced if normally closed sodium channel gates open to allow an influx of sodium ions.

Question 33

TTX

Answer 33

The involvement of sodium channels in
depolarization is indicated by the fact that the chemical tetrodotoxin (TTX), which blocks sodium channels, also blocks depolarization.

Question 34

tetraethylammonium
(TEA)

Answer 34

blocks potassium channels, also blocks hyperpolarization

Question 35

action potential (2)

What it is+details

Answer 35

• brief but very large reversal in an axon membrane’s polarity
• The voltage across the membrane suddenly reverses, making the intracellular side positive relative to the extracellular side, then abruptly reverses again to restore the resting potential

Question 36

The movement of ions in an action potential:

Answer 36

An action potential occurs when a large concentration of first Na and then K crosses the membrane rapidly. The depolarizing phase of the action potential is due to Na influx, and the hyperpolarizing phase is due to K efflux. Sodium rushes in and then potassium rushes out.

Question 37

Experimental results reveal that if an axon membrane is stimulated electrically while the solution surrounding the axon contains the chemical TEA (to block potassium channels), the result is a

Answer 37

smaller-than-normal ion flow due entirely to an Na influx

Question 38

Volatge activated channels (2)

what happens when they are closed+open?

Answer 38

• are closed when an axon’s membrane is at its resting potential: ions cannot pass through them.
• When the membrane reaches threshold voltage, the configuration of the voltage-activated channels alters: they open briefly,enabling ions to pass through, then close again to restrict ion flow

Question 39

Voltage activated channels sequence of events in light of an action potential (4)

Answer 39

1. Both sodium and potassium voltage activated channels are attuned to the threshold voltage of about –50 mV. If the cell membrane changes to reach this voltage, both types of channels open to allow ion flow across the membrane.
2. The voltage-activated sodium channels respond more quickly than the potassium channels. As a result, the voltage change due to Na influx takes place slightly before the voltage change due to K efflux can begin
3. Sodium channels have two gates. Once the membrane depolarizes to about +30 mV, one of the gates closes. Thus, Na influx begins quickly and ends quickly.
4. The potassium channels open more slowly than the sodium channels, and they remain open longer. Thus, the efflux of K reverses the depolarization produced by Na influx and even hyperpolarizes the membrane.

Question 40

Two time when the membrane is in absolutely refractory:

Answer 40

1. Stimulation of the axon membrane during the depolarizing phase of the action potential will not produce another action potential.
2. Nor is the axon able to produce another action potential when it is repolarizing

Question 41

relatively refractory

Answer 41

The phase where if the axon membrane is stimulated during hyperpolarization, another action potential can be induced, however, the second stimulation must be more intense than the first.

Question 42

Refractory periods result from

Answer 42

the way gates of the voltage-activated sodium and potassium channels open and close

Question 43

Opening and closing of Na gated channels

Resting potential+threhold+hyperpolarization

Answer 43

1. resting potential: gate 1 of the sodium channel depicted in; only gate 2 is open
2. threshold level of stimulation: gate 1 also opens. Gate 2, however, closes very quickly after gate 1 opens. This sequence produces a brief period during which both sodium gates are open. When both gates are open and when gate 2 is closed, the membrane is absolutely refractory
3. Hyperpolarization: Back to resting membrane position- only gate 2 is open (non voltage regulated)

Question 44

K+ channels are only open during

Answer 44

repolarization and hyperpolarization

Question 45

refractory periods prevents

Answer 45

action potential from reversing direction and returning to its point of origin

ex: To return to our domino analogy, once a domino falls, setting it up
again takes time. This is its refractory period. Because each domino
falls as it knocks down its neighbor, the sequence cannot reverse until
the domino is set upright again: the dominos can fall in only one
direction. The same principle determines the action potential’s
direction.

Question 46

How is action potential sped up in humans whoch have such intricate abilities and still react fast?

Answer 46

Glial cells play a role in speeding nerve impulses in the vertebrate nervous system. Schwann cells in the human peripheral nervous system and oligodendroglia in the central nervous system wrap around some axons, forming the myelin sheath that insulates it

Question 47

Action potentials cannot occur where

Answer 47

myelin is wrapped around an axon

Question 48

nodes of Ranvier

Answer 48

Unmyelinated gaps between successive glial cell wrappings are richly endowed with voltage-activated channels

Question 49

saltatory conduction

Answer 49

action potential jumps quickly from node to node

Question 50

two important consequences for myelin

Answer 50

• propagation becomes energetically cheaper, since action potentials regenerate only at the nodes of Ranvier, not along the axon’s entire length
• myelin improves the action potential’s conduction speed

Question 51

excitatory postsynaptic potentials (EPSPs)

Answer 51

Graded potentials that reduce (depolarize) the charge on the membrane toward the threshold level and increase the likelihood that an action potential will result

Question 52

inhibitory postsynaptic potentials (IPSPs)

Answer 52

IPSPs increase the charge on the membrane away from the threshold level and decrease the likelihood that an action potential will result.

Question 53

EPSPs are associated with

Answer 53

the opening of sodium channels, which allows an influx of sodium ions

Question 54

IPSPs are associated with (2)

Answer 54

the opening of potassium channels, which allows an efflux of potassium ions (or with the opening of chloride channels, which allows an influx of chloride ions)

Question 55

an action potential is not produced on the motor neuron’s —– and must reach the —— to begin

Answer 55

1. cell body membrane
2. the initial segment, an area rich in voltage-gated channels, the area near or overlapping the axon hillock,

Question 56

Temporal Summation

Answer 56

• 2 EPSP/IPSP occur in rapid succession, a single large EPSP/IPSP is produced.
• The two excitatory pulses at the same location are summed— added together to produce a larger depolarization of the membrane than either would induce alone

1 repeated firing

Question 57

Spatial Summation

Answer 57

Pulses that occur at approximately the same location on a membrane are summed

multiple seperate neuron fire together on one spot

Question 58

temporal summation is a property of

Answer 58

both EPSPs and IPSPs

Question 59

Initial segement (4)

Answer 59

• overlaps with axon hillock
• rich in voltage sensitive channels
• Where EPSP/IPSP are integrated
• Where action potential are initated

Question 60

Back propagation (3)

What it is+ what it may play a role in

Answer 60

• The reverse movement of an action potential from the initial segment into the dendritic field
• may play a role in plastic changes in the neuron that underlie learning.
• Back propagation may make the dendritic field refractory to incoming inputs