Chapter 4 - Cell Anatomy and Physiology

Question 1

electricity

Answer 1

a natural phenomenon that is defined as the flow of electric charge
- charge is a property of matter that can be quantified and comes in 2 types, positive and negative

Question 2

atoms

Answer 2

consist of protons (+), neutrons (0), and electrons (-)

Question 3

electrical current

Answer 3

the flow of electrically charged particles from one point to another, measured in ampere (A)

Question 4

electrical potential (voltage)

Answer 4

the difference in electrical charge between 2 points, and is measured in Volts with an instrument called a voltmeter

Question 5

ions

Answer 5

electrically charged particles that can be either positive or negative

Question 6

oscilloscope

Answer 6

a sensitive voltmeter that registers changes in voltage over time

Question 7

microelectrode

Answer 7

an electrode small enough to be placed in the axon

Question 8

speed of ions and electrons

Answer 8

ions have a max speed of 90 m/s, whereas electrons have a max speed of 270.000 km/s

Question 9

cations

Answer 9

positively charged ions

Question 10

anions

Answer 10

negatively charged ions

Question 11

factors influencing the movement of anions and cations in and out of cells

Answer 11

• diffusion
• concentration gradient
• voltage gradient

Question 12

diffusion

Answer 12

the movement of ions from a high concetration area to a low concentration area as a result of random motion

Question 13

concentration gradient

Answer 13

the difference in concentration between 2 areas

Question 14

voltage gradient

Answer 14

the difference in electrical charge between 2 areas

Question 14

resting potential

Answer 14

the uneven distribution of electrical charge between the inside and outside of the cell membrane

Question 15

resting potential when the axon is at rest

Answer 15

• intracellular side contains more K+ (potassium) and A- (large protein molecule)
• extracellular side contains more Na+ (sodium) and Cl- (chloride)
• overall inside is more negative than outside

Question 16

channels, gates, and pumps

Answer 16

maintain the resting potential
- A- proteins always remain within the cell due to the membrane being impenetrable to large molecules
- K+ and Cl- channels allow k+ and Cl- ions to pass freely
- gates on Na+ channels keep positively charged Na+ ions out
- Na+/K+ pumps push out 3 Na+ ions from the intracellular fluid and inject 2 K+ (3:2)
- allows the membrane voltage to remain at its resting value of -70 mV

Question 17

graded potentials

Answer 17

when the concentration of one of the ions at the unstimulated cell membrane changes, the voltage of the membrane changes
- these small fluctuations in the voltage across the cell membrane are called graded potentials

Question 18

hyperpolarization

Answer 18

when the inside of the membrane is stimulated with a negative voltage, the membrane voltage becomes more negative
- increases the polarity of the membrane (charge difference between the inside and outside becomes larger)

Question 19

depolarization

Answer 19

when a positive voltage is applied to the inside of the cell, the voltage becomes more positive
- polarity of the membrane is decreased (charge difference between inside and outside becomes smaller)

Question 20

how the extracellular side becomes more positive

Answer 20

• increase in the outflow of K+ ions
• increase in influx of Cl- through the Cl- channels

Question 21

action potential

Answer 21

a short but large reversal in the polarity of the membrane of an axon
- lasts about 1 ms and is an all-or-nothing potential
- triggered when the potential difference across the membrane exceeds a certain value (the firing threshold (-50 mV))
- intercellular side suddenly becomes relatively positive compared to the extracellular side, then quickly becomes more negative again (occurs when a high concentration of first Na+ and then K+ quickly cross the membrane)
- triggered by the axon hillock

Question 22

voltage-activated ion channels

Answer 22

underlie action potentials
- are sensitive to the membrane voltage, and open or close depending on the voltage

Question 23

phases of an action potential

Answer 23

1. cell is at resting potential (-70 mV)
2. when firing threshold is reached (-50 mV) the Na+ gate quickly opens, allowing the positive Na+ ions to flow inside the cell. This is the depolarization phase; voltage increases up to +30 mV. At this point the Na+ gates close
3. soon after the K+ gate also opens. This is the repolarization phase; the inside of the cell becomes more negative again (-70 mV)
4. K+ gates are slower than Na+ gates, so they remain open longer, thus the K+ efflux lasts longer and the inside of the cell becomes even more negative (hyperpolarization)
5. K+ gates close, and membrane goes back to resting potential (-70 mV)

Question 24

refractory period

Answer 24

a cell must wait until the action potential has ended before it can fire again
- result from the one-way gates of the voltage-sensitive Na+ and K+ channels that open and close
- due to refractory periods, neurons can only fire about 200 action potentials per second

Question 25

absolute refractory period

Answer 25

when an axon is in the depolarization and repolarization phases, a new action potential absolutely cannot be fired
- during the absolutely refractory period, stimulation of the axon membrane will not lead to a new action potential

Question 26

relative refractory period

Answer 26

when an axon is in the hyperpolarization phase, an increased electrical stimulation is required to produce another action potential
- during this phase, an action potential can be fired, but this requires a larger stimulation

Question 27

nerve impulse

Answer 27

the propagation of an action potential along a neuronal axon

Question 28

continuous conduction

Answer 28

the parts of an axon membrane that are close to where an action potential takes place are also brought to the firing threshold
- thus, their voltage-sensitive ion channels are activated, firing a new action potential
- spreads to adjacent parts of the membrane, which activates a new action potential
- a series of action potentials is propogated along the length of the axon

Question 29

saltatory conduction

Answer 29

axons are surrounded by a myeling sheath, which prevents continuous conduction because there are no adjacent gates that can be activated
- however there are gaps in the insulation layer (nodes of Ranvier) and the action potential can jump from knot to knot
- ranvier nodes are close enough to each other that if an action potential is activated in one node, it can activate an action potential in an adjacent node
- saltatory conduction is faster and costs less energy than continuous conduction

Question 30

excitatory postsynaptic potentials (EPSPs)

Answer 30

graded potentials that produce short depolarizations of a neuron membrane in response to stimulation
- because the voltage becomes less negative, this ensures that the neuron is more inclined to produce an action potential
- EPSPs are linked to an influx of Na+ ions

Question 31

inhibitory postsynaptic potentials (IPSPs)

Answer 31

graded potentials that produce short hyperpolarizations of a neuronal membrane in response to stimulation
- because the membrane voltage becomes more negative, this ensures that a neuron is less inclined to produce an action potential
- IPSPs are linked to an efflux of K+ ions or an influx of Cl- ions

Question 32

temporal summation

Answer 32

the relationship of 2 EPSPs or IPSPs that appear close to each other or equal
- adding up of graded potentials that occur in quick succession over time

Question 33

spatial summation

Answer 33

when 2 EPSPs or IPSPs take place shortly after each other in time, they also take place shortly after each other on the membrane
- adding up of graded potentials that occur close in space

Question 34

initial segment on the axon hillock

Answer 34

where the axon is attached to the cell body
- if the potential difference at the initial segment becomes -50 mV or even less negative, an action potential is generated, and the cell fires

Question 35

back propagation

Answer 35

when an action potential moves from the initial segment to the dendrites