BIOL 273 - Unit 2.3

Question 1

Graded potentials

Answer 1

could be depolarizations or hyperpolarization across the membrane
- occur in the dendrites or cell body of neurons

Question 2

How are graded potentials triggered

Answer 2

by the opening or closing of ion channels, allowing ions to enter from the ECF

Question 3

Why are graded potentials called graded

Answer 3

depends on how strong/weak the neuron becomes depolarized/hyperpolarized
(the amplitude of the potential is proprotional to the strength of the triggering event)

Question 4

Describe the travelling distance of graded potentials

Answer 4

short distance

Question 5

Why do graded potentials travel a short distance (2)

Answer 5

Graded potentials lose their strength due to
1. current leak (positive charges leak back w depolarization wave)
2. cytoplasmic resistance (cytoplasm restrcits flow of the current )

Question 6

What causes the ions to enter the cell (4)

Answer 6

1. Events after neurotransmitter binding
2. Signal strength (determined by number of ions entering the cell)
3. Depolarizing graded potentials
4. Hyperpolarizing graded potentials

Question 7

What happens after neurotransmitter binds to membrane receptors (3)

Answer 7

Used to start up graded potentials
1. Ion channels open
2. Ions move into or out of neuron along the elctrochemical gradient
3. A wave of depolarization and hyperpolarization spreads though the cell

Question 8

Describe depolarizing graded potentials

Answer 8

• coming closer to threshold potential (-55mV) by making the energy less negative from resting (-70mV)
• by doing this, it will increase the chance of exciting the axon to fire an action potential

Question 9

What is the depolarizing stimuli called

Answer 9

Excitatory Post synaptic Potentials (EPSPs)

Question 10

Describe hyperpolarizing graded potentials

Answer 10

When the neurons membrane potential becomes more negative, leading it farther away from the threshold

• which decreases the chance of exciting axon to fire and inhibit action potential

Question 11

What is the hyperpolarizing stimuli called

Answer 11

Inhibitory Post synaptic Potentials (IPSPs)

Question 12

Unlike graded potentials, how can a neuron carry a signal over long distances

Answer 12

via action potentials (for long distance transmission)

Question 13

Give two way action potentials differ from graded potentials

Answer 13

1. Action potentials are all identical, there is no volume control
2. They do not diminish in strength as they travel long distances through the neuron

Question 14

Describe the location of the initiation of action potentials and how does it work

Answer 14

start at the TRIGGER ZONE , to determine if a firing action will occur
(aka integrating center of the neuron)

Integrate signals from different places to determine if a firing action will occur

Question 15

Describe the location of the trigger zone of action potential in SENSORY NEURONS (afferent neuron)

Answer 15

adjacent to the receptor

Question 16

Describe the location of the trigger zone of action potential in EFFERENT NEURONS and INTERNEURONS

Answer 16

in axon hillock and the initial segment

Question 17

What is the minimum depolarization critical to trigger an action potential , what is it called

Answer 17

-55mV , called Threshold potential

Question 18

How can graded potentials initiate action potentials

Answer 18

graded potentials can sum together at the trigger zone to ultimate reach the threshold potential

Question 19

How can graded potentials sum to potentially become action potentials? (2)

Answer 19

1. Over space: spatial summation
2. Time: Temporal summation

Question 20

Phases of action potential: How does a membrane depolarize to threshold

Answer 20

voltage gated Na+ and K+ channels begin to open

rapid Na+ entry to depolarize cell (to a max of 30+ mV)

Question 21

Phases of action potential: what contributes to the peak of the action potential

Answer 21

Na+ channels close and slower K+ channels open

Question 22

Phases of action potential: what contributes in the repolariztion and hyperpolarization phase after reaching its peak AP

Answer 22

K+ exits results in membrane potential travelling towards resting membrane potential

Question 23

Phases of action potential: how does the membrane return to resting ion permeability

Answer 23

retention of K+ and leak of Na+ into the axon brings membrane potential back to -70 mV

Question 24

What are the two gates of the voltage gated sodium channels needed to regulate ion movement during an action potential

Answer 24

1. Activation gate: closed at resting membrane potential to prevent Na+ influx (opens quickly)
2. Inactivation gate: ball and chain of amino acids on cytoplasmic side of the membrane is open at resting membrane potential (close slowly)

Question 25

Describe how the voltage gated Na+ channel stimulate a positive feedback loop

Answer 25

1. Resting membrane potential
2. Depolarizing stimulus to -55mV stimulates the entire channel (both gates)
3. Activation gate opens: Na+ enters the cell
4. The Na+ entry causes further depolarization, causing more voltage gates Na+ channels to open
5. Inactivation gate closes to prevent further Na+ influx and end positive feedback (representing peak of action potential)

Question 26

How does the membrane potential return to the resting level?

Answer 26

K+ ions leave the cell - falling phase of action potential

Question 27

When does the refractory period occur

Answer 27

during the hyperpolarization phase

Question 28

What are the two parts that make up the refractory period

Answer 28

1. Absolute refractory period
2. Relative refractory period

Question 29

Describe the absolute refractory period

Answer 29

(lasts for approx 1 msec)
- found in the initial part of AP, the moment threshold potential is hit
- no other action potentials can be triggered at all (no matter how large the stimulus)

Question 30

Why are there no other action potential triggered during absolute refractory period

Answer 30

because sodium channels is in inactive state (closed gate)

Question 31

Describe the relative refractory period

Answer 31

another action potential can be fired if it is above the threshold (-55mV) called a suprathreshold

Question 32

Why is a suprathreshold needed to fire another action potential

Answer 32

because the potassium channels are still open so an excess of sodium is needed to reach threshold stimulus (more depolarization needed)

Question 33

Why is the refractory period important? (3)

Answer 33

1. Set the direction of current flow (trigger zone to axon)
2. Prevent sumation (more changes in membrane potential)
3. Prevents backward movement of action potential

Question 34

How can conduction of action potential occur in long distances without decreasing in strength

Answer 34

the positive feedback loop of sodium channels (new AP generated is identical to previous AP)

Question 35

What determines the speed of action potential along neuron (2)

Answer 35

1. Diameter of axon: giant axons lower resistance to speed conduction
2. Resistance of axon membrane: insulating axon reduces ion flow out of the cell which speeds conduction using myelin sheath

Question 36

How does axon become insulated to speed conduction of action potential (2)

Answer 36

axon insulated using myelin sheath :
1. in PNS: Schwann cells
2. in CNS: oligodendrocytes myelinating axons within interneurons

Question 37

What do you call the section of neuron that is not myelineated , what do they consist of

Answer 37

Node of ranvier, they are concentrated with voltage-gated sodium channels and potassium channels