Mod3-Obj9: Depolarisation/hyper-polarisation, graded and action potentials

Question 1

Resting membrane potential

Answer 1

A charge difference (voltage) exits across the plasma membrane

• External surface is positively charged
• Internal surface is negatively charged

Question 2

Resting membrane potential: Oppositely charged attract each other

Answer 2

• Energy is required to keep them apart

- Energy is released as they move towards each other

Question 3

An electrical current is…

Answer 3

The movement of charged particles

-Has the potential to do work

Question 4

Separating opposite charges across the plasma membrane

Answer 4

Generates a potential energy, measured in volts, known as the resting membrane potential

Question 5

Every cell in the body has a resting membrane potential

Answer 5

1. ) Differential distribution of ions
2. ) Selective membrane permeability
3. ) Na+K+ pump uses ATP energy to maintain differential distribution
   - Leakage channels, from an area of high concentration to low concentration, down a concentration gradient
   - In ECF lots of Na+ ion few K+ ions, more positive ions exit the cell than enter, more positive that inside
   - In ICF lots of K+ ions few Na+ ions, fewer positive charges (more negative) than outside=RELATIVE CHARGE DIFFERENCE

Question 6

In neurons the RMP is approximately…

Answer 6

-70mV

The minus sign indicates that the inside of a cell is negative relative to the outside

Question 7

Neurons are excitable because they can…

Answer 7

Change their membrane potential

-Generate electrical signals that facilitate neural communication

Question 8

Less negative, more positive

Answer 8

Depolarisation

Question 9

More negative, less positive

Answer 9

Hyperpolarisation

Question 10

Changes in RMP of neurons occur when…

Answer 10

A stimulus alters the permeability of the plasma membrane, which

• Opens membrane ion channels, which allows
• Na+ or K+ ions to flow across the membrane; down their chemical concentration gradient, along an electrical gradient (to an area of opposite charge)

Question 11

Ion flow of changes in RMP alters the…

Answer 11

• Na+ and K+ concentration in the ECF and ICF
• Overall charge on either side of the membrane
• Membrane potential (voltage across the membrane)

Question 12

There are two types of membrane channels

Answer 12

Leakage channels : always open

Gated channels: Open and closed in response to specific stimuli: chemicals, mechanical stimulation, voltage channels

Question 13

Chemically gated channels

Answer 13

Open in response to a chemical stimulus e.g.) binding of neurotransmitters
-Located in the plasma membrane of the dendrites and cell body

Question 14

Mechanically-gated channels

Answer 14

Open in response to mechanical stimulation e.g.) touch, vibration and pressure
Located in the plasma membrane of the dendrites and cell body

Question 15

Voltage-gated channels

Answer 15

Open and close in response to changes in the membrane potential (voltage) across the membrane
-Located in the plasma membrane of the axon and axon terminals (not present in the plasma membrane of the dendrites or cell body)

Question 16

Changes in membrane potential

Answer 16

The electrical signals used by neurons to relay sensory and motor information throughout the body are generated when Na+ or K+ ions flow across the plasma membrane and change the membrane potential (voltage)

Question 17

Changes in membrane potential are…

Answer 17

Relative to the RMP

• Occur when a gated channel opens and allows the movement of ions
• Are described by the terms depolarisation and hyperpolarisation

Question 18

Polarity

Answer 18

Is a state in which two properties are completely opposite

Question 19

Depolarisation

Answer 19

To decrease the “oppositeness”

-A reduction in membrane potential (decreasing the charge polarity across the membrane)

Question 20

Repolarise

Answer 20

Restore the “oppositeness”

Question 21

Hyperpolarise

Answer 21

To increase the “oppositeness”

-An increase in membrane potential (increasing the charge polarity across the membrane)

Question 22

Depolarisation: If gated channels that allow the passage of Na+ ions open:

Answer 22

• Influx of Na+ ions into ICF
• INTERIOR BECOMES LESS NEGATIVE
• Membrane potential moves towards or above zero e.g.) -70mV to -60mV

Question 23

Hyperpolarisation: If gated channels that allows the passage of K+ ions open:

Answer 23

• Efflux of K+ ions out of the ICF
• INTERIOR BECOMES MORE NEGATIVE (i.e. less positive)
• Membrane potential moves further from zero e.g.) -70mV to -80mV

Question 24

The nervous system generates two types of electrical signals:

Answer 24

1. ) Graded potentials

2. ) Action potentials (nerve impulse)

Question 25

Graded potentials

Answer 25

Short distance, short lived changes in membrane potential (localised)

• Either depolarisation or hyperpolarisation
• Usually generated in the dendrites or cell body of a neuron, when a stimulus causes chemically gated or mechanically gated channels to open

Question 26

Graded potentials are…

Answer 26

Proportional to the strength of the stimulus

-The stronger the stimulus=the greater the voltage charge the further the signal travels

Question 27

If a stimulus strong enough, a graded potential can:

Answer 27

• Travel from the site of stimulation (dendrites or cell body) to the initial segment of an axon
• Depolarise the initial segment to threshold (-55mV)
• Trigger the opening of voltage-gated Na+ channels
• generate an action potential

Question 28

Action potentials…

Answer 28

• Are long distance electrical signals
• Arise at the initial segment of an axon when voltage gated channels are stimulated to open
• Channels in membrane potential are independent of stimulus strength

Question 29

Action potentials don’t…

Answer 29

Decrease in size/strength with distance along axon

• Are all or none response
• Are self-propagating; once initiated, a chain reaction of action potentials will travel down the entire axon