Physiology Wk 2

Question 1

What is the potential related to

Answer 1

The uneven distribution of sodium, potassium and large intracellular protein anions between the intracellular and extracellular fluid and to the differential permeability of the plasma membrane to these ions

Question 2

What is the resting potential

Answer 2

The constant membrane potential present when a cell is electrically at rest and not producing electrical signals

Question 3

Which tissues are excitable

Answer 3

Nerve and muscle tissues

Question 4

What is polarisation

Answer 4

Charges are separated across the plasma membrane, so the membrane has potential
- anytime the membrane potential is other than 0 mv the membrane is in a state of polarisation

Question 5

What is mV for the membrane at resting potential

Answer 5

-70mV

Question 6

What happens during depolarisation

Answer 6

The membrane becomes less polarised and the inside becomes less negative than the resting potential with potential moving closer to 0mV (eg -70mV to -60mV).

Sodium ions rush into the cell via voltage gated ion channels

Question 7

What is repolarisation

Answer 7

The membrane returns to its resting potential after having been depolarised
- due to the flowing out of potassium ions

Question 8

What is hyperpolarisation

Answer 8

The membrane has become more polarised, the inside becomes more negative than the resting potential so farther away from the 0mV (-70mV to -80mV)

• due to the continuous outflow (leak) of potassium ions via potassium channels

Question 9

Give an example of what happens to membrane potential

Answer 9

If sodium ions move in (positively charged ions) the membrane depolarises (becomes less negative)

If the net outward flow of positively charged ions increases (potassium ions moves out) the name range hyperpolarises) becomes more negative inside

Question 10

What happens to gate opening and closing channels via gated channels

Answer 10

It occurs through a triggering event that causes a conformational change in shape of the protein that forms that gated channel

Question 11

What are the 4 types of gated channels

Answer 11

(1) Voltage-gated channels open or close in response to changes in membrane potential,

(2) chemically gated channels change shape in response to binding of a spe- cific extracellular chemical messenger to a surface membrane receptor,

(3) mechanically gated channels respond to stretching or other mechanical deformation, and

(4) ther- mally gated channels respond to local changes in tempera- ture (heat or cold).

Question 12

What are graded potentials

Answer 12

• short distance signals

are local changes in membrane potential that occur in varying grades or degrees of magnitude or strength. For example, membrane potential could change from 270 to 260 mV (a 10-mV graded potential) or from 270 to 250 mV (a 20-mV graded potential).

Question 13

What is the statement used for the triggering of graded potentials

Answer 13

The stronger a triggering event, the larger the
resultant graded potential.

For example - The stronger the triggering event is, the more gated Na1 channels open. As more gated Na1 channels open, more positive charges in the form of Na1 enter the cell. The more positive charges that enter the cell, the less negative (more depolarized) the inside becomes at this specialized region. This depolarization is the graded potential.

Question 14

What is the temporarily depolarised area called

Answer 14

Active area

Question 15

What happens to the active area inside the cell and outside the cell

Answer 15

Inside the cell- is relatively more positive than the neighbouring inactive areas that are still at resting potential

Outside the cell, the active area is relatively less positive than the adjacent inactive areas

Question 16

What is resistance

Answer 16

The hindrance to electrical charge movement - The greater the difference in potential, the greater the current flow; by contrast, the lower the resistance, the greater the current flow.

Question 17

Explain the process of current flow during a graded potential ( hint: triggering event)

Answer 17

The membrane of an excitable cell at resting potential

A triggering event opens ion channels, usually leading to net Na + entry that depolarises the membrane at this site and the adjacent inactive areas are still at resting potential

Local current flows between the active and adjacent inactive areas resulting in depolarisation of the previously inactive areas- so depolarisation spreads away from the point of origin

Question 18

Graded potentials die out over a short distance
Describe this

Answer 18

Current is lost across the plasma membrane as charge carrying ions in the form of K+ leak out through the ‘uninsulated’ parts of the membrane that is by diffusing outward down their electrochemical gradient through opening K+ leak channels

Question 19

What happens to the graded potential because of this

Answer 19

Due to the current loss the magnitude of the local current and graded potential progressively dismisses the farther away it moves from the initial area

Question 20

What are insulators

Answer 20

have high resistance and greatly hinder movement of charge

Question 21

What is decremental

Answer 21

Gradually decreasing

Question 22

What are action potentials

Answer 22

Are brief, rapid large changes in the membrane potential during which the potential actually reverses so that the inside of the excitable cell becomes more positive than the outside

Question 23

What happens when action potentials are conducted

Answer 23

Throughout the entire membrane nondecrementally - that is they do not diminish in strength as they travel form their sight of initiation throughout the remainder of the cell membrane

Question 24

What is the threshold potential

Answer 24

Depolarisation from the resting potential of -70mV proceeds slowly until it reaches a critical level known as the threshold potential - typically between -50-> -55mV

Question 25

What three formations can the Na+ gates exist

Answer 25

Closed but capable of opening - activation gate closed, inactivation gate open

Open or activated (both gates are open)

Closed and not capable of opening- (activation open, inactivation closed

Question 26

Describe the permeability changes and ion fluxes during an action potential

Answer 26

• resting potential: all voltage gated channels are closed
• at threshold Na+ activation gate opens and PNa+ rises
• Na+ enters the cell, causing explosive depolarisation to +30mV which generates rising phase of action potential
• At peak of action potential, Na+ inactivation gate closed and Pna+ falls, ending net movement of na + into cell. At the same time K+ activation gate opens and PK+ rises
• K+ leaves cell, causing its depolarisation to resting potential, which generates falling phase of action potential
• on return to resting potential, Na+ activation gate closes and inactivation gate oceans, resetting channel to respond to another depolarising triggering event
• further outward movement of K+ through still open K+ channel briefly hypeorpolarises membrane, which generates after hyperpolarisation
• K+ activation gate closes, and membrane returns to resting potential

Question 27

What is the Na+ K+ pump

Answer 27

Restores these ions to their original locations in the long run.
The movement of relatively few Na+ and K+ ions causes the large swings in the membrane potential that occur during the AP.

Question 28

LOOK AT GOODNOTES BOOK- ANATOMY OF NEURON

Question 29

LOOK AT GOODNOTES BOOK

Question 30

What is the refractory period

Answer 30

Prevents the “backward” current flow. During an action potential and slightly afterward, an area cannot be re stimulated by normal events to undergo another AP

Thus the RP ensures the AP can be propagated only in the forward direction along the axon

Question 31

What happens during the absolute refractory period

Answer 31

The portion of the membrane that has undergone an action potential cannot be re stimulated . The period corresponds to the time during which Na+ gates are not in their resting conformation

Question 32

What happens during relative refractory period

Answer 32

The membrane can be re stimulated only a strong stimulus than is usually unnecessary. This period corresponds to the time during which the K+ gates opened during the action potential has not closed yet, - there is also inactivation of voltage gated Na+ channels

Question 33

What is the all or none law

Answer 33

An excitable membrane either responds to a triggering event with a maximal action potential that spreads nondecrementally throughout the membrane or does not respond with a AP at all

Question 34

What are myelinated fibres

Answer 34

• in a myelinated fibre the impulse jumps from node to node, skipping over the myelinated sections of the axon (saltatory conduction)
• a myelinated fibre is surrounded by myelin at regular intervals

Question 35

Unmyelinated areas are

Answer 35

Nodes of ranvier

Question 36

In the PNS each patch of myelin sheath is formed by a

Answer 36

Separate SCHWANN CELL

Question 37

Why does saltatory conduction propagate APs more rapidly than contiguous conduction

Answer 37

Because APs does not have to be regenerated at myelinated sections but regenerated where unmyelinated sections of the axon are

Myelinated fibres conduct impulses 50 times faster than unmyelinated fibres of comparable size

Question 38

What is contiguous conduction

Answer 38

Local current flow between the active area at the peak of an action potential and the adjacent inactive area is still at resting potential reduces the resting potential un this contiguous inactive area which triggers an AP in the previously inactive area. The original active area returns to resting potential and the new active area induces an AP in the next adjacent inactive area by local current flow as the cycle repeats itself down the length of the axon

Question 39

Name the four zones of the neurone

Answer 39

Input zone- receives incoming signals from other neurones

Trigger zone- initiates action potentials

Conducting zone- conducts APs in undiminishing fashion, often over long distances

Output zone- releases the NT that influences other cells

Question 40

what are oligodendrocytes

Answer 40

in the CNS and provide insulation