Week 16: (B) Pacemaker activity of cardiac autorhythmic cells

Question 1

What is the threshold for cardiac auto rhythmic cells?

Answer 1

-40mV

Question 2

When an AP in generate by Ca2+ what direction does Na+ move?

Answer 2

higher conc outside cell, enter cell

Question 3

What does Na+ do to the membrane potential?

Answer 3

causes depolarisation

more positive

Question 4

What 2 phases can the pacemaker potential be split into?

Answer 4

early and late

Question 5

What is the early phase of pacemaker potential?

Answer 5

Na+ funny channels (lf) are open

Na+ moves into the cell down its conc gradient

Question 6

How long are voltage gated channels open?

Answer 6

finite period of time

Question 7

What happens when Na funny channels begin to close in the early stage of pace maker potential?

Answer 7

• different set of voltage gated ca2+ channels have been stimulated to open
• transient-type Ca2+ channels

Question 8

Does Ca2+ have a higher conc inside or outside the cell?

Answer 8

higher conc outside

move into the cell

Question 9

What type of ca2+ channel do funny type Na+ channels open?

Answer 9

transient-type Ca2+ channels

Question 10

What happens when the Ca2+ move into the cell via transient-type Ca2+ channels?

Answer 10

further depolarisation

bring membrane to threshold

Question 11

What occurs when a threshold has been reached?

Answer 11

an action potential can be initiated

Question 12

At threshold what type of Ca2+ channels are opened?

Answer 12

Long-lasting Ca2+ channels

Question 13

What occurs the long lasting Type calcium channels are open?

Answer 13

further depolarisation and gives rise to the upstroke of AP

Question 14

When do the L-type Ca2+ channels close?

Answer 14

at the peak of the AP

are only open transiently

Question 15

What channels are stimulated to open at the peak of AP?

Answer 15

voltage gated potassium channels

Question 16

What direction will k+ flow through its channel?

Answer 16

more K+ inside that outside
will flow to the outside of the cell
down their conc gradient

Question 17

What happens to the membrane potential when voltage gated K+ channels open?

Answer 17

mp becomes more negative

Question 18

What current is. generated when K+ leave the cell?

Answer 18

ionic current

Question 19

What does the ionic current give rise to in the AP?

Answer 19

the downstroke of AP

Question 20

What does hyperolarisation of the membrane potential stimulate?

Answer 20

funny Na+ channels

the next pacemaker potential is spontaneously initiated

Question 21

Why are they called funny channels?

Answer 21

typically voltage gated channels open when the mp becomes depolarised
but these channels open up when the potential becomes more negative at the end of re-polarisation form the previous AP

Question 22

Why is the cardiac ca2+ induced phase different from skeletal and nerve muscle?

Answer 22

cardiac: Na+ influx

skeletal and nerve: Ca2+ influx that makes the potential much more +ve