L7 - excitability of muscle cells

Question 1

what is a voltage dependence channel

Answer 1

channels that open and close depending on voltage

non linear relationship

Question 2

why are voltage dependant channels a non linear relationship

Answer 2

there is a peak voltage at which the channel is most open, increasing the voltage past this point the channel will start to close again

Question 3

describe time dependant channel

Answer 3

some voltage dependant channels will snap shut after a certain amount of time and enter an inactivated state

Question 4

describe voltage independant channel

Answer 4

opening and closing of channel is independent of voltage

Question 5

do K or Na channels inactivate quicker

Answer 5

Na

Question 6

in what muscle does the action potential not have a hyperpolarisation period

Answer 6

skeletal muscle

cardiac muscle

Question 7

define refractory period

Answer 7

a period where ion channels are inactivated, and cant return to closed/open state until the membrane has been repolarised - no AP possible

Question 8

define relative refractory period

Answer 8

period after the membrane has been repolarised, ion channels are open but repolarisation means it will be much harder to generate AP

Question 9

how does relative refractory period differ in skeletal muscle from neuronal AP and why

Answer 9

shorter, as there is no hyperpolarisation in skeletal muscle

Question 10

how long is the AP in cardiac muscle

Answer 10

(~300 ms)

Question 11

what is tetany and why is it important?

Answer 11

tetany is when many action potentials (that are fired successively) fuse together
allows prolonged contraction

Question 12

why is the refractory period in cardiac muscle so long?

Answer 12

forces the heart to relax before it can contract again, allowing time for heart to fill

prevents tetany
prevents arrhythmias

Question 13

what are the two types of smooth muscle excitation

Answer 13

action potentials -time dependant (ligand/voltage)

graded depolarisation - (time independent ligand/voltage)

Question 14

what can cause a graded depolarisation in smooth muscle?

Answer 14

vasoconstrictors

vasodilators

Question 15

what effect does
vasodilators
vasoconstrictors
have on the membrane potential

Answer 15

dilator - hyperpolarisation

constrictor - depolarisation

Question 16

are graded depolarisations time dependent or not

Answer 16

they are time independent

Question 17

examples of tissues that undergo graded depolarisation

Answer 17

most vascular smooth muscle 
aorta 
coronary artery 
pulmonary artery 
trachea

Question 18

examples of tissues that undergo time dependent depolarisation

Answer 18

ureter
bladder
ileum

Question 19

how does depolarisation lead to Ca2+ increase in skeletal muscle

Answer 19

voltage induced calcium release

1. depolarisation arrives at Ca2+ channel in T tubule, the channel is physically attached to the Ca2+ channel on SR
2. conformational change in T tubule channel opens SR channels
3. Ca2+ influx without the need for Ca2+ to enter from T tubule

Question 20

how does depolarisation lead to Ca2+ increase in cardiac muscle

Answer 20

calcium induced calcium release

1. Ca2+ enters cell and binds to Ca channel on SR
2. more Ca2+ released from SR

Question 21

what is the name for the point where T tubules meet the SR

Answer 21

diad

Question 22

how does depolarisation lead to Ca2+ increase in smooth muscle

Answer 22

1. Ca2+ enters cell and binds to calmodulin - contraction
   or
2. ligand binds to receptor activating 2nd messenger
3. 2nd messenger binds to SR causing Ca2+ release
4. Ca2+ binds to calmodulin - contraction

Question 23

what is the resting membrane potential of smooth muscle cells

Answer 23

~ - 55