Cardiac and smooth muscle

Question 1

How are cardiac myocytes differenct from other muscle

Answer 1

shorter, branched, and interconnected from end to end by structures called intercalated disks, visible as dark lines in the light microscope.

Question 2

What are the desmosomes

Answer 2

things in the intercalated discs. that link adjacent cells mechanically,

Question 3

what do the gap joints in intercalated disk do?

Answer 3

link adjacent cells electrically.

Question 4

Cardiac muscle thus acts as a …. of coupled cells, unlike skeletal muscle fibers, which are separate cells bundled together by …..

Answer 4

Cardiac muscle thus acts as a mechanical and electrical syncytium of coupled cells, unlike skeletal muscle fibers, which are separate cells bundled together by connective tissue.

Question 5

do the sacromeres of cardiac muscle contain thin and thick filaments

Answer 5

yes, similar array because striated

Question 6

How is the iniation of cardiac contraction different from skeletal

Answer 6

own pacemaker, instead of neurons

Question 7

what is the pacemaker of the heart

Answer 7

sinoatrial node.

Question 8

do cardiac myocytes receive synaptic input from autonomic neurons? explain

Answer 8

yes, but the sympathetic and parasympathetic divisions of the autonomic nervous systemuse these synapses to modulate rather than to initiate electrical activity and contractile force of cardiac muscle.

Question 9

How is the EC coupling of cardiac musle different

Answer 9

cardiac contraction has an absolute requirement for Ca 2+ influx through L-type Ca 2+ channels during the action potential.

Question 10

is the t tubule network of heart different to skeletal

Answer 10

simialr, except that a single terminal cisterna of the SR forms a dyad junction with the T-tubule rather than a triad junction.

Question 11

where are the T-tubules of cardiac myocytes located?

Answer 11

at the Z lines separating sarcomeres rather than at the A-I band junctions.

Question 12

how does the hearth get suffiecient CA2+ for contraction

Answer 12

Ca 2+ influx through the L-type Ca 2+ channels alone is not, however, sufficient to initiate contraction. Rather, this increase in [Ca 2+ ] i leads to an opening of the RYR Ca 2+ -release channels in the SR membrane.

Question 13

what is Ca 2+ -induced Ca 2+ release (CICR)

Answer 13

The resulting release of Ca 2+ from the SR amplifies the rise in [Ca 2+ ] i

Question 14

is the contribution of CICR greater to the rise of Ca than L-type?

Answer 14

yes

Question 15

what is different about troponin C in cardiac muscles

Answer 15

binds 3 Ca instead of 4 (skeletal)

Question 16

what does phospholamban (PLN) do

Answer 16

inhibits SR Ca-pump activity

Question 17

what does PKA do

Answer 17

phosphorylate PLN, so PLN ability to inhibit the SR Ca pump is lost.

Question 18

what is epinephrine and what does it do

Answer 18

ctivators of PKA, such as the neurotransmitter epinephrine, may enhance the rate of cardiac myocyte relaxation.

Question 19

is there frequency summation in cardiac muscle

Answer 19

no, Because cardiac muscle must contract only once with each heartbeat and must fully relax between each contraction,

Question 20

what does norepinephrine mediate and is?

Answer 20

a neurotransmitter released by the sympathetic nervous system. that modulates the contractile force generated during each individual muscle twitch

Question 21

is there multiple fiber summation at cardiac muscle

Answer 21

no, because the extensive electrical coupling between cardiac myocytes, as well as the requirement that cardiac muscle contract homogeneously

Question 22

how is contractile function of cardiac muscle regulated

Answer 22

either by modulating the magnitude of the rise in [Ca 2+ ] i or by altering the Ca 2+ sensitivity of the regulatory proteins.