L11 - Cardiac Smooth Muscle

Question 1

What are the three different types of muscle?

Answer 1

skeletal muscle, cardiac muscle and smooth muscle

Question 2

Which types of muscle are striated?

Answer 2

skeletal muscle and cardiac muscle

Question 3

Which type of muscle is unstriated?

Answer 3

smooth muscle

Question 4

Which type of muscle is voluntary?

Answer 4

skeletal muscle

Question 5

Which types of muscle are involuntary?

Answer 5

cardiac muscle and smooth muscle

Question 6

What determines striation?

Answer 6

the way that thick and thin filaments overlap

Question 7

How do action potentials pass from cell to cell in the heart?

Answer 7

the signal passes from cell to cell via intercalated disks

Question 8

Why is it important that an action potential is passed from cell to cell in the heart?

Answer 8

to allow for coordinated contractions

Question 9

How much longer do action potentials take in contractile cells in comparison to action potentials in neurons?

Answer 9

nearly 100x longer

Question 10

Why is it important that action potentials have longer duration in the heart?

Answer 10

allows for a sustained contraction instead of a twitch

Question 11

How are action potentials sustained in contractile cells?

Answer 11

opening voltage-gated calcium channels which results in a plateau phase

Question 12

How is calcium released in cardiac muscle?

Answer 12

calcium moving into the cell during the plateau phase of the action potential stimulates ryanodine receptors to release their own calcium stores (calcium dependent calcium release)

Question 13

What happens when calcium is released from ryanodine receptors in cardiac muscle?

Answer 13

results in Ca2+ spark which creates a Ca2+ signal with other summed Ca2+ sparks
Ca2+ ions bind to troponin to initiate contraction and relaxation occurs when Ca2+ unbinds from troponin

Question 14

What is Ca2+ exchanged with in cardiac muscle?

How is the Na+ gradient maintained?

Answer 14

Na+

the Na+ gradient is maintained by the Na+-K+-ATPase

Question 15

What is the role of pacemaker cells / autorhythmic cells?

Answer 15

generates spontaneous action potentials in cardiac muscle

Question 16

Where are pacemaker cells found?

Answer 16

in the nodes of the heart

Question 17

How do pacemaker cells spontaneously depolarise?

Answer 17

small amount of sodium results in a slight depolarisation and then T type calcium channels open which allows for the graded potential to reach threshold
once threshold is reached, L type calcium channels cause the rising phase of the AP

Question 18

Increasing Na+ leak conductance in cardiac autorhythmic cells should…
(increase heart rate / decrease heart rate / cause an unstable heart rate)

Answer 18

increase heart rate

Question 19

Where is smooth muscle located?

Answer 19

on the walls of blood vessels and surrounds the esophagus, stomach and intestines

Question 20

What is the role of smooth muscle in blood vessels?

Answer 20

controls diameter of vessels and blood pressure

Question 21

What is the role of smooth muscle which surrounds the esophagus, stomach and intestines?

Answer 21

produces movement of food through digestive system
childbirth
controlling bladder capacity

Question 22

What is the arrangement of smooth muscle?

Answer 22

often in bands or bundles

in walls of hollow organs: circular layer, longitudinal layer, random arrangement

Question 23

How are thick and thin filaments arranged in smooth muscle? What does this allow smooth muscle to do?

Answer 23

in a crossed pattern which allows smooth muscle to contract in all directions simultaneously

Question 24

What are the two different types of smooth muscle cell ‘units’?

Answer 24

single-unit smooth muscle cells and multi-unit smooth muscle cells

Question 25

What are the steps behind smooth muscle contraction?

Answer 25

smooth muscle Ca2+ binds with calmodulin (structurally similar to troponin-C)
myosin can only interact with actin when the myosin has been phosphorylated and this occurs when Ca2+ complex binds to and activates myosin kinase
cross-bridge cycle can begin

Question 26

What results in relaxation within a smooth muscle cell?

Answer 26

dephosphorylation of myosin with myosin phosphatase

Question 27

Why do smooth muscle cells contract differently to the rest of the muscle cells in the body?

Answer 27

slower but more efficient use of ATP