Q2-MB9/Smooth and Heart Muscle

Question 1

What are the 2 types of smooth muscle?

Answer 1

visceral (single unit) and multiunit

Question 2

how do single unit smooth muscle cells work?

Answer 2

In single-unit smooth muscle cells, the cells are electrically coupled so that electrical stimulation of one cell is followed by stimulation of adjacent smooth muscle cells.

Question 3

how do multiunit smooth muscle cells work?

Answer 3

multiunit smooth muscle cells are made of cells that rarely have gap junctions, therefore they are not electrically coupled

Question 4

What is the difference in control between multiunit and visceral smooth muscle cells?

Answer 4

multiunit cells are neurogenic (controlled by nerves) and visceral cells are myogenic (controlled by local factors, stretch, hormones)

Question 5

What is the difference in innervation between multiunit and visceral smooth muscle cells?

Answer 5

multiunit cells have rich inneravation while visceral cells have sparse innervation

Question 6

What is the difference in neuromusclar junctions between multiunit and visceral smooth muscle cells?

Answer 6

multiunit cells have well developed neuromusclar junctions while visceral cells have poorly developed neuromuscular junctions

Question 7

What is the difference in spontaneity between multiunit and visceral smooth muscle cells?

Answer 7

multiunit cells have no spontaneous activity while visceral cells have some pacemaker cells

Question 8

What is the difference in electrical coupling between multiunit and visceral smooth muscle cells?

Answer 8

multiunit cells have no electrical coupling between cells and visceral cells do have gap junctions that allow for electrical coupling

Question 9

What is the difference in action potentials between multiunit and visceral smooth muscle cells?

Answer 9

multiunit cells have no action potentials while visceral cells have action potentials and slow waves

Question 10

Why does smooth muscle have no striations?

Answer 10

actin and myosin filaments are less regularly arranged

Question 11

In smooth muslce, actin filaments are anchored to ________

Answer 11

dense bodies (anchoring site of actin)

Question 12

Are there T tubules in smooth muscle cells?

Answer 12

no

Question 13

is there troponin in smooth muscle cells?

Answer 13

no

Question 14

how developed is the sarcoplasmic reticulum in smooth muscle cells?

Answer 14

poorly developed SR

Question 15

Where does most of the Ca++ needed for contraction come from in smooth muscle cells?

Answer 15

extracellular fluid

Question 16

The thin filaments of smooth muscle have an _______ and _______ composition and structure similar to that in skeletal muscle

Answer 16

actin, tropomyosin

Question 17

crossbridge formation in smooth muscles isnt regulated by the troponin-tropomyosin complex, but instead by the regulatory protein ____________

Answer 17

calmodulin

Question 18

Explain how excitation-contraction coupling works in smooth muscle.

Answer 18

1. calcium binds to calmodulin
2. calcium-calmodulin complex activates myosin light chain kinase, which activates myosin allowing crossbridges to form
3. phosphorylated crossbridges cycle until they are dephosphorylated by myosin phosphatase
4. myosin ATPase activity is slow and muscle contraction is slow and sustained

https://www.youtube.com/watch?v=Q2GchCG-KHI

Question 19

Explain plasticity in smooth muscles.

Answer 19

stretch causes contraction (autoregulation of blood flow) but sustained stretch causes relaxation (urinary bladder)

Question 20

Where do heart muscle cells join at?

Answer 20

intercalated discs

Question 21

heart muscle cells are joined at intercalated discs which have ________ of low _______ resistance

Answer 21

intercalated discs, gap junctions, electrical

Question 22

compared to skeletal and smooth muscle, the SR in heart cells is ________ in development

Answer 22

intermediate

Question 23

sometimes in heart muscle cells, there is only 1 _________ per T tubule, and the tubules occur at the _________

Answer 23

terminal cisterna, Z line

Question 24

Where does calcium come from in heart muscle cells?

Answer 24

SR, extracellular fluid during action potential

Question 25

How long are action potentials in cardiac muscle?

Answer 25

150-300 milliseconds

Question 26

How long is action potential in skeletal muscles?

Answer 26

5 milliseconds

Question 27

are heart muscle cells action potentials longer than skeletal muscle cells?

Answer 27

YES A LOT LONGER (heart = 150-300ms, skeletal = 5ms)

Question 28

how does calcium enter a heart muscle cell?

Answer 28

The dihydropyridine receptor allows Ca++ from the T system into the cell where it activates the ryanodine receptor to release Ca++ from the S.R.

Question 29

How does calcium exit a heart muscle cell?

Answer 29

Ca++ exits the cell mainly by a Na/Ca exchanger

Question 30

The contraction mechanism of heart muscle is the same as ______ muscle

Answer 30

skeletal muscle,

Question 31

Explain contraction in heart muscle.

Answer 31

As long as cytosolic [Ca ++] remains elevated, and hence myosin binding sites are exposed, myosin will bind to actin, undergo a ratchet action, and contract the cardiac muscle cell.

Relaxation by reaccumulation of Ca++ by the SR, AND by proteins in the sarcolemma

Question 32

the skeletal muscle contracile mechanism is not directly affected by extracellular _____ concentrations

Answer 32

calcium

Question 33

smooth and cardiac muscle are very sensitive to ___________ and to agents which affect _____ entry into cells

Answer 33

calcium, calcium

Question 34

What will reduce the contractility of the heart and dilate blood vessels?

Answer 34

calcium channel blocking drugs

Question 35

heart muscle demonstrates the _________ relationship and the __________ phenomenon

Answer 35

length-tension, staircase

Question 36

does heart muscle show summation?

Answer 36

no

Question 37

can heart muscle show tetanus?

Answer 37

no

Question 38

filling of the ventricle is equivalent to ________ and aortic pressure is equivalent to __________

Answer 38

preload, afterload