LEC-4 Smooth Muscle Physiology

Question 1

Elevated blood pressure in the systemic circulation is referred to as _____________.

Answer 1

Hypertension

Question 2

Chronic hypertension may lead to _______________.

Answer 2

Cardiovascular disease

Question 3

In atherosclerotic vessels, smooth muscle surrounding the vessel is known to (regress/proliferate)

Answer 3

Proliferate

Question 4

Vascular smooth muscle may grow by (hypertrophy/hyperplasia/both).

Answer 4

Both

Question 5

Smooth muscle cells range anywhere from ___ - ___ μm in length and ___ - ___ μm in diameter.

Answer 5

20-500 μm in length 1-5 μm in diameter

Question 6

(T/F) Smooth muscle utilizes the same proteins and complexes as skeletal muscle for muscle contraction.

Answer 6

False. Skeletal muscle uses an actin/tropomyosin/troponin complex to complete muscle contraction. Smooth muscle, on the other hand, utilizes the following:

• Actin/tropomyosin/calmodulin/caldesmon complex.

Question 7

Adjacent smooth muscle cells make use of _____________, low-resistance electrical pathways between cells.

Answer 7

Gap junctions

Question 8

______________ serve as attachment points for thin actin filaments in smooth muscle cells, making them akin to Z-bands.

Answer 8

Dense bodies

Question 9

The sarcoplasmic reticulum in smooth muscle cells is (smaller/larger/the same size) in relation to the sarcoplasmic reticulum of skeletal muscle.

Answer 9

Smaller

Question 10

Small invaginations of the smooth muscle cell membrane are referred to as __________.

Answer 10

Caveolae

Question 11

The absence of structure regularity in smooth muscle cells is noted as the reason for the absence of __________.

Answer 11

Striations

Question 12

Myosin filaments within smooth muscle often have side-polar crossbridges, allowing for contraction of up to ___% of the fiber length versus the 30% that is possible in skeletal muscle.

Answer 12

80%

Question 13

Smooth muscle cells possess a (more/less) efficient ATPase than that of skeletal muscle. This results in (faster/slower) cycling of myosin cross-bridges.

Answer 13

• Less efficient
• Slower cycling

Question 14

Smooth muscle requires markedly (more/less) energy to complete a contraction than skeletal muscle.

Answer 14

Less

• Requires 1/10 - 1/300th the amount of energy as skeletal muscle

Question 15

Smooth muscle possesses a “latch mechanism” that facilitates (shortened/prolonged) contraction.

Answer 15

Prolonged

Question 16

(T/F) Due to the latch mechanism, once full contraction is achieved in smooth muscle, the amount of excitation and energy consumed to maintain contraction is greatly reduced.

Answer 16

True.

Question 17

The maximum force of smooth muscle contraction is (greater/less) than that of skeletal muscle.

Answer 17

Greater

Question 18

(T/F) It takes smooth muscle a considerable amount of time to return to its original state after being contracted or lengthened.

Answer 18

False. One of smooth muscle’s key characteristics is its ability to quickly return to its original state after contraction or lengthening. This allows smooth muscle to maintain the same amount of force within hollow organs.

Question 19

______________ is the activating kinase used within smooth muscle cells. It is bound by calmodulin and calcium to convert it to its active state, in which it phosphorylates myosin regulatory light chains, allowing for muscle contraction.

Answer 19

Myosin light chain kinase (MLCK)

Question 20

(T/F) Smooth muscle does not use sodium as its primary depolarizing agent. Instead, it uses calcium and calcium-activated proteins to conduct muscle contraction. Calcium also extracellularly enters the smooth muscle cell fairly often, instead of just from the sarcoplasmic reticulum during contraction.

Answer 20

True.

Question 21

Smooth muscle utilizes Ca2+-dependent ATPases along with the enzyme _______________ for muscle relaxation.

Answer 21

Myosin light chain phosphatase (MLCP)

Question 22

_________________ serves to dephosphorylate myosin chains in smooth muscle when relaxation is necessary.

Answer 22

Myosin light chain phosphatase

Question 23

(Visceral/Multi-unit) smooth muscle consists of hundreds to thousands of smooth muscle fibers organized into bundles or sheets that can contract as a single unit. Their membranes are adherent at multiple contact points and are joined via gap junctions for transmission of contractile forces and ion flows

Answer 23

Visceral (or unitary)

Question 24

(Visceral/Multi-unit) smooth muscle consists of discrete separate smooth muscle fibers that are each innervated by a single nerve ending and operate independently of the others. Their cellular surface is covered by matrix for insulation purposes.

Answer 24

Multi-unit

Question 25

Smooth muscle cell innervation is from (motor units/autonomic nerves).

Answer 25

Autonomic nerves

Question 26

What do visceral and multi-unit smooth muscle cells have in common?

Answer 26

* Contractions are slow in onset but are sustained for long periods of time with little energy input required * Innervation is autonomic, either from sympathetic or parasympathetic * Both superimpose their own contractions on an intrinsic "tone", or basal resting tension within the muscle

Question 27

(Visceral/Multi-unit) smooth muscle is capable of spontaneous activity initiated by **pacemaker cells**.

Answer 27

Visceral

Question 28

(T/F) Visceral smooth muscle is most often stimulated to contract by nerve impulses.

Answer 28

False. Visceral smooth muscle is not usually initiated by nerve impulses.

Question 29

What would the action potential of visceral smooth muscle look like in a non-pregnant uterus?

Answer 29

Image

Question 30

What would the action potential of visceral smooth muscle look like in a ureter?

Answer 30

Image

Question 31

What would the action potential of visceral smooth muscle look like in longitudinal muscle of the intestine or myometrium during parturition?

Answer 31

Image

Question 32

\_\_\_\_\_\_\_\_\_\_\_\_\_ refers to the time between an action potential and the start of contraction.

Answer 32

Latent period

Question 33

Smooth muscle has a markedly (longer/shorter) latent period than does skeletal muscle.

Answer 33

Longer

Question 34

(Visceral/Multi-unit) smooth muscle is most often activated by motor nerve stimulation, but it depolarizes **without action potential**.

Answer 34

Multi-unit

Question 35

(T/F) Multi-unit smooth muscle does not respond to stretch by developing tension.

Answer 35

True.

Question 36

What are the two possibilities of multi-unit smooth muscle contraction in the absence of action potentials?

Answer 36

* Local tissue chemical factors * Lack of oxygen, excess CO2, increased hydrogen ion concentration, increased lactic acid, increased body temp. * Various hormones * Epinephrine, norepinephrine, angiotensin, vasopressin, oxytocin, serotonin, or histamine.

Question 37

(Visceral/Multi-unit) smooth muscle utilizes contact junctions.

Answer 37

Multi-unit

Question 38

(Visceral/Multi-unit) smooth muscle utilizes diffuse junctions.

Answer 38

Visceral

Question 39

(Diffuse/Contact) junctions consist of vesicle-filled varicosities in the vicinity of smooth muscle cells. They possess a 1-5μm distance between cells along with a widely varying number of innervated cells.

Answer 39

Diffuse (Visceral smooth muscle)

Question 40

(Diffuse/Contact) junctions are morphologically similar to the neuromuscular junction of a skeletal muscle. They possess a 20nm synaptic cleft along with innervation for every cell.

Answer 40

Contact (Multi-unit smooth muscle)

Question 41

(T/F) Skeletal muscle has mitotic activity.

Answer 41

False. Skeletal muscle has **no mitotic activity**. Skeletal muscle regenerates through the use of **satellite cells**, which are considered to be adult muscle stem cells.

Question 42

Skeletal muscle regenerates through the use of \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, which are considered to be adult muscle stem cells.

Answer 42

Satellite cells

Question 43

(T/F) Cardiac muscle is hardly capable of any regeneration. Upon cellular injury, such as during a myocardial infarction, fibroblasts invade the damaged tissue, resulting in scarring.

Answer 43

True.

Question 44

(T/F) Smooth muscle cells possess no mitotic activity.

Answer 44

False. Smooth muscle cells **retain their mitotic activity**. They are capable of forming more smooth muscle cells.

Question 45

\_\_\_\_\_\_\_\_\_\_\_\_ is an endothelial cell-produced signaling molecule that allows for smooth muscle relaxation.

Answer 45

Nitric oxide (NO)