Block IV: Smooth muscle

Question 1

How is the cell shape in smooth muscle?

Answer 1

Spindle shaped cells and single nuclei per cell; nuclei centrally located

Question 2

is the smooth muscle striated?

Answer 2

no (no sarcomeres)

Question 3

diameter of fibers in smooth muscle?

Answer 3

Small diameter fibers (cells) = 2 -3 nuclear diameters across

Question 4

smooth muscle is electrically coupled by?

Answer 4

gap junctions; not much innervation

Question 5

identify

Answer 5

Microgaph of smooth muscle in both longitudinal and cross-section adjacent layers

Question 6

What structures are found in the smooth muscle that contain alpha actinin (cross-link for actin thin filaments in Z-band of skeletal and cardiac muscle?

Answer 6

Membrane attachment plaques & cytoplasmic dense bodies; which can serves as an
attachment point for actin thin filaments located within the cytoplasm of the smooth
muscle and also the intermediate filament cytoskeleton of the smooth muscle.

Question 7

identify

Answer 7

Smooth muscle LS

Question 8

identify

Answer 8

smooth muscle CX

Question 9

identify

Answer 9

EM of smooth muscle cut in crosssection. The arrows point to cytoplasmic dense
bodies and membrane attachment plaques

Question 10

How are thick and thin filaments of smooth muscle?

Answer 10

Thick & thin filaments are present, but not in form of ordered sarcomeres. The thick
filament has a different structure than in skeletal or cardiac muscle
– Side polar structure

Question 11

Explain the composition of the smooth muscle contraction

Answer 11

An array of intermediate filaments is bound to the cytoplasmic dense bodies & holds them in place in cell

Actin filaments of opposite polarity are bound to 2 sides of cytoplasmic dense bodies as in z-band in skeletal

Myosin thick filaments interact with actin from 2 different cytoplasmic dense bodies by a sliding filament mechanism giving contraction

Question 12

How is the sarcoplasmic reticulum is smooth msucle?

Answer 12

much less developed than in skeletal or cardiac. Typically consists just of small sacs of SR or tubules of SR

Question 13

How are t-tubules in smooth muscle?

Answer 13

T-tubules are absent

Question 14

Why arent t-tubules necessary?

Answer 14

Because of the small diameter of the smooth muscle cells, it is not necessary to have an elaborate system such t-tubules and terminal cisternae for the release of calcium all through out the smooth muscle cell at the same time.

Question 15

identify

Answer 15

smooth muscle longitudinally sectioned

Question 16

What does calcium regulation of contraction for smooth muscle consists of?

Answer 16

Regulation of contraction involves binding Ca+2 -Calmodulin to myosin light chain kinase and phosphorylation of myosin light chain, not tropomyosin-troponin complex

Question 17

What are some factors that can cause contraction or relaxation of smooth muscle?

Answer 17

This contraction in smooth muscle can be evoked by a variety of factors including: 1)
mechanical stimuli such as stretching of vascular smooth cell; (2) electrical
depolarizations of the cell by neurotransmitters or gap junctions; and (3) binding of
hormones and chemical factors such as vasopressin and angiotensin II to receptors
on the membrane of the smooth muscle. In addition, other signaling molecules such
as nitric oxide by binding to receptors on the smooth muscle may cause relaxation of
the smooth muscle. In most cases these factors all act through 2nd messengers

Question 18

Can mature skeeltal msucle divide?

Answer 18

No

Question 19

How does growth of skeletal muscle happen?

Answer 19

Growth of skeletal muscle is primarily by hypertrophy, the cells get larger in volume.

Question 20

How can regeneration of skeletal muscle happen?

Answer 20

Some regeneration or repair can take place, but this is by way of small relatively
undifferentiated fibers or cells called satellite cells which sit inside the basal
lamina of the muscle fiber

Question 21

Can cardiac muscle be regenerated?

Answer 21

Cardiac muscle normally can not divide or regenerate, although limited division
has been observed. Areas of damage are replaced with CT, and thus lose
functional ability to contract

Question 22

Can smooth muscle regenerate?

Answer 22

Smooth muscle cells retain their ability to divide and regenerate. They also can undergo hypertrophy and increase in size in areas such as the myometrium of the uterus under pregnancy