Smooth Muscle

Question 1

Smooth muscle properties

Answer 1

• Shorter and thinner
  –They have a single, centrally-located nucleus
  –No striations
  –No T-tubules
  –A poorly developed sarcoplasmic reticulum

Question 2

Why do smooth muscle fibres lack striation?

Answer 2

Although they contain actin and myosin, the filaments are thin and randomly arranged so that it lacks striations.

Question 3

Similarities between smooth and skeletal muscle striations

Answer 3

• Both contractile mechanisms depend on the action of actin and myosin;
• Both are triggered by membrane impulses and the release of calcium ions; and
• Both require ATP

Question 4

Differences between smooth and skeletal muscle striations

Answer 4

• Actin has no troponin
• Ccalcium required for contraction comes into the cell by diffusion from the extracellular fluid.
• More resistant to fatigue, slower, longer lasting contraction
• More energy efficient in that it can maintain a more forceful contraction for a longer period of time with the same amount of ATP.

Question 5

What is calmodulin and where is it found?

Answer 5

It is a calcium binding protein called calmodulin. This protein activates the actin and myosin crossbridge formation.

Question 6

Smooth muscle is under autonomous nervous system control. True or false?

Answer 6

True

Question 7

Nuerotransmitters of smooth muscle

Answer 7

• Acetylcholine (as in skeletal muscle)

* Norepinephrine.

Question 8

Difference between neurotransmitters of skeletal and smooth muscle

Answer 8

For smooth muscle, they can be either excitatory (causing muscle contraction), or inhibitory (prevent muscle contraction) depending on the receptor on the smooth muscle cell membrane, whereas, the neurotransmitter for skeletal muscle is always excitatory.

Question 9

Smooth muscle can be stimulated by certain hormones. True or false?

Answer 9

True

Question 10

Example of hormones stimulating smooth muscle

Answer 10

Oxytocin, which stimulates smooth muscle contraction in the walls of the uterus during childbirth.

Question 11

Types of smooth muscle fibres

Answer 11

Multiunit smooth muscle

Single unit smooth muscle

Question 12

Properties of multi unit smooth muscle

Answer 12

• Fibers are not very well organized
• Occur as separate fibers scattered throughout the sarcoplasm rather than in sheets.
• Requires stimulation by a motor nerve impulse from the autonomic nervous system.

Question 13

Multiunit smooth muscle fibres are found in…

Answer 13

…the irises of the eyes, arrector pili muscles, blood vessels, and large airways of the lung

Question 14

What type of smooth muscle is found in the walls of the hollow visceral organs such as the stomach, intestines, urinary bladder and uterus?

Answer 14

Single Unit or Visceral Smooth Muscle

Question 15

Which is the more common of the two types of smooth muscle?

Answer 15

Single Unit or Visceral Smooth Muscle

Question 16

Properties of single unit smooth muscle fibres

Answer 16

The muscle fibers are organized into sheets of cells held in close contact by gap junctions.

Question 17

Single unit smooth muscle fibres are organized into ___ layers

Answer 17

Two layers:
•Longitudinal layer
•Circular layer

Question 18

Describe the longitudinal layer of single unit smooth muscle

Answer 18

Outer layer directed longitudinally along the length of the structure. Contraction of this layer causes the structure to dilate and shorten

Question 19

Describe the circular layer of single unit smooth muscle

Answer 19

The inner layer arranged circularly around the structure. Contraction of this layer causes the structure to constrict and elongate.

Question 20

Intrinsic control of smooth muscle contraction is by…

Answer 20

Myogenic Response

Question 21

Describe the myogenic response of smooth muscle

Answer 21

Smooth muscle is stimulated to contract when it is stretched. It is able to distend, or stretch, without great increases in tension or tightness, allowing hollow organs to be filled. When smooth muscle reaches its stretching capacity, it will contract and force the contents out, e.g. intestines or urinary bladder.