DD - Smooth Muscle

Question 1

What types of control are involuntary muscles under?

Answer 1

Autonomic and Hormonal control

Question 2

Where is smooth muscle found? (4)

Answer 2

• Hollow organs
• Walls of passageways
• Eyes- Changes the size of the iris
• Skin- Causes hair to stand

Question 3

Describe features of the smooth muscle (4)

Answer 3

• Spindle-shaped (wide in the middle and tapered at the ends)
• Produce their own connective tissue Endomysium
• No striations or sarcomere but still have actin and myosin contractile proteins and filaments
• Contain dense bodies which anchor down thin filaments

Question 4

What do smooth muscle require?

Answer 4

An extracellular matrix which they secrete

• Anchors the smooth muscle cells into functional units

Question 5

What is the mechanism of calcium ions in smooth muscle? (7)

Answer 5

1. Ca2+ ions are released from ER or enter through caveolae.
2. Ca2+ ions form a complex with calmodulin
3. The ca2+-calmodulin complex activates myosin light chain kinase (MLCK)
4. MLCK phosphorylates the myosin light chain and activates myosin ATPase
5. Myosin is now able to bind to actin.
6. ATP-dependent contraction cycle ensues. The contraction continues as long as myosin is phosphorylated.
7. Phosphatase cleaves the phosphate group.

Question 6

What does Calmodulin act as in this pathway?

Answer 6

A secondary messenger

Question 7

1. When does muscle contraction end?
2. What keeps the muscle slightly contracted during cross-bridge detatchement?

Answer 7

1. When ATP-dependent calcium pumps actively transport Ca2+ ions back into the ER
2. Latch-bridges (without ATP)

Question 8

What are varicosities?

Answer 8

Swollen regions found in smooth muscle

• Each varicosity contains neurotransmitters which influence smooth muscle action

Question 9

What are the 2 types of smooth muscle cells?

Answer 9

1) Single-unit muscle- Muscle fibres are joined by gap junctions so the muscle contracts all together

• Found in visceral muscles (except the heart)

2) Multi-unit muscle- Rarely possess gap junctions and so are not electrically coupled
Stimulation is not spread to other cells

• Found in large blood vessels, airways and eyes

Question 10

How does salbutamol (inhalers) result in Bronchodilation? (5)

Answer 10

1. Beta2 Receptor agonist
2. ↑cAMP
3. ↑Phosphorylation of MLCK
4. Relaxation of bronchial smooth muscle
5. Bronchodilation

Question 11

Where does skeletal and smooth muscle work together?

Answer 11

Oesophagus

• Contains skeletal muscle at the top hence swallowing is voluntary

Question 12

How many layers of smooth muscle in the bladder?

Answer 12

3

• Inner Longitudinal
• Middle Circular
• Outer Longitudinal

Question 13

What is the uterine smooth muscle known as?

Answer 13

Myoterium

• Increases greatly during pregnancy in response to oestrogen
• Oxytocin acts to increase contraction