Muscle VIII

Question 1

Why is smooth muscle more variable than skeletal

Answer 1

• operates over a range of lengths
• layers run in several directions
• contract and relax much more slowly
• use less energy
• can sustain contraction without fatigue
• contraction initiated electrically or chemically

Question 2

What is smooth muscle controlled by

Answer 2

Autonomic nervous system

Question 3

Where does calcium come from in smooth muscle

Answer 3

Extracellular space and/or SR

Question 4

Characteristics of smooth muscle

Answer 4

• spindle shaped, uninucleated, thin
• 50-400um (short)

Question 5

What gives smooth muscle its smooth appearance

Answer 5

All the thin filaments run in different directions

Question 6

What is smooth muscle made up of

Answer 6

• intermediate filaments (non-contractile) and dense bodies (similar to z-lines) for cytoskeleton
• thin filaments are anchored to cell membrane or dense bodies
• each myosin is surrounded by actin
• myosin has hinged heads all along its length

Question 7

How is smooth muscle characterized

Answer 7

• location
• contraction pattern
• communication with neighbouring cells

Question 8

What is the location of the 6 groups of smooth muscle

Answer 8

• vascular
• gastrointestinal (digestive tract and associated organs i.e gallbladder)
• urinary (wall of bladder, ureters)
• respiratory (airway passages)
• reproductive (uterus and others)
• ocular (iris and ciliary body)

Question 9

What are the contraction patterns of smooth muscle

Answer 9

Phasic, cyclic phasic, tonic, cyclic tonic

Question 10

What is phasic smooth muscle

Answer 10

Usually relaxed
I.e. esophagus
Only contracts when stimulus

Question 11

What is cyclic phasic smooth muscle

Answer 11

Cycles between contraction and relaxation
I.e. intestines

Question 12

What is tonic smooth muscle

Answer 12

Usually contracted
I.e. sphincter
Relaxes in response to stimulus

Question 13

What is cyclic tonic smooth muscle

Answer 13

Contraction is varied as needed
I.e. vascular smooth muscle
- cycles level of contraction

Question 14

How does unitary (single unit). Smoot muscle communicate with neighbouring cells?

Answer 14

Contain gap junctions
- coordinated contraction as a single unit
- linked electrically

Question 15

What is another name for unitary smooth muscle

Answer 15

Visceral smooth muscle
- makes up walls of most visceral organs

Question 16

How does multi unit smooth muscle communicate with neighbouring cells?

Answer 16

Not electrically coupled
- all have neuronal input or close to varicosities
- need own stimulus

Question 17

What are examples of multi unit smooth muscle

Answer 17

Iris, ciliary body, male reproductive tract, uterus except prior to labor

Question 18

what is smooth muscle innervated by

Answer 18

Autonomic nervous system (sympathetic and parasympathetic)

Question 19

What does smooth muscle contract in response to

Answer 19

Synaptic transmission or electrical coupling

Question 20

What innervates smooth muscle

Answer 20

• multiple neurons, capable of releasing different neurotransmitters
• receptor subtype difference in muscle

Question 21

What can alter smooth muscle tension

Answer 21

Hormones, stretch and local factors, including paracrine signals, acidity, oxygen and carbon dioxide concentration, osmolarity