Smooth Muscle

Question 1

Where is smooth muscle located?

Answer 1

lines viscera GI tract, respiratory tract, blood vessels, reproductive system

Question 2

Describe the structure of smooth muscle?

Answer 2

• non-striated fibers
• spindle-shaped
• tapered

Question 3

Do smooth muscle have T-tubules?

Answer 3

no

Question 4

Is smooth muscle contraction voluntary or involuntary?

Answer 4

involuntary (spontaneous)

Question 5

What is smooth muscle contraction regulated by?

Answer 5

ANS (both sympathetic and parasympathetic systems)

Question 6

What is the function of smooth muscle in arteries and veins?

Answer 6

control vessel diameter (vasoconstriction/vasodilation) to regulate blood pressure

Question 7

What is the function of smooth muscle in intestine?

Answer 7

longitudinal and circular layers work together to participate in peristalsis

Question 8

What is peristalsis?

Answer 8

progressive and rhythmic contractions of smooth muscle that propel food through digestive tract

Question 9

What are the 2 layers of smooth muscle in intestine?

Answer 9

• longitudinal

- circular

Question 10

What does the longitudinal layer of intestine smooth muscle do?

Answer 10

constricts to allow food to go down GI tract

Question 11

What does the circular layer of intestine smooth muscle do?

Answer 11

constricts to prevent food from going up GI tract

Question 12

What is the function of smooth muscle in stomach?

Answer 12

longitudinal, circular, and oblique layers work together to mix food when it arrives in stomach, and propel it down to intestines

Question 13

What is the organization of smooth muscle in arteries and veins?

Answer 13

tunica media

Question 14

What is the tunica media made of?

Answer 14

made of smooth muscle cells and elastic tissue

Question 15

What does the tunica media surround?

Answer 15

artery and vein walls

Question 16

Where is the tunica media thicker?

Answer 16

thicker in arteries compared to veins – arteries have to sustain higher blood circulation, therefore thicker layer protects from damage

Question 17

What is the organization of smooth muscle in intestine?

Answer 17

two main layers of smooth muscle

• longitudinal layer
• circular layer

Question 18

What is the longitudinal layer of smooth muscle in intestine?

Answer 18

outer layer of muscle fibers that run parallel to long axis of organ

Question 19

What is the circular layer of smooth muscle in intestine?

Answer 19

inner layer of muscle fibers that run around circumference of organ

Question 20

What is the organization of smooth muscle in stomach?

Answer 20

3 layers of smooth muscle

• longitudinal layer (upper part of stomach)
• circular layer (middle part of stomach)
• oblique layer (lower part of stomach)

Question 21

Describe the innervation of smooth muscle by ANS

Answer 21

axon of postganglionic autonomic neuron branches once it hits smooth muscle

• innervates smooth muscle, but there’s no synaptic contact with smooth muscle

Question 22

What are varicosities?

Answer 22

swellings along axonal branches filled with neurotransmitters that are released on top of plasma membrane of smooth muscle fibers, and bind to their appropriate receptors

Question 23

What is a single-unit muscle?

Answer 23

one group of smooth muscle, with a single axon over the group of muscle fibers

Question 24

How are cells connected in single-unit muscle?

Answer 24

by gap junctions

• there are more gap junctions than in multi-unit muscle

Question 25

How do single-unit muscle contract as a unit?

Answer 25

excitation in one cell is rapidly transmitted to ‘connected’ cells – allows entire unit to contract synergistically at the same time

Question 26

Where are single-unit muscles found?

Answer 26

- walls of viscera: digestive, urinary, and reproductive tracts - walls of small blood vessels

Question 27

What are multi-unit muscle?

Answer 27

groups of smooth muscles separated by each other by branches of ANS neurons

Question 28

How do multi-unit muscle contract as a unit?

Answer 28

one unit can contract independently of the neighbouring units

Question 29

Where are multi-unit muscles found?

Answer 29

- walls of large blood vessels - small airways of lungs - muscle of eye (lens) - iris of eye - base of hair follicles

Question 30

What is a myosin molecule composed of?

Answer 30

- 2 myosin heads - 2 essential myosin light chains - 2 accessory myosin light chains

Question 31

Which myosin light chains get phosphorylated?

Answer 31

accessory myosin light chains

Question 32

What are the 2 sites on each of the myosin heads?

Answer 32

- site that binds to actin | - site that hydrolyzes ATP into ADP and Pi

Question 33

What are caveolae?

Answer 33

plasma membrane invaginations

Question 34

What do caveolae contain?

Answer 34

dihydropyridine receptors, through which influx of Ca2+ from ECF passes to enter sarcoplasm

Question 35

What do gap junctions allow?

Answer 35

direct electrical communication between adjacent smooth muscle fibers

Question 36

Where is gap junction?

Answer 36

membranes of two adjacent muscle fibres are very close to one another

Question 37

How are thin filaments arranged?

Answer 37

obliquely in cell

Question 38

What are thin filaments attached to?

Answer 38

- some attach to dense bodies in cytoplasm | - some attach to dense plaque of plasma membrane

Question 39

What do contractile units of smooth muscle consist of?

Answer 39

myosin and actin filaments attached to dense bodies in sarcoplasm or plasma membrane plaques

Question 40

Where are contractile units of smooth muscle?

Answer 40

stretch across cell, between plasma membrane plaques

Question 41

What happens when contractile apparatus is close to plasma membrane?

Answer 41

it binds to membrane via dense plaque on one end, and dense body (in cytoplasm) on other end

Question 42

What happens to inside contents of the cell when smooth muscle fiber is contracted?

Answer 42

everything gets wrinkled and shrinks all organelles in cell get caught into mesh of cytoskeletal proteins (including intermediate filaments)

Question 43

What is the contractile apparatus in skeletal and cardiac muscle?

Answer 43

sarcomere - organized - parallel to each other

Question 44

Pharmacomechanical Coupling Process

Answer 44

1. receptors bind to hormones/neurotransmitters 2. production of IP3 within cytoplasm 3. IP3 binds to IP3R - induces release of Ca2+ in SR into sarcoplasm **no need for membrane depolarization – pressure signalling causes depolarization

Question 45

Smooth Muscle Contraction Process

Answer 45

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