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SF3 > Physiology of Smooth Muscle- Dr. Allard > Flashcards

Physiology of Smooth Muscle- Dr. Allard Flashcards

1
Q

Smooth muscles are primarily found in what types of organs?

A

hollow organs

  • bladder: stretches to hold urine and contracts to push urine out
  • GI tract : mixes and propels fodo htrough the digestive tract
  • iris of the eye: dilates pupil
  • arteries and veins: controls blood pressure and flow
  • vas deferens: moves sperm along the reproductive tract
  • airways: expand and contract to regulate air flow in lung
  • uterus: stretches and proliferates to accommodate fetus and contracts for birth
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2
Q

What are the two types of smooth muscles and what is the difference between the two?

A
  • multi-unit: cells operate INDEPENDENTLY; each cell contracts on its own
  • single-unit: unitary or visceral; cells contract TOGETHER
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3
Q

Where are multi-unit cells found?

A
  • piloerector
  • iris of eye
  • vas deferens
  • ciliary body of eye
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4
Q

Where are visceral smooth muscles found?

A
  • in walls of hollow organs
  • GI tract
  • urinary bladder
  • blood vessels
  • respiratory tract
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5
Q

What is the most abundant type of smooth muscle?

A

visceral/single-unit/unitary smooth muscles

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6
Q

Which smooth muscle does not require stimulation from the ANS to contract?

A

single-unit

-even without an action potential, these smooth muscles can contract; all they need is that one calcium ion to initiate contraction

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7
Q

What allows unitary smooth muscles to contract together?

A

gap junctions

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8
Q

What is an important difference between skeletal and smooth muscles in terms of stimuli for contraction?

A
  • smooth muscles can have MULTIPLE stimuli for either contraction or relaxation BUT skeletal muscles just need ACh for contraction only (when the AP is done there is no more contraction)
  • on the sarcolemma of smooth muscles there is a variety of receptors that allow smooth muscles to respond to a variety of signals
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9
Q

What is the function of the longitudinal layer of the unitary smooth muscle?

A

-its contraction leads to DILATION of lumen and shortening of the organ

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10
Q

What is the function of the circular layer of the unitary smooth muscle?

A

-its contraction leads to CONSTRICTION of lumen and elongation of organ

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11
Q

What is the function of the oblique layer of the unitary smooth muscle?

A

it allows for mixing of food as it goes down the GI tract

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12
Q

What process does the circular and longitudinal smooth muscles allow for?

A

peristalsis

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13
Q

What is the difference between the sarcolemma of the smooth and skeletal muscles?

A

skeletal: very elaborate
smooth: pouchlike infoldings (caveolae) of sarcolemma for the function of sequestering calcium from outside of the cell; a lot of calcium channels found in the caveolae (pits) of smooth muscle

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14
Q

T/F. There are no sarcomeres, myofibrils, or T-tubules in smooth muscles.

A

True

  • that’s why smooth muscles do not have striations
  • smooth muscles still have myosin and actin; they are just not lined up in a regular consistent way
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15
Q

Why can smooth muscles contract and stretches much farther than skeletal muscles?

A
  • smooth muscles have myosin heads that run the entire length of the myosin filament and are oriented in opposing directions on each side (can contract 1/2 of its size)
  • skeletal muscle have region without myosin heads (can only contract 30% of its resting size)
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16
Q

What does calcium bind to in smooth muscle as there is no troponin (unlike skeletal muscle)?

A

calmodulin

17
Q

What are the thick and thin filaments?

A

thick filament = myosin

thin filament= actin

18
Q

How do the dense bodies keep the integrity of smooth muscles?

A

The intermediate filaments are connected to other intermediate filaments via dense bodies, which eventually are attached to adherens junctions (also called focal adhesions) in the cell membrane of the smooth muscle cell, called the sarcolemma.

dense bodies are attached

  • to IF (desmin or vimentin)
  • to actin filament
19
Q

Dense bodies in smooth muscles are analogous to what in skeletal muscles?

A

Z-bands

-They act as an anchoring point of the actin filaments.

20
Q

T/F. Smooth muscles are 100x stronger than skeletal cells.

A

True

21
Q

What is the difference phasic and tonic contractility in smooth muscles?

A

phasic smooth muscle:

  • contracts only periodically
  • AP stimulation from ANS
  • stay mostly at rest and contract periodically

tonic smooth muscle:

  • maintains a state of contraction
  • chemically stimulated without APs
22
Q

Which organs exhibit phasic contractility?

A

stomach and intestine

23
Q

Which organs exhibit tonic contractility?

A
  • blood vessels

- airways

24
Q

Which organs with smooth muscles are normally contracted?

A

sphincter

25
Q

Which organs with smooth muscles are normally relaxed?

A

esophagus, urinary bladder

26
Q

What is synonymous in smooth muscles to neuromuscular junction in skeletal muscles?

A
  • smooth muscles are innervated by autonomic nerve fibers at diffuse junctions
  • varicosities (bulbous swelling which have NT vesicles in them) of nerve fibers which store and release neurotransmitters into diffuse junctions (a wide synaptic cleft)
27
Q

Some unitary/visceral smooth muscles can be activated by stretch. Explain and give examples.

A
  • stretch opens mechanically gated cation channels (calcium) leading to depolarization and action potentials and contraction
  • examples include gut wall muscles and bladder
28
Q

Some smooth muscle cells have no nerve supply. They can depolarize spontaneously or in response to what type of stimuli that bind to what type of receptors?

A

chemical stimuli (hormones, CO2, pH) to G protein-linked receptors

29
Q

Neural stimulation of smooth muscles influences contraction or relaxation or both?

A

Response depends on neurotransmitter released and type of receptor molecules and thus neural stimulation can influence relaxation or contraction NOT just contraction like skeletal muscles

30
Q

Second messenger systems dictate smooth muscle cells responses that include what?

A
  • contraction
  • relaxation
  • growth
  • proliferation
31
Q

Describe the process of calcium release of second messenger systems in smooth muscles.

A

ACh is released by parasympathetic neurons.
Ach binds to M3muscarinic receptors in smooth muscle cells (e.g. digestive tract) and causes smooth muscle contraction.

  1. Gq protein binds to and activates PLC.
  2. PLC metabolizes PIP into IP3 and diacylglycerol (DAG)
  3. IP3 diffuses to SR and binds to specialized calcium channels.
  4. Calcium is released.

Calcium in cytosol leads to contraction.

SF3 (15 decks)

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