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BIOL1011 > Smooth muscle > Flashcards

Smooth muscle Flashcards

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1
Q

Why is smooth muscle called what it is?

A

it does not give the histological appearance of cross-striations

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2
Q

Is smooth muscle under voluntary or involuntary control? What controls its functions?

A

It is involuntary meaning it is under autonomic and hormonal control

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3
Q

What is smooth muscle specialised for?

How does this compare with skeletal muscle?

A

Smooth muscle is specialised for continuous contractions of relatively low force, under involuntary control

Whereas, Skeletal muscle is specialised for relatively forceful contractions of short durations and under fine voluntary control

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4
Q

Where is smooth muscle found?

A

It is present in the walls of hollow organs like the urinary, bladder, uterus, stomach and intestines

Also present in passageways, such as the arteries, and veins of circulatory system

And tracts of respiratory, urinary and reproductive systems

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5
Q

how many nuclei does a smooth muscle cell have and where is that nucleus located?

A

they have one nuclei per cell and it is located right in the middle of the cell

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6
Q

What is the shape of the cell’s described as?

A

Spindle shaped cells.

This means that they are wider in the middle than at the ends

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7
Q

What’s not present in smooth muscles?

A

T tubules

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8
Q

What’s on the outside/inside of the cell:

Circular smooth muscle

longitudinal smooth muscle

A

Longitudinal is found on the inside

circular is found on the outside

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9
Q

What are the 2 forms of smooth muscle?

A

circular smooth muscle

and

longitudinal smooth muscle

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10
Q

label this electronmicrograph of smooth muscle?

A
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11
Q

What do dense bodies contains and what’s their main function?

A

dense bodies contain lots of proteins and they help anchor filaments

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12
Q

What do smooth muscle produce and what is this called?

A

smooth muscle produces its own connective tissue, known as endomysium

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13
Q

What structures do smooth muscles not contain?

What structures do they have?

A

Don’t contain: striations, sarcomeres, T tubules

Do contains: actin, myosin, thin/thick filaments

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14
Q

What are Ca2+ ions supplied by ?

(2 regions)

A

They are supplied by the SR in the fibres

and

by sequestration from the extracellular fluid through membrane indentations called Calveoli

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15
Q

When the muscle contracts, does the distance between dense bodies becomes shorter or longer?

A

shorter

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16
Q

Label this relaxed/ contracted smooth muscle

A
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17
Q

What does the skeletal muscle act against?

What does smooth muscle act against?

A

Skeletal muscle acts against the skeleton

Smooth muscle acts against the extracellular matrix

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18
Q

The extracellular matrix that the smooth muscle acts against, secretes what?

A

collagen and glycoproteins

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19
Q

In smooth muscle, what is the tension generated by?

what is this tension transmitted through?

What overall effect does it cause?

A

The tension is generated by contraction and its transmitted through the focal adhesion densities to the surrounding connective tissue this allowing groups of cells to act as one

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20
Q

what does smooth muscle contraction depend on?

How is this mechanism different to skeletal muscle?

A

It is a Ca2+ dependant mechanism but smooth muscles does not contain troponin like skeletal muscle does

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21
Q

What are the steps to smooth muscle contraction?

A
  1. Ca2+ ions are released from caveolae/ SR
  2. Ca2+ ions form complex with calmodulin
  3. Ca2+ - calmodulin complex activates the myosin light chain kinase (MLCK)
  4. MLCK is phosphorylated and activates myosin ATPase activity
  5. myosin is now able to bind to actin
  6. ATP-dependant contraction cycle ensues
  7. contraction continues as long as myosin is phosphorylated
  8. Phosphatase cleaves the phosphate group
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22
Q

How is smooth muscle contraction stopped?

A

ATP-dependant calcium pumps actively transporting Ca2+ back into the SR and out of the cell

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23
Q

What is calmodulin sometimes referred to as?

A

CaM

OR

Calcium- modulated protein

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24
Q

What is CaM?

A

an intracellular target of the second messenger Ca2+

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25
Once CaM is bound to Ca2+ what happens?
the CaM acts as part of a calcium signal transduction pathway by interacting with kinases and phosphatases
26
What is CaM structurally similar to?
Troponin
27
What remains in the cytoplasm after contraction and why? Why is it important?
A low concentration of Ca2+. This helps to maintain muscle tone. This is important in certain tracts and around blood vessles
28
Most smooth muscle's must function for long periods of time without rest. What does this mean for their power output and the amount of energy they use?
They have a low power output and the contractions can continue without using large amounts of energy
29
Can some smooth muscle maintains contractions even as Ca2+ is removed and myosin kinase in inactivated (dephosphorylated)?
yes
30
How does the contraction of smooth muscles occur without the presence of Ca2+? Whats not needed? What does this allow to maintain?
Cross-bridges can form between myosin heads and actin, these are known as **latch-bridges.** This helps keep the thick and thin filaments linked together for long periods of time without the need for ATP This allows the maintaining of muscle 'tone' in smooth muscle that lines arterioles and other visceral organs
31
Name some things that can stimulate smooth muscle?
* Involuntary and contracts without nerve stimulation * hormones * stretch * metabolic state- CO2, low PH, O2 deficiency * autonomic nerve fibres stimulate multiple myocytes
32
What influences the contractile activity of smooth muscle?
neurotransmitters which are released by autonomic neuron endings
33
what do smooth muscles have instead of an end-plate region like the skeletal muscle's have?
swollen regions known as **varicosities**
34
What do varicosities contain? How are these released from the varicosities?
many vesicles filled with neurotransmitters, some of which are released when an AP passes the varicosity
35
What do varicosities form?
A single axon which is located along several muscle cells
36
What are a number of smooth muscle cells influcenced by? What is a single smooth muscle cell influenced by?
NUMBER of smooth muscle cells are influenced by the neurotransmitters released by a single neuron ONE smooth muscle cell is influenced by neurotransmitters from more than one neuron
37
What are the 2 types of units of smooth muscle cells?
single-unit smooth muscles and multi-unit smooth muscle
38
What unit is more common in smooth muscles?
single unit is more common
39
What is a single-unit smooth muscle?
The smooth muscle has its muscle fibres joined by gap junctions so that the muscle contracts as a single unit (the electrical signal is transferred across the gap junctions)
40
Where is single-unit smooth muscle found? What is it commonly called?
in the walls of all visceral organs (EXCEPT THE HEART) so is commonly called the **Visceral muscle**
41
What response does visceral muscle have? What does this mean?
**stress-relaxation response** This means that as the muscle of a hollow organs is stretched when it fills, the mechanical stress of the stretching will trigger contraction. This is immediatly followed by relaxation so that the organ does not empty its comtents prematurely
42
What does visceral muscle help maintain around the hollow organs?
muscle tone when the organ empties and shrinks, this prevents 'flabbiness' in the empty organ
43
What type of contraction does visceral organ produce? What does this allow?
A slow and steady contraction that allow substances, such as food in the digestive tract, to move through the body
44
Why are multi-unit smooth muscle not electrically coupled?
They rarely possess gap junctions
45
When a multi-unit is stimulated where does the impulse travel to?
The impulse doesn't spread from one cell to the next but instead is confined to the cell that was originally stimulated
46
Where does stimuli for the multi-unit smooth muscle come from?
**the autonomic nerves or hormones** but NOT from stretching
47
Where is multi-unit smooth muscle found?
around large blood vessels, in the respiratory airways and in the eyes
48
The fight or flight response leads to many physiological responses, it also causes chnages in smooth muscle activity. What type of changes does it cause?
* skin- smooth muscle in follicles can cause hair to stand on end * eye- iris in smooth muscle dilates * stomach, intestines and bladder * bronchodilation
49
What do gap junctions allow in single-unit smooth muscle? How is this different in multi-unit smooth muscle?
Gap junctions in single-unit smooth muscle allow the spread of the electrical activity between all cells so they all contract as a single unit Whereas, in multi-unit smooth muscle there is electrical isolation so when an impulse arrives only a few cells will contract as opposed to all
50
Label the bronchiole?
51
Label the layers of this electron microscrope image of a bronchiole
52
Give an example of a therapeutic targeting of smooth muscle?
Beta2 agonist. It is found in salbutamol inhalers. it targets Beta2 receptors (GPCR) located in bronchial smooth muscle, results in bronchodilation
53
Tell me the steps to how the Beta2 receptor agonsit causes bronchodilation
54
What coordinates the peristalic movement of the food bolus through the GI tract?
the longitudinal cross-sectional smooth muscles
55
what decreases peristalisis?
the fight and flight response
56
Whats the oesophagus?
A strong muscular tube that convery food from the oropharynx (part of the mouth) to the stomach
57
is swallowing volunatary or involuntary?
voluntary
58
whats an example of skeletal and smooth muscle working together?
swallowing
59
in the oesophagus, is the circular or longitudinal smooth muscle found on the inside/outside?
circular smooth muscle on inside longitudinal smooth muscle on outside
60
what is the ureter made of?
smooth muscle fibres
61
What process squeezes urine into the bladder?
peristalsis
62
What are the layers of smooth muscle of the bladder?
inner longitudinal middle circular outer longitudinal
63
label the ureter?
64
whats the myometrium?
the smooth muscle tissue of the uterus
65
during pregnancy how does the myometrium change?
it greatly increases in size?
66
what does the hormone oxytocin stimulate?
the contraction of myometrium. helps to expel the foetus from the uterus
67
Whats intravenous salbutamol been used for?
to relax the uterine smooth muscle to delay poremature labour-same mechanism as for bronchodilation
68
when oxytocin binds to a receptor, what does it trigger the release of? How does this then result in contraction?
it causes the release of Ca2+ from the SR. The Ca2+ ions bind to calmodulin which activates myosin light chain kinase (MLCK) which then results in contraction
69
Tell me the differences between smooth muscle and skeletal muscle excitation and the steps that lead to an external force being generated?
70
Tell me the stages to cross-bridge activation in smooth and skeletal muscle
71
because smooth muscle cells do not contain troponin, cross-bridge formation is not regulated by the troponin-tropomyosin complex but is instead regulated by what?
the regulatory proteins calmodulin

BIOL1011 (8 decks)

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