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BIOSCI 107 Part Two > Muscles: Smooth Muscle > Flashcards

Muscles: Smooth Muscle Flashcards

1
Q

Is smooth muscle voluntary

A

no - it is involuntary

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2
Q

Where is smooth muscle found?

A

Found in the wall of internal organs (gut, blood vessels, airways, bladder, reproductive organs, iris etc)

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3
Q

Structural features of smooth muscle

A

Spindle shaped, uninucleated cell, Not striated

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4
Q

Width of smooth muscle

A

5 µm

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5
Q

Length of smooth muscle

A

100-400 µm

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6
Q

Type of junction in single unit smooth muscles

A

gap junction so that they can act in unison (are electrically coupled)

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7
Q

Where are a single unit smooth muscle cells located

A

Found in most blood vessels and hollow organs (respiratory, digestive, urinary and reproductive tracts)

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8
Q

What is a multi-unit smooth muscle

A

tissue made of discrete bundles of independent cells which are densely innervated and contract only in response to its innervation

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9
Q

Examples of multi-unit smooth muscle

A

vas deferens, iris, piloerection

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10
Q

Function of inner “unitary” smooth muscle

A

It is circular and contracts = they narrow and mush up food

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11
Q

Function of outer “unitary” smooth muscle

A

It is longitudinal and contracts = making food move down tube

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12
Q

Does smooth muscle contain T-tubules

A

no

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13
Q

What does smooth muscle contain rather than T-tubules

A

caveolae

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14
Q

What is the function of caveolae

A

they are “dips” that increase smooth muscles SA to get more AP

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15
Q

What is the function of dense bodies in smooth muscle

A

Dense bodies act like z-lines to “anchor” actin to sarcolemma

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16
Q

Does unitary smooth muscle contain gap junctions

A

yes - to electrically connect cells

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17
Q

What is the sarcoplasmic reticulum like in smooth muscle?

A

it is under/poorly developed (has small volume)

18
Q

Does smooth muscle contain striaitons?

A

No

19
Q

Does smooth muscle contain actin and myosin filaments

A

Yes

20
Q

What does decreased organisation of myosin and actin allow smooth muscle to do?

A

It allows for greater shortening (contract more) and can operate over a large range of lengths (60 - 75% shortening possible)

21
Q

What initiates contraction in smooth muscle

A

voltage gated Ca2+ channels (relatively few Na+ channels)

22
Q

What triggers the opening of voltage gated Ca2+ channels

A

increase in intracellular Ca

23
Q

The three types of initiation of smooth muscle

A

neural, hormonal or spontaneous (myogenic)

24
Q

Smooth muscle calcium source

A

Extracellular and SR Regulation via voltage, hormones, neurotransmitters and specific ions

25
Q

Why is smooth muscle initiation of contraction a slower process

A

because it is enzyme regulated: energy conserving as smooth muscle doesn’t need to be pumping all the time

26
Q

What occurs in Stage 1 of the initiation of smooth muscle contraction: Increased intracellular Ca2+

A

Ca2+ enter the cytosol from the Extracellular fluid (ECF) via voltage- dependent or voltage- independent Ca2+ channels, or from the scant SR

27
Q

What occurs in Stage 2 of the initiation of smooth muscle contraction: Calmodulin (CaM) activation

A

Ca2+ binds to and activates calmodulin (instead of troponin)

28
Q

What occurs in Stage 3 of the initiation of smooth muscle contraction: Activation of kinase

A

The activated calmodulin then activates myosin light chain kinase (MLCK). MLCK is an enzyme

29
Q

What occurs in Stage 4 of the initiation of smooth muscle contraction: Phosphorylation of myosin

A

MLCK activates the myosin by phosphorylating it, which in turn activates the myosin ATPases.

30
Q

What occurs in Stage 5 of the initiation of smooth muscle contraction: Cross bridge cycle

A

Activated myosin forms cross bridges with actin of the thin filaments and shortening begins in the usual fashion.
Contraction occurs by the same actin-myosin interaction as in striated muscle (sliding filament) , but REGULATION IS MYOSIN (NOT ACTIN) BASED. Turning on switch is the phosphorylation of the myosin head. (maximum rate of crossbridge formation is low = slow contractions)

31
Q

When is MLCK active

A

MLCK is active only in the presence of a small Ca-binding protein, calmodulin (and only when it has Ca bound)

32
Q

Regulatory protein in smooth muscle contraction

A

In smooth muscle the reg protein is calmodulin, troponin complex is absent.

33
Q

What has to happen for myosin to hydrolyse ATP

A

Myosin does not hydrolyse ATP (to become energized) unless it is first phosphorylated (on the regulatory light chain, LC20 located on the neck of the myosin)

34
Q

When does a smooth muscle contraction end

A

Contraction ends when a myosin light chain phosphatase dephosphorylates the myosin light chain

35
Q

What removes Ca2+ from the intracellular space

A

Ca-ATPase in cytoplasm membrane is the primary mechanism for reducing intracellular Ca++

36
Q

What is Myosin Phosphatase (MLCP)

A

an enzyme that removes phosphate from myosin head (usually from Ca levels decreasing)

37
Q

The function of enzymes in smooth muscle contraction

A

Balance of two enzymes (putting/removing Ca) causes contraction (which is dominant)

38
Q

Specific activity of each enzyme in smooth muscle contraction

A

↑ MLCK activity (Ca2+ regulated) will favour contraction
↑ MLCP activity will favour relaxation
When intracellular Ca2+ drop MLCP activity will dominate

39
Q

what MUST be present for contraction to occur

A

phosphorylation of the myosin head

40
Q

What are diffuse junctions

A

When autonomic nerve fibres branch and touch the underlying smooth muscle fibres

41
Q

What do varicosities do in autonomic nerve fibres

A

they release their neurotransmitters into a wide synaptic cleft (a diffuse junction)

42
Q

What happens when a smooth muscle is stretched

A

Initially contract, effectively resisting the stretch (e.g. blood vessels trying to maintain blood flow constant) -stretch activated calcium channels.
But over time it slowly relaxes, adapting to the change in length (e.g. gut) - via calcium-dependent K+ channels, hyperpolarizing the membrane potential

BIOSCI 107 Part Two (17 decks)

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