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Physiology > Smooth Muscle > Flashcards

Smooth Muscle Flashcards

0
Q

Purpose of Smooth Muscle

A
  1. shorten to provide motility
  2. change shape of organ
  3. maintain sustained contractions to maintain tone
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1
Q

Location of Smooth Muscle

A

walls of hollow organs & tubes

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2
Q

Ultrastructure of smooth muscle

A

Arterioles = circumfrential
Intestines = longitudinal on top & transverse on bottom
Testicular ducts = unique square shape

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3
Q

Structural Properties of Smooth M.

A

nonstriated, spindle-shaped, single nucleus, involuntary

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4
Q

Types of Electrical Coupling in Smooth M.

A
  1. Multi-unit

2. Single unit

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5
Q

Multi-unit electrical coupling

A

cells aren’t electrically linked & are independently stimulated

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6
Q

Multi-unit electrical coupling allows

A

fine control of contraction

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7
Q

Cells involved in multi-unit electrical coupling are

A

insulated from each other by collagen

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8
Q

Examples of smooth muscle with multi-unit electrical coupling

A

iris, ciliary bodies, uterus (when pregnant)

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9
Q

Single Unit Electrical Coupling

A

most common type

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10
Q

How does single-unit electrical coupling work?

A

AP spreads through gap junction & there is one varicosity per multiple cells

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11
Q

Single Unit Electrical Coupling contraction

A

cells contract simultaneously

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12
Q

Examples of Single Unit Smooth M. Electrical Coupling

A

GI tract, urinary bladder, blood vessels, uterus (close to parturition)

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13
Q

Smooth M. Contractile Behavior Classifications

A
  1. Tonic Smooth M.

2. Phasic Smooth M.

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14
Q

Tonic Smooth M.

A

normally contracted muscle that generates variable steady state force

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15
Q

Tonic smooth muscle responds

A

to graded changed in Vm. It is proportional to Vm

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16
Q

Phasic Smooth M. Characteristics

A
  • rhythmic contractions (peristalsis)
  • voluntary intermittent activity
  • AP based
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17
Q

Smooth M. Contractile Arrangements

A

Scaffold System of intermediate filaments & dense bodies

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18
Q

intermediate filaments

A
  • scaffold around smooth m. cells

- do NOT aid in contraction

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19
Q

location of intermediate filaments

A

under membrane & surrounding nucleus

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20
Q

dense bodies

A

anchor actin filaments

21
Q

actin traversing between cells

A
  • actin enters dense body & leaves to interact with the next cell.
  • helps surrounding cells contract too!
22
Q

Smooth M. contraction length

A

more interaction between actin & myosin filaments

23
Q

Smooth M. myosin filaments

A
  • longer than skeletal m. myosin filaments
  • hinged heads located along entire length
  • “side-polar” cross-bridges
24
Q

Smooth m. myosin filaments allow

A

cells to contract to 80% of their length because of the scaffold vs 30% length contraction in skeletal m.

25
Q

Smooth M. Contraction depends on

A

MLCK/MLCP activity

26
Q

Smooth M. Contraction Mechanism

A

Ca influx (mostly from ECF) => Ca binds to Calmodulin => Ca-Calmodulin activates MLCK => MLCK phosphorylates MLC => Phosphorylated MLC activates myosin head allowing it to bind to actin => CONTRACTION

27
Q

MLCK stands for

A

myosin light chain kinase

28
Q

MLCK function

A

phosphorylation of MLC

29
Q

MLC =

A

myosin light chain

30
Q

MLCP

A

Myosin Light Chain Phophytase

31
Q

MLCP function

A

dephosphorylates myosin & decreases myosin/actin interaction

32
Q

MLCK:MLCP activity

A

determines level of smooth m. contraction

33
Q

Chemical Initiation of Smooth M. Contraction

A
  1. Intrinsic activity of pacemaker cells for single unit
  2. Neurotransmitters
  3. Hormones
  4. Pharmacological agents
34
Q

Intrinsic activity of pacemaker cells for single unit electrical coupling

A

stimulates AP in visceral smooth m.

35
Q

Neurotransmitters

A

1 varicosity/muscle cell in multi-unit

1 varicosity/multiple cells in single unit & communicate via gap junctions

36
Q

Pharmacological Agents

A

delivered via vaculature

37
Q

What is ABSOLUTELY necessary for SMOOTH m. contraction?

A

CALCIUM

38
Q

Mechanism for Initiation of VISCERAL Smooth M. Contraction

A

Stimulated by APs

39
Q

Mechanisms for Initiation of VASCULAR smooth m. contraction

A

stimulated by slow wave potentials by graded changes in Vm
AND
stimulated by hormones and pharmacological agents

40
Q

Hormone & Pharmacological Agent Effect on Vascular Smooth M. cells

A
  • no change in Vm

- still get contraction & relaxation

41
Q

Characteristics of Smooth M.

A
  • slow contraction
  • slow relaxation
  • less ATP used to generate same force as skeletal m.
  • use only 25-30% myostin-actin cross-bridges to generate max. amount of tension
42
Q

Slow contraction of smooth m. permitted by

A

slow ATP splitting by myosin ATPase

43
Q

Slow relaxation of smooth m. provided by

A

slow Ca removal by Na/Ca exchangers

44
Q

Latch State

A

Smooth m. only using 25-30% of myosin:actin cross-bridges to generate max. amount of tension

45
Q

Tonic contraction

A

keeps some level of basal tone to get latch state because of continuous stimulation

46
Q

Tonic contraction force

A

maintained by low ATP utilization

47
Q

Tonic contraction works by

A

lowering Ca => dephosphorylation of MLC while in attached state
(actin/myosin are slower to detach when MLC dephosphorylates)

48
Q

Relaxation of Smooth M. done by:

A

1st: Ca pumps
2nd: Ca ATPases.

49
Q

Smooth M. Ca ATPases

A

slower to act than those in striated muscle

Physiology (10 decks)

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