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SF3- Exam 1 > Physiology of Smooth Muscle > Flashcards

Physiology of Smooth Muscle Flashcards

1
Q

What are the two types of smooth muscle cells?

A
  • Multi-unit- cells function independently
  • Single- Unit- cells function as a single unit
    • ​Most abundant
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2
Q

Which organs/structures a made up of multi-unit smooth muscle?

A
  • Piloerector
  • Vas deferens
  • Iris of eye
  • Ciliary body of eye
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3
Q

Which organs/structures are made up of single-unit smooth muscle?

A
  • Gastrointestinal tract
  • Blood vessels
  • Urinary bladder
  • Respiratory tract

*Also found within the walls of holow organs, except the heart

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4
Q

Single unit smooth muscle is electrically coupled by _________.

A

Gap junctions

NOTE: This allows for stimulation of one cell to be followed by stimulation of adjacent cells

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5
Q

Both multi-unit and single- unit smooth muscle cells are innervated by _________.

A

ANS

REMEMBER: Smooth muscle is involuntary

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6
Q

What is peristalsis?

A

the involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wave-like movements that push the contents of the canal forward.

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7
Q

What type of potentials are exhibited by single-unit smooth muscle?

A

Slow wave potentions

Spontaneous action potentials (pace maker cells)

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8
Q

What are other names for single-unit smooth muscle?

A

Unitary

Visceral

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9
Q

What are the two layers of unitary smooth muscle? What does contraction of each type lead to?

A
  • Longitudinal layer
    • ​Contraction leads to dilation of lumen and shortening of organ
  • Circular layer
    • ​Contraction leads to constriction of lumen and elongation of organ

NOTE: The stomach has an oblique third layer of smooth muscle

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10
Q

Which unitary smooth muscle is being described below?

Long axis of cell runs parallel of long axis of organ

A

Longitudinal

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11
Q

Which unitary smooth muscle is being described below?

Long axis of cell circles the lumen or circumference of the organ

A

Circular

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12
Q

Circular and longitudinal layers of smooth muscle allow for ___________.

A

Peristalsis

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13
Q

In what ways does smooth muscle differ from skeletal muscle?

A
  • Spindle-shaped fibers-thin and short compared with skeletal muscle fibers
  • Single nucleus
  • Less structured SR
  • Pouchlike infoldings (caveolae) of sacolemma sequester Ca2+ from outside cell
  • NO sacromeres, myofibrils, or T tubules
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14
Q

Pouch-like infoldings called __________ of sarcolemma sequester Ca 2+ from outside cell.

A

Caveolae

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15
Q

How does the myosin-actin relationship differ in smooth muscle from skeletal muscle?

A
  • Actin and myosin filaments arranged non-uniformly
    • ​Myosin heads run the entire length of the myosin filament
    • Myosin heads are oriented in opposing directions on each side
    • Many more actin filaments per myosin filament
    • NO troponin
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16
Q

There is no troponin in smooth muscle. What binds Ca2+?

A

Calmodulin

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17
Q

What are the components of the microscopic structure of smooth muscle?

A
  • Intermediate filaments
  • Dense bodies
  • Gap Junctions
  • Caveolae
  • Nucleus
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18
Q

What are the characteristics of the intermediate filaments of smooth muscle?

A
  • Noncontractie fibers (desmin or vimentin)
  • Lattice like arrangement
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19
Q

Dense bodies of smooth muscle are analogous to which structure of skeletal muscles?

A

Z-bands

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20
Q

Dense bodies are attached to _______ and __________ and bind to __________.

A

Intermediate filaments; actin filament; endomysium

NOTE: Dense bodies contain alpha-actinin, which is also in z-band of skeletal muscle

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21
Q

Which smooth muscle is being described below?

  • Contracts only periodically
  • ​Action potential stimulation
A

Phasic

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22
Q

Which smooth muscle is being described below?

  • Maintians a state of contraction
  • Chemically stimulated without APs
A

Tonic

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23
Q

Which structures are normally contracted?

A

Sphintors

24
Q

Which structures are normally and partially cotnracted?

A

Blood vessels and airways

25
Q

Which structures are phasically active?

A

Stomach

Intestines

26
Q

Which structures are normally relaxed?

A

Esophagus

Urinary bladder

27
Q

True or false. Both skeletal and smooth muscles have neuromuscular junctions.

A

FALSE

*There is no NMJ in smooth muscle

28
Q

Smooth muscle is innervated by autonomic nerve fibers at _______ junctions.

A

Diffuse

29
Q

___________ of nerve fibers store and release neurotransmitters into diffuse junctions.

A

Varicosities

*Varicosities are bulbous swellings

30
Q

Response of a smooth muscle depends on what two factors?

A

Neurotransmitter released

Type of receptor molecules (i.e. stretch)

31
Q

Where do varicosities release their neurotransmitters?

A

Diffuse junction

32
Q

Does neural stimulation of smooth muscle produce a graded potential or action potential?

A

Both!

Either type of potential can be produced

33
Q

Some smooth muscle cells have no nerve supply. These cells are stimulated by hormones and chemicals. Explain the mechanism.

A

Cells depolarize spontaneously or in response to chemical stimuli that bind to G protein-linked receptors

NOTE: Chemical factors include hormones

34
Q

Acetylcholine is released by __________ neurons.

A

Parasympathetic

35
Q

Acetylcholine binds to ____________ recpetors in smooth muscle cells and cause smooth muscle _________ (contraction/relaxation).

A

M3 muscarininc; contraction

36
Q

What is the mechanism by which acetycholine causes smooth muscle contraction?

A
  1. Acetycholine binds to muscarinic receptor (which is a G-protein) causing a conformational change of the receptor
  2. Gq- protein binds to and activates phospholipase C
  3. Phospholipase C metabolizes PIP into IP3 and diacylglcerol (DAG)
  4. IP3 diffuses into sarcoplasmic reticulum and binds to specialized Ca2+ channels
  5. Ca2+ is released
37
Q

Epinephrine is released from _________.

A

Adrenal medulla

38
Q

Norepinephrine is released from ________ neurons.

A

Sympathetic

39
Q

What are the two major kinds of receptors to which norepinephrine binds? What action does each receptor produce?

A

alpha-receptors

  • Vasoconstriction
  • Iris dilation
  • Intestinal relaxation
  • Intestinal sphincter contraction
  • Bladder sphinctor contraction

beta- receptors

  • Vasodilation
  • Cardioacceleration
  • Interstinal relaxation
  • Uterus relaxation
  • Bronchiodilation
40
Q

From where is nitric oxide released?

A
  • Neurons of the intrinsic nervous system
  • CNS neurons
  • Endothelial cells
41
Q

Nitric oxide causes ________ (relaxation/contraction) of smooth muscle.

A

Relaxation

42
Q

Nitric oxide binds to ___________.

A

Guanylyl cyclase

*This activates the production of cGMP from guanosine triphosphate

43
Q

There are 3 paracrines that affect smooth muscle. What are they and what action do they cause?

A

Prostacyclin

  • Causes relaxation of smooth muscle

Endothelium-derived hyperpolarizing factor (EDHF)

  • Causes relaxation of vascular smooth muscle

Endothelin (ET)

  • Causes contraction of vascular smooth muscle
44
Q

By what mechanism does prostacyclin act on smooth muscle?

A
  • Released by endothelial cells
  • Binds to a cell surface receptor (IP) that leads to the production of cAMP
  • cAMP tends to causes relaxation of smooth muscle
45
Q

By what mechanism does EDHF act on smooth muscle?

A
  • Potassium- dependent mechanism
  • Causes relaxation of vascular smooth muscle
46
Q

By what mechanism does endothelin act on smooth muscle?

A
  • Peptides formed in the endothelial cells
  • G-protein coupled receptors
  • Causes contraction of vascular smooth muscle
47
Q

What is unique about the way Ca2+ is obtained in smooth muscle?

A

ca2+ is obtained from the SR and the extracellular space

48
Q

in smooth muscle, actin and myosin interact by ________________ mechanism.

A

Sliding filament

NOTE: ATP energizes sliding process and utilizes aerobic respiration

49
Q

What is the final trigger of smooth muscle contraction?

A

Intracellular Ca2+

50
Q

What are the steps to smooth muscle contraction?

A
  1. Calcium ions enter the cytosol from the ECF via voltage-dependent and voltage- independent Ca2+ channels or from the scant SR
    * Calcium- induced calcium release

​2. Calcium binds to and activates calmodulin

  1. Activated calmodulin activates the myosin light chain kinase enzymes (MLCK)
  2. The activated MLCK enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases
  3. Activated myosin has high affinity for actin and forms cross bridges with actin filaments. Shortening begins.

NOTE: Slow to contract and relax but maintains tension for prolonged periods with little energy cost

51
Q

Because smooth muscles maintain tension for prolonged periods, they require action for relaxtion. What actions are required?

A
  • Active transport of calcium into SR and ECF
  • Calcium detachment from calmodulin
  • Inactivation of MLCK
  • Myosin light chain phosphatase enzyme dephosphorylates myosin, which reduces myosin ATPase activity.
52
Q

___________ dephosphorylates myosin.

A

Myosin light chain phosphatase enzyme (MLCP)

*This reduces myosin ATPase activity

53
Q

At end of the power stoke myosin and actin remain latched together until __________ binds.

A

ATP

NOTE: Unphosphorylated myosin has a weak affinity for ATP

54
Q

Abrupt streches may cause muscle to _________, but continuous slow strectches may allow the muscles to _________.

A

Cotnract; extend

55
Q

Some cells contain stretch activated channels. The cell responds to stretch only briefly, then channels close. By what mechanism does this occur?

A
  • As Ca2+ is pumped out of cell, muscle relaxes and adapts to new length
    • This enables organs such as stomach and bladder to temporarily store increasing volume of contents
56
Q

Compare contraction and stretching capacity of smooth and skeletal muscle.

A

Smooth muscle

  • Can contract to half its resting length
  • Can eb stretched to twice its resting length

Skeletal muscle

  • Contracts maximally to 70% of its resting length
  • Stretches up to 30% beyond its resting length
57
Q

Hyperplasia

A

the enlargement of an organ or tissue caused by an increase in the reproduction rate of its cells

*Smooth muscles have the capacity for hyperplasia

SF3- Exam 1 (26 decks)

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