Topic 22 - Characteristics of smooth muscle Flashcards

1
Q

Words to include

A
  • Visceral organs
  • Protein lattices (dense bodies)
  • Intermediate filaments
  • Membrane plates
  • Cytoskeleton
  • Nucleus
  • Blood supply
  • Spindle shaped
  • Non-striated
  • Non-regular myofilaments
  • Intermediate filaments
  • T-tuble (ø)
  • Sarcomere (ø)
  • Sarcoplasmic reticulum (small)
  • Multi-unit smooth muscle
    • Eyes
      • M. ciliaris
    • Skin
    • Individual fibers
    • Gap junctions (ø)
    • Local depolarization
    • Collagen
    • Glycogen
    • Autonomic neuron varicosity
  • Single-unit smooth muscle
    • Hollow organs wall
    • Tubular organs wall
    • Spontaneous contraction
    • Gap junctions
    • Syncytium
    • Peristaltic movements
    • Bayliss effect
      • Self-reflection (myogenic response)
    • Autonomic neuron varicosity
    • Gastrointestinal muscles
    • Muscles of vessels
    • Bronchial muscles
    • Bladder of sphincters
  • Varicosities
    • Axon terminal
    • Neurotransmitters
  • Innervation
    • Serperately (multi)
    • Humoral regulation (single)
  • Ligand
    • ACh (multi)
      • Parasympathetic
    • Norepinephrine (multi)
      • Sympathetic
    • ACh (single)
    • Norepinephrine (single)
    • VIP (single)
    • NO (single)
    • ATP (single)
  • Receptor
    • Muscarinic (multi)
    • Alpha-1-R (multi) (single)
    • mACh-R (single)
    • Beta-2-R (single)
  • Smooth muscle sarcomere
    • F-actin α-helix
    • G-actin subunit
    • Myosin binding-site
    • Tropomyosin
      • Inactive status
      • Active status
    • Calmodulin-Ca2+ complex
    • Caldesmon
  • Sarcoplasmic reticulum
    • Action potential
    • Autonomic nerves
    • Caveoles
      • Rudimentary T-tubules
    • Sarcoplasmic tubule
  • Myolemma
    • Voltage gated Ca2+-channels
    • Ligand gated Ca2+-channels
      • Hormone activated
  • Actin
  • Myosin
    • MLC subunit
      • P-LCh
        • ADP+P
        • Non-phosphorylated
        • Phosphorylated
  • Prolonged tonic contraction
  • Cross-bridge cycle (lower frequency)
    • ATPase activity (low)
    • ATP catabolism (slow)
    • Myosin head power-stroke (slow)
    • 1 ATP/ cross bridge cycle
  • Action potential
    • Single-unit smooth muscles
    • Peak potential
      • Electric stimuli
      • Hormones
      • Spontaneously by pacemaker activity
    • AP with plateu
      • Prolonged repolarization
    • Humoral regulation
    • Metabolic regulation
  • Contraction
    • Sympathetic (alpha-1) neural AP
    • Parasympathetic (mACh) neural AP
    • Myolemma
    • Voltage gated ion channel
    • Calcium influx
    • Chemical ligands
    • Ligand gated ion channels
    • IP3 release
    • G-protein
    • Phospholipase C (PLC)
    • Sarcoplasmic reticulum
    • Calcium sequester vesicle
  • Relaxation
    • cAMP (↑)
    • CGMP (↑)
    • Calcium concentration (↓)
    • Sympathetic beta-2 receptor agonists
      • Epinephrine
      • VIP
    • NO
      • Capillary endothelium
    • ATP
      • Purinergic receptors
  • Local chemical factors
    • O2 Ø
    • O2 excess
    • H+ (↑)
    • Lactic acid level (↑)
    • K+ (↑)
  • Vasodilation
  • Spontaneous generation of SM AP
    • Pacemaker
    • Slow wave potential
      • Local potential
    • Self-excitatory
    • Spike potential (AP)
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2
Q

Where are smooth muscles found?

A
  • Visceral organs
    • Gastrointestinal muscles (single-unit)
    • Muscles of vessels (single-unit)
    • Bladder of sphincters (single-unit)
  • Bronchial muscles (single-unit)
  • Eyes - m. ciliaris (multi-unit)
  • Skin (multi-unit)
  • Develop from one cell and have only one nucleus
  • Can be formed throughout life
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3
Q

Basics of smooth muscles

A
  • Poor blood supply
  • Small, spindle shaped cells
  • Non-striated
  • Non-regular myofilaments
  • Intermediate filaments
  • Dense bodies
  • Small sarcoplasmic reticulum
  • T-tubules Ø
  • Sarcomere Ø
    • Each smooth muscle cell is like one giant sarcomere
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4
Q

What are the major types of smooth muscle?

A
  1. Multi-unit smooth muscle
  2. Single-unit smooth muscle
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5
Q

Multi unit smooth muscle

A
  • Individual fibers
  • Ø gap junctions
  • Contraction is independent in each fiber, and stimulated by nerves
  • Not trough AP
  • Spontaneous contraction is rare
  • Transmitters cause local depolarization
  • Fibers are isolated by:
    • Collagen
    • Glycogen
  • Innervation:
    • Induvidal innervation
  • Ligand:
    • Parasympathetic: ACh
    • Sympathetic: norepinephrine (and ATP)
  • Receptor:
    • Muscarinic
    • Alpha-1-receptor
  • Location:
    • M. ciliaris (eye)
      • Adjusting the diameter of the pupils according to the intensity of ligh
      • Altering the curvature of the lens in the eye
    • Skin
      • Changing the angle of hairs relative to skin surface
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6
Q

Single-unit smooth muscle

A
  • Millions of fibers contracting all at once, creating a functional system
  • Spontaneous contraction may happen
  • Lots of gap junctions
  • Fast penetration of ions
  • Fast spreading of AP
  • Within single-unit cells, the whole bundle or sheet contracts as a syncytium
  • Sustained contraction of the smooth muscle in walls transfers pressure to the content or the organ, while alternating contractions and relaxations lead to mixing of the content
  • Can also create waves of contraction = peristaltic movements
  • Bayliss effect: Extension of certain smooth muscles results in contraction
  • Self-reflection (myogenic response) of smooth muscle
    • Unrelated to neural and hormonal influences
  • Innervation:
    • Humoral regulation, active contraction and relaxation
  • Ligand:
    • ACh
    • Norepinephrine
    • VIP
    • NO
    • ATP
  • Receptor:
    • mACh receptor
    • Aplha-1 receptor
    • Beta-2 receptor
  • Location:
    • Walls of hollow and tubular organs
      • ​Gastrointestinal muscles
      • Muscles of vessels
      • Bronchial muscles
      • Bladder of sphincters
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7
Q

What is varicosities?

A
  • Varicosities: the axon terminal
  • A series of axon-like swelling, from autonomic neurons form motor units through the smooth muscle
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8
Q

Molecular structure of smooth muscle sarcomere

A
  • Myosin
    • Class II in SM
      • 2 heavy chains
        • 2 heads
      • 4 light chains
    • Thick filamet
    • MLC subunit:
      • P-LCh (ADP+P)
        • Non-phosphorylated: Ø bind to actin
        • Phosphorylated: can bind to actin → contraction
  • Actin
    • Attached to protein lattices (dense bodies)
      • Analogous to the Z-disc
    • Thin filaments
    • G-actin
    • F-actin
  • Tropomyosin
    • Inactive status: blocks 7 binding sites
    • Active status: in groove of α-helix lives binding sites
  • Calmodulin
    • Calmodulin-Ca2+ complex
    • Removes tropomyosin from binding sites
  • Caldesmon
    • Ø Ca2+ = caldemosin keeps tropomyosin on binding sites
  • Caveoles
    • Rudimetary T-tubules
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9
Q

Organization of acin-myosin filaments in smooth muscles

A
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10
Q

Sarcoplasmic reticulum is smooth muscles

A
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11
Q

Source of Ca2+

A
  1. Sarcoplasmic reticulum
  2. EC space
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12
Q

Channels found on the myolemma of smooth muscles

A
  • Voltage gated Ca2+ channels
    • More than in skeletal muscles
    • More than Na+ channels
  • Ligand gated Ca2+ channels
    • ​Hormone activated
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13
Q

Characteristics of smooth muscle contraction

A
  • Prolonged tonic contraction
    • Hours, days
    • Length of contraction is 30x longer than in skeletal muscles
  • Lower frequency of cross-bridge cycle
    • Reason:
      • Lower ATPase activity → Slower ATP catabolism → Slower myosin head power-stroke
  • Energetically economic
    • 1 ATP/cross-bridge cycle
      • Irrespective of the length of contraction
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14
Q

Factors causing contraction in smooth muscles

A
  1. Spreading of sympathetic (alpha1) or parasympathetic (mACh) neural AP to the myolemma and its effect on voltage gated ion channel
  2. Result: Ca2+ influx
  3. Binding of chemical ligands to ligand gated calcium channels
  4. IC IP3 release and G-protein or phospholipase C mediated, ligand gated, Ca2+ influx from sarcoplasmic reticulum or from a calcium sequester vesicle
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15
Q

Local chemical factors influencing smooth muscle contraction

A
  1. Lack of O2
  2. Excess of O2
  3. H+
  4. Lactic acid level ↑
  5. K+

Relaxation → vasodilation

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16
Q

Relaxation of smooth muscles

A
  • Relaxation is enhanced by every stimulus which can increase IC cAMP or CGMP level
    • Decreases IC Ca2+ concentration
  • Most important signal are:
    • Sympathetic beta2 receptor agonists
      • Epinephrine
      • VIP
    • NO (direct, or diffusible from capillary endothelium)
    • ATP (acts on purinergic receptors)

Relaxation → vasodilation

17
Q

Action potential in smooth muscles

A
  • AP occurs only in single-unit smooth muscles

  • Types of AP:
    1. Peak potential
      • Can be initiated:
        • Electric stimuli
        • Hormones
        • Generated spontaneously (by pacemaker activity)
    2. AP with plateau
      • Prolonged repolarization
  • Smooth muscle contraction functions under very intensive humoral and metabolic regulation (instead of intensive neural activation)
  • Spontaneous generation of SM AP
    • Pacemaker of slow wave potential
      • ​Slow wave potential is not an AP, but a local potential. If it increases above -35 mV, it initiates AP
      • Cause of slow wave potential is unknown
    • AP (spike potential)
    • Some SM are self-excitatory