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Year 1 - Term 2: Carriage of Oxygen > 6. Smooth & Cardiac Muscle > Flashcards

6. Smooth & Cardiac Muscle Flashcards

1
Q

What is this muscle?

A

Skeletal

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2
Q

What is this muscle?

A

Cardiac

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3
Q

What is this muscle?

A

Smooth

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4
Q

What are the characteristics of

a) skeletal muscle
b) cardiac muscle
c) smooth muscle

A

a) striated, multinuclear and peripheral, for locomotion, sarcomeres, Ca2+ binding=troponin
b) striated, meshwork, central nucleus, intrinsic myogenic activity, sarcomeres, Ca2+ binding=troponin
c) involuntary, non-striated, 1 nucleus per fibre, spindle shape, mechanical organ control, no sarcomeres, Ca2+=calmodulin

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5
Q

Do skeletal, cardiac and smooth have cellular junctions?

A

skeletal - none

cardiac - intercalated discs, gap junctions

smooth - gap junctions

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6
Q

What is an intercalated disc and where are they found?

A

Thickenning of sarcolemma, connects adjoining cardiac myocetes e.g desmosomes and gap junctions. Found in cardiac muscle only

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7
Q

Label A-F

A

A: gap junction

B: intercalated disc

C: sarcoplasmic reticulum

D: A band (thick)

E: I band (thin)

F: Z disc

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8
Q

Cardiac cells have automaticity and rhythmicity - what does this mean?

A

Can spontaneously generate electrical impulses (depolarise) in a regular and repetitive manner

(pacemaker cells in SAN and AVN)

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9
Q

Cardiac myocetes from an electical/functional syncytium - what does this mean?

A

Electrical impulses propagate between cells via gap junctions on intercalated discs, waves of depol. propagate to adjacent cells which contract in a synchronous fashion

NB: diff size/shape of APs in heart and many ion channels involved in response. Na+ Ca2+ depol, and K+ repol

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10
Q

What two types of cells are found in the heart?

A

Pacemaker cells (SAN, AVN, have automacity)

Ventricular cells (have refractory periods)

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11
Q

Describe the process of Ca2+ signalling during cardiac contraction.

A
  1. Na+ in, membrane depolarises, VGCa2+ channels open (L type)
  2. Ca2+ influx, intracellular Ca2+ increases triggering Ca2+ release from sarcoplasmic reticulum
  3. Ca2+ associates with troponin C in sarcomere and stimulates contraction (systole) (unmasks binding site for M to bind with A)
  4. Ca2+ released from sarcomere causes diastole and its reuptake into sarcoplasmic reticulum

NB: ATP hydrolosis provides energy to drive filament sliding

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12
Q

What happens to the heart under sympathetic and parasympathetic modulation?

A

Sympathetic: increased heart rate and contraction force, NA secretion and activation of beta1 adrenoreceptor

Parasympathetic: decreased heart rate, ACh secretion and activation of muscarinic receptors (M2)

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13
Q

Label A-D

What is this structure?

A

A: intermediate filament

B: dense body

C: mechanical junction coupling cells

D: gap junction for electrical and chemical communication

Smooth muscle

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14
Q

Describe smooth muscle.

What do intermediate filaments do?

What do dense bodies do?

What are the 2 types of attachments between cells?

A

Loose lattice of thick and thin filaments running obliquely across muscle.

Assist in transmission of contraction force

Attachements for thick and thin filaments

Mechanical and gap junctions (electical signals)

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15
Q

List the structures where smooth muscle is found

A
  • Bladder
  • Gut (oseophagus, stomach, intestines) (propel food through GI tract)
  • Uterus (deliver baby)
  • BVs (regulate BV diameter)
  • Bronchi (regulate airway diameter)
  • Urethra, bladder
  • Errector pili in skin
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16
Q

What innervates smooth muscle?

Where do nerves make multiple contacts with a smooth muscle cell? Describe the process.

What are the 2 forms of contraction initiation in smooth muscle?

A

ANS

Varicosities. They release NT into space surrounding muscle, NT receptors widely spread across postsynaptic membrane.

  1. gap junction connections 2. neuronal innervation (ANS)
17
Q

What are the 2 types of smooth muscle organisation?

What are the differences?

A
  1. multiunit SM 2. single unit SM

Multiunit SM: each cell receives synaptic input and contracts independantly, LITTLE ELECTRICAL COUPLING. For fine control and gradual responses e.g. intrinsic eye muscles, large BVs

Singleunit SM: ANS innervates 1 cell within sheet/bundle, AP propagated by gap junctions, WHOLE BUNDLE/SHEET CONTRACATS as functional syncytium. For slow, steady contractions e.g. visceral oragns - GI tract

18
Q

What types of cells are A and B?

A

A: Multiunit SM cell

B: Single unit SM cell

19
Q

Compare SM action potential generation to skeletal

A

AP in SM longer (10-50ms) than skkeletal (2ms)

SM depol depends mainly on opening of VGCa2+ channels

Ca2+ channels open more slowly than Na+ channels, so slower uptake and longer duration of AP than skeletal

Contribution of each ion depends of type of muscle e.g. in gut vs. bladder

20
Q

How can SM cells be like pacemaker cells?

A

Can be capable of initiating spontaneous electrical activity to generate regular and repetitive oscillation in membrane potential (slow waves)

21
Q

What are the two mechanisms leading to a rise in intracellular Ca2+ in SM?

A
  1. Membrane depol opens VGCa2+ channels
  2. Agonist-induced Ca2+ reease via IP3

Then for both: Ca2+ released from sarcoplasmic reticulum -> Ca2+ calmodulin -> activates myosin-light chain kinase -> MLCK phosphorylates myosin -> increases ATPase activity and allows M to bind A -> contraction

22
Q

How does SM contract?

A

Actin slides past myosin pulling on dense bodies -> DB pull on intermediate filmanet networks -> entire muscle fibre contracts (ends pulled towards centre)

23
Q

What are the 3 triggers for SM contraction?

A
  1. hormones
  2. neural stimulation
  3. local factors e.g. in certain locations like visceral organ walls, muscle stretching can trigger contraction
24
Q

What is the mechanism for parasympathetic and sympathetic control of bronchial SM?

What treatments work on each?

A

Parasympathetic: ACh/M3 type muscarinic receptors. Treatment: short/long acting muscarinic antagonists e.g. ipatropium, tiotropium

Sympathetic: Adrenalin/NA/beta-2 adrenergic receptor. Treatment: long or short acting beta agonists e.g. salmererool, salbutermol

Year 1 - Term 2: Carriage of Oxygen (53 decks)

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