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CardioRespiratory Year 1 > Microanatomy - Smooth and Cardiac Muscle > Flashcards

Microanatomy - Smooth and Cardiac Muscle Flashcards

1
Q

Describe the structure of smooth muscle

A
  • single nucleus in the central location
  • actin and myosin but no bands
  • no Z discs present
  • no T tubules
  • gap junctions
  • no neuromuscular junctions, contraction is intrinsic so therefore it is either neural or hormonal
  • calmodulin is what calcium binds to
  • non striated
  • involuntary
  • spindle shaped
  • loose lattice of thick and thin filaments that run obliquely across the muscles
  • Filaments of the contractile proteins are attached to the plasma membrane at junctional complexes
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2
Q

Function of smooth muscle

A
  • Provides mechanical control of an organ system
  • Regulation of the diameter of blood vessels
  • Regulating diameter of the airway
  • Propulsion of food through GI tract
  • Contraction of the uterus and delivery of baby
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3
Q

Describe the structure of cardiac muscle

A
  • single/double nucleus that is in the central location
  • actin and myosin which form distinct bands
  • has z lines
  • has T tubules at Z-disk diads
  • intercalated discs and gap junctions are between cells
  • no neuromuscular junctions are present as contraction is intrinsic
  • troponin is what calcium binds to
  • involuntary muscle
  • contractile elements are long thin myofibrils that contract as sacroemre shooters
  • branched
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4
Q

Describe the structure of skeletal muscle

A
  • multinuclear and in a peripheral location
  • actin and myosin form distinct bands
  • Z discs are present
  • T tubules are present at A-I junction traids
  • no cell junctions
  • neuromuscular junctions
  • troponin is what calcium binds to
  • voluntary
  • anchored to bone by tendons
  • clear cross striations consisting of actin and myosin
  • multi-nucleated and peripherally located nuclei
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5
Q

What is the function of skeletal muscle

A
  • Responsible for movement such as locomotion, maintenance of posture and breathing (via contraction of the diaphragm)
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6
Q

cardiac muscle is ….

A

energy intense, ATP require for filament contraction, supplied by a rich network of capillaries,

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7
Q

What are intercalated discs

A

These are the sites of the thickening of sarcolemma where the cardiac myocytes ar joined together

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8
Q

what type of cell junctions do intercalated discs contain

A
  • desmosomes and gap junctions
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9
Q

What do gap junctions in intercalated discs allow the cardiac muscle to do

A
  • Gap junctions link the cell electrically allowing the passage of ions from cell to cell enabling the action potential to spread between cardiac cells
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10
Q

describe how the cardiac muscle causes an action potential causing contraction of the heart

A
  • Does not require action potentials from nerve to depolarise, it can depolarise spontaneously to generate an electrical-impulses, this is called automaticity
  • Cardiac cells have rhythmicity that is they can generate action potentials in a regular and repetitive manner
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11
Q

What is automaticity

A

when muscle and other cells can depolarise spontaneously to generate an electrical impulse

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12
Q

What are the specialised properties of cardiac muscle

A
  • Cardiac myocytes form an electrical syncytium which means they are electrically joined together
  • Electrical impulses can propagate between cells via a gap junction located on the intercalated disc
  • Waves of depolarisation propagate to adjacent cells which contract in a synchronous wavelike fashion
  • This allows rapid synchronous depolarisation of the myocardium
  • The myocardium functions as a single contractile unit which is important for the pumping action of the heart
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13
Q

What are the key ion channels involved in the action potentail

A
  • repolarising currents the potassium ion channel is the important channel
  • depolarising current the sodium and calcium channels are important
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14
Q

Describe the properties of action potentials within the heart

A
  • Size and shape of the action potentials can differ between cells.
  • The shape of the cardiac action potential relates to its function within the heart.
  • Voltage-dependent ion channel proteins in the plasma membrane generate the action potentials.
  • Cells have different kinds of voltage-dependent ion channels
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15
Q

what are pacemaker cells in the cardiac muscle

A

the are the cells of the pacemaker tissues which are the SAN and AVN, they depolarise spontaneously this is called automaticity

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16
Q

when to atrial and ventricular cells display automaticity

A
  • only in disease not normally as normally automaticity is driven by pacemaker cells
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17
Q

what are the ventricular cells

A
  • these are the work cells, they have different shaped action potentials
  • they contract in an coordinated fashion to pump blood around the heart
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18
Q

describe the refractory period in the heart

A
  • Refractory period – during the refractory period the ion channels are inactivated and the muscle is unresponsive
  • Means that however hard the heart is stimulated individual contractions cannot fuse into a maintained tetanic contraction as it happens in skeletal muscle
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19
Q

How does calcium signalling causes cardiac muscle contraction

A
  1. Depolarisation of the membrane (sarcoplasm) (influx of sodium via sodium channels) opens voltage gated calcium channels
  2. Influx of calcium through voltage gated (L type) calcium channels in the cell membrane
  3. The rise in intracellular calcium triggers further calcium release from the sarcoplasmic reticulum (SR) by the ryanodine receptor (RyR)
  4. Calcium then associated with troponin C in the sarcomere to initate contraction in the cardiac muscle (systole)
  5. These events are terminated by release of calcium from the sarcomere (causing relaxation, diastole) and its reuptake into the sarcoplasmic reticulum
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20
Q

calcium is important for…

A

actin and myosin interaction

- ATP hydrolysis provides the energy to drive filament sliding

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21
Q

how is the heart innervated

A
  • parasympathetic and sympathetic
22
Q

what effect does the sympathetic system have on the heart

A
  • Increased heart rate and force of contraction

- Secretion of Noradrenalin and activation of ß1-adrenoreceptor.

23
Q

what effect does the parasympathetic system have on the heart

A
  • Decreased heart rate

- Secretion of Acetylcholine and activation of muscarinic receptors (M2)

24
Q

What is the smooth muscle definition

A
  • Smooth muscle is a heterogenous group of muscle with a range of physiological properties
25
Q

Where is smooth muscle found

A
  • Bladder
  • Gut – oesophagus, stomach and intestine
  • Uterus
  • Blood vessels
  • Bronchi
  • Urethra, bladder
  • Erector pili in the skin
26
Q

What do the dense bodies do in smooth muscles

A
  • Dense bodies severe as attachments for the thick and thin filaments, they are considered to be functionally equivalent to the Z lines of straited muscle
27
Q

What are the two types of attachment in smooth muscle

A
  • mechanical attachment

- gap junctions

28
Q

What are mechanical attachment between

A

between cells

29
Q

describe the action potential in smooth muscle

A
  • Different types of action potentials in different smooth muscles
  • A simple spike followed by a plateau
  • Spikes on top of slow waves
30
Q

Describe the pacemaker cells in smooth muscle

A
  • Many smooth muscle cells are capable of initiating spontaneous electrical activity (generated by pacemaker currents)
  • This can generate regular and repetitive oscillations in the membrane potential (Vm) slow waves
31
Q

How long does the action potential last in smooth muscle

A
  • Action potential in smooth muscle is long 10-50ms last longer than skeletal muscle which is 2ms
32
Q

what does depolarisation depend on in a smooth muscle cell

A
  • Depolarisation depends on opening of voltage gated calcium channels but sodium can also contribute
  • Calcium channels open more slowly than sodium channels thus slower upstroke and longer duration of action potentials compared to skeletal muscle
  • Contribution of each ion depends on type of muscle
33
Q

What initiates the contraction of smooth muscle

A
  • autonomic nervous system regulates it
34
Q

Describe the innervation of the smooth muscle

A
  • Varicosities on the end of the post ganglionic autonomic neurone release neurotransmitter into space surrounding the muscle, neurotransmitters are widely spread across the smooth muscle cell
35
Q

what regulates the function of smooth muscle

A
  • The degree by which these two forms (neuronal innervation and gap junction connections) are used is tissue specific
36
Q

What are the two types of smooth muscle organisation

A
  • Multi unit smooth muscle

- Single unit smooth muscle

37
Q

Describe the multiunit smooth muscle organisation

A
  • In multiunit smooth muscle each cell receives synaptic input and there is little electrical coupling.
  • Innervated individually
  • Each smooth muscle cell can contract independently of its neighbor.
  • Allows for fine control and gradual responses.
  • Similar to motor unit recruitment in skeletal muscle
38
Q

What is an example of multiunit smooth muscle organisation

A

• E.g. Intrinsic muscles of the eye (smooth muscle of the iris), and smooth muscle of the larger blood vessels.

39
Q

describe single unit smooth muscle

A
  • Autonomic nervous system innervates a single cell within a sheet or bundle
  • Action potential is propagated by gap junctions to neighbouring cells
  • Whole bundle or sheet contracts as a functional syncytium
40
Q

describe an example of single unit smooth muscle

A
  • Found in walls of visceral organs expect the heart which as cardiac muscle, therefore it is sometimes called visceral muscle
  • Visceral smooth muscle produces slow, steady contractions that allow substances such as food in the digestive tract to move through the body
41
Q

what are the ways that can produce a rise in intracellular calcium in smooth muscle

A
  1. Depolarisation of the membrane opens voltage gated calcium channels and calcium enters through voltage gated calcium channels
  2. Agonist induced released of calcium via IP3- agonist binds to G protein which activates phospholipase 3 which generates IP3 which acts on sarcoplasmic reticulum via an IP3 receptor and this generates calcium into the intercellular cytoplasm
42
Q

How does calcium act in smooth muscle

A
  1. Calcium binds to calmodulin which activates the enzyme myosin light chain kinases
  2. MLCK then phosphorylated the regulatory region on the myosin light chains associated with the myosin molecule
  3. Phosphorylation of the light chain increases ATPase activity and allows the myosin head groups to bind actin and undergo cross bridge cycling
43
Q

How does smooth muscle contract

A
  • The thin filaments slide past the thick filaments pulling on the dense bodies (connected to the sarcolemma)
  • The dense bodies pull on the intermediate filament’s networks throughout the sarcoplasm.
  • This arrangement causes the entire muscle fiber to contract, the ends are pulled toward the center, causing the midsection to bulge.
44
Q

how is smooth muscle controlled

A

triggers to cause smooth muscle contraction include..

  • hormones
  • neural stimulating by the ANS and local factors
  • in certain locations such as the wall of visceral organs stretching the muscle can trigger its contraction
45
Q

What is vascular smooth muscle

A
  • A particular type of smooth muscle found within the majority of the wall of blood vessels
46
Q

what are the receptors of smooth muscle that cause contraction (vasoconstriction)

A 
Adrenergic receptor (α1)
Muscarinic receptor (M2)
Endothelin receptor
Thromboxane receptor
Purinergic receptor (P2x)
47
Q

What are the receptors of smooth muscle that cause relaxation (vasodilation)

A 
Adrenergic receptor (β2)
Histamine receptor
Adenosine receptors
Prostacyclin (PGI2)
Purinergic receptor (P2y)
48
Q

what is bronchial smooth muscle

A
  • Smooth muscle from the trachea down to terminal bronchioles as it is under autonomic control
49
Q

what is the action of the parasympathetic system on the bronchial smooth muscle

A

bronchial constriction and mucus secretion via binding to the M3 type muscarinic receptor and releasing acetylcholine

50
Q

what is the treatments for the parasymthatpic system acting on bronchial smooth muscle

A
  • Short-acting muscarinic antagonists (SAMAs) such as ipratropium.
  • Long-acting muscarinic antagonists (LAMA) such as tiotropium).
51
Q

What is the action of the sympathetic nervous system on the bronchial smooth muscle

A

bronchial dilation it does this by the noradrenaline or adrenalines bindings the B2 adrenergic receptor

52
Q

What are the treatments for the sympathetic nervous system acting on bronchial smooth muscles

A
  • Short-acting beta agonists (SABAs) such as salbutermol which typically last 4–6 hours.
    • Long-acting beta agonists (LABAs) such as salmeterol which lasts 12 hours, cause dilation.

CardioRespiratory Year 1 (28 decks)

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