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Cardiorespiratory > 2. Smooth and Cardiac muscle > Flashcards

2. Smooth and Cardiac muscle Flashcards

1
Q

What are the three main types of muscle in the body?

A

Skeletal
Cardiac
Smooth

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2
Q

Describe skeletal muscle

A

Voluntary muscle
Anchored to bone by tendons
Multinucleate - these are peripherally located
Clear cross striations of actin and myosin
Important in locomotion and breathing
No cellular junctions
Neuromuscular junctions

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3
Q

Describe cardiac muscle

A

Involuntary muscle
Fibres have centrally located nuclei
Cardiac myocytes are organised in a branched meshwork of fibres which run in various directions
Intrinsic myogenic activity - responsible for beating of the heart
Contractile elements are similar to skeletal muscle - actin and myosin comprised of a sarcomere
Intercalated disks have gap junctions
No neuromuscular junctions

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4
Q

Describe smooth muscle

A

Involuntary
Non-striated
Spindle-shaped fibres (wide in the middle and tapered at both ends)
Single nucleus
Provides mechanical control of organ systems
Gap junctions
No neuromuscular junctions

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5
Q

Describe the composition of cardiac muscle in detail

A

Have myofibrils that are comprised of sarcomeres - run from Z disk to Z disk containing actin (thin) and myosin (thick)
Packed full of mitochondria - requires ATP for contraction
Contains sarcolemma - specialised plasma membrane in muscle cells - arranged so it runs into the fibres and action potentials can get right to where they’re needed
Contains gap junctions - connect the cells to each other - allow ions and very small molecules to pass through
Intercalated disks join the fibres together - these are sites of thickening of the sarcolemma where the cardiac myocytes are joined together

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6
Q

Describe cardiac myocytes and how they work with one another

A

These form ‘electrical syncytium’ or ‘functional syncytium’
The electrical impulses can propagate freely between cells in every direction
Cells contract in synchronous fashion - this is important for the pumping action of the heart
Wave of depolarisation propagates to the adjacent cells via the gap junctions in the intercalated disks - this allows rapid, synchronous depolarisation of the myocardium

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7
Q

Describe the composition of cardiac muscle in detail

A

Have myofibrils that are comprised of sarcomeres - run from Z disk to Z disk containing actin (thin) and myosin (thick)
Packed full of mitochondria - requires ATP for contraction
Contains sarcolemma - specialised plasma membrane in muscle cells - arranged so it runs into the fibres and action potentials can get right to where they’re needed
Contains gap junctions - connect the cells to each other - allow ions and very small molecules to pass through
Intercalated disks join the fibres together - these are sites of thickening of the sarcolemma where the cardiac myocytes are joined together
These disks also contain desmosomes and gap junctions - gap junctions link the cells electrically

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8
Q

Describe cardiac myocytes

A

These form ‘electrical syncytium’ or ‘functional syncytium’

The electrical impulse

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9
Q

Describe the sequence of action potentials in cardiac muscle

A

In muscle cells, the action potential is the first step in the chain of events which lead to the contraction
Many action potentials in the heart - properties of these vary with different locations of cardiac cells in the heart e.e. SA node, AV node, bundle of His, atrium, ventricle

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10
Q

What are the two different tissue types/types of cells in the heart?

A

Pacemaker tissue

Ventricular cells

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11
Q

Describe pacemaker tissue of the heart

A

SAN and AVN
Spontaneously depolarise
Have automaticity SO ability to initiate their own beat
Contain different ion channels - allows for initiation of different action potentials
Don’t have a steady, flat baseline - have a leaky baseline that causes the depolarisation

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12
Q

How is the cardiac muscle modulated by the autonomic nervous system

A

The autonomic nervous system can have both sympathetic and parasympathetic effects on the cardiac muscle/cardiac myocytes

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13
Q

Give the mechanisms of calcium signalling during cardiac contraction

A
  1. Depolarisation of the sarcolemma due to influx of Na+ causes opening of Ca2+ VGCs
  2. Cardiac contraction is initiated by the influx of the Ca2+ through the L type VGCs (LTCC) in the sarcolemma
  3. The rise in intracellular Ca2+ triggers further Ca2+ release from the sarcoplasmic reticulum (store of calcium) by the RYANODINE RECEPTOR (RyR)
  4. The calcium associates with troponin C in the sarcomere and this stimulates sarcoplasmic reticulum (systole)
  5. Release of Ca2+ from the sarcomere causes the relaxation (diastole) and it’s re-uptake into the sarcoplasmic reticulum by SERCA
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14
Q

List common areas where smooth muscle is found

A

(Provides mechanical control of organ systems)
Bladder
Uterus
Upper respiratory tract

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15
Q

Briefly describe smooth muscle

A

Involuntary
Non-striated muscle
Heterogenous group of muscle
Wide range of physiological properties

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16
Q

List common areas where smooth muscle is found

A 
(Provides mechanical control of organ systems)
Bladder
Uterus
Upper respiratory tract
Gut (oesophagus, stomach, intestines)
Blood vessels
Bronchi
Urethra
Erector pili in the skin
17
Q

Describe in detail the structure of smooth muscle

A

Loose lattice of actin and myosin - these run obliquely across the muscle (SO not striated)
Cytoskeletal intermediate filaments - these aid the transmission of force within muscle contraction
Dense bodies - serve as attachments for the actin and myosin (equate to Z lines in striated muscle)
Two types of attachment:
-Mechanical attachment between cells
-Gap junctions provide provide a pathway for electrical signals

18
Q

List common areas where smooth muscle is found

A

(Provides mechanical control of organ systems)
Bladder
Uterus
Upper respiratory tract

19
Q

Describe in detail the structure of smooth muscle

A

There

20
Q

What are the two different types of smooth muscle in terms of the way it is innervated?

A

Multiunit smooth muscle (works more like skeletal)

Single unit smooth muscle (works more like cardiac)

21
Q

Describe the mechanism of contraction of smooth muscle

A

Innervation occurs via the autonomic nervous system
Nerves make multiple contacts with the muscle cells called VARICOSITIES - these release neurotransmitter in space surrounding the membrane and the receptors are widely spread across the post-synaptic membrane
Gap junctions also permit electrical coupling between cells
Both are used in cells and the degree of each usage is tissue specific

22
Q

What are the two different types of smooth muscle?

A

Multiunit smooth muscle (works more like skeletal)

Single unit smooth muscle (works more like cardiac)

23
Q

Describe single unit smooth muscle

A

ANS innervates single cell within a sheet or bundle
Action potential is propagated by gap junctions to neighbouring cells
Contraction occurs as a bundle or sheet as a functional SYNCYTIUM
Generally produces slow, steady contractions - allows substances to move through the body e.g. digestive tract

24
Q

Where is single unit smooth muscle found?

A

Found in the walls of all visceral organs (apart from the heart)

25
Q

Describe single unit smooth muscle

A

ANS innervates single cell within a sheet or bundle
Action potential is propagated by gap junctions to neighbouring cells
Contraction occurs as a bundle or sheet as a functional SYNCYTIUM
Generally produces slow, steady contractions

26
Q

Where is single unit smooth muscle found?

A

Found in the walls of all visceral organs (apart from the heart)

27
Q

Describe the different action potentials that occur in smooth muscle

A

There are different types - simple spike, spikes followed by a plateau, spikes on top of slow waves
Action potentials last much longer than in skeletal muscle
Dependent on the opening of Ca2+ VGCs (sometimes Na+)
Ca2+ VGC open more slowly than Na+ and so there is a slower contraction compared to skeletal muscles
Contribution of each ion depends on the type of muscle

28
Q

Describe how smooth muscle can be regulated

A

Contraction stimulated by:
Hormones
Neural stimulation
ANS
Local factors
In certain locations, e.g. walls of visceral organs, stretching of muscle stimulates contraction (stretch-relaxation response)
Smooth muscle also expresses wide variety of neurotransmitter and hormone receptors

29
Q

Give the mechanism of contraction of smooth muscle

A
  • Thin filaments slide past the thick filaments and pull on the dense bodies
  • These dense bodies pull on the intermediate filament network throughout the sarcoplasm
  • This arrangement causes the entire muscle fibre to contract - ends are pulled towards the centre and the midsection bulges
30
Q

Describe how smooth muscle can be regulated

A

Contraction stimulated by:
Hormones
Neural stimulation
ANS
Local factors
In certain locations, e.g. walls of visceral organs, stretching of muscle stimulates contraction (stretch-relaxation response)
Smooth muscle also expresses wide variety of neurotransmitter and hormone receptors

31
Q

What are the two different types of smooth muscle?

A

Vascular smooth muscle

Bronchial smooth muscle

32
Q

Describe vascular smooth muscle

A

Found within, and composes, majority of the wall of blood vessels

33
Q

Describe the sympathetic impact on bronchiole smooth muscle

A

Causes bronchiole dilation
Adrenaline/Noradrenaline - B2 adrenergic receptor
Short acting beta agonists or long acting beta agonists

34
Q

Describe the parasympathetic impact on bronchiole smooth muscle

A

Causes bronchiole constriction
Mucus secretion
Actylcholine - muscarinic receptprs (M3)
Short acting or long acting - can be used as treatments

35
Q

Describe the sympathetic impact on bronchiole smooth muscle

A

Causes bronchiole dilation
Adrenaline/Noradrenaline - B2 adrenergic receptor
Short acting beta agonists or long acting beta agonists

36
Q

What is meant by the ‘excitation - contraction’ coupling in smooth muscle?

A

Excitation of the smooth muscle stimulates and is followed by the contraction of the smooth muscle
These two stages happen consecutively

Cardiorespiratory (11 decks)

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