MMED1005 Lecture Notes - Lecture 21: Vagus Nerve, Medulla Oblongata, Depolarization

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Cardiovascular system lecture 2: how does the heart work?
Learning objectives:
- Describe the structural and functional properties of cardiac muscle
- Explain the conduction system of the heart
- Describe the movement of blood during the cardiac cycle
- Define cardiac output
- Explain the intrinsic and extrinsic factors involved in the regulation of heart rate and
stroke volume
Main points:
- Cardiac muscle cells contain sarcomeres that are responsible for muscle contraction
- Blood flow through heart is determined by pressures in chambers and presence of
unidirectional valves
- The frequency of pacemaker action potentials drives heart rate which can be
increased by sympathetic stimulation and decreased by parasympathetic stimulation
- An increase in venous return will increase stroke volume. Stroke volume can also be
increased by stimulation of the SNS which increases force of contraction
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Muscle cells: also known as myocytes
- Found in 3 places:
o Attached to the skeleton (skeletal)
o Hollow organs (smooth)
Stomach, bronchi, blood vessels
o Heart (cardiac)
Skeletal muscle:
- Voluntary muscles (innervated by the somatic nervous system)
- Striated (due to overlapping thick and thin filament)
- Multinucleated
- Non-branched
- Primary role: movement of the body
Smooth muscle:
- Involuntary muscle (innervated by the ANS autonomic nervous system)
- Non-striated
- Single nucleus
- Tapered
- Primary role: move contents within a hollow organ (blood vessel, intestine)
Cardiac muscle:
- Involuntary muscle (ANS)
- Striated
- Single nucleus
- Branched
- Intercalated disks makes these cells unique from other muscle cells
- Primary role: pump blood out of the heart
- ***remember from the previous lecture that the myocardium (thickest, middle layer
of the heart) is comprised of muscle fibres
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Inside the muscle cell definitions: (sarco = flesh)
- sarcolemma: muscle cell membrane
- sarcoplasm: cytoplasm of a muscle cell
- sarcoplasmic reticulum: specialised endoplasmic reticulum of muscle cells
- sarcomere: structural unit of a myofibril
- transverse (T-) tubule: plasma membrane extends deep into the cell
Inside the muscle cell: myofibrils
- made up of myofibrils (intracellular structure)
- each myofibril contains repeated sections of sarcomere
- each sarcomere contains actin and myosin (proteins) that
slide past each other when the muscles contract and relax
Cardiac muscle:
- connected by intercalated discs
- intercalated discs have two components that form a
syncytium
o desmosomes
strong mechanical connections that tie
adjacent cells together
o gap junctions provide ionic and electrical
continuity between adjacent cells
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Document Summary

Describe the structural and functional properties of cardiac muscle. Explain the conduction system of the heart. Describe the movement of blood during the cardiac cycle. Explain the intrinsic and extrinsic factors involved in the regulation of heart rate and stroke volume. Cardiac muscle cells contain sarcomeres that are responsible for muscle contraction. Blood flow through heart is determined by pressures in chambers and presence of unidirectional valves. The frequency of pacemaker action potentials drives heart rate which can be increased by sympathetic stimulation and decreased by parasympathetic stimulation. An increase in venous return will increase stroke volume. Stroke volume can also be increased by stimulation of the sns which increases force of contraction. Found in 3 places: attached to the skeleton (skeletal, hollow organs (smooth, stomach, bronchi, blood vessels, heart (cardiac) Voluntary muscles (innervated by the somatic nervous system) Striated (due to overlapping thick and thin filament) Involuntary muscle (innervated by the ans autonomic nervous system)

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