LECTURE 9 Flashcards
structure of cardiac muscle
Mononucleated cells. 100µm in length
Striated: crossbands of the muscle contraction apparatus are visible (z-bands)
Intercalated discs between: made up of gap junctions, which allow the transmission of ions and the action potential
This arrangement means that the muscle works as a functional syncytium: it works as one unit.
3 specialist features for conduction in the cardiac muscle
desmosomes, intercalated discs and gap junction
specialist features for conduction in the cardiac muscle: desmosomes
hold the muscle cells together tightly
specialist features for conduction in the cardiac muscle: intercalated discs
link muscle cells together and contain desmosomes and gap junctions
specialist features for conduction in the cardiac muscle: gap junctions
Allow passage of action potentials from one cell to the next, very quickly – allows the cardiac muscle to function together as a syncytium
Difference in action potential in cardiac vs skeletal muscle
- Cardiac resting potential : -90mV (not -70mV)
- action potentials are slower
- extended refractory, depolarisation and repolarisation
What is hypoxia
- resting potential is higher
- affects Na and K ion channels
- can lead to arrythmias
Why do cardiac action potentials have a long refractory period
The long refractory period is essential to allow relaxation (and filling) of ventricles between contractions – if further action potentials were triggered too quickly, the heart would not function effectively as a pump.
What external influences can interrupt rhythm
- caffeine
- nicotine
What regulatory system co-ordinates heart contraction
autonomic nervous system
Neural control of Heart Rate
Sensory information from sensors (eg chemo and baro etc) is processed in the medulla oblongata
Triggers an ANS response
- Sympathetic NS (cardiac accelerator nerves) increase HR and contractility. Physical and emotional stress will increase HR
- Parasympathetic NS (Vagus nerves) decrease HR
factors that increase SA node firing
Muscarinic receptor antagonist
β Adrenergic receptor agonists
Circulating catecholamines
Hypokalemia
Hyperthyroidism
Hyperthermia
factors that decrease SA node firing
Muscarinic receptor agonist
β blockers
Ischaemia/hypoxia
Hyperkalemia
Sodium and calcium channel blockers
Hypothermia
which sex has a higher heart rate
females
what is tachycardia
increased heart rate (>100bpm) through stress, drugs, heart disease
If persistent, leads to death
