Smooth And Cardiac Muscle Flashcards
What is cardiac muscle responsible for?
Cardiac muscle is involuntary muscle with its intrinsic myogenic activity responsible for the beating of the heart
How are cardiac muscle fibres arranged?
Cardiac myocytes are organised in a branched mesh work of fibres with centrally located nuclei that run in various directions
What is smooth muscle responsible for?
Smooth muscle is involuntary non-striated muscle that provides mechanical control of organ systems
How are smooth muscle fibres arranged?
Smooth muscle fibres are spindle shaped fibre that have a singular nucleus and are arranged in rows
What are the specialised properties of cardiac muscle?
- cardiac monocytes form an electrical synctium or functional syncytium
- electrical impulses propagate between cells via gap junctions
- allows rapid synchronous depolarisation of myocardium
- myocardium acts as a singular contractile unit
- waves of depolarisation propagate to adjacent cells
What’s are intercalated discs in cardiac muscle and what do they contain?
- intercalated discs connect adjoining cardiac monocytes
- fascia adherens or anchoring junctions attach sarcomere to cell membrane
- desmosomes sites of adhesion keep cells connected when they contract
- gap junctions facilitate electrical communication
How is an action potential made in cardiac muscle?
- action potential is shaped by a delicate balance between fluxes of ions in and out of the cell
- depolarising currents are through sodium and calcium channels
- repolarising currents are through potassium channels
What is automaticity and rhythmicity in cardiac muscle?
- rhythmicity means cardiac cells can generate action potentials in a regular and repetitive manner
- automaticity means they can spontaneously generate an electrical impulse (depolarise)
What are the key points about action potentials in the heart?
- size and shape can differ between cells
- shape of cardiac AP relates to its function within the heart
- voltage-dependant ion channel proteins in plasma membrane generate APs
- cells have different kinds of voltage dependant on ion channels
What are pacemaker cells?
- cells of the sinoatrial and atrioventricular nodes (pacemaker tissues) that can depolarise spontaneously
Describe the process of calcium signalling
- depolarisation of membrane (influx of Na) opens voltage gated calcium channels
- influx of calcium through voltage gated calcium channels (LTCC)
- rise in intracellular calcium triggers further calcium release from sarcoplasmic reticulum by the ryonodine receptor
- calcium then associates with troponin C in the sarcomere to initiate contraction in cardiac muscle (systole)
- these events are terminated by the release of calcium from the sarcomere (causing relaxation diastole) and it’s re uptake into the sacroplasmic reticulum
Describe the effects of sympathetic innervation on cardiac muscle
- increases heart rate and force of contraction
- secretion of noradrenaline and activation of beta1 adrenoreceptor
Describe the effects of parasympathetic innervation on cardiac muscle
- decreased heart rate
- secretion of acetylcholine and activation of muscarinic receptors
How do ventricular cells contract?
- contract in a coordinated fashion to pump blood
- have a refractory period in which ion channels are inactivated and muscle is unresponsive
- however hard heart of stimulated individual contractions can’t fuse into a maintained tetanic contraction
Where is smooth muscle found?
Smooth muscle in found on the walls of organs and structures:
- bladder
- gut (oesophagus, stomach, intestines)
- Uterus
- blood vessels
- bronchi
- urethra
- erector pili in the skin
