Week 6 The cardiovascular system (control of contraction) Flashcards
Vertebrate hearts are neurogenic/myogenic?
Myogenic
Define Myogenic.
ability to generate spontaneous rhymical depolarisations
the rate of depolarisation varies
What are pacemaker cells?
specialized cardiac muscle cells which are more excitable than the others and therefore contract first (Cardiac muscle contracts without neural stimulation)
- fast intrinsic rhythm of firing - determunes contraction rate
- Fish - sinus venosus
- Other vertebrates - sinoatrial node (SAN)
What type of cell is this?
rod shapped cardiac myocyte.
How does cardic muscle vary from skeletal muscles or others?
How they are joined together through intercalated discs containing desosomes enables cells to be myogenic and communicate very well with eachother (unobstructedly - no walls that take time to pass) - fluid like movement, depolisation moves uninterrupedly.
Cardiac muscle: What is the role of desosomes and gap junctions?
- desosomes: transfer the force from cell to cell
- gap junctions: allow passage of electrical signals
Cardiac muscle: how are intercalated discs formed?
- formed from plasma membrane of 3 adjacent cells which are intertwined and bounded together by gap junctions and desosomes
- cells binding together mechanically, chemically and electrically results in their acting together
How does sacromeres of cardiac muscle differ from skeletal muscle?
- have the same banding patters
- but cardiac sarcomeres have branching fibrillar networks which are continuous in three dimesion throughout the cytoplasm
How does the sacroplasmic reticulum and the T system function?
- The plasma membrane invaginates traversely forming tubular system (T tubules) between cisternae.
- contain voltage-sensor proteins which activate when membranes depolarize
- induced sarcoplasmic reticulum to release Ca2+
- T tubules and adjacent cisternae form a diad
Uses of Energy (ATP) in the heart:
- enormous energy demand is related primarily to ATP-dependent processes driving Excitation Contraction coupling (movement of ions)
- about 70–75% of total intracellular ATP is used for force generation powering work output
- remaining 25–30% is used for basal metabolism
What is the key regulator of EC in the heart?
Sodium-Potassium Pump, maintains sodium levels with a careful change.’
permiability of sodium increase/decreases the action potencial in heart , meaning the distribution of these ions across the cardic cell membrane to maintain an electrochemical gradient.
What does Cardiac Na/K ATPase play a role in?
Na/K ATPase controls the Na/K pump.
- trans-membrane transport
- ion homeostasis
- electrical excitability
- control of cell volume and contractility
What are the properties of the pacemaker cells?
- small, few myofibrils, mitochondira & other organelles
- do NOT contract
- unstable resting membrane potencial (RMP) –> pacemaker potencial
What is the hierarchy of pacemakers?
different action potencials for the pacemakers
How does the cardiac conduction system work?
reliant on the desmosomes and gap junctions.
- conduction from SA to AV node via atrial muscle is slow
- contraction through AV node is slow - AV pause
- allows ventrivular filling to occur before passing on the electrical impulse
- prevents transmission of high rates from the atria
- conduction through the V is fast
- allows for apex to contract before base.
What is excitation - contraction coupling?
action potencial resulting in contraction
- action potencial generation (electrical activity based on ion movement) occurs first, resulting in the intracellular Ca2+ concentration altering, then resulting in the tension of cardiac muscle
EC coupling in cardiac muscles: detail with T-Tubules:
- AP enters from adjacent cells opening the Ca gates voltage channels, Ca2+ enters incuding local release of Ca.
- Ca2+ binds to troponin to initiate contraction
- relaxation occurs when Ca2+ unbinds
- Ca2+ pumped back into sarcoplasmic reticulum to be sotres ready for next contraction
Pacemaker Cell Action Potential: What occurs during pacemakerpotencial?
action potencial is the transient depolization of the cell
- unstable RMP ( resting metabolic potencial)
- ‘funny’ (pacemaker channels) channel opens, resuling in the:
- ↑permiability to Na+
- ↓K+ efflux (to balance charges)
- ↑membrane potencail
Pacemaker Cell Action Potential: What occurs during the steap incline?
- membrane near threshold
- T-type Ca2+ channels open resulting in depolarization & AP
Pacemaker Cell Action Potential: What occurs during action potencial?
- T-type Ca2+ channels open
- K+ channels open
- repolarisation of cell
What are the features of cardiac muscles that ensure a rapid spread of electrical activity?
Intercalated discs - link adjacent cells
- gap junctions (pathway for electrical current to spread from cell-cell)
- Electrotonic current speed
- desosomes (mechanically hold cells together)
What is the order of events for conduction?
- starts at SNA
- spreads through both A - internodal pathway
- passes though AVN
- spreads through V - bundles of His, Purkinje fibres
- contraction begins at apex
What is an AV nodal delay?
Delay = 0.1 s
- ensures that A contraction precedes V contraction
- allows complete centricular filling
What sets the heart rate (HR)?
the rate of action potencial firing in pacemakers
What are the hormones that control the HR?
- norepinephrine (increases HR) - sympatheic neurons
- epinephrine (increases HR) - adrenal medulla
- acetylcholine (decreases HR) - parasympatheic neurons
How do these hormones control the HR?
