Excitable Cells
- Created by: Labake
- Created on: 02-01-17 09:03
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- Excitable Cells
- Excitability of muscle cells are caused by ions that control membrane potential
- Energy used to generate heartbeat is conc. gradient of ions
- 1%= specialised conducting cells in SA node, AV node, Bundle of His, bundle branches and purkinje fibres
- 1 second reaction time to prolong the action potential for time for cells to contract
- 1%= specialised conducting cells in SA node, AV node, Bundle of His, bundle branches and purkinje fibres
- Membrane proteins control passage of ions and thus control generation and strength of heartbeat
- Cells at resting potential are highly NEGATIVE, when depolarised they become less negative
- Resting cells: High K+ conc, low Ca2+ and Na+ conc.
- When Ca2+ and Na+ can enter cells then they become depolarised (less negative)
- Conc. gradient maintained by ATPase ion pumps and Na+/K+ pumps
- K+ in the form of KCl (Cl- can't leave cell so keeps cell negative)
- When Ca2+ and Na+ can enter cells then they become depolarised (less negative)
- Resting cells: High K+ conc, low Ca2+ and Na+ conc.
- Cells at resting potential are highly NEGATIVE, when depolarised they become less negative
- Electrical activity of ions passes quickly to other cells and turns into mechanical action of contraction
- Cardiac muscle cells; intercalated discs for rapid simultaneous contraction
- Cells also short, strong and striated with electrical GAP junctions
- No chemical messengers or signals
- Cardiac muscle cells; intercalated discs for rapid simultaneous contraction
- Energy used to generate heartbeat is conc. gradient of ions
- Automaticity and ANS input
- Automaticity= heart beats without nervous input (generates own heartbeat)
- Heart still affected by hormones and ANS (AUTONOMIC NERVOUS SYSTEM)
- Slow spontaneous depolarisation in pacemaker cells
- Caused by Ca2+ channels opening
- Rapid depolarisation after -50mV threshold (Ca2+ channels)
- Repolarisation caused by K+ moving back in
- Muscarinic Acetylcholine receptors activates K+ pump
- Relaxation of actin -myosin fibres
- Ca2+ actively transported back into sarcoplasmic reticulum
- Ca2+ ATPase enzyme used for this
- Ca2+ actively transported back into sarcoplasmic reticulum
- Repolarisation caused by K+ moving back in
- Rapid depolarisation after -50mV threshold (Ca2+ channels)
- Caused by Ca2+ channels opening
- Rapid depolarisation in atrial and ventricular contractile muscle cells
- AP caused by FAST Na+ channels opening
- Repolarisation due to decrease in Na+
- Atrial contraction delay caused plateau region voltage gated Ca2+ channels (sustained depolarisation from Ca2+ induced Ca2+ release)
- Rapid repolarisation (to -90mV) occurs when Ca2+ channels close
- And K+ channels open (then hyper-polarisation to -70mV)
- Rapid repolarisation (to -90mV) occurs when Ca2+ channels close
- Atrial contraction delay caused plateau region voltage gated Ca2+ channels (sustained depolarisation from Ca2+ induced Ca2+ release)
- Repolarisation due to decrease in Na+
- AP caused by FAST Na+ channels opening
- Route of cardiac action potentials
- SA nodal cells (-60 milliVolts) produces cardiac excitation
- SA nodal cells depolarise (after -40mV threshold) and AP reaches AV node
- 100 millisecond DELAY occurs then atria contract
- Action Potential (generated by AV node cells) spreads along left and right bundles of His
- Action potential spreads to purkinje fibres and ventricles contract
- Action Potential (generated by AV node cells) spreads along left and right bundles of His
- 100 millisecond DELAY occurs then atria contract
- AV nodal cells also pacemakers but have lower AP frequency so overridden by SA nodal cells
- SA nodal cells depolarise (after -40mV threshold) and AP reaches AV node
- SA nodal cells (-60 milliVolts) produces cardiac excitation
- Lipid Bilayer reminder
- Impermeable to most molecules
- Allows flow of water and small lipophilic non polar molecules
- Electrical INSULATOR
- Has ligand gated ion channels
- Has G-protein receptors
- Has voltage gated ion channels
- Has mechanical gated ion channels
- Has voltage gated ion channels
- Has G-protein receptors
- ECG (Electro-cardiogram)
- QRS spikes= ventricular action potential
- If incorrect then left/right bundle block
- P wave= atrial contraction
- If absent then atrial fibrillation
- Electrodes placed in direction of depolarisation
- Negative reference electrodes catch positive signals approaching and vice versa
- T= ventricular repolarisation
- QRS spikes= ventricular action potential
- Excitability of muscle cells are caused by ions that control membrane potential
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