Exercise 6: Cardiovascular Physiology
Autorhythmicity- the hearts ability to trigger its own contractions. This occurs because the plasma membrane in the cardiac pacemaker muscle cells has REDUCED permeability to potassium ions but still allows sodium and calcium ions to slowly leak into the cells. The leakage causes a depolarization to occur, before repolarisation occurs, the muscle contracts.
Five Phases of Cardiac Action Potential:
Phase 0- Depolarization causes voltage-gated sodium channels in the cell membrane to open, increasing the flow of sodium ions into the cell which increases membrane potential.
-SODIUM MOVES INTO CELL!!!!!!!!!
Phase 1- the open sodium channels begin to inactivate, which decreases the flow of sodium into the cell therefore membrane potential falls slightly. Voltage gated potassium channels also close and the voltage gated calcium channels open. Potassium flow decrease out of the cell and the increase of calcium into the cell depolarize the membrane. * SODIUM CHANNELS CLOSE, POTASSIUM CHANNELS CLOSE, CALCIUM CHANNELS OPEN
Phase 2- this is the plateau phase, membrane is still depolarized. Potassium channels are still closed, and ( l-type) long lasting calcium channels stay open. Plateau lasts 0.2 seconds. * SODIUM CHANNELS CLOSE, POTASSIUM CHANNELS CLOSE, CALCIUM CHANNELS OPEN
Phase 3- membrane potential gradually falls to negative values. A second set of potassium channels open. A significant amount of potassium floods out of the cell. The decreasing membrane potential causes calcium to close, decreasing the amount of calcium flowing into the cell. Membrane is re-polarized until resting potential is reached. * POTASSIUM CHANNELS OPEN, CALCIUM CHANNELS CLOSE
Phase 4- the resting membrane potential is again established in cardiac muscle cells and is maintained until the next depolarization arrives from neighboring pacemaker cells.
Wave Summation- the skeletal muscle is stimulated with such frequency that muscle twinges overlap and result in stringer contraction than a single muscle twitch.
Tetanus- when wave summation stimulations are frequent enough that the muscle reaches a single fused state. Tetanus happens in SKELETAL muscle because it has a short absolute refractory period. Cardiac muscle is incapable of Tetanus because of its long refractory period.
Absolute Refractory Period- a period during which action potentials cannot be generated no matter giw strong the stimulus. (phase 3)
Relative Refractory Period- the period in time between the absolute refractory period and phase 4.
NOTE: The autonomic nervous system has two branches: the sympathetic and the parasympathetic nervous systems.
Sympathetic Nervous System: This system causes an increase in heart rate with the release of adrenaline and norepinephrine. ( fight or flight response)
Parasympathetic Nervous System: This system causes a decrease in heart rate with the release of acetylcholine.
Cholinergic- chemical modifier that inhibit, mimic or enhance the action of acetylcholine.
Adrenergic- Chemical modifiers that inhibit, mimic or enhance the action of epinephrine.
Agonist- modifier works in the same fashion as the neurotransmitter.
Antagonist- if the modifier works in opposition of the neurotransmitter
Vagal Escape- The resumption of the heartbeat, after stimulation by the vagus nerve.
Sinoatrial node (SA node) – is a cluster if autorythmic cardiac cells found in the right atrial wall in the human heart. The SA node has the fastest rate of spontaneous depolarization and for that reason it determines the heart rate, it is therefore called the PACEMAKER.
Homeothermic- ( e.g. Humans) maintenance of an internal body temperature within a selected range.
Hyperthermia- elevation in body temperature.
Hypothermia- body temperature decreases ( low body temp)
Poikilothermic- ( e.g. Frog) the internal body temperature changes depending on the temperature of its…