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level: 14.5 Control of heart rate

Questions and Answers List

level questions: 14.5 Control of heart rate

QuestionAnswer
The automatic system- Controls involuntary (subconscious) activities of internal muscles + glands
The two divisions of the automatic system- The sympathetic nervous system - The parasympathetic nervous system
The sympathetic nervous system- Stimulates effectors, so speeds up any activity - Controls effectors during exercise or experience powerful emotions - Helps us cope with stressful situations by increasing awareness
The parasympathetic nervous system- Inhibits effectors, so slows down any activity - Controls activities under normal resting conditions - Conserves energy + replenishes body's reserves
Sympathetic nervous system and parasympathetic nervous system working together- Normally oppose one another (antagonistic) - If 1 system contracts a muscle, the other relaxes - Activity of internal glands + muscles are regulated by a balance of the 2 systems
The cardiac muscle- Myogenic, its contration is initated from within itself - Rather than by nervous impulses from outside (neurogenic), like other muscles - In right atrium there is group of cells called sinoatrial node (SAN)
Sinoatrial node (SAN)- Where the initial stimulus for contraction originates - Has basic rhythm of stimulation that determines the beat of the heart, pacemaker
Control of the heart rate- The SAN sends out regular waves of electrical activity to both atrial walls causing contraction - The electrical waves are then passed onto the AVN, then to the bundle of His, with a slight delay - The bundle of His splits into the Purkynge tissue, causing contraction of both ventricles from the bottom up
Modifying the resting heart rate- Resting heart rate average = 70 bpm - Rate is altered to meet different demands for O2 e.g. exercise - Changes to rate controlled by medulla oblongata
Medulla oblongata - the two centres- A centre that increases heart rate, linked to SAN by sympathetic NS - A centre that decreases heart rate, linked to SAN by the parasympathetic NS
Chemoreceptors- Found in the wall of the carotid arteries (the arteries taht serve the brain) - Sensitive to changes in pH of blood that result form changes in CO2 conc. - In solution, CO2 forms an acid + lowers pH
Control by chemoreceptors (1)- When blood has a higher than normal conc. of CO2, its pH is lowered
Control by chemoreceptors (2)- The chemor. in the wall of the carotid arteries + aorta detect this - + increase the frequency of nervous impulses to the centre in the medualla oblongata that increase HR
Control by chemoreceptors (3)- This centre increases frequency of impulses via the sym. NS to the SAN - So increases rate of production of electrical waves by the sinoatrial node, increasing HR
Control by chemoreceptors (4)- Increased blood flow leads to more CO2 being removed by lungs - CO2 conc. of blood returns to normal
Control by chemoreceptors (5)- The pH of blood rises to normal - The chemor. reduce the frequency of nerve impulses to the medulla oblongata
Control by chemoreceptors (6)- The MO reduces frequency if impulses to sinoatrial node - So leads to reduction in HR
Pressure receptors- Found in walls of the carotid arterties + aorta
Control of pressure receptors (1)- When blood pressure is higher than normal, pressure receptors transmit more nervous impulses to centre of MO, decreasing HR - This centre sends impulses via the parasym. NS to the SAN - Decreasing HR
Control by pressure receptors (2)- When blood pressure is lower than normal, pressure receptors transmit more nervous impulses to centre of MO, increasing HR - This centre sends impulses via the symp. NS to the SAN - Increasing HR