| 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 |
