Autonomic: 

Sympathetic Nervous System: Parasympathetic Nervous System:
  • Stimulates effectors and so speeds up any activity
  • Used under stressful conditions by awareness and preparing for Fight or Flight
  • Inhibits effectors and results in them being slowed down
  • It controls activities under normal resting conditions
  • It is used to conserve energy and replenishing body reserves

The actions of the Sympathetic and Parasympathetic nervous systems work antagonistically.

Control of Heart Rate

  • Resting heart rate of an average adult is 70 BPM
  • However, the BPM must be able to change to accommodate demands for oxygen
  • Changes to the Heart Rate occurs in the Medulla Oblongata:
    • A centre which increases heart rate which is linked to the sinoatrial node by the sympathetic nervous system
    • A centre which decreases heart rate which is linked to the sinoatrial node by the Parasympathetic system

The response of each centre is determined by stimulation from receptors of:

  • Chemoreceptors: Change in chemical properties of the blood
  • Baroreceptors: Change in blood pressure

Chemoreceptors

  • Found in the carotid arties (arteries leading to the brain) and aorta
  • Sensitive to changes in pH (n.b. pH alters on CO2 concentrations)
    1) Increased CO2 concentrations lowers pH
    2) Chemoreceptors detect change and increase frequency of impulses to the medulla oblongata
    3) Centre increase frequency of impulses via sympathetic nervous system to SA node which increases heart rate
    4) Increased blood flow result in more CO2 being removed by lungs and thus CO2 concentration decreases
    5) pH of the blood returns back to normal
    6) Chemoreceptors reduce impulse frequency to medulla oblongata
    7) medulla oblongata reduces frequency of impulses to SA node which therefore decreases heart rate to normal

Baroreceptors
Found within the walls of the carotid arties and the aorta

 High Blood Pressure  Low Blood Pressure
 1) Baroreceptors transmit impulse to the medulla oblongata which decrease the heart rate
2) Medulla oblongata centre send impulses via parasympathetic nervous system to the SA node of the heart which decrease the heart rate
 1) Baroreceptors transmit impulse to the medulla oblongata which increases the heart rate
2) Medulla oblongata centre send impulses via sympathetic nervous system to the SA node of the heart which increases the heart rate