When a mammal detects a threat, such as a predator, its body prepares either to fight or to run away. This is the fight or flight response. It is coordinated by the hypothalamus and involves both the nervous system and hormones.1. Receptors detect the threat and impulses pass to the cerebrum, which recognises the danger and stimulates the hypothalamus.
2. The hypothalamus activates the sympathetic nervous system. Sympathetic neurones stimulate effectors directly, and also stimulate the adrenal medulla to release adrenaline into the blood.
3. The hypothalamus also releases corticotropin releasing factor (CRF) into the blood. This causes the anterior pituitary gland to release adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex to release corticosteroids such as cortisol.
Effects of the response:
• heart rate and stroke volume increase, so more blood reaches the muscles
• pupils dilate, letting more light into the eyes
• ventilation rate and depth increase and the bronchioles dilate, so more oxygen enters the blood
• arterioles to the digestive system and skin constrict and those to the muscles dilate, diverting blood to the muscles
• glycogen in the liver is converted to glucose, raising blood glucose for respiration
• sweating increases to cool the body
• hairs stand on end and mental awareness increases.Together these changes supply the muscles with more oxygen and glucose and make the animal more alert, so it is better able to fight or escape. Once the threat has passed, the parasympathetic nervous system returns the body to its resting state.
2. The hypothalamus activates the sympathetic nervous system. Sympathetic neurones stimulate effectors directly, and also stimulate the adrenal medulla to release adrenaline into the blood.
3. The hypothalamus also releases corticotropin releasing factor (CRF) into the blood. This causes the anterior pituitary gland to release adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex to release corticosteroids such as cortisol.
Effects of the response:• heart rate and stroke volume increase, so more blood reaches the muscles
• pupils dilate, letting more light into the eyes
• ventilation rate and depth increase and the bronchioles dilate, so more oxygen enters the blood
• arterioles to the digestive system and skin constrict and those to the muscles dilate, diverting blood to the muscles
• glycogen in the liver is converted to glucose, raising blood glucose for respiration
• sweating increases to cool the body
• hairs stand on end and mental awareness increases.Together these changes supply the muscles with more oxygen and glucose and make the animal more alert, so it is better able to fight or escape. Once the threat has passed, the parasympathetic nervous system returns the body to its resting state.