Q29 (b)

Criteria	Marks
• Identifies the main features of a role of the nervous system using an example<br>• Includes concepts of detection and response	3
• Identifies a role of the nervous system using an example	2
• Makes a correct statement about the nervous system<br>OR<br>• States an example	1

Suggested answer:
2 stages in homeostatsis include:

1. detecting change
2. counteracting the change
   Hypothalamus is an important control centre in the brain It receives information of stimuli from the internal and external environment via receptors, analyses it, and send instructions to effectors to carry out a response that counteracts the effects of the stimuli. This process is called negative feedback.
   Eg. Temperature regulation Thermoreceptors in the hypothalamus within brain and thermoreceptors in skin detect changes in temperature Too hot: Messages sent to effectors to cool body down. Eg. Vasodilation : Blood vessels widen, usually near surface of skin, with increase in blood flow to expel heat from the body Too cold: Messages sent to effectors to warm body up. Eg. Vasocontriction : Blood vessels narrow and contain heat to core of the body to stay warm. Erector muscles in skin contract to raise hairs up to produce an insulating layer of air to warm body. Rapid muscle contractions to induce shivering to generate heat to warm body.