Final answer:
Cerebrospinal fluid (CSF) functions to protect the brain and spinal cord, contains antibodies for immunological defense, and exchanges nutrients and waste products. The correct answer is option 3.
Step-by-step explanation:
The cerebrospinal fluid (CSF) has several crucial functions within the central nervous system (CNS). First and foremost, the CSF acts as a cushion for the brain and spinal cord, protecting them from impact and injury by absorbing shock, similar to a hydraulic buffer. This aspect of CSF shields delicate neural structures from the everyday jolts and knocks that occur as the body moves.
Another vital role of CSF is in the immunological defense of the CNS. It contains antibodies which help to protect the brain and spinal cord from pathogens, thus acting as a line of defense against infection. Additionally, CSF serves as a medium for the exchange of nutrients and waste products between the blood and the brain. It assists in the removal of waste products from the cerebral metabolism.
However, as to the options presented in the question, the function of 'CSF as a medium for excretion of waste product by nc to brain' is not entirely accurate as stated. While it is true that CSF is involved in the removal of waste, the phrase 'by nc to brain' is not clear. The abbreviation 'nc' typically refers to 'non-classical' in scientific literature, but it does not provide a clear context in this case. Assuming that 'nc' is a typo or an unclear abbreviation, the correct function would be the removal of waste products, but not specifically referenced as 'by nc to brain' since this does not represent a recognized process related to CSF.
The correct option that is not a function of cerebrospinal fluid is 'as a medium for excretion of waste product by nc to brain' because it does not correspond accurately with known functions of CSF.