Intramuscular (IM) injections

1.In the medical field, it is quite common to administer intramuscular (IM) injections. Why is an IM preferred over an injection directly into the
circulation? What muscles are best suited as sites for IM injections?
2.How does the nicotine in cigarettes initiate the process of facilitation and ultimately trigger action potentials? How does it lead to addiction?
3.What is spinal meningitis? What causes this condition and how does it ultimately affect the victim?
4.How can a blockage of CSF in an arachnoid granulation cause irreversible brain damage? What types of treatments can help prevent that damage?