Since (fixed rate) values are market determined, how are price changes reflected in the investment account for a security classified when held to maturity?

Debt securities are common investment vehicles and are exchanged (purchased and sold) in markets including numerous exchanges. Since (fixed rate) values are market determined, how are price changes reflected in the investment account for a security classified when held to maturity? What are the FASB accounting requirements for securities held to maturity? How does price influence return? What happens if the securities were purchased for the purpose of selling them? Provide a discussion of all potential scenarios and the relevant accounting requirements