The Latin word collum roughly translates as "the head and neck".
Italics are used in the sentence above because the italicized words are:

Question

Quizplus · Accepted Answer

The word collum is italicized because it is a Latin word that the reader may not know. Therefore, this is correct.
The scientific name of an organism is incorrect. The word collum is italicized because it is a Latin word that is unfamiliar to the reader. Nothing in the sentence involves a scientific name of an organism. 
Intended to be emphasized by the author is incorrect. The word collum is italicized because it is a Latin word that is unfamiliar to the reader. Nothing in the sentence involves an emphasis placed by the author. 
A proper title of something is incorrect. The word collum is italicized because it is a Latin word that is unfamiliar to the reader. Nothing in the sentence involves a proper title.

The Latin Word Collum Roughly Translates as "The Head and Neck