Definite Articles in Old Norse

Despite my recent graduation, I am still leading several groups for the THI Dead Languages Society and trying to get the group to become more solidified.  One of the groups I'm leading this semester is studying Old Norse, which is completely new for me and a lot of fun.  One of the most interesting things I've encountered is the use of the definite article.  In the languages I have studied at least peripherally (Latin, Old English, Greek, Spanish, and German to one degree or another) the definite article is either formed similarly to English by use of a separate word ("the") or like in Latin which effectively has no definite article (demonstrative pronouns can occasionally be used to get the point across).  However, Old Norse does something completely different.  In this language, the definite article is sometimes denoted by making an addition to a word's ending similar to case endings.  It looks something like this:

Alfr ser varg.

(An elf sees a wolf)

Alfrinn ser varginn.

(The elf sees the wolf)

Alfar sja varga.

(Elves see wolves).

Alfarnir sja vargana.

(The elves see the wolves)

Anyways, this just seemed really interesting to me.  I'm sort of curious how forming words and ideas this way might affect the way in which people communicate.  For instance, in English if you want to stress a word you might say "not just a thunderclap, but the thunderclap."  I guess you'd say something similar in Old Norse, only stressing the ending of the Old Norse word for thunderclap rather than a different word before it.  Would Old Norse even have a verbal device like this?  Maybe this a one verbal device which is lost on the language entirely.  I'll have to spend more time in the language before I get a better idea for what devices they have that we don't.