Cam Stuart (Mark Ruffalo) would be good company if he could just dial himself down. But he can’t. So when he offers a neighbor help with carrying her groceries, she can’t close her door in his face fast enough.

Perhaps things would have worked out differently if she’d known that Cam has bipolar disorder. His condition affects his ability not only to function in his neighborhood in Cambridge, Massachusetts, but also to live up to his responsibilities as a husband and father.

His wife, Maggie (Zoe Saldana), loves him, no matter what. The question is whether she can trust him to take care of their daughters Amelia (Imogene Wolodarsky) and Faith (Ashley Aufderheide) while she’s in New York pursuing a graduate degree.

Cam desperately wants to keep his family together. But that’s no small challenge.

Written and directed by Maya Forbes and set in the 1970s, the autobiographical “Infinitely Polar Bear” has the kind of vibe that made such movies of the era as “Five Easy Pieces” and “Dog Day Afternoon” so culturally resonant. There’s not much of a plot, but that’s not the point, anyway. In dealing with the dynamics of a specific family, Forbes strikes notes that are engagingly universal.

And in Ruffalo, she has just the right actor. Since his breakthrough in “You Can Count on Me,” he’s been so good in so many movies – even as Bruce Banner (alter ego of the Hulk) in the “Avengers” blockbusters – that he may be in danger of being taken for granted. But his range is immense. As the central character in “Polar Bear,” Ruffalo impressively explores the geography of a troubled mind, and makes the journey fascinating.

Saldana, who is best known for “Avatar,” “Star Trek” and “Guardians of the Galaxy,” delivers a down-to-earth performance that matches Ruffalo’s for emotional depth. Also fine are Wolodarsky (the director’s real-life daughter) and Aufderheide.

“Infinitely Polar Bear” is a much-needed reminder that the realm of film is still a place to encounter something other than comic-book scenarios.