No one could have seen “The Sessions” coming. But we should have. It’s as frank a film about sex as American movies are likely to give us for a long time (“Hope Springs” about sex therapy for a long married couple pales in comparison).

Its stars, though, are not glamour mongers making a flesh-filled shortcut to renown; they’re serious, hugely respected film and TV actors doing the sort of work that gets award nominations and the reverence – even awe – of colleagues.

It’s set in Berkeley, Calif., in 1988 and is based on the true story of a poet and journalist who wrote about his predicament. It’s about a quadriplegic who hires a sex surrogate to end the virginity his life has cursed him with. Childhood polio has left him incapable of movement from his neck down. His breathing is so difficult that he’s more comfortable usually sleeping in an iron lung.

That doesn’t mean, however, that he’s incapable of feeling, including everything required for sexual responsiveness and performance. It’s in his head, though, that sex looms so large in his life. He’s obsessed with not dying a virgin – and being able to explore as much as humanly possible this thing so important to his fellow creatures with the body that fate gave him.

It’s all he talks about with the Catholic priest who becomes his best friend.

Despite the physical wallop of fate, he has remained a man of enormous sweetness, great heart and no small wit. (“I believe in a God with a wild sense of humor who created me in his own image.”)

The actors playing the two men are close to ideal in a small indie film – John Hawkes as the paralyzed seeker and William H. Macy as the all-too-knowledgeable priest who does his young confessor the favor of being as frank and generous in his advice as a man can be. The priest refuses to answer questions with easy doctrine or the stock priestly responses that would make his own life easy. He tries to put himself inside his friend’s head and advise him as a man.

It is, of course, Hawkes whose performance is so often talked about as the kind of stunt performance so cynically called “Oscar bait.” His whole performance is virtually given from the neck up, which means that his voice most often has the slightly squashed quality of a man whose life is spent lying prone.

It is the priest – full of so much acquired worldliness from all the confessions he’s heard – who tells him about a world where there are such things as sex surrogates, women who, as therapy, instruct clients professionally in everything the client needs to know about having fulfilling and pleasurable sex and use their own bodies for the instruction. It is the priest who advises his friend to “go for it.”

They are not prostitutes, as the surrogate is quick to inform her client. A prostitute wants a client’s repeat business. A surrogate wants to finish her instructive – and participatory – sessions and never see him again. The client pays for six “sessions.”

We, in the audience, are wiser than that, of course. We suspect that this movie about glands, body parts, techniques, ejaculations and orgasms will find its way past all that – and the brain too – to that metaphorical piece of anatomy, the human heart, wherein so much more happens than the mere pumping and repumping of blood.

And, of course, it does. The quest of our hero to find sex winds up touching deeply the lives of everyone he knows – all the co-conspirators in his life, nurses, friends and, of course, the surrogate whose own body is the instrument of his instruction, pleasure and liberation.

It’s the most basic movie about sex that can’t help being so much more than the sum of its anatomical parts. That’s what happens here, for instance, when a lot of those parts are paralyzed and belong to a poet.

It is, I think, the performance of Helen Hunt as the surrogate that is the most fearless and startling in all of “The Sessions” and not just such abundant nudity for a beautiful 49-year-old actress, but the huge discipline of a performance that never at any single moment succumbs to the tiniest drop of melodrama or vulgarity. She is, all through the movie, the consummate professional – a married therapist who simply can’t avoid the tidal emotions that her “sessions” have awakened.

There is, similarly, nothing remotely fancy about the direction of Ben Lewin.

You spend all of “The Sessions” watching human need that is almost absolute – and a small society of people whose kindness is so large and absolute that they try to fill that need. What you understand about the human species when it’s over is a cause for great happiness as you leave the theater.

the sessions

3 and 1/2 stars

Starring: John Hawkes, Helen Hunt, William H. Macy

Director: Ben Lewin

Running time: 98 minutes

Rating: R for graphic nudity and total sexual frankness.

The Lowdown: A quadriplegic hires a sexual surrogate to introduce him to the sex he’s never had.