basically the same way.” She saw my confused expression and shook her head in disgust. “That’s the inner ear, remember? Those are the canals and this,” she pointed to a little ball in the centre, “is the cochlea, roughly equivalent to the retina in the eye. But instead of rods and cones this thing contains hair cells, receptors that respond to the physical vibrations caused by sound.”
She drew a little round ball with a hair poking out of it. “Like that.” She looked up. “I’m simplifying this, okay?”
Since I hadn’t taken a course in sensory physiology since my undergraduate years, I didn’t mind at all. She went back to her drawing.
“The important thing again is that each hair cell — each receptor — only responds to a narrow band of frequencies. The hair is literally pushed by the right frequency of sound,” she drew another little round ball with the hair bending over like a sapling in the wind, “and this mechanical stimulation triggers the sequence of chemical events that end with the nerve firing and a signal going to the brain. So what about the olfactory system?”
Above the amorphous brain — which was now attached to an eyeball and an inner ear — she drew a big schnoz with a question mark hanging off its tip. I started to laugh, but caught her expression: serious and intent. It wasn’t meant as a joke. She ignored my stifled guffaw and went right on talking.
“Given what we know about these other systems, we’d expect to find receptors, here in the epithelium lining the nose, that respond to chemicals suspended in the air or, in the case of aquatic animals, in the water that surrounds them. We’d also expect the receptors to be stimulus specific: each receptor should respond only to specific odours. The receptors should then feed their information to an olfactory centre in the brain.” She attached up the nose to a circle in the brain labelled OC.
“Simple, right? The trouble is, nobody can find a receptor. We’ve been looking for over fifty years, and we still can’t figure out which cells in the lining of the nose are the receptors. And then there’s the problem of the stimuli. Light and sound are easy to identify and they’re simple to manipulate and measure, so we can run tests to trace the neural pathways and understand how the visual and auditory systems work. But odours? Odours are just molecules, and there are millions, billions of molecules, all different, that can become suspended in air or water. And one odour might be made up of a thousand different molecules. So what’s stimulating the receptors? Are there different receptors responding to specific molecules or discrete classes of molecules? Perhaps, but we have no idea what those molecules might be, partly because we can’t identify a receptor, and basically, if we can’t find a receptor and we don’t know what the stimuli are, its hard to study the system. Enter Madden Riesler.”
“But he doesn’t work on olfaction. I’ve seen his records.”
Конец ознакомительного фрагмента.
Текст предоставлен ООО «ЛитРес».
Прочитайте эту книгу целиком, купив полную легальную версию на ЛитРес.
Безопасно оплатить книгу можно банковской картой Visa, MasterCard, Maestro, со счета мобильного телефона, с платежного терминала, в салоне МТС или Связной, через PayPal, WebMoney, Яндекс.Деньги, QIWI Кошелек, бонусными картами или другим удобным Вам способом.
