Nancy Rothwell, the Royal Institution Christmas lecturer, tells Alison Goddard how her dad inspired her.

The Christmas she was eight, Nancy Rothwell got more presents than ever before. Three months earlier she had contracted primary tuberculosis. "I didn't think it was that serious, but when it got to Christmas, I had more presents than I had ever seen before," she says. "I thought: 'Gosh, I really must be ill'."

It took Rothwell two years to recover from the disease, two years that she spent off school, being taught science by her father, a physiology lecturer. She recalls: "He used to bring back skeletons and books and things. He asked: 'How does this work?' so often that I would sometimes think: 'Oh not now, Dad'." Nonetheless, the experience awakened an interest in science and now, 35 years later, Rothwell is internationally renowned for her work on the brain. She is presenting this year's Royal Institution Christmas lectures for children - only the second woman to be invited in the history of the series (the first was Oxford scientist Susan Greenfield).

The series - which will be broadcast daily from December 28 - is called Staying Alive: the Body in Balance. "The lectures are not just about the way that animals and humans work," says Rothwell. "They are the story of how we adapt to rapid changes and how we regulate our functions to cope with, for example, a drop in temperature."

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To mark the 200th anniversary of the Royal Institution, the lectures will be preceded by an affectionate documentary. They were first given in 1826 by Michael Faraday, who discovered electricity, to 400 children of members. Faraday gave the lectures for the next 19 years. Other eminent scientists who have lectured include James Dewar, who invented the vacuum flask; Frank Whittle, who developed the jet engine; and George Porter, who shared the 1967 Nobel prize for chemistry for his technique by which extremely fast reactions such as photosynthesis could be studied. More recently, they have been given by David Attenborough, evolutionary biologist Richard Dawkins, physicist Frank Close and astronomer Carl Sagan. "The lectures are incredibly prestigious," says Rothwell. "I am really flattered to be giving them."

The documentary cameras follow Rothwell from her first audition, through her preparations and rehearsals, to her first lecture. There are some lighter moments - deciding what she should wear, for instance. "There were rumours that the BBC would take me shopping but I was disappointed to learn that I would have to return the clothes," Rothwell smiles. "My mum always asks me: 'What are you going to wear?'. I haven't given it a second thought and I probably won't until two minutes before I lecture. I am too busy."

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It is not the first time that Rothwell has appeared in front of the cameras: her postdoctoral work inspired a Horizon programme on the role of brown fat, which keeps animals warm in the cold and is crucial for hibernation. "I made friends with Caroline Van Den Brul, executive producer of Horizon," says Rothwell. "She suggested me for the Christmas lectures to Peter Day, director of the Royal Institution. I think that they wanted a biologist and they wanted a woman. And I have always been happy to talk to the public about science: if there is one thing I can do, it is talk."

Rothwell's PhD supervisor, whom she then worked with for a further eight years, particularly remembers her vivaciousness. Mike Stock, now professor of physiology at St George's Hospital Medical School, says: "She was a phenomenally active and impressive research student. You could have an idea sitting in the bar one evening and by the next day she would already have set it up and be running it."

Rothwell's energy paid dividends: she completed her PhD at Queen Elizabeth College (now part of King's College, London) in a mere two years. At the same time, she and Stock published a paper in Nature on the control of energy balance. In 1979 they published another Nature paper on the role of brown fat. "That is our main claim to fame," says Stock. "It has been cited 1,000 times." Since then, Rothwell has gone from strength to strength. "In teaching research students, it has always been my objective to maximise their potential," adds Stock. "Now I am in Nancy's shadow."

Rothwell moved to the University of Manchester in 1987. One of her PhD students takes a key role in the demonstrations that traditionally illustrate the Christmas lectures. The unfortunate student will be placed in a bath of water kept at the temperature of the North Sea. "He volunteered - he is doing it willingly," Rothwell protests. She heads the neuro-immunology group in the school of biological sciences, where she studies how the brain communicates with the immune system to co-ordinate responses to disease and injury. She also studies the causes of brain damage.

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"It is now accepted that the brain has an immune response", she says - in other words, that the brain itself can fight infection directly. "Our research aims to understand the mechanisms and mediators which contribute to interactions between the immune system and the brain." Rothwell hopes that by understanding how certain proteins can inflame the brain, her research team can identify new ways of treating strokes and illnesses such as Alzheimer's disease.

The brain was her first choice of subject for the Christmas lectures but was ruled out because Greenfield had recently covered it.

Instead, the first of the five lectures explores the range of senses that enables animals to survive. As well as sight, sound, smell, taste and touch there are hidden senses- "cells that can detect the temperature within and outside our bodies, and that can determine the levels of oxygen and carbon dioxide in the air and in our lungs, blood and tissues," says Rothwell.

Once an animal senses danger, the next step is to activate the appropriate physiological response. "The heart can respond, within a second, to a potential danger or a need within the body," says Rothwell. "It can adapt to training, stress and long-term needs." Rothwell will demonstrate this with the help of champion cyclist Chris Boardman.

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In her second lecture, Rothwell will calculate how long it takes to burn off a Christmas dinner. "In order to survive, animals must regulate their appetite, the amount and type of food eaten and the size of energy stores," says Rothwell. "What makes some animals fat and thin, and why do some animals store fat and lose it again?" Rothwell's third lecture - featuring the PhD student and the bath - will cover how the body regulates temperature. "Animals have developed a fascinating range of strategies to regulate body temperature," she says. "For example, to lose heat and keep cool, humans sweat, dogs pant, cats lick themselves and hippos wallow in the mud."

One fascinating demonstration is footage of birds that were reared in a planetarium and use the stars projected on to the dome to navigate. It demonstrates that animals have an internal calendar located in the brain, influencing behaviour such as when animals breed to allow the best chance of survival for their young. "Even individual cells can measure time," explains Rothwell. "These biological clocks can influence every aspect of our lives and might even tell cells and organisms when to die."

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Finally Rothwell will look at life at the extremes with the help of Antarctic explorer Mike Stroud and some desert meerkats, which will be allowed into the lecture theatre. Rothwell says: "I want to get people fascinated by physiology and make them understand a little more about what is behind things that we consider just everyday."