Smell

Main

Smell, or olfaction, is one of the special senses that allows humans and other animals to perceive odors in their environment. The sense of smell is part of the chemosensory system, which detects chemicals in the air. The olfactory system is part of the peripheral nervous system (PNS) that sends signals to the central nervous system (CNS) for processing. The process of smell detection involves several phases:

1. Odor molecules enter the nose and bind to olfactory receptors in the olfactory epithelium.

2. Olfactory receptors trigger electrical signals in sensory neurons.

3. Sensory neurons transmit signals through the olfactory nerve to the olfactory bulb in the brain.

4. The olfactory bulb relays the signals to other brain areas, including the piriform cortex, for processing and identification of the smell.

Terms

• Olfactory receptors: Proteins on the tips of sensory neurons in the nose that bind to odor molecules. Humans have about 450 different types of olfactory receptors.

• Olfactory epithelium: A strip of tissue at the back of the nose that contains millions of sensory neurons.

• Olfactory bulb: A structure at the base of the forebrain that receives signals from the sensory neurons and relays them to other brain areas for processing.

• Piriform cortex: A brain region that works to identify smells.

• Nervous system: The body's communication network, consisting of the brain, spinal cord, and nerves, which includes the olfactory system responsible for smell.

Analogy

The sense of smell is like a lock and key system. The locks are the olfactory receptors, and the keys are the odor molecules. Just as a specific key is needed to open a particular lock, certain odor molecules fit and activate certain receptors. For example, the receptors activated by the odor molecules of coffee allow your brain to identify the aroma of your morning cup of joe.

Misconception

Many people believe the human nose can only identify about hundreds of different smells. However, recent research suggests humans can distinguish far more odors than previously thought, perhaps even more than a trillion. Another common misconception is that the sense of smell is less important than other senses. In reality, smell plays a crucial role in taste, memory, emotion, and even warning us of dangers like smoke or spoiled food.

History

1. Ancient times: Ancient civilizations recognized the importance of smell in medicine, religion, and daily life.

2. 1800s: Anatomists described the olfactory system's structure, including the olfactory bulb and nerve.

3. 1991: Linda Buck and Richard Axel discovered olfactory receptors, revolutionizing the understanding of smell.

4. 2004: Buck and Axel awarded Nobel Prize in Physiology or Medicine for their work on olfactory receptors.

5. 2014: Study published suggesting humans can identify more than a trillion smells.

How to use it

1. Pay attention to how different foods smell. The aroma contributes significantly to the flavor you perceive, as smell and taste are closely linked. Pinch your nose while eating to observe how it changes the taste.

2. To sleep better in a hotel, bring a small item from home with a familiar scent, like a pillowcase or t-shirt. The comforting smell can help you relax and fall asleep more easily in an unfamiliar environment.

3. Use your sense of smell for safety. Sniff foods before eating to check for spoilage, and be alert to the smell of smoke that could indicate a fire. If you notice a gas smell in your home, it could mean a dangerous leak.

Facts

• The human nose can detect more than 1 trillion different odors.

• The sense of smell is 10,000 times more sensitive than the sense of taste.

• Humans have about 450 types of olfactory receptors, while dogs have around 2 times more.

• Loss of smell is a common symptom of COVID-19, with up to 50% of infected people experiencing it.

• Some people are born without a sense of smell, a condition called congenital anosmia that affects about 1 in 10,000 people.