What is the Sense of Smell?   (Biology)
Channel: Ali Hassan Memon
Date: 09/01/2018

The sense of smell (olfaction) is a chemosense, which means it detects the presence of certain chemicals. ... The odor molecules travel into the nose and up the nasal cavity, where they are detected by olfactory receptors.


The Sense of Smell: A Powerful Sense
How the sense of smell works
The sense of smell, just like the sense of taste, is a chemical sense. They are called chemical senses because they detect chemicals in the environment, with the difference being that smell works at dramatically larger distances than that of taste. The process of smelling goes more or less like this:

Vaporized odor molecules (chemicals) floating in the air reach the nostrils and dissolve in the mucus (which is on the roof of each nostril).
Underneath the mucus, in the olfactory epithelium, specialized receptor cells called olfactory receptor neurons detect the odor. These neurons are capable of detecting thousands of different odors.
The olfactory receptor neurons transmit the information to the olfactory bulbs, which are located at the back of the nose.
The olfactory bulbs has sensory receptors that are actually part of the brain which send messages directly to:
The most primitive brain centers where they influence emotions and memories (limbic system structures), and
“Higher” centers where they modify conscious thought (neo-cortex).
These brain centers perceive odors and access memories to remind us about people, places, or events associated with these olfactory sensations.
It is important to add that “Our sense of smell is 10,000 times more sensitive than any other of our senses and recognition of smell is immediate. Other senses like touch and taste must travel through the body via neurons and the spinal cord before reaching the brain whereas the olfactory response is immediate, extending directly to the brain. This is the only place where our central nervous system is directly exposed to the environment.” (von Have, Serene Aromatherapy)

The Sense of Smell and the Limbic System
The olfactory bulb is one of the structures of the limbic system and a very ancient part of the brain. As mentioned in the previous description of the olfactory process, the information captured by the sense of smell goes from the olfactory bulb to other structures of the limbic system.

The limbic system is a network of connected structures near the middle of the brain linked within the central nervous system. These structures “work together to affect a wide range of behaviors including emotions, motivation, and memory” (Athabasca University-Advance Biological Psychology Tutorials). This system deals with instinctive or automatic behaviors, and has little, if anything, to do with conscious thought or will.

The limbic system is also concerned with translating sensory data from the neo-cortex (the thinking brain) into motivational forces for behavior. The limbic system is centrally involved in the mediation between a person’s recognition of an event, their perception of it as stressful, and the resulting physiological reaction to it, mediated via the endocrine system: Stimuli are processed conceptually in the cortex, and passed to the limbic system where they are evaluated and a motivational response is formulated.