Chemosensory

What is the structure and function of the olfactory nerve (cranial nerve I)?

Answer: The olfactory nerve (CN I) originates in the olfactory mucosa where it receives sensory information from the air when we inhale, and transmits this information into the brain.

olfactory nerve cranial nerve I structure function

The olfactory nerve, sometimes called the first cranial nerve (CN I), is responsible for our sense of smell. Whereas some cranial nerves can be motor or sensory, the olfactory nerve is entirely sensory in nature, meaning that it does not innervate any muscles. Like the gustatory system, which gives us our sense of taste, olfaction is called a chemoreceptive system since it allows the body to detect chemicals.

First order olfactory neurons are responsible for receiving the inputs from the air. They send their axonal projections through the cribriform plate, a perforated section of bone at the base of the skull. From here, they form synapses onto second order olfactory neurons at an area called a glomerulus. These second order olfactory neurons exist in one of two types, called mitral cells or tufted cells. The second order neurons are the cells that make up the olfactory nerve. From here, they project into the prepiriform area of the brain, forming synapses with the third order neurons of the olfactory system.

The olfactory tract is currently believed to be one of the few areas of the brain where adult neurogenesis occurs. Among most cells in the brain or peripheral nervous system, the neurons do not regenerate once they die once a person reaches adulthood. However, scientists believe that the adult neurogenesis can replace the dying cells in the olfactory nerve since they are frequently exposed to the outside world.

The size of the olfactory nerve is different across species, depending on how much they use their sense of smell. Humans don't rely too much on olfaction to navigate, whereas animals such as dogs or rodents often have a very well developed olfactory system.