Physiology of Smell/Olfactory

Odor Molecules (odorants)

Enter the nasal cavity during breathing or sniffing.

Mucus

Odorants dissolve in the _____ covering the olfactory epithelium (located in the roof of the nasal cavity).

Cilia

The olfactory receptor cells/neurons (ORNs) have ______ that contain specific odorant receptors.

G-protein Coupled Receptor (GPCR)

Each receptor is what type?

G-protein Coupled Receptor (GPCR)

A molecular "switch" that helps transmit signals from receptors (like smell or taste receptors) to inside the cell

ORN - Adenyl Cyclase

Odorant binds to its receptor on the ___. This activates a G-protein (Golf) → stimulates ______ _______ (enzyme).

cAMP (cyclic AMP)

Adenyl cyclase converts ATP → ____

CAMP

Acts as a second messenger, opening cyclic nucleotide-gated (CNG) ion channels.

Depolarization

Na* and Cat ions to enter the neuron → ______________.

Olfactory Sensory Neuron (OSN)

Sends signal through the Olfactory nerve (CN I) to the brain.

Axons

The _____ of ORNs form the olfactory nerve (Cranial Nerve I).

Olfactory Bulb - Glomeruli

They axons project to the _________ ____, where they synapse in structures called ________.

Glomerulus

Each __________ receives input from ORNs (Olfactory Receptor Neurons) expressing the same receptor type.

Mitral - Tufted

These cells relay signals from glomeruli to higher brain areas (2).

Olfactory Tract

Signals travel from the olfactory bulb via this tract.

Primary Olfactory Cortex (Piriform Cortex)

For odor identification.

Amygdala

For emotional response to smells.

Entorhinal Cortex - Hippocampus

For odor memory and associations (2).

Hypothalamus

For autonomic and hormonal responses (e.g., appetite, reproduction).

Thalamus

Unlike other senses, smell does not relay through the ________ first before reaching the cortex.

Olfactory Bulb

The main brain part responsible for smell.