olfaction

Olfaction

Sense of smell

Response to airborne chemicals (odorants)

Influence behavior, avoiding hazard, influence mate choice, parent and infant bonding

Ties to memories and emotion

Decreased ability to smell is an early predictor of Alzheimer’s disease

Olfactory dysfunction due to disease or injures is associated with depression

Odors

Detected by receptor cels in patch of epithelium, olfactory mucosa, in the roof of nasal cavity

Roof of nasal cavity: olfactory cells close to the brain

Not well ventilated as lower nasal cavity

Forcible sniffing is needed to identify an order/ locate its source

Olfactory mucosa

Covers 5 cm² of superior concha, cribriform plate, and nasal septum of each nasal fossa

Consists of 10-20 million olfactory cells as well as epithelial supporting cells and basal stem cells

The rest of nasal cavity is lined by nonsensory respiratory mucosa

Contains olfactory receptors

At upper region of nasal cavity

Olfactory tracts

Carry sensory information from olfactory bulbs to primary olfactory cortex

Olfactory cells

Neurons

Spaced like bowling’s pins

Widest part of cell contained nucleus in the cell body

The neck and head are modified dendrite with a swollen tip

The head have 10-20 cilia

Found in olfactory mucosa

Olfactory hairs

The head bears 10-20 cilia

Immobile

Have binding sites for odor molecules

Lie in tangled mass embedded in thin layer of mucus

Basal end of each cells tapers to axon

Axons collect into small fasciles that leave the nasal cavity through pores (cribriform foramina) in ethmoid bone

Fascicles are CN I

Only neurons directly exposed to external environment

Life span of 60 days

Replaceable

Basal cells divide and differentiate into new olfactory cells

Projection pathways

Olfactory cell axon pass through the roof of nose—> olfactory bulbs (beneath the frontal lobes of brain—> synapse with dendrites of neurons (mitral cells and trusted cells)

Olfactory cell axons reach up shear as mitral and tufted cell dendrites reach down to meet each other in spheroidal clusters (glemeruli)

Glomerulus

All olfactory axons lead to one glemerulus come from cells with same receptor type

Each glomerulus dedicated to a particular type of odor

Higher brain interpret complex orders by decoding signals from a combo of odor-specific glemeruli

Similar to the way our visual system decodes all colors of spectrum using inpu of 3 basic color of eye