CorpusHuman Anatomy
Special SensesNeural pathway

Olfactory pathway

Also known as: olfactory tract, olfactory striae, piriform cortex, primary olfactory cortex, entorhinal cortex, orbitofrontal cortex

Olfactory receptor neurons → olfactory bulb → olfactory tract → (lateral olfactory stria) → primary olfactory cortex (piriform cortex, amygdala, entorhinal cortex) — the only sensory pathway that reaches the cortex without first relaying in the thalamus.

Show on body map Smell and Taste — Chemoreceptors

Overview

Mitral and tufted cell axons leave the bulb in the olfactory tract, which runs back in the olfactory sulcus and, at the olfactory trigone just in front of the anterior perforated substance, divides into lateral and medial olfactory striae (an intermediate stria is variable).

The lateral olfactory stria carries most fibres directly to the primary olfactory cortex: the piriform cortex (at the junction of frontal and temporal lobes — the main centre for odour identity), periamygdaloid cortex and cortical amygdala (emotional and social significance), anterior part of the entorhinal cortex (link to the hippocampus and memory), and the olfactory tubercle and anterior olfactory nucleus. The medial stria projects to the septal area and, via the anterior commissure, to the contralateral bulb. Olfactory cortex is paleocortex (three-layered allocortex).

Olfaction is unique in that it reaches the cortex without a prior thalamic relay. Secondary projections do reach the thalamus: piriform cortex → mediodorsal nucleus of the thalamus → orbitofrontal cortex (conscious odour discrimination and integration with taste into flavour), alongside direct piriform–orbitofrontal connections. Further projections to the hypothalamus and brainstem mediate feeding, autonomic and endocrine responses, and the direct links to the amygdala and hippocampus explain the unusually powerful link between smells, emotion and autobiographical memory (the "Proust effect").

Location

Olfactory bulb (anterior cranial fossa) → olfactory tract → anterior perforated substance → medial temporal lobe (uncus, piriform and entorhinal cortex, amygdala) and orbitofrontal cortex.

Parts & subdivisions

  1. Olfactory nerve (CN I)
    Olfactory fila through the cribriform plate.
  2. Olfactory bulb
    Glomerular processing; mitral/tufted output neurons.
  3. Olfactory tract and striae
    Lateral stria → primary olfactory cortex; medial stria → septal area and contralateral bulb via the anterior commissure.
  4. Primary olfactory cortex
    Piriform cortex, periamygdaloid cortex/amygdala, anterior entorhinal cortex, olfactory tubercle — no thalamic relay.
  5. Orbitofrontal cortex
    Secondary olfactory cortex (via mediodorsal thalamus and directly); conscious perception, flavour, reward value.

Function

  • Odour identification, discrimination and memory
  • Emotional and motivational responses to odours (amygdala, hypothalamus)
  • Flavour perception (convergence with taste in orbitofrontal and insular cortex)
  • Reflexes: salivation, gastric secretion, sneezing, nausea to noxious odours

Clinical significance

Uncinate seizures

Focal seizures arising in the medial temporal lobe (uncus/amygdala) often begin with an olfactory aura — a brief, unpleasant smell (e.g. burning rubber) — sometimes with lip-smacking and déjà vu.

Testing CN I

Each nostril is tested separately with non-irritating odours (coffee, peppermint, vanilla); ammonia or vinegar stimulate trigeminal endings and should not be used. Unilateral anosmia is easily missed if both nostrils are tested together.

Mnemonics

Thalamus bypass

"Smell skips the thalamus": every other sense relays in the thalamus before reaching its primary cortex; olfaction goes straight to piriform cortex and reaches the thalamus (mediodorsal nucleus) only secondarily.

Compiled from standard anatomy and physiology references — see the Special Senses sources. For education only; not medical advice.