lecture - olfaction pathway

OLFACTION

CHRISTOPHER E. CALAQUIAN, MD, DPBO-HNS

RHINENCEPHALON

• Rostral portion of the brain

• Consists of the (1)olfactory nerves,

(2)olfactory bulbs,

(3)olfactory tracts,

(4)a portion of the anterior perforated substance,

(5)pyriform region of the cortex,

(6)entorhinal cortex of the parahippocampus and

(7)the corticomedial division of the amygdala

PERIPHERAL OLFACTORY APPARATUS

• Found in a specialized area of the nasal mucosa ------OLFACTORY EPITHELIUM

• Pseudostratified columnar olfactory epithelium on the superior concha, the roof of the nasal chamber, and upper portion of the septum

• Scents or chemicals trigger/stimulate receptors in the epithelium via voltage channels or ligand-receptor mediated 2nd messenger system

LATERAL MEDIAL

PATTERN OF PERIPHERAL APPARATUS

olfactory epithelium

olfactory nerves

cribriform plate of -------------------------

ethmoid

olfactory bulb

OLFACTORY BULBS AND PATHWAYS

• OLFACTORY BULB - contains layers of different neuron cell types (laminar)

Mitral cells - receive direct synaptic input from olfactory nerve fibers and send out their axons to the lateral olfactory tract

CROSSING OVER

• Occurs in the anterior olfactory nucleus

• Located in the olfactory stalk

• contains cells coming from the olfactory portion of the anterior commissure

• sends fibers from IPSILATERAL bulb to CONTRALATERAL bulb

Crossing over

(Olfactory trigone)

Anterior OlfactoryNucleus

Lateral OlfactoryNucleus

OLFACTORY TRACT

• Has two stria - a medial and a lateral striae

MEDIAL STRIAE ANTERIOR

OLFACTORY NUCLEUS

LATERAL STRIAE LATERAL OLFACTORY NUCLEUS

LATERAL OLFACTORY TRACT

• Mitral cells that skirts the lateral margin

anterior perforated substance

pyriform cortex (primary olfactory cortex)

entorhinal cortex (secondary olfactory cortex)

amygdala

Entorhinal

Primary olfactory

PRIMARY OLFACTORY CORTEX

• THREE layered paleocortex, older than the neocortex of the visual, auditory and somatosensory systems

• The olfactory cortex connects with the neocortex via :

(1) projections directly to the orbitofrontal cortex

(2) projections to the thalamus* which connects to the orbitofrontal cortex

OrbitofrontalCortex

OLFACTORY DISCRIMINATION

• Subserved by the connection of the olfactory cortex to the orbitofrontal cortex

• When severed in experimental animals, they cannot discriminate or identify differences in odor (although they can only distinguish the presence or absence of the odor)

• May also be possible via connections with the temporal lobe

AMYGDALA

• Regulation of the chemosensory control of social behaviors

sexual

aggressive

maternal responses

ENTORHINAL AREA, AMYGDALA & HIPPOCAMPUS

• Integration of olfactory information with visual, auditory and somatosensory information

• Learned emotional response

Amygdala

Parahippocampus

NERVES AFFECTING OLFACTION

Trigeminal(Pterygopalatine)