2. OLFACTORY NERVE
CNI: OVERVIEW
āø olfactory nerve (CN I) is the ļ¬rst andĀ shortest cranial
nerve
āø is a special visceral afferent nerve, which transmits
information relating toĀ smell
āø Embryologicallly, the olfactory nerve is derived from
theĀ olfactory placodeĀ (a thickening of the ectoderm
layer), which also give rise to the glial cells which
support the nerve
4. OLFACTORY NERVE
CNI: ANATOMICAL COURSE - NASAL EPITHELIUM
Anatomical Course of theĀ Olfactory NerveĀ
āø involves the transmission of special sensory information from the
nasal epitheliumĀ to the primary olfactory cortex of the brain
Nasal Epithelium
āø sense of smell is detected byĀ olfactory receptors located within
theĀ nasal epithelium
āø axons (ļ¬la olfactoria) assemble into small bundles of true olfactory
nerves, which penetrate the small foramina in the cribriform plate
of the ethmoid bone and enter the cranial cavity
5. OLFACTORY NERVE
CNI: ANATOMICAL COURSE - OLFACTORY BULB
Olfactory Bulb
āø Once in the cranial cavity, the ļ¬bres enter theĀ olfactory bulb,Ā which
lies in the olfactory groove within the anterior cranial fossa
āø The olfactory bulb is an ovoid structure which contains specialized
neurones, calledĀ mitral cells
āø The olfactory nerve ļ¬bres synapse with the mitral cells, forming
collections known asĀ synaptic glomeruli
āø From the glomeruli, second order nerves then pass posteriorly into
the olfactory tract
7. OLFACTORY NERVE
CNI: ANATOMICAL COURSE - OLFACTORY TRACT
āø The olfactory tract travels posteriorly on the inferior surface of theĀ frontal lobe
āø As the tract reaches the anterior perforated substance (an area at the level of the
optic chiasm) it divides into medial and lateral stria:
āø Lateral striaĀ āĀ carries the axons to the primary olfactory cortex, located within
the uncus of temporal lobe
āø Medial striaĀ ā carries the axons across the medial plane of the anterior
commissure, where they meet the olfactory bulb of the opposite side
āø The primary olfactory cortex sends nerve ļ¬bres to many other areas of the brain,
notably the piriform cortex, the amygdala, olfactory tubercle and the secondary
olfactory cortex
āø These areas are involved in the memory and appreciation of olfactory sensations
8. OLFACTORY NERVE
CNI: SENSORY FUNCTION
āø sensory function of the olfactory nerve is achieved via
theĀ olfactory mucosa
āø mucosal layer not onlyĀ senses smell, but it also detects
the more advanced aspects of taste
āø Bowmanās glandsĀ present in the mucosa secrete mucus
āø located in the roof of the nasal cavity and is composed
ofĀ pseudostratiļ¬ed columnarĀ epithelium which contains
a number of cells:
9. OLFACTORY NERVE
CNI: SENSORY FUNCTION
āø BasalĀ cells
āø form the new stem cells from which the new olfactory cells can develop
āø SustentacularĀ cellsĀ
āø tall cells for structural support
āø are analogous to the glial cells located in the CNS
āø Olfactory receptorĀ cellsĀ āĀ bipolar neurons which consist of two processes:
āø Dendritic process projects to the surface of the epithelium, where they project a number of
short cilia, the olfactory hairs, into the mucous membrane
āø These cilia react to odors in the air and stimulate the olfactory cells
āø Central process (also known as the axon) projects in the opposite direction through the
basement membrane
14. References
āø These slide reļ¬ect a summary of the contents of
TeachMeAnatomy.info and are to be used for
educational purposes only in compliance with the
terms of use policy.
Speciļ¬c portions referenced in this summary are as
follows:
āø https://teachmeanatomy.info/head/cranial-nerves/
olfactory-cni/
Additional sources are referenced on the slide
containing that speciļ¬c content.