Dr. Ahmed Fathalla Ibrahim

OLFACTORY PATHWAYOLFACTORY PATHWAY

OLFACTORY PATHWAYOLFACTORY PATHWAY

• Composed of two neuronesComposed of two neurones

• Only sensory pathway that does not Only sensory pathway that does not project via thalamusproject via thalamus

OLFACTORY PATHWAYOLFACTORY PATHWAY

First Order Neurone: First Order Neurone: ciliated nerve ciliated nerve cells in olfactory epithelium of nasal cells in olfactory epithelium of nasal cavitycavity

Axons (olfactory nerve fibers) (olfactory nerve fibers) enter cranial cavity through cribriform plate cribriform plate of ethmoid of ethmoid to reach the olfactory bulbthe olfactory bulb

OLFACTORY PATHWAYOLFACTORY PATHWAYSecond Order Neurone: Second Order Neurone: mitral cells in mitral cells in

olfactory bulbolfactory bulb Axons form the olfactory tract the olfactory tract that

passes backward on inferior surface of on inferior surface of frontal lobefrontal lobe then divides (just before reaching optic chiasma) into 3 stria 3 stria (lateral, intermediate & medial)

Most of fibers run in lateral olfactory lateral olfactory striastria (in depth of lateral fissure) (in depth of lateral fissure) & terminate in Primary Olfactory Cortex Primary Olfactory Cortex (Uncus)(Uncus)

OLFACTORY PATHWAYOLFACTORY PATHWAY

Primary Olfactory cortex is connected to the Olfactory Association Cortex Olfactory Association Cortex (anterior part of parahippocampal (anterior part of parahippocampal gyrus or entorhinal cortex)gyrus or entorhinal cortex)

Both Primary & Association cortex are called Pyriform CortexPyriform Cortex

Cells of Spiral Ganglion (in cochleaCells of Spiral Ganglion (in cochlea))

Dorsal & Ventral Cochlear NucleiDorsal & Ventral Cochlear Nuclei

Trapezoid BodyTrapezoid Body

Lateral LeminiscusLateral Leminiscus Superior Superior Olivary Olivary NucleusNucleus

Nucleus of Nucleus of Lateral Lateral

LeminiscusLeminiscus

Inferior ColliculusInferior Colliculus

Medial Geniculate NucleusMedial Geniculate Nucleus

Primary Auditory CortexPrimary Auditory Cortex

Auditory Association CortexAuditory Association Cortex

Inferior ColliculusInferior Colliculus

Auditory RadiationAuditory RadiationRetrolenticular Part of ICRetrolenticular Part of IC

Dorsal & Ventral Cochlear NucleiDorsal & Ventral Cochlear Nuclei

Cells of Spiral GanglionCells of Spiral Ganglion

Medial Geniculate NucleusMedial Geniculate Nucleus

Primary Auditory CortexPrimary Auditory Cortex

Auditory Association CortexAuditory Association Cortex

Commissural fibersCommissural fibers

Cochlear nerveCochlear nerve Cochlear nerveCochlear nerve

NOTES ON AUDITORY PATHWAYNOTES ON AUDITORY PATHWAY• Cochlear nerve makes dendritic contact with Cochlear nerve makes dendritic contact with

hair cells of hair cells of Organ of Corti Organ of Corti (in Cochlear Duct)(in Cochlear Duct)• Superior Olivary Nucleus & Nucleus of Superior Olivary Nucleus & Nucleus of

Lateral Leminiscus: Lateral Leminiscus: modulate transmission modulate transmission of auditory information to cochlear nerve by:of auditory information to cochlear nerve by:

1.1. Sending inhibitory fibers through Sending inhibitory fibers through vestibulocochlear nerve ending in Organ of vestibulocochlear nerve ending in Organ of CortiCorti

2.2. Establishing connection with motor Establishing connection with motor neurones supplying tensor tympani & neurones supplying tensor tympani & stapedius muscles stapedius muscles

NOTES ON AUDITORY PATHWAYNOTES ON AUDITORY PATHWAY

• Representation of cochlea is bilateral at Representation of cochlea is bilateral at all levels rostral to cochlear nucleiall levels rostral to cochlear nuclei

SS

LL

Late ral Late ral VestibulospinalVestibulospinal

tracttract

AHCsAHCs

MedialMedialVestibulospinalVestibulospinal

tracttract

NVPNVP(Thalamus)(Thalamus)

Vestibular AreaVestibular Area

Abducent NucleusAbducent Nucleus

Trochlear NucleusTrochlear Nucleus

Occulomotor NucleusOcculomotor Nucleus

VestibularVestibularGanglionGanglion

Vestibular nerveVestibular nerve

Hair CellsHair Cellsin Vestibule in Vestibule

& Semicircular & Semicircular CanalsCanals

AA

BB

A + B = Medial Longitudinal fasciculusA + B = Medial Longitudinal fasciculus

VESTIBULAR PATHWAYVESTIBULAR PATHWAY

Cochlear nerveCochlear nerve

MM

II

Median PlaneMedian Plane

AHCsAHCs

Vestibular NucleiVestibular Nucleiin Rostral in Rostral MedullaMedulla

ICPICPFlocculonodular Flocculonodular LobeLobe(Cerebellum)(Cerebellum)

NOTES ON NOTES ON VESTIBULAR PATHWAYVESTIBULAR PATHWAY

The first Order Neurones: The first Order Neurones: Cells of Cells of Vestibular ganglionVestibular ganglion located in Internal located in Internal Auditory MeatusAuditory Meatus

The second Order Neurones: The second Order Neurones: Cells of Cells of Superior, Lateral, Medial & Inferior Superior, Lateral, Medial & Inferior Vestibular NucleiVestibular Nuclei located beneath the located beneath the lateral part of floor of 4lateral part of floor of 4thth ventricle ventricle

NOTES ON NOTES ON VESTIBULAR PATHWAYVESTIBULAR PATHWAY

Medial Longitudinal fasciculus: formed Medial Longitudinal fasciculus: formed of both descending & ascending fibers:of both descending & ascending fibers:

1.1.Descending (medial vestibulospinal Descending (medial vestibulospinal tract) tract) to anterior horns cells to anterior horns cells for for control control of body posture & balanceof body posture & balance

2.2.Ascending Ascending to Occulomotor, Trochlear & to Occulomotor, Trochlear & Abducent Nuclei Abducent Nuclei (Motor Nuclei for (Motor Nuclei for extraoccular muscles for extraoccular muscles for coordination coordination of head & eye movementsof head & eye movements

NOTES ON NOTES ON VESTIBULAR PATHWAYVESTIBULAR PATHWAY

Vestibular area: Vestibular area:

1.Located in the lower part of postcentral the lower part of postcentral gyrus (head area) gyrus (head area)

2.Responsible for conscious awareness conscious awareness of vestibular sensationof vestibular sensation