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OLFACTORY & VESTIBULOCOCHLEAR PATHWAYS

OLFACTORY & VESTIBULOCOCHLEAR PATHWAYS. Dr. Ahmed Fathalla Ibrahim. OLFACTORY PATHWAY. OLFACTORY PATHWAY. Composed of two neurones Only sensory pathway that does not project via thalamus. OLFACTORY PATHWAY.

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OLFACTORY & VESTIBULOCOCHLEAR PATHWAYS

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  1. OLFACTORY & VESTIBULOCOCHLEAR PATHWAYS Dr. Ahmed Fathalla Ibrahim

  2. OLFACTORY PATHWAY

  3. OLFACTORY PATHWAY • Composed of two neurones • Only sensory pathway that does not project via thalamus

  4. OLFACTORY PATHWAY • First Order Neurone: ciliated nerve cells in olfactory epithelium of nasal cavity • Axons (olfactory nerve fibers) enter cranial cavity throughcribriform plate of ethmoidto reach the olfactory bulb

  5. OLFACTORY PATHWAY • Second Order Neurone: mitral cells in olfactory bulb • Axons form the olfactory tract that passes backward on inferior surface of frontal lobe then divides (just before reaching optic chiasma) into 3 stria(lateral, intermediate & medial) • Most of fibers run in lateral olfactory stria(in depth of lateral fissure) & terminate in Primary Olfactory Cortex (Uncus)

  6. OLFACTORY PATHWAY • Primary Olfactory cortex is connected to the Olfactory Association Cortex (anterior part of parahippocampalgyrus or entorhinal cortex) • Both Primary & Association cortex are called Pyriform Cortex

  7. Auditory Association Cortex Auditory Association Cortex Primary Auditory Cortex Primary Auditory Cortex Auditory Radiation Retrolenticular Part of IC Medial Geniculate Nucleus Medial Geniculate Nucleus Inferior Colliculus Inferior Colliculus Commissural fibers Nucleus of Lateral Leminiscus Lateral Leminiscus Superior Olivary Nucleus Trapezoid Body Dorsal & Ventral Cochlear Nuclei Dorsal & Ventral Cochlear Nuclei Cochlear nerve Cochlear nerve Cells of Spiral Ganglion (in cochlea) Cells of Spiral Ganglion

  8. NOTES ON AUDITORY PATHWAY • Cochlear nerve makes dendritic contact with hair cells of Organ of Corti(in Cochlear Duct) • Superior Olivary Nucleus & Nucleus of Lateral Leminiscus: modulate transmission of auditory information to cochlear nerve by: • Sending inhibitory fibers through vestibulocochlear nerve ending in Organ of Corti • Establishing connection with motor neurones supplying tensor tympani & stapedius muscles

  9. NOTES ON AUDITORY PATHWAY • Representation of cochlea is bilateral at all levels rostral to cochlear nuclei

  10. VESTIBULAR PATHWAY Vestibular Area NVP (Thalamus) A + B = Medial Longitudinal fasciculus Median Plane Occulomotor Nucleus Trochlear Nucleus Abducent Nucleus A Flocculonodular Lobe (Cerebellum) ICP S M Vestibular Nuclei in Rostral Medulla L I Medial Vestibulospinal tract Vestibular nerve Late ral Vestibulospinal tract Vestibular Ganglion B Hair Cells in Vestibule & Semicircular Canals Cochlear nerve AHCs AHCs

  11. NOTES ON VESTIBULAR PATHWAY • The first Order Neurones: Cells of Vestibular ganglion located in Internal Auditory Meatus • The second Order Neurones: Cells of Superior, Lateral, Medial & Inferior Vestibular Nuclei located beneath the lateral part of floor of 4th ventricle

  12. NOTES ON VESTIBULAR PATHWAY • Medial Longitudinal fasciculus: formed of both descending & ascending fibers: • Descending (medial vestibulospinal tract) to anterior horns cells for control of body posture & balance • Ascending to Occulomotor, Trochlear & Abducent Nuclei (Motor Nuclei for extraoccular muscles for coordination of head & eye movements

  13. NOTES ON VESTIBULAR PATHWAY • Vestibular area: • Located in the lower part of postcentralgyrus (head area) • Responsible for conscious awareness of vestibular sensation

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