Olfactory nerve

Organization of the cranial nerves Sensory nerves Motor nerves Mixed nerves Olfactory Optic ...

Organization of the cranial nerves

Sensory nerves	Motor nerves	Mixed nerves
Olfactory Optic Vestibular – cochlear	Occulomotor Trochlear Abducent Accessory Hypoglossal	Trigeminal Facial Glossopharyngeal Vagus

Motor nuclei of the cranial nerves

Somatic motor nuclei

General visceral motor nuclei

They receive impulses from the cerebral cortex trough Cortico – nuclear fibers These fibers originated from the pyramidal cells of the inferior part of the pre central gyrus (Area 4) & the adjacent part of the post central gyrusThe fibers descend through the corona radiate & genu of the internal capsule They pass through the midbrain just medial to the corticospinal fibers & synapse with the cranial nerve nuclei Bilateral connections are present for all cranial motor nuclei except for: Part of the facial nucleus that supplies the muscles of the lower part of the face Part of the hypoglossal nucleus that supplies the genioglossus muscle

They form the cranial outflow of the parasympathetic part of the ANS Edinger Westphal nucleus (III nerve) Superior salivatory & Lacrimal nuclei (VII nerve) Inferior salivatory nucleus                (IX nerve) Dorsal motor nucleus (X nerve)

1) Olfactory nerve

• It’s a sensory nerve : Sensation of smell
• Olfactory receptor : 1^st order neuron
• Nerves fibers
  
  • Unmyelinated & runs through the cribriform plate of the ethmoid bone
  • Doesn’t pass through the thalamus (No connection with thalamic nuclei)
• Olfactory area of the cerebral cortex is area 28

Examining the olfactory nerve

• Use a common bedside substance like soap, fruit or etc to each nostril separately (Close the other)
• Don’t use irritable substance like NH₃ (It will stimulate TGN – V)
• Defects
  
  • Anosmia : Absence of smell (Sub frontal meningioma, head injury, Craniotomy & Catarrh – Inflammation of the mucus membranes)
  • Hallucinations of smell : in temporal lobe seizures

2) Optic nerve



Parts of the optic pathway
 

Part	Explanation
Origin of the optic nerve	Fibers of the optic nerve are the axons of the ganglionic layer of the retina They converge on the optic disc & leave the eye as the optic nerve Fibers of the optic nerve are myelinated (By oligodendrocytes) Optic nerve leaves the orbital cavity through the optic canal
Optic chiasma	The fibers from the nasal ½ of each retina (Including the nasal ½ of the macula) cross the midline enter the optic tract opposite side The fibers from the temporal ½ of each retina (Including the temporal ½ of the macula) pass to the optic tract of the same side
Optic tract	Emerges from the optic chiasma Most fibers synapse with nerve cells in the LGB Few fibers pass to the pretectal nucleus & the superior colliculus of the midbrain are responsible for light reflexes
Lateral geniculate body (LGB)	It’s a thalamic nucleus
Optic radiation	It’s the axons of the nerves of LGB Pass through the internal capsule & terminates in the visual cortex (Area 17 – Occupies the upper & lower lips of the calcarine sulcus) Visual association area (Area 18 & 19) are responsible for recognition of objects & perception  of color
Neurons of the visual pathway	Rods & Cones (Specialized receptor neurons in the retina) Bipolar neurons (Connect the rods & cones to ganglion cells) Ganglion cells (Axons pass to the LGB) Neurons of the LGB (Axons pass to the cerebral cortex)