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Olfactory nerve

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

image

  • It’s a sensory nerve : Sensation of smell
  • Olfactory receptor : 1st 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

image

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)
Olfactory nerve Olfactory nerve Reviewed by Radiology Madeeasy on August 08, 2010 Rating: 5
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