MedicalLecture Notes

Somatic motor nuclei

General visceral motor nuclei

1. They receive impulses from the cerebral cortex trough Cortico – nuclear fibers
2. 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 gyrus
3. The fibers descend through the corona radiate & genu of the internal capsule
4. They pass through the midbrain just medial to the corticospinal fibers & synapse with the cranial nerve nuclei
5. Bilateral connections are present for all cranial motor nuclei except for:
   1. Part of the facial nucleus that supplies the muscles of the lower part of the face
   2. Part of the hypoglossal nucleus that supplies the genioglossus muscle
   3. They form the cranial outflow of the parasympathetic part of the ANS

1. Edinger Westphal nucleus (III nerve)
2. Superior salivatory & Lacrimal nuclei (VII nerve)
3. Inferior salivatory nucleus                (IX nerve)
4. Dorsal motor nucleus (X nerve)

Part

Explanation

1. Fibers of the optic nerve are the axons of the ganglionic layer of the retina
2. They converge on the optic disc & leave the eye as the optic nerve
3. Fibers of the optic nerve are myelinated (By oligodendrocytes)
4. Optic nerve leaves the orbital cavity through the optic canal

1. 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
2. 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

1. Emerges from the optic chiasma
2. Most fibers synapse with nerve cells in the LGB
3. Few fibers pass to the pretectal nucleus & the superior colliculus of the midbrain are responsible for light reflexes

It’s a thalamic nucleus

1. It’s the axons of the nerves of LGB
2. Pass through the internal capsule & terminates in the visual cortex (Area 17 – Occupies the upper & lower lips of the calcarine sulcus)
3. Visual association area (Area 18 & 19) are responsible for recognition of objects & perception  of color

1. Rods & Cones (Specialized receptor neurons in the retina)
2. Bipolar neurons (Connect the rods & cones to ganglion cells)
3. Ganglion cells (Axons pass to the LGB)
4. Neurons of the LGB (Axons pass to the cerebral cortex)

1. By a Snellen’s chart held at 6m from the patient (if space is limited at 3m with a mirror)
2. Acuity greater than 6/60 is dependent on the macular vision
3. Each eye is tested separately
4. If the patient cannot see the largest (Designated 60), reduce the test distance
5. If at 1m ‘60’ letter cannot be read, use:
   1. Counting fingers held up at 1m
   2. Hand movements
   3. Perception of light
   4. If a patient cannot read 6/6 check the vision again using a pinhole occluder (Only the central light pass to the retina) – Can differentiate patients with poor vision due to:
      1. Refractory errors (Myopic – Short sighted, Hypermetrophia – Long sighted, Astigmatism – Cornea is not uniformly curved & light is not evenly focused on the retina)
      2. Ocular or neurological conditions

1. Moving finger test
   1. The finger should be kept more than midway between you & the patient
   2. Patient closes one eye & fixes the gaze on your eye
   3. Red pin confrontation test
      1. Use a red hatpin (d = 0.5cm) held at equidistance between you & the patient
      2. Use exactly same conditions above
      3. Check whether the patient & you see the pin at the same time
      4. Binocular testing

1. Acquired defects
   1. Red color vision can be affected in optic nerve disease & macular disease
   2. Use a red target & check the difference of vision in both eyes separately
   3. Congenital defects          : Use a Ischihara color vision test

1. Papilloedema
2. Optic atrophy
3. Pigmentary retinal degeneration
4. Vascular diseases