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Home , Oculomotor nucleus, Optic nerve

Cranial II, III, IV & VI

Neuroanatomy block-Anatomy-Lecture 13

Editing file Objectives

At the end of the lecture, students should be able to:

01 List the cranial nuclei related to occulomotor, trochlear, and abducent nerves in the stem. 02 Describe the type and site of each nucleus. 03 Describe the site of emergence and course of these 3 nerves. 04 Describe the important relations of occulomotor, trochlear, and abducent nerves in the . 05 List the orbital muscles supplied by each of these 3 nerves. Color guide

06 Describe the effect of lesion of each of these 3 nerves. ● Only in boys slides in Green ● Only in girls slides in Purple 07 Describe the optic and visual pathway. ● important in Red ● Notes in Grey Extra-Ocular Muscles 7 muscles 1. Levator palpebrae superioris. (Elevates the upper eyelid) 2. Medial rectus.(medial) 3. Lateral rectus.(lateral) 4. Superior rectus.(upward and medially ) 5. Inferior rectus.(downward and medially) 6. Superior oblique.(downward and laterally) 7. Inferior oblique.(upward and laterally) ❖ All muscles of the are supplied by the , EXCEPT LR6 lateral rectus (by abducens) + SO4 superior oblique (by trochlear)

Brain stem (Lateral view) Brain (Ventral view) 3 Oculomotor Nerve

➢ Motor for most of extraocular muscles. ➢ Also carries preganglionic parasympathetic fibers to the pupillary constrictor () and ciliary muscles (accomodation).

Has two nuclei

Accessory nucleus Main (Edinger-Westphal nucleus)

❖ Lies in the at the ❖ Lies dorsal to the main motor level of , nucleus. ❖ located in the periaqueductal ❖ receives Fibres from the pretectal . nucleus for the direct and consensual pupillary reflexes, and Corticonuclear fibers for ❖ Its cells are preganglionic parasympathetic neurons.

4 Oculomotor Nerve

➔ It curves ventrally through the and the in the midbrain. from the ➔ The nerve emerges on the anterior surface of oculomotor nucleus the midbrain in the accompany the oculomotor nerve fibers to the medial to crus cerebri/. orbit, where they terminate in the ciliary ➔ Then it passes forward between posterior ganglion (one of the parasympathetic ganglion of cerebral and superior cerebellar arteries. the head & )Postganglionic fibers pass ➔ In the it runs in the through the to the eyeball, lateral wall of the , then it where they supply: divides into superior and inferior divisions ❏ Constrictor pupillae muscle of the iris which pass to the orbit through the superior ❏ Ciliary muscle. orbital fissure to the orbit

Axons from the Edinger-Westphal nucleus

oculomotor nerve

5 Oculomotor Nerve The results of Lesion Lateral squint. (since medial is affected and 1 only lateral is working) Oculomotor Nerve

Ptosis (drooping of the eyelid). 2

responsible (double vision). Diplopia always supplies accompanies squint for 3

Pupillary dilatation Motor to Elevation of upper 4 eyelid (open the eye). ● Levator palpebrae superioris ● Superior rectus muscle Loss of accommodation ● Medial rectus muscle Turning the 5 ● eyeball upward, Inferior rectus muscle downwards and ● medially. The eyeball is fully abducted and 6 depressed (down and out) because of the unopposed activity of lateral rectus and Constriction of the superior oblique. Parasympathetic (pupillary fibers to reflex) ● Constrictor pupillae ● note: The preganglionic parasympathetic fibers run superficially in the ● Ciliary muscles Accommodating nerve and are therefore the first axons to suffer when a nerve is affected reflex of the . by external pressure. Consequently, the first sign of compression of the oculomotor nerve is ipsilateral slowness of the to light.

6 (IV) 4th Cranial Nerve ➢ Type: Motor ➢ location: of Small motor nucleus in the periaqueductal grey matter at the level of of the midbrain. ➢ Course of the nerve: ★ Fibers curve backwards and decussate. ★ The nerve emerges immediately caudal to the inferior colliculus, on the dorsal surface of . ( it is the only cranial nerve to emerge from the dorsal surface). ★ It passes forward through middle cranial fossa in the lateral wall of the cavernous sinus.(trochlear and oculomotor run in the lateral wall and abducens runs medial to them). ★ The nerve then enters the orbit through the superior orbital fissure

Lesion results in: Function: Supplies: 1. diplopia Rotates the eyeball 2. Inability to rotate the eyeball inferolaterally. downwards and laterally. (only one muscle) So, the eye deviates; upward and

slightly inward (medially).

This person has difficulty in walking downstairs

7 Abducent Nerve (VI) 6th Cranial Nerve ➢ Only one motor nucleus. ➢ Lies in caudal in the floor of the 4th ventricle. close to the middle line, in a line with 3rd, 4th & 12th nerves. ➢ Fibers of looping around the abducent nucleus forms the facial colliculus. ➢ It emerges from the ventral aspect of brainstem, at the junction of the pons and the pyramid of the . ➢ It passes through the floor of cavernous sinus, lying below and lateral to the ➢ Then it enters the orbit through the superior orbital fissure.

➢ It supplies: the which rotates the eyeball laterally ; (abduction).

Abducent Nerve Lesion

● medial squint: Inability to direct the affected eye laterally ● nuclear lesion:may also involve the nearby nucleus or axons of the facial nerve, causing paralysis of all facial muscles in the ipsilateral side.

# Oculomotor lateral squint| Abducent medial squint

8 (II) 2nd Cranial Nerve

● Type: sensory ● Function: Vision ● Lesion : defects and loss of , a defect of vision is called .

Visual Pathway

Optic Optic Optic nerve tract radiation

Lateral Optic geniculate Visual body cortex ”nucleus”

9 Visual Pathway Photoreceptors: Rods & Cones of the Three orders neurons pathway :

1 Bipolar cells of retina

Ganglion cells of retina. 2 Their axons form the optic nerve

Neurons in the lateral geniculate body. 3 Their axons terminate in primary .

10 Visual Pathway Optic nerve

01● Axons of retinal ganglion cells converge at the and pass as the optic nerve.

02● Then the nerve passes posteromedially in the orbit.

03● Then exits through the to enter the middle cranial fossa to form the optic chiasma.

Optic Chiasma

➔ Fibers from the nasal (medial) half of retina decussate in the chiasm and join uncrossed fibers from the temporal (lateral) half of the retina to form the .

➔ The decussation of nerve fibers in the chiasm results in the right optic tract conveying impulses from the left visual field and vice versa.

➔ The partial crossing of optic nerve fibers in the optic chiasma is a requirement for binocular vision.

11 Visual Pathway Optic Tract

➢ 01 Mainly terminate in the (LGB), lateral geniculate body of the thalamus (3rd order neuron). ● From the lateral geniculate nucleus (third-order neuron), thalamocortical fibres project through the retrolenticular part of the posterior limb of the internal capsule as the ● which terminates in the primary visual cortex of the .

02 ➢ A few fibers terminate in and superior colliculus. ➔ These fibers are related to light reflexes.

Visual Cortex

The primary visual cortex

is located predominantly on the medial surface of the occipital is extensive, including the whole of the occipital lobe, the lobe in the region above, below and behind the calcarine sulcus. adjacent posterior part of the parietal lobe. This cortex is It’s occupies the upper and lower lips of the calcarine sulcus on involved in interpretation and recognition of objects and the medial surface of occipital lobe .(area 17 of Brodmann's of color, depth, motion, and other aspects of classification) vision.

# The primary cortex: I saw something, while Association cortex: what did I see (recognition & interpretation) The visual association cortex # Each primary cortex has an association cortex.

12 Visual Defects

Bitemporal Contralateral Monocular Blindness Hemianopia Homonymous Hemianopia

● “Loss Of Vision In The Affected Eye “ Compression of the optic Vascular and neoplastic lesions ● Disease of the eyeball (, chiasm by an adjacent of the optic tract, optic radiation , retinal pituitary tumor or occipital cortex detachment, & methyl alcohol poisoning) ● disease of the optic nerve (, optic nerve tumors)

For your knowledge : •A person may not be able to see objects on their right or left sides () if the optic tract or radiation or visual cortex is affected. •Or may have difficulty seeing objects on their outer visual fields () if the is involved. •The pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical . Pretectal nuclei are bilateral group of highly interconnected nuclei located near the junction of the midbrain and .

13 Only on the boy’s slides. Pigmentosa

It is an inherited metabolic disorder of the Definition photoreceptor and retinal pigment epithelial cells.

It is due to mutation of a key protein called Rhodopsin Cause in the retinal photoreceptors.

➢ Progressive night blindness ➢ Peripheral visual field constriction Complications ➢ Pigmentation of the retina visible on ophthalmoscopy

Affected The type of affected photoreceptor is Rods. photoreceptor

14 Practice Q5: Compression of the optic chiasm leads to? Q1: The oculomotor nerve has? A. monocular blindness A. Motor fibers B. bitemporal hemianopia B. Sympathetic fibers C.contralateral homonymous hemianopia C. Sensory fibers D. B and C D. Parasympathetic fibers Q6:The primary visual cortex occupies the upper and lower lips of the? Q2: The edinger-westphal nucleus receives fibers from corticonuclear fibers for? A.Calcarine sulcus on the medial surface of the occipital lobe A.Stretch reflex B.Parieto-occipital sulcus on the lateral surface of the cerebral hemisphere B. Pupillary reflex C.Calcarine sulcus on the lateral surface of the cerebral hemisphere C. Accommodation reflex D.Parieto-occipital sulcus on the medical surface of the cerebral hemisphere D. Non of them Q7: Which retinal fibers are present in the left optic tract? Q3: Lesion of trochlear nerve results in? A.Left temporal and left nasal fibers A. Lateral squint B. Right temporal and left nasal fibers B. Loss of accommodation C. Right temporal and right nasal Fibers C. Inability to rotate the eyeball infero-laterally D.Left temporal and right nasal fibers D. Non of them Q8 : Abducens nerves supplies? Q4: First order neurons of optic nerve are? A. Inferior oblique muscle A. Bipolar cells of retina B.Inferior oblique muscle B. Ganglion cells of retina C. Lateral rectus muscle C. lateral geniculate body D. All of the above D. rods and cones

Answers: Q1(A&D) Q2(C) Q3(C) Q4(A) Q5(B) Q6(A) Q7(D) Q8(C) 15 Members board

Team leaders

● Abdulrahman Shadid ● Ateen Almutairi Girls team : Boys team: ● Ajeed Al Rashoud ● Mohammed Al-huqbani ● Taif Alotaibi ● Salman Alagla ● Noura Al Turki ● Ziyad Al-jofan ● Amirah Al-Zahrani ● Ali Aldawood ● Alhanouf Al-haluli ● Khalid Nagshabandi ● Sara Al-Abdulkarem ● Omar Alammari ● Renad Al Haqbani ● Sameh nuser ● Nouf Al Humaidhi ● Abdullah Basamh ● Jude Al Khalifah ● Alwaleed Alsaleh ● Nouf Al Hussaini ● Mohaned Makkawi ● Rahaf Al Shabri ● Abdullah Alghamdi ● Danah Al Halees ● Rema Al Mutawa ● Amirah Al Dakhilallah ● Maha Al Nahdi Contact us: ● Razan Al zohaifi ● Ghalia Alnufaei Editing file most probably you don't need this