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Home , Chiasm (anatomy), Oculomotor nucleus, Optic chiasm, Optic nerve

Cranial II, III, IV & VI (Optic, Oculomotor, Trochlear, & Abducens)

Lecture (13) ▪ Important ▪ Doctors Notes Please check our Editing File ▪ Notes/Extra explanation

ه هذا العمل مب ين بشكل أسا يس عىل عمل دفعة 436 مع المراجعة { َوَم نْ يَ َت َو َ ّكْ عَ َلْ ا َّْلل فَهُ َوْ َحْ سْ ُ ُُْ} والتدقيق وإضافة المالحظات وال يغ ين عن المصدر األسا يس للمذاكرة ▪ Objectives

At the end of the lecture, students should be able to: ✓ List the cranial nuclei related to occulomotor, trochlear, and abducent nerves in the stem. ✓ Describe the type and site of each . ✓ Describe the site of emergence and course of these 3 nerves. ✓ Describe the important relations of oculomotor, trochlear, and abducent nerves in the ✓ List the orbital muscles supplied by each of these 3 nerves. ✓ Describe the effect of lesion of each of these 3 nerves. ✓ Describe the optic and visual pathway. Recall the how these nerves exit from the brain stem: Optic (does not exit from brain stem) Occulomotor: ventral (medial aspect of crus cerebri) Trochlear: dorsal midbrain (caudal to ) Abducent: ventral (junction b/w pons & pyramid) Brain (Ventral view) Brain stem (Lateral view) Extra-Ocular Muscles

7 muscles: (ترفع جفن العين) .Levator palpebrae superioris 1- Origin: from the roof of the orbit (4) Recti muscles: *Rectus: ماشي على ( Superior rectus (upward and medially 2- الصراط (Inferior rectus (downward and medially 3- المستقيم 4- Medial rectus (medial) (medial) 5- Lateral rectus (lateral) How to remember the 2 فحركته muscles not supplied by نفس اسمه -اسمها عكس وظيفتها- :Oblique muscles (2) 6- Superior oblique (downward and laterally) Oblique: CN3? Superior oblique goes -1 منحرفOrigin: from the roof of the orbit 7- Inferior oblique (upward and laterally) up (superior) and turns around (oblique) a notch يمشي Origin: from the anterior floor or pulley and its supply is عكس كالمه NB. All muscles of the are supplied trochlear which in latin (بكرة) by the , EXCEPT SO4 means pulley superior oblique (by trochlear) and LR6 2- Lateral rectus function: abduction and lateral rectus (by abducens)C is supplied by abducens Occulomotor (III) 3rd Cranial Nerve o Motor for most of extraocular muscles. o Also carries preganglionic parasympathetic fibers to the pupillary constrictor and ciliary muscles. o Has two nuclei: 1- Main occulomotor nucleus; • Lies in the mid brain (posterior part of the ), at the level of located in the periaqueductal . 2- Accessory nucleus (Edinger-Westphal nucleus); • Lies dorsal to the main motor nucleus. • Its cells are preganglionic parasympathetic neurons. • It receives; Corticonuclear fibers for (1) , and from the pretectal nucleus for the direct and consensual (2) pupillary reflexes. Occulomotor (III) 3rd Cranial Nerve o from the curve ventrally through the tegmentum* and the in the midbrain. o The nerve emerges on the anterior surface of the midbrain in the medial to crus cerebri/. o Then it passes forward between posterior Extra cerebral and superior cerebellar arteries. o In the it runs in the lateral wall of the **, then it divides into superior and inferior divisions which pass to the orbit through the superior orbital fissure. *Recall: the midbrain is divided into a dorsal part (Tectum) **Cavernous sinus: one of the Dural Venuses sinuses, trochlear & and a ventral part (Tegmentum) occulomotor run in the lateral wall and abducent runs in the floor Occulomotor (III) 3rd Cranial Nerve o Axons from the Edinger-Westphal nucleus accompany the oculomotor nerve fibers to the orbit, where they terminate in the ciliary (one of the parasympathetic ganglion of the head & ) o Postganglionic fibers pass through the to the eyeball, where they supply: • Constrictor pupillae muscle of the iris • Ciliary muscle.

Extra Occulomotor (III) 3rd Cranial Nerve Occulomotor nerve supplies: o Motor to: 1. Levator palpebrae superioris 2. Superior rectus muscle 3. Medial rectus muscle 4. Inferior rectus muscle 5. o Parasympathetic fibers to: 1. Constrictor pupillae 2. Ciliary muscles It is responsible for; • Elevation of upper eyelid (open the eye) (by levator palpebrae superioris). • Turning the eyeball upward, downwards and medially. • Constriction of the () • Accommodating reflex of the . Occulomotor (III) 3rd Cranial Nerve

Lesion results in: 1. Lateral squint. (since medial is affected and only lateral is working) 2. (drooping of the eyelid). 3. (double vision). Diplopia always accompanies squint 4. Pupillary dilatation. 5. Loss of accommodation. 6. The eyeball is fully abducted and depressed (down and out) because of the unopposed activity of lateral rectus and superior oblique. The preganglionic parasympathetic fibers run superficially in the nerve and are therefore the first axons to suffer when a nerve is affected by external pressure. Consequently, the first sign of compression of the occulomotor nerve is ipsilateral slowness of the to light. Trochlear (IV) 4th Cranial Nerve o Type: motor o Small motor nucleus located in the periaqueductal grey matter at the level of inferior colliculus of the midbrain. o Fibers curve backwards and decussate. o The nerve emerges immediately caudal to the Extra inferior colliculus, on the dorsal surface of brain stem. (recall it is the only cranial nerve to emerge from the dorsal surface). o It passes forward through middle cranial fossa in the lateral wall of the cavernous sinus* below the 3rd cranial nerve o The nerve then enters the orbit through the superior orbital fissure (with oculomotor). **Cavernous sinus: one of the Dural Venuses sinuses, trochlear & occulomotor run in the lateral wall and abducent runs in the floor Trochlear (IV) 4th Cranial Nerve

o It supplies; , (only one muscle). o Its function; Rotates the eye ball downwards and laterally. o Lesion of results in • diplopia (double vision) & • Inability to rotate the eyeball infero-laterally. o So, the eye deviates; upward and slightly inward (medially). o This person has difficulty in walking downstairs

مايتحرك فبالتالي مايقدر ينزل من الدرج كرسي متحرك عجلة بكرة Trochlear* Abducent (VI) 6th Cranial Nerve o Only one motor nucleus. o Lies in caudal pons in the floor of the 4th ventricle. o Lies close to the middle line, in a line with 3rd, 4th & 12th nerves (All motor). o Fibers of looping around the abducent nucleus forms the facial colliculus. (recall from of : The abducent nucleus lies medially, and below it is the fiber of the facial nerve which goes above and around it and forms the facial colliculus) o It emerges from the ventral aspect of brainstem, at the junction of the pons and the pyramid of the . Extra ** لو حصل راح يتأثر هذا النيرف ***ألنه يمشي مسافة طويلة فهو اكثر نيرف معرض ان يحصل له مشكلة Abducent (VI) 6th Cranial Nerve o It passes through the floor of cavernous sinus, lying below and lateral to the ** o Then it enters the orbit through the superior orbital fissure. o It supplies; the which rotates the eye ball laterally ; (abduction). Lesion results in: o Inability to direct the affected eye laterally, so it result in (medial squint*). o A nuclear lesion may also involve the nearby nucleus or axons of the facial nerve, causing paralysis of all facial muscles in the ipsilateral side. *Occulomotor  lateral squint| Abducent  medial squint Optic (II) 2nd Cranial Nerve o Type: Special sensory N. o Function: Vision o Lesion results in: defects and loss of , a defect of vision is called . Visual Pathway 1. . 2. Optic . 3. . 4. Lateral geniculate body (nucleus). In 5. . 6. . Visual Pathway o Photoreceptors: Rods & Cones of the o Three neurons pathway

1st order neurons: Bipolar cells of retina

2nd order neurons: Ganglion cells of retina. Their axons form the optic nerve 3rd order neurons: Neurons in the lateral geniculate body. Their axons terminate in primary visual cortex. Extra Visual Pathway Optic nerve

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

• Then the nerve passes posteromedially in the orbit.

• Then exits through the (optic nerve & pass through it) to enter the middle cranial fossa to form the Extra optic chiasma. Visual Pathway Optic Chiasma o 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 optic tract. o The of nerve fibers in the chiasm results in the right optic tract conveying impulses from the left visual field and vice versa. o The partial crossing of optic nerve fibers in the optic chiasma is a requirement for . Which retinal fibres are present in the left optic tract? Fibers from left temporal and right nasal. Visual Pathway Optic Tract

Fibers in the optic tracts: o A few fibers terminate in and superior colliculus. o These fibers are related to light reflexes.

o Mainly terminate in the (LGB), lateral geniculate body of the thalamus (3rd order neuron).

o 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 optic radiation,

o which terminates in the primary visual cortex of the .

o The primary visual cortex is located predominantly on the medial surface of the hemisphere in the region above and below the calcarine sulcus. Visual Pathway Visual Cortex o The primary visual cortex (area 17* of Brodmann's) occupies the upper and lower lips of the calcarine sulcus on the medial surface of the cerebral hemisphere. o The visual association cortex (area 18) is extensive, including the whole of the occipital lobe, the adjacent posterior part of the parietal lobe. This cortex is involved in interpretation and recognition of objects and of color, depth, motion, and other aspects of vision. (مجرد رؤية) The primary cortex: I saw something* Association: what did I see (recognition & interpretation) Note: each primary cortex has an association cortex * بالعربي تشبهVI  visual 17 Visual Defects

1. Disease of the eyeball (, , retinal JUST READING (EXTRA) detachment, & methyl alcohol poising) and disease of the optic nerve (, optic nerve tumors) lead to : loss of For you: Visual field deficits • A person may not be able to see vision in the affected eye (monocular blindness). objects on their right or left sides 2. Compression of the by an adjacent pituitary tumor leads () if the to: bitemporal hemianopia. optic tract or radiation or visual cortex is affected. • Or may have difficulty seeing objects 3. Vascular and neoplastic lesions of the optic tract, optic radiation or on their outer visual fields (bitemporal occipital cortex produce: contralateral homonymous hemianopia. hemianopsia) if the optic chiasm 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 . Only on the boy’s slides Pigmentosa o is an inherited metabolic disorder of the photoreceptor and retinal pigment epithelial cells. o It is due to mutation of a key protein in the retinal photoreceptors. o Which protein? Rhodopsin. o There is: • Progressive night blindness • Peripheral visual field constriction • Pigmentation of the retina visible on ophthalmoscopy. o Which type of photoreceptor is affected? Rods. OPTIC OCCULOMOTOR TROCHLEAR ABDUCENT *Special sensory N. *Motor to: *Motor to Superior *Only one motor nucleus. *Function: Vision. 1. Levator palpebrae oblique muscle. *It forms the facial *Lesion results in: visual superioris *Its function; Rotates the colliculus. field defects and loss of 2. Superior rectus muscle eye ball downwards and *It supplies; the lateral visual acuity, anopsia. 3. Medial rectus muscle laterally. rectus muscle which 4. Inferior rectus muscle rotates the eye ball *Visual Pathway 5. Inferior oblique muscle. *Lesion of trochlear nerve laterally ; (abduction). 1. Optic nerve. *Parasympathetic fibers results in 2. Optic chiasm. to: 1- Constrictor pupillae • diplopia (double vision) *Lesion: 3. Optic tract. and 2- Ciliary muscles. • Inability to rotate the -Inability to direct the 4. Lateral geniculate body eyeball inferolaterally. So, affected eye laterally, so it (nucleus). *Lesions: the eye deviates; upward result in (medial squint*). 5. Optic radiation. 1. Lateral squint. and slightly inward -A nuclear lesion may also 6. Visual cortex 2. Ptosis. (medially). involve the nearby 3.Diplopia. This person has difficulty nucleus or axons of the 4. Pupillary dilatation. in walking downstairs facial nerve, causing 5. Loss of accommodation. paralysis of all facial 6. The eyeball is fully muscles in the ipsilateral abducted and depressed. side.

*Occulomotor  lateral squint| Abducent  medial squint MCQs (1) The occulomotor nerve has? (6) Abducens nerves supplies? A) Motor fibers B) Sensory fibers A) Inferior oblique muscle B) Inferior oblique muscle C) Sympathetic fibers D) Parasympathetic fibers C) Lateral rectus muscle D) All of the above

(2) The edinger-westphal nucleus receives fibers from (7) Compression of the optic chiasm leads to? corticonuclear fibers for? A) monocular blindness B) bitemporal hemianopia A) Stretch reflex B) Pupillary reflex C) contralateral homonymous hemianopia D) C) Accommodation reflex D) Non of them (8) Which of the following nerves runs in the floor of the (3) Lesion of trochlear nerve results in? cavernous sinus? A) Lateral squint A) III B) IV B) Loss of accommodation C) VI D) V C) Inability to rotate the eyeball infero-laterally D) Non of them (9) Which retinal fibers are present in the left optic tract? A) Left temporal and left nasal fibers (4) First order neurons of optic nerve are? B) Left temporal and right nasal fibers A) Bipolar cells of retina B) Ganglion cells of retina C) Right temporal and left nasal fibers C) lateral geniculate body D) Medial geniculate body D) Right temporal and right nasal Fibers

(5) The primary visual cortex occupies the upper and lower (10) Abducent nerve together with facial nerve forms? lips of the? A) Inferior colliculus B) Superior colliculus A) Calcarine sulcus on the medial surface of the cerebral hemisphere C) Facial colliculus D) Lateral collicullus B) Calcarine sulcus on the lateral surface of the cerebral hemisphere C) Parieto-occipital sulcus on the lateral surface of the cerebral hemisphere D) Parieto-occipital sulcus on the medical surface of the cerebral hemisphere Answers

(1) A&D (6) C (2) C (7) B (3) C (8) C (4) A (9) B (5) A (10) C SAQ Name all muscles supplies by the nerves below and what movement is lost due the their injury. Occulomotor: (A) Muscles: (B) Lesion: 1. Levator palpebrae superioris 1.Lateral squint 2. Superior rectus muscle 2.Ptosis 3. Medial rectus muscle 3.Diplopia 4. Inferior rectus muscle & 4.Pupillary dilatation 5.Inferior oblique muscle 5.Loss of accommodation 6.The eyeball is fully abducted and depressed (down and out) because of the (2) Trochlear: unopposed activity of lateral rectus and superior oblique (A) Muscles: Superior oblique muscle (B) Lesion: Diplopia & Inability to rotate the eyeball infero-laterally

(3) Abducent: (A) Muscles: lateral rectus muscle (B) Lesion: Inability to direct the affected eye laterally, so it result in (medial squint). Good luck Special thank for team436

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Team Members: Abdulaziz Aldukhayel Abdulrahman Alduhayyim Rinad Alghoraiby Rawan Mishal ▪ References: 1.Girls’ & Boys’ Slides Twitter.com/Anatomy437 2.Greys Anatomy for Students [email protected] 3.TeachMeAnatomy.com