Cranial nerve i and ii

cranial nerve 1 and 2

1. Cranial nerve I and II Dr Parag Moon Senior Resident, Dept. Of Neurology, GMC Kota.

2. Anatomy First order neurons-bipolar sensory cells in olfactory epithelium (superior nasal concha , upper nasal septum, roof of the nose) Tiny knobs on cilia-sites of chemosensory signal transduction. Specific odorants stimulate specific receptor cells. Central processes of olfactory neurons- unmyelinated axons Olfactory nerve

3. Form approximately 20 branches on each side- olfactory nerves . Penetrate cribriform plate of ethmoid bone, acquire a sheath of meninges , synapse in olfactory bulbs. Basal cells in olfactory epithelium can regenerate. Within olfactory bulbs , synapse on dendrites of mitral and tufted cells in olfactory glomeruli .

4. Second order neurons-axons of mitral cells Course posteriorly through olfactory tracts in olfactory grooves beneath frontal lobes Divide into medial and lateral olfactory striae . Medial olfactory stria terminate on medial surface of cerebral hemisphere in paraolfactory area, subcallosal gyrus and inferior part of cingulate gyrus . Lateral olfactory stria terminate in uncus , anterior hippocampal gyrus , piriform cortex, entorhinal cortex, and amygdaloid nucleus

5. History Unilateral or bilateral Altered taste Past head injury; Smoking Recent upper-respiratory infection Systemic illness Nutrition Exposure to toxins, medications or illicit drugs. CLINICAL EXAMINATION

6. Before evaluating smell- nasal passages are open. Smell is tested using nonirritating stimuli. Avoid irritating substances-stimulate trigeminal nerve Examine each nostril separately while occluding other with eyes closed Perception more important than accurate identification University of Pennsylvania smell identification test (UPSIT) and Connecticut chemosensory test..

7. Term Definition Anosmia No sense of smell Hyposmia decrease in the sense of smell Hyperosmia overly acute sense of smell Dysosmia Impairment or defect in the sense of smell Parosmia Perversion or distortion of smell Phantosmia Perception of an odor that is not real Presbyosmia Decrease in the sense of smell due to aging Cacosmia Inappropriately disagreeable odors Coprosmia fecal scent Olfactory agnosia Inability to identify or interpret detected odors

8. Causes of anosmia / hyposmia Smoking Pregnancy Chronic rhinitis Dental trauma Deviated nasal septum Intranasal tumors (e.g., epidermoid carcinoma) Neuro -olfactory tumor ( esthesioneuroblastoma ) Nasal polyps Antihistamines Propylthiouracil Olfactory dysgenesis Cadmium toxicity Chemical burns of the olfactory epithelium Vitamin deficiency (B6, B12, A) Postviral Zinc or copper deficiency General anesthesia Kallmann's syndrome Olfactory groove meningioma Craniocerebral trauma, including surgery Frontal lobe tumor , especially glioma Alzheimer's disease Parkinson's disease Normal aging Multiple sclerosis Sellar / parasellar tumor Congenital anosmia Meningitis Korsakoff's syndrome Familial dysautonornia Te mporal lobectomies Refsums disease

9. 5 cm in length Extends from ganglion cell layer of retina to optic chiasm. Divided into Intraocular:1mm Intraorbital:25mm Intracanalicular:9mm Intracranial:12-16mm Organized into 400 to 600 fascicles separated by connective tissue septae . Intraorbital portion-surrounded by fat Optic nerve

10. Macula-point of central fixation and greatest visual acuity and color perception. Small shallow depression temporal to disc Fovea (L. “pit”) centralis -depression that lies in center of macula. Foveola -tinier depression in center of fovea. Point of most acute vision as overlying retinal layers are pushed aside Optical center of eye Macula-central 15° of vision Optic nerve

11. Optic disc, or papilla- ophthalmoscopically visible tip of intraocular portion of optic nerve. 1.5 mm by 1.8 mm vertical ellipse Pink to yellowish-white disc. No receptor cells Does not respond to visual stimuli-physiologic blind spot Macula-forms center of retina Macular fixation point- center of clinical visual field (VF).

12. Blood supply to optic nerve head-circle of Zinn -Haller, Composed of 2 often not connected semicircles of short posterior ciliary arteries. NAION- drop in perfusion pressure in short posterior ciliary arteries is culprit. Segmental disc edema corresponding to the semicircle compromised

13. Retinal ganglion cell axons form retinal nerve fiber layer (NFL) Exit through lamina cribrosa (L. “sieve”) Myelinated at posterior end of optic nerve head Myelin-CNS myelin 1.2 million fibers in each optic nerve;

14. Intracranial dura at posterior globe fuses with Tenon's capsule Adherent in optic foramen to periosteum . Pia and arachnoid fuses with sclera where nerve terminates Intracranial meninges extend forward along optic nerves for a variable distance, forming vaginal sheaths . Variations in vaginal sheath anatomy Intervaginal space -small subdural and a larger sub- arachnoid space

15. Intraorbital portion- lies within muscle cone. Before entering optic canal, surrounded by annulus of Zinn formed by origins of rectus muscles. Superior and medial recti partially originate from sheath of optic nerve. Length of intraorbital portion greater than length of orbit Blood supply- pial vascular plexus and branches of ophthalmic artery; distally central retinal artery also contributes intraneural branches.

16. Intracanalicular portion- into cranium through optic canal Orbital opening of canal-vertical ellipse; intracranial end-horizontal ellipse 1.2 cm in length, and located in lesser wing of sphenoid bone. Dural sheath fused to periosteum -immobilizing nerve. Medial wall of canal-thinnest part Blood supply-ophthalmic artery.

17. Intracranial portion- travel 12-16 mm to optic chiasm. Ophthalmic arteries above, internal carotid arteries superiorly and medially, and anterior cerebral arteries that cross over optic nerves and are connected by anterior communicating artery. Posterior to cavernous sinus-join together to form optic chiasm; Blood supply-branches of internal carotid and ophthalmic arteries.

18. Optic chiasm-lies about 10 mm above pituitary gland, separated by suprasellar cistern. Fibers from temporal retina continue directly back: nasal retina decussate to enter opposite optic tract. Fibers from inferior nasal quadrant loop forward into opposite optic nerve for a short distance before turning back again, forming Wilbrand's knee.

19. Some of upper nasal fibers loop back briefly into ipsilateral optic tract before decussation . In chiasm, fibers from upper retinal quadrants lie superior: lower quadrants inferior Inferior nasal fibers decussate anteriorly and inferiorly: superior nasal fibers cross posteriorly and superiorly Macular fibers -decussate as a group, forming a miniature chiasm within chiasm, primarily posterior superior portion.

20. Cavernous sinuses and carotid siphons lie just lateral to chiasm Anterior cerebral and anterior communicating arteries front and above Third ventricle and hypothalamus behind and above. Sella tursica and sphenoid sinus lie below. Ophthalmic artery- same dural sheath through canal and orbit. 8 mm to 12 mm posterior to globe, artery enters nerve and runs along its center to optic disc -central retinal artery Divides at disc head into superior and inferior branches.

21. 55% of axons of optic tract- contralateral nasal retina; 45% ipsilateral temporal retina 80% visual afferents and 20% pupillary afferents. Fibers from upper retina-medial position, inferior retina lateral. PMB-dorsal and lateral position, Majority of fibers terminate at LGB. Six neuronal layers in the LGB Ipsilateral temporal hemiretina synapse in layers 2, 3, and 5;contralateral nasal hemiretina synapse in layers 1, 4, and 6.

22. Geniculocalcarine tract, or optic radiations Terminate in calcarine cortex of occipital lobe Pass through retrolenticular portion of internal capsule and then fan out. Upper retinal fibers upper, and lower retinal fibers lower in optic radiation

23. Inferior retinal fibers arch anteriorly into temporal lobe, sweeping forward and laterally above inferior horn of ventricle then laterally, down, backward. Meyer's loop (loop of Meyer and Archambault ). Fibers from superior retina run directly back in deep parietal lobe in external sagittal stratum, lateral to posterior horn of lateral ventricle

24. Primary visual cortex ( calcarine area or striate cortex )- Brodmann's area 17 on medial surface of occipital lobe. Lower retinal fibers - lower lip of calcarine fissure ( lingual gyrus ) Upper retinal fibers -upper lip of the calcarine fissure ( cuneus ). Most peripheral parts of retina-most anteriorly in calcarine cortex Macular -More posterior its calcarine representation.

25. Visual acuity Minimum visibility -smallest area that can be perceived Minimum separability -ability to recognize the separateness of two close points or lines Snellen chart for distance and near card for near In infants and children- blink to threat or bright light, following movements, pupillary reactions Acuity- line where more than half of characters are accurately read Clinical examination

26. Distance from test chart, 20 or 6-numerator, and distance at which smallest type read by patient should be seen by a person with normal acuity-denominator. RAPD or Marcus gunn pupil Swinging light test Light shone into a pupil and then quickly switched to other one. If one pupil dilates, even slightly, when light is switched-RAPD present in that eye.

27. Near vision Jaeger chart Newspaper want-ad text is approximately J-0, regular newsprint J-6, and newspaper headlines J-17. Counts fingers (CF), hand motion (HM), light perception (LP), or no light perception (NLP). Count fingers at 5 ft-20/800.

28. Non organic visual loss Ask to sign Schmidt- Rimpler test- look toward his hand Join the forefingers Menace test Ask patient look into a large mirror that can be held and moved. Tilting and moving the mirror will elicit OKN responses

29. Color Vision; Day and Night Vision Color plates or pseudoisochromatic plates (Ishihara, Hardy-Ritter-Rand ) In neurologic disease, red perception usually lost first Compare brightness or intensity of examining light in one eye versus other

30. Visual field Normal VF- 90 degrees to 100 degrees temporally, about 60 degrees nasally, 50 degrees to 60 degrees superiorly, and 60 degrees to 75 degrees inferiorly Examination most accurate in an individual who is alert and cooperative and maintain fixation. Confrontation test Moving pen light Menace reflex

31. Formal visual field testing Central fields-tangent screen Peripheral fields- perimetry Notation numerator-test object size and denominator-distance from screen

32. Kinetic perimetry entails moving a test object along various meridians and noting when it is detected. E.g., Goldmann White and colored test objects varying in size from 1 mm to 5 mm Smaller test object, smaller VF. If size of a VF defect is same with all test objects-steep, or abrupt, margins. If larger with smaller test objects-gradual, or sloping margins

33. Automated static perimetry Humphrey Visual Field Analyzer Normal patients may appear to have abnormal VF due to large number of erroneous responses that can occur during automated testing

34. Direct opthalmoscopy Small aperture-examining an undilated pupil, large aperture-dilated pupil Red-free filter-examining blood vessels, looking for hemorrhages , and nerve fiber layer Red reflex-assessed from distance of 12 in to 15 in. Areas of primary concern- disc, macula, and arteries

35. Disc normally round or vertically oriented slight oval. Nasal margin slightly blurred Peripheral neuroretinal rim and central cup. Physiologic cup-slight depression in center of disc that is less pinkish than rim and shows a faint latticework due to underlying lamina cribrosa . Rim is elevated slightly above cup.

36. Myelinated axons-normal optic disc yellowish white. Paler temporally where papillomacular bundle (PMB) enters. When scleral opening small, disc consists entirely of neuroretinal tissue, and inconspicuous or nonexistent cup. More vulnerable to anterior ischemic optic neuropathy- disc at risk. N ormal cup-to-disc ratio-0.1 to 0.5.

37. Macula-dark area that lies about 2 disc diameters temporal to and slightly below disc. Appears darker than surrounding retina because of thinner retina Area of macula devoid of large blood vessels. Fovea centralis appears pinpoint of light reflected from center of macula. Macula may be seen more easily with a red-free filter, if patient looks directly into light

38. Photostress Test In macular disease, photoreceptors require longer to recover from bleaching of retinal pigments after exposure to a bright light. Baseline visual acuity Then shining a bright light (e.g., a fresh penlight) into eye for 10 seconds Determine time required for visual acuity to return to baseline. Mainly useful with unilateral disease Optic nerve disease-normal photostress test.

39. Papilledema Four stages of -early, fully developed, chronic, and atrophic. Fully developed-elevation of disc surface, humping of vessels crossing disc margin, obliteration of disc margins, peripapillary hemorrhages , cotton wool exudates, engorged and tortuous retinal veins, and marked disc hyperemia Early papilledema -loss of previously observed spontaneous venous pulsations (SVPs). SVPs=200 mm H2O ICT

40. Pseudopapillodema Common causes-optic nerve drusen, myelinated nerve fibers, remnants of primitive hyaloid artery (Bergmeister's papilla), tilted discs, extreme hyperopia. Optic nerve drusen , or hyaloid bodies Acellular , calcified hyaline deposits within optic nerve that may elevate and distort disc . Present 2%, bilateral in 70% Highly refractile , rock-candy appearance .

41. In papilledema - disc is usually hyperemic ; margin blurriness at superior and inferior poles early in process; blood vessels look normal except for fullness of veins; NFL is dull with retinal blood vessels obscured because of retinal edema . In pseudopapilledema disc color remains normal; blurriness of disc margin may be irregular,disc may have a lumpy appearance; blood vessels on the disc frequently look anomalous; NFL is clear. If in doubt, consult an ophthalmologist.

42. Optic neuritis Ischemic optic neuropathy Optic nerve compression Papillophlebitis Optic nerve infiltration ( carcinomatous , lymphomatous ) Sarcoidosis Diabetic papillopathy Tobacco-alcohol amblyopia Nutritional deficiency, especially vitamin B12 Drugs Toxins Hereditary optic neuropathy ( Leber , Kjer ) Glaucoma Causes of optic atrophy

43. Chiasmal Lesions Pituitary tumors Craniopharyngiomas Meningiomas Gliomas Carotid aneurysms Demyelination Ischemia Radionecrosis

44. Thanks

45. Inderbir Singh's Textbook of Human Neuroanatomy (Fundamental and Clinical) DeJong’s The Neurological Examination, Sixth Edition Optic Nerve: Anatomy, Function, And Common Disorders;edward A. Margolin , Rajeshvar K . Sharda;Ophthlmology Rounds; May/June 2014 Volume 6, Issue 3 The optic nerve: a clinical perspective;Pasquale Montaleone;UWOMJ | 79:2 | Fall 2012 References