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Neuroanatomy

Basic Science Course in Veterinary and Comparative Ophthalmology JUNE 2016 Connections from Visual Areas

• Other lobes of ipsilateral hemisphere • contralateral hemisphere via • stem – LGB – Rostral colliculus – – Central

• All brain divisions involved – Telencephalon (cerebral hemispheres) – (thalamic structures and geniculate bodies) – Mesencephalon () – ( and ) – Myelencephalon (aka ) CNS • Cranial cervical (C2-C4)(sensory to ) • Cranial thoracic spinal cord (T1-T3) (sympathetic) Peripheral Nervous System PNS • Most of the cranial (CNs) • II, III, IV, V, VI, VII directly & VIII (indirectly) Peripheral Nervous System • C2-C4 spinal nerves • T1-T3 spinal nerves, , vagosympathetic trunk, cranial cervical , postganglionic fibers Nomenclature

Human/Zoo Superior Inferior Anterior posterior

NAV Dorsal Ventral Rostral caudal More on terminology

The same Or different • Afferent- sensory • Afferent-Projecting to a structure • Efferent- motor • Efferent- Projecting from a structure Even More

E(fferent) A(fferent)

S(omatic) V(isceral) S V

S(pecial) G(eneral) S G S G S G

SSE GSE SVE GVE SSA GSA SVA GVA vol. motor motor auto. motor sight limb, body & taste organ to limbs, to chewing, head sensory smell sensory extraocular mm facial mm Telencephalon Cerebral Hemispheres • and integration of vision – Occipital • Voluntary control of and eyelids – of frontal/parietal lobes Occipital

• Caudal hemispheres – Longitudinal and transverse fissures • Marginal, ectomarginal, caudal suprasylvian, caudal composite, splenial, and occipital gyri Cortical Gyri and Sulci

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* Part of occipital cortex Cortical Gyri and Sulci

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* Part of occipital cortex Visual Cortex

• – Striate cortex • Stripe of Gennari (layer IV) • Brodman area 17 • Visual I • 6 neuronal layers – Parastriate cortex • Brodman area 18 • Visual II – Peristriate cortex • Brodman area 19 • Visual III Visual Cortex

• Occipital lobe – Striate cortex • Stripe of Gennari • Brodman area 17 • Visual I • 6 neuronal layers – Parastriate cortex • Brodman area 18 • Visual II – Peristriate cortex Extrastriate cortex or visual association area • Brodman area 19 • Visual III Point of Central Vision

• Beagle – 11.3 mm rostral to interaural line & 8.3 mm from midline • Greyhound – 15.6mm &8.5 • Cat – Junction of marginal and endomarginal gyri • Other- ?? Connections to Visual Areas • Lateral geniculate body (LGB) via (within the ) Connections to Visual Areas

• Other lobes of ipsilateral hemisphere • Parastriate and peristriate cortex via association fibers Connections from Visual Areas

• Other lobes of ipsilateral hemisphere • contralateral hemisphere via corpus callosum • Brain stem – LGB – Rostral colliculus – Pontine nuclei – Reticular formation Diencephalon

• Optic • • LGB • Internal capsule • • Diencephalon

• – Crossed fibers • Most and fish-100% • Cat ~65% • Dog ~75% • Large animals ~80-90% – Uncrossed fibers give binocular vision • Optic tract • LGB • Internal capsule • Hypothalamus Diencephalon

• Optic chiasm • Optic tract – Y-fastest • to LGB – X-intermediate • To pretectum – W-slowest • To rostral colliculus • LGB • Internal capsule • Hypothalamus • Thalamus Optic Tract Connections • LGB • Pretectum • Rostral colliculus • Hypothalamus • Accessory of optic tract Diencephalon

• Optic chiasm • Optic tract • LGB • Internal capsule • Hypothalamus • Thalamus Lateral Geniculate Body (actually dorsal in domestic ) • Retinotopic organization • Dorsal nucleus more complex- projects to visual cortex • Ventral nucleus aka pregeniculate nucleus- connects with pulvinar in thalamus and peristriate area (??) LGB

• Dorsal nucleus is curved laminar structure- parvocellular alternating white and gray matter • Fibers enter on concave surface magnocellular • 3 layers in cat and 6-7 in • A, AI, B or 1-6 – A and B receive crossed fibers (1[deepest],4,6) – AI receives uncrossed fibers (2,3,5) Diencephalon

• Optic chiasm • Optic tract • LGB • Internal capsule • Hypothalamus • Thalamus Conscious Vision Path • • Optic n. • Optic chiasm • Optic tract • LGB () • Internal capsule (optic radiation) • Occipital cortex (synapse) Diencephalon

• Optic chiasm • Optic tract • LGN • Internal capsule • Hypothalamus – UMN to ANS • Thalamus Diencephalon

• Optic chiasm • Optic tract • LGN • Internal capsule • Hypothalamus • Thalamus Mesencephalon • Pretectum • Tectum dorsally • ventrally Pretectum • Pretectal nuclei • Caudal commissure- +/- • pathway – Retina, optic n, optic chiasm, optic tract, pretectal nuclei (synapse), parasym. nucleus of CN III (synapse), preganglionic fibers in CN III, ciliary g (synapse), postganglionic fibers (synapse) Pupillary Light Reflex Pathway

• Contralateral and ipsilateral projections from pretectal nucleus to parasympathetic nuclei of CN III • [Edinger-Westphal nucleus] • [accessory ] • [anteromedian nucleus] Tectum • Layered Rostral Colliculi • Topographic • Visuomotor coordination • Receives fibers from optic * tract via brachium of rostral colliculus Rostral Colliculus

• 7 layers of alternating white (4) and gray matter (3) • Also has corticotectal fibers, spinotectal fibers, trigeminal , caudal colliculus, and reticular formation Rostral Colliculus

• Efferents to ipsilateral • Superficial layer pons projections tend to • Contralateral ascend projections in • Deep layer projections tend to descend • Contralateral projections in tectotegmentospinal tract Tectum

• UMN to sympathetic • Tectotegmentospinal vs in T1-T3 tectospinal tracts • Hypothalamus to – Tectotegmentospinal tectum tract • UMN sympathetic • Then tectum to spinal • = lateral tectospinal tract cord – Tectospinal tract • Orient eyes, head and in response to visual input • =medial tectospinal tract – Spinotectal tract • Movements of neck, head, eyes toward objects Tegmentum

• Motor NCBs of CNs associated with mesencephalon * • CN III&IV, therefore LMN nuclei are in mesencephalon • Oculomotor, trochlear nuclei , parasympathetic nucleus of CN III Motor Nuclei of CN III and IV • Oculomotor nucleus (GSE) (red) – LMN to most Parasympathetic nucleus of CN III extraocular mm. Oculomotor nucleus Nuclei of CN III and IV • (GSE) – LMN to dorsal oblique m – [Only CN that completely crosses the midline and only one that projects from dorsal brain] Tegmentum afferents efferents • via medial • To extraocular mm. longitudinal fasciculus (MLF) • To orbital/ocular smooth • Cortical and reticular mm. projections • Pretectal nuclei Tegmentum

• MLF, extraocular nuclei, and nucleus Nuclei of CN III • Parasympathetic nucleus of CN III (GVE)

– Autonomics to and parasym. nucleus of CN III ciliary mm. These fibers Oculomotor nucleus surround the fibers from oculomotor nucleus Parasympathetic nucleus of CN III • Pupillary light reflex pathway Mesencephalon sensory • Input via CN V possibly proprioceptive fibers of CN III, IV, VI • Fibers enter at pons regions and turn rostrally forming the mesencephalic sensory tract and nucleus Metencephalon

• Ventral metencephalon = pons • Still have MLF, Trigeminal leminscus • Principal (pontine) tract and nucleus of CN V • Reticular formation Metencephalon • Ventral metencephalon = pons • Still have MLF, tectospinal tr, , spinotectal tr • Principal (pontine) tr and nucleus of CN V, corticopontocerebellar tr • Reticular formation Metencephalon • Corticoponto- cerebellar tract • From cortex via long. fibers of pons • Synapse in pontine nuclei • Fibers cross midline and enter cerebellum via middle • Part of menace response path Metencephalon • Corticoponto- cerebellar tract • From cortex via long. fibers of pons • Synapse in pontine nuclei • Fibers cross midline and enter cerebellum via middle cerebellar peduncle • Part of menace response path Menace Response Path • NOT a reflex- requires conscious vision path • Learned (10-12 wks in SA, 1-2 wks in LA) • Requires and cerebellum

• 4 pr of vestibular nuclei • Projections ascend and descend in and to cerebellum • MLF and • Afferents from CN VIII, flocculonodulus and of cerebellum Vestibular System

• 4 pr of vestibular nuclei • Projections ascend and descend in brainstem and to cerebellum • MLF and vestibulospinal tract • Afferents from CN VIII, flocculonodulus and fastigial nucleus of cerebellum Vestibular System • 4 pr of vestibular nuclei • Projections ascend and descend in brainstem and to cerebellum • MLF and vestibulospinal tract • Afferents from CN VIII, flocculonodulus and fastigial nucleus of cerebellum (most medial of ) Palpebral/Corneal Reflex

• Ophthalmic/maxillary branches of CN V • Enter pons in spinal tract of V and travel caudally into myelencephalon • Synapse in nucleus of spinal tract of V • Travel to facial nucleus and synapse • Facial n. Myelencephalon

• Aka medulla oblongata • Tracts passing through as • Several motor nuclei with pons (MLF, associated with trigeminal lemniscus, eyes/adnexa including tectospinal tract, parasympathetic nuclei tectotegmentospinal • Sensory tracts tract, vestibulospinal associated with tract, spinotectal tract, etc eyes/adnexa • Pathways for menace, palpebral, corneal also travel in myelencephalon Myelencephalon

• As with pons, portions of the vestibular nuclei and reticular formation Myelencephalon

• CN V enters at pons but many of fibers turn caudally through this region • Spinal Tract of V • Nucleus of spinal tract is immediately medial Myelencephalon

• Synapse in nucleus, then 2nd order fibers cross midline and travel rostrally to thalamus, synapse, then to parietal cortex Pons vs Myelencephalon Nucleus of CN VI

• – Myelencephalon or pons – Same column as oculomotor and trochlear nuclei, GSE – MLF from vestibular nuclei – Innervates lateral rectus and retractor bulbi mm. Myelencephalon • Motor nuclei associated with CNs • Abducens nucleus – GSE type • Afferents to abducens via MLF • [pons] Myelencephalon

• Motor nuclei associated with CNs • Facial nucleus (#135) – SVE type • Motor side of corneal/palpebral/ dazzle/menace • Afferents are from cerebellum, nucleus of spinal tract of V Menace Response Path • Conscious vision path • Association fibers to motor cortex (synapse) • Through internal capsule, mesencephalon, pontine nucleus in pons (synapse, • Cross to middle cerebellar peduncle • Cerebellum (synapse) • Facial nucleus and () • blink Myelencephalon

• “” pathway from eye/adnexa – Synapse in nucleus, then 2nd order fibers cross midline and travel rostrally to thalamus, synapse, then to parietal cortex

• Palpebral/corneal reflex – Ophthalmic/maxillary branches of CN V, enter at pons and travel in spinal tract of V to myelencephalon, synapse in nucleus of spinal tract of V, travel to facial nucleus and synapse, from facial nucleus to Myelencephalon

• CNs VII and VIII Myelencephalon

• Parasympathetic nucleus of CN VII – Aka rostral/superior salivatory nucleus • GVE type • Projects to lacrimal gland • ?gland of 3rd ? • Afferents from hypothalamus Spinal Cord

• Cranial cervical spinal cord – Tracts passing through • Tectospinal, tectotegmentospinal, spinotectal tracts – Spinal tract and nucleus of V – Sensory fibers from lids to C2-C4 spinal nerves and cord • T1-T3 spinal cord Spinal Cord

• Cranial cervical spinal cord – Tracts passing through • Tectospinal, tectotegmentospinal, spinotectal tracts – Spinal tract and nucleus of V – Sensory fibers from lids to C2-C4 spinal nerves and cord • T1-T3 spinal cord Spinal Cord

• Cranial cervical spinal cord – Tracts passing through • Tectospinal, tectotegmentospinal, spinotectal tracts – Spinal tract of V – Sensory fibers from lids to C2-C4 spinal nerves and cord • T1-T3 spinal cord Spinal Cord

• Tectospinal tract – MLF w/in ventral – Ipsilateral rostral colliculus to ventral horn of cervical segments • Tectotegmentospinal tract – – Contralateral rostral colliculus to T1-T3 segments – UMN for sympathetics of eye

• Most are involved w/eye • CN II, III, IV, V, VI, VII and adnexa directly , and VIII • Generally exit ventral to (indirectly) lateral surface of brain • Innervation is not • Small % contribution from segmental contralateral nuclei • 3 unofficial plexi • Fibers are ipsilateral – Superficial projections peripherally – Orbital (except CN IV) – Occipital • CN IV exits dorsal brainstem and complete contralateral peripheral projection Trunk vs. Head

• Head-paraxial and mesenchyme • Trunk- somite Superficial Plexus

• CN V & VII • Just deep to platysma/cutaneus facei mm. • Here CN VII is “motor to facial mm” including eyelid mm. • Here CN V is “sensory to head” including adnexa Orbital Plexus

• CN III, ophthalmic & maxillary of CN V, postganglionic sympathetics from cranial cervical ganglion • w/in periorbita • CN II, IV, VI in same area but do not exchange fibers Occipital Plexus

• CN VII, IX, X, XI, XII and postganglionic sympathetics • External to tympano- occipital fissure and within middle ear cavity Exit Foramina CN II-optic n.

• Sensory side of PLR, menace response, and conscious vision pathways • Technically extension of diencephalon, ergo and CSF • SSA fibers with NCBs in ganglion cell layers of retina CN III- oculomotor n. • GSE fibers from oculomotor nucleus to majority of extraocular mm. CN III- oculomotor n. • of PLR Parasym. Nucleus of CN III • GVE from parasympathetic nucleus of CN III to iris and ciliary mm. Postganglionic NCBs in ciliary g. CN III- oculomotor n. • Motor nerve of PLR • GVE from parasympathetic nucleus of CN III to iris and ciliary mm. Postganglionic NCBs in ciliary g. CN IV-trochlear n. • Motor n to dorsal oblique m. • GSE • NCBs in trochlear nucleus to CONTRAlateral muscle CN V-trigeminal n.

• of palpebral and corneal reflex • 3 big branches with separate exit foramina CN V-trigeminal n.

• Maxillary and ophthalmic with eye/ • GSA fibers in maxillary and ophthalmic branches CN V-trigeminal n.

• NCBs in trigeminal (semilunar) ganglion in petrous temporal bone CN V-trigeminal n.

• Will be joined by sympathetics (to ophthalmic n. branches) and parasympathetics (to maxillary) of other sources CN VI- abducens n. • Motor nerve to lateral rectus and retractor bulbi mm. • Also to striated muscle strip to 3rd eyelid of cat (active, not passive) CN VII-facial n.

• Motor nerve of corneal, palpebral reflexes and menace response • SVE fibers and GVE fibers for ocular functions CN VII-facial n. • Parasympathetic nucleus of CN VII via facial to to lacrimal gland CN VII-facial n.

• Parasympathetic nucleus of CN VII via facial to pterygopalatine ganglion to lacrimal gland CN VII-facial n.

• Facial nucleus projects via facial n. • auriculopalpebral br to eyelid CN VIII-vestibulocochlear n

• Indirect influence with ocular functions via cerebellar and vestibular nuclei • SSA type C2-C4 spinal nerves

• Sensory nerves from eyelids • GSA • Ipsilateral to cervical spinal cord with NCBs in spinal ganglia T1-T3 spinal nerves • Preganglionic sympathetic fibers (GVE) • Via to sympathetic trunk • To vagosympathetic trunk • Synapse in cranial cervical ganglion • Postganglionic fibers through middle ear cavity • Joins branches of CN V to eye • Innervates iris and ciliary mm. T1-T3 spinal nerves • Preganglionic sympathetic fibers • Via ramus communicans to sympathetic trunk • To vagosympathetic trunk T1-T3 spinal nerves • Synapse in cranial cervical ganglion • Postganglionic fibers through middle ear cavity • Joins branches of CN V to eye • Innervates iris and ciliary mm. T1-T3 spinal nerves • Joins branches of CN V to eye • Innervates iris and ciliary mm. • In cats, short ciliary nn. have sensory and parasym./ long cilary nn. have sensory and sym. – long ciliary join short ciliary just before entering • In dogs, short ciliary nn. have sensory, parasym. and sym.

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