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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 corpus callosum • Brain stem – LGB – Rostral colliculus – Pontine nuclei – Reticular formation Central Nervous System • All brain divisions involved – Telencephalon (cerebral hemispheres) – Diencephalon (thalamic structures MYELENCEPHALON and geniculate bodies) – Mesencephalon (midbrain) – Metencephalon (cerebellum and pons) – Myelencephalon (aka medulla oblongata) Central Nervous System CNS • Cranial cervical spinal cord (C2-C4)(sensory to eyelids) • Cranial thoracic spinal cord (T1-T3) (sympathetic) Peripheral Nervous System PNS • Most of the cranial nerves (CNs) • II, III, IV, V, VI, VII directly & VIII (indirectly) Peripheral Nervous System • C2-C4 spinal nerves • T1-T3 spinal nerves, sympathetic trunk, vagosympathetic trunk, cranial cervical ganglion, 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, hearing head sensory smell sensory extraocular mm facial mm Telencephalon Cerebral Hemispheres • Perception and integration of vision – Occipital cortex • Voluntary control of eyes and eyelids – Motor cortex of frontal/parietal lobes Occipital Lobe • Caudal hemispheres – Longitudinal and transverse fissures • Marginal, ectomarginal, caudal suprasylvian, caudal composite, splenial, and occipital gyri Cortical Gyri and Sulci * * * * * * * * Part of occipital cortex Cortical Gyri and Sulci * * * * * * Part of occipital cortex Visual Cortex • Occipital lobe – 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 optic radiation (within the internal capsule) 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 chiasm • Optic tract • LGB • Internal capsule • Hypothalamus • Thalamus Diencephalon • Optic chiasm – Crossed fibers • Most birds 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 nucleus of optic tract Diencephalon • Optic chiasm • Optic tract • LGB • Internal capsule • Hypothalamus • Thalamus Lateral Geniculate Body (actually dorsal in domestic mammals) • Retinotopic organization • Dorsal nucleus more complex- projects to visual cortex • Ventral nucleus aka pregeniculate nucleus- connects with pulvinar in thalamus and peristriate area (?accommodation?) 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 humans • 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 • Retina • Optic n. • Optic chiasm • Optic tract • LGB (synapse) • 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 • Tegmentum ventrally Pretectum • Pretectal nuclei • Caudal commissure- +/- • Pupillary light reflex 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 oculomotor nucleus] • [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 lemniscus, caudal colliculus, and reticular formation Rostral Colliculus • Efferents to ipsilateral • Superficial layer pons projections tend to • Contralateral ascend projections in • Deep layer projections tectospinal tract tend to descend • Contralateral projections in tectotegmentospinal tract Tectum • UMN to sympathetic • Tectotegmentospinal vs neurons 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 neck 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 • Trochlear nucleus (GSE) – LMN to dorsal oblique m – [Only CN that completely crosses the midline and only one that projects from dorsal brain] Tegmentum afferents efferents • Vestibular nuclei via medial • To extraocular mm. longitudinal fasciculus (MLF) • To orbital/ocular smooth • Cortical and reticular mm. projections • Pretectal nuclei Tegmentum • MLF, extraocular nuclei, and eye smooth muscle nucleus Nuclei of CN III • Parasympathetic nucleus of CN III (GVE) – Autonomics to iris 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, trigeminal lemniscus, 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 cerebellar peduncle • 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 cerebrum and 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 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 deep cerebellar nuclei) 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,
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