VISUAL SYSTEM q Perception of Ø shape Ø motion Ø color Ø qTwo pathways Øretina – cortex •visual perception • Øretina – brainstem, diencephalon •eye movements •circadian photoentrainment •accommodation •pupillary reflexes Light passes through the cornea, aqueous humor, lens, and vitreous body to form an image on the retina. Macula lutea + fovea centralis = areas of the highest visual acuity Fundus oculi RETINA 10 layers: mainly separated by cell bodies (nuclear layers) and axons (plexiform layers) q 5 main cell types: § photoreceptors § bipolar cells § horizontal cells § amacrine cells § ganglion cells § § q Photoreceptors: § rods and cones § involved in transduction converting the light signal into a nerve impulse § q neurons with serial (vertical) connection § the main visual pathway § photoreceptors → bipolar cells → ganglion cells qneurons with parallel (horizontal) connection §modulation of the visual information by retina §horizontal cells §amacrine cells qCones (7 million) §cluster at fovea (macula lutea) §detect color in bright light = photopic vision § q Rods (100 million) §outside the fovea §sensitive to shape and movement = scotopic vision CONES q 3 different types with three different photopigments: blue, green and red q Each type is maximally sensitive to the wavelength that corresponds to the specific color range (spectral sensitivity) GANGLION CELLS qP cells (80%) §ganglion cells that monitor cones §smaller, more numerous §axons end on parvocellular laminae of LGN §provide information about fine detail and color § qM cells (10%) §ganglion cells that monitor rods §relatively large §axons end on magnocellular laminae of LGN §provide information about a general form of an object, motion, and shadows in dim light qnon-P non-M cells (10%) §projection to subcortical nuclei, koniocellular cells of LGN § § PRIMARY VISUAL PATHWAY q The primary visual pathway connects the retina with lateral geniculate nucleus and primary visual cortex (retinogeniculostriate pathway) q It is responsible for detection of shape, movement and color 1st neuron (photoreceptors) 2nd neuron (bipolar cells) 3rd neuron (ganglion cells) LGN Optic chiasm Primary visual cortex CN II Optic tract Optic radiation q LGN is composed of 6 layers q Layers 1 and 2 contain larger neurons q Layers 3 - 6 contain smaller neurons LATERAL GENICULATE NUCLEUS (LGN) q Ipsilateral input enters layers 2,3 and 5 q Contralateral input enters layers 1, 4 and 6 q LGN contains the topographic representation of what the retina “ sees”. This retinotopic map is sent to the cortex. q LGN modulates and regulates the flow of visual information to the primary visual cortex q cortex can control efficiency of thalamic input optic radiation (geniculocalcarine fibres) runs under the temporal lobe to the occipital lobe GENICULOSTRIATE PATHWAY RETINOTOPIC REPRESENTATION q Nasal and temporal visual fields q Reversed to opposite halves of retinal representative fields (hemiretinas) q Inverted and reversed q Nasal visual fields project to temporal hemiretinas and their axons do not cross at the optic chiasm q Temporal visual fields project to nasal hemiretinas and their axons cross at the optic chiasm RETINOTOPY q Most of the visual field is shared by the two eyes (binocular field) q Representation of different parts of the visual field is disproportionate in size VISUAL CORTEX PRIMARY VISUAL CORTEX (V1) q Most LGN axons terminate in V1 q All V1 neurons respond to visual stimuli exclusively q Ablating V1 results in blindness in the contralesional hemifield (homonymous hemianopsia) q q qElectrical stimulation of V1 elicits visual sensations https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Fullvf.png/300px-Fullvf.png https://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Rhvf.png/300px-Rhvf.png VISUAL ASSOCIATION CORTEX Dorsal Stream Øspatial orientation Øbinocular fusion/depth perception Øthe location, the movement and the movement direction and velocity of objects in space Ventral Stream Ørecognize objects and colors Øread text Ølearn and remember visual objects (e.g., words and their meanings) Ø Brachium colliculi superioris VISUAL PATHWAYS TO SUBCORTICAL STRUCTURES q to the suprachiasmatic nucleus of hypothalamus q to the pretectum of the midbrain q to the superior colliculus q q q q PUPILARY LIGHT REFLEX q a reflex that controls the diameter of the pupil, in response to the intensity of light (luminance) that falls on the retina of the eye q mydriasis: dilation of the pupil q q miosis: constriction of the pupil http://cal.vet.upenn.edu/projects/giphys/review/plr.gif ACCOMMODATION http://163.178.103.176/fisiologia/neurofisiologia/objetivo_3/Clayman91c.jpg http://image.slidesharecdn.com/refractorymediaofeyes4march10-100313063054-phpapp01/95/refractory-me dia-of-eye-s4-march-10-23-728.jpg?cb=1268461914 http://www.rci.rutgers.edu/~uzwiak/AnatPhys/Audition_files/image008.jpg 1st order neuron §bipolar neuron of the spiral ganglion §dendrites make synapses with hair cells §axons form the cochlear part of CN VIII https://s-media-cache-ak0.pinimg.com/736x/7e/49/9c/7e499c4235f2b562fe6110fc31fa98aa.jpg 2nd order neuron §ventral cochlear nucleus → trapezoid body → lateral lemniscus §dorsal cochlear nucleus → lateral lemniscus 3rd order neuron §nucleus of inferior colliculus → brachium c.i. 4th order neuron §medial geniculate nucleus → radiatio acustica (internal capsule) Brachium colliculi inferioris http://www.zainea.com/brainstem.gif PRIMARY AUDITORY CORTEX gyrus temporalis superior (gyri temporales transversi of Heschl) - area 41 + 42 http://scienceblogs.com/thoughtfulanimal/wp-content/blogs.dir/351/files/2012/04/i-fd4466953eae4a1f6 3c1ea0eebedefd6-wernicke.jpg Two functionally significant features: qtonotopical organization qbilateral projection DESCENDING PATHWAYS qfeedback system processing ascending information qenhance signals qsupress noise qmainly functions of the superior olivary complex qfocus on a particular speaker and inhibit other voices q changes in the motion of the head (kinetic) and in the position of the head with respect to gravity (static) q 3 afferent sources: the eyes, general proprioceptive receptors throughout the body, and the vestibular receptors in the inner ear q to maintain equilibrium, to direct the gaze of the eyes, and to preserve a constant plane of vision VESTIBULAR APPARATUS q Labyrinth of static apparatus § macula utriculi – orientation in horizontal position § macula sacculi – orientation in vertical position § qLabyrinth of kinetic apparatus § cristae ampullares of semicircular ducts https://susankannasjackiegunderson.wikispaces.com/file/view/vestibular_system.gif/220257758/572x317 /vestibular_system.gif qHair cells in the maculae of the saccule and the utricle respond to linear acceleration (gravity). qHair cells in the cristae ampullares in the semicircular ducts respond to angular acceleration (rotation of the head). http://www.pixelatedbrain.com/images/sld_corn/06/cu06_1_pin3.jpg VESTIBULAR PATHWAY q 1st order neuron – vestibular ganglion (utriculoampullar nerve, saccular nerve, posterior ampullar nerve) q 2nd order neuron – vestibular nuclei (superior, inferior, medial, lateral) http://vmede.org/sait/content/Anatomija_mixailov_t2/7_files/mb4_015.jpeg Connections with the cerebellum qvestibular portion of the CN VIII – inferior cerebellar peduncles – ipsilateral vestibulocerebellum qvestibular nuclei – inferior cerebellar peduncles – vestibulocerebellum maintenance of balance Connections with the spinal cord to motoneurons that innervate axial and proximal limb muscles qlateral vestibulospinal tract §from lateral vestibular nucleus §uncrossed § terminating at all levels of the spinal cord §excitatory influences for extensors § qmedial vestibulospinal tract §from medial vestibular nucleus §bilateral §descends in the MLF §terminates mainly at cervical levels §coordination of head position and eye movements § § Connections with the brain stem q ascending portion of MLF Ø CN III, IV, VI Ø Darkschewitsch and Cajal nuclei Ø coordination of eye movements in response to head movements Ø Connection with the thalamus (cortex) conscious perception of movement and gravity Olfactory region 1st order neuron – bipolar olfactory neurons 2nd order neuron – mitral cells – olfactory tract 3rd order neuron – olfactory tubercle 4th order neuron – dorsomedial nucleus of thalamus Orbitofrontal cortex (perception of olfactory information) Taste buds q receptor cells (replaced about every 9-10 days by differentiating basal cells) q supporting columnar cells q basal cells 1st order neuron – §CN VII –geniculate ganglion Ø via lingual nerve and chorda tympani Ø via greater petrosal nerve Ø §CN IX – inferior ganglion of CN IX § §CN X – inferior ganglion of CN X 2nd order neuron - rostral part of the solitary nucleus 3rd order neuron – ventral posteromedial nucleus of thalamus Primary gustatory cortex q a. 43 in the postcentral gyrus q insula Illustrations were copied and lecture was prepared from: Noback CH.R. et al: The Human Nervous System: Structure and Function. Humana Press, Totowa, New Jersey, Sixth ed. Neuroscience Online, the Open-Access Neuroscience Electronic Textbook Department of Neurobiology and Anatomy University of Texas Medical School at Houston