ACTIVITIES Complete Diagrams PNS 18 and 19 Complete PNS 23 Worksheet 3 #1 only Complete PNS 24 Practice Quiz
THE SPECIAL SENSES Introduction Vision
RECEPTORS Structures designed to respond to stimuli Variable complexity
GENERAL PROPERTIES OF RECEPTORS Transducers Receptor potential Generator potential
GENERAL PROPERTIES OF RECEPTORS Stimulus causing receptor potentials Generator potential in afferent neuron Nerve impulse
SENSATION AND PERCEPTION Stimulatory input Conscious level = perception Awareness = sensation
GENERAL PROPERTIES OF RECEPTORS Information conveyed by receptors Modality Location Intensity Duration
ADAPTATION Reduction in rate of impulse transmission when stimulus is prolonged
CLASSIFICATION OF RECEPTORS Stimulus Modality Chemoreceptors Thermoreceptors Nociceptors Mechanoreceptors Photoreceptors
CLASSIFICATION OF RECEPTORS Origin of stimuli Exteroceptors Interoceptors Proprioceptors
SPECIAL SENSES Vision Hearing Olfaction Gustation
VISION INTRODUCTION 70% of all sensory receptors are in the eye Nearly half of the cerebral cortex is involved in processing visual information Optic nerve is one of body s largest nerve tracts
VISION INTRODUCTION The eye is a photoreceptor organ Refraction Conversion (transduction) of light into AP s Information is interpreted in cerebral cortex
Eyebrow Eyelid Eyelashes Site where conjunctiva merges with cornea Palpebral fissure Lateral commissure Eyelid Medial commissure (a) Surface anatomy of the right eye Figure 15.1a
Orbicularis oculi muscle Eyebrow Palpebral conjunctiva Cornea Eyelashes Bulbar conjunctiva Conjunctival sac Orbicularis oculi muscle (b) Lateral view; some structures shown in sagittal section Figure 15.1b
ACCESSORY STRUCTURES Lacrimal apparatus Lacrimal gland and ducts that connect to nasal cavity Lacrimal secretion (tears) Dilute saline solution Mucus, antibodies, and lysozyme Blinking spreads the tears toward medial commissure Drain into the nasolacrimal duct
Lacrimal sac Lacrimal gland Excretory ducts of lacrimal glands Lacrimal punctum Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril Figure 15.2
ACCESSORY STRUCTURES Six extrinsic eye muscles
Superior oblique muscle Superior oblique tendon Superior rectus muscle Lateral rectus muscle Inferior rectus Inferior oblique muscle muscle (a) Lateral view of the right eye Figure 15.3a
Muscle Lateral rectus Medial rectus Superior rectus Inferior rectus Inferior oblique Superior oblique Action Moves eye laterally Moves eye medially Elevates eye and turns it medially Depresses eye and turns it medially Elevates eye and turns it laterally Depresses eye and turns it laterally Controlling cranial nerve VI (abducens) III (oculomotor) III (oculomotor) III (oculomotor) III (oculomotor) IV (trochlear) (c) Summary of muscle actions and innervating cranial nerves Figure 15.3c
THE EYEBALL Wall of eyeball contains three layers (tunics) Fibrous Vascular Sensory (retinal)
THE EYEBALL Three layers 1) Fibrous tunic Sclera Cornea
Sclera Cornea Scleral venous sinus Fibrous Tunic Figure 15.4a
Corneal Edema
THE EYEBALL Three layers 2) Vascular tunic (uvea) Choroid Ciliary body Ciliary processes Ciliary muscle Iris
Ciliary body Ciliary zonule (suspensory ligament) Sclera Choroid Iris Pupil Cornea Lens Scleral venous sinus VascularTunic Figure 15.4a
THE EYEBALL Three layers 3) Retina Photoreceptor neurons Rods and Cones Bipolar neurons Ganglion neurons Optic nerve Optic disc
Ciliary body Ciliary zonule Cornea Iris Pupil Sclera Choroid Retina Macula lutea Fovea centralis Optic nerve Lens Scleral venous sinus Retina Central artery and vein of the retina Optic disc (blind spot) Figure 15.4a
Ganglion cells Bipolar cells Photoreceptors Rod Cone Amacrine cell Horizontal cell Pathway of signal output Pigmented Pathway of light layer of retina (b) Cells of the neural layer of the retina Figure 15.6b
Pathway of light Optic disc Neural layer of retina Pigmented layer of retina Choroid Sclera Central artery and vein of retina Optic nerve (a) Posterior aspect of the eyeball Figure 15.6a
Blood supply to the retina
THE EYEBALL Photoreceptors Rods More numerous at peripheral region Dim light Indistinct, fuzzy, non-color peripheral vision About 100 million per eye
THE EYEBALL Photoreceptors Cones Red, blue and green Highest density in macula lutea Concentrated in fovea centralis Operate in bright light High-acuity color vision
Central artery and vein emerging from the optic disc Macula lutea Optic disc Retina Figure 15.7
THE EYEBALL Lens Biconvex, transparent, flexible Attached to ciliary body by suspensory ligaments Allows precise focusing of light on the retina Forms a partition Creates an anterior and posterior cavity
Emmetropic eye (normal) Focal plane Focal point is on retina. Figure 15.14 (1 of 3)
Iris Lens epithelium Lens Cornea Corneal epithelium Corneal endothelium Aqueous humor Anterior segment (contains aqueous humor) Anterior chamber Posterior chamber Scleral venous sinus 1 Aqueous humor is formed by filtration from the capillaries in the ciliary processes. 2 Aqueous humor flows from the posterior chamber through the pupil into the anterior chamber. Some also flows through the vitreous humor (not shown). 3 Aqueous humor is reabsorbed into the venous blood by the scleral venous sinus. 3 Cornealscleral junction Bulbar conjunctiva Sclera 2 1 Cornea Posterior segment (contains vitreous humor) Ciliary zonule (suspensory ligament) Ciliary body Ciliary processes Ciliary muscle Lens Figure 15.8
THE PHYSIOLOGY OF VISION Visual acuity Ratio of distances 20/20 20/40 Less visual acuity 20/15 More visual acuity
THE PHYSIOLOGY OF VISION 5 processes produce a visual image 1. Refraction 2. Accommodation 3. Pupil constriction 4. Convergence 5. Photoreception
REFRACTION The bending of light rays
Focal length is fixed in the eye Emmetropic eye (normal) Focal plane Focal point is on retina. Figure 15.14 (1 of 3)
REFRACTION Light passing through a convex lens (as in the eye) is bent so that the rays converge at a focal point The image formed at the focal point is upside-down and reversed right to left
Sympathetic activation Nearly parallel rays from distant object Lens Ciliary zonule Ciliary muscle Inverted image (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Figure 15.13a
REFRACTION Refracting media Light is refracted by Cornea Aqueous humor Lens Vitreous humor Change in lens curvature Allows for fine focusing of an image
ACCOMMODATION Eye is adapted for distance vision Ciliary muscle is relaxed = lens is flat As light moves closer greater curvature required Ciliary muscle contracts = lens is curved
Sympathetic activation Nearly parallel rays from distant object Lens Ciliary zonule Ciliary muscle Inverted image (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Figure 15.13a
Divergent rays from close object Parasympathetic activation Inverted image (b) Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge. Figure 15.13b
ACCOMMODATION Near vision Accommodation Ciliary muscles contract Eye strain Near point Maximum bulge Aging
CLOSE VISION Close vision requires Accommodation Pupil constriction Prevents most divergent light rays from entering the eye Convergence Medial rotation of the eyeballs toward the object being viewed (binocular vision)
CONSTRICTION OF THE PUPIL Contraction of the circular muscles Contraction of the radial muscles
PHOTORECEPTION Sensory transduction Light energy is converted into nerve impulses Takes place in retina Photoreceptors
PHOTORECEPTION Rods and cones Outer segment of each contains visual pigments Molecules that change shape as they absorb light
Pigmented layer Outer segment Inner segment Process of bipolar cell Inner fibers Rod cell body Cone cell body Outer fiber Synaptic terminals Rod cell body Nuclei Mitochondria Connecting cilia The outer segments of rods and cones are embedded in the pigmented layer of the retina. Melanin granules Apical microvillus Discs containing visual pigments Discs being phagocytized Pigment cell nucleus Basal lamina (border with choroid) Figure 15.15a
Rod discs Visual pigment consists of Retinal Opsin (b) Rhodopsin, the visual pigment in rods, is embedded in the membrane that forms discs in the outer segment. Figure 15.15b
11-cis-retinal Vitamin A 2H + Oxidation Reduction 2H + 2 Regeneration of the pigment: Enzymes slowly convert all-trans retinal to its 11-cis form in the pigmented epithelium; requires ATP. 11-cis-retinal Rhodopsin Dark Light Opsin and All-trans-retinal 1 Bleaching of the pigment: Light absorption by rhodopsin triggers a rapid series of steps in which retinal changes shape (11-cis to all-trans) and eventually releases from opsin. All-trans-retinal Figure 15.16
In the dark Na + Ca 2+ In the dark, cgmp opens sodium channels and depolarizes photoreceptors Photoreceptor cell (rod) Inhibitory neurotransmitter is released (glutamic acid) Ca 2+ Bipolar cells are constantly inhibited in the dark Bipolar cell Ganglion cell Figure 15.18 (1 of 2)
Breakdown of rhodopsin causes closing of sodium channels Photoreceptor cell (rod) In the presence of light bipolar cells are not inhibited Bipolar cell Ganglion cell In the light Light Ca 2+ 1 cgmp-gated channels are closed, so Na+ influx stops; the photoreceptor hyperpolarizes. 2 Voltage-gated Ca 2+ channels close in synaptic terminals. 3 No neurotransmitter is released. 4 Lack of IPSPs in bipolar cell results in depolarization. 5 Depolarization opens voltage-gated Ca 2+ channels; neurotransmitter is released. 6 EPSPs occur in ganglion cell. 7 Action potentials propagate along the optic nerve. Figure 15.18 (2 of 2)
PHOTORECEPTION Excitation of cones Method of excitation is similar to that of rods There are three types of cones Named for the colors of light absorbed: blue, green & red Light absorbed depends upon opsins present
PHOTORECEPTION Adaptation to light Rhodopsin is completely bleached in daylight No contribution to daylight vision
PHOTORECEPTION Light adaptation Occurs when moving from darkness into bright light Large amounts of pigments are broken down instantaneously Produces glare Pupils constrict Dramatic changes in retinal sensitivity Rod function ceases Cones and neurons rapidly adapt Visual acuity improves over 5 10 minutes
PHOTORECEPTION Dark adaptation Occurs when moving from bright light into darkness The reverse of light adaptation Cones stop functioning in low-intensity light Pupils dilate Rhodopsin accumulates in the dark Retinal sensitivity increases within 20 30 minutes
PHOTORECEPTION Duplicity theory Why do we have 2 kinds of photoreceptors? Neural circuits for night are not suited for day Rods:Bipolar cell 600:1 Spatial summation of large field = poor detail Cones:Bipolar cell 1:1 Best for detail in small receptive fields
VISUAL PATHWAY TO THE BRAIN Axons from medial portion of each retina cross at optic chiasma Continue as optic tracts Optic radiation fibers connect to the primary visual cortex in the occipital lobes Visual input from both eyes is interpreted by brain Distance Depth perception
Fixation point Suprachiasmatic nucleus Pretectal nucleus Lateral geniculate nucleus of thalamus Optic nerve Optic chiasma Optic tract Uncrossed (ipsilateral) fiber Crossed (contralateral) fiber Optic radiation Superior colliculus Occipital lobe (primary visual cortex) The visual fields of the two eyes overlap considerably. Note that fibers from the lateral portion of each retinal field do not cross at the optic chiasma. Figure 15.19a
ABNORMALITIES OF VISION Myopia (nearsightedness) Close objects seen clearly Image is focused in front of the retina Correction = concave lens
ABNORMALITIES OF VISION Hyperopia (farsightedness) Distant objects seen clearly Image is focused behind the retina Correction = convex lens
ABNORMALITIES OF VISION Astigmatism Detached retina Conjunctivitis Glaucoma Cataract Diplopia Night blindness Color blindness Macular Degeneration
Astigmatism ABNORMALITIES OF VISION
ABNORMALITIES OF VISION Detached retina
Conjunctivitis ABNORMALITIES OF VISION
Glaucoma ABNORMALITIES OF VISION
Cataract ABNORMALITIES OF VISION
Diplopia ABNORMALITIES OF VISION
ABNORMALITIES OF VISION Nightblindness
ABNORMALITIES OF VISION Colorblindness
ABNORMALITIES OF VISION Macular degeneration
QUESTIONS? Activity Special Senses 20, #11-25