Chapter 10c Sensory Physiology 2013 Pearson Education Inc The Vestibular Apparatus Series of interconnected fluid filled chambers Otolith organs ear Saccule and utricle Linear acceleration and head position Semicircular canals Rotational acceleration Filled with endolymph 2013 Pearson Education Inc Figure 10 22a 1 ESSENTIALS Equilibrium Figure 10 22a 1 ESSENTIALS Equilibrium Figure 10 22b 2 ESSENTIALS Equilibrium Crista Movement of the endolymph pushes on the gelatinous cupula and activates the hair cells Endolymph Cupula Hair cells Nerve Supporting cells Figure 10 22b 3 ESSENTIALS Equilibrium Crista Movement of the endolymph pushes on the gelatinous cupula and activates the hair cells Brush moves right Stationary board Bristles bend left Cupula Bone Endolymph Hair cells Bone Direction of rotation of the head When the head turns right endolymph pushes the cupula to the left Figure 10 22c 2 ESSENTIALS Equilibrium Macula Nerve fibers Otoliths are crystals that move in response to gravitational forces Gelatinous otolith membrane Hair cells Figure 10 22c 3 ESSENTIALS Equilibrium Macula Head in neutral position Macula Gravity Figure 10 22c 4 ESSENTIALS Equilibrium Macula Head tilted posteriorly Gravity Otolith Figure 10 23 EQUILIBRIUM PATHWAYS Vestibular branch of vestibulocochlear nerve VIII Vestibular apparatus Cerebral cortex Thalamus Reticular formation Cerebellum Vestibular nuclei of medulla Somatic motor neurons controlling eye movements The Eye and Vision Light enters the eye Focused on retina by the lens Photoreceptors transduce light energy into Neural pathways process electrical signals into electrical signal visual images 2013 Pearson Education Inc Figure 10 24 EXTERNAL ANATOMY OF THE EYE Lacrimal gland secretes tears Muscles attached to external surface of eye control eye movement Upper eyelid Sclera Pupil Iris Lower eyelid The orbit is a bony cavity that protects the eye Nasolacrimal duct drains tears into nasal cavity Figure 10 25 ANATOMY SUMMARY The Eye Figure 10 25a ANATOMY SUMMARY The Eye Sagittal section of the eye Zonules attach lens to ciliary muscle Lens bends light to focus it on the retina Canal of Schlemm Aqueous humor Cornea Pupil changes amount of light entering the eye Iris Optic disk blind spot region where optic nerve and blood vessels leave the eye Central retinal artery and vein emerge from center of optic disk Optic nerve Fovea region of sharpest vision Ciliary muscle contraction alters curvature of the lens Vitreous chamber Retina layer that contains photoreceptors Sclera is connective tissue Figure 10 25b ANATOMY SUMMARY The Eye Optic disk Central retinal artery and vein Fovea Macula the center of the visual field View of the rear wall of the eye as seen through the pupil with an ophthalmoscope Figure 10 26a 1 of 3 Dorsal view Eye Optic tract Optic chiasm Optic nerve Figure 10 26b 2 of 3 Neural pathway for vision lateral view Eye Optic nerve Optic chiasm Optic tract Lateral geniculate body thalamus Visual cortex occipital lobe Figure 10 26c 3 of 3 Optic nerve Optic chiasm Optic tract Lateral geniculate body thalamus Visual cortex occipital lobe Collateral pathways leave the thalamus and synapse in the midbrain to control constriction of the pupils Light Eye Midbrain Cranial nerve III controls pupillary constriction The Pupil Light enters the eye Size of the pupil modulates light that reaches photoreceptors Shape of lens focuses the light Pupillary reflex is a consensual reflex Standard part of neurological examination 2013 Pearson Education Inc The Lens Optics describes light behavior and properties Light entering eye is refracted or bent Cornea and lens Influence angle of light when it meets the lens 2013 Pearson Education Inc Figure 10 27a ESSENTIALS Optics of the Eye A concave lens scatters light rays Concave lens Parallel light rays Figure 10 27b ESSENTIALS Optics of the Eye A convex lens causes light rays to converge Focal point Convex lens Parallel light rays Focal length The focal length of the lens is the distance from the center of the lens to the focal point Figure 10 27c ESSENTIALS Optics of the Eye Parallel light rays pass through a flattened lens and the focal point falls on the retina Focal length Light from distant source Light from distant source Lens flattened for distant vision Focal length Figure 10 27d ESSENTIALS Optics of the Eye For close objects the light rays are no longer parallel The lens and its focal length have not changed but the object is seen out of focus because the light beam is not focused on the retina Image distance Lens Object Object image Object distance P Image distance Q Focal length of lens F Figure 10 27e ESSENTIALS Optics of the Eye To keep an object in focus as it moves closer the lens becomes more rounded Focal length Lens rounded for close vision Image distance now equals focal length Accommodation Process by which the eye adjusts lens shape to keep objects in focus Near point of accommodation in the closest distance at which the lens can focus an object Presbyopia is loss of accommodation 2013 Pearson Education Inc Figure 10 27f ESSENTIALS Optics of the Eye The lens is attached to the ciliary muscle by inelastic ligaments zonules Ciliary muscle Lens Ligaments Cornea Iris Figure 10 27g ESSENTIALS Optics of the Eye When ciliary muscle is relaxed the ligaments pull on and flatten the lens Ciliary muscle relaxed Lens flattened Ligaments pulled tight Cornea Figure 10 27h ESSENTIALS Optics of the Eye When ciliary muscle contracts it releases tension on the ligaments and the lens becomes more rounded Ciliary muscle contracted Lens rounded Ligaments slacken Figure 10 27j ESSENTIALS Optics of the Eye Myopia or near sightedness occurs when the focal point falls in front of the retina Myopia corrected with a concave lens Figure 10 27i ESSENTIALS Optics of the Eye Hyperopia or far sightedness occurs when the focal point falls behind the retina Hyperopia corrected with a convex lens Astigmatism Usually caused by a cornea that is not a perfectly shaped dome resulting in distorted images 2013 Pearson Education Inc Figure 10 28 THE ELECTROMAGNETIC SPECTRUM h t g n e e v a W l 400 nm 450 nm 500 nm 550 nm 600 nm 650 nm 700 nm y g r e n E Visible light Gamma rays X rays UV Infrared Micro waves Radio waves 10 5 nm 10 3 nm 1 nm 103 nm 106 nm 109 nm 1 m 103 m Phototransduction Converts light energy into electrical signals Photoreceptors Rods and cones Modified ganglion cells contain melanopsin to respond to changing light