Orbital Region General Sensation and Vision General Sensation and Orbital Region Topic Objectives Be able to identify the four basic conditions necessary for sensation Be able to apply the characteristics of sensation to unique clinical and pathological conditions ID: 773499
Download Presentation The PPT/PDF document "Orbital Region General Sensation and Vis..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Orbital Region General Sensation and Vision
General Sensation and Orbital Region: Topic Objectives Be able to identify the four basic conditions necessary for sensation Be able to apply the characteristics of sensation to unique clinical and pathological conditions Distinguish how sensory intensity is coded in action potentials and how processing enhances signal identification Apply referred pain signals to specific organs or internal areas of the body Be able to identify all structures of the eye and orbit. Be able to apply the cardinal directions to eye movement and in identifying the causes of basic palsies and nerve involvement. Be able to compare the physiological reasons for emmetropia , myopia, hyperopia, presbyopia, cataract and glaucoma. Be able to contrast field of vision vs. optic field, and the effect of lesions to optic nerve, optic chiasma, and optic tract
Generalized Sensation Physiology Sensation –state of awareness of external and internal conditions of the body Four conditions for sensation: 1. Adequate stimulus 2. Adequate receptor (transducer) 3. Conduction 4. Translation (interpretation)
Brain’s Assumption in Translating Assumption: Source of light is from above
Reversing X pattern; notice shading.
How many triangles? Assumption: Straight lines should connect.
Which dark line is larger? Assumption: perspective
Face Recognition
Characteristics of Sensation Modality –ability to interpret nerve impulses differently Projection –referral of sensation to point of origin Adaptation –decrease in sensitivity of receptors to continued stimulation Phasic (fast) Tonic (slow)Some receptors never adapt (pain, cold, etc.)Afterimage –persistence of sensation after stimulus ceases
Classification of Receptors Type of Sensory Information Relayed Exteroreceptors, Enteroreceptors, Proprioceptors Type of Stimulus Transduced Mechanoreceptors, Thermoreceptors, Chemoreceptors, and Nociceptors Complexity of Receptor Simple structure (usually single cell) – most general senses Complex structure (many cells) –special senses
Receptor Physiology Stimulation of a receptor leads to the generation of a receptor (generator) potential in its membrane. These are usually excitatory, and are similar to the EPSPs found in neurons If the receptor potential reaches the threshold potential for the sensory neuron; it fires an AP into the CNS Strength of the stimulus is therefore encoded by the number of AP generated Sensations may be sharpened through Lateral Inhibition
Lateral Inhibition - -
General Senses Cutaneous –skin receptors Proprioception –sense of body position Nociception –pain perception (chemoreceptors that perceive locally secreted warning hormones (prostaglandins))
Distribution of Cutaneous Receptors
Sensitivity of Skin due to Receptive Fields
Cutaneous Receptors
Proprioceptors
Muscle sensors Muscle spindles (Intrafusal fibers: -senses degree of length of muscle fibers and the rate of change in length Golgi Tendon organs –sense tension within tendon
Relationship of Stretch to AP
Referred Pain Illustrates projection.
General Pathway of Perception
Orbital Region
Accessory Structures of the Eye
Eyelid
Lacrimal Apparatus
Outer Eye
Superficial Orbit
Extrinsic Ocular Muscles
Arrangement of Posterior Orbit Optic Nerve Occulomotor Abducens Trochlear
Action and Innervation of Ocular Muscles Which cranial nerve is injured?
Orbital Blood Supply Internal Carotid Middle Meningeal Ophthalmic Facial v. to Cavernous sinus Ophthalmic
Eye Anatomy
(Canal of Schlemm) Aqueous Humor Flow Glaucoma results from inadequate drainage of Aqueous Humor leading to increase pressure in the eye.
(90% of glaucomas)
Iris controls amount of light entering the eye. Parasympathetic fibers via the oculomotor nerve and ciliary ganglion Sympathetic fibers via the superior cervical ganglion through the internal carotid plexus
Distant Vision
Near Vision (Accomodation)
Near and Far-sightedness
Astigmatism and Presbyopia Astigmatism –results from imperfections in the resolving structures in the eye (lens and/or cornea) Presbyopia is the loss of near vision with age; resulting from a decrease in elasticity of the lens.
Increase lens opacity with age. Cataract
Retina Cellular Arrangement
Special Areas of Retina
Blind Spot Optic N. Optic Disc (blind spot)
Photoreceptors: Cones and Rods Three populations of cones
Rod’s and Cone’s Photopigments
Retinal Bleaching
Light Signal Transduction
Visual Processing