General Sensation and Vision Orbital Region General Sensation and Vision
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
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
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
Extrinsic Ocular Muscles
Arrangement of Posterior Orbit Trochlear Optic Nerve Occulomotor Abducens
Action and Innervation of Ocular Muscles
Action and Innervation of Ocular Muscles Which cranial nerve is injured?
Orbital Blood Supply Ophthalmic Middle Meningeal to Cavernous sinus Internal Carotid Facial v.
Eye Anatomy
Aqueous Humor Flow (Canal of Schlemm) Glaucoma results from inadequate drainage of Aqueous Humor leading to increase pressure in the eye.
Iris controls amount of light entering the eye.
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 Disc (blind spot) Optic N.
Photoreceptors: Cones and Rods Three populations of cones
Rod’s and Cone’s Photopigments
Retinal Bleaching
Visual Processing