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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:
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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
Ophthalmic
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