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

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

Extrinsic Ocular Muscles

Arrangement of Posterior Orbit Trochlear -to sup. oblique Optic Nerve Occulomotor -to sup. rectus, med. rectus, inf. rectus, inf. oblique, and levator palpebrae superioris Abducens -to lateral rectus

Action and Innervation of Ocular Muscles

Action and Innervation of Ocular Muscles Which cranial nerve and muscle 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

Light Signal Transduction

Visual Processing