Sensory Systems
How many different sensory receptors are hard at work during a roller coaster ride?
Tortora Page 266 Sensations • Definition: • State of awareness of internal or external conditions of the body
Tortora Page 266 Sensations • Four conditions for a sensation to occur: • Threshold stimulus. • A receptor to pick up the stimulus. • Conduction of impulse. • Translation by brain into sensation.
Tortora Page 266 Sensations • Stimulus results in a generator potential. • Depolarization of receptor membrane. • Follows afferent pathway to thalamus. • From thalamus, action potential goes to cerebrum Molecules in food stimulate generator potentials in taste buds
Tortora Page 266 Sensations • 4 Characteristics of a sensation. • Projection • “connects” sensation in cerebrum to correct part of body. • Example: Brain knows that you just burned the tip of the pinky finger on the left hand.
Tortora Page 266 Sensations • 4 Characteristics of a sensation. • Adaptation • Decrease in sensitivity with continued non threatening stimulation. • Example: A person living near the railroad tracks sleeps through the passing of the train
Tortora Page 266 Sensations • 4 Characteristics of a sensation. • Afterimages • Sensation persists even though stimulus is removed. • Exampe: You look at a bright object. It remains as a vision for a period of time after looking away.
Tortora Page 266 Sensations • 4 Characteristics of a sensation. • Modality • Type of stimulation. • Example: Vision Vs smell Vs touch
Tortora Page 266 Receptors • Classification based on location: • Exteroceptors • Visceroceptors • Proprioceptors
Tortora Page 266 Receptors • Classification based on type of stimulus: • Mechanoreceptor • Thermoreceptor • Nociceptor • Electromagnetic receptor • Chemoreceptor
Tortora Page 266 Receptors • Classification based on type of complexity: • Simple • Complex
Accessory Structures of the Eye • Eyelids • Eyebrows • Lacrimal apparatus • Lacrimal gland • Lacrimal canals. • Nasolacrimal duct. • Role of lysozyme: antibacterial. Lacrimal apparatus from Gray’s Anatomy
Tortora Page 266-267 Structures of the Eye • Eye lies within a cavity called the orbit.
Tortora Page 197 Structures of the Eye • Muscles that move the eye: • Inferior rectus • Lateral rectus • Superior rectus • Medial rectus • Inferior oblique • Superior oblique
Tortora Page 266-267 Structures of the Eye • Eye has three layers. • Fibrous tunic • Vascular tunic • Nervous tunic
Tortora Page 266-267 Structures of the Eye • Fibrous tunic consists of: • Sclera • Cornea • Conjunctiva
Tortora Page 266-267 Structures of the Eye • Vascular tunic consists of • Choroid • Ciliary body • iris
Tortora Page 266-267 Structures of the Eye • Nervous tunic consists of • Retina • Rods & cones • Detached retina
Tortora Page 266-267 Structures of the Eye • Lens • Suspensory ligaments • cataracts
Tortora Page 266-267 Structures of the Eye • Anterior Cavity • Anterior chamber • Posterior chamber • Aqueous humor • Intraocular pressure • Glaucoma
Tortora Page 266-269 Structures of the Eye • Posterior Cavity • Filled with vitreous humor
Tortora Page 268-269 Structure of the Retina • Retina covers the choroid layer. • Consists of three zones of neurons • photoreceptors • Bipolar • Ganglion neurons
Tortora Page 268-269 Photoreceptors • Modified dendrites. • Highly specialized. • Rods • Cones
Tortora Page 268-269 Photoreceptors • Modified dendrites. • Highly specialized. • Cones • Cones are concentrated around the central fovea.
Visual Pathway Tortora Page 268-269 • Generator potential is created by rods and cones. • Bipolar neurons • Ganglion neurons. • Optic nerve II. • 3rd order neuron.
Tortora Page 271-272 Formation of Image on Retina • Four processes are needed to form an image on the retina. • First • Extrinsic muscles cause convergence of eyes on object. • Depth perception.
Tortora Page 271-272 Formation of Image on Retina • Second • Pupils constrict so as to center the light entering the eye.
Tortora Page 271-272 Formation of Image on Retina • Third • Refraction (bending of the light rays) occurs due to; • Cornea • Aqueous humor • Lens • Vitreous humor
Tortora Page 271-272 Formation of Image on Retina • Fourth • Accomodation - the lens changes shape so as to focus image on the retina.
Tortora Page 271-272 Stimulation of Photoreceptors • Photopigments are molecules that change structure when struck by light • Small amounts of light cause rhodopsin to break down. • Results in opsin and retinal A. • Starts generator potential. • Reforms quickly. • Daylight overwhelms rods.
Tortora Page 271-272 Stimulation of Photoreceptors • Three types of cones • Red • Green • Blue • Each contains a different photoreceptor. • All need abundance of light • All break down with intense light but quickly reform. • Most common form of color blindness is lack of red or green cones.
