Sensory Systems

How many different sensory receptors are hard at work during a roller coaster ride?

Sensations Definition:Definition: –State of awareness of internal or external conditions of the body Tortora Page 266

Sensations Four conditions for a sensation to occur: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.Stimulus results in a generator potential. –Depolarization of receptor membrane. –Follows afferent pathway to thalamus. –From thalamus, action potential goes to cerebrum Tortora Page 266 Molecules in food stimulate generator potentials in taste buds

Sensations 4 Characteristics of a sensation.4 Characteristics of a sensation. –Projection “connects” sensation in cerebrum to correct part of body.“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.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.4 Characteristics of a sensation. –Adaptation Decrease in sensitivity with continued non threatening stimulation.Decrease in sensitivity with continued non threatening stimulation. Example: A person living near the railroad tracks sleeps through the passing of the trainExample: A person living near the railroad tracks sleeps through the passing of the trainTortora Page 266

Sensations 4 Characteristics of a sensation.4 Characteristics of a sensation. –Afterimages Sensation persists even though stimulus is removed.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.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.4 Characteristics of a sensation. –Modality Type of stimulation.Type of stimulation. Example:Vision Vs smell Vs touchExample:Vision Vs smell Vs touchTortora Page 266

Receptors Classification based on location:Classification based on location: –Exteroceptors –Visceroceptors –Proprioceptors Tortora Page 266

Receptors Classification based on type of stimulus:Classification based on type of stimulus: –Mechanoreceptor –Thermoreceptor –Nociceptor –Electromagnetic receptor –Chemoreceptor Tortora Page 266

Receptors Classification based on type of complexity:Classification based on type of complexity: –Simple –Complex Tortora Page 266

Accessory Structures of the Eye EyelidsEyelids EyebrowsEyebrows Lacrimal apparatusLacrimal apparatus Lacrimal glandLacrimal gland Lacrimal canals.Lacrimal canals. Nasolacrimal duct.Nasolacrimal duct. Role of lysozyme: antibacterial.Role of lysozyme: antibacterial. Lacrimal apparatus from Gray’s Anatomy

Structures of the Eye Eye lies within a cavity called the orbit.Eye lies within a cavity called the orbit. Tortora Page

Structures of the Eye Muscles that move the eye:Muscles that move the eye: –Inferior rectus –Lateral rectus –Superior rectus –Medial rectus –Inferior oblique –Superior oblique Tortora Page 197

Structures of the Eye Eye has three layers.Eye has three layers. –Fibrous tunic –Vascular tunic –Nervous tunic Tortora Page

Structures of the Eye Fibrous tunic consists of:Fibrous tunic consists of: –Sclera –Cornea –Conjunctiva Tortora Page

Structures of the Eye Vascular tunic consists ofVascular tunic consists of –Choroid –Ciliary body –iris Tortora Page

Structures of the Eye Nervous tunic consists ofNervous tunic consists of –Retina –Rods & cones –Detached retina Tortora Page

Structures of the Eye LensLens –Suspensory ligaments –cataracts Tortora Page

Structures of the Eye Anterior CavityAnterior Cavity –Anterior chamber –Posterior chamber –Aqueous humor –Intraocular pressure –Glaucoma Tortora Page

Structures of the Eye Posterior CavityPosterior Cavity –Filled with vitreous humor Tortora Page

Structure of the Retina Retina covers the choroid layer.Retina covers the choroid layer. Consists of three zones of neuronsConsists of three zones of neurons –photoreceptors –Bipolar –Ganglion neurons Tortora Page

Photoreceptors Modified dendrites. Highly specialized. –Rods –ConesTortora Page

Photoreceptors Modified dendrites.Modified dendrites. Highly specialized.Highly specialized. –Cones –Cones are concentrated around the central fovea. Tortora Page

Tortora Visual Pathway Generator potential is created by rods and cones.Generator potential is created by rods and cones. Bipolar neuronsBipolar neurons Ganglion neurons.Ganglion neurons. Optic nerve II.Optic nerve II. 3rd order neuron.

Formation of Image on Retina Four processes are needed to form an image on the retina.Four processes are needed to form an image on the retina. FirstFirst –Extrinsic muscles cause convergence of eyes on object. –Depth perception. Tortora Page

Formation of Image on Retina SecondSecond –Pupils constrict so as to center the light entering the eye. Tortora Page

Formation of Image on Retina ThirdThird –Refraction (bending of the light rays) occurs due to; CorneaCornea Aqueous humorAqueous humor LensLens Vitreous humorVitreous humor Tortora Page

Formation of Image on Retina FourthFourth –Accomodation - the lens changes shape so as to focus image on the retina. Tortora Page

Stimulation of Photoreceptors Photopigments are molecules that change structure when struck by lightPhotopigments are molecules that change structure when struck by light Small amounts of light cause rhodopsin to break down.Small amounts of light cause rhodopsin to break down. Results in opsin and retinal A.Results in opsin and retinal A. Starts generator potential.Starts generator potential. Reforms quickly.Reforms quickly. Daylight overwhelms rods.Daylight overwhelms rods. Tortora Page

Stimulation of Photoreceptors Tortora Page Three types of conesThree types of cones –Red –Green –Blue Each contains a different photoreceptor.Each contains a different photoreceptor. All need abundance of lightAll need abundance of light All break down with intense light but quickly reform.All break down with intense light but quickly reform. Most common form of color blindness is lack of red or green cones.Most common form of color blindness is lack of red or green cones.