Topic 11: Senses Sensory Receptors Part of the nervous system that detects a stimulus A sensory receptor could be: o o o Types of Sensory Receptors: o Chemoreceptors: detects chemicals ( ) o Photoreceptors: detects light (found in ) o Thermoreceptors: detects changes in . Bulb of Krause: sensitive to temperatures o Mechanoreceptors: detect movement ( ) . Meissner’s corpuscles: sensitive to . Pacinian corpuscles: sensitive to . Ruffini corpuscles: senses changes in o Pain receptors ( ): detects tissue damage o Osmoreceptors: detects changes in the Sense of Touch: o Tactile corpuscles: touch receptors found in the of skin and around hair follicles Senses of pressure: located in tissues beneath the skin, near joints, muscles and other deep tissues Sense of Temperature: free nerve endings found distributed within the skin o Separate receptors for hot and cold Sense of Position o Propioceptors: receptors that maintain muscle tone and good posture in order to coordinate movements Sense of Pain o o o o o How Pain is Perceived How to Manage Pain Endorphins: naturally released chemicals that impair the flow of pain signals Aspirin: slows the production of pain signaling molecules Morphine: mimics endorphins Sense of Taste Taste: chemoreceptors that detect chemicals dissolved in fluid (tastebuds) Five Main Flavors: o o o o o Sense of Smell (Olfaction) Chemoreceptors that bind to specific substances Olfactory nerve carries impulses from the smell receptors to the and Vomeronasal organ: sensitive to Sense of Sight Protected by: o o o o o Structure of the Eye o Outer layer: . Sclera: . Cornea: o Middle layer: . Pupil: . Iris: . Cilary body: . Choroid: o Inner layer: . Lens: . Aqueous humor: . Vitreous humor: . Retina Rods: receptors for Cones: receptors for Macula lutea: an area that contains the o Fovea centralis: largest concentration of cells that has the sharpest vision Optic nerve: leads to , which in turn sends signals to the cortex How Photoreceptors Work o Rods: disks which consist of : a light absorbing pigment made up of (protein) and Retinal Vitamin A, which helps to manufacture pigments for the rods o Cones: three types that are sensitive to , and light Visual Processing o Connect to photoreceptors to receive, process and integrate visual signals o Different neurons inside the brain respond to different visual patterns o Region where the optic nerve exists in the eye is known as the . Accommodation: the shape of the lens adjusts so that incoming light rays fall on the retina o Curvature of the lens determines the extent to which light rays will bend . Flat: focuses on objects . Rounder: focuses on objects Light Pathway Light waves (bend) once they enter the eye. Muscles of the adjust the pupil Muscle adjusts the lens ( ) Light stimulates receptor cells of the Optic nerve transmits impulses to the brain lobe interprets the impulse Disorders of the Eye 1. Hyperopia: (light focuses beyond the retina) 2. Myopia: (light focuses before the retina) 3. Astigmatism: irregular curvature of the 4. Strabismus: lack of eyeball coordination a. Convergent: eye deviates toward the b. Divergent: eye deviates 5. Conjunctivitis: infection of the conjunctiva 6. Cataract: cloudiness of the lens a. Surgery can remove the lens and implant an artificial one 7. Glaucoma: excess pressure of the a. Can lead to destruction of some optic nerve fibers 8. Retinal detachment: retina detaches from the layer 9. Macular degeneration: deterioration of the central area of the Sense of Hearing/Balance Structure of the Ear Outer ear: adapted to gather sound . Pinna: projecting from the side of the head that collects sound waves and directs them into the canal Middle ear: amplifies and transmits air waves to the inner ear . Ear drum ( ): vibrations transmit sound waves to middle ear bones . Ossicles (bones) Mallus Incus Stapes Inner ear: contains the bony labyrinth . Vestibule: two bony chambers that contain receptors for . Semicircular canals: 3 projecting bony tubes containing cells which are stimulated by fluid movements in canals . Cochlea: looks like a snail shell and contains 2 fluid filled compartments and receptors for How do we hear? Organ of Corti: contains ciliated receptor cells inside the cochlea . Sound waves enter the and cause vibrations in the . The , and transfer the vibrations to the oval window . Vibrations of the oval window are transferred to the canal, which contains the organ of Corti . The organ of Corti contain hairs that transfer impulses to the nerve which then carries the impulse to the brain How do we maintain balance? Macula: mechanoreceptors in the vestibule detect movement in and planes Cristae: mechanoreceptors in the semicircular canal detect and movement Otoliths: calcium carbonate granules found within special membranes that stimulate the hair cells to detect position Disorders of the Ear Otits Media: bacterial or viral infection of the ear Otitis Externa: “swimmer’s ear” – an infection of the auditory canal caused by a fungus or bacterium Conductive hearing loss: results from the inability of sound waves to pass from the outer to the inner ear . May be a result of an obstruction within the ear canal or blockages of the Eustachian tube or damage to the tympanic membrane . Otosclerosis: hereditary bone disorder which prevents the vibration of the stapes may also cause conductive hearing loss Presbycusis: slow progressive hearing loss associated with age Vertigo: feeling of dizziness due to an inflammation of the bony labyrinth Tinnitus: ringing, roaring, clicking or hissing sound in the ears due to: . Sensory Adaptation Phenomenon in which receptors adjust themselves to a continuous stimulus so that the sensation becomes less acute Receptors adapt at different rates: o Receptors for temperature and pressure adapt rapidly o Receptors for pain do not adapt .