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Chapter 6 The Peripheral Nervous System: Afferent Division & Special Senses V edit. Pg. 185-232 VI edit. Pg. 181-231 VI edit. Pg. 183-235 Organization of the Nervous System Neuronal Circuit © Brooks/Cole - Thomson Learning Sensory Receptors Devices capable of detecting and measuring a particular physical parameter A) B) C) D) Chemoreceptors: mediate sense of smell and taste Pain receptors: sensitive to tissue damage Thermoreceptors: detect changes in temperature Mechanoreceptors (propioreceptors, baroreceptors, stretch receptors): sense changes in pressure, tension, movement E) Photoreceptors: mediate sense of vision Information conveyed by these receptors is processed in the brain as a sensation (perception) Sensory Receptors Somatic Senses Special Senses Sensory receptors associated with: Sensory receptors associated with: Skin Joints Muscles Viscera Smell Taste Hearing/Equilibrium Vision Sensory Transmission: Receptor Potential Sensory Transmission: Generator Potential Sensory Transmission: Sensory transmission is graded: the strongest the stimulus, the more action potentials are generated (or depolarizing responses) From Neuron to Brain, IV Ed. The larger the receptor potentials , the greater the frequency of action potentials Adaptation Ability of a receptor to limit its response despite continuous stimulation Tonic receptors Phasic receptors Adaptation in Somatic Senses Touch and pressure Receptors: Free nerve endings, Meissner‘s corpuscle, Pacinian corpuscle Temperature Pain Receptors: Free nerve endings receptors divided into cold receptors (10-20 degrees) and warm receptors (25-45 degrees) Receptors: Free nerve ending receptorsVisceral pain receptors, Cutaneous pain receptors Meissner‘s corpuscle: found in hairless parts of skin near epidermis. Mediate sense of light touch and texture sensations. Pacinian corpuscle: found in dermis. Mediate crude touch and vibrations Undergo Adaptation Divided into: fast conducting, myelinated A-delta receptors mediating sharp pain and slow conducting, unmyelinated C-type receptors mediating chronic pain and visceral pain Undergo Adaptation No adaptation Adaptation in Special Senses Smell Olfactory receptors in nasal cavity Undergo Adaptation Taste Hearing Taste buds receptors in Hair cells in inner tongue, cheek, roof of the ear mouth, walls of pharynx Sense sweet, bitter, sour and salty tastes Sense low and high frequencies sounds Undergo Adaptation No adaptation Eye Anatomy © Brooks/Cole - Thomson Learning Structure of the Eye Outer Middle Inner Tunica Cornea Sclera Ciliary body Iris Lens Choroid coat Retina A) Cornea: Transparent layer of connective tissue with very few cells. It contains little blood supply but a significant nerve innervation B) Cornea continues with sclera on back of the eye A) Iris: Layer of connective tissue and smooth muscle cells. Amount of melatonin in iris determines eye color B) Divide the anterior cavity into an anterior chamber and a posterior chamber containing aqueous humor C) Function: regulate the amount of light coming into the eye Control of Pupillary Size A) Lens: Transparent layer of connective tissue/dead cells with few cells and a lot of intercellular material. Accumulation of opaque fibers causes cataract B) Lens are attached to suspensory ligaments that are attached to ciliary body C) Function: focus/accommodation D) The anterior chamber between the cornea and the lens is filled with the aqueous humor secreted by the ciliary body E) Accumulation of aqueous humor cause glaucoma A convex lens concentrates all light rays into the focal point Function of the Lens Focus of light rays on the retina Disorders associated with the lens: cataracts, stigmatism, myopia (nearsightedness), heperopia (farsightedness) Control of the thickness of the lens can be used to focus the light rays coming from distant or close objects A) Lens: Transparent layer of connective tissue/dead cells with few cells and a lot of intercellular material. Accumulation of opaque fibers causes cataract B) Lens are attached to suspensory ligaments that are attached to ciliary body C) Function: focus/accommodation D) The anterior chamber between the cornea and the lens is filled with the aqueous humor secreted by the ciliary body E) Accumulation of aqueous humor cause glaucoma Lens and Ciliary Body Accommodation: Ability to change the shape of the lens to focus an object in the retina Far-light sources require a flat lens Near-light sources require a rounded lens Accommodation: Ability to change the shape of the lens to focus an object in the retina Far-light sources require a flat lens Near-light sources require a rounded lens Accommodation Close Object Distant Object Ciliary muscle contract (+ Parasympathetic NS) Ciliary muscle relax (+ Sympathetic NS) Suspensory ligaments relax Suspensory ligaments contract Thick (round) lens Thin (flat) lens Eye Anatomy-Retina © Brooks/Cole - Thomson Learning Retinal Structure Photoreceptors The retina contains two kind of photoreceptors: cones and rods. Cones mediate color vision (day vision), are less sensitive to light but have the highest acuity (sharpness) Optic Disk and Macula Lutea Fovea-depression in the retina where light strike the cones directly Optic disc (Blind spot)site where optic nerve leaves and blood vessels enter the eye) Macula-area with highest number of cones Structure of Photoreceptors Rods Cones Active at night Active at daylight Absorb all visible wavelengths Absorb light of a particular wavelength (red, green, blue) More sensitive to light Less sensitive Lowest acuity Highest acuity Contain the photopigment rhodopsin Contain the photopigment iodopsin Rods Photopigment Rhodopsin = Opsin + retinene http://www.blackwellpublishing.com/matthews/rhodopsin.html Dark Phototransduction (process of converting the light stimuli into electrical signals) High concentration of cyclic GMP Na+ channels open in outer segment Takes place in outer segment Membrane depolarization Takes place in retina (Spreads to synaptic terminal) Opens Ca2+ channels in synaptic terminal Release of inhibitory transmitter (inhibition) Bipolar cells inhibited No action potential in cell ganglion cell No action potential propagation to Takes place in synaptic terminal Light (Absorption of light) Activation of photopigment Activation of transducin Takes pace in outer segment (Through a cascade of reaction) Decrease in cyclic GMP Closure of Na+ channels in outer segment Membrane hyperpolarization (theto receptor (Continue the nextpotential) page) (Spreads to synaptic terminal) Takes pace in synaptic terminal Closure of Ca2+ channels in synaptic terminal Release of inhibitory transmitter (Removal of inhibition) Bipolar cells disinhibited (or, in effect, exited) Graded potential change in bipolar cell (If of sufficient magnitude to bring ganglion cell to threshold) Action potential in ganglion cell Propagation of action potential to visual cortex in the occipital lobe of the brain visual perception http://www.physpharm.fmd.uwo.ca/undergrad/medsweb/L1Eye/Eye.swf Takes place in retina Light Adaptation Adaptation of photoreceptor sensitivity to light At low levels of illumination photoreceptors are more sensitive to light. Sensitivity decreases as the level of illumination increases Sensitivity is regulated by calcium ions. Ca2+ ions decrease activity of guanylate cyclase (make less cGMP) and decrease receptor affinity for cGMP Color Vision Photopigments in Cones Color Blindness Occurs as the result of losing a particular type of cone Visual Inversion At the beginning of visual processing the image projected into the retina is upside down and backward because of bending of the light rays Visual Pathway http://www.sumanasinc.com/webcontent/anisamples/neurobiology/visualpathways.html Binocular Vision Originate because overlapping visual fields from both eyes at the same time Visual Pathway Photoreceptors (Retina) Optic nerve Thalamus Cortex (Occipital lobe, Primary visual cortex) Vision (visual sensation) Ear Anatomy © Brooks/Cole - Thomson Learning Ear External Pinna External auditory meatus Tympanic membrane Middle Inner Ear Ossicles Cochlea Middle ear cavity Vestibular apparatus Auditory tube Sound wave Air vibrations generated by alternating areas of high and low pressure of air molecules Sound wave: Can a sound wave be generated in a vacuum? Structure of the Ear endolymph perilymph Hearing Pinna directs sound wave toward ear canal Sound wave hits tympanic membrane Tympanic membrane vibrations are transmitted to the malleus (amplification) Stapes convert vibrations into fluid movements in the cochlea Tympanic Reflex Outward movement Inward movement Organ of Corti contains hair cells-the sensor for hearing Hair cells in organ of Corti transform fluid movements into electrical signals http://www.blackwellpublishing.com/matthews/ear.html High frequency sounds (tone or pitch) are detected at the base of the cochlea. Low frequency sounds are detected at the tip of the cochlea =high energy Stiff basilar membrane =low energy Flexible basilar membrane http://www.spacehike.com/multiwavelength.html Inner hair cells transform mechanical waves into an electrical signals Auditory nerve Sound waves Vibration of tympanic membrane Vibration of middle ear bones Vibration of oval window Fluid movement within cochlea Vibration of round window Vibration of basilar membrane Dissipation of energy (no sound perception) In ear (continue to next slide) Bending of hairs of receptor hair cells of organ of Corti as basilar membrane movement displaces these hairs in relation to overlying tectorial membrane in which the hairs and embedded Graded potential changes (receptor potential) in receptor cells Changes in rate of action potentials generated in auditory nerve Propagation of action potentials to auditory cortex in temporal lobe of brain for sound perception Vestibular apparatus Vestibular apparatus Semicircular canals Otolith organs Utricle Saccule Function: sense rotational acceleration of the head (angular movement) Function: sense linear movements of the head and position of the head relative to gravity Hair cells in the ampulla transform fluid movements into electrical signals Endolymph Structure of the Ampulla in Semicircular Canal Acceleration of the head causes movement of the endolymph and bending of the cupula on the opposite direction Utricle and saccule contain the otolith organ to sense changes in linear acceleration Hair cells in otolith organs Kinocilium Stereocilia Otoliths (or ear stones) Gelatinous layer Hair cells Supporting cells Sensory nerve fibers Activation of hair cells in utricle and saccule by changes in head position and linear acceleration Gravitational force Figure 6.43b Page 225 Slide 70 Movement of head will change weight distribution of otolith due to gravity, resulting in bending of hair cells Figure 6.43c Page 225 Slide 71 When there is a linear movement of head, otolith will try to lag behind due to inertia, resulting in bending of hair cells Hearing/Balance Pathway Hair cells (Organ of Corti/Otolith organs/Ampulla) (Auditory N. Vestibulocholear N.) Medulla Oblongata Cortex (Temporal lobe) SENSATION OF HEARING & BALANCE Hearing/Equilibrium Senses Hearing Static Equilibrium Dynamic Equilibrium (linear movements (angular movements of the head) of the head) Functional organ: Cochlea Otolith organs: Utricle and Saccule Semicircular canals Hair cells located in: Organ of Corti in Cochlea Base of Utricle and Saccule Ampulla Hair cells undergo deformation from tectorial membrane Hair cells undergo deformation from otolith (calcium carbonate crystal or ear stones) Hair cells undergo deformation from cupulla