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General Senses Sensations detected by simple receptors General Senses (cont’d) Touch and Pressure Temperature Pain Body position Touch and Pressure Cutaneous Sensations Located within the skin Meissner’s corpuscles – fine touch Hairless skin Fingers, palms, soles, lips, external genitals Krauses’s end bulbs Like Meissner’s, but in mucous membranes of mouth Touch and Pressure (cont’d) Merkel’s discs - less common Epidermis Light touch receptors Pacinian corpuscles – deep pressure Deep regions of skin, around joints and tendons,in some visceral organs Touch and Pressure (cont’d) Ruffini’s corpuscles – deep & continuous pressure Deep in dermis, hypodermis, and joint capsules Temperature Poorly understood Free nerve ending in skin Detects hot and cold Can even cause pain Pain Informs brain of homeostatic imbalances Visceral pain Visceral organs Stomach or intestinal cramps, heartburn, or headache Pain (cont’d) Referred pain Major nerve impulses share pathways Ex. Originates from the heart and is felt in arm Body Position Proprioceptors Skeletal muscle, joints, ligaments & CT of bones & muscles Constantly advise brain of our own movements Degree of muscle contraction, amount of tension in tendons, position of a joint, position of head relative to the ground Enables you to control your body movements Body Position (cont’d) Muscle spindles Receptors between a tendon and a skeletal muscle Detect when a muscle is stretched and initiates a reflex that resists that stretch Helps maintain muscular tone and body posture Special Senses Smell Taste Sight Hearing Smell and Taste Receptors are chemoreceptors Respond to chemicals in solution Smell Olfaction Thousands of olfactory receptors in roof of nasal cavity Found high in nasal cavity Smell (cont’d) Sniffing helps to bring in more air (containing odors) over the olfactory mucosa Olfactory pathways are closely linked to the limbic (emotional expression) system Odors recall memories and arouse emotional responses Taste Gustation Gustatory (taste) cells are located in the taste buds Scattered throughout oral cavity Most of 10,000 on papillae on surface of tongue Others found on roof of the mouth & walls of pharynx Taste (cont’d) Gustatory cells surrounded by supporting cells – gustatory hairs (microvilli) Protrude through the taste pores where they are stimulated Taste (cont’d) Taste and appreciation of foods is influenced by the sense of smell and the temperature and texture of foods. Taste Sensations Sweet Sour Bitter Salty Each concentrated in a region on the tongue Coffee, cinnamon, garlic, pepper – combination Sight Depends on photoreceptors 70% of all receptors External/Accessory Structures Extrinsic eye muscles aim the eyes for following moving object and convergence External/Accessory Structures (cont’d) Lacrimal apparatus Series of ducts and glands Produce a saline solution – washes and lubricates the eye External/Accessory Structures (cont’d) Eyelids – protect Eyelashes Ciliary glands – modified sweat glands between eyelashes Meibomian glands – produce oily secretion that lubricates the eye External/Accessory Structures (cont’d) Conjunctiva – delicate membrane Lines eyelids and covers part of the outer surface of eye Secretes mucus – helps lubricate Conjunctivitis – inflammation Pinkeye - highly contagious Structure of the Eye Fibrous Tunic Vascular Tunic Sensory Tunic Fibrous Tunic Thick, outermost layer Sclera – “white of the eye” Posterior Thick , tough protective layer Provides shape to eyeball Fibrous Tunic (cont’d) Cornea Anterior Transparent – “window” of the eye – allows light in Bulges outward slightly Vascular Tunic Middle Layer Abundance of blood vessels Choroid – provides nutrition to internal eye structures Prevents light’s scattering Vascular Tunic (cont’d) Thick ciliary body Help control lens shape Vascular Tunic (cont’d) Colored iris Opening Pupil – regulates amount of light entering Vascular Tunic (cont’d) Lens - behind the pupil and iris Cataract - when transparency is lost Held by suspensory ligaments attached to ciliary body Separates eye into 2 main compartments – anterior (aqueous) and posterior (vitreous) chambers Fluid Aqueous humor clear, watery fluid circulated and recycled through the bloodstream Helps maintain intraocular pressure Glaucoma – drainage is blocked, pressure increases Possible blindness Fluid (cont’d) Vitreous humor thickened, gellike Helps prevent eyeball from collapsing Sensory Tunic Inner layer of the eyeball Contains the retina Detection of light and transport of impulse to optic nerve Sensory Tunic (cont’d) Millions of photoreceptors Distributed over entire retina, except where optic nerve leaves the eyeball Blind spot (optic disc) Sensory Tunic (cont’d) Two types of photoreceptors Rods and cones Sensory Tunic (cont’d) Rods Black and white Sensitive to small levels of light Most dense at periphery of retina Night blindness – rod function seriously hampered Sensory Tunic (cont’d) Cones Color Require more light Provides sharper image Densest in center of retina Fovea centralis – lateral to each blind spot – only cones – greatest visual acuity Color blindness – due to a congenital lack of one or more of the cone types Pathway of Light Through the Eye Light rays bend when they pass from air to the fluids and solids of the eyeball Refraction The lens changes shape Accommodation Errors of Refraction Myopia - nearsightedness Hyperopia - farsightedness Astigmatism – unequal curvatures in different parts of the cornea. All are correctable with lenses Errors of Refraction (cont’d) Presbyopia “Old person’s vision” Many people over 50 – lens is non-accommodating due to loss of elasticity of lens Difficult to focus close up Pathway of Light Cornea aqueous humor (through pupil) aqueous humor lens vitreous humor retina Physiology of Vision Image formed on retina Rods and cones convert light waves to a series of signals Result in generation of action potential in ganglion cells Physiology of Vision (cont’d) Rods and cones contain pigments that decompose when exposed to light Pigment decomposition leads to nerve impulse generation Visual Pathways Electrical signals pass from photoreceptors to bipolar neurons to ganglion cells Action potential is generated Leave retina via optic nerve as nerve impulses transmitted to optic cortex. Result is vision Binocular Vision Overlap of visual fields and inputs from both eyes (binocular vision) to each optic cortex provide for depth perception (3D vision) Eye Reflexes Convergence Movement of eyes medially when we view close objects Photopupillary Exposure to bright light causes pupils to constrict Accommodation pupillary Pupils constrict when we view close objects Hearing and Equilibrium Audation Detected by mechanoreceptors Deep within the ear The Ear Outer ear Middle ear Inner Ear Outer Ear Auricle (pinna)outer appendage External auditory canal Outer Ear (cont’d) Together direct sound waves to the eardrum (tympanic membrane) Separates outer from middle ear Sound transmission only Middle Ear Tympanic cavity Air-filled cavity within temporal bone Middle Ear (cont’d) Ossicles and auditory tube Ossicles transmit vibratory motion from the eardrum to the oval window Middle Ear (cont’d) Ossicles and auditory tube (cont’d) Auditory tube links middle ear with the throat Allows pressure to be equalized on both sides of eardrum Middle Ear (cont’d) Ossicles and auditory tube (cont’d) Otitis media – inflammation of the middle ear Common result of sore throat Middle Ear (cont’d) Sound transmission only Tympanic membrane (ear drum) 3 auditory ossicles (smallest bones in body) Malleus (hammer) Incus (anvil) Stapes (stirrup) Middle Ear (cont’d) Ossicles convert sound waves into vibrations and transmit to the oval window Opening in tympanic cavity -opens to cochlea Vibrations from stapes cause fluids to move, stimulating hearing receptors Inner Ear Bony labyrinth Winding, complicated series of passageways Inner Ear (cont’d) Bony chambers in temporal bone Semicircular canals Vestibule 3 loops that lie at right angles to one another Chamber between canals and cochlea Within both canals and vestibule - equilibrium receptors Inner Ear (cont’d) Bony chambers in temporal bone (cont’d) Cochlea Looks like snail shell Hearing receptors Inner Ear (cont’d) Bony labyrinth filled with plasmalike fluid called perilymph Suspended in perilymph membranous labyrinth Contains a thicker fluid called endolymph Inner Ear (cont’d) Organ of Corti Located in the cochlea Contains receptors that respond to waves Auditory Nerve Pathway Hair cells in organ of Corti convert motion of endolymph to release neurotransmitters Initiates a nerve impulse Carried to the medulla midbrain thalamus terminates in temporal lobe of cerebral cortex Deafness Conduction deafness Something interferes with conduction of sound vibrations to the fluids of the inner ear Build up of ear wax Fusion of ossicles Ruptured ear drum Otitis media Deafness (cont’d) Sensorineural deafness Degeneration or damage to receptor cells in Organ of Corti, to cochlear nerve, or to neurons of auditory cortex. Often results from extended listening to loud sounds Deafness (cont’d) Sensorineural deafness (cont’d) Presbycussis Type of sensorineural deafness By age of 60 Loss in ability to hear high tones and speech sounds Becoming more common in younger people Deafness (cont’d) Hearing aids more helpful with sensorineural Also cochlear implants with sensorineural The Sense of Equilibrium Detected by receptor cells in inner ear Static Sensation of body position detected by vestibules The Sense of Equilibrium (cont’d) Dynamic Sensations of rapid movement detected by semicircular canal Receptor region – crista ampularis The Sense of Equilibrium (cont’d) Sight and proprioceptors (muscles and tendons) also important in providing info used to control balance