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Somatic and Special Senses The Senses Somatic Senses are general senses of touch ◦ Temperature ◦ Pressure ◦ Pain Special senses are ◦ Smell ◦ Taste ◦ Sight ◦ Hearing ◦ Equilibrium All of these senses occur when “stimuli” are received through sensory receptors. These stimuli are converted to an electrical message that is carried to the brain and interpreted. Types of Receptors Chemoreceptors: detect chemicals; such as taste and smell Mechanoreceptors: detect changes in pressure; touch pressure, hearing , balance and blood pressure Thermoreceptors: detect changes in temperature Photoreceptors: detect changes in light, responsible for vision Somatic Senses Touch and Pressure ◦ Merkel disk: found in the stratum basal and perceive very light touch ex; lips and fingertips ◦ Meissner corpuscle: found in the dermis of hairless skin and perceive light touch ex; lips, fingertips and palms ◦ Pacinian corpuscles: found in the lower dermis, subcutaneous. Responds to heavy pressure Somatic Senses Temperature ◦ Cold receptors: located in the stratum basale; perceive temperatures between 50o and 105oF ◦ Hot receptors: located in the dermis; perceive temperatures between 90o and 118oF Somatic Senses Pain ◦ Nociceptors are found in every tissue except the brain ◦ Pain is caused by tissue damage Excessive stretching Prolonged muscular contraction Inadequate blood flow Presence of certain chemicals Somatic Senses: Pain Tissue injury/irritation release of prostaglandins stimulate receptors PAIN prostaglandins are slowly removed from area Pain remains until all prostaglandins are removed Pain serves as a protective function; it lets you know that tissue damage is taking place Acute vs. Chronic pain Acute: sharp pain, conducted rapidly Chronic: dull pain conducted slowly Referred Pain Tissue damage that takes place in the organs of the body may cause pain in a different area. This happens because pain impulses travel along common pathway and the brain can’t tell where tissue damage is occurring. Ex: tissue damage that takes place in the heart may be perceived as pain in the arm; brain misinterprets location of tissue injury The Sense of Taste Taste buds house the receptor organs Location of taste buds ◦ Most are on the tongue ◦ Soft palate ◦ Cheeks Figure 8.18a–b The Tongue and Taste The tongue is covered with projections called papillae ◦ Filiform papillae – sharp with no taste buds ◦ Fungifiorm papillae – rounded with taste buds ◦ Circumvallate papillae – large papillae with taste buds Taste buds are found on the sides of papillae Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas Taste Sensations Sweet receptors: Sugars, Saccharine Sour receptors: Acids Salty receptors: Metal ions Bitter receptors Alkaloids Umami: Amino Acid called glutamate-savory as in meats, cheese (protein heavy foods) Taste pores are openings where food falls into and are tasted Gustatory hairs help direct food into the taste pore Anatomy of Taste Buds Figure 8.18 Chemical Senses – Taste and Smell Both senses use chemoreceptors ◦ Stimulated by chemicals in solution ◦ Taste has five types of receptors ◦ Smell can differentiate a large range of chemicals Both senses complement each other and respond to many of the same stimuli Olfaction – The Sense of Smell Olfactory receptors are in the roof of the nasal cavity ◦ Chemicals must be dissolved in mucus for detection Impulses sensed via the olfactory nerve Humans can recognize over10,000 scents Olfactory Epithelium Figure 8.17 The Eye and Vision Photoreceptors receive stimuli 70% of all sensory receptors are in the eyes Each eye has over a million nerve fibers Protection for the eye ◦ Most of the eye is enclosed in a bony orbit ◦ A cushion of fat surrounds most of the eye Accessory organs of the eye Eyelid:covers the eye moistens, protects the eye Conjunctiva: lines the inner surface of the eyelid and outer surface of eye Accessory organs of the eye Lacrimal gland: secretes tears; above eye. Lacrimal ducts carry tears into nasal cavity Lacrimal sac collects tears, sends to nasal cavity Tears keep eye moist but also contain the enzyme lysozyme which reduces eye infections Extrinsic Eye Muscles Muscles attach to outer surface of the eye Produce eye movements Figure 8.2 Structure of the eye The eye is a hollow muscular structure about 2.5cm in diameter. It is filled with fluid that gives it shape Figure 8.3a Structure of the Eye Sclera: White covering known as the “white of the eye” Cornea: Transparent, central anterior portion, covering ◦ Allows for light to pass through ◦ Repairs itself easily ◦ The only human tissue that can be transplanted without fear of rejection Structure of the Eye Optic nerve: carries visual impulses to the brain Choroid coat: middle layer of the eye; contains lots of blood vessels to nourish eye Structure of the Eye Iris: a ring of muscular tissue that forms the opening that determines how much light enters the eye ◦ Muscles contract pupil is small ◦ Muscles relax (dilate) pupil is large Structure of the Eye Vitreous humor: Gel substance behind lens ◦ Keeps the eye from collapsing ◦ Lasts a lifetime and is not replaced Aqueous humor: a thin fluid that fills the anterior chamber of the eye (between the cornea and lens) ◦ Constantly being formed and drained. ◦ When it doesn’t drain -glaucoma (vision going gray Structure of the Eye Retina: inner lining of the eye Macula-center of visual acuity Macular degeneration- separation of retina causes blindness Structure of the Eye Retina: Contains receptor cells (photoreceptors) ◦ Rods: dim vision, peripheral vision, gray tones, found on edge of retina ◦ Cones: blue, red, green cones, each sensitive to a different wavelength Cones are densest near the fovea centralis (center of macula):area of retina with only cones Structure of the Eye No photoreceptor cells are at the optic disk, or blind Signals pass from photoreceptors thru the retina to the optic nerve Structure of the Eye Lens: biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body Figure 8.3a Structure of the Eye Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects Figure 8.9 Visual Pathway Photoreceptors of the retina are stimulated by an object Stimulates the Optic nerve Message travels across the optic chiasma to the brain Figure 8.11 Common Disorders of the Eye Conjunctivitisinflammation of the membrane that lines the eye Cataract-lens loses its flexibility and transparency (cloudy) Glaucoma-increased pressure in the fluid of the eye-interferes with optic nerve functioning Common Disorders of the Eye Myopia-(nearsightedness)objects at a distance are blurry (CAN see near) PresbyopiaFarsightedness due to age-lens becomes stiff and yellowish-can’t focus close up-especially in low light – usually happens between 40-45 years old Common Disorders of the Eye Amblyopia-”lazy eye”one eye has poor vision Strabismus-also called lazy eye-eyes are not aligned with ,each other “crossed eyes” Color blindness is the result of lack of one cone type The Ear Houses two senses ◦ Hearing ◦ Equilibrium (balance) Receptors are mechanoreceptors Different organs house receptors for each sense Anatomy of the Ear Ear is divided into 3 areas: Outer (external) Middle ear, Inner ear Figure 8.12 External Ear Pinna (auricle): Collects sounds with funnel shape External auditory canal: narrow chamber in the temporal bone, Lined with skin & Ceruminous (wax) glands Ends at the tympanic membrane (eardrum) Carries sound to the middle ear Figure 8.12 The Middle Ear Air-filled cavity within the temporal bone Only involved in the sense of hearing Tympanic membrane: aka eardrum; cone-shaped, responds to sound waves by moving back and forth Bones of the Middle Ear ◦ Malleus (hammer) ◦ Incus (anvil) ◦ Stapes (stirrip) • Vibrations from eardrum move the malleus • These bones transfer sound to the inner ear Figure 8.12 Middle Ear/Tympanic Cavity Two tubes associated with the middle ear: 1. The opening from the auditory canal, covered by the tympanic membrane 2. The Eustachian or auditory tube connecting the middle ear with the throat Allows for equalizing pressure during yawning or swallowing. This tube is otherwise collapsed Site of ear infections; tubes in your ears are plastic tubes that keep Eustachian tube open Inner Ear or Bony Labyrinth Includes organs for hearing and balance A labyrinth of bony chambers in temporal bone includes: Cochlea, Vestibule Semicircular canals Figure 8.12 Inner Ear: Semicircular canals Loops that extend into each “dimension” Full of jello-like fluid and hairs As you move the jello pulls on the hairs which sends a message to the brain about your position Inner Ear: Cochlea Shell shaped organ that sends sound vibrations through the round window to the…… Organ of corti: contains sensory receptors that transmit “hearing” impulses to brain Inner Ear:Vestibule Contains fluid, little stones called otoliths and hairs When head moves fluid with otoliths move the hairs this sends a message to the brain on position of the head Equilibrium Static ◦ Helps you maintain stability and posture of the head and body when not in motion ◦ Occurs in the vestibule which contains hairs that bend according to position of head Vs Dynamic ◦ Helps you maintain balance when you are in motion ◦ Occurs in the semicircular canals which are loops of fluid that move hairs depending on the position of the body Balance Common Disorders of the Ear Otitis media: ear infection Labyrinthitisinflammation of the inner ear causes vertigo (dizziness) Meniere’s (MAIN-eeairz) Disease-chronic condition that affects the labyrinth and leads to progressive hearing loss
