Chapter 10 – Somatic Senses

Types of Receptors Chemoreceptors Pain receptors Thermoreceptors Chemical concentrations Pain receptors Detect tissue damage Thermoreceptors Changes in temperature Mechanoreceptors Changes in pressure or movement Photoreceptors Light energy

Sensations Feeling that occurs when the brain interprets sensory impulses Depends on area of brain that receives the impulse Projection brain sends the sensation back to its apparent source Sensory adaptations Sensory impulses sent at decreasing rates until receptors fail to send impulses unless there is a change in strength of the stimulus

Touch and Pressure Receptors Sensory nerve fibers Found in epithelial tissues Sense touch and pressure Meissner’s corpuscles Are flattened connective tissue sheaths found in hairless portions of skin (Ex. Lips) Respond to the light motion of objects that barely touch the skin

Touch and Pressure Receptors Pacinian corpuscles Made of connective tissue Found in deeper subcutaneous layers, muscle tendons, joint ligaments Respond to heavy pressure and deep pressure

Temperature Senses Heat receptors Cold receptors Triggered at 77 - 113 degrees Fahrenheit Cold receptors Triggered at 50 - 68 degrees Fahrenheit

Sense of Pain Free nerve endings Stimulated due to tissue damage Visceral Pain Receptors (referred pain) Only receptors in viscera to produce sensations Referred pain - felt in at location other than where the painful stimulus is originating Occurs due to common nerve pathway leading from skin to internal organs

Pain Nerve Fibers Acute pain fibers Chronic pain fibers sensation of sharp pain seldom continues once stimulus is removed Chronic pain fibers dull, aching pain may continue after stimulus ceases Pain impulses sent to thalamus, hypothalamus, and cerebral cortex

Regulation of Pain Impulses Enkephalins Suppress acute and chronic pain impulses Serotonin Stimulates other neurons to release enkaphalins Endorphins Pain-suppressing, morphine-like actions Natural pain control sent by brain

Olfactory Organs Contain olfactory receptor cells (chemoreceptors) Smell receptors Cilia Sensitive part of the receptors Chemical detected once dissolved in watery- fluid surrounding cilia

Sense of Taste Taste buds Taste sensations Found in papillae of tongue Modified epithelial cells that serve as receptors Chemical must be dissolved in saliva to be tasted Taste sensations Sweet – near tip of tongue Sour – along lateral edges of tongue Salty – tip and upper portion of tongue Bitter – back of tongue Umami – MSG taste

Sense of Taste

Flavor = taste + smell

Aging and Taste After age 50, ability to smell and taste decrease Membranes lining nose become thinner & drier  olfactory nerve deteriorate # taste buds decrease with age  more difficult to detect sweet/salty  foods taste more bitter As people age, their food tastes more bland  eat less  possible malnutrition

Sense of Hearing - Parts of the Ear External Section Consists of: Auricle – collects sound-waves External auditory meatus – passageway for sound Middle Section Tympanic Membrane (ear drum) Auditory ossicles – malleus, incus, and stapes Transmit and amplify sound Inner Section Cochlea – hearing organ Semi-circular canals function in equilibrium Organ of Corti – houses receptors (hair cells)

Parts of the Ear

Ear Disorders Otitis Media Tinnitus Ear infection May require Eustachian tubes Tinnitus Ringing of the ear Sometimes accompanied with Meniere’s disease Spontaneous episodes of vertigo

The Structures of the Eye

Eyelid Skin covers lids outer surface Muscles orbicularis oculi & levator palpebrae superioris Conjunctiva - mucous membrane that lines the inner eye Conjunctivitis – inflammation of conjunctiva (pink eye)

Conjunctivitis

Visual Accessory Organs Lacrimal gland Secretes tears Secretes tears continuously over the eye and into the nasal cavity Lysozyme- enzyme that is an antibacterial agent against eye infections Extrinsic muscles Attached to the sclera and move eye in various directions

Strabismus – misalignment of eyes

Structures of the Eye Cornea Sclera Optic nerve Window of the eye Helps focus entering light rays Sclera White portion of the eye Protects eye & attaches extrinsic muscles Optic nerve Found in the back of the eye Transmits stimuli to the optic lobe

Structures of the Eye Ciliary body Choroid Coat Lens Iris Forms internal ring around the eye Choroid Coat Nourishes tissues of eye and keeps inside dark Lens Behind iris and pupil Focuses light Affected during cataract formation Iris Smooth-muscle diaphragm that adjusts amount of light entering Colored portion of eye

Cataracts

Structures of the Eye Aqueous humor Pupil Watery fluid between cornea and lens Nourishes and maintains shape of eye Glaucoma – causes damage to optic nerve due to built up pressure Pupil Circular opening in the center of the iris

Glaucoma

Structures of the Eye Retina Vitreous humor Contains photoreceptor cells Fovea centralis – sharpest point of vision in retina Optic disk – where nerve fibers leave eye to join optic nerve Blind spot Vitreous humor Fluid of the inner eye Supports internal parts and maintains the shape

Visual Receptors of Retina Rods Provide colorless vision in dim light and general outlines of objects Cones Detect color and provide sharp images in bright light Move eyes so image falls on the fovea centralis Contains the highest concentration of cones

Visual Pigments Rods Contain Rhodopsin (visual purple) Breaks down opsin (protein) and retinal (form of Vitamin A) in presence of light Cones Contain Iodopsins Three sets of cones, each containing a different visual pigment Wavelength of light determines the color perceived from it Each of the three pigments is sensitive to different wavelengths of light Color perceived depends upon which sets of cones the light stimulates If all three sets are stimulated, the color is white If none are stimulated, the color is black

Eye Disorders Myopia Hyperopia Astigmatism Diabetic retinopathy Color blindness

Myopia - “Nearsighted”

Hyperopia - “Farsighted”

Astigmatism

Diabetic Retinopathy

Color Blindness – caused because of faulty cone formation

Visual Acuity Clearness or sharpness of visual perception First number distance between person and chart Second number represents the # of feet a person with normal acuity would have to stand to see the same object clearly 20-200 legally blind

Vision Tests

Are the squares inside the blue and yellow squares all the same color?

Bezold effect The smaller squares inside the blue and yellow squares are all the same color. They seem different (magenta and orange) because a color is perceived differently depending on its relation to adjacent colors (here blue or yellow depending on the outer square).

Are the horizontal lines straight or crooked?

Café Wall Illusion The horizontal lines are straight, even though they do not seem straight.  In this illusion, the vertical zigzag patterns disrupt our horizontal perception.

Does Lincoln’s face look normal?

Some neurons in the brain seem specialized in processing faces Some neurons in the brain seem specialized in processing faces. Faces are usually seen upright. When presented upside down, the brain no longer recognizes a picture of a face as a face but rather as an object. Neurons processing objects are different from those processing faces and not as specialized. As a consequence these neurons do not respond to face distortions as well. This explains why we miss the weird eyes when the face is inverted.

Can you see a baby?

Illusory Contour The baby’s head is on the left, the baby’s feet are against the trunk of the tree on the right. Illusory Contour: a form of visual illusion where contours are perceived without a luminance or color change across the contour

How quickly can you say the color of the words below?

Genetics of Taste

PTC = phenylthiocarbamide Discovered in 1931 by when a DuPont chemist named Arthur Fox accidentally released a cloud of fine crystalline PTC in the lab. A nearby colleague complained of the bitter taste, while Dr. Fox tasted nothing. Fox continued to test the taste buds of family and friends, setting the groundwork for future genetic studies.

Genetics of PTC Tasting Gene for tasting PTC (Tas2r38) is located on Chromosome 7. PAV = taster (T), AVI = non-taster (t), AAV = another allele PAV-PAV = TT = very bitter PAV-AVI = Tt = somewhat bitter AVI-AVI = tt = non-taster General Population: 70% Tasters, 30% Non-tasters TAS2R38

Bitter tastes = Result of selection pressures? Thiocynate Compounds (bitter taste) found in broccoli, cauliflower, mustard family Tasters: avoid these foods in diet Nontasters: more varied diet, include green leafy veggies Thiocynates might inhibit thyroid function  tasters may have protection against thyroid diseases

Bitter tastes = Result of selection pressures? Poisons = bitter taste Tasters: part of hunter-gatherer societies? Genetic Drift Europeans: all 3 alleles (PAV, AVI, AAV) Asians: AAV allele rare Native Americans: 98% have PAV allele only

Denver Museum of Nature and Science Expedition Health: Genetics of Taste Study Purpose of Study: Is ability to taste bitter compounds related to what foods you eat, your % body fat, and BMI? Is your ability to taste bitter compounds related to your genetic ancestry?

Substances related to PTC Thiourea (thiocarbamide) – very bitter!!! Sodium benzoate – sweet, salty, bitter, no taste Food preservative

Family Pedigree Tasters: Supertasters (TT) Tasters (Tt) Non-tasters (tt)