Senses Chapter 9 PDF

Senses Sense: ability to perceive stimuli Sensation: conscious awareness of stimuli received by sensory neurons Sensory receptors: sensory nerve endings that respond to stimuli by developing action potentials Classification of Senses Classification of the Sense...

Senses Sense: ability to perceive stimuli Sensation: conscious awareness of stimuli received by sensory neurons Sensory receptors: sensory nerve endings that respond to stimuli by developing action potentials Classification of Senses Classification of the Sense The senses are classified based on the location of the sensory receptors as well as the types of stimuli involved Types of Senses General senses: receptors over large part of body that sense touch, pressure, pain, temperature, and itch somatic provide information about body and environment visceral provide information about internal organs Special senses: smell, taste, sight, hearing, and balance Types of Receptors Mechanoreceptors: detect movement Example, touch, pressure, vibration Chemoreceptors: detect chemicals  Example, Odors Photoreceptors: detect light Thermoreceptors: detect temp. changes Nociceptors: detect pain Merkel’s disk: detect light touch and pressure Hair follicle receptors: detect light touch Meissner corpuscle: deep in epidermis localizing tactile sensations Ruffini corpuscle: deep tactile receptors detects continuous pressure in skin Pacinian corpuscle: deepest receptors associated with tendons and joints detect deep pressure, vibration, position Sensory Receptors in the Skin The sensory receptors of the skin vary in structure and sensitivity, allowing us to interact with our environment while still maintaining homeostasis. Pain Pain is an unpleasant perceptual and emotional experience Pain can be localized or diffuse. Localized: sharp, pricking, cutting pain rapid action potential Diffuse: burning, aching pain slower action potentials Pain Control Local anesthesia: action potentials suppressed from pain receptors in local areas chemicals are injected near sensory nerve General anesthesia: loss of consciousness chemicals affect reticular formation Referred Pain Referred Pain originates in a region that is not source of pain stimulus felt when internal organs are damaged or inflamed sensory neurons from superficial area and neurons of source pain converge onto same ascending neurons of spinal cord Areas of Referred Pain Areas of Referred Pain on the Body Surface Pain from the indicated internal organs is referred to the surface areas shown. Olfaction Olfaction is the: sense of smell occurs in response to odorants receptors are located in nasal cavity and hard palate we can detected 10,000 different smells Olfaction Process 1. Nasal cavity contains a thin film of mucous where odors become dissolved. 2. Olfactory neurons are located in mucous. Dendrites of olfactory neurons are enlarged and contain cilia. 3. Dendrites pick up odor, depolarize, and carry odor to axons in olfactory bulb (cranial nerve I). 4. Frontal and temporal lobes process odor. Olfactory Epithelium and Olfactory Bulb Taste Taste buds: sensory structures that detect taste located on papillae on tongue, hard palate, throat Inside each taste bud are 40 taste cells Each taste cell has taste hairs that extend into taste pores The Tongue Taste Process 1. Taste buds pick up taste and send it to taste cells. 2. Taste cells send taste to taste hairs. 3. Taste hairs contain receptors that initiate an action potential which is carried to parietal lobe. 4. Brain processes taste. Types of Tastes 1. Sweet 2. Sour 3. Salty 4. Bitter 5. Umami Certain taste buds are more sensitive to certain tastes. Taste is also linked to smell. Pathways for the Sense of Taste The facial nerve (anterior two-thirds of the tongue), glossopharyngeal nerve (root of the tongue) all carry taste sensations. The trigeminal nerve carries tactile sensations from the anterior two- thirds of the tongue. The chorda tympani from the facial nerve (carrying taste input) joins the trigeminal nerve. Vision Accessory Structures Eyebrow: protects from sweat shade from sun Eyelid/Eyelashes: protects from foreign objects lubricates by blinking The Eye and Accessory Structures Conjunctiva: thin membrane that covers inner surface of eyelid Lacrimal apparatus: produces tears Extrinsic eye muscles: help move eyeball Lacrimal Gland Structures Extrinsic Eye Muscles Anatomy of Eye Hollow, fluid filled sphere Composed of 3 layers (tunics) Divided into chambers The Eye Fibrous Tunic Outermost Tunic Sclera: firm, white outer part helps maintain eye shape, provides attachment sites, protects internal structures Cornea: transparent structure that covers iris and pupil allows light to enter and focuses light Vascular Tunic Middle tunic Contains blood supply Choroid: black part (melanin) delivers O and nutrients to retina 2 Ciliary body: helps hold lens in place Suspensory ligaments: help hold lens in place Lens: flexible disk  focuses light onto retina Iris: colored part surrounds and regulates pupil Pupil: regulates amount of light entering lots of light = constricted little light = dilated Lens and Ciliary Body The Iris Nervous Tunic Innermost tunic Retina: covers posterior 5/6 of eye contains 2 layers Pigmented retina: outer layer keeps light from reflecting back in eye Sensory retina: contains photoreceptors (rods and cones) contains interneurons Rods: photoreceptor sensitive to light 20 times more rods than cones can function in dim light Cones: photoreceptor provide color vision 3 types blue, green, red Retinal Rod Pigments and Pigment Protein Rhodopsin: photosensitive pigment in rod cells Opsin: colorless protein in rhodopsin Retinal: yellow pigment in rhodopsin requires vitamin A Effects of Light on Rhodopsin 1. Light strikes rod cell 2. Retinal changes shape 3. Opsin changes shape 4. Retinal dissociates from opsin 5. Change rhodopsin shape stimulates response in rod cell which results in vision 6. Retinal detaches from opsin 7. ATP required to reattach retinal to opsin and return rhodopsin to original shape Effect of Light on Rhodopsin When exposed to light, rhodopsin is activated as retinal changes shape and detaches from opsin. ATP is needed to recombine the opsin and retinal. The Retina Rods and cones synapse with bipolar cells of sensory retina Horizontal cells of retina modify output of rods and cones Bipolar and horizontal cells synapse with ganglion cells Ganglion cells axons’ converge to form optic nerve Macula: small spot near center of retina Fovea centralis: center of macula where light is focused when looking directly at an object only cones ability to discriminate fine images Optic disk: white spot medial to macula blood vessels enter eye and spread over retina axons exit as optic nerve no photoreceptors called blind spot Ophthalmoscopic View of the Retina (a) This view shows the posterior wall of the left eye as seen through the pupil. Notice the vessels entering the eye through the optic disc. The macula, with fovea centralis in the center, is located lateral to the optic disc (b) Demonstration of the blind spot. Close your right eye. Hold the drawing in front of your left eye and stare at the +. Move the drawing toward your eye. At a certain point, when the image of the spot is over the optic disc, the red spot seems to disappear. Chambers of the Eye Anterior chamber: located between cornea and lens filled with aqueous humor (watery) aqueous humor helps maintain pressure, refracts light, and provide nutrients to inner surface of eye Posterior chamber: located behind anterior chamber contains aqueous humor Vitreous chamber: located in retina region filled with vitreous humor: jelly-like substance vitreous humor helps maintain pressure, holds lens and retina in place, refracts light Functions of the Eye The eye functions much like a camera. The iris allows light into the eye, which is focused by the cornea, lens, and humors onto the retina. The light striking the retina produces action potentials that are relayed to the brain. Light refraction and image focusing are two important processes in establishing vision. Light Refraction Bending of light Focal point: point where light rays converge occurs anterior to retina object is inverted Focusing Images on Retina Accommodation: lens becomes less rounded and image can be focused on retina enables eye to focus on images closer than 20 feet Focusing by the Eye The focal point (FP) is where light rays cross, (a) when viewing a distant image, the lens is flattened and the image is focused on the retina (b) In accommodation foe near vision, the lens becomes more rounded, allowing the image to be focused on the retina. Neuronal Pathway for Vision Optic nerve: leaves eye and exits orbit through optic foramen to enter cranial cavity Optic chiasm: where 2 optic nerves connect Optic tracts: route of ganglion axons Visual Pathway (a) Pathways for both eyes (superior view), (b) Photograph of transverse section of the brain showing the visual nerves, tracts and pathways (inferior view) (c) Overlap of the fields of vision (superior view) Visual Defects Myopia: nearsightedness image is in front of retina Hyperopia: farsightedness image is behind retina Presbyopia: lens becomes less elastic reading glasses required Astigmatism: irregular curvature of lens glasses or contacts required to correct Color Blindness: absence or deficient cones primarily in males Glaucoma: increased pressure in eye can lead to blindness Chart to Determine Color Blindness These color blindness charts demonstrate the differences in color perception associated with some forms of color blindness, (a) A person with normal vision can see the number 74, whereas a person with red-green color blindness sees the number 21, (b) A person with normal vision can see the number 5, A person with red-green blindness sees the number 2. The Ear The organs of hearing and balance are located in the ears. Each ear is divided into three areas: 1. the external ear 2. the middle ear 3. the inner ear The External Ear Extends from outside of head to eardrum Auricle: fleshy part on outside External auditory meatus: canal that leads to eardrum Tympanic membrane: eardrum thin membrane that separates external and middle ear The Middle Ear Air filled chamber with ossicles Malleus (hammer): bone attached to tympanic membrane Incus (anvil): bone that connects malleus to stapes Stapes (stirrup): bone located at base of oval window Oval window: separates middle and inner ear Eustachian or auditory tube: opens into pharynx equalizes air pressure between outside air and middle ear The Inner Ear Set of fluid filled chambers Bony labyrinth: tunnels filled with fluid 3 regions: cochlea, vestibule, semicircular canals Membranous labyrinth: inside bony labyrinth filled with endolymph Endolymph: clear fluid in membranous labyrinth Perilymph: fluid between membranous and bony labyrinth Cochlea: snail-shell shaped structure where hearing takes place Scala vestibuli: in cochlea filled with perilymph Scala tympani: in cochlea filled with perilymph Cochlea duct: in cochlea filled with endolymph Spiral organ: in cochlear duct contains hair cells Tectorial membrane: in cochlea vibrates against hair cells Haircells: attached to sensory neurons that when bent produce an action potential Vestibular membrane: wall of membranous labyrinth that lines scala vestibuli Basilar membrane: wall of membranous labyrinth that lines scala tympani Structure of the Ear A medial view of the three regions of the ear: the external ear, middle ear and inner ear. Structure of the Inner Ear (a) Bony labyrinth. The outer surface (gray) is the periosteum lining the inner surface of the bony labyrinth, (b) In this cross section of the cochlea, the outer layer is the periosteum lining the inner surface of the bony labyrinth. The membranous labyrinth is very small in the cochlea and consists of the vestibular and basilar membrane membranes. The space between the membranous and bony labyrinth consists of two parallel tunnels; the scala vestibule and the scala tympani, (c) An enlarged section pf the cochlear duct (membranous labyrinth) (d) A greatly enlarged individual sensory hair cell, (e) Scanning electron micrograph of the microvilli of a hair cell. Hearing Process 1. Sound travels in waves through air and is funneled into ear by auricle. 2. Auricle through external auditory meatus to tympanic membrane. 3. Tympanic membrane vibrates and sound is amplified by malleus, incus, stapes which transmit sound to oval window. 4. Oval window produces waves in perilymph of cochlea. 5. Vibrations of perilymph cause vestibular membrane and endolymph to vibrate. 6. Endolymph cause displacement of basilar membrane. 7. Movement of basilar membrane is detected by hair hairs in spiral organ. 8. Hair cells become bent and cause action potential is created. Effect of Sound Waves on Middle and Inner Ear Structures Sound waves in the air are conducted through the ear until they stimulate hair cells in the spiral organ. Balance (Equilibrium) Static equilibrium: associated with vestibule evaluates position of head relative to gravity Dynamic equilibrium: associated with semicircular canals evaluates changes in direction and rate of head movement Balance Vestibule: inner ear contains utricle and saccule Maculae: specialized patches of epithelium in utricle and saccule surround by endolymph contain hair cells Otoliths: gelatinous substance that moves in response to gravity attached to hair cell microvilli which initiate action potentials Location and Structure of the Macula (a) Location of the utricular and saccular maculae within the vestibule, (b) Enlargement of the utricular macula, showing hair cells and otoliths, (c) Enlarged hair cell, showing the microvilli (d) Colorized scanning micrograph of otoliths Function of the Vestibule in Maintaining Balance (a) In an upright position, the maculae don’t move, (b) When the position of the head changes, as when a person bends over, the maculae respond by moving in the direction of gravity. Balance Semicircular canals: dynamic equilibrium sense movement if any direction Ampulla: base of semicircular canal Crista ampullaris: in ampulla Cupula: gelatinous mass contains microvilli float that is displaced by endolymph movement Semicircular Canals (a) Location of the ampullae of the semicircular canals (b) Enlargement of the crista ampullaris, showing the cupula and hair cells (c) Enlargement of a hair cell Function of the Crista Ampullaris (a) As a person to tumble, the semicircular canals (b) move in the same direction as the body (blue arrow). The endolymph in the semicircular canals tends to stay in place as the body and the ampular begin to move. As a result, the cupula is displaced by the moving endolymph (red arrow) in a direction of movement.