The General and Special Senses
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9 The General and Special Senses The General Senses Sensory Basics • Sensory receptors—Specialized cells or cell processes that monitor external or internal conditions. Simplest are free nerve endings. The General Senses More Sensory Basics • Receptive field—The area monitored by a single receptor cell • Adaptation—Reduction in sensitivity at a receptor or along a sensory pathway in the presence of a constant stimulus. The General Senses General versus Special Senses • General senses—Temperature, pain, touch, pressure, vibration, and proprioception. Receptors throughout the body • Special senses—Smell, taste, vision, balance, and hearing. Receptors located in sense organs (e.g., ear, eye). The General Senses Receptors and Receptive Fields The General Senses Key Note Stimulation of a receptor produces action potentials that propagate along the axon of a sensory neuron. The frequency or pattern of action potentials contains information about the stimulus. A person’s perception of the nature of that stimulus depends on the path it takes inside the CNS. The General Senses Pain Definitions • Nociceptors—Receptors for tissue damage to lead to the sensation of pain • Referred pain—Perception of pain in a part of the body not actually stimulated • Fast (prickling) pain—Localized pain carried quickly to the CNS on myelinated axons • Slow (burning) pain—Generalized pain carried on slow unmyelinated axons The General Senses Referred Pain The General Senses Temperature • Thermoreceptors detect temperature change • Free nerve endings • Found in dermis, skeletal muscle, liver, hypothalamus • Fast adapting • Cold receptors greatly outnumber warm receptors The General Senses Touch, Pressure, and Position • Mechanoreceptors—Receptors that respond to physical distortion of their cell membranes. • Tactile receptors—Sense touch, pressure, or vibration • Baroreceptors—Sense pressure changes in walls of blood vessels, digestive organs, bladder, lungs • Proprioceptors—Respond to positions of joints and muscle The General Senses Tactile Receptors • Fine touch or pressure receptors • Highly detailed information about a stimulus • Crude touch or pressure receptors • Poorly localized information about a stimulus • Important types: root hair plexus, tactile disks, tactile corpuscles, lamellated corpuscles, Ruffini corpuscles The General Senses Tactile Receptors in the Skin The General Senses Baroreceptors • Provide pressure information essential for autonomic regulation • Arterial blood pressure • Lung inflation • Digestive coordination • Bladder fullness The General Senses Baroreceptors and the Regulation of Autonomic Functions The General Senses Proprioceptors • Monitor joint angle, tension in tendons and ligaments, state of muscular contraction • Include: • Muscle spindles • Golgi tendon organs The General Senses Chemical Detection • Chemoreceptors respond to chemicals dissolved in body fluids that surround them and monitor the chemical composition of blood and tissues • Chemicals that can be sensed include: • Carbon dioxide • Oxygen • Hydrogen ion The General Senses Locations and Functions of Chemoreceptors The Special Senses—Smell Olfactory Organs • Olfactory epithelium • Olfactory receptor cells • Neurons sensitive to odorants • Supporting cells • Basal (stem) cells • Olfactory glands • Mucus-secreting cells The Special Senses—Smell The Olfactory Organs The Special Senses—Smell The Olfactory Organs The Special Senses—Smell The Olfactory Pathways • Axons from olfactory receptors penetrate cribriform plate of ethmoid bone • Synapse in olfactory bulb • Olfactory tract projects to: • Olfactory cerebral cortex • Hypothalamus • Limbic System The Special Senses—Taste Taste (Gustatory) Receptors • Taste buds • Found within papillae on tongue, pharynx, larynx • Contain gustatory cells, supportive cells • Taste hairs (cilia) extend into taste pores • Sense salt, sweet, sour, bitter • Also sense umami, water • Synapse in medulla oblongata The Special Senses—Taste Gustatory Receptors The Special Senses—Taste Gustatory Receptors The Special Senses—Taste Gustatory Receptors The Special Senses Key Note Olfactory information is routed directly to the cerebrum, and olfactory stimuli have powerful effects on mood and behavior. Gustatory sensations are strongest and clearest when integrated with olfactory sensations. The Special Senses—Vision Accessory Structures of the Eye • Eyelids (palpebra) and glands • Superficial epithelium of eye • Conjunctiva • Lacrimal apparatus • Tear production and removal • Extrinsic eye muscles The Special Senses—Vision The Lacrimal Apparatus • Lacrimal gland produce tears • Bathe conjunctiva • Contain lysozyme to attack bacteria • Tears drain into nasal cavity • Pass through lacrimal canals, lacrimal sac, nasolacrimal duct The Special Senses—Vision The Accessory Structures of the Eye The Special Senses—Vision The Accessory Structures of the Eye The Special Senses—Vision Extrinsic Eye Muscles • Move the eye • Six muscles cooperate to control gaze • Superior and inferior rectus • Lateral and medial rectus • Superior and inferior oblique The Special Senses—Vision The Extrinsic Eye Muscles The Special Senses—Vision The Extrinsic Eye Muscles The Special Senses—Vision Layers of the Eye • Fibrous tunic • Outermost layer • Vascular tunic • Intermediate layer • Neural tunic • Innermost layer The Special Senses—Vision The Sectional Anatomy of the Eye The Special Senses—Vision The Sectional Anatomy of the Eye The Special Senses—Vision The Sectional Anatomy of the Eye The Special Senses—Vision Layers of the Eye • Fibrous tunic • Sclera • Dense fibrous connective tissue • “White of the eye” • Cornea • Transparent • Light entrance The Special Senses—Vision Layers of the Eye • Vascular tunic • Iris • Boundary between anterior and posterior chambers • Ciliary body • Ciliary muscle and ciliary process • Attachment of suspensory ligaments • Choroid • Highly vascular The Special Senses—Vision Functions of the Vascular Tunic • Provide a route for blood vessels • Control amount of light entering eye • Adjust diameter of pupil • Secrete and absorb aqueous humor • Adjust lens shape for focusing The Special Senses—Vision The Pupillary Muscles The Special Senses—Vision Layers of the Eye • Neural tunic (Retina) • Outer pigmented part • Absorbs stray light • Inner neural part • Detects light • Processes image • Communicates with brain The Special Senses—Vision Organization of the Retina • Photoreceptor layer • Bipolar cells • Amacrine, horizontal cells modify signals • Ganglion cells • Optic nerve (CN II) The Special Senses—Vision Retinal Organization The Special Senses—Vision Retinal Organization The Special Senses—Vision Retinal Organization The Special Senses—Vision Chambers of the Eye • Two cavities • Ciliary body, lens between the two • Anterior cavity • Anterior compartment Between cornea and iris • Posterior compartment Between iris and lens • Posterior cavity • Vitreous body The Special Senses—Vision The Aqueous Humor • Secreted by ciliary processes into posterior chamber • Flows into anterior chamber • Maintains eye shape • Carries nutrients and wastes • Reabsorbed into circulation • Leaves at canal of Schlemm • Excess humor leads to glaucoma The Special Senses—Vision Eye Chambers and the Circulation of Aqueous Humor The Special Senses—Vision The Lens • Supported by suspensory ligaments • Built from transparent cells • Surrounded by elastic capsule • Lens and cornea focus light on retina • Bend light (refraction) • Accommodation changes lens shape The Special Senses—Vision Focal Point, Focal Distance, and Visual Accommodation The Special Senses—Vision Focal Point, Focal Distance, and Visual Accommodation The Special Senses—Vision Focal Point, Focal Distance, and Visual Accommodation The Special Senses—Vision Focal Point, Focal Distance, and Visual Accommodation The Special Senses—Vision Focal Point, Focal Distance, and Visual Accommodation The Special Senses—Vision Image Formation The Special Senses—Vision Image Formation The Special Senses—Vision Visual Abnormalities The Special Senses—Vision Visual Abnormalities The Special Senses—Vision Visual Abnormalities The Special Senses—Vision Visual Abnormalities The Special Senses—Vision Visual Abnormalities The Special Senses—Vision Key Note Light passes through the cornea, crosses the anterior cavity to the lens, transits the lens, crosses the posterior chamber, and then penetrates the retina to stimulate the photoreceptors. Cones, most abundant at the fovea and macula lutea, provide detailed color vision in bright light. Rods, dominant in the peripheral retina, provide coarse color-free vision in dim light. The Special Senses—Vision Visual Physiology • Photoreceptors—Cells specialized to respond to photons, packets of light energy • Two types of photoreceptors • Rods • Highly sensitive, non-color vision • In peripheral retina • Cones • Less sensitive, color vision • Mostly in fovea, center of macula lutea Site of sharpest vision The Special Senses—Vision Photoreceptor Anatomy • Outer segment • Discs with visual pigments • Light absorption by rhodopsin • Opsin + retinal • Inner segment • Synapse with bipolar cell • Control of neurotransmitter release • Effect on bipolar cells The Special Senses—Vision The Structure of Rods and Cones The Special Senses—Vision The Visual Pathway • Ganglion cells axon converge at optic disc • Axons leave as optic nerve (CN II) • Some axons cross at optic chiasm • Synapse in thalamus bilaterally • Thalamic neurons project to visual cortex • Located in occipital lobes • Contains map of visual field The Special Senses—Vision The Visual Pathway Equilibrium and Hearing Sensory Functions of the Inner Ear • Dynamic equilibrium • Static equilibrium • Hearing Equilibrium and Hearing Overview of the Ear • Chambers, canals filled with fluid endolymph • Bony labyrinth • Surrounds membranous labyrinth • Surrounded by fluid perilymph • Consists of vestibule, semicircular canals, cochlea • External, middle ear feed sound to cochlea Equilibrium and Hearing Anatomy of the Ear • External ear • Pinna (auricle) • External acoustic canal • Tympanic membrane (eardrum) • Middle ear • Auditory ossicles • Connect tympanic membrane to inner ear • Auditory tube • Connection to nasopharynx Equilibrium and Hearing Anatomy of the Inner Ear • Vestibule • Membranous sacs • Utricle • Saccule • Receptors for linear acceleration, gravity • Semicircular canal with ducts • Receptors for rotation • Cochlea with cochlear duct • Receptors for sound Equilibrium and Hearing Receptors of the Inner Ear • Hair cells • Mechanoreceptors • Stereocilia on cell surface • Bending excites/inhibits hair cell • Information on direction and strength of mechanical stimuli Equilibrium and Hearing The Anatomy of the Ear Equilibrium and Hearing The Structure of the Middle Ear Equilibrium and Hearing The Anatomy of the Ear Equilibrium and Hearing The Anatomy of the Ear Equilibrium and Hearing Equilibrium • Semicircular ducts • Connect to utricle • Contains ampulla with hair cells • Stereocilia contact cupola • Gelatinous mass distorted by fluid movement • Detects rotation of head in three planes • Anterior, posterior, lateral ducts Equilibrium and Hearing Equilibrium (continued) • Saccule and utricle • Hair cells cluster in maculae • Stereocilia contact otoliths (heavy mineral crystals) • Gravity pulls otoliths • Detect tilt of head • Sensory axons in vestibular branch of CN VIII Equilibrium and Hearing The Vestibular Complex Equilibrium and Hearing The Vestibular Complex Equilibrium and Hearing Overview of Hearing • Sound waves vibrate tympanic membrane • Ossicles transfer vibration to oval window • Oval window presses on perilymph in vestibular duct • Pressure wave distorts basilar membrane • Hair cells of organ of Corti press on tectorial membrane Equilibrium and Hearing The Cochlea and the Organ of Corti Equilibrium and Hearing The Cochlea and the Organ of Corti Equilibrium and Hearing Auditory Pathways • Hair cells excite sensory neurons • Sensory neurons located in spiral ganglion • Afferent axons form cochlear branch of vestibulocochlear nerve (CN VIII) • Synapses in cochlear nucleus in medulla • Neurons relay to midbrain • Midbrain relays to thalamus • Thalamus relays to auditory cortex (temporal lobe) in a frequency map Equilibrium and Hearing Pathways for Auditory Sensations Equilibrium and Hearing Key Note Balance and hearing both rely on hair cells. Which stimulus excites a particular group depends on the structure of the associated sense organ. In the semicircular ducts, fluid movement due to head rotation is sensed. In the utricle and saccule, shifts in the position of otoliths by gravity is sensed. In the cochlea, sound pressure waves distort the basilar membrane. Aging and the Senses Impact of Aging on Sensory Ability • Gradual reduction in smell and taste sensitivity as receptors are lost • Lens changes lead to presbyopia (loss of near vision) • Chance of cataract increases • Progressive loss of hearing sensitivity as receptors are lost (presbycusis)
