Chapter 9 - The General and Special Senses

C h a p t e r 9 The General and Special Senses Copyright © 2010 Education, Inc. Sensory receptors connect our internal and external environments with the nervous system Sensory Receptors Specialized cells that monitor specific conditions in the body or external environment When stimulated, a receptor passes information to the CNS in the form of action potentials along the axon of a sensory neuron Sensory Receptors Sensation The arriving information from these senses Perception Conscious awareness of a sensation Sensory Receptors The Detection of Stimuli Receptor sensitivity: Each receptor has a characteristic sensitivity Receptive field: Area is monitored by a single receptor cell The larger the receptive field, the more difficult it is to localize a stimulus Receptors and Receptive Fields Sensory Receptors The Interpretation of Sensory Information Arriving stimulus: Takes many forms: physical force (such as pressure) dissolved chemical sound light Sensory Receptors The Interpretation of Sensory Information Sensations: Taste, hearing, equilibrium, and vision provided by specialized receptor cells Communicate with sensory neurons across chemical synapses Sensory Receptors Adaptation Reduction in sensitivity of a constant stimulus Your nervous system quickly adapts to stimuli that are painless and constant Sensory Receptors General Senses Describe our sensitivity to: Temperature Pain Touch Pressure Vibration Proprioception Sensory Receptors Special Senses Olfaction (smell) Vision (sight) Gustation (taste) Equilibrium (balance) Hearing Sensory Receptors Stimulation of a receptor produces action potentials along the axon of a sensory neuron The frequency and pattern of action potentials contain information about the strength, duration, and variation of the stimulus Your perception of the nature of that stimulus depends on the path it takes inside the CNS General sensory receptors can be classified by the type of stimulus that excites them Classifying Sensory Receptors General sensory receptors are divided into four types by the nature of the stimulus that excites them Nociceptors (pain) Thermoreceptors (temperature) Mechanoreceptors (physical distortion) Chemoreceptors (chemical concentration) Pain Nociceptors (also called pain receptors) Are common in the superficial portions of the skin, joint capsules, within the periostea of bones, and around the walls of blood vessels May be sensitive to temperature extremes, mechanical damage, and dissolved chemicals, such as chemicals released by injured cells Figure 15–2 Pain Nociceptors Are free nerve endings with large receptive fields: Branching tips of dendrites Not protected by accessory structures Can be stimulated by many different stimuli Two types of axons: Type A and Type C fibers Pain Nociceptors Myelinated Type A fibers: Carry sensations of fast pain, or prickling pain, such as that caused by an injection or a deep cut Sensations reach the CNS quickly and often trigger somatic reflexes Relayed to the primary sensory cortex and receive conscious attention Pain Nociceptors Type C fibers: Carry sensations of slow pain, or burning and aching pain Cause a generalized activation of the reticular formation and thalamus You become aware of the pain but only have a general idea of the area affected Referred Pain Temperature Thermoreceptors Also called temperature receptors Are free nerve endings located in: The dermis Skeletal muscles The liver The hypothalamus Temperature Thermoreceptors Temperature sensations: Conducted along the same pathways that carry pain sensations Sent to: the reticular formation the thalamus the primary sensory cortex (to a lesser extent) Touch, Pressure, and Position Mechanoreceptors Sensitive to stimuli that distort their plasma membranes Contain mechanically gated ion channels whose gates open or close in response to Stretching Compression Twisting Other distortions of the membrane Touch, Pressure, and Position Tactile receptors Provide the sensations of touch, pressure, and vibration: Touch sensations provide information about shape or texture Pressure sensations indicate degree of mechanical distortion Vibration sensations indicate pulsing or oscillating pressure Tactile Receptors in the Skin Tactile Receptors in the Skin Tactile Receptors in the Skin Tactile Receptors in the Skin Tactile Receptors in the Skin Tactile Receptors in the Skin Touch, Pressure, and Position Baroreceptors Monitor change in pressure Consist of free nerve endings that branch within elastic tissues in wall of distensible organ (such as a blood vessel) Respond immediately to a change in pressure, but adapt rapidly Baroreceptors Touch, Pressure, and Position Proprioceptors Monitor: Position of joints Tension in tendons and ligaments State of muscular contraction Touch, Pressure, and Position Major Groups of Proprioceptors Muscle spindles: Monitor skeletal muscle length Trigger stretch reflexes Golgi tendon organs: Located at the junction between skeletal muscle and its tendon Stimulated by tension in tendon Monitor external tension developed during muscle contraction Chemical Detection Chemoreceptors Respond only to water-soluble and lipid-soluble substances dissolved in surrounding fluid Receptors exhibit peripheral adaptation over period of seconds Classifying Sensory Receptors Chemoreceptors Located in the: Carotid bodies: near the origin of the internal carotid arteries on each side of the neck Aortic bodies: between the major branches of the aortic arch Receptors monitor pH, carbon dioxide, and oxygen levels in arterial blood Chemoreceptors Olfaction, the sense of smell, involves olfactory receptors responding to chemical stimuli Figure 17–1a Smell (Olfaction) Olfactory Organs Provide sense of smell Located in nasal cavity on either side of nasal septum Made up of two layers: Olfactory epithelium Lamina propria The Olfactory Organs Smell (Olfaction) Olfactory Glands Secretions coat surfaces of olfactory organs Olfactory Receptors Highly modified neurons Olfactory reception: Involves detecting dissolved chemicals as they interact with odorant-binding proteins Smell (Olfaction) Olfactory Pathways Axons leaving olfactory epithelium: Collect into 20 or more bundles Penetrate cribriform plate of ethmoid Reach olfactory bulbs of cerebrum where first synapse occurs Axons leaving olfactory bulb: travel along olfactory tract to reach olfactory cortex, hypothalamus, and portions of limbic system Smell (Olfaction) Olfactory Discrimination Can distinguish thousands of chemical stimuli CNS interprets smells by the pattern of receptor activity Olfactory Receptor Population Considerable turnover Number of olfactory receptors declines with age Gustation, the sense of taste, involves taste receptors responding to chemical stimuli Taste (Gustation) Gustation provides information about the foods and liquids consumed Taste receptors (or gustatory receptors) are distributed on tongue and portions of pharynx and larynx Clustered into taste buds Taste (Gustation) Taste buds Associated with epithelial projections (lingual papillae) on superior surface of tongue Three types of lingual papillae: Filiform papillae: provide friction do not contain taste buds Fungiform papillae: contain five taste buds each Circumvallate papillae: contain 100 taste buds each Gustatory Receptors Taste (Gustation) Gustatory Discrimination Primary taste sensations: Sweet Salty Sour Bitter Taste (Gustation) Additional human taste sensations Umami: Characteristic of beef/chicken broths and Parmesan cheese Receptors sensitive to amino acids, small peptides, and nucleotides Water: Detected by water receptors in the pharynx Taste (Gustation) Gustatory Discrimination Dissolved chemicals contact taste hairs Bind to receptor proteins of gustatory cell Salt and sour receptors: Chemically gated ion channels Stimulation produces depolarization of cell Sweet, bitter, and umami stimuli: G proteins: gustducins Internal eye structures contribute to vision, while accessory eye structures provide protection Accessory Structures of the Eye Provide protection, lubrication, and support Includes The palpebrae (eyelids) The superficial epithelium of eye The lacrimal apparatus Accessory Structures of the Eye Accessory Structures of the Eye The Eye Three Layers of the Eye Outer fibrous tunic Middle vascular tunic Inner neural tunic Eyeball Is hollow Is divided into two cavities: Large posterior cavity Smaller anterior cavity The Extrinsic Eye Muscles The Eye The Eye The Eye The Fibrous Tunic Sclera (white of eye) Cornea Limbus (border between cornea and sclera) The Eye Vascular Tunic (Uvea) Functions Provides route for blood vessels and lymphatics that supply tissues of eye Regulates amount of light entering eye Secretes loose and reabsorbs aqueous humor that circulates within chambers of eye Controls shape of lens, which is essential to focusing The Pupillary Muscles The Eye The Neural Tunic (Retina) Outer layer called pigmented part Inner neural part: Contains visual receptors and associated neurons Rods and cones are types of photoreceptors: rods: do not discriminate light colors highly sensitive to light cones: provide color vision densely clustered in fovea, at center of macula lutea Retinal Organization Retinal Organization Retinal Organization The Eye The Neural Tunic (Retina) Inner neural part: Bipolar cells: neurons of rods and cones synapse with ganglion cells Horizontal cells: extend across outer portion of retina Amacrine cells: comparable to horizontal cell layer where bipolar cells synapse with ganglion cells Figure 17–6a The Eye The Chambers of the Eye Ciliary body and lens divide eye into: Large posterior cavity (vitreous chamber) Smaller anterior cavity: anterior chamber: extends from cornea to iris posterior chamber: between iris, ciliary body, and lens The Eye Smaller anterior cavity Aqueous humor: Fluid circulates within eye Diffuses through walls of anterior chamber into canal of Schlemm Re-enters circulation Intraocular pressure: Fluid pressure in aqueous humor Helps retain eye shape The Eye Large Posterior Cavity (Vitreous Chamber) Vitreous body: Gelatinous mass Helps stabilize eye shape and supports retina The Eye Chambers The Eye The Lens Lens fibers: Cells in interior of lens No nuclei or organelles The Eye The Lens Light refraction: Bending of light by cornea and lens Focal point: specific point of intersection on retina Focal distance: distance between center of lens and focal point The Eye The Eye Light Refraction of Lens Accommodation: Shape of lens changes to focus image on retina Astigmatism: Condition where light passing through cornea and lens is not refracted properly Visual image is distorted Visual acuity: Clarity of vision “Normal” rating is 20/20 The Eye Image Formation Photoreceptors respond to light and change it into electrical signals essential to visual physiology Visual Physiology Rods Respond to almost any photon, regardless of energy content Cones Have characteristic ranges of sensitivity Visual Physiology Anatomy of Rods and Cones Outer segment with membranous discs Inner segment: Narrow stalk connects outer segment to inner segment Visual pigments: Is where light absorption occurs Derivatives of rhodopsin (opsin plus retinal) Retinal: synthesized from vitamin A Visual Physiology Photoreception Photon strikes retinal portion of rhodopsin molecule embedded in membrane of disc Opsin is activated Bound retinal molecule has two possible configurations: 11-cis form 11-trans form Visual Physiology Figure 17–16 Visual Physiology Color Vision Integration of information from red, green, and blue cones Color blindness: Inability to detect certain colors Visual Physiology Light and Dark Adaptation Dark: Most visual pigments are fully receptive to stimulation Light: Pupil constricts Bleaching of visual pigments occurs Visual Physiology The Visual Pathways Begin at photoreceptors End at visual cortex of cerebral hemispheres Message crosses two synapses before it heads toward brain: Photoreceptor to bipolar cell Bipolar cell to ganglion cell Equilibrium sensations originate within the inner ear, while hearing involves the detection and interpretation of sound waves Anatomy of the Ear The External Ear Auricle: Surrounds entrance to external acoustic meatus Protects opening of canal Provides directional sensitivity External acoustic meatus: Ends at tympanic membrane (eardrum) Tympanic membrane: Is a thin, semitransparent sheet Separates external ear from middle ear The Anatomy of the Ear The Ear The Middle Ear Also called tympanic cavity Communicates with nasopharynx via auditory tube: Permits equalization of pressures on either side of tympanic membrane Encloses and protects three auditory ossicles: Malleus (hammer) Incus (anvil) Stapes (stirrup) The Structure of the Middle Ear The Ear The Inner Ear Contains fluid called endolymph Bony labyrinth surrounds and protects membranous labyrinth Subdivided into: Vestibule Semicircular canals Cochlea The Inner Ear The Ear The Inner Ear Vestibule: Encloses saccule and utricle Receptors provide sensations of gravity and linear acceleration Semicircular canals: Contain semicircular ducts Receptors stimulated by rotation of head Cochlea: Contains cochlear duct (elongated portion of membranous labyrinth) Receptors provide sense of hearing The Ear The Inner Ear Round window: Thin, membranous partition Separates perilymph from air spaces of middle ear Oval window: Formed of collagen fibers Connected to base of stapes Equilibrium Sensations provided by receptors of vestibular complex Hair cells Basic receptors of inner ear Provide information about direction and strength of mechanical stimuli Equilibrium The Semicircular Ducts Are continuous with utricle Each duct contains: Ampulla with gelatinous cupula Associated sensory receptors Stereocilia — resemble long microvilli: are on surface of hair cell Kinocilium — single, large cilium The Semicircular Ducts Equilibrium The Utricle and Saccule Provide equilibrium sensations Are connected with the endolymphatic duct, which ends in endolymphatic sac Maculae: Oval structures where hair cells cluster Statoconia: Densely packed calcium carbonate crystals on surface of gelatinous mass Otolith (ear stone) = gel and statoconia Equilibrium Equilibrium Pathways for Equilibrium Sensations Vestibular receptors Activate sensory neurons of vestibular ganglia Axons form vestibular branch of vestibulocochlear nerve (VIII) Synapse within vestibular nuclei Hearing Cochlear duct receptors Provide sense of hearing The Cochlea and Organ of Corti The Cochlea and Organ of Corti Hearing Auditory Ossicles Convert pressure fluctuation in air into much greater pressure fluctuations in perilymph of cochlea Frequency of sound: Determined by which part of cochlear duct is stimulated Intensity (volume): Determined by number of hair cells stimulated Sound and Hearing Sound and Hearing Hearing Auditory Pathways Cochlear branch: Formed by afferent fibers of spiral ganglion neurons: enters medulla oblongata synapses at dorsal and ventral cochlear nuclei information crosses to opposite side of brain: ascends to inferior colliculus of mesencephalon Figure 17–31 Hearing Auditory Pathways Ascending auditory sensations: Synapse in medial geniculate nucleus of thalamus Projection fibers deliver information to auditory cortex of temporal lobe Pathways for Auditory Sensations Aging is accompanied by a noticeable decline in the special senses Smell and Aging Olfactory neuron recycling slows, leading to decreased sensitivity Taste and Aging Number of taste buds is reduced, and sensitivity is lost Vision and Aging Lens stiffens Lens clouds Blood vessels grow in retina Hearing and Aging Loss of elasticity in tympanic membrane