Chapter 17 the Special Senses

Chapter 17 The Special Senses

An Introduction to the Special Senses  Five Special Senses 1. Olfaction 2. Gustation 3. Vision 4. Equilibrium 5. Hearing

17-1 Smell (Olfaction)  Olfactory Organs o Provide sense of smell o Located in nasal cavity on either side of nasal septum o Made up of two layers 1. Olfactory epithelium 2. Lamina propria

17-1 Smell (Olfaction)  Layers of Olfactory Organs o Olfactory epithelium contains: . Olfactory receptors . Supporting cells . Basal (stem) cells

17-1 Smell (Olfaction)  Layers of Olfactory Organs o Lamina propria contains: . Areolar tissue . Blood vessels . Nerves . Olfactory glands

17-1 Smell (Olfaction)  Olfactory Glands o Secretions coat surfaces of olfactory organs  Olfactory Receptors o Highly modified neurons

17-1 Smell (Olfaction)  Olfactory Pathways o Axons leaving olfactory epithelium . Collect into 20 or more bundles . Penetrate cribriform plate of ethmoid . Reach olfactory bulbs of cerebrum where first synapse occurs

17-1 Smell (Olfaction)  Olfactory Pathways o Axons leaving olfactory bulb: . Travel along olfactory tract to reach olfactory cortex, hypothalamus, and portions of limbic system o Arriving information reaches information centers without first synapsing in thalamus

17-1 Smell (Olfaction)  Olfactory Discrimination o Can distinguish thousands of chemical stimuli o CNS interprets smells by the pattern of receptor activity  Olfactory Receptor Population o Considerable turnover o Number of olfactory receptors declines with age

17-2 Taste (Gustation)  Gustation o Provides information about the foods and liquids consumed  Taste Receptors (Gustatory Receptors) o Are distributed on tongue and portions of pharynx and larynx o Clustered into taste buds

17-2 Taste (Gustation)  Taste Buds o Associated with epithelial projections (lingual papillae) on superior surface of tongue

17-2 Taste (Gustation)  Four Types of Lingual Papillae

© 2015 Pearson Education, Inc. 1. Filiform papillae . Provide friction . Do not contain taste buds 2. Fungiform papillae . Contain about five taste buds each 3. Vallate papillae . Contain 100 taste buds each 4. Foliate papillae .

17-2 Taste (Gustation)  Taste Buds o Contain: . Basal cells . Gustatory receptor cells o Extend taste hairs through taste pore o Survive only 10 days before replacement . Monitored by cranial nerves that synapse within solitary nucleus of medulla oblongata o Then on to thalamus and primary sensory cortex

17-2 Taste (Gustation)  Gustatory Discrimination o Four primary taste sensations 1. Sweet 2. Salty 3. Sour 4. Bitter

17-2 Taste (Gustation)  Additional Human Taste Sensations o Umami . Characteristic of beef/chicken broths and Parmesan cheese . Receptors sensitive to amino acids, small peptides, and nucleotides o Water . Detected by water receptors in the pharynx

17-2 Taste (Gustation)  Gustatory Discrimination o Dissolved chemicals contact taste hairs o Bind to receptor proteins of gustatory cell o Salt and sour receptors . Chemically gated ion channels

17-2 Taste (Gustation)  End Result of Taste Receptor Stimulation o Release of neurotransmitters by receptor cell . Dendrites of sensory afferents wrapped by receptor membrane . Neurotransmitters generate action potentials in afferent fiber

17-2 Taste (Gustation)  Taste Sensitivity o Exhibits significant individual differences o Some conditions are inherited . For example, phenylthiocarbamide (PTC) o 70 percent of Caucasians taste it but 30 percent do not o Number of taste buds . Begins declining rapidly at age 50

17-3 Accessory Structures of the Eye  Accessory Structures of the Eye o Provide protection, lubrication, and support . Include: o The palpebrae (eyelids) o The superficial epithelium of eye o The lacrimal apparatus

17-3 Accessory Structures of the Eye  Eyelids (Palpebrae) o Continuation of skin o Blinking keeps surface of eye lubricated, free of dust and debris o Palpebral fissure . Gap that separates free margins of upper and lower eyelids

17-3 Accessory Structures of the Eye  Eyelids (Palpebrae) o Medial canthus and lateral canthus . Where two eyelids are connected o Eyelashes . Robust hairs that prevent foreign matter from reaching surface of eye

17-3 Accessory Structures of the Eye  Superficial Epithelium of Eye o Lacrimal caruncle . Mass of soft tissue . Contains glands producing thick secretions . Contributes to gritty deposits that appear after good night’s sleep o Conjunctiva . Epithelium covering inner surfaces of eyelids (palpebral conjunctiva) and outer surface of eye (ocular conjunctiva)

17-3 Accessory Structures of the Eye  Lacrimal Apparatus o Produces, distributes, and removes tears o Fornix . Pocket where palpebral conjunctiva joins ocular conjunctiva o Lacrimal gland (tear gland) . Secretions contain lysozyme, an antibacterial enzyme

17-3 Accessory Structures of the Eye  Tears o Collect in the lacrimal lake o Pass through: . Lacrimal puncta . Lacrimal canaliculi . Lacrimal sac . Nasolacrimal duct o To reach inferior meatus of nose

17-3 The Eye  Three Layers of the Eye 1. Outer fibrous layer 2. Intermediate vascular layer 3. Deep inner layer

17-3 The Eye  Eyeball

17-3 The Eye  The Fibrous Layer o Sclera (white of the eye) o Cornea o Corneal limbus (border between cornea and sclera)

17-3 The Eye  Vascular Layer (Uvea) Functions 1. Provides route for blood vessels and lymphatics that supply tissues of eye 2. Regulates amount of light entering eye 3. Secretes and reabsorbs aqueous humor that circulates within chambers of eye 4. Controls shape of lens, which is essential to focusing

17-3 The Eye  The Vascular Layer o Iris . Contains papillary muscles o Change diameter of pupil

17-3 The Eye  The Vascular Layer o Ciliary Body . Extends posteriorly to level of ora serrata o Serrated anterior edge of thick, inner portion of neural tunic . Contains ciliary processes, and ciliary muscle that attaches to suspensory ligaments of lens

17-3 The Eye  The Vascular Layer o The choroid . Vascular layer that separates fibrous and inner layers posterior to ora serrata . Delivers oxygen and nutrients to retina

17-3 The Eye

© 2015 Pearson Education, Inc.  The Inner Layer o Outer layer called pigmented part o Inner called neural part (retina) . Contains visual receptors and associated neurons . Rods and cones are types of photoreceptors o Rods . Do not discriminate light colors . Highly sensitive to light o Cones . Provide color vision . Densely clustered in fovea, at center of macula

17-3 The Eye  Inner Neural Part o Bipolar cells . Neurons of rods and cones synapse with ganglion cells o Horizontal cells . Extend across outer portion of retina o Amacrine cells . Comparable to horizontal cell layer . Where bipolar cells synapse with ganglion cells

17-3 The Eye  Horizontal and Amacrine Cells o Facilitate or inhibit communication between photoreceptors and ganglion cells o Alter sensitivity of retina  Optic Disc o Circular region just medial to fovea o Origin of optic nerve . Blind spot

17-3 The Eye  The Chambers of the Eye o Ciliary body and lens divide eye into: . Large posterior cavity (vitreous chamber) . Smaller anterior cavity o Anterior chamber . Extends from cornea to iris o Posterior chamber . Between iris, ciliary body, and lens

17-3 The Eye

© 2015 Pearson Education, Inc.  Aqueous Humor o Fluid circulates within eye o Diffuses through walls of anterior chamber into scleral venous sinus (canal of Schlemm) o Reenters circulation  Intraocular Pressure o Fluid pressure in aqueous humor o Helps retain eye shape

17-3 The Eye  Large Posterior Cavity (Vitreous Chamber) o Vitreous body . Gelatinous mass . Helps stabilize eye shape and supports retina .

17-3 The Eye  The Lens o Lens fibers . Cells in interior of lens . No nuclei or organelles . Filled with crystallins, which provide clarity and focusing power to lens o Cataract . Condition in which lens has lost its transparency

17-3 The Eye  Light Refraction o Bending of light by cornea and lens o Focal point . Specific point of intersection on retina o Focal distance . Distance between center of lens and focal point

17-3 The Eye  Light Refraction of Lens o Accommodation . Shape of lens changes to focus image on retina o Astigmatism . Condition where light passing through cornea and lens is not refracted properly . Visual image is distorted

17-4 Visual Physiology  Visual Physiology o Rods . Respond to almost any photon, regardless of energy content o Cones . Have characteristic ranges of sensitivity

17-4 Visual Physiology  Anatomy of Rods and Cones o Outer segment with membranous discs o Inner segment . Narrow stalk connects outer segment to inner segment

17-4 Visual Physiology  Anatomy of Rods and Cones o Visual pigments . Is where light absorption occurs . Derivatives of rhodopsin (opsin plus retinal) . Retinal synthesized from vitamin A

17-4 Visual Physiology  Color Vision o Integration of information from red, green, and blue cones o Color blindness . Inability to detect certain colors .

17-4 Visual Physiology  Photoreception o Photon strikes retinal portion of rhodopsin molecule embedded in membrane of disc . Opsin is activated . Bound retinal molecule has two possible configurations o 11-cis form

17-4 Visual Physiology  Recovery after Stimulation o Bleaching . Rhodopsin molecule breaks down into retinal and opsin o Night blindness . Results from deficiency of vitamin A

17-4 Visual Physiology  Light and Dark Adaptation o Dark . Most visual pigments are fully receptive to stimulation o Light . Pupil constricts . Bleaching of visual pigments occurs .

17-4 Visual Physiology  The Visual Pathways o Begin at photoreceptors o End at visual cortex of cerebral hemispheres o Message crosses two synapses before it heads toward brain . Photoreceptor to bipolar cell . Bipolar cell to ganglion cell

17-4 Visual Physiology  Ganglion Cells o Monitor a specific portion of a field of vision o M Cells . Are ganglion cells that monitor rods . Are relatively large . Provide information about: o General form of object o Motion o Shadows in dim lighting

17-4 Visual Physiology  Ganglion Cells o P cells . Are ganglion cells that monitor cones . Are smaller, more numerous

17-4 Visual Physiology  Ganglion Cells o On-center neurons . Are excited by light arriving in center of their sensory field . Are inhibited when light strikes edges of their receptive field o Off-center neurons . Inhibited by light in central zone . Stimulated by illumination at edges

17-4 Visual Physiology  Central Processing of Visual Information o Axons from ganglion cells converge on optic disc o Penetrate wall of eye o Proceed toward diencephalon as optic nerve (II) o Two optic nerves (one for each eye) reach diencephalon at optic chiasm

17-4 Visual Physiology  Visual Data o From combined field of vision arrive at visual cortex of opposite occipital lobe . Left half arrive at right occipital lobe . Right half arrive at left occipital lobe o Optic radiation . Bundle of projection fibers linking lateral geniculates with visual cortex

17-4 Visual Physiology  The Field of Vision o Depth perception . Obtained by comparing relative positions of objects between left-eye and right-eye images

17-4 Visual Physiology  The Brain Stem and Visual Processing o Circadian rhythm . Is tied to day–night cycle . Affects other metabolic processes

17-5 The Ear  The External Ear

17-5 The Ear  The External Ear o External acoustic meatus . Ends at tympanic membrane (eardrum) o Tympanic membrane . Is a thin, semitransparent sheet . Separates external ear from middle ear

17-5 The Ear  The External Ear o Ceruminous glands . Integumentary glands along external acoustic meatus . Secrete waxy material (cerumen) o Keeps foreign objects out of tympanic membrane o Slows growth of microorganisms in external acoustic meatus

17-5 The Ear  The Middle Ear o Also called tympanic cavity o Communicates with nasopharynx via auditory tube . Permits equalization of pressures on either side of tympanic membrane o Encloses and protects three auditory ossicles 1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup)

17-5 The Ear  Vibration of Tympanic Membrane o Converts arriving sound waves into mechanical movements o Auditory ossicles conduct vibrations to inner ear o Tensor tympani muscle . Stiffens tympanic membrane o Stapedius muscle . Reduces movement of stapes at oval window

17-5 The Ear

© 2015 Pearson Education, Inc.  The Internal Ear o Contains fluid called endolymph o Bony labyrinth surrounds and protects membranous labyrinth o Subdivided into: . Vestibule . Semicircular canals . Cochlea

17-5 The Ear  The Internal Ear o Vestibule . Encloses saccule and utricle . Receptors provide sensations of gravity and linear acceleration o Semicircular canals . Contain semicircular ducts . Receptors stimulated by rotation of head

17-5 The Ear  The Internal Ear o Cochlea . Contains cochlear duct (elongated portion of membranous labyrinth) . Receptors provide sense of hearing

17-5 The Ear  The Internal Ear o Round window . Thin, membranous partition . Separates perilymph from air spaces of middle ear o Oval window . Formed of collagen fibers . Connected to base of stapes

17-5 The Ear  Stimuli and Location o Sense of gravity and acceleration . From hair cells in vestibule o Sense of rotation . From semicircular canals o Sense of sound . From cochlea

17-5 The Ear

© 2015 Pearson Education, Inc.  Equilibrium o Sensations provided by receptors of vestibular complex o Hair cells . Basic receptors of inner ear . Provide information about direction and strength of mechanical stimuli

17-5 The Ear  The Semicircular Ducts o Are continuous with utricle o Each duct contains: . Ampulla with gelatinous cupula . Associated sensory receptors . Stereocilia – resemble long microvilli o Are on surface of hair cell . Kinocilium – single large cilium

17-5 The Ear  The Utricle and Saccule o Provide equilibrium sensations o Are connected with the endolymphatic duct, which ends in endolymphatic sac

17-5 The Ear  The Utricle and Saccule o Maculae . Oval structures where hair cells cluster o Statoconia . Densely packed calcium carbonate crystals on surface of gelatinous mass . Otolith (ear stone)  gelatinous matrix and statoconia

17-5 The Ear  Pathways for Equilibrium Sensations o Vestibular receptors . Activate sensory neurons of vestibular ganglia . Axons form vestibular branch of vestibulocochlear nerve (VIII) . Synapse within vestibular nuclei

17-5 The Ear  Four Functions of Vestibular Nuclei 1. Integrate sensory information about balance and equilibrium from both sides of head

© 2015 Pearson Education, Inc. 2. Relay information from vestibular complex to cerebellum 3. Relay information from vestibular complex to cerebral cortex . Provide conscious sense of head position and movement 4. Send commands to motor nuclei in brain stem and spinal cord

17-5 The Ear  Eye, Head, and Neck Movements o Reflexive motor commands . From vestibular nuclei . Distributed to motor nuclei for cranial nerves  Peripheral Muscle Tone, Head, and Neck Movements o Instructions descend in vestibulospinal tracts of spinal cord

17-5 The Ear  Eye Movements o Sensations of motion directed by superior colliculi of the midbrain o Attempt to keep focus on specific point o If spinning rapidly, eye jumps from point to point . Nystagmus o Have trouble controlling eye movements o Caused by damage to brain stem or inner ear

17-5 The Ear  Hearing o Cochlear duct receptors . Provide sense of hearing

17-5 The Ear  Hearing o Auditory ossicles . Convert pressure fluctuation in air into much greater pressure fluctuations in perilymph of cochlea . Frequency of sound o Determined by which part of cochlear duct is stimulated . Intensity (volume) o Determined by number of hair cells stimulated

17-5 The Ear  Hearing o Cochlear duct receptors . Basilar membrane o Separates cochlear duct from tympanic duct

17-5 The Ear  An Introduction to Sound o Pressure waves . Consist of regions where air molecules are crowded together . Adjacent zone where molecules are farther apart . Sine waves o S-shaped curves

17-5 The Ear  Pressure Wave o Wavelength . Distance between two adjacent wave troughs o Frequency . Number of waves that pass fixed reference point at given time . Physicists use term cycles instead of waves o Hertz (Hz) number of cycles per second (cps)

17-5 The Ear  Pressure Wave o Pitch . Our sensory response to frequency o Amplitude . Intensity of sound wave . Sound energy is reported in decibels

17-5 The Ear  Auditory Pathways o Cochlear branch . Formed by afferent fibers of spiral ganglion neurons o Enters medulla oblongata o Synapses at dorsal and ventral cochlear nuclei o Information crosses to opposite side of brain . Ascends to inferior colliculus of midbrain

17-5 The Ear  Auditory Pathways o Ascending auditory sensations . Synapse in medial geniculate nucleus of thalamus . Projection fibers deliver information to auditory cortex of temporal lobe

17-5 The Ear  Effects of Aging on the Ear o With age, damage accumulates . Tympanic membrane gets less flexible . Articulations between ossicles stiffen . Round window may begin to ossify