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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Fundamentals of Anatomy & Physiology
Frederic H. M
artini
Lecture 13: Chapter 17The Special SensesPage: 549 - 589
Lecturer: Dr. BarjisRoom: P313Phone: (718) 260-5285E-Mail: [email protected]
Learning Objectives
• Describe the sensory organs of smell, and trace the olfactory pathways to their destination in the brain.
• Identify the accessory and internal structures of the eye, and explain their function.
• Explain how light stimulates the production of nerve impulses, and trace the visual pathways to their destination in the brain.
• Describe the structures of the external and middle ear and explain how they function.
Learning Objectives
• Describe the parts of the inner ear and their roles in equilibrium and hearing.
• Trace the pathways for the sensations of equilibrium and hearing to their destinations in the brain.
• Contain olfactory epithelium with olfactory receptors, supporting cells, basal cells• Olfactory receptors are modified neurons
• Surfaces are coated with secretions from olfactory glands
• Olfactory reception involved detecting dissolved chemicals as they interact with odorant binding proteins
Olfaction
Olfactory organs
The Olfactory Organs
• Olfactory pathways• No synapse in the thalamus for arriving
information• Olfactory discrimination
• Can distinguish thousands of chemical stimuli• CNS interprets smells by pattern of receptor activity
• Olfactory receptor population shows considerable turnover
• Number of receptors declines with age
Olfaction
• Clustered in taste buds• Associated with lingual papillae
Gustation
Taste receptors
• Contain basal cells which appear to be stem cells
• Gustatory cells extend taste hairs through a narrow taste pore
Taste buds
Gustatory Reception
• Taste buds are monitored by cranial nerves• Synapse within the solitary nucleus of
the medulla oblongata• Then on to the thalamus and the primary
sensory cortex
Gustatory pathways
• Primary taste sensations• Sweet, sour, salty, bitter• Receptors also exist for umami and
water• Taste sensitivity shows significant
individual differences, some of which are inherited
• The number of taste buds declines with age
Gustatory discrimination
• Eyelids (palpebrae) separated by the palpebral fissue
• Eyelashes• Tarsal glands• Lacrimal apparatus
Vision
Accessory structures of the eye
Eternal Features and Accessory Structures of the Eye
external structures of the eye
• Conjunctiva covers most of eye• Cornea is transparent anterior portion
Lacrimal apparatus
• Secretions from the lacrimal gland contain lysozyme
• Tears form in the lacrimal glands, wash across the eye and collect in the lacrimal lake
• Pass through the lacrimal punctae, lacrimal canaliculi, lacrimal sac and nasolacrimal duct
The eye
• Three layers• Outer fibrous tunic
• Sclera, cornea, limbus• Middle vascular tunic
• Iris, ciliary body, choroid• Inner nervous tunic
• Retina
The Sectional Anatomy of the Eye
internal structures of the eye
• Ciliary body• Ciliary muscles and ciliary processes,
which attach to suspensory ligaments of lens
• Retina• Outer pigmented portion• Inner neural part
• Rods and cones
The Sectional Anatomy of the Eye
The Pupillary Muscles
retina
• Retina contains rods and cones• Cones densely packed at fovea (center of
the macula lutea)• Retinal pathway
• Photoreceptors to bipolar cells to ganglion cells, to the brain via the optic nerve• Axons of ganglion cells converge at blind spot (optic disc)
• Horizontal cells and amacrine cells modify the signal passed along the retinal neurons
The Organization of the Retina
The Organization of the Retina
• Ciliary body and lens divide the anterior cavity of the eye into posterior (vitreous) cavity and anterior cavity
• Anterior cavity further divided• anterior chamber in front of eye• posterior chamber between the iris and
the lens
Eye anatomy
The Circulation of Aqueous Humor
• Aqueous humor circulates within the eye• diffuses through the walls of anterior
chamber • passes through canal of Schlemm• re-enters circulation
• Vitreous humor fills the posterior cavity. • Not recycled – permanent fluid
Fluids in the eye
• Posterior to the cornea and forms anterior boundary of posterior cavity• Posterior cavity contains vitreous humor
• Lens helps focus• Light is refracted as it passes through
lens• Accommodation is the process by which
the lens adjusts to focus images• Normal visual acuity is 20/20
Lens
Image Formation
Figure 17.10
Accommodation
Visual Abnormalities
• Rods – respond to almost any photon• Cones – specific ranges of specificity
Visual physiology
Rods and Cones
• Outer segment with membranous discs• Narrow stalk connecting outer segment to
inner segment• Light absorption occurs in the visual
pigments• Derivatives of rhodopsin
Photoreceptor structure
Photoreception
Animation: Photoreception (see tutorial)
Photoreception
Bleaching and Regeneration of Visual Pigments
• Integration of information from red, blue and green cones
• Colorblindness is the inability to detect certain colors
Color sensitivity
• Dark adapted – most visual pigments are fully receptive to stimulation
• Light adapted – pupil constricts and pigments bleached.
retinal adaptation
• Large M-cells monitor rods• Smaller more numerous P cells monitor
cones
the visual pathway
Convergence and Ganglion Cell Function
• Vision from the field of view transfers from one side to the other while in transit
• Depth perception is obtained by comparing relative positions of objects from the two eyes
Seeing in stereo
The Visual Pathways
• Input to suprachiasmic nucleus affects the function of the brainstem
• Circadian rhythm ties to day-night cycle, and affects metabolic rates
Visual circadian rhythm
Anatomy of the ear – External Ear• Auricle or pinnae surrounds the ear• External acoustic meatus ends on
tympanic membrane
Equilibrium and Hearing
Both equilibrium and hearing are provided by receptors of the inner ear
The Anatomy of the Ear
• Communicates with pharynx via pharyngotympanic membrane
• Middle ear encloses and protects the auditory ossicles
Middle ear
The Middle Ear
• Membranous labyrinth contains endolymph• Bony labyrinth surrounds and protects
membranous labyrinth• Vestibule• Semicircular canals• Cochlea
Inner ear
Figure 17.22
The Inner Ear
• Vestibule contains the utricle and saccule• Semicircular canals contain the
semicircular ducts• Cochlea contains the cochlear duct
Components of the inner ear
• Round window separates the perilymph from the air spaces of the middle ear
• Oval window connected to the base of the stapes
• Basic receptors of inner ear are hair cells• Provide information about the direction
and strength of stimuli
Windows
• Anterior, posterior and lateral semicircular ducts are continuous with the utricle• Each duct contains an ampulla with a
gelatinous cupula and associated sensory receptor
• Saccule and utricle connected by a passageway continuous with the endolymphatic duct• Terminates in the endolymphatic sac• Saccule and utricle have hair cells
clustered in maculae• Cilia contact the otolith (statoconia)
Equilibrium
The Vestibular Complex
The Vestibular Complex
The Vestibular Complex
• Vestibular receptors activate sensory neurons of the vestibular ganglia
• Axons form the vestibular branch of cranial nerve VII
• Synapses within the vestibular nuclei
Vestibular neural pathway
Pathways for Equilibrium Sensation
• Cochlear duct lies between the vestibular duct and the tympanic duct
• Hair cells of the cochlear duct lie within the Organ of Corti
• Intensity is the energy content of a sound• Measured in decibels
Hearing
The Cochlea
The Organ Of Corti
• Sound waves travel toward tympanic membrane, which vibrates
• Auditory ossicles conduct the vibration into the inner ear• Tensor tympani and stapedius muscles
contract to reduce the amount of movement when loud sounds arrive
• Movement at the oval window applies pressure to the perilymph of the cochlear duct
• Pressure waves distort basilar membrane• Hair cells of the Organ of Corti are pushed
against the tectoral membrane
Pathway of sound
Sound and Hearing
Sound and Hearing
Neural pathway
• Sensory neurons of hearing are located in the spiral ganglion of the cochlea
• Afferent fibers form the cochlear branch of cranial nerve VIII• Synapse at the cochlear nucleus
You should now be familiar with:
• The sensory organs of smell, and the olfactory pathways in the brain.
• The accessory and internal structures of the eye, and their functions.
• How light stimulates the production of nerve impulses, and the visual pathways.
• The structures of the external and middle ear and how they function.
• The parts of the inner ear and their roles in equilibrium and hearing.
• The pathways for the sensations of equilibrium and hearing.