Lecture 13: Chapter 17 The Special Senses Page: 549 - 589 Lecturer: Dr. Barjis Room: P313 Phone: (718) 260-5285 E-Mail: ibarjis@citytech.cuny.edu

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.

Olfaction Olfactory organs 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

The Olfactory Organs

Olfaction 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

Gustation Taste receptors Clustered in taste buds Associated with lingual papillae

Taste buds Contain basal cells which appear to be stem cells Gustatory cells extend taste hairs through a narrow taste pore

Gustatory Reception

Gustatory pathways 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 discrimination 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

Accessory structures of the eye Vision Accessory structures of the eye Eyelids (palpebrae) separated by the palpebral fissue Eyelashes Tarsal glands Lacrimal apparatus

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

Eye anatomy 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

The Circulation of Aqueous Humor

Fluids in the eye 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

Lens 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

Image Formation

Accommodation Figure 17.10

Visual Abnormalities

Visual physiology Rods – respond to almost any photon Cones – specific ranges of specificity

Rods and Cones

Photoreceptor structure Outer segment with membranous discs Narrow stalk connecting outer segment to inner segment Light absorption occurs in the visual pigments Derivatives of rhodopsin

Photoreception Animation: Photoreception (see tutorial)

Photoreception

Bleaching and Regeneration of Visual Pigments

Color sensitivity Integration of information from red, blue and green cones Colorblindness is the inability to detect certain colors

retinal adaptation Dark adapted – most visual pigments are fully receptive to stimulation Light adapted – pupil constricts and pigments bleached.

the visual pathway Large M-cells monitor rods Smaller more numerous P cells monitor cones

Convergence and Ganglion Cell Function

Seeing in stereo 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

The Visual Pathways

Visual circadian rhythm Input to suprachiasmic nucleus affects the function of the brainstem Circadian rhythm ties to day-night cycle, and affects metabolic rates

Equilibrium and Hearing Both equilibrium and hearing are provided by receptors of the inner ear Anatomy of the ear – External Ear Auricle or pinnae surrounds the ear External acoustic meatus ends on tympanic membrane

The Anatomy of the Ear

Middle ear Communicates with pharynx via pharyngotympanic membrane Middle ear encloses and protects the auditory ossicles

The Middle Ear

Inner ear Membranous labyrinth contains endolymph Bony labyrinth surrounds and protects membranous labyrinth Vestibule Semicircular canals Cochlea

The Inner Ear Figure 17.22

Components of the inner ear Vestibule contains the utricle and saccule Semicircular canals contain the semicircular ducts Cochlea contains the cochlear duct

Windows 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

Equilibrium 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)

The Vestibular Complex

The Vestibular Complex

The Vestibular Complex

Vestibular neural pathway Vestibular receptors activate sensory neurons of the vestibular ganglia Axons form the vestibular branch of cranial nerve VII Synapses within the vestibular nuclei

Pathways for Equilibrium Sensation

Hearing 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

The Cochlea

The Organ Of Corti

Pathway of sound 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

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.