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: 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.

• 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.