chapter 17: the special senses muse bio 2440 w12 lecture #6 5/24/12

Chapter 17: The Special Senses

Muse Bio 2440 w12Lecture #6 5/24/12

Comparison of General and Special Senses

General Senses Include somatic

sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations.

Scattered throughout the body.

Simple structures.

Special Senses Include smell, taste,

vision, hearing and equilibrium.

Concentrated in specific locations in the head.

Anatomically distinct structures.

Complex neural pathway.

Olfaction: Sense of Smell Olfactory epithelium contains 10-100 million

receptors. Olfactory receptor- a bipolar neuron with cilia

called olfactory hairs.

- Respond to chemical stimulation of an odorant molecule.

Supporting cells- provide support and nourishment.

Basal cells- replace olfactory receptors.

Olfactory Epithelium and Olfactory Receptors

Olfactory Epithelium and Olfactory Receptors continued…

Smell (Olfaction)

Olfactory Pathways

Arriving information reaches information centers

without first synapsing in thalamus

Physiology of Olfaction

Can detect about 10,000 different odors. Odorant binds to the receptor of an olfactory

hair→ G-protein activation→ activation of adenylate cyclase→ production of cAMP→ opening of Na+ channels→ inflow of Na+ →generator potential→ nerve impulse through olfactory nerves→ olfactory bulbs→ olfactory tract→ primary olfactory area of the cerebral cortex.

Olfactory transduction

Summary of sense of smellOdorant molecule binds one of 10-100 million receptors.Conformational change in receptor interacts with G proteinG protein activates adenylate cyclase to generate cAMPcAMP opens Na+ channels to initiate depolarization. Information on number of action potentials decoded by olfactorybulbs.

Animals have greater numbers of receptors thus better sense of smellUsually 10,000 times greater.

Gustation: Sense of Taste

Taste bud

Taste

15-11

Taste (Gustation)

Gustatory Discrimination

Primary taste sensations

Sweet (sugars)

Salty

Sour (acids)

Bitter (alkali)

umami - savory (fat)

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: (proteins that bind GTP- secondary messengers)

gustducins

Anatomy of Taste Buds and Papillae Taste bud- made of three types of epithelial

cells: supporting cells, gustatory receptor cells and basal cells.

About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore.

Taste buds are found in the papillae. Three types of papillae: vallate

(circumvallate), fungiform and foliate.

Physiology of Gustation

Five types of taste: sour, sweet, bitter, salty and umami.

Tastant dissolves in saliva → plasma membrane of gustatory hair→ receptor potential→ nerve impulse via cranial nerves VII, IX and X→ medulla→ thalamus→ primary gustatory area of the cerebral cortex.

Gustatory Pathway

Neuronal Pathways for Taste

Chorda tympani (part of VII): carry sensations from anterior one-third of tongue (except from circumvallate papillae

Cranial nerve IX and X carry information from posterior one-third tongue, circumvallate papillae, superior pharynx, epiglottis.

Information goes to medulla oblongata where decussation takes place and information projects from there to the thalamus. Then projects to taste area of cortex (extreme inferior end of the postcentral gyrus)

15-17

Specialist taste buds map to certain regions of tongueMaps differ somewhat , but generally

Actions of the Major Tastants

15-19

Vision or Sight

Visible light: 400-700 nm.

Accessory Structures of the Eye Eyelids or palpebrae-

Eyelashes and eyebrows-

Extrinsic eye muscles-

Accessory Structures of the Eye

The Lacrimal Apparatus

Tears from the lacrimal apparatus- lacrimal glands→ excretory lacrimal ducts→ lacrimal puncta→ lacrimal canals→ nasolacrimal sac→ nasolacrimal duct.

Anatomy of the Eyeball

The Eye

Figure 17–4b The Sectional Anatomy of the Eye.

Wall of the Eyeball Three layers:

Fibrous tunic- outer layer Sclera “white” of the eye Cornea-transparent coat

Vascular tunic or uvea- middle layer Choroid Ciliary body consists of ciliary processes and ciliary muscle Iris lens (alpha crystalin protein)

Retina- inner layer Optic disc Macula lutea- fovea centralis

Responses of the Pupil to Light

Pupil is an opening in the center of the iris.

Contraction of the circular muscles of the iris causes constriction of the pupil.

Contraction of the radial muscles causes dilation of the pupil.

Interior of the Eyeball Lens-

lack blood vessels, consists of a capsule with proteins (crystallins) in layers; transparent.

Lens divides the eyeball into two cavities: anterior and posterior.

Anterior cavity- further divided into anterior and posterior chambers. Both are filled with aqueous humor.

Posterior cavity (vitreous chamber)-filled with vitreous body.

Cavities of the Eyeball

Refraction of Light Rays

Refraction is the bending of light rays.

The cornea and lens refract light rays.

Most refraction done at corneal level - repair with corneal re-mapping (keratotomy)

Accommodation and the Near Point of Vision

Increase in the curvature of the lens for near vision is called accommodation.

Near point of vision is the minimum distance from the eye that an object can be clearly focused.

Refraction Abnormalities and their Correction Nearsightedness (myopia)- close objects

seen clearly. Image is focused in front of the retina. Correction- use of concave lens.

Farsightedness (hyperopia)- distant objects seen clearly. Image is focused behind the retina. Correction- use of convex (magnifyer) lens.

Most scientists

The Eye

Figure 17–6c Photograph of the Retina as Seen through the Pupil.

Most cones in fovea

Retina

15-35

Rods and Cones Named after the shapes of their outer

segments. Rod- (more sensitive to light, but no color ) Cones- three types: red, green and blue. Outer segment- contains photopigments.

Transduction of light energy into receptor potential occurs here.

Inner segment- contains the nucleus, Golgi complex and mitochondria.

Structure of Rod and Cone Photoreceptors Back of eye

Front of eye

Photoreceptors

15-38

Photopigments Two parts: opsin (four types, three in the cones

and one in the rod) and retinal (light absorbing part).

Rhodopsin- photopigment in rods. Cone photopigments- three types. (one for each

color)

Absorption of light by a photopigment → structural changes.

Bleaching and Regeneration of Photopigment

Rod disc in outer segment

Discmembrane

cis-retinal

opsin Isomerizationof retinal

Light

Rhodopsinmolecule

Coloredphotopigment(rhodopsin)

1

Rod disc in outer segment

Discmembrane

cis-retinal

opsin

opsin

Isomerizationof retinal

Light

trans-retinal

Trans-retinalseparatesfrom opsin(bleaching)

Rhodopsinmolecule

Coloredphotopigment(rhodopsin)

1

2

Rod disc in outer segment

Colorless products

Discmembrane

cis-retinal

opsin

opsin

opsin

Isomerizationof retinal

Light

trans-retinal

Retinalisomeraseconverts trans- to cis-retinal

trans-retinal

Trans-retinalseparatesfrom opsin(bleaching)

Rhodopsinmolecule

Coloredphotopigment(rhodopsin)

1

23

Rod disc in outer segment

Colorless products

Discmembrane

cis-retinal

cis-retinal

opsin

opsin

opsin

opsin

Cis-retinalbinds to opsin(regeneration)

Isomerizationof retinal

Light

trans-retinal

Retinalisomeraseconverts trans- to cis-retinal

trans-retinal

Trans-retinalseparatesfrom opsin(bleaching)

Rhodopsinmolecule

Coloredphotopigment(rhodopsin)

1

23

4

15-42

Bleaching and Regeneration of Photopigment1. Isomerization: In darkness, retinal has a

bent shape called cis-retinal. Absorption of photon causes straightening of the retinal (trans-retinal).

2. Bleaching: trans-retinal separates from opsin.

3. Regeneration: trans-retinal→ cis-retinal.

Light and Dark Adaptation

Light adaptation: Dark → light. Faster. Dark adaptation: Light →dark. Slow. Cones regenerate rapidly whereas rhodopsin

regenerates more slowly.

Operation of Rod Photoreceptors

Rods Bipolar photoreceptor cells; black and white vision. Found over most of retina, but not in fovea. More sensitive to

light than cones. Protein rhodopsin changes shape when struck by light; and

eventually separates into its two components: opsin and retinal Retinal can be converted to Vitamin A from which it was originally

derived. In absence of light, opsin and retinal recombine to form rhodopsin.

Rods are unusual sensory cells: when not stimulated they are hyperpolarized. Light causes them to depolarize.

Depolarization of rods causes depolarization of bipolar cells causing depolarization of ganglion cells

Light and dark adaptation: adjustment of eyes to changes in light. Happens because of changes in amount of available rhodopsin.

15-46

Color Blindness and Night Blindness Color blindness- inherited inability to

distinguish between certain colors. Result from the absence of one of the three types

of cones. Most common type: red-green color blindness.

Night blindness or Nyctalopia- vitamin A deficiency.

Cones Bipolar receptor cells. Responsible for color vision and

visual acuity. Numerous in fovea and

macula lutea; fewer over rest of retina.

As light intensity decreases so does our ability to see color.

Visual pigment is iodopsin: three types that respond to blue, red and green light

Overlap in response to light, thus interpretations of gradation of color possible: several millions

15-48

Processing of Visual Input

Receptor potential in rods and cones→ graded potentials in bipolar neurons and horizontal cells→ nerve impulses in ganglion cells→ optic nerve→ optic chiasm→ optic tract→ thalamus→ primary visual area of cerebral cortex in occipital lobe.

Visual Pathway

Visual field ofleft eye

Temporalhalf

Visual field ofright eye

Temporalhalf

Nasalhalf

Midbrain

Left eye

Temporalretina

Opticradiations

Left eye and its pathways

Primary visual area of cerebralcortex (area 17) in occipital lobe

Lateral geniculate nucleusof the thalamus

Opticradiations

Midbrain

Temporalretina

Nasalretina

Right eye

Right eye and its pathways

Nasalhalf

Nasal retina

1 1

Visual field ofleft eye

Temporalhalf

Visual field ofright eye

Temporalhalf

Nasalhalf

Midbrain

Left eye

Temporalretina

Opticradiations

Left eye and its pathways

Primary visual area of cerebralcortex (area 17) in occipital lobe

Lateral geniculate nucleusof the thalamus

Opticradiations

Midbrain

Temporalretina

Nasalretina

Right eye

Right eye and its pathways

Nasalhalf

Nasal retina

1 1

22

Visual field ofleft eye

Temporalhalf

Visual field ofright eye

Temporalhalf

Nasalhalf

Midbrain

Left eye

Temporalretina

Opticradiations

Left eye and its pathways

Primary visual area of cerebralcortex (area 17) in occipital lobe

Lateral geniculate nucleusof the thalamus

Opticradiations

Midbrain

Temporalretina

Nasalretina

Right eye

Right eye and its pathways

Nasalhalf

Nasal retina

1 1

22

33

Visual field ofleft eye

Temporalhalf

Visual field ofright eye

Temporalhalf

Nasalhalf

Midbrain

Left eye

Temporalretina

Opticradiations

Left eye and its pathways

Optictract

Primary visual area of cerebralcortex (area 17) in occipital lobe

Lateral geniculate nucleusof the thalamus

Opticradiations

Midbrain

Temporalretina

Nasalretina

Right eye

Right eye and its pathways

Nasalhalf

Nasal retina

1 1

2244

33

Visual field ofleft eye

Temporalhalf

Visual field ofright eye

Temporalhalf

Nasalhalf

Midbrain

Left eye

Temporalretina

Opticradiations

Left eye and its pathways

Optictract

Primary visual area of cerebralcortex (area 17) in occipital lobe

Lateral geniculate nucleusof the thalamus

Opticradiations

Midbrain

Temporalretina

Nasalretina

Right eye

Right eye and its pathways

Nasalhalf

Nasal retina

1 1

2244

5 5

33

Visual field ofleft eye

Temporalhalf

Visual field ofright eye

Temporalhalf

Nasalhalf

Midbrain

Left eye

Temporalretina

Opticradiations

Left eye and its pathways

Optictract

Primary visual area of cerebralcortex (area 17) in occipital lobe

Lateral geniculate nucleusof the thalamus

Opticradiations

Midbrain

Temporalretina

Nasalretina

Right eye

Right eye and its pathways

Nasalhalf

Nasal retina

1 1

2

3

24

34

5 5

6 6

Neuronal Pathways

15-52

Anatomy of the Ear Three main regions:

External (outer) ear- auricle or pinna, external auditory canal, and tympanic membrane.

Ceruminous glands- Middle ear- auditory ossicles: malleus, incus and

stapes.

Auditory (eustachian) tube. Internal (inner) ear- Labyrinth: bony and

membranous. Bony labyrinth- perilymph and membranous labyrinth- endolymph. Oval window and round window- membranous regions.

Anatomy of the Ear

The Middle Ear and the Auditory Ossicles

The Internal Ear

The Internal Ear Three parts: the semicircular canals, the

vestibule (both contain receptors for equilibrium) and the cochlea (contains receptors for hearing).

Semicircular canals: anterior, posterior and lateral.

Ampulla- Vestibule consists of two sacs: utricle and

saccule.

Semicircular Canals, Vestibule and Cochlea

Semicircular Canals, Vestibule and Cochlea

Tectorial membrane

Basilar membrane

Sprial organ

Inner hair cell

Outer hair cells

Inner phalangeal

cells

Outer phalangeal

cells

Cochlea Snail-shaped. Section through the cochlea shows three

channels: cochlear duct, scala vestibuli and scala tympani.

Helicotrema Vestibular membrane Basilar membrane Spiral organ or Organ of Corti- hair cells.

Physiology of Hearing Audible sound range: 20-20,000 Hz. Sound waves→ auricle→ external auditory

canal→ tympanic membrane→ malleus→ incus→ stapes→ oval window→ perilymph of the scala vestibuli→ vestibular membrane→ endolymph in the cochlear duct→ basilar membrane →hair cells against tectorial membrane → bending of hair cell stereocilia→ receptor potential→ nerve impulse. Sound wave → scala tympani→ round window.

Be able to trace sound thru ear

Events in the Stimulation of Auditory Receptors

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

3

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

34

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

34

5Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

34

5

6

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

34

5

6

7

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

34

5

6

78

8

Scalavestibuli

Cochlear duct(contains endolymph)

Scalatympani

Perilymph

Basilarmembrane

Cochlea

Sound waves

HelicotremaStapes vibratingin oval window

Malleus Incus

External auditorycanal

Tympanicmembrane

Secondary tympanicmembrane vibratingin round window Auditory tube

Vestibular membrane

Middle ear

Tectorial membrane

Spiral organ(organ of Corti)

1 2

34

5

6

78

8

9

The Ear

Figure 17–30 Frequency Discrimination.

end

Response map

high low

Effect of Sound Waves on Points Along the Basilar Membrane

15-66

Opening of K+ Channels

15-67

The Auditory Pathway

Physiology of Equilibrium

Two types of equilibrium:

Static- maintenance of the body position relative to the force of gravity.

Dynamic- maintenance of body position (mainly head) in response to rotational acceleration and deceleration.

Receptors for equilibrium are hair cells in the utricle, saccule and semicircular canals and are collectively called vestibular apparatus.

Location and Structure of Receptors in the Maculae

Otolithic Organs: Saccule and Utricle Macula- small thickened regions within the

saccule and utricle. Sensory structures for static equilibrium. Also detect linear acceleration and

deceleration. Contain hair cells and supporting cells. Stereocilia and kinocilium together called hair

bundle. Otolithic membrane rests on the hair cells

and contain otoliths.

Static Labyrinth Utricle has macula oriented parallel to base of skull Saccula has macula oriented perpendicular to base of skull Macula: specialized epithelium of supporting columnar cells

and hair cells with numerous stereocilia (microvilli) and one cilium (kinocilium) embedded in gelatinous mass weighted by otoliths

15-72

–Gelatinous mass moves in response to gravity bendinghair cells and initiating action potentials–Otoliths stimulate hair cells with varying frequencies–Patterns of stimulation translated by brain intospecific information abouthead position or acceleration

Physiology of Equilibrium continued Tilting of the head forward→ sliding of the

otolithic membrane bending the hair bundles→ receptor potential→ vestibular branch of the vestibulocochlear nerve.

Location and Structure of the Semicircular Ducts

Semicircular Ducts Crista, a small elevation in the ampulla

contain hair cells and supporting cells. Cupula, a mass of gelatinous material

covering the crista. Head movement→ semicircular ducts and

hair cells move with it→ hair bundles bend→ receptor potential→ nerve impulses→ vestibular branch of the vestibulocochlear nerve.

Cupula in Still Position versus Rotation

Kinetic Labyrinth Three semicircular canals filled with

endolymph: transverse plane, coronal plane, sagittal plane

Base of each expanded into ampulla with sensory epithelium (crista ampullaris)

Cupula suspended over crista hair cells. Acts as a float displaced by fluid movements within semicircular canals

Displacement of the cupula is most intense when the rate of head movement changes, thus this system detects changes in the rate of movement rather than movement alone.

15-77

Equilibrium Pathway

Hair cells of utricle, saccule and semicircular ducts→

Vestibular branch of the vestibulocochlear nerve →brain stem → cerebellum and thalamus→ cerebral cortex.

End of lesson