Speacial Senses

7/26/2019 Speacial Senses

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Chemical Sense: gustation(taste) and olfaction(smell) complement each other (chemoreceptors)

Taste receptors are excited by food chemicals dissolved in saliva

Smell receptors are excited by air borne chemicalsdissolved in fluids coating nasal membranes

Supporting cells(sustentacular):

Form a capsule, containing 4-20 gustatory cells

Insulate gustatory cells from each other

Gustatory (receptor) cells:

Each contains gustatory hair (microvilli) which protrude through the taste pore

Gustatory hairs: sensitive portions (receptor membranes) of gustatory cells

Taste cells are shed every 7-10 days

Chemoreceptors are the primary neuron (dendrite) of the gustatory pathway

Basal cells:

Replace gustatory cells

1stsupportive cell then develop into gustatory cell

Most taste buds are found in papillae

Circumvallate:

Largest and least numerous

7-12 form an inverted V at the back of the tongue

Fungiform (mushroom-shaped):

Taste buds mainly found here

Scattered over the entire tongue surface

Foliate papillae:

Contain numerous taste buds

Side of the walls

Filiform:

Pointed thread-like

Cover 2/3of tongue

Contain no taste buds in humans


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Basic taste sensation:

1. Sweet (tip of tongue): organic substance including sugar, saccharin, alcohols, some amino acids

2. Sour (side of tongue): acids and hydrogen ions

3.

Salty (tip of tongue): metal ions (inorganic salts)

4.

Bitter (back of tongue): alkaloids (nicotine, caffeine, morphine) and aspirin5.

Umami: amino acids (glutamate and aspartate), beef, cheese, monosodium glutamate

6.

Water: found in pharynx sends info. To hypothalamus and other blood volume and water

balance controlling structures

Physiology of Taste: For chemical to be tasted it must dissolve in saliva, diffuse into taste pore, and

contact gustatory hairs

Gustatory hairs contain neurotransmitters

Food chemical binding to the receptors in gustatory cell membrane induces a graded

depolarizing potential that cause neurotransmitter release

Neurotransmitter binding to the associated sensory dendrites ultimately triggers action

potential in these fibers

The Gustatory Pathway:

Afferent fibers carrying taste info. From tongue are found primarily in 3 cranial nerves

Face N (CN VII):anterior 2/3 of tongue

Glossopharyngeal N (CN IX):posterior 1/3 of the tongue and pharynx

Vagus N (CN X):impulses from epiglottis and lower pharynx

All of these send afferent impulses to medulla where they synapse in the solitary

nucleus, and from there impulses stream to the thalamus and ultimately gustatorycortex in insula

Also project to hypothalamusand limbicsystemto appreciate what we are tasting

Taste is 80% smell

Mouth also contains thermoreceptors, mechanoreceptors, and nociceptors

Temp. And texture of foods can enhance or detract from their taste

Olfactory Epithelium and Sense of Smell:

Olfaction detects chemicals (odorants) in solution

The organ of smell is a yellow-tinged patch (about 5cm2) of pseudostratified epithelium called

olfactory epithelium- located in the roof of the nasal cavity

Olfactory epithelium: covers the superior nasal concha on each side of nasal septum

Contains millions of bowling pin-shaped olfactory receptors cells


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Olfactory Receptor (odorant-binding proteins) cells

Bipolar neuron

Slender, unmyelinated

Contain olfactory cilia (nonmotile)

Olfactory cilia at distal end, these respond to odors(odorants)

Supporting (sustentacular) cells:

Columnar cells of mucosa (bulk of epithelium)

Contain a yellow-brown pigment , which gives olfactory epithelium its yellow hue

Produces mucus that covers olfactory cilia (mucous captures and dissolves airborne odorants)

Basal cells:

Stem cells continually producing olfactory receptors

Believed to only move 15-30 kinds of R/C, yet we can distinguish thousands of smells But believed to only be 7 primary smells

Activation of olfactory R/C:

To be smelled it must be in gaseous state volatile as it enters the nasal cavity

Must dissolve(water soluble) in the fluid coating the olfactory epithelium(mucous)

Olfactory Pathway:

Odor is picked up by the hair cells

Axons of the olfactory receptor cells (which pass through cribriform plate) synapse withdendrites of mitral cells in the olfactory bulb (CN I)

When mitral cells are activated, impulses flow from olfactory bulbs via olfactory tracts

(composed of mitral cell axons) to two main destinations:

To olfactory cortex(temporal lobe) via thalamus; where smells are consciously

interpreted and identified(only one type of sensation)

2nd

pathways bypasses the thalamus and flows directly via subcortical route to

hypothalamus, amygdala, and other regions of the limbic system, which elicits

emotional response

Granule cells: Inhibit mitral cells in the glomeruli which helps contribute to the adaptation process

Eye and Vision:

Accessory Structures that protect the eye:

1.

Eyebrows:

Short coarse hairs superior to eyes


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They help shade the eyes from sunlight and prevent perspiration triclking down the

forehead from reaching the eyes

Supplied with sebaceous glands for protection

Deep to the eyebrows are orbicularis oculi (depresses the eyebrow) and corrugator

muscles (moves it medially)

2.

Eyelids(palpebrae)

Separated by the palpebral fissure (opening between upper and lower eyelid)

Meet at the medial and lateral angles of the eye (medial and lateral canthi

[commissures])

Contain sebaceous and sudoriferous glands

Upper eye lid has its own muscle: levator palpebrae superiors

Supported internally by CT sheets called tarsal plates

from superficial to deep each eyelid contains epidermis, dermis, subcutaneous areolar

CT, fibers of orbicularis oculi muscles, tarsal plate (thick CT fold), meibomian glands

(modified sebaceous glands), and cilliary glands (gland of Zeis) modified sweat glands

3.

Eyelashes:

Innervated by nerve endings (hair follicle receptors) for protection (triggers reflex

blinking)

4. Conjunctiva:

Thin mucus membrane; maintains eye moisture and is continually washing surface of

eye

o

Palpebral conjunctiva: lines the inner surface of eyelids

o Bulbar conjunctiva: lines anterior surface of eyeball

o Conjunctival sac: recesses formed at the junction of palpebral-bulbar

conjunctiva

5.

Lacrimal apparatus:

Located in superior lateral portion of orbit

Continually releases a dilute saline solution called lacrimal secretion (tears) into superior

part of the conjunctival sac through several small excretory ducts

1.

Blinking spreads the tears downward and across the eyeball to the medial

commissure

2.

Through the lacrimal punctatears enter the lacrimal canaliculi

3.

From canaliculithe tears drain into lacrimal sacand then into nasolacrimal duct to

the inferior nasal meatusof nasal cavity

Lacrimal fluid contains mucus, antibodies, and lysozyme(enzyme that destroys

bacteria)

o

Cleanses and protectsthe eye surface as it moistens and lubricates it

o

About 1 L a day

Structure of the Eye:

Fibrous Tunic:


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Dense avascular CT

Composed of the sclera and cornea

Function:

1.

Mechanical support and some protection

2.

Attachment of extrinsic eye muscles

3.

The cornea assists in focusing

Sclera:

Forms posterior portion and bulk of the fibrous layer

Glistening white and opaque

white of the eye Fibrous CT (continuous with dura mater of brain[optic nerve])

Protects and shapes the eyeball and provides a sturdy anchoring site for extrinsic eye

muscles

Cornea:

Anteriorly, continuation of sclera (transparent)

Avascular (not connected to immune system) but well innervated (pain R/C)

Lets light enter the eye; major light-bending apparatus of the eye

Sclera-cornea junction (called corneal limbus): is the scleral venous sinuous(canal of

Schelmm), drains aqueous humor

Vascular Tunic: (uvea)

Contains choroid, cilliary body and iris

Function:

1. Route for BV and lymphatics

2.

Regulates the amount of light entering the eye

3.

Secretes and reabsorbs the aqueous humor controls the lens shape4.

Highly pigmented for light absorption

Choroid:

BV rich, dark brown membrane that forms the posterior five-sixths of the vascular layer

Brown pigment (melanocytes) helps absorb light, preventing it from scattering and

reflecting within the eye (which would cause confusion)

Cilliary Body:

Extension of the choroid anteriorly

Thickest portion that encircles the lens

Consists of:

1.

Ciliary muscles: control lens shape

2.

Ciliary process: contain capillaries that secrete the fluid that fills the cavity of

anterior segment of eyeball (aqueous humor)

3.

Suspensory ligaments: attaches lens to cilliary body

Iris:

Visible colored part of the eye, most anterior portion of the vascular layer


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Laies between the cornea and the lens and is continuous with the cilliary body

posteriorly

Circular (pupillary constrictor) muscle (anterior/constricts/parasympathetic)

Radial (pupillary dilator) muscle (posterior/dilate/sympathetic)

Doughnut-shaped structure that regulates the amount of light entering the eye, through

the pupil

Sensory or Nervous tunic (retina) inner most layer:

Internal/posterior portion of the eye (ends at ora serrata anteriorly) consists of 2 layers:

Outer pigment layer:

single-cell-thick lining, abuts the choroid, extends anteriorly to cover cilliary body and

posterior face of iris

pigmented epithelial cells absorb light and prevent it from scattering in the eye,

contains phagocytes and stores vitamin A

Inner layer:

Transparent, extends anteriorly to the posterior margin of the cilliary body

Containing millions of photo receptors

3 Types of Neurons:

1.

Photoreceptors (rods and cones):

light activated, when light strikes them they produce an action potential

Rods:

o more numerous 20 to 1

o dim-lightand peripheral visionreceptors

o

more sensitive to light then cones are, but do not provide either sharp images

or color vision

Cones:

o Specialized for color vision and visual acuity (sharpness)

Macula lutea (yellow spot)

o Lateral to the blind spot of each eye

o Contains mostlycones

o Fovea centralis:

Contains onlycones

Sharpest vision area

2.

Bipolar cells:

Synapse bilaterally with photoreceptors and ganglion cells

3.

Ganglion cells:

Whose axon leave as optic nerve through the optic disc

Lens:

Held by suspensory ligaments to cilliary body


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Biconvex,flexible, enclosed by thin elastic capsule allows for precise focusing of light

Made of simple cuboidal epitheliumthat differentiates into lens fibers. These specialized cells

have lost their nuclei and some organelles.

Contain clear proteins call crystallins that form the body of lens

Eyeball is divided into two smaller segments (anterior and posterior)

1. Anterior Segment: divided into two chambers (anterior and posterior)

Anterior chamber: between cornea and iris

Posterior chamber: between iris and lens

Entire anterior segment is filled with aqueous humor

Aqueous humor: a clear fluid (like blood plasma or CSF) is continually produced and

secreted by cilliary processes(capillaries) into posterior chamber flows through the lens

and is drained by Scleral venous sinusin the anterior chamber

2.

Posterior segment: from the lens to posterior wall

Filled with clear gel called vitreous humor; formed during embryonic development andis not replaced

3 functions:

o Transmits light and causes refraction

o Supports the posterior surface of the lens and holds the neural retina firmly

against the pigmented layer

o Contributes to intraocular pressure, helping counteract the pulling force of the

extrinsic eye muscles

Physiology of Vision:

4 basic processes:

1.

Refraction:

Light bends when passing from one medium to another

The eye has 4 media as it passes from air into the eye:

1.

Anterior surface of cornea from air

2.

Posterior surface of cornea to aqueous humor

3.

Anterior surface of lens from aqueous humor

4.

Posterior surface of lens to vitreous humor

For focusing on close objects three reflex responses occur:

2.

Accommodation: (adjustment of the lens)

Increases refractory power of the lens

When cilliary muscles contract they pull the cilliary body forward and inward causing a

decreased tension of the suspensory ligaments

3.

Constriction of pupil:


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Pupil size reduces to prevent most divergent light rays from entering the eye

4. Convergence:

Medial rotation of the eyeballs by the medial rectus muscles so that each is directed toward the

object being viewed. The closer the object, the greater the degree of convergence required

Real Images are inverted and mirror reversal on retina, but the brain will compensate and reverse retinalimage

Excitation of rods: receptors for dim light

Rods contain a photosensitive pigment called rhodopsin, consists of scotopsinplus 11-cis retinal

(visual yellow) derivate of vitaminA

Vitamin A is oxidized to 11-cis-retinal form and then combined with opsin to form rhodopsin

Sequence: light strikes rod, rhodopsin breaks into its components (which dont absorb light) this

chemical breakdown stimulates an action potential

Very light sensitive like moonlight or candlelight can cause breakdown this allows for night

vision and peripheral vision

Absorbs all spectrum of light but only seen in gray tones

Excitation of cones:receptors for bright light and color; provides vivid colors and acuity

Contains retinaland photopsin(opsin of cones)

Requires much brighter light to activate it

3 types of cones with different combinations of retinal and photopsin, each absorb light

differently therefore they will respond to different wavelengths, green red and blue

Visual pathways to the brain:

1.

From rods and cones ->

2.

Bipolar neurons->

3.

Ganglionic cells (ganglionic cell initiate nerve impulse)

4.

Ganglion axon leaves eyeball as the optic nerve (CN II)->

5.

Crosses at the optic chiasmwhere medial fibers from each eye cross over to the opposite side

(Decussation) and then join lateral fibers from opposite eye (lateral fibers dont cross-> they

form optic tracts(bilaterally)

6.

Travel to thalamus(lateral geniculate nucleus) fibers synapse

7.

Pass to occipital lobe via optic radiation

The Ear: Hearing and Balance:

Outer Ear: consists of auricle (pinna), external auditory canal, tympanic membrane (eardrum)

Auricle:

Trumpet-shaped flap of elastic cartilage


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Designed to collect sound waves and direct them inward (most effective from front and

side)

External auditory canal:

Extends from auricle to eardrum (2.5 cm long)

Made of bone covered with elastic cartilage

The entire canal is lined with skin bearing hairs, sebaceous glands, and apocrine sweat

glands called ceruminous glands-secrete cerumen (provides a sticky trap for foreign

bodies and repels insects

Tympanic membrane (eardrum:

Between outer and middle ear

Thin, translucent, CT membrane covered by skin on its external face and by mucosa

internally

Shaped like a flattened cone, with apex protruding medially into middle ear

Transfers sound energy to the tiny bones of the middle ear and sets them into vibration

Middle Ear (Tympanic cavity):

Small, air-filled, mucosa-lined cavity in the petrous portion of the temporal bone

Between eardrum and bony wall of inner ear

Posterior wallcommunicates with mastoid process

Anterior wallwith auditory tube (pharyngotympanic) links middle ear with nasopharynx (tubes

help equalize pressure on both sides of tympanum )

Auditory ossicles:

Malleus, incus, and stapes (synovial joints)

Malleus(hammer) secured to eardrum and to incus

Incus(anvil) articulates with both bones (malleus and stapes)

Stapes(stirrups) attaches to incus and fits into oval window

Function: transmit motion vibration from eardrum into oval window (cochlea)

Tensor tympani and stapedius muscles: contract to prevent loud noise from damaging the

hearing receptors

Inner Ear (labyrinth): deep in temporal bone

2 major divisions: bony labyrinth and membranous labyrinth

Bony or osseous labyrinth:

3 divisions

Vestibule, cochlea, and semicircular canals

Lined with endosteum, filled with perilymph (fluid similar to CSF and continuous with it)


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Membranous labyrinth:

Continuous series of membranous sacs and ducts contained within the bony labyrinth

Lined with epithelium and containing endolymph (which floats in perilymph) within the bony

labyrinth

Vestibule:

Center cavity of bony labyrinth between cochlea and semicircular canals

In its lateral wall is the oval window

Membranous labyrinth sacs: saccule and utricle- house equilibrium receptor regions called

maculae that respond to the pull of gravity and report on changes of head position

Semicircular canals:

Anterior, posterior and lateral semicircular canal

Through each semicircular canal is semicircular duct which communicates with the utricle Each duct has ampulla(enlarged swelling at one end), which houses an equilibrium receptor

region called crista ampullaris

Respond to angular (rotational) movements of head

Cochlea:

Coils for about 2.5 turns around a bony pillar called modiolus (central core)

Cochlear duct along with osseous spiral lamina divide the cavity of the bony cochlea into three

separate chambers or scale

Cochlear duct:

runs through the center of modiolus and ends blindly at cochlear apex

houses spiral organ (of Corti),the receptor organ for hearing

Scala vestibule:

Superior to the cochlear duct, continuous with vestibule and abuts the oval window

Scala media:

the cochlear duct itself

filled with endolymph

Scala tympani:

Terminates at the round window

Inferior to cochlear duct

Scala vestibule and scala tympanicontain perilymph and connect at the cochlear apex through

helicotrema

Physiology of Hearing:

1.

Sound waves must be propagated through air, membranes, bones and fluids to reach and

stimulate receptor cells in the spiral organ (of Corti)


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2.

Airborne sound entering external acoustic meatus strikes the tympanic membrane and sets it

vibrating

3.

Auditory ossicles vibrate, amplifying the motion of tympanic membrane and transferring it to

the oval window

4.

Pressure waves created by the stapes pushing on the oval window move through the fulid in the

scala vestibule

5.

Sounds with frequencies below hearing travel through the helicotrema and do not excite hair

cells

6.

Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and

deflecting hairs on inner hair cells

Static Equilibrium:

Sensory receptors are the maculae(one in each saccule and utricle)

These receptors monitor position of the head in space(FXN: control in posture)

Macula:

Contain hair cells with otoliths(calcium carbonate crystals)

When the cilia of these cells are distorted (by otoliths being drawn by gravity) they

initiate nerve impulse and signal the change of position

Innervated by vestibular branch of the CN VIII

Dynamic Equilibrium:

Receptors are called crista ampullaris(composed of supporting cells [covered by cupula-gell

mass]) in semicircular canals

The canals are position in three planes:

Frontal, sagittal, and lateral

Permits detection of imbalance in all 3 planes

For angular movements mostly (but also acceleration and deceleration)

With movement of head, endolymph moves over cupula and distorts hair cells, initiating a nerve

impulse

Innervated by vestibular branch of the CN VIII

Sensorineural:

Nerve deafness

Due to damage of neuronal structures from cochlear hair cells to cerebral cortical cells Most common cochlear nerve damage

Conduction:

Anything that would hamper sound conduction to the fluids of the internal ear

Ex. Earwax, ruptured eardrum, M/C: otitis media(inflammation of middle ear) and otosclerosis

(fusion of ossicles)


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Speacial Senses