LESSON # 23

Special Senses: 1- Olfaction (smell)2- Gustation (taste)3- Vision4- Equilibrium and Hearing

1- Olfaction (smell) 2- Gustation (taste)

3- Vision4- Equilibrium and Hearing

1- Olfaction (smell)It is provided by paired olfactory organs, which are located in the nasal cavity on either side of the nasal septum.

Special Senses:

Olfactory organ:Olfactory epitheliumLamina propria

Cribriform plate of ethmoid

Olfactory bulbOlfactory tract

Olfactory nerve fibers

Olfactory epithelium:

Lamina propria

1- Regenerative basal cellsThey divide to replace worn out olfactory receptors cells.

2- Olfactory receptors cells

3- Supporting cells

It consists of areolar connective tissue with blood vessels and nerves.

Olfactory (Bowman)

gland

Their secretions absorb water and form a thick pigmented mucus.

Cilia

They are enlargements that project beyond the epithelial surface and provide the base for up to 20 cilia.

They contain receptors called odorant-binding proteins that match specific odorant particles. They can only be stimulated by water-soluble and lipid-soluble particles that can diffuse through the overlaying mucus. Depolarization is produced the G protein-second messenger mechanism.

Odorants are small organic molecules. The strongest smells are associated with molecules of high solubility both in water and lipids.

They are highly modified neurons sensitive to odorants.

They are epithelial cells

Olfactory nerve fibers

Knob

Olfactory bulb

Olfactory tract

Primary olfactory cortex(temporal lobe)

Limbic systemHypothalamus

Arriving information reaches information centers without first synapsing in thalamus (all other sensations are relayed from processing centers in the thalamus).

The parallel distribution of smell information in the limbic system and hypothalamus explains the profound emotional and behavioral response, as well as memories, that can be triggered by certain smells.

Olfactory PathwaysAxons leaving the olfactory epithelium collect into 20 or more bundles and penetrate cribriform plate of ethmoid to reach the olfactory bulbs.

2- Gustation (taste)Taste receptors (or gustatory receptors) are distributed on tongue and portions of pharynx, larynx, and epiglottis.By the time we reach the adulthood, the taste receptors of the pharynx, larynx and epiglottis have decreased in importance and abundance.

1- Circumvallated papilla

2- Fungiform papilla

3- Filliform papilla

They for a V near the posterior margin of the tongue.They can contain as many as 100 taste buds.

They are small and contain about five taste buds.

They provide friction that helps the tongue move objects around the mouth.They do not contain taste buds.

Taste Receptors

Taste poreBasal cells

They divide to produce daughter cells that mature in stages.

Transitional cells

They mature to become gustatory cells.

Gustatory cells

Taste hairs (microvilli)

Dendrites of sensory neurons

Cranial nerves VII (facial), and IX (glossopharyngeal).

Dissolved chemicals bind to receptor proteins and produce depolarization of the cell by two mechanisms: 1- Open chemically gated ion channels. 2- G protein-second messenger mechanism.

Gustatory Pathways

Cranial nerves that synapse within solitary nucleus of medulla oblongata, then on to thalamus and primary sensory cortex.

Gustatory cortex (Insula)

A conscious perception of taste is produced as the information received from the taste buds is correlated with other sensory data:

1- Information about the texture of food.

2- Information about taste-related sensations such as “peppering” or “burning hot”.

3- Information about smell from olfactory receptors.

The result of taste receptor stimulation is the release of neurotransmitters by the receptors cells.

The dendrites of the sensory neurons are tightly wrapped by folds of the receptor plasma membrane, and neurotransmitter release generates an action potential in the afferent fibers.

Lacrimal gland

Lacrimal sac

Nasolacrimal duct

It produces tears.

It collects tears and carries them to the nasolacrimal duct.

It drains excess of tears to the nasal cavity.

Accessory Structures of the Eye

Lacrimal gland ducts

They carry the tears to the lacrimal sac.

Superior and inferior lacrimal canaliculi

Lateral cantus

Medial cantus

Palpebral conjunctiva

Lower eyelid

Opening of nasolacrimal

duct

Lacrimal caruncle

3- Vision

Superior rectus

(eye looks up)

Lateral rectus Medial rectus(eye rotates

laterally)(eye rotates

medially)

Inferior rectus

(eye looks down)

Superior oblique(eye rolls, looks down &

to the side)

Inferior oblique(eye rolls, looks up &

to the side)

Trochlea

Extrinsic Muscles of the Eye

MUSCLE ACTION INNERVATION

SUPERIOR RECTUS

INFERIOR RECTUS

LATERAL RECTUS

MEDIAL RECTUS

SUPERIOR OBLIQUE

INFERIOR OBLIQUE

OCULOMOTOR (III)

OCULOMOTOR (III)

OCULOMOTOR (III)

OCULOMOTOR (III)

ABDUCENS (VI)

TROCHLEAR (IV)

EYE LOOKS UP

EYE LOOKS DOWN

EYE ROTATES LATERALLY

EYE ROTATES MEDIALLY

EYE ROLLS, LOOKS DOWN & TO THE SIDE

EYE ROLLS, LOOKS UP & TO THE SIDE

Innervation of the Extrinsic Muscles of the Eye

Superior rectus

(eye looks up)

Lateral rectus

Medial rectus(eye rotates

laterally)(eye rotates

medially)

Inferior rectus

(eye looks down)

Superior oblique(eye rolls, looks down &

to the side)

Inferior oblique(eye rolls, looks up &

to the side)

Trochlea

Oculomotor (pair III)

Oculomotor (pair III)

Oculomotor (pair III)

Innervation of the Extrinsic Muscles of the Eye

Oculomotor (pair III)

Trochlear nerve (pair IV)

Abducens nerve (pair VI)

LAYERS OF THE EYE BALL

1- The fibrous tunic

2- The vascular tunic or uvea

Cornea (clear outer part) (It allows the light to come in)

Sclera or white of the eye (protects and gives shape to the eyes)

Iris (pigmented areas and intrinsic muscles that controls the size of the pupil)

Choroid ( vascular layer the nourishes the retina)

3- Neural tunic or retina

Neural partPigmented part

Ciliary body Ciliary muscle (tension the suspensory ligaments)Ciliary process (produces the aqueous humor)

Choroid

Ciliary body

IrisCornea

Sclera

Neural part

Pigmented part

Neural tunic (retina):

Fibrous tunic: Vascular tunic (uvea):

Lens

Anterior cavity

Posterior cavity

Anterior chamber

Posterior chamber

Layers and Chambers of the Eye Ball

Optic nerve

Fovea centralisIt contains only cones, which are responsible for the sharpest vision.

Optic discIt is called also blind spot because contains no photoreceptors.

Cornea

Sclera

It allows the light to come in.

Pupil It allows the light to come in.

It protects & gives the shape to the eyes

ChoroidIt nourishes the retina and absorbs excess of light.

Ciliary processes

Ciliary muscle

Ciliary Body:

Iris It controls the size of the pupil.

It focuses the light in the retina.

LensPosterior

cavityIt contains vitreous humor, which maintains the shape of the lens & prevents collapse

It contains aqueous humor that nourishes the lens & the cornea because they do not have blood vessels.

Anterior chamber

Posterior chamber

Anterior cavity

It drains the aqueous humor. The obstruction raises the intraocular pressure and glaucoma results.

Sclera venous sinus (canal of Schlemm)

They connect the photo- receptors to the ganglion cells.

They are neurons whose axons forms the optic nerve. They carry visual information.

They provide color vision

They detect light in dim light and provide black and white vision.

Histological Organization of the Retina

Photoreceptors

Pigmented part

Neural part

Cones

Rods

Bipolar cells

Ganglion cells

Amacrine cells

Horizontal cells

They adjust the sensitivity of the retina by either facilitating or inhibiting the communication between the photoreceptors and the ganglion cells.

It absorbs light preventing visual echoes.

Lig

ht

4- Equilibrium and HearingThe special senses of equilibrium and hearing are provided by the ear.

Pinna or auricleEar canal

Ceruminous glands Tympanic membrane

Ossicles Pharyngotympanic or auditory or eustachian tube

Membranous labyrinth Bonny labyrinth

Vestibule Semicircular canals Cochlea

External Ear Middle Ear Inner Ear

External Ear M

iddle Ear

Internal Ear

Anatomy of the Ear

The External Ear

Ear canal

Tympanic membrane

Pinna or auricle

It protects the opening of the canal and provides directional sensitivity.

It focus and directs the sound waves into the tympanic membrane.

It transmits the sound waves to the middle ear ossicles.

The Middle Ear

Stapedius muscle

Malleus (hammer)

Incus (anvil)

Stapes (stirrup)Its base is bound to the oval window.

Tensor tympani muscle

It tenses the tympanic membrane reducing the amount of movement possible.

It pulls the stapes, reducing movement of the stapes in the oval window.

Auditory tubeIt equalizes the pressures on either side of the tympanic membrane.

Its handle is attached to the tympanic membrane.

Semicircular canals Semicircular ducts

Bony labyrinth

Membranous labyrinth

Bony labyrinth

Membranous labyrinth

Perilymph

Endolymph Vestibule

Utricle SacculeThey contain the maculae (receptors for sensations of gravity and linear acceleration).

They contain the cristae (receptors for rotational movements of the head).

Ampulla

CochleaIt contains the organs of Corti (receptors for hearing).

The Internal EarEquilibrium:

Hearing:

2- Gravity (maculae in the vestibule). 3- Rotational movement of head (cristae in the ampulla).

1- Linear acceleration (maculae in the vestibule).

Organ of Corti in the cochlea.

Hearing: Organ of Corti in the cochlea.

The basic receptor mechanism is the same for both senses: hair cells, which are mechanoreceptors.

Equilibrium: 2- Gravity (maculae in the vestibule). 3- Rotational movement of head (cristae in the ampulla).

1- Linear acceleration (maculae in the vestibule).