LESSON # 23

1. LESSON # 23 • Special Senses: • 1- Olfaction (smell) • 2- Gustation (taste) • 3- Vision • 4- Equilibrium and Hearing

2. Special Senses: • 1- Olfaction (smell) • 3- Vision • 2- Gustation (taste) • 4- 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. Olfactory bulb Olfactory tract Olfactory nerve fibers Cribriform plate of ethmoid Olfactory organ: Olfactory epithelium Lamina propria

3. Olfactory (Bowman) gland Their secretions absorb water and form a thick pigmented mucus. Lamina propria It consists of areolar connective tissue with blood vessels and nerves. Olfactory epithelium: 1- Regenerative basal cells They divide to replace worn out olfactory receptors cells. 2- Olfactory receptors cells They are highly modified neurons sensitive to odorants. Knob 3- Supporting cells They are enlargements that project beyond the epithelial surface and provide the base for up to 20 cilia. Olfactory nerve fibers They are epithelial cells Odorants are small organic molecules. The strongest smells are associated with molecules of high solubility both in water and lipids. 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.

4. Olfactory Pathways • Axons leaving the olfactory epithelium collect into 20 or more bundles and penetrate cribriform plate of ethmoid to reach the olfactory bulbs. Olfactory bulb Olfactory tract • 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. Limbic system Hypothalamus Primary olfactory cortex (temporal lobe) • Arriving information reaches information centers without first synapsing in thalamus (all other sensations are relayed from processing centers in the thalamus).

5. 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 They for a V near the posterior margin of the tongue. They can contain as many as 100 taste buds. 2- Fungiform papilla They are small and contain about five taste buds. 3- Filliform papilla They provide friction that helps the tongue move objects around the mouth. They do not contain taste buds.

6. Taste Receptors They mature to become gustatory cells. They divide to produce daughter cells that mature in stages. Transitional cells Basal cells Taste pore Taste hairs (microvilli) Cranial nerves VII (facial), and IX (glossopharyngeal). Dissolved chemicals bind to receptor proteins and produce depolarization of the cell by two mechanisms: Dendrites of sensory neurons Gustatory cells 1- Open chemically gated ion channels. 2- G protein-second messenger mechanism.

7. Gustatory Pathways • Cranial nerves that synapse within solitary nucleus of medulla oblongata, then on to thalamus and primary sensory cortex. • 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. 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. Gustatory cortex (Insula) 2- Information about taste-related sensations such as “peppering” or “burning hot”. 3- Information about smell from olfactory receptors.

8. Lacrimal caruncle Accessory Structures of the Eye Lacrimal gland Lateral cantus Lacrimal sac Medial cantus Lower eyelid Palpebral conjunctiva Nasolacrimal duct Opening of nasolacrimal duct 3- Vision Lacrimal gland ducts Superior and inferior lacrimal canaliculi They carry the tears to the lacrimal sac. It produces tears. It collects tears and carries them to the nasolacrimal duct. It drains excess of tears to the nasal cavity.

9. Extrinsic Muscles of the Eye (eye looks up) Superior rectus Inferior oblique Lateral rectus Superior oblique Trochlea Medial rectus Inferior rectus (eye rolls, looks down & to the side) (eye rotates medially) (eye rotates laterally) (eye rolls, looks up & to the side) (eye looks down)

10. Innervation of the Extrinsic Muscles of the Eye MUSCLE ACTION INNERVATION SUPERIOR RECTUS EYE LOOKS UP OCULOMOTOR (III) INFERIOR RECTUS OCULOMOTOR (III) EYE LOOKS DOWN MEDIAL RECTUS EYE ROTATES MEDIALLY OCULOMOTOR (III) LATERAL RECTUS EYE ROTATES LATERALLY ABDUCENS (VI) EYE ROLLS, LOOKS DOWN & TO THE SIDE SUPERIOR OBLIQUE TROCHLEAR (IV) EYE ROLLS, LOOKS UP & TO THE SIDE INFERIOR OBLIQUE OCULOMOTOR (III)

11. Innervation of the Extrinsic Muscles of the Eye (eye looks up) Superior rectus Inferior oblique Lateral rectus Trochlea Superior oblique Medial rectus Inferior rectus Oculomotor (pair III) (eye rolls, looks down & to the side) Trochlear nerve (pair IV) (eye rotates laterally) (eye rotates medially) Abducens nerve (pair VI) Oculomotor (pair III) (eye rolls, looks up & to the side) Oculomotor (pair III) Oculomotor (pair III) (eye looks down)

12. Sclera or white of the eye (protects and gives shape to the eyes) Choroid ( vascular layer the nourishes the retina) Ciliary muscle (tension the suspensory ligaments) Ciliary body Ciliary process (produces the aqueous humor) Neural part Pigmented part LAYERS OF THE EYE BALL 1- The fibrous tunic Cornea (clear outer part) (It allows the light to come in) 2- The vascular tunic or uvea Iris (pigmented areas and intrinsic muscles that controls the size of the pupil) 3- Neural tunic or retina

13. Layers and Chambers of the Eye Ball Vascular tunic (uvea): Fibrous tunic: Fovea centralis Posterior chamber Optic disc Pigmented part Optic nerve Neural part Cornea Sclera Choroid Ciliary body Iris Anterior cavity Anterior chamber Lens Posterior cavity Neural tunic (retina): It contains only cones, which are responsible for the sharpest vision. It is called also blind spot because contains no photoreceptors.

14. It allows the light to come in. Pupil Posterior cavity Posterior chamber It focuses the light in the retina. Ciliary processes Ciliary muscle Lens Cornea Anterior chamber It allows the light to come in. Sclera It contains vitreous humor, which maintains the shape of the lens & prevents collapse Choroid Iris Anterior cavity Ciliary Body: It contains aqueous humor that nourishes the lens & the cornea because they do not have blood vessels. It controls the size of the pupil. Sclera venous sinus (canal of Schlemm) It drains the aqueous humor. The obstruction raises the intraocular pressure and glaucoma results. It nourishes the retina and absorbs excess of light. It protects & gives the shape to the eyes

15. Pigmented part Cones Rods Bipolar cells Ganglion cells Neural part Amacrine cells Horizontal cells Histological Organization of the Retina It absorbs light preventing visual echoes. They provide color vision Photoreceptors They detect light in dim light and provide black and white vision. Light They connect the photo- receptors to the ganglion cells. They are neurons whose axons forms the optic nerve. They carry visual information. They adjust the sensitivity of the retina by either facilitating or inhibiting the communication between the photoreceptors and the ganglion cells.

16. 4- Equilibrium and Hearing Anatomy of the Ear The special senses of equilibrium and hearing are provided by the ear. External Ear Middle Ear Inner Ear Pinna or auricle Ossicles Membranous labyrinth Ear canal Pharyngotympanic or auditory or eustachian tube Bonny labyrinth Ceruminous glands Vestibule Semicircular canals Tympanic membrane Cochlea Internal Ear External Ear Middle Ear

17. The External Ear It transmits the sound waves to the middle ear ossicles. Pinna or auricle It protects the opening of the canal and provides directional sensitivity. Tympanic membrane It focus and directs the sound waves into the tympanic membrane. Ear canal

18. The Middle Ear Tensor tympani muscle It tenses the tympanic membrane reducing the amount of movement possible. Malleus (hammer) Stapes (stirrup) Stapedius muscle Its handle is attached to the tympanic membrane. Its base is bound to the oval window. It pulls the stapes, reducing movement of the stapes in the oval window. Incus (anvil) It equalizes the pressures on either side of the tympanic membrane. Auditory tube

19. The Internal Ear 1- Linear acceleration (maculae in the vestibule). Equilibrium: 2- Gravity (maculae in the vestibule). Bony labyrinth 3- Rotational movement of head (cristae in the ampulla). Membranous labyrinth Hearing: Organ of Corti in the cochlea. Ampulla Saccule They contain the cristae (receptors for rotational movements of the head). Utricle Semicircular canals Semicircular ducts Endolymph Perilymph Bony labyrinth Membranous labyrinth Vestibule Cochlea They contain the maculae (receptors for sensations of gravity and linear acceleration). It contains the organs of Corti (receptors for hearing).

20. 1- Linear acceleration (maculae in the vestibule). Equilibrium: 2- Gravity (maculae in the vestibule). 3- Rotational movement of head (cristae in the ampulla). The basic receptor mechanism is the same for both senses: hair cells, which are mechanoreceptors. Hearing: Organ of Corti in the cochlea.