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Transcript
LESSON # 23 Special Senses: 1- Olfaction (smell) 2- Gustation (taste) 3- Vision 4- Equilibrium and Hearing Special Senses: 1- Olfaction (smell) 2- Gustation (taste) 3- Vision 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 Olfactory Their secretions absorb (Bowman) water and form a thick gland pigmented mucus. Olfactory nerve fibers 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. Knob They are enlargements that project beyond the epithelial surface and provide the base for up to 20 cilia. 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. 2- Olfactory receptors cells They are highly modified neurons sensitive to odorants. 3- Supporting cells They are epithelial cells Odorants are small organic molecules. The strongest smells are associated with molecules of high solubility both in water and lipids. 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 Limbic system profound emotional and behavioral Hypothalamus response, as well as memories, that can be triggered by certain smells. 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). 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. Taste Receptors Transitional They mature to become cells gustatory cells. Basal cells They divide to produce daughter cells that mature in stages. Dendrites of sensory neurons Cranial nerves VII (facial), and IX (glossopharyngeal). Taste pore Gustatory Taste hairs cells (microvilli) 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. The result of taste receptor stimulation is the release of neurotransmitters by the receptors cells. Gustatory cortex (Insula) 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. 2- Information about taste-related sensations such as “peppering” or “burning hot”. 3- Information about smell from olfactory receptors. 3- Vision Accessory Structures of the Eye Lacrimal gland ducts Lacrimal caruncle Superior and inferior lacrimal canaliculi Lacrimal gland They carry the tears to the lacrimal sac. It produces tears. Lateral cantus Medial cantus Palpebral conjunctiva Lower eyelid Lacrimal sac It collects tears and carries them to the nasolacrimal duct. Nasolacrimal duct It drains excess of tears to the nasal cavity. Opening of nasolacrimal duct Extrinsic Muscles of the Eye (eye looks up) Trochlea Superior oblique (eye rolls, looks down & to the side) Superior rectus Lateral rectus (eye rotates laterally) Medial rectus (eye rotates medially) Inferior oblique (eye rolls, looks up & to the side) Inferior rectus (eye looks down) Innervation of the Extrinsic Muscles of the Eye MUSCLE ACTION INNERVATION SUPERIOR RECTUS EYE LOOKS UP OCULOMOTOR (III) INFERIOR RECTUS EYE LOOKS DOWN OCULOMOTOR (III) MEDIAL RECTUS EYE ROTATES MEDIALLY LATERAL RECTUS EYE ROTATES LATERALLY SUPERIOR OBLIQUE INFERIOR OBLIQUE EYE ROLLS, LOOKS DOWN & TO THE SIDE EYE ROLLS, LOOKS UP & TO THE SIDE OCULOMOTOR (III) ABDUCENS (VI) TROCHLEAR (IV) OCULOMOTOR (III) Innervation of the Extrinsic Muscles of the Eye (eye looks up) Trochlea Superior oblique (eye rolls, looks down & to the side) Trochlear nerve (pair IV) Superior rectus Oculomotor (pair III) Lateral rectus (eye rotates laterally) Abducens nerve (pair VI) Inferior oblique (eye rolls, looks up & to the side) Oculomotor (pair III) Medial rectus (eye rotates medially) Oculomotor (pair III) Inferior rectus Oculomotor (pair III) (eye looks down) LAYERS OF THE EYE BALL 1- The fibrous tunic Sclera or white of the eye (protects and gives shape to the eyes) Cornea (clear outer part) (It allows the light to come in) Choroid ( vascular layer the nourishes the retina) 2- The vascular tunic or uvea Ciliary body Ciliary muscle (tension the suspensory ligaments) Ciliary process (produces the aqueous humor) Iris (pigmented areas and intrinsic muscles that controls the size of the pupil) 3- Neural tunic or retina Neural part Pigmented part Layers and Chambers of the Eye Ball Anterior chamber Posterior chamber Fibrous tunic: Cornea Sclera Anterior cavity Lens Vascular tunic (uvea): Iris Ciliary body Choroid Neural tunic (retina): Posterior cavity Neural part Pigmented part Optic disc It is called also blind spot because contains no photoreceptors. Optic nerve Fovea centralis It contains only cones, which are responsible for the sharpest vision. Pupil Lens It focuses the light in the retina. Ciliary Body: Ciliary processes It allows the light to come in. Cornea Posterior cavity It allows the light to come in. It contains vitreous humor, which maintains the shape of the lens & prevents collapse Anterior chamber Anterior cavity Posterior chamber It contains aqueous humor that nourishes the lens & the cornea because they do not have blood vessels. Ciliary muscle Iris 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. Choroid It nourishes the retina and absorbs excess of light. Sclera It protects & gives the shape to the eyes Histological Organization of the Retina Pigmented part It absorbs light preventing visual echoes. Cones Photoreceptors Rods They provide color vision They detect light in dim light and provide black and white vision. Bipolar They connect the photoreceptors to the ganglion cells. cells Ganglion They are neurons whose axons forms the optic nerve. They carry cells visual information. Neural part Light Amacrine cells They adjust the sensitivity of the retina by either facilitating or inhibiting the communication Horizontal cells between the photoreceptors and the ganglion cells. 4- Equilibrium and Hearing Anatomy of the Ear The special senses of equilibrium and hearing are provided by the ear. External Ear Pinna or auricle Ear canal Ceruminous glands Tympanic membrane Middle Ear Inner Ear Ossicles Pharyngotympanic or auditory or eustachian tube External Ear Membranous labyrinth Bonny labyrinth Internal Ear Vestibule Semicircular canals Cochlea The External Ear Tympanic membrane Pinna or auricle It protects the opening of the canal and provides directional sensitivity. Ear canal It focus and directs the sound waves into the tympanic membrane. It transmits the sound waves to the middle ear ossicles. The Middle Ear Incus (anvil) Malleus (hammer) Its handle is attached to the tympanic membrane. Auditory tube It equalizes the pressures on either side of the tympanic membrane. Tensor tympani muscle It tenses the tympanic membrane reducing the amount of movement possible. Stapes (stirrup) Its base is bound to the oval window. Stapedius muscle It pulls the stapes, reducing movement of the stapes in the oval window. Equilibrium: Hearing: 1- Linear acceleration (maculae in the vestibule). 2- Gravity (maculae in the vestibule). 3- Rotational movement of head (cristae in the ampulla). The Internal Ear Bony labyrinth Membranous labyrinth Organ of Corti in the cochlea. They contain the cristae Ampulla (receptors for rotational movements of the head). Semicircular canals Semicircular ducts Bony labyrinth Perilymph Membranous labyrinth Endolymph Vestibule Utricle Saccule They contain the maculae (receptors for sensations of gravity and linear acceleration). Cochlea It contains the organs of Corti (receptors for hearing). Equilibrium: 1- Linear acceleration (maculae in the vestibule). 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.