17_Special Senses.pptx

Special Senses Chapter 13, Human Anatomy (LibreTexts) "Olfactory System Large Unlabeled" by Andrewmeyerson is licensed under CC BY-SA 3.0 Sensory Receptors – Cell Types • Structural (cell type or location) vs Functional classification • Structural classification: based on cell type • Free nerve e...

Special Senses Chapter 13, Human Anatomy (LibreTexts) "Olfactory System Large Unlabeled" by Andrewmeyerson is licensed under CC BY-SA 3.0 Sensory Receptors – Cell Types • Structural (cell type or location) vs Functional classification • Structural classification: based on cell type • Free nerve ending • Encapsulated ending • Receptor cell "Receptor Types" by OpenStax is licensed under CC BY 4.0 Sensory Receptors - Location • Structural classification: based on location of stimuli • Exteroceptor: responds to stimuli arising outside of the body (i.e. receptors for vision, smell, touch, etc) • Interoceptor: responds to chemical or pressure stimuli arising inside of the body (i.e. receptors for blood pressure or blood oxygen levels) • Proprioceptor: responds to positional or movement stimuli arising inside of the body (i.e. receptors for balance or muscle state) Sensory Receptors - Functions • Functional classification: based on type of stimuli • • • • • Chemoreceptor: chemical Photoreceptor: light Nociceptor: pain Mechanoreceptor: pressure Thermoreceptor: temperature Special and General Senses • Special senses: localized in special organs of the head region • • • • • Gustation (taste) Olfaction (smell) Vision Hearing Equilibrium (balance) • General senses: localized in the skin and internal organs • • • • • Touch Pain Pressure Temperature Tension Gustation (Taste) Gustation (Taste) – Papillae • The tongue is the sensory organ for taste. • On the tongue, raised bumps called papillae (singular = papilla) contain the structures for gustatory transduction. • There are four types of papillae, based on their appearance: 1. 2. 3. 4. Circumvallate papillae Foliate papillae Filiform papillae Fungiform papillae "The Tongue" by OpenStax is licensed under CC BY 4.0 Gustation (Taste) – Taste Buds and Cells • Within the structure of the papillae are taste buds that contain gustatory cells. • Within each taste bud, there are three cell types: • Gustatory receptor cells: Chemoreceptors that detect tastants via extensions called gustatory microvilli, or taste hairs • Supporting cells (aka Transitional): Support and sustain the gustatory receptor cells. • Basal cells: Stem cells that differentiate into gustatory receptor cells, which are replaced regularly. "The Tongue" by OpenStax is licensed under CC BY 4.0 Gustation (Taste) – Neuronal Pathway • Gustatory receptor cells transmit information through the facial (CN VII) or glossopharyngeal (CN IX) nerves through the thalamus, which acts as a relay station, and into the primary gustatory cortex of the insula. Olfaction (Smell) Olfaction (Smell) – Olfactory Epithelium • The nasal cavity is the sensory organ for smell. • The nasal cavity houses our olfactory or smell receptors within the olfactory epithelium, which is found on the roof of the nasal cavity. "Olfactory System" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Olfaction (Smell) – Cells and Glands • There are three cell types in the olfactory epithelium: • Olfactory receptor neurons: Bipolar neurons that act as chemoreceptors to detect odorants via extensions called olfactory hairs. • Supporting cells: Support and sustain the olfactory receptor cells. • Basal cells: Stem cells that differentiate into olfactory receptor cells, which are replaced regularly. "Olfactory System" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Olfaction (Smell) – Cells and Glands • Just deep to the olfactory epithelium is the lamina propria which houses olfactory glands that produce a layer of mucus that acts to dissolve odorants. • The axons of the olfactory receptor neurons cross the bone that makes the roof of the nasal cavity and deliver the olfactory information to the olfactory bulb for processing. "Olfactory System" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Olfaction (Smell): Neuronal Pathway • From the olfactory bulb, the olfactory nerve (CN I) transmits information directly to the primary olfactory cortex of the temporal lobe, without going to the thalamus. Vision Vision – Eye and Photoreceptors • The eye is a special sensory organ that allows vision. • Our sense of vision is based on how light bounces off the objects around us. Light stimuli are detected by sensory receptors called photoreceptors, which are found only in the eye. Accessory Structures of the Eye • Structures that protect the eyes: • Bony orbits • Eyelashes and eyebrows • Eyelids (aka palpebrae): include thin layer of skin, muscle and fibers and tarsal glands that produce secretions to prevent tear overflow and to lubricate eyelids. • Lacrimal apparatus Eyelids • The inner lid is a thin membrane known as the palpebral conjunctiva. The conjunctiva connects the eyelids to the eyeball. At the connection with the eyeball, a thin layer called the ocular conjunctiva forms a continuous layer on the external and anterior surface of the eye (except for the corneal region). • The ocular conjunctiva is superficial to the white part of the eye which is called the sclera and does not cover the clear surface of the anterior eye called the cornea. • The conjunctiva contains blood vessels and nerves that support the avascular sclera and detect foreign particles entering the eye. Accessory Structures of the Eye Sclera Ocular conjunctiva "Eye in the Orbit Labeled" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Lacrimal Apparatus • Produces and drains lacrimal fluid (tears). • Reduces friction of the eyelids, continuously cleans the anterior surface of the eye, and prevents bacterial infection through the action of lysozyme. Flow of Tears 1. Tears are produced by the lacrimal gland, located within the superolateral depression of each orbit. 2. The superior and inferior lacrimal puncta are small openings to drain the lacrimal fluid into channels called the superior and inferior lacrimal canaliculi. 3. From there, the lacrimal fluid enters the lacrimal sac and drains into the nasolacrimal duct that delivers it into the nasal cavity where it mixes with the mucus. "Lacrimal Apparatus" by Chiara Mazzasette is licensed under CC BY-SA 4.0 / A derivative from the original work Structure of the Eye • Made by three layers of tissue called tunics: 1. Fibrous tunic includes the white sclera made of dense irregular connective tissue and the clear cornea that bends the light coming into the eye. 2. Vascular tunic composed of three parts: • Choroid houses the blood vessels that supply and drain blood from the tunics of the eye. • Ciliary body is composed of ciliary muscles and is attached to the lens by suspensory ligaments. The lens focuses the light to the retina. • Iris (colored part of the eye) is composed of pigmented layers and two layers of smooth muscle called the sphincter pupillae and dilator pupillae, that open and close the pupil which is the black hole at the center of the eye. 3. Neural tunic or retina contains the photoreceptors involved in receiving and processing light. Iris muscles "Iris Muscles" by MikeRun is licensed under CC BY-SA 4.0 Structure of the Eye • Divided in two cavities: 1. Anterior cavity: between the cornea and lens, filled with aqueous humor which is a clear liquid that removes waste products. 2. Posterior cavity: space behind the lens, filled with vitreous humor which is a clear jelly-like substance that helps maintain the eye shape. Structure of the Eye "Structures of the Eye Labeled" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Retina I • Composed of several layers of cells, connected to each other. From deep to superficial: • Photoreceptors called rods for light (black/white) vision and cones for color vision. • Horizontal cells • Bipolar cells • Amacrine cells • Retinal ganglion cells (RGCs): their axons collect at the optic disc and leave the eye as the optic nerve (CN II). Photoreceptor "Figure 36 05 02" by OpenStax is licensed under CC BY 4.0 Retina II • At the exact center of the retina is a small area known as the fovea centralis. Area around the fovea is called macula lutea. At the fovea, the retina lacks the supporting cells and blood vessels, and only contains photoreceptors. Therefore, visual acuity, or the sharpness of vision, is greatest at the fovea. • Axons making the optic nerve and blood vessels leave eye through optic disc at the posterior side of the eye. • Optic disc does not have light-sensitive cells (photoreceptors), so no light can be processed there. The optic disc creates a blind spot in our vision. Fovea "Anatomy of the fovea - English labels" by Cenveo is licensed under CC BY 4.0 Light Pathway 1. Light arrives at the eye(s). 2. Cornea bends light as it enters the eye. 3. Light passes through aqueous humor in the anterior chamber without bending. 4. Iris controls amount of light entering eye by contracting or dilating. 5. Lens focuses the light on fovea centralis of the retina. 6. Light passes through the vitreous humor and lands on the retina. Neuronal Pathway of Vision • Photoreceptors activate and send electrical signals to other cells, and then to optic nerves. • The optic nerves extending from both eyes eventually cross at an X-shaped region called the optic chiasm. Most of the visual information from the eyes will cross over into the opposite side of the brain. • From the optic chiasm, information is transmitted through the thalamus, and sent to the primary visual cortex of the occipital lobe. Hearing (Audition) and Balance (Equilibrium) Hearing and Balance – Hair Cells • The ear houses the sensory organs for: • Balance (or Equilibrium): Awareness of the head's position in space. • Hearing: Perception of vibrations, or sound waves, that travel through the air. • In both cases, mechanoreceptors called hair cells detect the stimulus and transmit information to the vestibulocochlear nerve (CN VIII). Qi, W., Ding, D., Zhu, H. et al. Efficient siRNA transfection to the inner ear through the intact round window by a novel proteidic delivery technology in the chinchilla. Gene Ther 21, 10–18 (2014). https://doi.org/10.1038/gt.2013.49 Structures of the Ear "External, Middle and Inner Ear" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work External Ear • The auricle is the fleshy structure that convey sounds into the auditory (ear) canal. • At the end of the canal is the tympanic membrane that vibrates and transforms sound waves into mechanical waves. "External, Middle and Inner Ear" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Middle Ear • The middle ear consists of a space spanned by three small bones called ossicles (malleus, incus, and stapes) that conduct the mechanical waves from the tympanic membrane to the oval window. • The middle ear is connected to the pharynx through the Eustachian (or auditory) tube, which helps equilibrate air pressure across the tympanic membrane. "External, Middle and Inner Ear" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Inner Ear • Three separate regions: 1. Cochlea responsible for hearing 2. Vestibule responsible for balance 3. Semicircular canals responsible for balance • The inner ear is responsible for transforming mechanical waves into electrical signals, which are then sent to the brain through the vestibular and cochlear branches of the vestibulocochlear nerve (CN VIII). "External, Middle and Inner Ear" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Inner Ear • The inner ear is made of a bony labyrinth whose walls are made of the temporal bone found in this region. The bony labyrinth is filled with perilymph. • The bony labyrinth is lined with a membranous labyrinth that separate tubes and spaces and contains the sensory organs for hearing and balance. The membranous labyrinth is filled with endolymph. "Ear Anatomy Internal Ear" by BruceBlaus is licensed under CC BY 3.0 Audition (Hearing) - Cochlea • The cochlea is a spiral-shaped tube, divided into three compartments: the scala vestibuli, cochlear duct and scala tympani (from superior to inferior). All compartments are filled with endolymph. • Stapes is attached to the oval window, which is located at the beginning of the scala vestibuli. • At the uppermost tip of the cochlea, the scala vestibuli curves over the top of the cochlear duct and becomes the scala tympani, that returns to the base of the cochlea, ending at the round window. • As vibrations of the ossicles travel through the oval window, the fluid of the scala vestibuli and scala tympani moves in a wave-like motion. Cross Section of the Cochlea "Cochlea" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Audition (Hearing) – Organs of Corti • The cochlear duct contains several organs of Corti, which transduce the wave motion of the two scala into neural signals. • The organs of Corti lie on top of the basilar membrane, which is the side of the cochlear duct located between the organs of Corti and the scala tympani. • The organs of Corti contain hair cells, which are named for the hairlike stereocilia extending from the cell’s apical surfaces. • The stereocilia extend up from the hair cells to the overlying tectorial membrane, which is attached medially to the organ of Corti. • When the pressure waves from the scala move the basilar membrane, the tectorial membrane slides across the stereocilia. This bends the stereocilia either toward or away from the tallest member of each array, which causes an electrical signal to be generated. Hair Cells of the Organ of Corti "Cochlea-crosssection" by Oarih & Fred the Oyster is licensed under CC BY-SA 3.0 Histology of the Cochlea "Cochlea Micrograph Labeled" by Chiara Mazzasette is licensed under CC BY 4.0 / A derivative from the original work Audition (Hearing) – Neural Pathway • The hair cells of the Organ of Corti transmit their electrical signals to the cochlear branch of the vestibulocochlear nerve (CN VIII). • All information from the vestibulocochlear nerve is sent into the brain and through the thalamus, with auditory perception processed in the primary auditory cortex of the temporal lobe. Equilibrium (Balance) • There are two regions within the vestibular apparatus that sense equilibrium: the vestibule, composed of the utricle and saccule, and the semicircular canals. • The vestibule detect static equilibrium, the position of the head when we are not in motion, and linear acceleration, forward and backward movements either as the entire body moves (like in a car accelerating or decelerating) or the head flexes and extends (think shaking the head "yes"). • The semicircular canals detect rotational acceleration, when the head or entire body turns or spins (like in the teacups of Disneyland). Equilibrium (Balance) – Vestibule • The vestibule contains two membranous labyrinth structures called the utricle and saccule. • Hair cells (similar to the cochlear ones) are located in maculae of the utricle and saccule. The stereocilia of the hair cells extend into a viscous gel called the otolithic membrane, on top of which is a layer of calcium carbonate crystals, called otoliths. • When the head moves, the otoliths move and the otolithic membrane bends the stereocilia of the hair cells, which generates an electrical signal. Linear Acceleration Coding by Maculae "Maculae and Equilibrium" by OpenStax is licensed under CC BY 3.0 Equilibrium (Balance) – Semicircular Canals • There are three semicircular ducts enclosed by the membranous labyrinth, the anterior, posterior, and horizontal ducts. At the base of each of these ducts are three ampullae. • The hair cells within each ampulla are embedded in a region of the membranous labyrinth called the crista ampullaris. The hair cells extend their stereocilia and kinocilium into a gelatinous layer called the cupula. • As the head rotates in a plane parallel to the semicircular canal, the fluid lags, deflecting the cupula in the direction opposite to the head movement, and bending the stereocilia of the hair cells, generating an electrical signal. Rotational Coding by Semicircular Canals "Equilibrium and Semicircular Canals" by OpenStax is licensed under CC BY 3.0 Equilibrium (Balance) – Neural Pathway • The hair cells of the vestibule and semicircular canals transmit their electrical signals to the vestibular branch of the vestibulocochlear nerve (CN VIII). • All information from the vestibulocochlear nerve is sent into the brain and through the thalamus, with equilibrium processed in cerebral nuclei, the cerebellum, and the brain stem.