Session 22 Neuro 2 PowerPoints_Parmar 2024.pptx

Session 22 Neuro 2 Mayur S. Parmar, Ph.D. Assistant Professor of Pharmacology Department of Foundational Sciences Email : [email protected] l Phone : 813-574-5357 Dr. Kiran C. Patel College of Osteopathic Medicine Nova Southeastern University, Tampa Bay/Clearwater Campus 1 2 Lecturio  Tympanic membr...

Session 22 Neuro 2 Mayur S. Parmar, Ph.D. Assistant Professor of Pharmacology Department of Foundational Sciences Email : [email protected] l Phone : 813-574-5357 Dr. Kiran C. Patel College of Osteopathic Medicine Nova Southeastern University, Tampa Bay/Clearwater Campus 1 2 Lecturio  Tympanic membrane: Amplifies sound waves so they are stronger when they enter the inner ear.  Middle ear: Transforms air pressure waves to fluid pressure waves. Transmit vibrations of the tympanic membrane to the inner ear.  Inner ear: Transduces fluid pressure waves into nerve impulses transmitted to the brain.  Cochlea: Turn those physical vibrations into electrical impulses the brain can identify as sounds (transduction of sound).  Semicircular canals: For balance and detection of motion. 3 Video Library/Physiology/Neurophysiology/Hearing: Hearing Structure and Function Lecturio Video Library/Physiology/Neurophysiology/Hearing: Hearing Structure and Function 4 Lecturio 5 Video Library/Physiology/Neurophysiology/Hearing: Hearing Structure and Function Lecturio Key Points:  Basilar membrane: a stiff band of tissue that runs between Scala media and Scala tympani.  Pressure wave causes a certain section of the basilar membrane to vibrate back and forth.  The membrane is covered in more than 20,000 fibers and gets longer farther down the membrane.  All fibers resonate at different frequencies.  Fibers near the cochlea's base are short and narrow, while those at the end are long and loose.  Short fibers respond to high-frequency vibrations, whereas long fibers resonate at low frequencies. 6 Video Library/Physiology/Neurophysiology/Hearing: Hair Cells and Semicircular Channels 7 Video Library/Physiology/Neurophysiology/Hearing: Hair Cells and Semicircular Channels Lecturio Key Points:  How loud a sound is registered depends on the wave amplitude or the difference between the high and low pressure created in the air by the sound wave.  High-pitched noises → shorter waves move in and out more quickly, while fewer, slower fluctuations result in a lower pitch. 8 Video Library/Physiology/Neurophysiology/Hearing: Hair Cells and Semicircular Channels Lecturio Video Library/Physiology/ Neurophysiology/Hearing: Hearing Structure and Function 9 Organ of Corti The cochlea and organ of Corti. A. Cross-section through the cochlea. B. The organ of Corti. Organ of Corti: receptor organ of hearing / primary structure for hearing  The inner and outer hair cells share the common feature of having their apical surfaces immersed in the endolymph, the fluid of the Scala media.  Inner hair cells –  Flask shaped  Innervated mostly by afferent nerves  Outer hair cells –  Rod shaped  Innervated predominantly by efferent nerves Lecturio  The stereocilia of the inner hair cells are longer than those of the outer hair cells. Video Library/Physiology/Neurophysiology/Hearing: Hearing Structure and Function  Only the longest stereocilia contact the tectorial membrane that overlays the hair cells.  Hair cells of the cochlea respond to the deformation of stereocilia touching the tectorial membrane. 10 Mechanism of hair cell activation Lecturio  Detail of the organ of Corti at rest (A) and with upward movement of the basilar membrane (B).  The upward movement causes the stereocilia to bend because of shear forces produced by the relative displacement of the hair cells and the tectorial membrane. Video Library/Physiology/Neurophysiology/Hearing: Hair Cells and Semicircular Channels  Displacement of stereocilia toward the kinocilium opens nonselective cation channels.  K+ entry causes depolarization of hair cell membrane.  Depolarization results in Ca2+ entry and exocytosis of neurotransmitters.  Depolarization of auditory neurons. 11 Vestibular system  A sensory system.  Responsible for providing our brain with information about motion, head position, and spatial orientation.  Involved with motor functions that allow us to keep our balance, stabilize our head and body during movement, and maintain posture. Lecturio 12 Video Library/Physiology/Neurophysiology/Balance: Vestibular Structure and Function Semicircular canals in the vestibular system play a crucial role in maintaining balance and movement.  Semicircular ducts contain endolymph that is typically arranged in a circular pattern. Cristae ampularis  The hair cells in the semicircular canals are associated with the cristae ampularis.  Cristae ampularis is characterized by the capula.  Capula is a mucopolysaccharide.  A prominent body associated with the cristae ampularis.  Angular acceleration in one direction causes the capula to bend in the opposite direction, leading to the stimulation of hair cells.  As the head rotates, the capula bends in the opposite direction of the head rotation. Lecturio 13 Video Library/Physiology/Neurophysiology/Balance: Vestibular Structure and Function  The otolith organs sense gravity and linear acceleration or deceleration (due to movement initiation in a straight line).  Persons or animals without otolith organs or defective otoliths have poorer abilities to sense motion and orientation to gravity. This figure shows a close-up of the inner ear. Otolithic organs Video Library/Physiology/Neurophysiology/Balance: Otolith Organs Description https://www.dizziness-and-balance.com/anatomy/ ear/otoliths.html Otolith Organs Function Utricle Located next to the semicircular canals. Most sensitive to gravity detects changes in head position from an upright position. Saccule Located near the cochlea. Most sensitive to gravity detects changes in head position from a recumbent position. Dark cells Black dots surrounding the utricle and saccule. Non-sensory epithelial cells produce endolymph, the inner fluid of the inner ear. 14 Lecturio https://www.dizziness-and-balance.com/anatomy/ ear/otoliths.html Extremely oversimplified schematic of the orientation of the otoliths meant to give one a general idea of their orientation. This is a much more accurate schematic of the otoliths, showing their orientation in 3 dimensions.  The utricle is approximately in the horizontal plane.  The utricle is not entirely horizontal, and the saccule is somewhat tilted.  The striola in each case is indicated by the dotted line.  Detect horizontal motions (left and right acceleration, e.g., driving a car).  The saccule in the sagittal plane.  Detect vertical translational motions (up and down acceleration; e.g., elevator) Video Library/Physiology/Neurophysiology/Balance: Otolith Organs  Striola: The line found in both the sacculus and utricle that divides the hair cells into two populations with opposing hair bundle polarities. 15  Macula and Otolithic Membrane:  Both the utricle and saccule contain a specialized region called the macula. The macula contains hair cells and supporting cells.  The hair cells are topped with hair bundles that are embedded in a gelatinous layer.  Above the gelatinous layer lies a membrane called the otolithic membrane, which contains otoconia (small calcium carbonate crystals).  Function:  The otolithic organs detect linear acceleration and changes in head position.  When the head tilts → otolithic membrane moves relative to the hair cells due to gravity. This movement bends the hair bundles → generates a https://www.ncbi.nlm.nih.gov/books/NBK10792/ (A) Cross section of the utricular macula showing hair bundles projecting into the gelatinous layer when the head is level. (B) Cross section of the utricular macula when the head is tilted. (C) Orientation of the utricular and saccular maculae in the head; arrows show orientation of the kinocilia. signal in the hair cells.  This signal is then transmitted to the brain via the afferent nerve fibers of the vestibular component of cranial nerve number VIII, the vestibulocochlear nerve.  Specificity:  Macula sacculi measure vertical translational motions, while the macula utriculi measure horizontal motions. Video Library/Physiology/Neurophysiology/Balance: Otolith Organs 16  In the utricular macula, the kinocilia are directed toward the striola.  In the saccular macula, the kinocilia point away from the striola.  The hair cells align with respect to the kinocilium.  Note that, given the utricle and sacculus on both sides of the body, there is a continuous representation of all directions of body movement. https://www.ncbi.nlm.nih.gov/books/NBK10792/ (A) Cross section of the utricular macula showing hair bundles projecting into the gelatinous layer when the head is level. (B) Cross section of the utricular macula when the head is tilted. (C) Orientation of the utricular and saccular maculae in the head; arrows show orientation of the kinocilia. 17 Video Library/Physiology/Neurophysiology/Balance: Otolith Organs https://www.ncbi.nlm.nih.gov/books/NBK10792/ Forces acting on the head and the resulting displacement of the otolithic membrane of the utricular macula.  For each of the positions and accelerations due to translational movements, some hair cells will be maximally excited, whereas another set will be maximally inhibited.  A tilt along the axis of the striola will excite the hair cells on one side while inhibiting the hair cells on the other side.  Note that head tilts produce displacements similar to certain accelerations. 18 Video Library/Physiology/Neurophysiology/Balance: Otolith Organs Vestibular pathway  The generated potentials are transferred from the first neuron as part of the vestibulocochlear nerve to the vestibular nuclei inside the rhombencephalon and to the second neuron.  From this point on, the crossed and uncrossed pathways continue on to the nucleus ventralis posterior of the thalamus.  The impulses are then transmitted to the vestibular areas of the cerebrum. Impairment of vestibular function.  Damage due to the loss of vestibular hair cells will impair vestibular function.  Damage to the vestibular nuclei will impair vestibular function.  Damage to cranial nerve VIII will impair vestibular function. 19 Resources  Lecturio  Ganong's Review of Medical Physiology, 26th ed.  Quantitative Human Physiology (2012) book - Chapter – 4.7 – Hearing  Article: The Otolith Organs: The Utricle and Sacculus 20