SIGNAL TRANSDUCTION and its biochemistry
- 1. DEPARTMENT OF BIOCHEMISTRY FACULTY OF BASIC MEDICAL SCIENCES BAYERO UNIVERSITY, KANO COURSE CODE AND TITLE ENDOCRINOLOGY AND SIGNAL TRANSDUCTION (BCH 8214) TOPIC: BIOCHEMISTRY OF HEARING PRESENTED BY HARUNA TSOHO BALA SPS/23/MBC/00016 HASHIM IBRAHIM SPS/23/MBC/00014
- 2. CONTENTS INTRODUCTION FUNCTIONAL ANATOMY OF DIFFERENT PARTS OF EAR CENTRAL AUDITORY PATHWAYS CONCLUSION REFRENCES
- 3. WHAT IS HEARING Generally Hearing is the sensation of sound. Hearing or the auditory perception is the ability to perceive sounds by detecting vibrations, changes in the pressure of the surrounding medium through time, through an organ such as the ear (Tortora, 2009).
- 4. Introduction: Ear is the main organ for hearing. sound wave enters the outer ear and cause the ear drum to vibrate. These vibrations pass along the middle ear via three small bones known as the ossicles. The ossicles amplify the vibrations and transmit them on to cochlea in the inner ear. Hair cells in the cochlea moves in response to the vibrations and send electrical signals along the auditory nerve to the brain which converts the vibrations into sound we can understand (Tortora, 2009).
- 5. ANATOMY OF THE EAR
- 6. EAR • The ear is the organ of hearing as well as balancing anatomically • The ear is divided into three parts. • The external ear • The middle ear • The inner ear. • The external ear • the external ear consist of three component • Pinna (Auricle) the visible, outer part of the ear that helps capture sound waves and direct them into the ear canal. it is made of cartilage and soft tissue.
- 7. Cont. 2. External Acoustic Meatus (ear canal) The tube-like structure that channels sound waves from the pinna to the ear drum(tympanic membrane).it is approximately 2.5 cm long in adults. 3.Tympanic Membrane (Eardrum): the thin, vibratory membrane that separates the external ear from the middle ear.it convert sound waves into mechanical vibrations.
- 8. Cont. These components work togather to direct, and transmit sound to the inner ear INNER EAR The inner ear is made up of several important components that play key roles in hearing and balance. These components include cochlea A spiral-shaped, fluid –filled structure responsible for converting sound vibration into neutral signals. It contains hair cells that detect sound waves and send electrical signals to the brain.
- 9. Inner Ear (Cochlea): Sensory Transduction Endolymph and Perilymph Endolymph: Rich in K⁺ (potassium), low in Na⁺— produced by the stria vascularis. Perilymph: Opposite composition—high Na⁺, low K⁺. This ionic gradient is essential for electrochemical transduction.
- 10. Hair Cells Located in the Organ of Corti on the basilar membrane. Stereocilia on hair cells bend in response to fluid movement caused by sound. Bending opens mechanotransduction channels (mainly involving tip links between stereocilia), allowing K⁺ and Ca²⁺ to enter the cell from endolymph.
- 11. Signal Transduction Influx of K⁺ and Ca²⁺ depolarizes the hair cell. This leads to the release of neurotransmitter lutamate at the base of the hair cell. Glutamate activates AMPA receptors on the auditory nerve fibers. Auditory nerve (cranial nerve VIII) carries the signal to the brainstem.
- 12. Neurotransmitters Neurotransmitters play a crucial role in the hearing process by transmitting signals from the ear to the brain. Sound Detection in the Cochlea Sound waves enter the ear and are transformed into mechanical vibrations, which are transmitted to the cochlea in the inner ear. Inside the cochlea, hair cells (sensory cells) detect these vibrations and convert them into electrical signals.
- 13. Neurotransmitter Release When hair cells are stimulated by sound, they release glutamate, the primary neurotransmitter in the auditory system. Glutamate is released into the synapse between hair cells and the auditory nerve fibers (spiral ganglion neurons).
- 14. Signal Transmission to the Brain The glutamate activates AMPA and NMDA receptors on the auditory nerve fibers. This triggers action potentials (nerve impulses) that travel along the auditory nerve to the brainstem, then through various brain regions (e.g., inferior colliculus, thalamus, and finally the auditory cortex).
- 15. Other Neurotransmitters Involved Acetylcholine (ACh): Used by efferent fibers (from brain to ear) to modulate hair cell sensitivity. GABA & Glycine: Inhibitory neurotransmitters used in auditory brainstem circuits to help process sound localization and timing. Dopamine & Serotonin: Also modulate auditory processing, though their exact roles are still being studied.
- 17. Conclusion • Hearing involves mechanical vibrational, fluid dynamics, ions channel function, neurotransmitters release, and electrical signaling all working in correct to allow us to perceive sound. The precise biochemistry of these processes is crucial for normal hearing, and disruptions at any stage can lead to hearing impairments.
- 18. REFERENCES 1. Tortora GJ and Derrickson BH (2009), principle of Anatomy and physiology (12th ed.), Danvers and wild indiapvt. Ltd, 332-336. 2. KC T and Gautam R(2014), essentialtext book of Anatomy and physiology (1st ed.),Samiksha publication pvt.Ltd,191-194. 3. URL: http://drfasih.com/mechanism-of- hearing/(Assessed on july 09,2018).