Mechanism of Hearing (presentation)

Presentation on mechanism on hearing

1. Mechanism of Hearing P resented by: Roshan Timilsina B .pharmcy 2 nd sem . Pharmaceutical seminar 1 st Pharmaceutical seminar 1st 1 7/13/2018

2. Contents: INTRODUCTION FUNCTIONAL ANATOMY OF DIFFERENT PARTS OF EAR PHYSIOLOGY OF HEARING CENTRAL AUDITORY PATHWAYS CONCLUSION REFRESENCES Pharmaceutical seminar 1st 2 7/13/2018

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. Pharmaceutical seminar 1st 3 7/13/2018

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 the response to the vibrations and send electrical signals along the auditory nerve to the brain which converts the vibrations into sound we can understand. Pharmaceutical seminar 1st 4 7/13/2018

5. Anatomy of ear Pharmaceutical seminar 1st 5 7/13/2018

6. Ear: The ear is the organ of the hearing as well as balancing anatomically. The ear is divided into three parts. The external ear The middle ear The inner ear Pharmaceutical seminar 1st 6 7/13/2018

7. The external ear: The external ear is formed by 2 parts i.e Auricle or pinna The external acoustic meatus Tympanic membrane Pharmaceutical seminar 1st 7 7/13/2018

8. Role of external ear in hearing The pinna: It is the first part of ear that reacts with sound .The function of pinna is to act like funnel and assist in directing the sound further into the ear. The pinna is essential due to the difference in pressure inside and outside the ear. Pharmaceutical seminar 1st 8 7/13/2018

9. The ear cannel: Once the sound waves have passed the pinna, they move two to three centimetres into the auditory canal before hitting the eardrum, also known as tympanic membrane. The function of ear canal is to transmit sound from pinna to the eardrum. Pharmaceutical seminar 1st 9 7/13/2018

10. CONTINUE… THE EARDRUM: Ear drum is the end point of the external ear. The eardrum is extremely sensitive and pressure from sound wave makes the ear drum vibrate. The auditory canal is slightly curved in order to protect the eardrum and also it automatically amplifies low and less penetrating sound of human voice. Pharmaceutical seminar 1st 10 7/13/2018

11. The middle ear Middle ear or tympanic cavity is a small , narrow, irregular compressed chamber situated within the temporal bone. It is separated from external auditory meatus by tympanic membrane. Middle ear consists of the following structures. Auditory ossicles Auditory muscles Eustachian tube Pharmaceutical seminar 1st 11 7/13/2018

12. Role of middle ear in hearing The middle ear is the part of ear between the eardrum and the oval window. The middle ear transmit the sound from the outer ear to inner ear. Bones of the middle ear: The vibrated waves from the eardrum are transmitted further into the ear via three bones .they are: Malleus Incus Stapes These three bones forms a kind of bridge and is connected to the oval window. Pharmaceutical seminar 1st 12 7/13/2018

13. CONTINUE… THE OVAL WINDOW: The main function of the oval window is to amplify the sound before they move to inner ear . THE ROUND WINDOW: It allows fluid in the cochlea to move THE EUSTACHIAN TUBE: The function of eustachian tube is to equalise the air pressure inside and outside the ear. Pharmaceutical seminar 1st 13 7/13/2018

14. The inner ear: Internal ear is a membranous structure enclosed by a bony labyrinth in petrous part of temporal bone It consists the sense organs of hearing and equilibrium Cochlea is the sense organ for hearing Organ of corti which is the receptor organ for hearing is situated in cochlea inside inner ear Pharmaceutical seminar 1st 14 7/13/2018

15. ROLE OF INNER EAR IN HEARING The inner ear is the innermost part of the ear which consists of the cochlea, the vestibular and auditory nerve. COCHLEA : The cochlea resembles a snail shail which is filled with fluid. When the fluid moves inside the cochlea , thousands of microscopic hair fibres comes in motion. The hair fibres send auditory nerve which is connected to the auditory center of the brain. In cochlea sound waves are transformed into electrical impulses which are sent to brains The brain then translets the impulses into sound that we know and understand Pharmaceutical seminar 1st 15 7/13/2018

16. Physiology of Hearing: Physiology of hearing can be discussed as follows. Stimuli Conduction of sound waves Transduction of sound waves Neural transmission of signals Encoding of signals Pharmaceutical seminar 1st 16 7/13/2018

17. Stimuli or sound waves: Stimuli for the receptor of hearing are sound waves. Sound is a form of energy produced by a vibrating object. Physical properties of sound : range: range of human hearing is appox 20-20000 hertz. Pitch: is the subjective produce by frequency of sound. Higher the frequency greater the pitch. Frequency: number of waves per second. Pharmaceutical seminar 1st 17 7/13/2018

18. CONDUCTIONS OF SOUND WAVE: Role of external ear: Pinna collects and reflects the sound waves into the external auditory meatus. External auditory meatus conducts the sound waves to tympanic. Its s-shaped course helps in amplyfing the sound. Role of middle ear: Conduction of sound stimulus by tympanic membrane to ear ossicles. Tympanic membrane vibrations are transmitted Pharmaceutical seminar 1st 18 7/13/2018

19. Transduction of sound wave: Transduction of mechanical sound wave into electricl signals occurs in the organ of corti of inner ear Sound wave entering the inner ear spread along the scala vestibulei as traveling wave. As the sound energy passes from scala vestibuli to scala tympani, it causes the basilar membrane to vibrate. The up and down moments of the basilar membrane in turn causes the organ of corti to vibrate up and down. The bending of stereocilla stimulates the hair cells Pharmaceutical seminar 1st 19 7/13/2018

20. NEURAL TRANSMISSION OF SIGNALS: The electrical signals from hair cells are transmitted through a complex auditory pathway to the auditory cortex. Pharmaceutical seminar 1st 20 7/13/2018

21. Neural processing of auditory information: In the auditory cortex the sound wave in the form of nerve impulse is processed and perceived. Neural processing of auditory information involves : Encoding of frequency ( pitch determination) Encoding of intensity (determination of loudness) Feature detection and Localization of sound in space Pharmaceutical seminar 1st 21 7/13/2018

22. CONTINUE…. In this section the wave frequency are converted into electrical signals . Hair cells present in the cochlea of the inner ear is responsible for this. The electrical singals are carried to the auditory center in the brain through vestibulocochlear nerve.it is a cranial nerve which enters into the brainstem just beneath the cerebellum. The auditory center in the brain converts the wave signals into sound that we can understand. Pharmaceutical seminar 1st 22 7/13/2018

23. Auditory Nervous pathway Pharmaceutical seminar 1st 23 7/13/2018

24. Auditory nervous pathways The auditory pathways conveys the special of hearing. Information travels from the receptor in the organ of corti of the inner ear to the central nervous system carried by the vestibulocochlear nerve. This pathway ultimately reaches the primary auditory cortex for conscious perception in auddition. Pharmaceutical seminar 1st 24 7/13/2018

25. CONCLUSION: The pinna funnels sound wave into the ear canal. The sound waves will travel to the tympanic membrane. The mallus will receive the sound and amplify the vibrations across the ossicles in the middle ear. The osicles push the sound waves with greater vibrations to the oval window. These vibrations in the oval window will generate fluid within the vestibular duct to move the waves into cochlear duct. These wave cause tectorial membrane to bounce. And also movement of basilar membrane cause hair cells to bend Pharmaceutical seminar 1st 25 7/13/2018

26. Continue… 6. When the hair cell bend, ion channel open and release neurotransmitters into the synapse with the sensory neurone. Causing it to change the rate of AP firing to the brain via cochlear nerve. The cochlear nerve carries the impulses to primary auditory neurons in the medulla . Then the info will go to the secondary neurons in the midbrain and thalamus before projecting into the auditory cortex Pharmaceutical seminar 1st 26 7/13/2018

27. REFRESENCES 1. Tortora GJ and Derrickson BH (2009), Principles of Anatomy and Physiology ( 12 th Ed.), Danvers and Wiley India Pvt. Ltd, 332-336. 2. KC T and Gautam R(2014), Essential Text Book of Anatomy and Physiology (1 st Ed.),Samiksha Publication Pvt. Ltd, 191-194. 3. URL: http://drfasih.com/mechanism-of-hearing/ (Assessed on July 09, 2018) .   Pharmaceutical seminar 1st 27 7/13/2018

28. ANY QUESTIONS ???? Pharmaceutical seminar 1st 28 7/13/2018