Fisiología de la audición👂🔊| APRENDE DE FORMA SENCILLA SOBRE CÓMO OÍMOS 🧠🎧

Exploring the Human Auditory Process

Overview of the Ear Structure

• The ear is divided into three main parts: external, middle, and inner ear. Each part plays a crucial role in hearing.

• The cochlea in the inner ear is essential for both hearing and balance, relying on specialized receptors known as hair cells. This video focuses specifically on hair cells involved in hearing.

Function of the External Ear

• The external ear consists of the auricle (or pinna), which captures sound waves and directs them to the external auditory canal. This structure resembles a labyrinth, aiding in sound capture.

• Sound waves travel through the auditory canal to reach the tympanic membrane (eardrum), marking the boundary between the external and middle ear. The eardrum vibrates in response to sound waves, facilitating sound transmission.

Mechanics of Sound Transmission

• The tympanic membrane's diagonal shape helps absorb sound wave impacts effectively, similar to how an American football player positions themselves before being tackled. This design minimizes disruption from incoming sounds.

• Following the tympanic membrane is the middle ear cavity filled with air, housing three tiny bones: malleus (hammer), incus (anvil), and stapes (stirrup). These bones convert acoustic energy into mechanical energy vital for hearing processes.

Importance of Eustachian Tube

• The Eustachian tube connects the middle ear to the nasopharynx; it typically remains closed but opens during swallowing or yawning to equalize air pressure—crucial for proper ossicle movement during hearing activities.

• Blockage or infection can lead to conditions like otitis media due to its direct connection with respiratory pathways; this highlights its significance in maintaining auditory health during illnesses such as colds.

Inner Ear Components

• Movement of ossicles is regulated by muscles that adjust their vibrations; this includes tensor tympani muscle pulling on malleus and stapedius muscle affecting stapes' position against oval window—key for effective sound transmission into inner ear structures.

• The inner ear comprises two main components: bony labyrinth filled with perilymph and membranous labyrinth containing endolymph rich in potassium—essential for sensory functions related to balance and hearing within cochlea structures like semicircular canals and organ of Corti.

Cochlea Structure

• The cochlea is a spiral-shaped structure approximately 35 mm long that resembles a snail shell; it plays a pivotal role in converting mechanical vibrations into neural signals interpreted by the brain as sound.

Cochlear Anatomy and Function

Structure of the Cochlea

• The cochlea consists of three parts: vestibular ramp, cochlear ramp, and tympanic ramp. The vestibular and tympanic ramps are filled with perilymph, while the cochlear ramp contains endolymph, which is rich in potassium.

• The Reissner's membrane separates the vestibular and cochlear ramps, whereas the basilar membrane divides the tympanic and cochlear ramps. This basilar membrane is crucial as it supports the organ of Corti containing hair cells essential for hearing.

Key Components Involved in Hearing

• The stria vascularis is located in contact with the cochlear ramp and continuously secretes potassium into the endolymph. Additionally, the auditory nerve emerges from direct contact with hair cells, particularly inner hair cells.

• Understanding these structures is vital; when uncoiling the cochlea, one can observe that the oval window directly contacts the vestibular ramp.

Sound Transmission Process

• Sound waves traveling through the external ear reach ossicles in the middle ear, ultimately moving against the stapes (stirrup), which presses against the oval window.

• Movement at this oval window displaces perilymph within the vestibular ramp, propagating through to helicotrema where it connects to tympanic ramp before being dampened at round window.

Organ of Corti Mechanics

• As perilymph moves through ramps, membranes also shift; notably, movement of basilar membrane elevates it. This elevation causes cilia on outer hair cells to interact with tectorial membrane.

• Inner and outer hair cells play distinct roles: inner hair cells primarily generate action potentials while outer hair cells produce a protein called prestin that aids in amplifying sound signals.

Signal Transduction Mechanism

• When cilia move towards kinocilium (the tallest cilium), mechanosensitive potassium channels open leading to depolarization of outer hair cells which then release prestin enhancing basilar membrane movement.

• Similarly, when inner hair cell cilia touch tectorial membrane due to ongoing movement from perilymph displacement, they also open potassium channels causing depolarization that triggers calcium influx.

Neurotransmitter Release and Auditory Pathway

• Calcium entry into inner hair cells initiates neurotransmitter release towards first-order sensory neurons—these neurons are critical for transmitting auditory information.

• Inner hair cells account for 95% of synaptic connections with first-order sensory neurons; thus their role is pivotal in converting mechanical energy into electrical signals sent to brain for interpretation.

Understanding Cochlear Function and Hearing Loss

Cochlear Structure and Sound Frequency Processing

• The cochlea is structured to differentiate sound frequencies; the rigid, narrow base responds to high-frequency sounds, while the wider, flexible apex responds to low-frequency sounds. This anatomical design allows the brain to identify different types of sounds based on where electrical impulses originate in the cochlea.

• Once sound signals reach the cochlear nucleus, they are transmitted bilaterally to various brain regions including the superior olivary complex, inferior colliculus, thalamus, and ultimately to auditory cortex areas 42 and 43 of Brodmann.

Types of Hearing Loss

• Hearing loss can be categorized into three main types:

• Conductive hearing loss: Caused by blockages in the external auditory canal (e.g., earwax).

• Central hearing loss: Results from damage to nerves along the auditory pathway from the cochlea to the brain.

• Sensorineural hearing loss: Arises from defects in inner ear structures like hair cells due to exposure to loud noises.

Sound Measurement and Impact on Hearing

• Sound is measured by frequency (in Hertz), with lower frequencies perceived as bass and higher frequencies as treble. Amplitude is measured in decibels; lower amplitudes indicate softer sounds while higher amplitudes denote louder sounds.

• Prolonged exposure to sounds above 85 decibels can lead to hearing loss because such pressure levels are too intense for hair cells in the organ of Corti. Sounds between 120-160 decibels (like gunfire) are considered painful.

Everyday Sound Levels

• Common sound levels include:

• 90-110 dB: Extremely loud (e.g., chainsaw).

• 60-80 dB: Loud but manageable (e.g., alarm clock or traffic).

• 40-50 dB: Moderate noise level (e.g., light rain).

• 30 dB or less: Very quiet (e.g., whisper).

Human Auditory Range