CAP 53 3/5: Órgano de Corti l Fisiología de Guyton

Organ of Corti Function and Structure

In this section, the video discusses the function and structure of the organ of Corti located within the cochlea.

Organ of Corti Location and Composition

• The organ of Corti is situated inside the cochlea, which consists of three tubes forming a large coiled structure.

Cochlear Cavities and Divisions

• Within the cochlea, there are three cavities: vestibular branch, middle ramp or cochlear duct, and tympanic ramp.

• The middle ramp or cochlear duct houses the organ of Corti.

• A membrane called the basilar membrane rests beneath the organ of Corti.

• The vestibular ramp is separated from the middle ramp by Reissner's membrane.

• Between the middle ramp and tympanic ramp lies the basilar membrane.

Function of Organ of Corti

This part delves into the primary function and significance of the organ of Corti in converting vibrational responses into nerve impulses.

Role and Importance

• The organ of Corti converts vibrational responses from the basilar membrane into nerve impulses through hair cells known as sensory receptors.

• These hair cells are primarily responsible for this conversion process.

• Two types of hair cells exist: inner hair cells (approx. 3500 per cochlea) arranged in a single row, and outer hair cells (up to 12000 per cochlea) organized in multiple rows.

• Inner hair cells receive around 90-95% of nerve fibers from the cochlear nerve, crucial for their sensory function.

• Outer hair cells amplify faint sounds while reducing excessively loud noises to protect the inner ear from damage.

Hair Cell Characteristics

• Inner hair cells have a size of approximately 12 micrometers each, whereas outer hair cells measure about 8 micrometers in size.

• Both types receive nerve fibers but serve distinct functions: inner cells convert vibrations to nerve impulses while outer cells amplify sound waves delicately to prevent harm to hearing organs.

Understanding the Mechanism of Cochlear Function

In this section, the intricate process of cochlear function is explained, detailing how various structures within the ear interact to facilitate hearing.

Cochlear Function Process

• The elevation of the vestibular cavity causes the reticular membrane to rise, leading to movement in the Corti's pillars towards the modiolus, resulting in a reverse movement of stereocilia.

• Stereocilia are rigid and connected to the tectorial membrane; thus, when hair cells move inward, stereocilia remain fixed in position.

• As the basilar membrane ascends towards the vestibular ramp, it triggers ciliary movement, causing depolarization in both outer and inner hair cells.

• The basilar membrane elevation initiates a shift in structures within the cochlea, culminating in outward movement of hair cells.

• Conversely, when the basilar membrane descends towards the inferior ramp, it induces hyperpolarization by moving hair cells inward.

Role of Outer Hair Cells in Hearing Amplification

This segment delves into the significance of outer hair cells in amplifying sound and their impact on hearing acuity.

Outer Hair Cells Amplification

• Despite being fewer in number than inner hair cells, outer hair cells play a crucial role as they amplify sounds through their function.

• Malfunctioning outer hair cells can lead to hypoacusis due to their role in stiffening or relaxing the basilar membrane for sound transmission.

Mechanism of Inner Hair Cells Sensory Transduction

Exploring how inner hair cells convert mechanical vibrations into neural signals for auditory perception.

Inner Hair Cells Sensory Conversion

• Inner hair cells transform vibrational movements from the basilar membrane into neural impulses essential for auditory processing.

Understanding the Mechanism of Hearing

In this section, the process of hearing and how sound waves are converted into nerve impulses are discussed in detail.

Membrane Movement and Channel Activation

• The membrane must be open for the process to occur.

• As the basilar membrane ascends, cilia move outward, opening ion channels.

• Potassium channels open due to filament tension, leading to cell depolarization.

Nerve Impulse Generation

• Cell depolarization triggers glutamate vesicle release towards nerve fibers.

• Glutamate release at synapse generates a nerve impulse.

Role of Potassium in Hearing Mechanism

This part delves into the significance of potassium levels and potentials in the hearing mechanism.

Potassium Levels and Endolymph Function

• Understanding nuclear potential is crucial for action potential generation.

• Endolymph rich in potassium is vital for Corti organ activation.

Electrical Potential Differences

• Endolymph has high potassium levels with a membrane potential of 80mV.