Hearing

Special Senses: Hearing

Slide 1: Introduction to Special Senses Hearing

Structures Involved

  • Outer Ear:

    • Composed of the auricle (pinna) which collects and directs sound waves, leading to the eardrum (also known as the tympanic membrane).

    • Function: Gathers sound from the environment and channels it toward the eardrum.

  • Middle Ear:

    • Contains three tiny bones called ossicles that amplify sound vibrations.

  • Inner Ear:

    • Includes the cochlea, involved in hearing, and semicircular canals, responsible for balance.

Slide 2: Learning Objectives

  • Describe structures of the outer ear and their functions.

  • Describe structures of the middle ear and their functions.

  • Explain anatomy of the cochlea and how sounds are detected.

  • Differentiate between conductive and sensorineural hearing loss.

  • How to remember: Think of the ear as a series of funnels and pathways focusing sound inward.

Slide 3: The Ear Anatomy Overview

  • External Ear:

    • Refers to all structures leading up to the eardrum.

  • Middle Ear:

    • Contains ossicles responsible for transmitting sound to the inner ear.

  • Inner Ear:

    • Comprises cochlea (for hearing) and semicircular canals (for balance).

    • The lateral 2/3 of the ear canal is curved which helps sound travel effectively.

    • The medial 1/3 is bony without glands, which can lead to dryness and irritation.

Slide 4: External Ear Structure

  • Auricle (Pinna):

    • The visible part of the ear, made of elastic cartilage.

    • Function: Collects and directs sound waves into the ear canal, helping in sound localization.

  • Ear Canal (External Auditory Meatus):

    • Lateral 2/3: Curved and cartilaginous, contains glands that produce earwax (cerumen), which prevents itching, moisturizes the canal, and helps repel water.

    • Medial 1/3: Bony structure without glands, leading to dryness.

    • Self-Cleaning: Lined with epithelial cells that migrate outward to keep the canal clean.

    • Note: “Ingrate laterally” refers to how the ear canal is directed sideways to help funnel sound towards the eardrum.

Slide 5: Tympanic Membrane (Eardrum)

  • Characteristics: Highly mobile, flexible, and cone-shaped.

  • Examination: A healthy tympanic membrane shows a characteristic cone of light and is concave with the center pushed inwards (displaced medially).

Slide 6: Diseases of Middle Ear

  • Common Issues:

    • Partial Effusion: Accumulation of fluid in the middle ear without infection; may cause discomfort.

    • Complete Effusion: Severe fluid buildup leading to significant issues like hearing loss.

    • Ruptured Tympanic Membrane: Can cause pain and hearing loss.

Slide 7: Anatomy of the Middle Ear

  • Components:

    • Air-filled chamber in the temporal bone.

    • The ossicles amplify sound vibrations (discussed further in next slide).

    • Oval Window: The membrane that the stapes presses against to transmit sound vibrations from the ossicles into the cochlea.

Slide 8: Auditory Tube (Eustachian Tube)

  • Function: Connects the middle ear with the throat (pharynx).

  • Role: Equalizes pressure on either side of the eardrum.

  • Aging Effect: Its function changes with age, potentially affecting pressure regulation.

Slide 9: Ossicles Structure

  • Ossicles: Three tiny bones in the middle ear

    • Malleus: Attached to the tympanic membrane (eardrum).

    • Incus: Connects the malleus to the stapes.

    • Stapes: Connects to the oval window, transmitting sound vibrations into the inner ear.

      • Note: The stapes is located at the base of the oval window and is critical in the process of sound transmission.

Slide 10: Inner Ear Hearing Structures

  • Cochlea: A spiral-shaped, fluid-filled structure that contains mechanoreceptors responding to auditory waves.

  • Mechanoreceptors: Specialized sensory cells that detect sound vibrations; hair cells within the cochlea play a crucial role by translating these vibrations into signals sent to the brain.

Slide 11: Cochlear Duct

  • Structures: Includes the vestibular membrane, tectorial membrane, and basilar membrane.

Slide 12: Spiral Organ

  • Hair Cells in the Cochlea: Cells that convert sound vibrations into neural signals.

  • What do they do:

    • Controlled by the cochlear nerve, which sends information to the brain.

    • They push against the tectorial membrane, allowing for signal transformation.

Slide 13: Hearing Process

  1. Sound travels in waves through air and is directed into the ear by the auricle.

  2. Sound traverses through the external auditory meatus to the tympanic membrane.

  3. The tympanic membrane vibrates when sound hits it, amplifying the sound through the malleus, incus, and stapes before it reaches the oval window.

  4. The oval window produces waves in the cochlea, affecting the vestibular membrane.

  5. This causes a vibration in the basilar membrane.

  6. Hair cells in the spiral organ detect this movement creating action potentials.

  7. Action potentials are conveyed via the vestibulocochlear nerve to the brain.

  8. The brain perceives and interprets the sound.