🥇 OÍDO 2/3. Anatomía del OÍDO MEDIO. Cadena de HUESECILLOS

Anatomy of the Middle Ear

Overview of the Ear Structure

• The ear consists of three main parts: external ear, middle ear, and inner ear. The external ear includes the pinna and external auditory canal. The middle ear is discussed in this video, while the inner ear will be covered in a subsequent installment.

Introduction to the Middle Ear

• The middle ear is defined as everything located behind the tympanic membrane, which separates it from the external ear. This section will focus on the tympanic cavity and its components.

Components of the Middle Ear

• Key structures include:

• Tympanic Cavity: Contains air-filled space behind the tympanic membrane.

• Eustachian Tube: Also known as pharyngotympanic tube; connects to the nasopharynx and helps equalize pressure in the middle ear. More details were provided in a previous video about the pharynx.

Communication Pathways

• The middle ear communicates:

• Downward through Eustachian tube with nasopharynx.

• Posteriorly via mastoid tympanic canal with mastoid portion of temporal bone.

• It is crucial for understanding how infections can spread from one area to another within these structures.

Limits of Tympanic Cavity

• The tympanic cavity has six limits resembling a cube:

• Roof (superior limit)

• Anterior limit

• Posterior limit

• Floor (inferior limit)

• Medial limit

• Lateral limit

• Each boundary plays a role in defining its structure and function within hearing processes.

Tympanic Membrane Details

Structure and Function

• The tympanic membrane serves as an external boundary for the middle ear, vibrating in response to sound waves that travel through the external auditory canal. It is attached to temporal bone's tympanic lamella, facilitating sound transmission into deeper structures of hearing.

Composition of Tympanic Membrane

• Composed of three layers:

• External layer: Epidermis facing external auditory canal.

• Internal layer: Simple cubic epithelium lining mucosa of middle ear.

• Fibrous lamella between both layers provides structural integrity during vibration events caused by sound waves.

Physical Characteristics

• Diameter approximately one centimeter; shape may vary slightly among individuals (round or oval).

• Features include:

• Tympanic Annulus: A fibrous ring around edges providing support.

• Handle of Malleus: Visible on inner face; important for transmitting vibrations further into auditory system components like ossicles.

Understanding the Tympanic Membrane and Its Anatomy

Anatomy of the Tympanic Membrane

• The tympanic membrane consists of two portions: the tense portion, which is smooth and well-inserted at the edges of the temporal bone, and the flaccid portion located between posterior and anterior folds.

• The flaccid portion is less tense than the lower part of the membrane, which is referred to as the anterior-inferior quadrant. This area reflects light in a cone shape when healthy.

• A visible cone of light in this quadrant indicates a healthy tympanic membrane; absence may suggest inflammation or otitis media.

• Key structures include the handle of the malleus (hammer), its tip forming a navel, and associated nerves like the chorda tympani, a branch of the facial nerve.

Limits of the Tympanic Cavity

External Limit

• The external limit includes not only the tympanic membrane but also an area above it known as recess and pitin panic, containing parts like heads of malleus and incus.

Roof and Floor

• The roof (tec mind) separates middle ear from cranial fossa; it's made up of a bony lamella called chin tech.

• The floor (jugular wall), formed by jugular fossa, houses important structures such as superior bulb of internal jugular vein.

Anterior Wall Structures

• In examining medial vision, three key structures are identified in anterior wall: duct for muscle passing through (muscle to hammer), entrance to Eustachian tube, and groove for carotid duct.

• This anterior wall structure provides better visibility into components like malleus muscle and tympanic tube orifice.

Posterior Wall Overview

Anatomy of the Middle Ear and Its Structures

Overview of Key Structures in the Middle Ear

• The stapes muscle is located near the pyramidal eminence, which is positioned at the back of the middle ear. The antrum and mastoid cells are also significant structures within this area.

• Communication between the tympanic cavity and the antrum occurs through a small opening known as the mastoid tympanic canal or alytus ar, facilitating auditory function.

Medial Wall of the Middle Ear

• The medial wall, referred to as the labyrinthine wall, connects the middle ear to the inner ear. This space is notably small, measuring only 2 to 6 millimeters between key structures.

• In a lateral view of this wall, several important features can be identified:

• The duct of the external semicircular canal,

• The facial nerve duct,

• The oval window (vestibular window), covered by stapes bone.

Additional Features in Medial Wall

• A bony lamella called cochlear process separates the oval window from the round window below it. Additionally, there exists a prominent structure known as tympanic promontory.

• The tympanic plexus, primarily formed by glossopharyngeal nerve fibers, is also found in this region alongside other critical components like:

• Lateral semicircular canal,

• Facial nerve canal,

• Oval and round windows.

Summary of Medial Wall Structures

• Key anatomical features include:

• Prominence left by facial nerve duct,

• Lateral semicircular duct,

• Cochlear process separating oval from round windows.

Ossicles of the Middle Ear

• The middle ear contains three ossicles: malleus (hammer), incus (anvil), and stapes (stirrup). These are crucial for sound transmission.

• Each ossicle has distinct anatomical features; for instance:

• Malleus includes handle and head with neck area defined post-head.

Detailed Structure of Malleus and Incus

• Malleus anatomy includes:

• Handle insertion point on membrane via lateral process,

• Neck following head structure.

• Incus consists of a body articulating with malleus head and branches extending horizontally/vertically. It features a lenticular process that connects with stapes.

Anatomy of the Middle Ear: Key Structures and Functions

Overview of the Bones and Their Branches

• The middle ear consists of three bones, each with one head and two branches: anterior and posterior. The anterior branch supports the base of the stirrup, which covers the oval window.

Articulations Between Ear Bones

• Two synovial joints are present in the middle ear:

• Malleolar Joint: A reciprocal socket type joint between the malleus and incus, allowing for axial movement.

• Saddle Joint: Formed between the lenticular process of the incus and head of stapes, enabling extensive mobility. This joint can theoretically allow six movements due to its design.

Stapes and Oval Window Connection

• The connection between stapes and oval window is a fibrous joint known as tympanic syndesmosis, differing from other synovial joints in terms of structure and function. It plays a crucial role in sound transmission to inner ear structures like vestibule.

Muscles Associated with Hearing

• Tensor Tympani Muscle:

• Originates from pharyngo-tympanic tube cartilage.

• Inserts into handle of malleus; innervated by a branch of lower maxillary nerve (trigeminal nerve).

• Its primary function is to tighten tympanic membrane for better hearing sensitivity.

• Stapes Muscle:

• Originates from pyramidal eminence on temporal bone.

• Inserts into neck and head of stapes; innervated by facial nerve.

• Responsible for rotating stapes outward, aiding in sound modulation within the ear.

Innervation Details

• The tympanic membrane receives sensory innervation:

• External face innervated by trigeminal (V) and vagus (X) nerves.

• Internal face primarily innervated by glossopharyngeal (IX) nerve, which also supplies mucosa in pharyngo-tympanic tube.

Vascular Supply to Middle Ear

• Blood supply to middle ear comes mainly from external carotid artery through branches such as:

• Posterior auricular artery supplying both middle and external ears.

• Anterior tympanic artery providing additional vascular support specifically to middle ear structures.