CSDS 131 - Anatomy Quiz

Outer ear function

responsible for gathering sounds from the environment and funneling them into the auditory system

Outer Ear importance

shapes sound energy to enhance the acoustical properties for better understanding of speech

Anatomy of Outer Ear

Auricle (pinna)

External Auditory Canal (EAC): Tympanic Membrane (eardrum)

The Auricle

made entirely of cartilage, covered with skin

Key landmarks: helix, antihelix, tragus, lobule

Functions to collect and direct sound waves in the ear canal

Assists in sound localization - determine the direction of sounds

Helix

outer rim of the ear

Antihelix

a curved prominence parallel to the helix

Tragus

a small pointed eminence of the external ear

Lobule (ear lobe)

the lower fleshy part

External Auditory Canal (EAC)

Approximately 1 inch (2.5 cm) in length in adults

Contains two sections: Outer cartilaginous portion & Inner Bony Portion

Functions as a resonator, enhancing sounds betwen 2000 to 7000 Hz

Outer Cartilaginous portion

contains hair follicles and ceruminous glands

Inner Bony Portion

lined with skin, lacks hair and glands (very sensitive)

Tympanic Membrane (eardrum)

thin concave and semi-tranparent membrane

Divide into pars tensa and pars flaccida

Vibrates in response to sound waves, transmitting these vibrations to the ossicles in the middle ear

Pars tensa

the large tense portion

Pars flaccida

the smaller, more flexible part

Physiology of the Outer Ear

enhances sound frequencies important for human speech (2000-5000 Hz)

EAC serves to protect the delicate TM from foreign objects and trauma

natural oils and cerumen produced in EAR help maintain the ear’s cleanliness by trapping dust and debris

“funnel for sound”

Middle Ear Function

an air-filled cavity that plays a crucial role in hearing by transmitting sound vibrations from the outer ear to the inner ear

Middle Ear Location

it is located between the external auditory canal and the inner era

Anatomy Structure of the Middle Ear

almost an oval, air fill space about 2 cm³ in volume, roughly one-half inch hight, wide and one-quarter inch deep

Anatomy Boundaries of the Middle Ear

Roof: thin layer of bone separating it from the brain

Floor: located above the jugular bulb

Anterior Wall: Adjacent to the carotid artery

Medial Wall: Next to the labyrinth of the inner ear

Posterior Wall: Near the mastoid process

Lateral Wall: Contains the tympanic membrane

Epitympanic Recess: the space in the middle ear above the tympanic membrane

Key Components of the Middle Ear

Ossicles: Malleus, Incus, Stapes

Eustachian Tube

Middle Ear Muscles: Stapedius Muscles, Tensor tympani muscle (both contract medially and bilaterally in response to loud sounds)

Malleus

the manubrium is embedded in the tympanic membrane

Incus

connects the malleus to the stapes

Stapes

footplate fits into the oval window, transmitting vibrations to the inner ear

Eustachian Tube

connects the middle ear to the nasopharynx

Eustachian Tube anatomy

lined with ciliated epithelium, the superior one-third is bony and the inferior two-thurds is cartilaginous

Stapedius muscle

controls the stapes’ movements, reduces vibrations, and protects the inner ear from loud sounds

Tensor tympani muscle

tenses the tympanic membrane by pulling the malleus medially

Physiology of the Middle Ear

Sound transmission

Impedance Matching

Pressure Equalization

Protective Mechanism

Sound transmissions

the middle ear transforms sound energy from air to fluid in the cochlea (hydraulic process)

Impedance Matching

the tympanic membrane’s larger surface area compared to the oval window concentrates sound pressure

the level action of the ossicles amplifies sound pressure by a factor of 23 (approximately 30 dB gain)

Pressure Equalization

Eustachian tube maintains equal air pressure to optimize the movement of the tympanic membrane and ossicles

Dysfunction can cause a sensation of fullness, pain, and possible rupture of the tympanic membrane

Protective mechanisms

The acoustic reflex involves contraction of the stapedius muscle in response to loud sounds, protecting the inner ear from potential damage

Non-Auditory Middle Ear Anatomy

Facial Nerve (VII Cranial Nerve)

Chorda Tympani Nerve

Facial Nerve

runs alongside the auditory nerve, with a branch (chorda tympani) that provides taste sensation to the anterior two-thirds of the tongue

Chorda Tympani Nerve

Often encountered in the middle ear surgery and may be sacrificed, causing temporary taste disturbances

Inner ear function

essential for both hearing and balance

Inner Ear components

consists of the cochlea (responsible for hearing) and the vestibular system (responsible for balance)

Inner ear location and structure

In the temporal bone

Consists of a bony labyrinth filled with a fluid called perilymph and a membranous labyrinth filled with endolymph

Inner ear key parts:

Cochlea

Vestibule

Semicircular Canals

Cochlea

spiral-shaped organ responsible for converting sound waves into nerve impulses

It contains three fluid-filled chambers: scala vestibuli, scala media, and scala tympani

Vestibule

the central part of the bony labyrinth, which contains the utricle and saccule, two strcutres involved in balance

Semicircular Canals

three looped structures oriented at right angels to each other, filled with endolymph and responsible for detecting rotational movements

detect angular acceleration (rotational movements). Each canal has an enlarged area called the ampulla, which contains the crista, an end organ responsible for sensing rotational movement

Vestibular Mechanism Function

the vestibular system maintains balance and spatial orientation by dectecting changes in head position and movement

Vestibular Mechanism Components

Utricles and Saccule

Semicircular Canals

Utricles and Saccule

membranous sacs within the vestibule that detect linear acceleration and head position relative to gravity (detect elevator moves up and down)

Physiology of Balance

is maintained through inputs from the vestibular system, visual system, and proprioceptive information rom muscles and joints

Movement of fluids within the vestibule and semicircular canals stimulates hair cells, which send signals to the brain to interpret balance and spatial orientation

Dysfunction can lead to vertigo and nystagmus (involuntary eye movements)

Auditory Mechanism

Cochlea

Scala Media

Scala Vestibuli and Scale Tympani

Organ of Corti

Basilar Membrane

Scala Media (cochlear duct)

filled with endolymph and houses the organ of Corti, the sensory organ of hearing

Scala Vestibuli and Scala Tympani

filled with perilymph and communicate at the apex of the cochlea through the helicotrema (PEP)

Organ of Corti

Located on the basilar membrane and contains hair cells (inner and outer) that convert mechanical energy into electrical signals.

Inner hair cells primarlily responsible for sending auditory signals to the brain

outer hair cells enhance sound sensitivity and frequency discrimination

Basilar Membrane

Varies in width and stiffness along its length, allowing it to respond to different frequencies

Movement of this causes deflection of hair cells, initiating the process of hearing

Physiology of Auditory mechanism

Sound transmission: sound waves cause the stapes to move, psuhing the oval window and creating waves in the perilymph

Theory of Tonotopicity

Electrical Potentials: different fluids in the cochlea have unique ionic compositions, crucial for generating the electrical potentials needed for signal transductions, the cochlear microphonic and action potential are critical electrical signlas that represent the intital stages of auditory processing

Theory of tonotopicity

Because we dectedct frequencies at certain parts of the cochlea we could theoretically point to a certian part and determine what Hz is located there

Higher frequencies near the base

Lower frequencies near the apex

The Vestibulocochlear Nerve and Pathways Function

The auditory nerve (8th cranial nerve) and central auditory pathways are essential for transmitting sound information form the ear to the brain and processing auditory information

The Vestibulocochlear Nerve and Pathways Components

the auditory nerve consists of two main parts: the cochlear nerve (responsive for hearing) and the vestibular nerve (responsible for balance)

Anatomy of the 8th Cranial Nerve Structure

The auditory nerve passes from the cochlea through the internal auditory canal, beginning at the cochlear modiolus and terminating at the brain’s base

The nerve fibers form a cylindrical bundle:

basal fibers: form the outer portion of the nerve trunk (high frequencies)

apical fibers: form the center of the nerve trunk (low frequencies)

The internal auditory canal also contains the vestibular portion of the 8th nerve, the internal auditory artery, and the facial nerve (7th cranial nerve)

Anatomy of the 8th Cranial Nerve Pathway

The auditory extends beyond the internal auditory canal to attach to the brainstem at the cerebellopontine angle

At this junction the auditory and vestibular portions of the 8th nerve separate

Cochlear nerve fibers ascend to the ventral cochlear nucleus and descend to the dorsal cochlear nucleus

Physiology of the 8th Nerve Ascending pathways

provide stimulation from one ear to both sides of the brain, allowing bilateral processing of auditory information

multiple crossover points (decussations) ensure that auditory signals are represented on both sides of the brain

Physiology of the 8th Nerve Descending Pathways

carry feedback signals from the brain to the cochlea and other lower audiotry centers

This feedback can be inhibitory or excitatory, modifying the response of neurons to incoming sound stimuli