Comprehensive PRAXIS 5343 Audiology Study Guide

Examination Overview and Foundation Content

The PRAXIS 5343 Audiology test is a computer-based examination that can be taken at home or in a testing center. It consists of $120$ selected-response (multiple choice) questions administered over a $2$-hour period. The curriculum is divided into five core sections: Foundations ($24$ questions) covering acoustics, anatomy, physiology, pathophysiology, and psychometrics; Prevention and Screening ($12$ questions) focusing on education, risk identification, and program performance; Assessment ($42$ questions) including behavioral and physiologic evaluations, vestibular testing, and communication of results; Intervention ($30$ questions) covering treatment planning, device selection, and rehabilitation for auditory and vestibular impairments; and Professional and Ethical Responsibilities ($12$ questions) regarding legal, ethical, and interprofessional practice.

Basic Anatomical Planes and Terminology

To understand the anatomy of the auditory system, one must be familiar with anatomical orientation. Superior refers to structures located above, while inferior refers to those below. Anterior designates the front, and posterior designates the back. Medial structures are closer to the midline, whereas lateral structures are further away. Anatomical planes include the sagittal plane, which divides the body into left and right; the coronal plane, which divides the body into front and back; and the transverse plane, which divides the body into top and bottom. Extrinsic refers to structures outside an organ, while intrinsic refers to those inside. The outer ear anatomy includes the pinna components: scapha, helix, antihelix, triangular fossa, concha, tragus, antitragus, and the auricular lobule (earlobe).

Anatomy and Function of the External Ear

The External Auditory Meatus, or ear canal, is approximately $2.5-3.0\,cm$ long and $0.75\,cm$ in diameter. The outer $1/3$ is cartilaginous and contains sebaceous and ceruminous glands, while the inner $2/3$ is bony, housed by the tympanic and squamous portions of the temporal bone and the condyle of the mandible. In children, the bony portion is not mature until approximately $3$ years of age. The canal has an "S" shape and becomes narrower as it approaches the tympanic membrane. It is innervated by several cranial nerves: V (Trigeminal), VII (Facial), IX (Glossopharyngeal), and X (Vagus). Nerves IX and X are notably responsible for the gag reflex or fainting responses.

The functions of the external ear include collecting and funneling sound into the canal and providing an amplification boost of approximately $15-20\,dB$. This gain is due to the decrease in area, which increases sound pressure, especially for frequencies at or above $2000\,Hz$. The resonance of the ear canal provides the greatest amplification boost at approximately $3\,kHz$. Frequency-specific gain is also influenced by the head and torso, a concept known as the Head Related Transfer Function (HRTF). The ear is sensitive to the direction of sound, or azimuth, which is critical for localization. For low-frequency sounds (below $2\,kHz$), localization relies on Interaural Timing Differences (ITDs), which are speed-of-sound dependent. For high-frequency sounds (above $2\,kHz$), localization relies on Interaural Level Differences (ILDs) and the head shadow effect.

Anatomy and Physiology of the Middle Ear

The middle ear is an air-filled space consisting of the tympanic cavity (proper and attic), the aditus ad antrum (a narrow passage leading to the antrum), and the mastoid air cells. The chorda tympani, a branch of the facial nerve responsible for taste, runs along the top of the eardrum. The tympanic membrane (TM) is a thin, cone-shaped, oval membrane roughly $0.1\,mm$ thick and $8-9\,mm$ in diameter. It is suspended by the annular ligament within the bony annulus. The ossicular chain consists of the malleus, incus, and stapes, which are suspended by the tensor tympani and stapedius tendons. The Eustachian tube, which is shorter and flatter in children, connects the middle ear to the nasopharynx to provide aeration, drainage, and pressure equalization. Its initial $1/3$ is osseous and remains open, while the inner $2/3$ is cartilaginous and closed, meeting at a point called the isthmus.

The middle ear serves as an impedance-matching transformer to overcome the energy loss that occurs when sound moves from air to the fluid-filled cochlea. Without this mechanism, significant energy would be reflected. The system provides roughly $33\,dB$ of gain through three mechanisms: the area advantage (the largest contributor), curved membrane buckling, and the lever action of the ossicles (the malleus is longer than the incus). The Middle Ear Transfer Function (METF) resembles a band-pass filter with peak transmission at approximately $1\,kHz$. Low reflectance occurs between $1-4\,kHz$, with increased reflectance at frequencies below $1\,kHz$ due to stiffness and above $4\,kHz$ due to mass.

Anatomy and Physiology of the Inner Ear

Housed within the temporal bone, the inner ear comprises the osseous cochlea, which resembles a snail shell with $2.2-2.9$ turns. It coils around a bony core called the modiolus. The membranous cochlea contains different fluids with specific ionic compositions: perilymph (high $Na+$, low $K+$, $0\,mV$ potential), endolymph (low $Na+$, high $K+$, $80\,mV$ potential), and cortilymph inside the tunnel of Corti. The Organ of Corti is the sensory organ of hearing, containing hair cells, supporting cells, and the stria vascularis, which maintains the endolymph's charge.

There are two types of hair cells. Outer hair cells (OHCs) are cylinder-shaped, embedded in the tectorial membrane, and have a resting potential of $-60\,mV$. They act as the cochlear amplifier via electromotility driven by the prestin motor protein, providing gain for soft sounds and sharpening frequency tuning. Inner hair cells (IHCs) are flask-shaped, suspended in endolymph, and have a resting potential of $-40\,mV$. Upon depolarization, IHCs release the neurotransmitter glutamate to communicate with Type I afferent neurons. The basilar membrane (BM) is tonotopically organized; high frequencies displace the base, and low frequencies displace the apex. As sound levels increase, the BM displacement broadens and the traveling wave peak shifts basally.

The Auditory Nerve and Central Pathways

The auditory nerve (Cranial Nerve VIII) contains $25,000-30,000$ neurons. Their cell bodies are located in the spiral ganglion. Type I afferent neurons represent $90-95\%$ of the nerve, are myelinated, and synapse on a single IHC. Type II afferent neurons represent $5-10\%$ of the nerve, are unmyelinated, and synapse on multiple OHCs. The nerve travels through the internal auditory meatus alongside the facial nerve (VII). Action potentials are generated through a sequence: glutamate uptake opens $Na+$ channels, leading to an excitatory postsynaptic potential (EPSP). If the threshold is exceeded, depolarization occurs (inward $Na+$), followed by repolarization (outward $K+$) and hyperpolarization. During the absolute refractory period, no further action potentials can fire.

Neurons have spontaneous firing rates categorized as low (<0.5/s), medium ($0.5-18/s$), and high (>18/s). High spontaneous rate neurons have low thresholds and narrow dynamic ranges ($40\,dB$ saturation), while low spontaneous rate neurons have high thresholds and wide dynamic ranges. Frequency is coded via "place locking" (all frequencies) and "temporal/phase locking" (<5\,kHz). The auditory pathway consists of the cochlear nerve, cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus (LL), inferior colliculus (IC), medial geniculate body (MGB), and the auditory cortex (AC). The SOC is the first place where binaural information is integrated: the Lateral Superior Olive (LSO) processes ILDs, and the Medial Superior Olive (MSO) processes ITDs.

Vestibular Anatomy and Physiology

The vestibular system includes the vestibule, which connects the auditory and vestibular portions of the inner ear. It houses the utricle and saccule for sensing linear acceleration (horizontal and vertical, respectively) and the semicircular canals (SCCs) for angular acceleration. There are three SCCs: lateral (horizontal), anterior (superior), and posterior, which work in pairs (Lateral R/L; R-Anterior/L-Posterior [RALP]; L-Anterior/R-Posterior [LARP]). The sensory structures are the maculae in the otolith organs (containing otoconia) and the cristae ampullaris in the SCCs (covered by the cupula).

Central vestibular function is governed by several reflexes and pathways. The Vestibulo-Ocular Reflex (VOR) stabilizes vision during head movement. The Vestibulo-Spinal Reflex (VSR) maintains an upright posture, and the Vestibulo-Cerebelllar Reflex (VCR) stabilizes the head relative to gravity. The vestibular nuclei (superior, lateral, medial, and inferior) distribute information throughout the central nervous system. The Superior Vestibular Nerve innervates the lateral SCC, superior SCC, and utricle. The Inferior Vestibular Nerve innervates the saccule and the posterior SCC. The cerebellum is responsible for the calibration and repair of these systems. Oculomotor movements are also critical: saccades (rapid shift), pursuit (smooth tracking), and optokinetic (sustained movement) reflexes ensure stable vision.

Embryology and Language Development

Auditory structures derive from three germ layers: the ectoderm (ear canal), mesoderm (ossicles), and endoderm (Eustachian tube). The inner ear develops from the otic placode into the otocyst. The cochlea matures from base to apex. While structures are mature at birth, myelination and central processes continue into childhood. Language development follows a critical period ($0-5$ or $7$ years). Milestones include vowel acquisition by $6$ months and consonants by $11-12$ months. Hearing loss significantly impacts phonological awareness, literacy, and vocabulary. The order of auditory behavior development is detection, discrimination, identification, and comprehension. A Speech Intelligibility Index (SII) of over $80\%$ is targeted for adequate auditory access.

Acoustics and Psychoacoustics

Sound is a longitudinal wave consisting of compressions (increased air density) and rarefactions (decreased density). Simple harmonic motion is described by amplitude (loudness), frequency ($f = \frac{1}{T}$, perceived as pitch), and phase ($0-360^{\circ}$). The wavelength ($\lambda$) is calculated as $\lambda = \frac{c}{f}$ where $c = 343\,m/s$. Complex waves consist of a fundamental frequency ($F0$) and harmonics (multiples of $F0$). Resonances of the vocal tract are called formants ($F1$ and $F2$ are most important for vowels).

Sound level is measured in decibels (dB), which is a ratio. $dB\,SPL$ (Sound Pressure Level) uses a reference of $20\,\mu Pa$. $dB\,HL$ (Hearing Level) is referenced to the median threshold of normal-hearing adults for a specific frequency. To convert, the formula is $RETSPL + HL = SPL$. Psychoacoustic concepts include: recruitment (abnormal loudness growth in sensorineural loss), binary summation (sounds are $3\,dB$ louder binaurally near threshold, $6\,dB$ at supra-threshold), and the inverse square law (doubling distance decreases sound level by $6\,dB$). Speech frequencies for comprehension range from $100-5000\,Hz$. Consonants provide clarity (high frequency), while vowels provide volume (low frequency).

Pathophysiology: Genetic and Acquired Disorders

Genetic disorders are categorized by inheritance patterns: Autosomal Dominant ($50\%$ recurrence, vertical inheritance), Autosomal Recessive ($25\%$ recurrence, horizontal inheritance, requires two copies), X-linked (male to female carrier), and Mitochondrial (maternal transmission). Connexin $26$ is the most common cause of genetic SNHL. Major syndromes include:

• Usher: vision loss and vestibular impairment.

• Waardenburg: white forelock and heterochromia.

• Pendred: enlarged vestibular aqueduct and goiter.

• Alport: kidney problems and progressive HL.

• CHARGE: coloboma, heart defects, atresia, etc.

• Treacher Collins: atresia, microtia, and facial abnormalities.

• Branchio-oto-renal (BOR): branchial cysts and renal abnormalities.

Acquired conditions include: otosclerosis (fixation of the stapes, Carhart's notch at $2\,kHz$), Meniere's disease (fluctuating low-frequency loss, vertigo, and aural fullness), acoustic neuroma (benign tumor on CN VIII, causing asymmetry), and noise-induced hearing loss (notch at $3-6\,kHz$). Vestibular disorders include BPPV (otoconia in SCCs, treated with Epley maneuver), Vestibular Neuritis (vertigo without hearing loss), and Labyrinthitis (vertigo with hearing loss).

Audiological Evaluation: Behavioral Testing

Behavioral evaluation begins with pure tone audiometry. Threshold ($\theta$) is the lowest level a patient responds to $50\%$ of the time using the modified Hughson-Westlake method ($down\,10\,dB, up\,5\,dB$). Air conduction (AC) tests the entire system, while bone conduction (BC) bypasses the outer and middle ear to test the cochlea. Standard Interaural Attenuation (IA) values are $40\,dB$ for supra-aural headphones and $60\,dB$ for inserts. Masking is required if the AC threshold of the test ear minus the IA is greater than or equal to the BC threshold of the non-test ear. Speech testing includes the Speech Recognition Threshold (SRT), using spondee words, and Word Recognition Scores (WRS), usually presented at $40\,dB\,SL$ relative to the SRT.

Pediatric testing varies by age: Behavioral Observation Audiometry (BOA) for $0-6$ months, Visual Reinforcement Audiometry (VRA) for $6-30$ months, and Conditioned Play Audiometry (CPA) for $30\,months - 5\,years$. For organic and non-organic loss, specialized tests like the Stenger (for asymmetrical loss) or the Lombard effect are utilized. In cases of malingering, the SRT and PTA usually show poor agreement (differences greater than $15\,dB$).

Audiological Evaluation: Physiologic Testing

Physiologic tests provide objective data. Tympanometry measures middle ear admittance. Type A is normal; Type B indicates fluid or perforation (depending on volume); Type As reflects stiffness (otosclerosis); and Type Ad reflects hyper-mobility (disarticulation). Acoustic Reflex Thresholds (ART) are usually $70-90\,dB$ above behavioral thresholds. Reflex decay is used to screen for retrocochlear pathology.

Otoacoustic Emissions (OAEs) measure OHC function. Distortion Product OAEs (DPOAEs) use two tones ($f1$ and $f2$) to evoke a response at $2f1-f2$. Auditory Brainstem Response (ABR) measures neural synchrony through five waves: Wave I (distal VIII nerve), Wave III (CN/SOC), and Wave V (LL/IC). ECoG (Electrocochleography) is useful for diagnosing Meniere’s via the $SP/AP$ ratio (abnormal if >0.4). Auditory Steady State Response (ASSR) is used for threshold prediction at specific frequencies. For facial nerve integrity, Electroneuronography (ENOG) is used to calculate the percentage of neural degeneration.

Vestibular Assessment and Rehabilitation

Vestibular testing includes Videonystagmography (VNG), which evaluates oculomotor function (saccades, pursuit), positioning (Dix-Hallpike for BPPV), and calorics (measuring the VOR via temperature changes in the ear canal). The acronym COWS describes caloric direction: Cool Opposite, Warm Same. Other tests include Video Head Impulse Testing (vHIT) for high-frequency SCC function, Rotary Chair for bilateral weakness, and VEMPs (Cervical and Ocular) to test the saccule and utricle respectively. Posturography (CDP) assesses the integration of visual, vestibular, and somatosensory systems. Rehabilitation for BPPV involves maneuvers like the Epley (posterior canal) or the BBQ roll (horizontal canal). General vestibular rehab focuses on adaptation and substitution exercises.

Intervention: Hearing Aids and Implantable Devices

Hearing aid (HA) candidacy is based on audiometric data, communication needs, and motivation. Components include a microphone (acoustic to electrical), amplifier (digital signal processing), and receiver (electrical to acoustic). Gain can be linear or nonlinear (compression). Wide Dynamic Range Compression (WDRC) provides more gain for soft sounds than loud sounds. Verification is conducted via Real Ear Measures (REMs) to ensure prescriptive targets (like NAL-NL2 or DSL) are met. Validation uses questionnaires like the COSI or APHAB.

For those who do not benefit from HAs, Cochlear Implants (CIs) are an option. CIs bypass hair cells to stimulate the auditory nerve directly. Programming involves establishing T-levels (threshold) and C/M-levels (comfort). Bone Anchored Hearing Aids (BAHA) are used for conductive/mixed losses or single-sided deafness. Hearing Assistive Technology Systems (HATS), such as FM or RM systems, improve the signal-to-noise ratio in difficult listening environments.

Professional and Ethical Responsibilities

Audiologists must adhere to the ASHA Code of Ethics, which emphasizes patient welfare, professional competence, and integrity. Legal mandates include HIPAA (privacy), FERPA (educational privacy), and IDEA (Individuals with Disabilities Education Act). IDEA Part C covers infants ($0-3$ years) and involves an Individualized Family Service Plan (IFSP), while Part B covers school-aged children ($3-21$ years) via an Individualized Education Program (IEP). Section $504$ of the Rehabilitation Act provides accommodations for those who do not qualify for special education. Evidence-based practice (EBP) integrates research, clinical expertise, and patient values. Supervision of audiology assistants requires a licensed audiologist who retains full legal responsibility for patient care.