SLHS 652 Exam #4

Main synaptic structures found along the CAP

• VIIIth nerve

• Cochlear nucleus

• Superior olivary complex

• Lateral lemniscus

• Inferior colliculus

• Medial geniculate body

• Primary auditory cortex

Brainstem levels/locations of synaptic structures from brainstem to cortex

• Cochlear nucleus: located on lateroposterior aspect of the caudal pons

• Superior olivary complex: located in pons

• Lateral lemniscus: located in upper pons

• Inferior colliculus: located in posterior aspect of midbrain

• Medial geniculate body: located in thalamus in dorsal and caudal aspect

Nuclei of synaptic structures

• CN: dorsal CN, posterior ventral CN, anterior ventral CN

• SOC: medial superior olive, lateral superior olive, medial nucleus of trapezoid body

• LL: dorsal LL and ventral LL

• IC: central nucleus, dorsal cortex, lateral nucleus

• MGB: ventral, medial, dorsal (+ pulvinar and posterior nuclei)

Primary auditory cortex (AI) location in brain

Temporal lobe on Heschel’s Gyrus

Role of the CAP

Carries auditory signals from periphery to brain

General function of the brainstem auditory nuclei

auditory neurons must encode and decipher the frequency, spatial, and timing properties of sound (both speech and environment)

General principals of the CAP

• numerous central auditory brainstem nuclei (CN, SOC, LL, IC, MGB)

• all have multiple nuclei

• all are tonotopically organized

• all have multiple connections to each other and to higher and lower stations

• all have multiple cell types with differing physiological responses

Purpose of the different cell types in the auditory nuclei

designed to process and manipulate incoming signals, maintain fidelity of signal, and deliver it with as much clarity as possible

Special function of the SOC

First station where both ears are represented

Acoustic reflex pathway: contralateral pathway

• signal received by the ipsilateral ear, signal is sent to the ipsilateral cochlear nucleus (VCN)

• signal travels to the contralateral SOC

• travels to the contralateral facial nerve nucleus (FN)

• travels to the contralateral stapedius muscle which contracts tightening the TM

What’s significant about layer 4

Contains most of the input from lower centers

Five elements of the vestibular system

• 3 semicircular canals

• Vestibule (utricle and saccule)

Name the 3 semicircular canals. How are they oriented?

• Anterior SCC

• Lateral (horizontal) SCC

• Posterior SCC

Oriented at a 90 degree angle

Describe the physical characteristics of the three semicircular canals

• all unequal in length

• measure about .8mm in diameter

• each have an ampulla (more than 2x diameter)

Contents of the ampulla

• sensory apparatus of the SCCs

• contain hair cells that sit on crista ampullaris

• hair cell stereocillia are embedded in cupula

What are the dimensions of the vestibule and some of its characteristics?

• 5 mm front to back, 3 mm side to side

• osseous portion has recesses for structures and holes for nerve fibers to pass to retrocochlear structures

What is the utricle and its location?

• Larger soft tissue structure housed in vestibule

• located in posterior superior aspect of vestibule

What is the saccule and its location?

• Smaller soft tissue structure

• Located in anterior inferior portion of vestibule

What are otoconia?

Calcium carbonate crystals (lay atop otolithic membrane)

How many vestibular nerve fibers are there in Scarpa’s Ganglion?

About 20,000

Where does Scarpa’s Ganglion center the brainstem and where do the fibers distribute from there?

• At cerebellopontine angle

• travel to brainstem to somatosensory cortex

Roles of vestibular system

• primary organ of equilibrium, motion and spatial orientation

• input to nervous system involved in motor control, eye movement

What two systems does the vestibular system rely on? What kind of input do they provide?

• Visual and propriceptive systems

• visual activity, track moving objects, hand movement (eyes move opp. direction)

Relationship between vestibular system and controlling eye movements when head is in motion

oculomotor and vestibulocular reflex, ability to visually track moving object

Name and role of each semicircular canal

• Anterior SCC: shoulder to shoulder

• Lateral SCC: side to side

• Posterior SCC: front to back

Role of utricle

signals linear motions of head (mostly back/forward and side/side)

Role of saccule

signals linear motion of head (mostly acceleration/deceleration and up/down)

What effect does alcohol have on the vestibular system?

Alters the gravity of the endolymph in the SCCs (causes dizziness, spinning sensation)

How often does dizziness occur in population of 40+ years?

40%

How often do falls occur by age group?

• 65+: 28-35%

• 75+ 42-49%

Define psychoacoustics

Way to quantify the perception of sound

Range of loudness (dB) that humans can hear?

0-140 dB