Neural Basis Final Exam

inner hair cell position and function

responsible for conveying place and timing concerning point of maximum perturbation by traveling wave

in a single, longitudinal row along the internal side of the organ of Corti, within the cochlear duct of the inner ear

outer hair cell position and function

amplifying sound arriving at cochlea by means of active response to incoming auditory system

located in the Organ of Corti within the cochlea of the inner ear, arranged in three to four neat rows

e basilar membrane

and are found on the outer side of the tunnel of Corti, positioned closer to the outer spiral sulcus

directional depolarization of hair cells

deflection of cilia (both cells have) by traveling wave of cochlea causes depolarization of hair cell with subsequent activation of VIII nerve

tip links connect cilia so they moves a a unit

movement of cilia opens ion channels allowing K+ to enter hair cells

Potassium depolarizes hair cell in same manner as depolarization of a neuron, initiating a response in the VIII nerve fibers

inner- depolarizes and activates nerve

outer- shortens post depolarization

age/size of brain maturation

structural maturation continues until about age 32.

While physical size reaches roughly 90% of adult capacity by age 5, critical refinement—particularly in the prefrontal cortex—continues through the mid-20s and into the early 30s.

age/size of brain degeneration

significant brain shrinkage (about 5% per decade) and cognitive decline frequently accelerate after age 60–70

steady loss of brain volume, typically starting around age 35, accelerating after age 60 to a reduction of over 0.5% per year

inner ear developmental milestones

pinna- week 6; swelling called oracle helix in mesenchyme on either side of 1st pharyngeal groove become pinna

external auditory meatus- week 8- 18; indentation in myoscheme will become EAM

week 8-9; tube is filled with embryonic fluid that fetus is floating in and doesn’t want to enter into any of this through an opening

inner ear- days 22-24: begins as otic pit and then otic placode

day 32- edges of black coat fuse to form otic vesicle which is primordial membranous labyrinth

week 8-12- otic vesicle (primordial membranous labyrinth) gives rise to all of inner ear; saccular portions differentiate into saccules and cochlear ducts

week 17- all scalae are present

week 9-11- VIII nerve fibers to migrate to spiral ganglion

week 8-12- semicircular canals come from utricular portion; cochlear duct develops from saccular portion

week 20- inner ear is adult size

week 25- fetus can respond to sound

week 27- VIII nerve myelination begins

week 28- ABR can be licited

cochlear devlopmental milestones

week 8- can see all turns of cochlea

week 11- see scala tympani

week 17- all scalae are present

week 9-11- VIII vestibulocochlear nerve form spinal ganglion

weeks 22-25- fetus can hear

•Newborns can localize sounds

–By 5 months you can condition an infant to localize to one side versus the other

–By 5 years the child is as good as an adult at localization

•Speech discrimination

–Rapid improvement in late childhood and is mature by 12 years

postnatal EAM, TM, and Pinna changes

EAM grows to 25-30 mm in adults

TM- adult size in 7th fetal month, orientation is horizontal in infants than at 2-3 years

pinna- grows more rapidly between birth and 3 years; anterior portion grows into adulthood

postnatal middle ear and auditory tube

middle ear cavity volumes increases until 20 years

auditory tube- cartilaginous portion increases in volume as adulthood approaches

portnalatal development of inner ear

inner ear structures are essentially complete at birth

postnatal development of inner ear and auditory pathways

cochlea- complete by 3 months

VIII vestibulocochlear nerve complete at 3 months and myelineated by 24 months

auditory pathway growth and development

•Brainstem nuclei continue to develop, maturing at 1-1/2 years

•Olivocochlear system matures at 6 months

•Myelin on pathways continue to develop through 4 years

•ABR is present at birth, but continues to develop and mature through childhood

•Efferent system matures around 6 mo.

•VIII nerve myelin complete at 24 months

•Auditory cortex myelin complete at12 years!

development of auditory acuity

•Hearing function develops into adolescence

–At birth, threshold is between 25 and 45 dB HL

•6 month old has near-adult threshold above 4 K Hz but low frequencies have higher thresholds

–Threshold improves to 10-15 dB HL by 5 years

•Frequency discrimination

–Adults can hear 1% difference in frequency (JND) between 2 tones

–At 12 months, infants hear a 2% difference

–Achieve adult levels by 11 years old

•Intensity discrimination

–Adult can hear that tones are different if they are 1-2 dB different from each other

–5 month old hears as different if the level difference is 6 dB

–Develops into adulthood

relationship between aging and cerebrospinal fluid spaces

As individuals age, the volume of the brain tends to decrease due to neurodegeneration and other age-related structural changes.

This can lead to an enlargement of the ventricles and increased periventricular spaces, often seen in neuroimaging studies. Additionally,

the production and reabsorption of CSF may also decline, potentially contributing to altered pressure and flow dynamics in the CNS.

relationship between aging and changes in grey matter

As individuals age, there is a significant loss of grey matter volume in the brain, particularly in areas associated with cognitive functions.

This reduction is linked to neurodegenerative processes, leading to cognitive decline and impairments in memory, learning, and executive functions.

The decline in grey matter begins as early as middle age and continues throughout later years.

What is the traveling wave in the context of hearing?

The traveling wave refers to the wave of displacement that occurs in the cochlear fluid as sound vibrations enter the cochlea.

It starts at the base of the cochlea and travels towards the apex, where different frequencies stimulate specific regions of the basilar membrane.

This wave is crucial for the process of converting sound vibrations into neural signals that can be interpreted by the brain.

auditory cranial nerve muscle innervation

The auditory cranial nerve, also known as the vestibulocochlear nerve (CN VIII), innervates the inner ear structures involved in hearing and balance(hair cells)

While it does not innervate muscles directly, its function is closely related to the perception of sound and spatial orientation, with connections to the brainstem and other cranial nerves that may be involved in reflexive actions related to auditory stimuli.

development from the neural plate

The neural plate arises from the ectoderm during embryonic development and thickens to form the neural tube, which will eventually develop into the central nervous system.

neural plasticity

strongest in early life

experience-dependent learning

language exposure shapes auditory cortex

brain development

synaptogenesis (birth or beginning)→ pruning (the brain's natural, necessary process of eliminating weak, unused, or redundant neural connections (synapses) to improve efficiency and strengthen crucial pathways)→ specialization (specific areas of the brain are dedicated to processing particular types of information or performing distinct tasks)

myelination improves speed and efficiency

critical/sensitive periods

aging (peripheral changes

presbycusis- age-related HL that does not include HL from noise exposure or disease conditions, just means aging and not working as well, degeneration of of hair cells, blood supply, and spiral ganglion deterioration

high-frequency loss

hair cell degeneration

reduced cochlear function

aging (central auditory changes)

slower neural processing

reduced temporal resolution

difficulty in noise

aging (brain changes

cortical atrophy

reduced neural synchrony

compensatory recruitment (bilateral activation)

types of hearing loss

Hearing loss can be categorized into three main types: conductive, sensorineural, and mixed.

Conductive hearing loss- occurs when sound is not conducted effectively through the outer ear canal to the eardrum and the tiny bones of the middle ear, often due to blockages or damage.

Sensorineural hearing loss- results from damage to the inner ear or the auditory nerve pathways, affecting the ability to hear faint sounds and hear clearly in noisy environments.

Mixed hearing loss- is a combination of both conductive and sensorineural loss, indicating issues in both sound conduction and nerve transmission.