The document describes the anatomy and function of the human auditory system. It discusses the external, middle, and inner ear anatomy. It explains how sound is transduced by the cochlea's basilar membrane and organ of Corti into neural signals. Frequency tuning occurs due to the cochlea's tonotopic organization. Sound localization involves interaural intensity and timing differences processed in the superior olivary nucleus. Auditory pathways project from the cochlea to the auditory cortex. Common auditory disorders include noise-induced and presbycusis hearing loss damaging hair cells.
This presentation explains the working of the ear... It is best for medical students.. It includes all the key points necessary for an exam too... So this presentation can also be used as a notes for your exams...
olfactory system and functioning, pathway of olfaction, neural tract involved in olfaction , endocrine pathway of olfaction, cells and neurons involved in olfaction
This presentation explains the working of the ear... It is best for medical students.. It includes all the key points necessary for an exam too... So this presentation can also be used as a notes for your exams...
olfactory system and functioning, pathway of olfaction, neural tract involved in olfaction , endocrine pathway of olfaction, cells and neurons involved in olfaction
The Ear, Anatomy, Physiology, Clinical diseases, and pathology, hearing testsHamzehKYacoub
Ear is composed of three parts: External ear, middle ear, and the Inner ear.
Hearing tests (Rinne's and Weber's tests).
Most important hearing and ear diseases are included.
Auditory brainstem responses are generated by the
activity in structures of the ascending auditory
pathways that occurs during the first 8–10 ms
after a transient sound such as a click sound has
been applied to the ear.
Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
Follow us on: Pinterest
Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
Selleck adjusted his fitness routine as he aged to suit his body's needs. Today, his workouts focus on maintaining flexibility, strength, and cardiovascular health. He incorporates low-impact exercises such as swimming, walking, and light weightlifting. This balanced approach helps him stay fit without putting undue strain on his joints and muscles.
Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
Best Ayurvedic medicine for Gas and IndigestionSwastikAyurveda
Here is the updated list of Top Best Ayurvedic medicine for Gas and Indigestion and those are Gas-O-Go Syp for Dyspepsia | Lavizyme Syrup for Acidity | Yumzyme Hepatoprotective Capsules etc
Adv. biopharm. APPLICATION OF PHARMACOKINETICS : TARGETED DRUG DELIVERY SYSTEMSAkankshaAshtankar
MIP 201T & MPH 202T
ADVANCED BIOPHARMACEUTICS & PHARMACOKINETICS : UNIT 5
APPLICATION OF PHARMACOKINETICS : TARGETED DRUG DELIVERY SYSTEMS By - AKANKSHA ASHTANKAR
Local Advanced Lung Cancer: Artificial Intelligence, Synergetics, Complex Sys...Oleg Kshivets
Overall life span (LS) was 1671.7±1721.6 days and cumulative 5YS reached 62.4%, 10 years – 50.4%, 20 years – 44.6%. 94 LCP lived more than 5 years without cancer (LS=2958.6±1723.6 days), 22 – more than 10 years (LS=5571±1841.8 days). 67 LCP died because of LC (LS=471.9±344 days). AT significantly improved 5YS (68% vs. 53.7%) (P=0.028 by log-rank test). Cox modeling displayed that 5YS of LCP significantly depended on: N0-N12, T3-4, blood cell circuit, cell ratio factors (ratio between cancer cells-CC and blood cells subpopulations), LC cell dynamics, recalcification time, heparin tolerance, prothrombin index, protein, AT, procedure type (P=0.000-0.031). Neural networks, genetic algorithm selection and bootstrap simulation revealed relationships between 5YS and N0-12 (rank=1), thrombocytes/CC (rank=2), segmented neutrophils/CC (3), eosinophils/CC (4), erythrocytes/CC (5), healthy cells/CC (6), lymphocytes/CC (7), stick neutrophils/CC (8), leucocytes/CC (9), monocytes/CC (10). Correct prediction of 5YS was 100% by neural networks computing (error=0.000; area under ROC curve=1.0).
Muktapishti is a traditional Ayurvedic preparation made from Shoditha Mukta (Purified Pearl), is believed to help regulate thyroid function and reduce symptoms of hyperthyroidism due to its cooling and balancing properties. Clinical evidence on its efficacy remains limited, necessitating further research to validate its therapeutic benefits.
Knee anatomy and clinical tests 2024.pdfvimalpl1234
This includes all relevant anatomy and clinical tests compiled from standard textbooks, Campbell,netter etc..It is comprehensive and best suited for orthopaedicians and orthopaedic residents.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
1. The Auditory System
Csilla Egri, KIN 306 Spring 2012
The system that allows you to hear the most annoying sound in the world
2. Outline
Anatomy of the ear
Sensory transduction
Cochlea
Organ of Corti
Frequency tuning
Auditory pathways
Localization of sound
Auditory disorders
2
4. Anatomy of the Ear: External
Ear4
folds of pinna
provide cues about
vertical location of
sound
gathers and focuses
sound energy on
tympanic membrane
5. Anatomy of the Ear: Middle Ear
5
amplifies vibrations of
tympanic membrane to oval
window
matches low acoustic
impedance of air to high
acoustic impedance of
fluid of the inner ear
Eustachian tube
6. Anatomy of the Ear: Inner Ear
6
connected to the middle ear
via two openings:
oval window (entrance)
& round window (exit)
contains the cochlea
a coiled tube separated
into three fluid filled
partitions
location of the Organ of
Corti, the sensory organ
responsible for sound
transduction
perilymph
endolymph
B&L Figure 8-17Eustachian tube
Cochlea – partially unravelled
Helicotrema or apex
Perilymph ≈ CSF
What is the composition of
CSF compared to plasma?
7. Sensory Transduction:
Overview7
1. Ossicles amplify sound
wave from tympanic
membrane to oval window
2. Creates pressure wave in
cochlear fluid
3. Deforms basilar
membrane causes round
window to bulge out
4. Motion of basilar
membrane is transduced
into action potentials by
hair cells in organ of
Corti located along the
basilar membrane
8. Cochlea:
cross-section8
Reissner’s membrane
separates scala media
from scala vestibuli
Basilar membrane
separates scala media
from scala tympani
Tectorial membrane
attached along one edge
of the wall to scala media
Organ of Corti
Located in scala media
on top of basilar
membrane
B&B Figure 13-9
9. Cochlea: Organ of Corti
9
contains hair cells with
sterocilia embedded into the
tectorial membrane
outer hair cells:
stereocilia are arranged
in V-like structure in
three parallel rows
inner hair cells:
stereocilia are arranged
linearly in single row
90% of afferents
synapse on inner
hair cells
As basilar membrane moves up/down with pressure waves, stereocilia of hair
cells bend against tectorial membrane
10. Sensory Transduction:
Hair cells10
Stereocilia coupled by “tip links”
Upward displacement of basilar
membrane bends stereocilia
towards kinocillium
Opens mechanically gated non-
selective cation channels =
depolarization
Excitatory neurotransmitter
released = AP in afferent nerve
fibre
Not all afferent fibres fire AP in
response to particular sound
frequency
B&B Figure 13-15
Endolymph
High [K+
]
Perilymph
Low [K+
]
+80mV
-60mV
0mV
11. Frequency Tuning of Basilar
Membrane11
Due to geometry of basilar
membrane
Base: narrower & stiffer
Vibrates at higher
frequencies
Apex: wider & more flexible
Vibrates at lower
frequencies
Maximal firing of afferent
fibers depends on
location along basilar
membrane
Frequency tuning: tonotopic
mapping of frequency in the
basilar membrane and organ
of Corti
12. Auditory Pathways
12
Cochlear afferents synapse on cochlear nuclei in the medulla on the same side
Most second order neurons cross over and synapse in the superior olivary nucleus
Receives input from both ears (binaural)
Medial and lateral superior olive (MSO and LSO) important in computing location
of sound
13. Auditory Pathways
13
Ascend via the lateral meniscus tract on ipsilateral side to the inferior colliculus in the
midbrain
Fourth order neurons travel to the medial geniculate nucleus (MGN) in the thalamus
Terminate in the primary auditory cortex in the temporal lobe
Tonotopic organization maintained from cochlear nuclei to auditory cortex
14. Sound Localization
14
two strategies to localize the horizontal position of sound sources,
depending on the frequency
frequencies above 3 kHz use interaural intensity differences
computed by neural circuitry in the lateral superior olive (LSO) and
the medial nucleus of the trapezoid body (MNTB)
frequencies below 3 kHz use interaural time differences
computed by neural circuitry in the medial superior olive (MSO)
B&B Figure 14-15
15. Interaural Intensity Differences:
LSO and MNTB15
cochlear nucleus on same side as
location of sound directly excites
LSO
LSO excites inhibitory
interneurons in contralateral
MNTB
Contralateral LSO inhibited
Excitation/inhibition arrangement
sends maximal signal to auditory
cortex on same side as sound
16. Interaural Time Differences:
MSO16
MSO neurons are coincident detectors:
respond only when excitatory signals arrive
simultaneously
Anatomical differences in connectivity
allow each MSO neuron to be sensitive
to sound source from particular location
17. Auditory Cortex
17
Primary auditory cortex corresponds to Broadmann’s area
_____ and ______
Sends projections to auditory association area
Discrimination of sound patterns
Wernicke’s area: language comprehension
Lesion to this area results in receptive aphasia
Wernicke’s area
18. Auditory Disorders
18
Sensorineural hearing loss
Dysfunctions of the inner ear, vestibulocochlear nerve or
auditory cortex
Most common cause is damage to hair cells. Two
examples include:
Noise induced hearing loss
Caused by auditory trauma or long term exposure to loud
sounds
Leads to structural damage or complete degeneration and
loss of hair cells
Sensory presbycusis
Age related hearing loss
Hair cell damage caused by factors other than auditory
trauma
Often occurs in both ears
WebCT readings: Sensorineural Hearing Loss
19. Objectives
After this lecture you should be able to:
Describe the structure and function of the outer, middle,
and inner ear
Relate the anatomical organization of the cochlea and
associated structures to sensory transduction of sound
Explain how damage to these structures can cause hearing
loss
Differentiate between the mechanisms for localization of
horizontal sound above and below 3kHz
Outline the neuronal pathway from the cochlea to the
auditory cortex
19
20. 20
1. What is the first location in the auditory pathway that
receives input from both ears?
2. What does tonotopic organization mean?
3. Endolymph closely resembles the ionic composition of
intra or extracellular fluid of a typical neuron?
Test your knowledge
The auditory system is one of the engineering masterpieces of the human body. At the heart of the system is an array of miniature acoustical detectors packed into a space no larger than a pea. These detectors can faithfully transduce vibrations as small as the diameter of an atom, and they can respond a thousand times faster than visual photoreceptors. Such rapid auditory responses to acoustical cues facilitate the initial orientation of the head and body to novel stimuli, especially those that are not initially within the field of view. Although humans are highly visual creatures, much human communication is mediated by the auditory system; indeed, loss of hearing can be more socially debilitating than blindness. From a cultural perspective, the auditory system is essential not only to language, but also to music, one of the most aesthetically sophisticated forms of human expression. For these and other reasons, audition represents a fascinating and especially important aspect of sensation, and more generally of brain function.
Because of arcing shape of pinna, reflected path of sound coming from above is shorter than that of sounds from below, therefore two sets of sounds arrive at different intervals in the ear.
The first stage of the transformation of sound waves into neural signals occurs at the external and middle ears, which collect sound waves and amplify their pressure, so that the sound energy in the air can be successfully transmitted to the fluid-filled cochlea of the inner ear.
Tympanic membrane = ear drum
Resonant frequency means that sound energy near this frequency is boosted or amplified, which allows us to hear sound best at this frequency. Most human speech sounds are distributed in the bandwidth around 3 kHz. Most vocal communication occurs in the low-kHz range because transmission of airborne sound is less efficient at higher frequencies, and the detection of lower frequencies is difficult for animals the size of humans.
Convolutions of pinna shaped to transmit more high-frequency components from elevated source than source at ear level. This effect can be demonstrated by recording sounds from different elevations after they have passed through an artificial external ear; when the recorded sounds are played back via earphones, so that the whole series is at the same elevation relative to the listener, the recordings from higher elevations are perceived as coming from positions higher in space than the recordings from lower elevations.
The term “impedance” in this context describes a medium's resistance to movement.
eustachian tube connects middle ear to nasopharaynx
facilitates equalization of pressure on opposite sides of tympanic membrane
Normally, when sound travels from a low-impedance medium like air to a much higher-impedance medium like water, almost all (more than 99.9%) of the acoustical energy is reflected. The middle ear overcomes this problem and ensures transmission of the sound energy across the air-fluid boundary by boosting the pressure measured at the tympanic membrane almost 200-fold by the time it reaches the inner ear.
Two mechanical processes occur within the middle ear to achieve this large pressure gain.
The first and major boost is achieved by focusing the force impinging on the relatively large-diameter tympanic membrane on to the much smaller-diameter oval window, the site where the bones of the middle ear contact the inner ear.
A second and related process relies on the mechanical advantage gained by the lever action of the three small interconnected middle ear bones, or ossicles (i.e., the malleus, incus, and stapes), which connect the tympanic membrane to the oval window.
Less protein than plasma with similar electrolyte composition (but more Cl-, less Ca2+ and K+)
oval window opens to scala vestibuli and connects to space adjacent to oval window; scala tympani connects to round window
scala vestibuli and scala tympani are filled with perilymph; scala media is filled with endolymph
the cochlear partition does not extend all the way to the apical end of the cochlea, such that scala vestibuli and scala tympani connect through opening near the apex called the helicotrema
as a result of this structural arrangement, inward movement of the oval window displaces the fluid of the inner ear, which causes the round window to bulge out slightly and deforms the basilar membrane
as pressure wave travels through scala vestibuli it pushes down on scala media and causes basilar membrane to bow into scala tympani
bowing of basilar membrane creates shear force relative to tectorial membrane causing it to tilt and bending tips of embedded stereocilia
scala media is separated from scala vestibuli by Reissner’s membrane and from the scala tympani by the basilar membrane
tectorial membrane is attached along one edge to wall of scala media
Other wall is called stria vascularis
Rods of corti help provide a rigid scaffold for hair cells and surrounding support cells in the organ of corti
90% of afferents receive input from inner hair cells, thus these are the most important for transduction of sound. Function of outer hair cells is less clear.
There are efferent connections as well, which synapse on outer hair cells, perhaps helping tune the sterecoilia and adjust sensitivity to sound.
Mechanotransduction in the hair cell. A, The hair bundle on the apical side of the cell has one large kinocilium, which is a true cilium with a 9 + 2 arrangement of microtubules, as well as 50 - 150 stereocilia, which contain actin and are similar to microvilli. Endolymph, which has a very high [K+], bathes the apical surface. Perilymph, with a much lower [K+], bathes the basolateral surface. Each cell contacts an afferent and efferent axon. B, At rest, a small amount of K+ leaks into the cells, driven by the negative membrane potential and high apical [K+]. Mechanical deformation of the hair bundle towards the kinocilium increases the opening of non-selective cation channels at the tips of the stereocilia, allowing K+ influx, depolarizing the cell, activating voltage-sensitive Ca++ channels on the basal membrane, causing release of synaptic vesicles, and stimulating the postsynaptic membrane of the accompanying sensory neuron. C, Mechanical deformation of the hair bundle away from the kinocilium causes the non-selective cation channels to close, leading to hyperpolarization and reduced transmitter release. D, The graph shows the relative conductance of a hair cell on the y axis, and the displacement of the hair bundle on the x axis. A displacement of only 0.5 μm, roughly the diameter of a single stereocilium, nearly saturates the conductance change. (D, Data from Crawford AC, Fettiplace R: Auditory nerve responses to imposed displacements of the turtle basilar membrane. Hearing Res 12:199-208, 1983.)the ionic composition of the endolymph is high in K+ ( 145mM) and low in Na+ (2mM)
Downward deflection of basilar membrane results in hyperpolarization
Tonotopy in the auditory system begins at the cochlea, the small snail-like structure in the inner ear that sends information about sound to the brain. Different regions of the basilar membrane in the organ of Corti, the sound-sensitive portion of the cochlea, vibrate at different sinusoidal frequencies due to variations in thickness and width along the length of the membrane. Nerves that transmit information from different regions of the basilar membrane therefore encode frequency tonotopically.
Frequency tuning within the inner ear is attributable in part to the geometry of the basilar membrane, which is wider and more flexible at the apical end and narrower and stiffer at the basal end. One feature of such a system is that regardless of where energy is supplied to it, movement always begins at the stiff end (i.e., the base), and then propagates to the more flexible end (i.e., the apex).
Apical end is 100x more compliant than basal end.
Because the basilar membrane vibrates maximally at different positions for different frequencies of sound, it acts like mechanical frequency analyzer.
Traveling waves along the cochlea. A traveling wave is shown at a given instant along the cochlea, which has been uncoiled for clarity. The graphs profile the amplitude of the traveling wave along the basilar membrane for different frequencies and show that the position where the traveling wave reaches its maximum amplitude varies directly with the frequency of stimulation.
Georg von Békésy, working at Harvard University, showed that a membrane that varies systematically in its width and flexibility vibrates maximally at different positions as a function of the stimulus frequency. Using tubular models and human cochleas taken from cadavers, he found that an acoustical stimulus initiates a traveling wave of the same frequency in the cochlea, which propagates from the base toward the apex of the basilar membrane, growing in amplitude and slowing in velocity until a point of maximum displacement is reached. This point of maximal displacement is determined by the sound frequency.
The points responding to high frequencies are at the base of the basilar membrane, and the points responding to low frequencies are at the apex, giving rise to a topographical mapping of frequency called TONOTOPY.
Complex sounds made up of many frequencies produce similarly complex pattern of vibration along basilar membrane.
Tonotopic organization: The spatial layout of frequencies in the cochlea along the basilar membrane is repeated in other auditory areas in the brain. This is called tonotopic organization. The primary auditory pathway begins with the auditory receptors in the cochlea. These synapse on spiking neurons in the spiral ganglia, the axons of which form the auditory (8th cranial) nerve. These then lead to the cochlear nucleus, then to the superior olive, then to the inferior colliculus, then to the medial geniculate nucleus, and finally on to auditory cortex.
Crossing of the Fibers. Significant number of nerve fibers cross the brain and make connections with neurons on the side opposite from the side of the ear in which they begin. This happens very early on in the auditory system. Inter-aural comparisons are an important source of information for the auditory system about where a sound came from (see spatial localization below).
The tonotopic organization of the cochlea is maintained in the three parts of the cochlear nucleus, each of which contains different populations of cells with quite different properties. In addition, the patterns of termination of the auditory nerve axons differ in density and type; thus, there are several opportunities at this level for transformation of the information from the hair cells.
One set of pathways from the cochlear nucleus bypasses the superior olive and terminates in the nuclei of the lateral lemniscus on the contralateral side of the brainstem. These particular pathways respond to sound arriving at one ear only and are thus referred to as monaural. Some cells in the lateral lemniscus nuclei signal the onset of sound, regardless of its intensity or frequency. Other cells in the lateral lemniscus nuclei process other temporal aspects of sound, such as duration. The precise role of these pathways in processing temporal features of sound is not yet known. As with the outputs of the superior olivary nuclei, the pathways from the nuclei of the lateral lemniscus converge at the midbrain.
The superior olive receives binaural inputs and is important for sound localization (discussed on next slides).
Space is not mapped on the auditory receptor surface; thus the perception of auditory space must somehow be synthesized by circuitry in the lower brainstem and midbrain.
Neurons within this auditory space map in the colliculus respond best to sounds originating in a specific region of space and thus have both a preferred elevation and a preferred horizontal location, or azimuth. Although comparable maps of auditory space have not yet been found in mammals, humans have a clear perception of both the elevational and azimuthal components of a sound's location, suggesting that we have a similar auditory space map. (Information is based on experiments in the barn owl, an extraordinarily proficient animal at localizing sounds.)
Many neurons in the inferior colliculus respond only to frequency-modulated sounds, while others respond only to sounds of specific durations. Such sounds are typical components of biologically relevant sounds, such as those made by predators, or intraspecific communication sounds, which in humans include speech. The inferior colliculus is evidently the first stage in a system, continued in the auditory thalamus and cortex, that analyzes sounds that have particular significance
Human voice frequency ranges from about 60Hz to 7 kHz.
20 Hz to about 20,000 Hz rangge of hearing
Interaural: ear to ear difference
Intensity simply means the loudness of the sound, the ear facing the sound hears it louder than the opposite ear because the head casts a sound shadow. At the cochlea, intensity coded for by the amplitude of the sound wave
As amplitude increases:
basilar membrane vibrates more strongly, hair cells release NTs at higher rates
Stronger vibration of basilar membrane activates hair cells even in surrounding areas
High threshold hair cells activated as well
Low frequency sounds need to be detected via a different mechanism because the wavelenght of the sound is longer than the size of the head. Longer sound waves are diffracted around the head and differences in interaural intensity no longer occur. The delay in which the sound reaches each ear is used to compute the location,
The head acts as an acoustical obstacle because the wavelengths of the sounds are too short to bend around it.
Excitatory axons project directly from the ipsilateral anteroventral cochlear nucleus to the LSO (as well as to the MSO).
Note that the LSO also receives inhibitory input from the contralateral ear, via an inhibitory neuron in the MNTB. This excitatory/inhibitory interaction results in a net excitation of the LSO on the same side of the body as the sound source.
For sounds arising directly lateral to the listener, firing rates will be highest in the LSO on that side; in this circumstance, the excitation via the ipsilateral anteroventral cochlear nucleus will be maximal, and inhibition from the contralateral MNTB minimal.
In contrast, sounds arising closer to the listener's midline will elicit lower firing rates in the ipsilateral LSO because of increased inhibition arising from the contralateral MNTB.
For sounds arising at the midline, or from the other side, the increased inhibition arising from the MNTB is powerful enough to completely silence LSO activity.
Note that each LSO only encodes sounds arising in the ipsilateral hemifield; it therefore takes both LSOs to represent the full range of horizontal positions.
Lateral superior olive neurons encode sound location through interaural intensity differences.
LSO neurons receive direct excitation from the ipsilateral cochlear nucleus; input from the contralateral cochlear nucleus is relayed via inhibitory interneurons in the MNTB.
This arrangement of excitation-inhibition makes LSO neurons fire most strongly in response to sounds arising directly lateral to the listener on the same side as the LSO, because excitation from the ipsilateral input will be great and inhibition from the contralateral input will be small.
In contrast, sounds arising from in front of the listener, or from the opposite side, will silence the LSO output, because excitation from the ipsilateral input will be minimal, but inhibition driven by the contralateral input will be great.
Note that LSOs are paired and bilaterally symmetrical; each LSO only encodes the location of sounds arising on the same side of the body as its location.
MSO cells work as coincidence detectors, responding when both excitatory signals arrive at the same time.
For a coincidence mechanism to be useful in localizing sound, different neurons must be maximally sensitive to different interaural time delays.
The axons that project from the anteroventral cochlear nucleus evidently vary systematically in length to create delay lines. (Remember that the length of an axon multiplied by its conduction velocity equals the conduction time.)
These anatomical differences compensate for sounds arriving at slightly different times at the two ears, so that the resultant neural impulses arrive at a particular MSO neuron simultaneously, making each cell especially sensitive to sound sources in a particular place.
Diagram illustrating how the MSO computes the location of a sound by interaural time differences. A given MSO neuron responds most strongly when the two inputs arrive simultaneously, as occurs when the contralateral and ipsilateral inputs precisely compensate (via their different lengths) for differences in the time of arrival of a sound at the two ears. The systematic (and inverse) variation in the delay lengths of the two inputs creates a map of sound location: In this model, E would be most sensitive to sounds located to the left, and A to sounds from the right; C would respond best to sounds coming from directly in front of the listener.
The human auditory cortex. Broadmanns area 41, 42
Tonotopic: Of or being a structural arrangement, as in the auditory pathway, such that different tone frequencies are transmitted separately along specific parts of the structure.
Frequency, pitch, direction, other? (noise vs. sound?)
(A) Diagram showing the brain in left lateral view, including the depths of the lateral sulcus, where part of the auditory cortex occupying the superior temporal gyrus normally lies hidden. The primary auditory cortex (A1) is shown in blue; the surrounding belt areas of the auditory cortex are in red.
(B) The primary auditory cortex has a tonotopic organization, as shown in this blowup diagram of a segment of A1.
Both can get progressivley worse (impair ability to hear lower frequencies) both impair abilities to hear high frequency sounds
Tonotopic: Of or being a structural arrangement, as in the auditory pathway, such that different tone frequencies are transmitted separately along specific parts of the structure.