Audition

Alternate phases of compression and decompression of molecules of the medium

Alternate phases of compression and decompression in vacuum

Sound waves are associated with pressure changes called sound pressure.

Pressure waves are longitudinal vibrations of molecules of the medium

335 m/s in air - 0°C at sea level

44 m/s in air - 20°C at sea level

297 m/s in air - 0°C at sea level ,

1450 m/s in water - 20°C at sea level.

335 m/s in water - 0°C at sea level

1450 m/s in water - 20°C at sea level

344 m/s in air - 20°C at sea level

1250 m/s in water - 20°C at sea level

The crests of these waves are areas of high density, called compressions.

The troughs are called rarefactions.

The troughs are called compression.

Sounds are waves of air molecules.

Amplitude determines Pitch

Amplitude determines Loudness

Frequency determines Loudness

Frequency determines Pitch

Frequency is the rate at which the source produces sound waves

Low pitched or bass sounds have low frequencies.

High-pitched or treble sounds have low frequencies.

A healthy, young person can hear sounds with frequencies from 20 to 20,000 Hz.

The ability to hear high pitch sounds (high frequencies) increases with age –
this condition is called presbycusis.

The ability to hear high pitch sounds (high frequencies) declines with age – this condition is called presbycusis.

Male hearing range decreases more quickly than the female.

The sound of human speech is mainly in the range 300 to 3,000 Hz.

This very wide range of values is converted into a logarithmic scale of decibels range of 0 dB to 300 dB.

This very wide range of values is converted into a logarithmic scale of decibels range of 0 dB to 140 dB.

Sound waves are silent if their compressions are dense.

The amplitude of the acoustic pressure is measured in pascals (Pa).

Threshold of hearing (10-16 W/m2 = 0 B = 0 dB).

Loud conversation (10-12 W/m2 = 4 B = 40 dB).

Ordinary conversation (10-9 W/m2 = 7 B = 70 dB).

Threshold of pain (10-3 W/m2 = 13 B = 130 dB).

The pitch of the average male voice is 120 Hz while of the female voice is 250 Hz.

Noise is sound composed of many related frequencies.

harmonics is sound composed of many unrelated frequencies.

Sounds are complex mixtures of pure tones. (accords)

The auditory system is maximally sensitive between 500 – 5,000 Hz

The Frequency response is determined by the functional anatomy of the ear.

The auditory system is maximally sensitive between 200 – 2,000 Hz

Sound is FELT above 130dB

Consists of the tympanic membrane and the external auditory meatus (auditory canal).

Sound waves travel through the meatus and impinge on the brain.

The Meatus acts as a resonator

The Pinna funnels sound waves into the meatus.

Binaural localization relies on the comparison of auditory input from two separate auditory detectors (ears).

The auricle ensures reliable transmission of speech.

Convergence and amplification of the sound.

Localization of the source of the high pitch sound is based on assessment of difference of amplitude and time

Decompression of the sound pressure.

Conduction of the sound through the lever system of auditory ossicles.

Defensive mechanism of the ear – function of the tympanic reflex.

Language (foreign) is shifted higher, needs to be louder

The handle of the malleus is attached to the centre of the tympanic membrane

The malleus forms a rigid connection with the incus and they act as a single lever.

The incus forms flexible connection with the malleus.

Footplate of stapes moves in and out at the round window

Contraction - increase sound conduction

Tensor tympani muscle – pulls the handle of the malleus inward

Stapedius muscle – pulls the stapes outward

Loud sound in high frequencies

Adaptation to continuous high intensities sound
- to mask low-frequencies sound in loud environment

Reduce sound by 30dB

Consist of vestibule and cochlea

Helicoterma – connection between scala tympani and scala vestibuli

Scala vestibuli – to oval window;

Scala media has 3 walls; basilar memb, Reissner's memb. and stria vascularis

Scala tympani – to round window

Organ of corti is placed in cochlear duct

Perilymph – scala vestibuli

Endolymph – scala tympani

Potential gradient across hair cells about 140 mV

In scala media

Hair cells and various supporting cells

Cones and rods

The rods of Corti

Inner hair cells 3,500 - supplied by myelinated fibers

Outer hair cells 3,500 - supplied by myelinated fibers

Outer hair cells 15,000 - supplied by unmyelinated fibers

Inner hair cells 15,000 - supplied by unmyelinated fibers

From superior olivary nucleus – olivocochlear fibers

Bipolar neurons from spiral ganglion within the modiolus

90% of fibers innervate inner hair cells

Axons enter the auditory-vestibular nerve

On afferent fibers that contact the inner
hair cells

From superior olivary nucleus – olivocochlear fibers

On afferent fibers that contact the inner
hair cells

Bipolar neurons from spiral ganglion within the modiolus

On outer hair cells

Helps to improve frequency discrimination

Different parts of the basilar membrane have the same resonance frequencies.

Basilar membrane up – reticular lamina up and toward the modiolus

Basilar membrane up – reticular lamina down and away from modiolus

Tectorial membrane holds the tips of the outer hair cells stereocilia

Inner hair cells cilia’s are bend by movement of endolymph

Neurones of the spiral ganglion – to auditory nerve.

Neurones of the ventral (and dorsal) cochlear nucleus – to lateral lemniscus.

Neurones of the superior colliculi.

Neurones of the Inferior olives.

Neurones of the medial geniculate body (MGN) of the thalamus to auditory cortex

Area 41 of Brodmann division in temporal lobe

Low frequencies are represented rostrally and laterally,

High frequencies – caudally and medially

High frequencies – caudally and laterally

Secondary auditory cortex 42, 22, 52 Brodmann’s area

Has stereocilia with actin and kinocilia

Connect to efferent fibers with glutamine

Endolymph is low in K+

Mechano-sensitive non-selective channels, opened by tip links on hair cells

Hair cells bending to stereocilia - de -polarize producing sound

Semicircular system and Cochlea use different receptors

Semicircular system is responsible for equilibrium

Cochlea is responsible for sound

Olivary nucleus connects to neuron from left and right ear

The right ear is the 1st to hear sounds

The left ear is the 1st to hear sounds

The right ear has a shorter pathway to the brain

The left ear has a shorter pathway to the brain

Ossicles - Tympanic memb. - Basilar memb. - Perilymph to endolymph - Cochlea

Tympanic memb. - Ossicles - Basilar memb. - Cochlea - Perilymph to endolymph

Tympanic memb. - Ossicles - Perilymph to endolymph - Basilar memb. - Cochlea

Ossicles - Tympanic memb. - Perilymph to endolymph - Cochlea- Basilar memb.

Vibration of skull - Perilymph to endolymph - Basilar membrane - Cochlea

Vibration of skull - Cochlea - Perilymph to endolymph - Basilar membrane

Vibration of skull - Cochlea - Basilar membrane - Perilymph to endolymph

Vibration of skull - Basilar membrane - Cochlea - Perilymph to endolymph

Nerve deafness is impairment of the auditory nerve

Conduction deafness is impairment of structures of the ear that conduct sound to cochlea

Nerve deafness impairment of structures of the ear that conduct sound to cochlea

Bone conduction in conduction deafness is normal

Acumetry – Quantitative

Audiometry - Quantitative and Qualitative

Tuning fork tests - Qualitative

Tuning fork tests - Quantitative

Acumetry - Qualitative

Rinne test - comparison of the patient’s bone conduction to examiner’s bone conduction.

Rinne test – comparison of the patient’s air (ossicular) conduction of sound to the bone conduction.

Weber test - differentiation between conduction and nerve deafness.

Schwabach test – comparison of the patient’s bone conduction to examiner’s bone conduction.

Normal hearing - (positive rinne) sound is heard twice as long by air conduction as by bone conduction

Conductive deafness in right ear - (negative rinne) sound is heard longer by bone conduction than by air conduction

Conductive deafness in right ear - (positive rinne) sound is heard longer by air conduction than by bone conduction

Perceptive deafness of right ear - (positive rinne) sound is heard longer by air conduction than by bone conduction

Conductive deafness in right ear - Sound lateralizes to the better ear

Normal hearing - Sound does not lateralize to either side; heard equally well in both ears.

Perceptive deafness of right ear - Sound lateralizes to the better ear

Conductive deafness in right ear - sound lateralizes to defective ear, few sound are carried through external and middle ear.

Longer - conduction disorder – longer than normal bone conduction

Is a method based on comparing bone conduction to a normal subject to the patient

Shorter - nerve disorder - shorter than normal bone conduction

Is a method based on comparing bone conduction to a deaf subject to the patient

Assessment of the distance of hearing.

Normal ear can hear whisper voice from 6m (young humans – even 20 m).

1-3m – mild hearing loss.

3-6m – moderate hearing loss.

< 1m – severe hearing loss.

> 6m – normal hearing.

Otolith organ – signals linear acceleration

Semicircular canals – signal rotational acceleration

Utricle – signal vertical acceleration

Sacculus – signal horizontal acceleration

3rd neuron - flocculonodular lobe of the cerebellum - posture

II neuron – here terminate vestibular nerves in: flocculonodular lobe of the cerebellum - posture

II neuron – here terminate vestibular nerves in: ipsilaterally four-part vestibular nuclei

1st neuron – vestibular ganglion (Scarpa’s ganglion):
supplies the cristae and macula

3rd neuron - vestibular ganglion (Scarpa’s ganglion):
supplies the cristae and macula

Abducens nucleus - The medial lateral fascicle (mlf) projects from the Vestibulocochlear nucleus to the oculomotor nucleus

Vestibulocochlear nerve - from the peripheral vestibular sensors to the vestibular nuclei in the brainstem (vn)

Two-neuron arc, during a head movement to the right

The oculomotor nucleus - The left lateral rectus muscle (lr) and the right medial rectus muscle (mr) get contracted, turning the eyes to the left.

With the eyes open 3 sensory systems provide input to cerebellum to maintain truncal stability. These are vision, olfaction and vestibular sense.

Mild lesions in one vestibular or proprioception system cannot be compensated by vision

When the patient closes their eyes, visual input is removed and instability can be brought out.

In vestibular malfunction direction of falling is direction of slow phase of nystagmus

Is a jerky movement of the eye with slow and quick components.

The direction of nystagmus is identified by the direction of the quick component.

The quick component is initiated by impulses from the labyrinths.

The slow component is triggered by a center of the brainstem.

Secondary nystagmus is involved with the slow phase in the opposite direction. It continues for 1min.

Secondary nystagmus is involved with the rapid phase in the same direction. It continues for 20-30 s.

Trigger by angular acceleration, which activate movement of eye opposite direction to head movement.

Pathology causing vestibular nystagmus can be lesions of brainstem or Menier's disease

Optokinetic – reflex that maintain visual fixation on stationary point while the body rotates

Caloric test - toward the warmer ear

Caloric test - post-rotatory nystagmus

Barany rotation test - post-rotatory nystagmus