Bio Psych Final - Hearing and Balance

Sound

a psychological experience created by the brain in response to changes in air pressure that are received by the auditory system

Frequency

• The number of cycles per second in a sound wave.

• Determines the pitch

• Measured in Hz

• Lower pitch has a longer wave, higher pitch has shorter wave

Amplitude

• The magnitude of a wave; determines loudness

• Measured in dB

• Shorter height of wave = quieter; Taller wave = Louder

What parts make up the outer ear?

Pinna, Skull, Eardrum (tympanic membrane)

• Pinna channels sound waves into the ear canal

• Eardrum vibrates in response to sound waves, transmitting those vibrations to the middle ear bones

What parts make up the middle ear?

• Malleus (hammer), Incus (anvil), stapes (stirrup)

  • These bones move due to vibration of the eardrum, which is amplified through the movement of these bones (goes from an air to a fluid environment; must amplify)

• Eustachian tube/Auditory Tube

  • Important for maintaining pressure equilibrium as well as draining excess fluid

What parts make up the inner ear?

• Cochlea: A spiral-shaped, fluid-filled structure that converts sound vibrations into electrical signals. These signals are sent to the brain via the auditory nerve.

• Vestibular Labyrinth: Containing the Semicircular canals; detects head movements and position, providing the brain with information about motion and spatial orientation to aid with balance; connects to the brain via the vestibular nerve

• Vestibulocochlear Nerve: 8th cranial nerve; connects inner ear to brain through the cochlea and vestibular labyrinth and is made up of the cochlear nerve and the vestibular nerve

What makes up the cochlea?

1. Scala Vestibuli

• Location: Upper chamber of the cochlea.

• Function: Begins at the oval window where the stapes transmits sound vibrations. These vibrations travel through the perilymph fluid in the scala vestibuli.

• Role: Transfers sound energy into the cochlea and toward the scala media.

2. Scala Media (Cochlear Duct)

• Location: Middle chamber, between scala vestibuli and scala tympani.

• Function: Filled with endolymph, and contains the organ of Corti, which houses the hair cells (sensory receptors for hearing).

• Role: Transduces mechanical vibrations into electrical signals sent through the auditory nerve.

3. Scala Tympani

• Location: Lower chamber of the cochlea.

• Function: Filled with perilymph like the scala vestibuli; extends from the helicotrema (the apex of the cochlea) to the round window.

• Role: Dissipates the energy of the sound wave and helps maintain fluid movement within the cochlea.

4. Oval Window

• Location: At the base of the cochlea; connected to the stapes.

• Function: Vibrated by the stapes bone of the middle ear.

• Role: Transfers sound vibrations from the middle ear into the fluid of the scala vestibuli in the cochlea.

5. Round Window

• Location: Below the oval window at the base of the cochlea.

• Function: A flexible membrane that bulges outward in response to fluid movement in the cochlea.

• Role: Relieves pressure created by the fluid waves in the cochlea, allowing the perilymph to move freely and enabling proper stimulation of the hair cells.

What is the Organ of Corti

• In the Inner Ear

• Transduces mechanical signal to action potential (electrical signals) through Inner Hair Cells

• Outer Hair Cells work to amplify sound

• Send nerve impulses to the brain via the cochlear nerve

Stereocilia?

Stereocilia has a mechanically-gated ion channel, and when the stereocilia is displaced by auditary signal the ion channels open for Calcium and Potassium to rush into the cell, depolarizing it and sending an action potential.

What are the three theories of hearing?

• Frequency theory - pitch is determined by the frequency with which hair cells in the cochlea fire, and consequently by the rate at which nerve impulses are sent

• Place theory - pitch is determined by the location of the greatest vibration on the basilar membrane

• Volley theory - neurons respond to a sound by firing action potentials slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain

What are the auditory tracts in the brain?

• Cochlea → Cochlear Nucleus (medulla) → Superior Olivary Complex (pons) → Inferior Colliculus (midbrain) → Medial Geniculate Nucleus (thalamus) → Auditory Cortex (temporal lobe)

• Ipsilateral tract is the pathway from the ear to the same side of the brainstem

• Contralateral tract is the pathway from the ear to the opposite side of the brainstem

Auditory Localization?

• Duplex theory: The brain calculates a sound location based on differences in timing and intensity

• Superior Olivary Complex, as well as pinna and outer ear, help to localize

• Contralateral tract enables comparison of signals from both ears for localization and spatial hearing → happens at superior olivary nucleus

Why do we listen to music?

The striatum responds highly to pleasurable music → reward pathway

• Regulates mood and arousal

• Promotes physical and psychological health

• Enhances concentration (e.g., neurosurgeons)

• Coordinates movement (e.g, armies)

• Increases stamina and motivation

• Contributes to personal growth

Music as Therapy

• It reduces stress hormone levels

• It reduces pain perception (as it distracts or shifts focus)

• Increases opioid production

• Techno music: increases cortisol, adrenocorticotropic hormone and NE levels

• Also activates regions of the brain spared by Alzheimer’s Disease, so can act to help those affected by it

Brain Structure Difference in Musicians

• Motor cortex, frontal lobes, and auditory cortex are more developed in musicians than non-musicians

• Precentral gyrus, Heschl’s gyrus, and Superior Parietal Cortex have more gray matter volume in musicians

Hearing Loss

• Hearing loss is decreased sensitivity to sound, ranging from moderate to severe

• Deafness is a loss of hearing so profound that speech cannot be perceived even with the use of hearing aids

What are the types of deafness?

• Conduction deafness - Outer or Middle Ear problem (Pinna, Ear Canal, or Ear Drum OR Malleus, Incus, or Stapes)

• Sensorineural deafness - Cochlear or Auditory Nerve Lesions (damage to inner ear); can possibly be fixed by cochlear implants

• Central deafness - Stroke, toxins, heredity; something wrong with the pathway in the brain, such as if a tumor is on the superior olivary complex

Types of Hearing Loss Symptoms

• Ototoxic (or ear-damaging) effects may be caused by some antibiotics, platinum-containing chemotherapy drugs, loop diuretics for hypertension/swelling

• Tinnitus, a sensation of noises or ringing in the ears; often due to a damage of hair cells (loud sounds, ototoxic drugs)

Ways to aid hearing loss

• Hearing aids - amplify sounds

• Teflon prosthetics for fused ossicles

• Cochlear implants to stimulate the nervous system

What is the role of the Vestibular System?

– detects head position

– detects motion

– stabilizes head/body balance during movement

– helps maintain posture

- made up of the semicircular canals, ampulla, utricle and saccule (Semicircular canals connected through ampullae to the utricle, which connects to the saccule)

What are the functions of the three semicircular canals?

Semicircular canals detect rotation of the head:

• Pitch: Downward and upward head movement

• Yaw: Side to side head movement (right and left)

• Roll: Tilting of the head

Function of Ampulla?

Connects the semicircular canals to the utricle; has the cupula (hair cells in the ampulla) which can be displaced by endolymph flow, sending neuro-signals of head displacement to the brain to help with balance and spatial awareness

Function of Utricle and Saccule

The utricle and saccule detect linear acceleration and static position, aided by tiny crystals, called otoliths, that overlie the hair cells in these structures and maximize the deflection of hair cells in response to movement

• Utricle detects horizontal acceleration

• Saccule detects vertical acceleration

• Detect linear acceleration and head position, but not head rotation

Vestibulospinal tract

• Downward signals of movement and sensations

• Center is the vestibular nucleus

• Cerebellar connection - motor regulation and balance system

• Semicircular canal connection

• Abducens nucleus → eye movement from left and right

• Oculomotor nucleus → blinking, moving eyes up and down

Vestibulo-Ocular Reflex

helps us keep eyes on a target while our head moves

Vestibular System Complications

• Motion sickness: The feeling of nausea caused by unnatural passive movement due to conflicting visual and vestibular information.

• Vertigo: sensation of motion or spinning; certain head movements trigger vertigo