15.4 Special Senses: The Rise of Maculae

What is hearing?

The reception of an air sound wave that is converted to a fluid wave.

What happens after the sound wave is converted into a fluid wave?

The fluid wave stimulates cochlear hair cells, which send impulses to the brain for interpretation.

Do all auditory fibers cross over?

No, some fibers cross over while others do not. Both auditory cortices receive input from both ears

How is the perception of pitch determined?

Impulses from hair cells in different positions along the basilar membrane are interpreted by the brain as specific pitches

How does the brain detect loudness?

Determined by the increase in the number of action potentials (frequency) when hair cells experience larger deflections

How does the brain localize sound?

Localization depends on the relative intensity and timing of sound waves reaching both ears. If timing is increased on one side, the brain interprets the sound as coming from that side

What is equilibrium?

the response to various head movements that rely on input from the inner ear, eyes, and stretch receptors

What structures monitor static and dynamic equilibrium?

Vestibular receptors monitor static equilibrium, and semicircular canal receptors monitor dynamic equilibrium

What is the vestibular apparatus?

It is a system of equilibrium receptors located in the semicircular canals and vestibule of the inner ear

What is the macula?

A flat epithelial patch containing hair cells with supporting cells. It is involved in monitoring equilibrium

What are stereocilia and kinocilium?

Stereocilia are hair-like projections on hair cells, and kinocilium is the true stereocilium. Stereocilia are embedded in the otolith membrane

How do the utricle and saccule maculae differ?

Utricle maculae are horizontal with vertical hairs and respond to horizontal changes (e.g., head tilting), while saccule maculae are vertical with horizontal hairs and respond to vertical changes (e.g., elevator movement)

What happens when the hairs in a macula bend toward the kinocilium?

It depolarizes hair cells, increases neurotransmitter release, and sends more impulses to the brain

What happens when the hairs in a macula bend away from the kinocilium?

It hyperpolarizes hair cells, reduces neurotransmitter release, and decreases impulse generation

What is the crista ampullaris?

the receptor for rotational acceleration, located in the ampulla of each semicircular canal

What stimulates the crista ampullaris?

It is excited by rotational (angular) movements of the head, such as body twirling.

How do crista ampullaris receptors respond to head rotation?

Inertia in the ampullary cupula causes the endolymph in the semicircular ducts to move in the opposite direction of body rotation, bending the hair cells

What happens when hair cells in the crista ampullaris bend?

Bending toward the kinocilium depolarizes hair cells, sending rapid impulses to the brain, while bending away hyperpolarizes them, reducing impulse rate

How do hair cells in complementary semicircular ducts respond to head rotation?

Depolarization occurs in one ear while hyperpolarization occurs in the other ear, allowing the brain to detect rotational movements

What is vestibular nystagmus?

Abnormal eye movement during and after rotation, often accompanied by vertigo.

What happens during vestibular nystagmus when rotation begins and ends?

Eyes drift in the opposite direction of rotation, then rapidly jump toward the direction of rotation. When rotation stops, eyes continue in the direction of spin, then jerk rapidly in the opposite direction

Where does equilibrium information go in the brain?

It travels to reflex centers in the brainstem to allow quick, reflexive responses to imbalance.

What three types of input are used for balance and orientation?

Vestibular receptors, visual receptors, and somatic receptors.

What can happen if there is a problem with equilibrium?

It can cause nausea, dizziness, loss of balance, and nystagmus in the absence of rotational stimuli

What causes motion sickness?

occurs when visual input conflicts with equilibrium input, leading to symptoms like excess salivation, pallor, rapid breathing, and sweating.

How is motion sickness treated?

Anti-motion drugs can be used to depress vestibular input and relieve symptoms.