LECTURE 23 special senses 2 hearing and equilibrium

1- auricle, 2- auditory canal, 3- tympanic membrane, 4- malleus, 5-incus, 6-stapes, 7-oval window, 8-cochlea

1- auricle, 2- auditory canal, 3- tympanic membrane, 4- malleus, 5-incus, 6-stapes, 7-oval window, 8-cochlea

What are the eight structures that sound waves need to traverse from the auricle to reach the inner ear?

Auricle, auditory canal, and tympanic membrane (or eardrum).

Which three components constitute the external ear?

It directs sound waves into the auditory canal

What is the purpose of the auricle?

Sound originates from a vibrating object and travels in waves created by the back and forth vibration of the surrounding air molecules.

How is sound produced? and the sound waves?

Auditory canal

Which passage links the outer ear (auricle) to the eardrum (tympanic membrane)?

In the auditory canal. Ear wax helps to clean and lubricate the ear canal and prevent the entry of bacteria, water and foreign objects.

Where can cerumen be found, and what role does it serve?

(a) Eardrum. (b) By vibrating in response to sound waves. Movement of the eardrum by these vibrations displaces the auditory ossicles.

(a) What alternative term is used for the tympanic membrane? (b) How does this membrane contribute to the transmission of sound waves?

The auditory ossicles (malleus, incus, and stapes) and the oval window.

What are the four components that make up the middle ear?

(a) Malleus. (b) Malleus, incus, and stapes.)

(a) To which ossicle are the vibrations of the tympanic membrane transmitted? (b) Can you list the three ossicles in the sequence from the one connecting the outer ear to the middle ear?

They amplify the vibrations increasing the sound wave pressure. The inner ear consists of a liquid (not air), so the vibrations must transfer into a liquid – Vibrating or moving particles of liquid is much harder than moving particles of air.

What role do the ossicles play in the auditory system? Why do we need to increase sound wave pressure before reaching the inner ear?

Tensor tympani and stapedius. They attenuate sound levels by dampening vibration of the ossicles.

What are the two muscles associated with the ossicles, and what are their functions?

The oval window.

Aside from the incus, which structure is in contact with the stapes?

One is the membranous labyrinth, which is enclosed by the other, the bony labyrinth.

What are the names of the two labyrinths found in the inner ear, and which one is enclosed within the other?

(a) Semicircular canals, vestibule, and cochlea. (b) Semicircular canals and vestibule with equilibrium, cochlea with hearing. )

(a) What are the three components of the bony labyrinth, and (b) which ones are associated with equilibrium and hearing, respectively?

(a) Perilymph is inside the bony labyrinth, endolymph is inside the membranous labyrinth.(b) the perilymph

(a) In the context of the inner ear, where is the perilymph located, and where is the endolymph situated? (b) Which of these fluids is more similar in composition to cerebrospinal fluid (CSF)?

It consists of the cochlear duct, semi-circular ducts, utricle and the saccule (the last two structures are inside the vestibule).

What makes up the membranous labyrinth?

(a) 3 chambers: scala vestibuli, scala media, and scala tympani. (b) The scala media (also known as the cochlear duct))

(a) The cochlea consists of how many chambers, and what are their names (tip:indicated by the term "scala")? (b) Which of these chambers contains endolymph?

The perilymph from the endolymph

The vestibular membrane separates which two fluids??

the scala media

Which chamber (scala) within the cochlea corresponds to the cochlear duct?

(a) Organ of Corti or The spiral organ. (b) Scala media (or cochlear duct). (c) Tectorial membrane)

(a) What are the two names for the receptor organ responsible for hearing? (b) In which chamber is it located, and (c) which membrane covers it?

(a) It is a sensory epithelium (the organ for hearing). (b) Tectorial membrane on the top and basilar membrane (at the base)

(a) What is the Organ of Corti? (b) Which two membranes surround the Organ of Corti (i.e. are in close proximity to it)?

The outer hair cells (OHCs)

The Organ of Corti consists of two types of cochlear hair cells. Which of these cell types is more prevalent?

The outer hair cells (OHCs) receive descending inputs from the brain to assist with the modulation of inner hair cells (IHC) function. The IHCs are the responsible for hearing transmission.

What are the functions of the cochlear hair cells?

(a) The inner hair cells (IHCs) in the Organ of Corti (in the cochlear duct). (b) Transduction, in this specific case: mechanotransduction

(a) Which cells are responsible for converting mechanical vibrations produced by sound into electrical signals, and where are these cells located? (b) What is the term for this conversion process?

Upward movement of the basilar membrane which produces the mechanical bending of the hairs with the tectorial membrane (on top)

What leads to the mechanical bending of the hair bundle toward the longer stereocilia in the IHCs?

(a) Positive mechanical deformation (=mechanical deformation of the hair bundle toward the longer stereovilli). (b) K+ influx into the cell will cause depolarization of the membrane.

(a) What serves as the stimulus for the opening of mechanosensitive channels that allow potassium ions to enter or exit? (b) What is the consequence in terms of membrane potential?

(a) The depolarization of the membrane caused by the influx of K+. (b) The release of synaptic vesicles with neurotransmitters with will stimulate the sensory neuron.

(a) What triggers the opening of voltage-sensitive Ca2+ channels in the hair cells, and (b) what is the outcome of the influx of this ion?

(a) Downward movement of the basilar membrane. (b) Close K+ channels. (c) Hyperpolarization: not transmission of hearing signal.

(a) What induces a negative mechanical bending of the stereocilia in the hair cells?, (b) how does this affect the K+ channels?, and (c) what is the ultimate impact on the membrane potential of these cells?

(a) CN VIII: The vestibulocochlear nerve, that consists of the vestibular and cochlear nerves. (b) Cochlear nucleus, superior olive, inferior colliculus (midbrain), medial geniculate nucleus (MGN, thalamus).

(a) What cranial nerve is responsible for transmitting auditory signals from the ear to the brain? (b) Can you list the four nuclei associated with the auditory projection pathway in their sequential order?

Temporal lobe

In which lobe of the cerebral cortex is the primary auditory cortex located, which is responsible for conscious sound perception?

3 semicircular ducts, utricle and saccule (in the vestibule).

What makes up the vestibular apparatus or system?

(a) Hair cells (in the crista and macula). (b) The vestibular nerve, part of the CN VIII.

(a) What are the sensory receptors for the vestibular system, and (b) which nerve is linked to them?

The utricle and saccule are parts of the inner ear (membranous labyrinth) involved in the sense of balance (part of the vestibular system).

What are the utricle and saccule? Where are they located?

macula

What is the name of the sensory epithelium found in the utricle and saccule?

(a) The crista, or crista ampullaris, is a sensory epithelium that contains hair cells. (b) A cupula, gelatinous structure primarily composed of glycoproteins.

(a) What is the crista, and where is it situated? (b) What is located above the receptor cells in the crista ampullaris?

(a) Small calcium carbonate crystals (b) In the macula of saccule and utricle, specifically in the otolith membrane located on top of the receptor hair cells.

(a) What are otoliths (or otoconia)? (b) Where can otoliths be found in the vestibular system?

Hair cells are the sensory receptors of the vestibular system, they monitor head position and movement.

What is the primary function of the hair cells in the macula and crista?

The vestibular apparatus maintains balance & awareness of the body's spatial orientation

What is the function of the vestibular apparatus?

The semicircular ducts and crista ampullaris.

Which structure(s) are responsible for detecting head rotation in different planes?

(a) Static equilibrium: sense head positions; linear acceleration: straight line motions, such as when riding in a car or an elevator. (b) Hair cells in the macula

(a) Can you explain what static equilibrium and linear acceleration are, and (b) which inner ear structures are involved in detecting them?

Macula utriculi detect the tilt of the head. When you tilt your head down to read a book for example, the heavy gelatinous membrane (containing otoliths) bends the stereocilia, stimulating the hair cells in the macula

How is the tilt of the head detected, and what is the role of otoliths in this process?

The utricle detects linear accelerations and head-tilts in the horizontal plane and the macula of the saccule in the vertical plane.

What does the macula utricle detect, and what about the macula of the saccule?

Semicircular ducts and crista ampullaris.

Which inner ear structures detect angular acceleration or rotational head movement?

Endolymph

What type of fluid moves through the ducts during head rotation?

The movement of endolymph through the duct (caused by rotation of the head) will move the stereocilia in the hair cells of the ampulla (the cupula is pushed over)

What causes the stereocilia in the hair cells of the ampulla to move?