Neuro 202 Quiz 7

How are the hair cells of the utricle and sacculus arranged and what does this allow them to detect?

hair cells and their stereocilia of the utricle and sacculus are arranged so linear acceleration in all directions can be detected.

Where do the vestibular nuclei project to? What is the purpose of each connection?

1. Cerebellum - Adjust motor movements to preserve balance. 2. Cranial nerve nuclei for nerves III, IV and VI in brainstem (oculomotor, trochlear, abducens) - Allow you to keep your eyes focused on a target when moving the head. Vestibulo-ocular Reflex. 3. Vital centers of medulla - Adjusts breathing and blood pressure based on body position 4. Ventroposterior (VP) Thalamus - These connections are then sent to the cerebral cortex and are thought to provide the conscious perception of body position/movement.

What are the inputs to the vestibular nuclei? What is the purpose of each? Why are the vestibular nuclei highly interconnected?

1. Cerebellum - feedback from muscle movement 2. Visual system - focuses eye movements 3. Muscle spindles - stretch receptors located in skeletal muscles that detect changes in muscle length; help with unexpected changes in balance. Highly interconnected to analyze information from both inner ears! Cross communication!

What are the functions of the vestibular system?

1. Detects head position and head movement 2. Relays signals to motor neurons to control posture and maintain balance 3. Relays signals to motor neurons that control the eyes to aid in visual fixation during movement 4. Provides the sense of "up" vs "down" and where our bodies are in space 5. Change respiration and circulation based off body position

What are the structures found in the labyrinth?

1. Three semicircular canals in each ear located at right angles to each other 2. Two otolith organs in the vestibule - the utricle and the sacculus.

How does information from the muscle spindles of the neck and vestibular nuclei contribute to the detection of balance?

1. When you lose your balance, the vestibular system is activated since the right side of head tilts. Muscle spindles in neck DO NOT change length and no activation! This is why you would fall. 2. When you consciously bend your neck with no loss of balance, the vestibular system is activated since you tilt your head. Muscle spindles in neck DO change length and activity changes.

What are the three types of angular movements of the head that can be detected by the semicircular canals and what are examples of each? What is the brain able To do with this information?

1. Yaw - left/right (shaking head no) 2. Pitch - nose up/down (shaking head yes) 3. Roll - ears up/down The brain can put all of the information together to determine the angular movements of the head

What two types of information do the otolith organs detect?

1. the force of linear acceleration - when force is applied to an object that moves in a line. (stopping/starting in a car, elevator) 2. gravity - position of the head with respect to gravity.

Where are the hair cells of the semicircular canals located? What is the orientation of the kinocilium in this structure?

Confined to a swelling at the end of each canal called the ampulla. The kinocilium point toward the vestibule in each ampulla.

What are otoconia?

Crystals that fill the otolithic membrane making it much more dense

Where is the vestibular system located in the inner ear?

In the labyrinth of inner ear

What is positional vertigo? What causes it and how is it treated?

Occurs when a small piece of the otolithic membrane breaks off and presses against the cupula. Treated with repositioning exercises and will break down over time.

What is Meniere's disease? What causes it and how is it treated?

Results from sudden pressure changes in the inner ear. No known cause of production of excess endolymph. Treatment by destroying the inner ear on the affected side.

What structures are found on the hair cells of the vestibular system? What does their arrangement look like? What fluid surrounds them?

Stereocilia arranged in a stair-case pattern with the longest one called the kinocilium. Stereocilia are surrounded in endolymph.

Where do the neurons with vestibular information in vestibulocochlear nerve terminate? Where are these structures located?

The axons of the vestibulocochlear nerve (which contains the vestibular neurons) project to the vestibular nuclei, which are found in the brainstem near the junction between the pons and medulla.

How do the semicircular canals on opposite sides of the head respond to angular acceleration of the head/body? Use the example of sitting up straight and turning your head.

The fluid inside the semicircular canals (endolymph) lags behind because of inertia (stays where it was). The endolymph bends the cupula and therefore also bends the stereocilia, changing their firing. Opposite responses happen in the semicircular canals on each side of the head. When sitting up straight and turning head to the left, in the left ampulla, endolymph moves towards the kinocilium resulting in lots of action potentials being fired. In the right ampulla, endolymph moves away from the kinocilium, resulting in no action potentials being fired.

What type of information do semicircular canals detect?

The force of angular acceleration: when a force is applied to an object that moves around an axis. This occurs when the head turns around the neck or the entire body turns.

What are the stereocilia of the hair cells of the semicircular canals embedded in? What is its density compared to endolymph?

The stereocilia in the ampulla are embedded in a gel called the cupula, which has the same density as endolymph.

What happens when the hair cells of the vestibular system bend? Why does this occur?

The stereocilia of the hair cells are linked to mechanically-gated potassium channels that allow (or restrict) the movement of potassium ions when they bend. The direction of bending in the kinocilia determines if hair cells are depolarized or hyper polarized. Towards the kinocilium depolarizes and away from the kinocilium hyperpolarizes.

What happens when the stereocilia of the hair cells in the vestibular system bend towards the kinocilium vs away from the kinocilium or are straight?

Towards the kinocilium depolarizes the hair cell and away from the kinocilium hyperpolarizes the hair cell. If the stereocilia are straight up and down, the hair cell is at rest and there will be some glutamate released and few A.P.'s sent.

What are the common symptoms of general disfunction of the vestibular system?

Vertigo, dizziness, inappropriate eye movements (nystagmus), poor balance, nausea, loss of perception of up and down.

What does alcohol do to the cupula of the crista ampullaris and how does this help contribute to motion sickness/spinning of being drunk?

When excessive alcohol is consumed, it can enter the cupula of the crista ampullaris. This makes it denser than surrounding endolymph (when it should be the same density). This essentially turns the crista ampullaris into an otolith organ (a macula), which gives sensation of spinning and overcompensation of movements.

What is the entire sensory apparatus of the ampulla called?

the crista ampullaris (cupula + hair cells)

What is the entire sensory apparatus of the otolith organs called?

the macula (hair cells + membrane)

What type of information does the macula of the utricle detect compared to the macula of the sacculus?

the macula of the utricle detects linear acceleration in the horizontal plane and gravity by tilting the head. the macula of the sacculus detects linear acceleration in the vertical plane and gravity by tilting the head (elevator)

What are the stereocilia of the hair cells of the otolith organs embedded in? What is its density compared to the surrounding endolymph?

the otolith organs, utricle and sacculus, are embedded in a heavy membrane called the otolithic membrane. Its density is much heavier than endolymph.

What nerve innervates the hair cells of the vestibular system and where are the soma of these neurons located?

the vestibule-cochlear nerve (VIII). The soma of the neurons in this nerve are found in Scarpa's ganglion.

What happens when the stereocilia of the hair cells in the macula are bent?

they depolarize and release glutamate onto the vestibulocochlear nerve.