Special Senses | Vestibule | Maculae: Utricle & Saccule

Summary

This video provides an in-depth explanation of the vestibular system, focusing on the utricle and saccule, which detect changes in head position and movement. It explores how the otolithic membrane reacts to linear and vertical acceleration, triggering responses in hair cells. The script discusses the role of stereocilia, how they affect action potentials, and the neurotransmitters released, such as glutamate and aspartate. It also details the structure and function of Type I and Type II vestibular hair cells, their connections to the vestibular ganglion, and the overall importance of the system for balance and spatial orientation.

Takeaways

• 😀 The vestibular system detects changes in head movement and position using structures like the utricle and saccule.
• 😀 The utricle responds to horizontal (linear) accelerations and head tilting, while the saccule responds to vertical acceleration.
• 😀 The otolithic membrane in the utricle and saccule moves in response to acceleration, which affects the hair cells within these structures.
• 😀 When the stereocilia of hair cells bend toward the kinocilium, ion channels open, causing depolarization and increasing action potential frequency.
• 😀 If stereocilia move away from the kinocilium, ion channels close, leading to hyperpolarization and a decrease in action potential frequency.
• 😀 The type 1 vestibular hair cells have a bulbous shape with a calyx-like nerve terminal, while type 2 cells are cylindrical with a bouton-like nerve terminal.
• 😀 The vestibular ganglion (also known as Scarpas ganglion) transmits information from the hair cells to the brain.
• 😀 Glutamate and aspartate are key neurotransmitters released by the vestibular hair cells during depolarization.
• 😀 The movement of the otolithic membrane and the resulting activity of the hair cells help detect head movements and changes in orientation.
• 😀 The vestibular system plays a crucial role in maintaining balance and spatial awareness by processing signals related to head movement and acceleration.
• 😀 The concept of linear acceleration and vertical acceleration is essential for understanding how the vestibular system works in response to various head movements.

Q & A

What is the role of the otolithic membrane in the vestibular system?

The otolithic membrane responds to linear and vertical accelerations, moving in response to changes in the position of the head. This movement affects the stereocilia of hair cells, altering their action potentials.

How does linear acceleration affect the otolithic membrane and stereocilia?

During linear acceleration, the otolithic membrane moves, causing the stereocilia to bend towards the kinocilium. This bending increases action potentials and triggers neurotransmitter release.

What happens to the action potentials when the stereocilia bend towards the kinocilium?

When the stereocilia bend towards the kinocilium, ion channels open, allowing potassium and calcium ions to flow into the cell. This depolarizes the cell, leading to an increase in action potentials and the release of neurotransmitters like glutamate and aspartate.

What is the difference between Type 1 and Type 2 vestibular hair cells?

Type 1 hair cells have a bulbous shape at their basolateral end and a calyx-like afferent nerve terminal, while Type 2 hair cells are cylindrical with a bouton-like afferent nerve terminal.

What happens when the stereocilia bend away from the kinocilium?

When the stereocilia bend away from the kinocilium, the tip links relax, closing the ion channels. This causes the cell to hyperpolarize, reducing or stopping the release of neurotransmitters and action potentials.

Why is calcium important for neurotransmitter release in the vestibular system?

Calcium plays a key role in the release of neurotransmitters by facilitating the fusion of synaptic vesicles with the cell membrane. This allows the neurotransmitters, such as glutamate and aspartate, to be released by exocytosis.

What neurotransmitters are released by the vestibular hair cells?

The two main neurotransmitters released by vestibular hair cells are glutamate and aspartate.

What is the function of the vestibular ganglion?

The vestibular ganglion, also called Scarpa's ganglion, contains the cell bodies of afferent neurons that transmit signals from the vestibular hair cells to the central nervous system.

How do the otolithic organs respond to vertical and linear accelerations?

The utricle responds to horizontal linear acceleration and head tilting, while the saccule responds to vertical acceleration. Both organs move the otolithic membrane, which in turn alters the stereocilia of the hair cells.

What effect does hyperpolarization have on the vestibular hair cells?

Hyperpolarization of the vestibular hair cells, caused by the stereocilia bending away from the kinocilium, reduces or prevents neurotransmitter release and stops action potentials from being sent to the brain.