Physiology Lecture: Vestibular System and Ear Anatomy

Objective

• Focus on the vestibular system, particularly its structure and role in balance.
• Cover anatomy of the ear: external, middle, inner ear.
• Aim to provide foundational understanding from basic anatomy to physiology.

Ear Anatomy Overview

• External Ear: Orange section on diagrams.
• Middle Ear: Pink section on diagrams.
• Inner Ear: Key focus due to its role in balance.

Inner Ear Structure

• Comprised of the cochlea, semicircular canals, and otolith structures (utricle and saccule).
• Semicircular canals are crucial for detecting rotational movements.
• Otolith organs (utricle and saccule) detect gravitational changes and linear movements.

Vestibular System

• One of three major sensory systems (others: visual, somatosensory).
• Located in the inner ear, contributes to balance and spatial orientation.
• Abnormalities can cause dizziness and vertigo.

Sensory Inputs and Balance

• Semicircular canals detect head rotations.
• Utricle and saccule manage gravitational and linear motion.
• Action potentials from vestibular nerves send information to the brain.

Equilibrium

• Dynamic Equilibrium: Senses of rotation or movement.
• Static Equilibrium: Senses positioning (linear/constant state).
• Balanced equilibrium prevents dizziness or vertigo.

Vestibular Apparatus

• Composed of three semicircular canals (anterior, posterior, horizontal) oriented in different directions.
• Otolith organs (utricle and saccule) provide head position information relative to gravity.

Vestibular Reflexes

• Vestibulo-Ocular Reflex (VOR): Keeps vision stable during head movements.
• Caloric Test: Uses temperature changes in the ear to test vestibular function.

Common Pathologies

• Benign Paroxysmal Positional Vertigo (BPPV): Caused by displaced calcium carbonate crystals in semicircular canals.
• Treatment: Epley maneuver helps reposition these crystals.

Nystagmus

• Involuntary eye movement indicating vestibular system issues.
• Types include horizontal, vertical, or rotational movements.

Key Terminology

• Ampulla: Bulging at the end of semicircular canals containing hair cells for detecting motion.
• Hair Cells: Sensory receptors that trigger action potentials when moved.

Cranial Nerves and Balance

• Vestibular Nerve (Cranial Nerve VIII): Key role in transmitting balance information.
• Other Related Nerves: Involve ocular movement and coordination.

Summary

• Balance relies on complex interplay between various sensory inputs, primarily the inner ear structures.
• Proper function prevents dizziness and maintains equilibrium.
• Abnormalities can be diagnosed through maneuvers and tests, with treatments available to manage conditions like BPPV.