Vestibular Apparatus Overview

Overview

This lecture explains the vestibular apparatus of the ear, focusing on how the semicircular canals, utriculus, and sacculus help maintain posture and balance.

Vestibular Apparatus: Structure & Functions

• The vestibular apparatus is part of the inner ear, separate from the cochlea (which is for hearing).
• It is essential for maintaining both posture (body position) and balance (stability during movement).
• The main structures involved are the semicircular canals, utriculus, and sacculus.

Semicircular Canals & Balance

• There are three semicircular canals, each detecting movement in a different plane (up/down, forward/backward, side to side).
• Canals are filled with endolymph fluid that moves when the head moves, stimulating receptors.
• The receptor in each canal is called the crista (plural: cristae).
• Movement of endolymph bends the ampulla (a jellylike structure), which bends the crista, generating an electrical impulse.
• The impulse is sent to the cerebellum (in the brain) via the auditory nerve.
• The cerebellum processes the impulse and sends instructions to muscles to restore balance.
• In exams, key points to include: change in speed/direction, stimulation of cristae, impulse conversion, transmission to cerebellum, and muscle response.

Utriculus, Sacculus & Posture

• Utriculus and sacculus are two swellings below the semicircular canals, detecting head position (posture).
• Utriculus detects horizontal (lying down) position; sacculus detects vertical (upright/standing) position.
• Both contain receptor cells called the macula (plural: maculae), sensitive to gravity.
• A change in head position stimulates the macula, converting the stimulus into an impulse.
• The impulse goes to the cerebellum via the auditory nerve, which then sends signals to muscles to adjust posture.
• For exams: describe change in head position, stimulation of macula, impulse conversion, transmission to cerebellum, and posture correction by muscles.

Key Terms & Definitions

• Vestibular apparatus — Inner ear structure responsible for posture and balance.
• Semicircular canals — Three fluid-filled tubes detecting head movement in different planes.
• Crista — Receptor in semicircular canals detecting movement.
• Utriculus & Sacculus — Swollen regions sensing head position (horizontal and vertical).
• Macula — Receptor cells in utriculus and sacculus, detecting position using gravity.
• Cerebellum — Brain region controlling balance and muscle tone.
• Auditory nerve — Nerve pathway transmitting balance and posture information to the brain.

Action Items / Next Steps

• Review diagrams of the vestibular apparatus, labeling all key parts.
• Practice explaining the difference between posture and balance.
• Prepare flashcards using the key terms and definitions.
• Work through possible exam questions describing the role of semicircular canals and the utriculus/sacculus.