Overview
This lecture covers the structure and function of the vestibular apparatus, focusing on the semicircular canals, utriculus, and sacculus, and explains how these structures maintain posture and balance.
Vestibular Apparatus Overview
- The vestibular apparatus is part of the inner ear, separate from the cochlea (hearing organ).
- It is essential for maintaining posture (body position) and balance (body movement stability).
- Key components: semicircular canals, utriculus, and sacculus.
Semicircular Canals and Balance
- There are three semicircular canals, each detecting movement in a different plane (up/down, forward/back, left/right).
- Canals are filled with a fluid called endolymph that moves when the head moves.
- Movement of endolymph stimulates the receptor cell group called cristae in the canals.
- The cristae convert the stimulus into an impulse sent via the vestibular/auditory nerve to the cerebellum.
- The cerebellum processes the impulse and sends instructions to muscles to restore or maintain balance.
- Exam answers must mention: change in speed/direction, stimulation of cristae, conversion to impulse, transmission to cerebellum, and muscle response.
Utriculus, Sacculus, and Posture
- Utriculus and sacculus are swollen regions below the semicircular canals.
- The utriculus is responsible for detecting horizontal (lying down) positions; sacculus detects vertical (standing upright) positions.
- Both contain receptor cells called maculae, which respond to changes in head position due to gravity.
- Change in head position stimulates the macula, converting the stimulus into an impulse sent via the auditory nerve to the cerebellum.
- The cerebellum then directs muscles to adjust posture accordingly.
- Answer structure for exams: note position change, stimulation of macula, impulse creation, message to cerebellum, and signal to muscles for posture.
Key Terms & Definitions
- Vestibular apparatus — structures in the inner ear involved in balance and posture.
- Semicircular canals — three fluid-filled tubes sensing head movement in three planes.
- Endolymph — fluid inside the semicircular canals.
- Cristae — receptor cells in the semicircular canals detecting movement.
- Utriculus and sacculus — inner ear structures detecting head position (posture).
- Macula(e) — receptor cells in utriculus and sacculus sensing orientation relative to gravity.
- Cerebellum — brain area controlling balance and muscle tone.
- Auditory nerve — nerve transmitting balance/posture impulses to the brain.
Action Items / Next Steps
- Review the diagram of the vestibular apparatus, memorizing locations of key structures.
- Practice writing full-mark answers as outlined for exam questions on balance and posture.
- Prepare flashcards with key terms and their functions.