Overview
This lecture explains the structure and function of the vestibular apparatus—specifically the semicircular canals, utriculus, and sacculus—in maintaining human posture and balance.
Vestibular Apparatus Overview
- The vestibular apparatus is the part of the inner ear involved in posture and balance, not hearing.
- It is located separately from the cochlea, which is responsible for hearing.
Semicircular Canals and Balance
- There are three semicircular canals, each detecting motion in a different plane: up/down, forward/backward, and left/right.
- Canals are filled with endolymph fluid; its movement stimulates sensory receptors.
- The receptor in each canal is called the crista.
- Movement of the endolymph bends the cupula in the ampulla, stimulating the crista to convert the stimulus to a nerve impulse.
- The impulse travels via the auditory nerve to the cerebellum, which processes information to maintain balance.
- The cerebellum sends signals to muscles to restore or maintain balance.
Utriculus, Sacculus, and Posture
- Utriculus and sacculus are two swollen regions beneath the semicircular canals.
- Their main function is detecting changes in posture (body's position: upright, lying down, or moving between these).
- Utriculus detects horizontal position; sacculus detects vertical position.
- Each contains a receptor called the macula, which senses gravity to determine body orientation.
- A change in head position stimulates the macula, which converts the stimulus to a nerve impulse.
- The impulse travels via the auditory nerve to the cerebellum, which directs muscles to adjust posture.
Key Terms & Definitions
- Vestibular apparatus — part of the inner ear responsible for balance and posture.
- Semicircular canals — three fluid-filled tubes in the inner ear detecting angular motion.
- Crista — receptor in the semicircular canals that detects movement.
- Endolymph — fluid inside the semicircular canals.
- Utriculus (utricle) — inner ear structure that detects horizontal head position.
- Sacculus (saccule) — inner ear structure that detects vertical head position.
- Macula — sensory receptor in utriculus and sacculus sensitive to gravity.
- Cerebellum — part of the brain coordinating posture and balance.
Action Items / Next Steps
- Review the differences between balance (semicircular canals) and posture (utriculus and sacculus).
- Practice full-mark explanation bullet points for exams.
- Study the defined key terms for quick recall.
- Prepare any questions on this topic for clarification in the next class.