Specific Sensory Systems Special Senses – Balance (The Vestibular System)

Question 1

What is The Utricle and Saccule?

Answer 1

• Also contain mechanoreceptors sensitive to displacement of projecting hairs
• Provide information on linear acceleration of the head
• Utricle: hair cells point straight up – respond to horizontal accelerations and tipping of the head in the horizontal plane
• Saccule: hair cells project at right angles to those in the utricle – respond to vertical accelerations (i.e., jumping) and gravitational effects when going from lying down to standing

Question 2

What is The Vestibular System?
(Vestibular Apparatus)

Answer 2

Vestibular Apparatus

• Found in the inner ear in temporal bone
• Semicircular canals (3) + utricle + saccule
• Connects to the cochlear duct
• Filled with endolymph
• Hair cells detect change in motion and position of the head by a similar mechanism as audition hair cells

Question 3

What are The Semicircular Canals

Answer 3

Detect angular acceleration during head flexion/extension, lateral flexion and rotation

• Receptor cells contain stereocilia – found encapsulated by the cupula, a gelatinous mass, that extends to the ampulla (the enlarged region at the base of the semicircular canals)
• Head movement -> movement of semicircular canals and ampulla (attached to the skull) -> fluid in canals pushes against the hair cells -> stereocilia bend -> propagation of APs

Question 4

The Semicircular Canals

make Q

• Hair cells only respond to changes in rotation
• If the head spins continuously at a steady velocity (spinning round and round on a tire swing)  fluid in the semicircular canals move at the same rate at the head  stereocilia return to their resting position