Problem 5 - Biology: The Dynamic Science

Question

The following situation is associated with movement and position in the human body: a. Statoliths in statocysts bend sensory hairs and trigger action potentials. b. If sensory hairs in the utricle are oriented horizontally and those in the saccule are oriented vertically, the person is lying down. c. When the head rotates, the endolymph in the semicircular canal pulls the cupula with it to activate sensory hair cells. d. Displacement of the utricle and saccule generates action potentials. e. If the body is spinning at a constant rate and direction, the cupula is displaced and action potentials are initiated.

Step-by-Step Solution

Answer

The presented situations describe the working of the structures in the vestibular system of the ear and how they help in maintaining balance and perceiving body position. Action potentials are triggered when movements or changes in position cause displacement of specific parts (statoliths, utricle, saccule, and cupula) in the vestibular system.

Step 1: Understanding Statoliths in Statocysts

Statoliths in statocysts are present in the vestibular system of the ear. They are dense calcium carbonate granules that move in response to gravity. When these statoliths move, they bend the underlying sensory hairs in the gelatinous mass triggering action potentials.

Step 2: The role of Utricle and Saccule

The utricle and saccule are two structures in the vestibular system that help detect linear acceleration and gravitational pull. These structures have sensory hairs. When a person is lying down, the sensory hairs in the utricle are horizontally oriented and those in the saccule are vertical. This change in hair orientation triggers respective action potentials.

Step 3: Understanding Role of Semicircular Canal and Cupula

When the head rotates, the motion of the fluid - endolymph within the semicircular canal, pulls the cupula, a gelatinous structure, with it. This displacement of the cupula triggers the cells present on it and activates the sensory hair cells.

Step 4: Utricle and Saccule Displacement

Displacement of the utricle and saccule, due to body movement or change in body position, stimulates sensory hair cells, and this generates action potentials which are transmitted to the brain.

Step 5: Effect of Constant Spinning

If the body is spinning at a constant rate and direction, the continuous fluid motion in semicircular canals causes continuous displacement of the cupula. This continuous displacement leads to continued triggering of action potentials.