Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 198 convey information about rotational movements of the head. Sensory receptors in the semicircular ducts respond to rotational movements of the head. These hair cells are active during a movement but are quiet when the body is motionless. For example, as you rotate your head to the left, receptors stimulated in the semicircular ducts inform you of how fast the movement is, and its direction. The saccule and the utricle provide information about your position with concerning gravity. If you stand with your head tilted to one side, these receptors communicate your head’s angle and whether your head tilts forward or backward. The saccule and the utricle are also triggered by sudden speed. When your car accelerates from a stop, the saccular and utricular receptors give you the impression of increasing speed. Pathways for Equilibrium Sensations Sensory fibers from these ganglia form the vestibular branch of the vestibulocochlear nerve (VIII). These fibers innervate neurons within the pair of vestibular nuclei at the boundary between the pons and the medulla oblongata. The two vestibular nuclei have four functions. Hearing The receptors of the cochlear duct provide a sense of hearing that enables us to detect the quietest whisper yet remain functional in a noisy room. The receptors responsible for auditory sensations are hair cells similar to those of the vestibular complex. However, their placement within the cochlear duct and the organization of the surrounding accessory structures shield them from stimuli other than sound. In transporting vibrations from the tympanic membrane to the oval window, the auditory of 368 The Inner Ear The superficial shapes of the inner ear are created by a layer of dense bone known as the bony labyrinth. The walls of the bony labyrinth are continuous with the surrounding temporal bone. A delicate network of fluid-filled tubes, called the membranous labyrinth , extend from the inner contours of the bony labyrinth. The receptors of the inner ear are located within those tubes. Between the bony and membranous labyrinths flows perilymph , a liquid whose properties closely resemble those of cerebrospinal fluid. The membranous labyrinth contains endolymph , a fluid with electrolyte concentrations different from those of typical body fluids. The bony labyrinth can be separated into the vestibule, three semicircular canals, and the cochlea. The vestibule is made of a pair of membranous sacs: the saccule and the utricle, or sacculus and utriculus. Receptors in the saccule and utricle provide sensations of gravity and linear acceleration. The cochlea , a snail shell, is a spiral-shaped, bony chamber that contains the cochlear duct of the membranous labyrinth. Receptors within the cochlear duct provide the sense of hearing. The duct is sandwiched between a pair of perilymph-filled chambers. The entire complex makes turns around a central bony hub, much like a snail shell. The walls of the bony labyrinth consist of dense bone everywhere except at two small areas near the base of the cochlear spiral. The round window is a delicate, membranous partition that separates the perilymph of the cochlear chambers from the air- filledmiddle ear. Collagen fibers connect the bonymargins of the opening, known as the oval window, to the base of the stapes. Equilibrium The semicircular ducts