Question

Internal ear is filled with (a) perilymph (b) endolymph (c) lymph (d) both (a) and (b).

Short answer

The inner ear is filled with both perilymph and endolymph, therefore the correct answer is (d) both (a) and (b).

Step-by-step solution

Understand the Anatomy of the Inner Ear

The inner ear consists of a complex system of tubes and chambers called the labyrinth. The labyrinth has two main fluid-filled sections: the bony labyrinth, filled with perilymph, and the membranous labyrinth, which lies within the bony labyrinth and is filled with endolymph.

Identify the Correct Fluids

Consider the two fluids mentioned that are found within the inner ear's labyrinth. Perilymph is the fluid between the membranous labyrinth and the bone that encloses it, and endolymph is the fluid that is inside the membranous labyrinth.

Select the Option That Includes Both Fluids

Given the options, we want to select the one that correctly identifies both types of fluids present in the inner ear. The options are individually mentioning either perilymph or endolymph, and one option lists both.

Conclude with the Correct Answer

Since both perilymph and endolymph are found in the inner ear, the correct answer would be the one that includes both. Option (d) 'both (a) and (b)' correctly encompasses the presence of both perilymph and endolymph.

Key concepts

Perilymph

In understanding the inner ear, one of the key fluids that play a crucial role in hearing is perilymph. This fluid fills the space within the bony labyrinth, which is one of the two major divisions of the internal ear structure.

Perilymph has a consistency similar to that of cerebrospinal fluid, and it's significant because it serves as a cushioning agent, protecting the delicate structures within the inner ear. Additionally, perilymph acts to conduct sound vibrations from the ossicles to the cochlea where these vibrations can be translated into nerve impulses. Despite its protective qualities, perilymph is also rich in sodium ions, differing in composition from endolymph which has a prevalence of potassium ions.

Endolymph

The counterpart to perilymph is endolymph, another essential fluid within the inner ear's vestibular system. Endolymph is enclosed within the membranous labyrinth, which is itself nestled inside the bony labyrinth.

This fluid is particularly interesting due to its unique ionic composition; it has a higher concentration of potassium compared to the perilymph. The high potassium content is vital for the proper function of hair cells located within the cochlea and vestibular system. These hair cells are responsible for translating mechanical movements stimulated by sound or head movements into electrical signals that the brain interprets as sound or spatial orientation, respectively.

Labyrinth Anatomy

The labyrinth is a fascinating component of the ear's anatomy, aptly named for its intricate structure. It comprises two main sections: the bony labyrinth and the membranous labyrinth. The bony labyrinth is a network of hollow cavities within the temporal bone, consisting of the cochlea (involved in hearing), vestibule (which supports balance), and the semicircular canals (also involved in balance).

Inside the bony labyrinth is the membranous labyrinth, a continuous series of membrane-walled sacs and tubes. This system contains the sensory organs for balance and hearing and is bathed in the potassium-rich endolymph, which contrasts with the sodium-rich perilymph filling the space between the bony and membranous labyrinth.

Biology of Hearing

The biology of hearing is a complex process that begins with sound waves entering the ear and ending with the brain interpreting these signals as sounds. When sound waves reach the inner ear, they create vibrations in the perilymph of the cochlea.

Hair Cell Activation

These vibrations pass through the cochlear duct, disturbing the endolymph and causing the hair cells to bend. The bending of these hair cells opens ion channels which convert the mechanical energy into electric impulses.

Neural Signal Transmission

The auditory nerve then carries these impulses to the brain, leading to the perception of sound. Each step is crucial, and the distinct roles of perilymph and endolymph are vital for the proper functioning of this auditory system.