The key difference between endolymph and perilymph is that endolymph is the physiological fluid present within the membranous labyrinth of the inner ear, while perilymph is the physiological fluid present within the bony labyrinth that surrounds the membranous labyrinth of the inner ear.
The inner ear contains two physiological fluids that play very important roles. They are endolymph and perilymph. Endolymph is the intracellular fluid, while perilymph is the extracellular fluid. Endolymph is rich in potassium and low in sodium and calcium. In contrast, perilymph is rich in sodium and low in potassium and calcium. The ionic difference in these fluids contributes to the positive endocochlear potential, which is very important in auditory function.
What is Endolymph?
Endolymph is the fluid found within the membranous labyrinth of the inner ear. It is also known as Scarpa’s fluid. The major ion in the endolymph is potassium. Endolymph fluid is low in sodium. The relative concentrations of potassium and sodium in endolymph are 154 mM and 0.91 mM, respectively.
The inner ear anatomically contains two parts; the bony labyrinth and the membranous labyrinth. The membranous labyrinth is located within the bony labyrinth. Within the membranous labyrinth, there is a fluid called endolymph. Endolymph has a high positive electrical potential, which is about 80–120 mV in the cochlea. This is due to its high concentration of positively charged ions. However, nearby fluids such as perilymph have lower electrical potential. This electrical potential difference allows potassium ions to flow into the sensory receptor cells called hair cells during mechanical stimulation of the hair bundle. Usually, the hair cells are at a negative electrical potential of about -50 mV. Ultimately, hair cell transduces the mechanical force of head movement into neural signals in the brain. Because of this, the brain perceives external sound. Other than that, endolymph also helps in maintaining balance. Furthermore, disruption of the endolymph by jerky movements may cause a disease known as motion sickness. In addition, endolymphatic hydrops has also been linked to a disease known as Ménière’s disease.
What is Perilymph?
The location of perilymph is between the outer wall of the membranous labyrinth and the wall of the bony labyrinth. Therefore, it is the fluid that surrounds the membranous labyrinth. The major cation in perilymph is sodium. It has a low amount of potassium. The sodium and potassium concentration values in the perilymph are 138 mM and 6.9 mM. The perilymph is also known as Cotunnius’ liquid and liquor cotunnii.
Perilymph is also known as the fluid contained within the bony labyrinth. Usually, perilymph surrounds and protects the membranous labyrinth of the inner ear. Moreover, the perilymph contains a large number of proteins, such as extracellular enzymes and immunoglobulins. These proteins are important for immune responses and metabolism. Furthermore, perilymph and endolymph together participate in an unidirectional flow of sound, which is interrupted in diseases such as Ménière’s disease.
What are the Similarities Between Endolymph and Perilymph?
- Endolymph and perilymph are two physiological fluids found in the inner ear.
- Both are also known as cochlear fluids.
- Both have potassium and sodium ions in different concentrations.
- They play a pivotal role in external sound transduction to the brain.
- The disruption of both fluids’ functions can cause diseases.
What is the Difference Between Endolymph and Perilymph?
Endolymph is the physiological fluid within the membranous labyrinth of the inner ear. At the same time, perilymph is the physiological fluid inside the bony labyrinth, which surrounds the membranous labyrinth of the inner ear. Thus, this is the key difference between endolymph and perilymph.
The infographic below presents the differences between endolymph and perilymph in tabular form for side-by-side comparison.
Summary – Endolymph vs Perilymph
The inner ear comprises a bony labyrinth and a membranous labyrinth, and it is filled with two different types of fluids known as endolymph and perilymph. Endolymph is present within the membranous labyrinth, while perilymph fills the space inside the bony labyrinth, which surrounds the membranous labyrinth. So, this is the key difference between endolymph and perilymph. Both fluids fulfill a pivotal role in external sound transduction to the brain.