The myodural bridges' existence in the sperm whale

Abstract

Recent studies have identified that the myodural bridge (MDB) is located between the suboccipital muscles and cervical dura mater in the posterior atlanto-occipital interspace within humans. The myodural bridge has been considered to have a significant role in physiological functions. However, there is little information about the myodural bridge in marine mammals; we conducted this study to investigate and examine the morphology of the myodural bridge in a sperm whale. We also aim to discuss the physiological functions of the myodural bridge. In this study, a 15.1-meter long sperm whale carcass was examined. Multiple methods were conducted to examine the bridges of the sperm whale which included dissection, P45 plastination and histological analysis. This study confirmed the existence of the myodural bridge in the sperm whale and shows there are two types of the bridge in the sperm whale: one type was the occipital-dural bridge (ODB), the other type was the MDB. A large venous plexus was found within the epidural space and this venous plexus is thought to contain a great amount of blood when in deep water and thus the movements of suboccipital muscles could be a unique power source that drives cerebrospinal fluid circulation.

Existence and Features of the Myodural Bridge in Gentoo Penguins: a morphological study

“…This direct connection between the RCDmi and the SDM of the Nephocaena phocaenoides might create a more pronounced effect of the RCDmi muscle on the SDM [19]. Furthermore, the present authors have confirmed that sperm whales have two different origins of their MDB: one origin is from the ODB (occipital dural bridge) which originates from the periosteal surface of the occiput and fuses with the dura mater [20], and the other bridge (MDB) originates from the RCDmi, which transmits the tension from the RCDmi to the dura mater. The MDB stabilizes the dura mater, the spinal cord, and the ODB [20].…”

“…Furthermore, the present authors have confirmed that sperm whales have two different origins of their MDB: one origin is from the ODB (occipital dural bridge) which originates from the periosteal surface of the occiput and fuses with the dura mater [20], and the other bridge (MDB) originates from the RCDmi, which transmits the tension from the RCDmi to the dura mater. The MDB stabilizes the dura mater, the spinal cord, and the ODB [20]. The MDB, observed in the atlanto-occipital interspace of penguins, is primarily composed of dense connective tissue fibers originating from the RCDmi muscle.…”

“…Interestingly, it was previously found that the RCDmi muscle of the Nephocaena phocaenoides was located on the deep surface of the RCDma, and the RCDmi was observed originating from occiput [19]. Furthermore, the RCDmi of the sperm whale was priviously found to originate from the dorsal aspect of the occipital squama [20]. This spatial distribution of the .…”

“…In1995 Hack et al initially proposed the concept of the MDB [1]. Numerous researchers have since studied the MDB in detail, confirming the MDB's existence in both humans [1][2][3][4][5][6][7] and animals [18][19][20][21][22][23][24]. These researchers have further hypothesized about the putative physiological functions of the MDB [8-17].…”

“…According to rencent reports, MDB dysfunction may occur with pathological conditions of the RCPmi muscle, resulting in the generation of cervicogenic headache, and other craniofacial disorders [13][14][15][16][17]. In recent years, researchers have found that the MDB is a universal structure in mammals [18], including marine mammals (Nephocaena phocaenoides and sperm whales) [19,20]. The MDB also exists in reptiles (Siamese crocodile and Trachemys scripta elegans) [21,22], as well as in birds (Rock pigeons and Gallus domesticus) [23,24].…”