Acoustico lateralis system..,,.,,

Nisar Ahmad

1. ACOUSTICO LATERALIS SYSTEM SUBJECT: Physiology NAME: NISAR AHMAD, Saif - ur -Rehman & Amna S abir M.SC 4 TH DEPARTMENT OF ZOOLOGY

2. ACOUSTICO LATERALIS SYSTEM Acoustico is the inner-ear region and Lateralis is the lateral-line organs located in the skin, forming a sensory system that conveys environmental information to the brain of a fish: the lateral-line organs respond to changes in water pressure and displacement, the inner ear responds to sound and gravity. Generally such a system is found in aquatic lower vertebrates (e.g. lampreys, sharks, bony fish, and one or two amphibians).

3. In sharks, hearing and vibration detection (The Acoustico-Lateralis System) are fundamentally linked. For sharks the inner ears are nestled inside the posterior part of the braincase on top of the head. The only external manifestation of a shark's ears are two small openings on top of the head, just behind the eyes, known as endolymphatic pores.

4. Structure of the Lateral Line and the Inner Ear: The functional unit of both the shark inner ear and lateral line is the hair cell. Each hair cell consists of a more-or-less globular basal body from one end of which project a series of cilia (hair-like structures). One of these cilia, called aklinocilium , is much longer than the others.

5. The Inner Ear: The shark inner ear is a fluid-filled structure consisting of a cartilaginous sac to which is attached three semicircular cartilaginous tubes. These fluid-filled tubes are set at right angles to one another and are lined with hair cells. Each semicircular tube responds only to accelerations within the plane parallel to its orientation.

6. Sound Detection: Recently de-classified U.S. Navy studies have revealed that the ocean is criss-crossed by meandering ribbons of very cold, dense water surrounded by warmer, less dense water. Since sound travels more efficiently in dense materials, these liquid ribbons act as 'sound tunnels'.

7. Hair cells The hair cells are the primary auditory receptor cells and they are also known as auditory sensory cells, acoustic hair cells, auditory cells or cells of Corti . The organ of Corti is lined with a single row of inner hair cells and three rows of outer hair cells.

8. Pillar cells are found in the organ of Corti and act as supporting cells for hair cells. They are divided into two types: inner and outer . Boettcher's cells are found in the organ of Corti where they are present only in the lower turn of the cochlea. Claudius' cells are found in the organ of Corti located above rows of Boettcher's cells.

9. Deiters ' cells (phalangeal cells) are a type of neuroglial cell found in the organ of Corti and organised in one row of inner phalangeal cells and three rows of outer phalangeal cells.

10. Hensen's cells are high columnar cells that are directly adjacent to the third row of Deiters ’ cells. Hensen's stripe is the section of the tectorial membrane above the inner hair cell. Nuel's spaces refer to the fluid filled spaces between the outer pillar cells and adjacent hair cells and also the spaces between the outer hair cells. Hardesty's membrane is the layer of the tectoria closest to the reticular lamina and overlying the outer hair cell region. Reissner's membrane is composed of two cell layers and separates the scala media from the scala vestibuli . Huschke's teeth are the tooth shaped ridges on the spiral limbus that are in contact with the tectoria and separated by interdental cells.

11. Lateralis System: Lateral line system, also called lateralis system, a system of tactile sense organs, unique to aquatic vertebrates from cyclostome fishes (lampreys and hagfish) to amphibians, that serves to detect movements and pressure changes in the surrounding water. It is made up of a series of mechanoreceptors called neuromasts (lateral line organs) arranged in an interconnected network along the head and body.

12. Lateral Line Structure and Function: The shark lateral line consists of a fluid-filled, hair cell-lined tube extending along each flank, just beneath the skin. This tube connects to the external environment via secondary fluid-filled tubules that branch off from the main tube and penetrate the skin at regular intervals. The lateral line system is visible on the surface of the skin by the presence of small pores known as mechanosensory neuromasts .

13. Lateral Line use in Feeding Behaviour The best known behavioural use of the lateral line in sharks is in prey detection. Other uses of the lateral line, particularly in bony fish, include schooling behaviour , social communication, hydrodynamic imaging, predator avoidance and rheotaxis .

14. Function:

15. The major unit of functionality of the lateral line is the neuromast . The neuromast is a mechanoreceptive organ which allows the sensing of mechanical changes in water. There are two main varieties of neuromasts located in animals, canal neuromasts and superficial or freestanding neuromasts

16. Electric Sense Organs : Evolved from lateral line neuromastorgans Found in many bony fishes e.g., sturgeon and elasmobranchs(sharks and their relatives) Extremely sensitive to electric current, such as those produced by muscle movements