Nervous system of fish; a detailed study

Nervous system of fish; a detailed study

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  PRESENTED BY: KHADEEJAAZHAR MAHNOOR BAIG
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  INTRODUCTION: In fishes nervoussystem is the primary mechanism to coordinating and integrating body activities The stimuli are received by the nervous system through sense organs. Functioning of nervous system- based on the electrical properties of it's functional units- neurons  Nervous system is derived from ectoderm Nervous system divisible into: Central nervous system Peripheral nervous system Autonomous nervous system
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   Fish possessa well developed nervous system consisting of brain, spinal cord and the nerves whose function is to coordinate the activities of the body.  Brain: shows considerable variations in its size in relation to the body in different species and does not occupy the entire cranial cavity. The space b/w cranium and brain is full of gelatinous substance.  Fish typically have quite small brains relative to body size compared with other vertebrates. › 1/5th size of similarly sized mammal or bird.  But, in is some fishes like mormyrids and have large brains.
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   Teleostean brainis divided into three region:  Prosencephalon (fore brain)  Mesencephalon (mid brain)  Rhombencephalon (hind brain)
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  o Two gangliosof almost equal size are present in the epithalamus and are called the habenulae. o Hebenulae receives a massive afferent input from the pineal gland and a moderate input from the olfactory region and telencephalon. o The grandular pineal body arise from dorsal wall of dicephalon and is considered to be an endocrine gland.
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   Hypothalamus exercisescontrol over the endocrine system of the fish through hypophysis. It contains neurosecretory cells and their secretions are carried to the hypophysis, influencing its activities.
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  o Mesencephalon consistof dorsally situated optic tectum and ventral situated tegmentum. o The optic tectum forms two optic lobes. o The optic tectum projects into optocoel and forms a pair of torus longitudinalis which is a characteristic feature of all the teleost. Function as a correlation centre for photostatic and gravistatic area of brain
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   Metencephalon consistsof cerebellum.  The cerebellum is a single lobed structure that is usually very large, typically cerebellum is the biggest part of brain.  Hagfish and lampreys have relatively small cerebellum but at the other hand, the cerebellum of mormyrids (Elephant fish) is massively developed.  Metencephalon is particularly involved in swimming & in balance, as it maintains body posture by coordinating muscular activities.
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   Myelencephalon alsocalled as brain stem.  It is the most posterior part of the brain.  It controls the functions of the muscles and body organs.  In case of bony fishes, Myelencephalon or brain stem is concerned with respiration and osmoregulation.
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  The spinal nervesarise in pairs from the spinal cord and are metamerically arranged. Each spinal nerve has a dorsal and a ventral root originating from spinal cord and is of a mixed type containing both sensory and motor fibres. Both the roots join to form the mixed nerve which emerges out of the vertebral column through the inter- vertebral aperture. The dorsal root is mainly sensory while the ventral one contains motor fibres.
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  Ten pairs ofcranial nerves in fishes: › First pair- Olfactory nerve › Second pair- Optic nerve › Third pair-Oculomotor nerve › Forth pair- Trochlear nerve › Fifth pair- Trigeminal nerve › Sixth pair- Abduscens nerve › Seventh pair – Facial nerve › Eighth pair- Auditory nerve › Ninth pair- Glossopharyngeal › Tenth pair- Vagus nerves
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   OLFACTORY NERVE:It carries smell impulse.  OPTIC NERVE: It carries visual impulse.  OCULOMOTOR NERVE: It allows movement of the eye muscles & constriction of pupil.  TROCHLEAR NERVE: It enables movement of oblique muscles of eyes. Oblique muscles are the muscles which are responsible for eye movement.  TRIGEMINAL NERVE: This nerve is responsible for sending pain, touch and temperature sensations from face to brain.
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   ABDUCENS NERVE:The abducens nerve functions to innervate the lateral rectus muscles of eyeball.  FACIAL NERVE: It control facial movements by innervating facial muscles.  AUDITORY NERVE: Also called cochlear nerve, is cranial nerve responsible for hearing. It is the sensory nerve that transfers auditory information from the cochlea( auditory area of the inner ear) to the brain.  GLOSSOPHARYNGEAL NERVE: It has both sensory( sensation) and motor (movement) functions. It is responsible for taste & swallowing.  VAGUS NERVE: It is responsible for the regulation of internal organ functions, such as digestion, heart rate & respiratory rate.
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   The autonomicnervous system consists of ganglia, fibers, and of both the sympathetic and parasympathetic parts.  Autonomic nervous system is generally less prominent in fish. This system does not possess many typical functions of a nervous system, and is placed under this category mainly because its parts are closely connected to either the brain or spinal cord.
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   This systemis composed of parasympathetic and sympathetic parts, used to activate and inactivate muscles of different parts of body systems.  Ganglia, the main component of this system, contain fibers used to connect the nervous system to the muscles of the body.