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Nervous System Of A Frog
Transcript of Nervous System Of A Frog
I. Central Nervous System (CNS)
(i) Brain (encephlon)
(ii) Spinal cord (myelon) II. Peripheral Nervous System (PNS)
(i) Cranial Nerves
(ii) Spinal nerves III. Autonomic Nervous System (ANS) THE CENTRAL NERVOUS SYSTEM This is divisible into an ANTERIOR portion- the BRAIN- lying in the cavity of the cranium; and a POSTERIOR PORTION- the SPINAL CORD- which lies in the neural canal of the vertebral column. There is no sharp line of demarcation between the two portions, which are directly continuous with each other. THE FROG'S BRAIN FUNCTION: To control and coordinate functions of body cells, tissues and organ systems so they act harmoniously as a unit. STRUCTURE: Brain is very soft and is enclosed in a cartilaginous cranium (chondocranium) which has two occipital condyles for attachment with atlas. Frog's brain is divided into 3 parts: 1. FOREBRAIN- comprises of olfactory lobes, paired cerebral hemispheres and unpaired diencephalon. 2. MIDBRAIN- characterized by a pair of optic lobes. 3. HINDBRAIN- consists of cerebellum and medulla oblongata. FOREBRAIN OLFACTORY LOBES
Location: These are two rounded or oval lobes at the anterior end of brain.
Function: center of sense of smell CEREBRUM OR CEREBRAL HEMISPHERES
Location: These are two oblongated hemispheres lying immediately behind the olfactory lobes.
Function: seat of intelligence, thought and memory and contorols voluntary and spontaneous actions, center of sight, smell DIENCEPHALON
Location: rectangular part that is located between the optic lobes behind and posterior to the cerebral hemispheres.
Function: The floor of diencephalon is beset with the center of autnonomic NS. MIDBRAIN OPTIC LOBES
Location: These are the oval hollow vessicels on the dorsal side of the brain and forming the widest part of brain.
Function: The optic lobes are seats of sense of sight. the midbrain also controls the activities of eye muscles. HINDBRAIN CEREBELLUM
Location: The cerebellum is in the form of a narrow band in front of the medulla and behind the optic lobes. It is not well developed in frogs.
Function: The cerebellum is the balancing organ and controls the mechanism of autonomic and voluntary movements. MEDULLA OBLONGATA
Location: It is the most posterior part of the brain. Its anterior part is broader than the posterior and is hollowed out by a broad triangular cavity (metacoel).
Function: Governs the involuntary actions. The nerves arising from medulla supply impulses to heart, lungs, stomach etc.
FROG'S SPINAL CORD External structure of spinal cord The spinal cord is the posterior continuation of brain which extends posteriorly into the central canal of vertebral column. It starts from the foramen magnum, runs through the entire length of neural canal and ends posteriorly in the last vertebra in the form of a thin filament (filum terminale). FUNCTIONS OF SPINAL CORD: 1. The spinal cord is seat of reflex action. Therefore, it controls and originates impulses in response to such sensory stimuli which are independent of the brain.
2. It serves as a pathway to such sensory stimuli which are passed to the brain. PERIPHERAL NERVOUS SYSTEM A peripheral portion, the nerves themselves, which connect the central portion with the skin, sense organs, muscles, viscera etc. and serve to convey impulses from these parts to the brain and cord, or motor impulses from the central organs to themselves. SPINAL NERVES OF A FROG 10 pairs of nerves (left, right) arise from the side of the spinal cord Each nerve arising by two roots, a ventral (anterior) and a dorsal (posterior), which unite at their point of exit from the vertebral canal through intervertebral foramen. Emerge between vertebrae 1st Spinal Nerve (Hypoglossal)
Location: emerges out from the neural canal through the first pair of intervertebral foramina between the 1st and 2nd vertebra
Function: Called such because it innervates the muscles of tongue, jaws and hyoid. 2nd and 3rd Special Nerve
Location: Leave the canal between the 2nd & 3rd and 3rd & 4th vertebrae respectively.
Function: The second spinal nerve receives the branches of the 1st & 3rd spinal nerves to form a brachial plexus to the shoulder and forelimb region. 4th, 5th and 6th Spinal Nerve
Location: Leave vertebral canal between 4th & 5th , 5th & 6th and 6th & 7th vertebrae respectively.
Function: These nerves are small and supply the muscles and skin of the body wall. SPINAL NERVES SPINAL NERVES 7th, 8th and 9th Spinal Nerves
Location: The 7th nerve leaves the canal between 7th & 8th vertebrae, the 8th nerve between 8th & 9th vertebrae and the 9th nerve between the 9th or sacral sacral vertebrae and the urostyle.
Function: The 7th, 8th and 9th spinal nerves together form the sciatic plexus, from which branches are given to the large intestine, bladder, oviducts. 10th Spinal Nerve (Coccygeal)
Location: Emerges through a small hole in the side of the urostyle near its anterior end.
Function: It gives branches to the bladder, cloaca and oviducts. CRANIAL NERVES OF A FROG Extending from the lateral surfaces of the brain to the parts of the body. There are 10 pairs of cranial nerves in a frog. CRANIAL NERVES OF A FROG AUTONOMIC NERVOUS SYSTEM Frog also possess special type of nerves which are connected directly to visceral organs of the body and control the involuntary activities. The fibers of these nerves issue from the cranial and spinal nerves and end in the glands, alimentary canal and unstriped muscles. The system of these nerve fibers is known as Autonomic Nervous System and comprises two separate group of nerve fibers: (1) Sympathetic Nervous System
(2) Parasympathetic Nervous System SYMPATHETIC NERVOUS SYSTEM- which is activated mainly during emergency or stressful situation.
Function: initiates the organs to work PARASYMPATHETIC NERVOUS SYSTEM- active during moments of rest and repose.
Function: slows down the speed For example, if a frog is feared, the sympathetic nerves enhance heart beating and conversion of glycogen into sugar in liver, but the parasympathetic fibers slowly remove this effect to bring the normal condition. Sympathetic VS. Parasympathetic HEADLESS FROG IS STILL KICKING! FROG VS. MAN Frogs have 10 pairs of cranial nerves and 10 pairs of spinal nerves Man has 12 pairs of cranial nerves and 30 pairs of spinal nerves The relative size of the cerebrum in frog is much smaller and they lack cerebral cortex. The relative size of man's cerebrum is much bigger and they possess cerebral cortex. FROG AND MAN each brain appears to have two (2) hemispheres Both are classified as vertebrates, with a spine and nerves that spread across the body. each brain has a spinal cord descending from it