THE NERVOUS SYSTEM:
There are various organ systems functioning in the body.These functions are regulated,controlled and coordinated for proper functioning by a system called nervous system.Functional unit of nervous system is neuron.
Central nervous system:
The central nervous system is the coordinating center of whole neural mechanism.IT include the following parts:
Brain is highly specialized delicate organ of the human body weighing about 1.2 kg.It is protected by a bony case or cranium.It is composed of soft nervous tissues covered by three membranes together known as meninges.The three membranes are:durameter(outer),piameter(inner)and arachnoid(middle)The substance composing the brain is differentiated into grey matter and white matter.Grey matter forms the outer layer and is formed of cell bodies or cytons of neurons.While the white matter lies inside and are formed from the nerve fibres of the neurons.
The space between these layers is filled with a clear slightly alkaline fluid thats act as a water cushion protecting brain and spinal cord from physical impact known as Cerebrospinal fluid.This fluid is formed by the choroid plexuses of lateral,third and fourth ventricles.
STRUCTURE OF HUMAN BRAIN:
This part is highly developed and is divided into Cerebrum and diencephalon.
The cerebrum is the largest and most prominent part of the brains.It consists of two large ovoid cerebral hemispheres partly separated from each other medially by a deep longitudinal groove called longitudinal cerebral fissure.the two hemisphere are connected together by a horizontal sheet of nerve fibres called Corpus Callosum.Each of two cerebral hemispheres is divided into 4 areas on the basis of the bones of the cranium as frontal,parietal,temporal and occipital lobes by three deep fissures i.e central,lateral and parieto occipital sulcus.The outer layer of cerebrum is the cerebral cortex.It has numerous folds like convolutions which greatly increases the surface area.The ridges of these convolution are gyri and depressions between them are called sulcus.The number and pattern of convolutions is associated withe the degree of intelligence.
#It governs all man's mental activities which is involved in memory,intelligence and sense of responsibility,thinking,reasoning moral senses and learning.
#It is also concerned with the sensor ,feeling including the feeling of pain,temperature,touch,light,hearing,taste and smell.
#It also controls will emotions and speech.
#Each cerebral hemisphere controls opposit voluntary muscle contractio.
#It also acts as a control on many reflex acts that originate involuntarilyi.e weeping ,laughing etc.
It lies between cerebral hemisphere and mid brian,and is a small and depressed structures.The upper surface of diencephalon is hidded is considered as thalamus.Thalamus is an organ for the perception of certain crude sensations such as extremes of heat,cold and pain.The hypothalamus is composed of a no of a groups of nerve cells.It is situated below and infront of thalamus and above pituitary gland.It is linked to the posterior lobe of the pituitary gland by nerve fibres and to anterior lobe by a complex system of blood vessel.Its functions are associated with hormones secretion,thirst and water balance,body temperature ,emotional reactions ,biological clocks or circadian rhythms.
It is the middle part of the brain and lies between forebrain and hindbrain.It is about 2cm long.It consists of two round pairs of round elevations on the dorsal part called corpora quadrigemina.The corpora quadrigemina contain nuclei of nerves.The ventral part of mid brain contains cererbral peduncles or crura cerebri.These are in the form of thick fibrous tracts and contains reflex centres.The cerebral peduncles contain nuclei of the third and fourth pairs of cranial nerves.These tracts connect cerebellum and cerebrum.
#The nuclei of the corpora quadrigemina are the centres of visual and auditor reflexesi.e they regulate the complex movements of the body in response to sudden optic and acoustic stimuli.
#The cerebral peduncles transmit motor impulses to limb muscles from cerebrum.
It consits of pons varolii,medulla oblongata and cerebellum.
It is the second largest part of the brain and located just below the posterior part of the cerebrum being partly overlapped.It has 2 cerebellar hemispheres like cerebrum.The outer cerebellar cortex is made of grey matter,which is not convoluted but is transversed by numerous forrows.Central part is made up of white matter.Cerebellum is partly divided into three lobes.They are:unpaired median portion called Vermis and two lateral lobes called lateral hemispheres.Each cerebellar hemisphere is connected with the brain stem on the same side by three arms of white matter called cerebellar peduncles.
#It regulates and coordinates contraction of skeletal muscles.
#It modulates and moderates voluntary movements initiated in cerebrum.
#It maintains equilibrium and controls posture.
#It makes body movements smooth,steady and coordinated.
It is situated infront of cerebellum and above medulla oblongata.Its fibres connect the two halves of the cerebellum and join medulla oblongata with the mid brain.It coordinates muscles movements on two sides of the body.
It lies between the pons varolii and the spinal cord.Its cavity is called 4th ventricle of metacoel.it consists of white matter.It is continuous withe the spinal cord.
Medulla oblongata is the centre for the vital activities such as cardiac,respiratory and vasometer.it controls complex activities such as heart action,respiration,sneezing and coughing.
Mid brain,pons varolii and medulla oblongata together for the brain stem.
VENTRICLES OF HUMAN BRAIN:
Ventricles are the cavity within the brain.These consists of cerebrospinal fluid.Ventricles are 4 in number.
a)Right and lateral ventricles:
These cavities lies within the cerebral hemispheres,one on each side of the median plane just below the corpus callosum.They communicate with the third ventricle by a channel known as Foramen of monro.
it is a cavity situated below the lateral ventricles between the two parts of the thalamus.It communicates with the fourth ventricles by channel known as cerebral aqueduct or iter.
This ventricle is lozenge shaped cavity situated below and behind the third ventricle,between the cerebellum and pons varolii.it is continuos between the central canal of spinal cord.
It is long whitish thick walled tube of nervous tissue contained within the neural canal of vertebral column.It extends from the medulla oblongata of the brain,gradually tapering upto the lumbar region.It is about 45 cm long in adult and has the thickness of about the little finger.Like brain it is composed of grey matter and white matter.The grey matter is the centre of the cord and white matter is found on the periphery.
The grey matter of spinal cord is H shaped in cross section projecting into two dorsal horns,vertically into two horms and one on dorsal septum and ventral fissure.In each half of spinal cord ,the white matter is divided into three columns or funiculi.These are:one anterior,one posterior and two lateral funiculi.Each funiculus is formed of nerve tracts.
A cord segment gives origin to a pair of spinal nerves.In man there are 31 segment of spinal cord corresponds to one pair of spinal nerves.
#It serves as a centre for spinal reflexes.
#It acts as a link between spinal nerve and brain.Thus it participate in conscious actions.
#it acts as pathways to form the brain.