Central Neural System

CENTRA NEURAL SYSTEM Cerebrospinal - Fluid (CSF) This fluid is clear and alkaline in nature just like lymph. CSF is present in ventricles of brain, subarachnoid space of brain & spinal cord. C.S.F. is formed in choroid plexus found in the ventricles of the brain. Functions of C.S.F.: Protection of Brain: It acts as shock absorbing medium and works as cushion. It provides buoyancy to the brain, so net weight of the brain is reduced from about 1.4 kg to about 0.18 kg. (A) Fore Brain The fore brain consists of Cerebrum, Diencephalon (containing epithalamus, thalamus, hypothalamus) and off actor lobe. (1) Cerebrum: Cerebrum forms the major part of the brain which is most developed in human. Central/Rolandic sulcus Frontal lobe Parietal lobe Temporal lobe Occipital lobe -Parieto-occipital sulcus Forebrain Cerebrum Cerebral hemisphere Corpus callosum Thalamus Hypothalamus Midbrain Pons Cerebral aqueduct Lateral/Sylvian sulcus Hindbrain-Cerebellum Medulla Spinal cord Structure of human brain Dorso-lateral surface of cerebral hemisphere Cerebrum consists of two cerebral hemispheres; on the dorsal surface a longitudinal groove is present between two cerebral hemispheres called as median fissure. Both the cerebral hemispheres remain connected with each other by curved thick white nerve fiber called corpus callosum found in only higher mammals. (Largest commissure of brain) Each cerebral hemisphere is divided into 4 lobes-Anterior, Middle, Posterior and Lateral. Anterior lobe is also called frontal lobe (largest lobe) while middle lobe is called as parietal lobe. Frontal lobe is separated by central sulcus or Rolandic sulcus from parietal lobe. Posterior lobe is called as occipital lobe, it is separated from parietal lobe by a sulcus called parietal occipital sulcus. Lateral lobe or temporal lobe is separated from frontal lobe & parietal lobe by incomplete sulcus called lateral sulcus/sylvian sulcus. The outer part of cerebral hemisphere is called Cerebral cortex and thrown into prominent folds. These folds are found as ridges and grooves on dorsal surface of cerebral hemisphere. Ridge are known as Gyri while grooves are called sulci. Gyri and sulci increase the surface area of cerebrum and provide additional space for more neurons. The cerebral cortex referred to as the gray matter due to its greyish appearance. The neuron cell bodies are concentrated here giving the colour. This thick layer of gray matter is also known as Neopallium/Pallium in higher vertebrates. The cerebral cortex contains three types of functional areas: Sensory area: Analysis of sensory impulses eg. Somesthetic area for general sensation (Touch, Pain, Temperature etc.) Motor area: Generation of motor impulses eg. Broca's area for fine movement of tongue and speech. Motor area for voluntary movement of limb muscles. Association area: These are large regions that are neither clearly sensory nor motor in function. They are responsible for certain complex functions like: Intersensory association: As you are aware that all sensory inputs like touch, sound, light, smell are sent to brain. These different sensations require association and inter connection with each other for their proper interpretation. Memory: Memory of past events is recorded by the association areas also with the different lobes of the cerebrum. Memory is basically of two types: Short term memory and long-term memory. Communication: The ability of communication also controlled by the association areas of cerebral cortex. Function of cerebrum: It is the most important part of brain because it controls and regulates different part of brain. This is the centre of conscious senses, will power, voluntary movements, knowledge, etc. Different sense organs send impulse here and in this part of brain, analysis and coordination of impulse is done then messages are transferred to organs. S.No. Name of area 1 Location Function Prefrontal cortex Frontal lobe 2 Seat of intelligence, knowledge, creative ideas, imagination, memory (organ of mind). Motor area Frontal lobe 3 Analysis of all type of voluntary muscle Broca's area (Motor speech area) Frontal lobe Analysis for speech. If this area is injured, the person is unable to speak (aphasia), even though muscle concerned are not paralyzed. 4 Auditory area Temporal lobe Analysis of sound. 5 Olfactory area Temporal lobe Analysis of smell. 6 Wernicke's area (Sensory speech area) Temporal lobe Analysis of language. Sensory analysis of speech. 7 Gustatory area Parietal lobe Analysis of taste. 8 Somesthetic area Parietal lobe Analysis of touch, pain, pressure. knowledge about the body position and taking in the information from the surrounding environment. 9 Occipital area (Visual cortex area) Occipital lobe Analysis of vision. 2. Diencephalon It is small chamber like posterior part of fore brain which is covered by cerebrum. It consists of 3 parts: a. Epithalamus b. Thalamus c. Hypothalamus a. Epithalamus: It form the roof of diencephalon. Pineal body (Epiphysis cerebri) is found on epithalamus & control sexual maturity. b. Thalamus: It forms upper lateral wall of Diencephalon. It forms 80% of diencephalon. It acts as a relay centre. It receives all sensory inputs from all part of body & these impulses are send to the cerebral cortex. Cerebrum wraps around the thalamus. It is a major coordinating centre for sensory & motor signaling. c. Hypothalamus: It forms the lower or ventral part of diencephalon. It lies at the base part thalamus. The hypothalamus contains a number of centres which control body temperature. urge for eating and drinking (Hunger and thirst). It also contains several groups of neurosecretory cells, which secrete hormone called hypothalamic hormone. A cross like structure is found on anterior surface of hypothalamus called as optic chiasma, through Infundibulum pituitary body is attached to middle part of hypothalamus. Corpus mammillae or corpus albicans or mammillary body is found on the posterior part of hypothalamus. (Mammal are character) Hypothalamus controls: 1. Thermoregulation 2. Behavior and emotion 3. Endocrine control 4. Biological clock system 5. ANS control. Limbic system: The inner part of cerebral hemispheres and a group of associated deep structures like amygdala. Hippocampus etc. form a complex structure called Limbic system. Along with the hypothalamus, it is involved in the regulation of sexual behavior, expression of emotional reactions (eg., excitement pleasure, rage, fear) and motivation, olfaction and autonomic responses. 3. Olfactory Lobe: One pair of broad bean size organ called olfactory lobe / bulb are found on the ventral surface of frontal lobe of cerebral hemisphere. It is a small, spherical and solid structure in human brain. It is connected to olfactory area / center (temporal lobe) through olfactory tract and are extensions of the brain's limbic system. Function: It is supposed to be the center of smelling power. Some animal like are sharks and dogs have well developed olfactory lobes. Frontal lobe Temporal lobe Cerebellum- Occipital lobe Olfactory lobe Olfactory tract -Olfactory centre -Optic chiasma -Midbrain -Pons Medulla oblongata Spinal cord Posterior Optic lobe or colliculi or corpora quadrigemina Iter or Aqueduct of sylvius or cerebral aqueduct Crura cerebri or crus cerebri or cerebral peduncle Ventral view of Brain MID BRAIN Anterior FIG: T. S. OF MID BRAIN