Brain: It is central processing unit of body and acts as command and Control system of body. It regulates all processes of body.
process of formation of brain: It is formed from neural tube and the neural crests make Peripheral nervous system. the spinal Cord is also formed from posterior part of neural tube..png)
After 3-4 weeks of fertilization 3 primary vesicles are formed in anterior part of neural tube which are prosenceplalon, mesencephalon and Rhombencephalon. Further , prosencephalon get differentiated into telencephalon and diencepralon while rhombencephalon get differentiated into metencephalon and mylencephalon.
⇒ Telencephalon forms Cerebrum (cerebral hemispheres) .
⇒ Diencephalon forms thalamus, hypothalamus and epithalamus.
⇒ mesencephalon fooms mid brain.
⇒ Metencephalon forms pons and cerebellum.
⇒ myelencephalon forms medulla oblongata.
Location and protection:
Brain lies in Skull inside cranium or brain box . the cranium consists of 8 bones connected by white fibrous tissue and Joints are Called Shuter. The bones are Frontal bone-1, Parietal bone-2, Temporal bone-2, occipital bone-1, Ethmoid bone - 1 And Spheroid bone-1.
Meninges: @ DAP
are coverings of brain made up of connective tissue. There are 3 meninges which protects brain.
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* Duramater: Tough outer membrane formed from collagen fibers which is durable and vascular. It has two membranes; outer periosteal membrane and inner meningeal membrane. The space between these two membrane is called dural space or dural venous sinus.
☆ Arachnoidmater: Middle wavy and avascular layer. space between duramater and arachnoidmater is Called subdural space which Contains serous fluid. It is present only in mammals.
☆ piamater: Inner, thin , delicate and vascular membrane which lies on the surface of brain. space between
arachnoidmater and piamater is Called subarchnoid space which remains filled with Cerebrospinal fluid.
• Cerebrospinal fluid (CSF): is clear, alkaline fluid present in subarachnoid space,ventricles of brain and Central canal of Spinal cord. Lymph is not present in CNS So, function of lymph is performed by Cerebrospinal fluid. About 150 ml CSF is present. It is regularly produced by Choroid plexus.
⇒ It Protects CNS by absorbing shock and injuries.
⇒ It Provides Cushion to CNS.
⇒ It Provides nutrients to CNs.
⇒ It absorbs metabolic waste of CNS.
⇒ It acts as middle man between blood and CNS.
⇒ It provides buoyancy to CNS and reduces weight of CNS.
some terms related to CNS.
⇒ Grey matter: Group of cell bodies of neuron.
⇒ white matter: Group of nerve fibers (axons).
⇒ Cortex: outer part
⇒ Medulla: Inner part
⇒ Nucleus: mass of Cell bodies in white matter.
⇒ Tract: Bundle of nerve fibers in CNS which carry impulse from anterior end towards posterior end or vice-verca.
. Ascending tract Carry information towards anterior end from Posterior Side while descending tract Carry information towards posterior end from anterior side.
• Commissures: Carry Impulse from right to left and vice-verca.
• Association fibers: carry information within same part from top to bottom and vice verCa.
Brain ( Encephalon)
Parts of brain:
Brain consists of 3 main parts: forebrain, midbrain and hindbrain.
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Fig: Human Brain
Forebrain (prosencephalon) : It is Anterior part of brain and consists of Olfactory lobes, Cerebrum and diencephalon.
• olfactory lobes (Rhinencephalon): Are not well developed in human. A pair of olfactory lobes are present and visible Only from lower side. Each olfactory lobe is short club shaped with Olfactory bulb and olfactory tract. It receives sense of smell by olfactory Nerve and relays that Sense to temporal lobe of Cerebrum.
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• Cerebrum (Telencephalon): It is largest part of brain and occupies 80% part of total brain. It Consists of two cerebral hemispheres. the right and left cerebral hemisphere are divided by a deep longitudinal fissure. Two Cerebral hemisphere remain Connected with each other by Corpus Callosum which is largest commissure and about 10cm long and Consists of millions of nerve fibers. Its anterior end is called genu while Posterior end Consists of fold Called as splenium. This splenium remains Connected with fornix(a tract).
on the surface of each cerebral hemisphere a number of elevations Called gyri and depressions Called sulci are present. Deep depressions are Called fissures.
The outer surface of Cerebral hemisphere is Called Cerebral Cortex and Consists of grey matter. It is about 4mm in thickness and Consists of 6 layers. Inner to Cortex, Cerebral medulla is present which Consists of white matter.
Inside each Cerebral hemisphere, a Cavity is present Called lateral ventricle. these two lateral ventricles remain connected with third ventricle ( Cavity of diencephalon) by foramen of Monro.
Each Cerebral hemisphere has 4 lobes: Frontal lobe, parietal lobe, temporal lobe and occipital lobe.
• Frontal lobe and parietal lobe are demarcated by Central fissure.
• Temporal lobe is demarcated with frontal and parietal lobe by Lateral fissure or sylvian fissure .
• Parieto-occipital fissure separates parietal lobe and occipital lobe.
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Fig: lobes of Cerebralhemisphere
• Frontal lobe: The largest lobe located in front and has motor area for voluntary movements, premotor area for involuntary movements, association area for memory, thinking, reasoning, vision, ideas etc.
It makes Coordination between Sensory area and motor area. It Creates motor information with response to sensory input.
Broca's area - motor speech area is present in it which develops speech from thoughts is present in it. It is responsible for the movement of tongue, vocal cords, lips etc. for the production of sound.
• parietal lobe: It is middle part and has somaesthetic Centre for Sensory inputs of general Sensation of touch , pain, temperature, pressure, taste etc. except smell.
• Temporal lobe: It is Side part and has Centres for smell and hearing ( auditory Centre).
wernicke's area - sensory speech area is present which interprets the audio /visual input and generates thoughts.
• occipital lobe: It is backside and has centre for vision.
☆ In Cerebrum (Cerebral Cortex) has 3 type of areas :
• sensory area: which receives Sensory information.
• Association area: It occupies maximum area and it processes sensory input. It is area for memory, thinking, reasoning, ideas etc.
• motor area: It sends information ( processed result with response to sensory input) to effector Parts.
• Diencephalon: It remains embedded in Cerebrum and visible only from back side. It Consists of epithalamus, thalamus and hypothalamus. Its Cavity is Called diocoel or third ventricle.
• Epithalamus: is non-nervous and forms roof of diencephalon. Its anterior region is Called anterior Choroid plexus which produces CSF. Its posterior part Contains a stalk Called pineal stalk which has pineal gland which produces hormone melatonin.
• Thalamus: on the lateral wall of diocoel two thalami are present each on either side. they are mass of Cell bodies.
they act as relay Centre and sends Information to higher Centres of brain. they have reticular activating system ( RAS) to filter information.
• Hypothalamus: It is floor of diencephalon and has pituitary stalk with pituitary gland. It Connects nervous system with endocrine system and regulates endocrine System. It has neurosecretory cells which produces hormone releasing factors, hormone inhibiting factors and hormones of posterior pituitary.
It has Centres for sleep, sexual behaviour, emotions, endocrine system, appetite , ANS, temperature regulation, thirst etc. [@ 2(SEAT)]
It has suprachiasmatic nucleus which is primary biological clock of body.
• Limbic system: Emotional brain:
Hypothalamus and some structures around it like Amygdela, Hippocampus, mammilary bodies, septum, Cingulate gyrus etc. form a lip like Structure around hypothalamus Called Limbic system. It also includes some part of epithalamus and thalamus.
• Amygdela: responsible for fear and anger.
• Hippocampus: responsible for long term memory. It is GPS system of human body.
• Mammilary bodies: responsible for smell.
• septum: responsible for sexual arouse.
• Cingulate gyrus: lies just above corpus callosum and is responsible to regulate emotions and pain. It is also involved in Predicting and avoiding negative consequences.
• Amygdela: responsible for fear and anger.
• Hippocampus: responsible for long term memory. It is GPS system of human body.
• Mammilary bodies: responsible for smell.
• septum: responsible for sexual arouse.
• Cingulate gyrus: lies just above corpus callosum and is responsible to regulate emotions and pain. It is also involved in Predicting and avoiding negative consequences.
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Fig: Limbic system
• Mid Brain:
It is middle part of brain and remains Covered by Cerebrum in front. It Consists of crura Cerebri or Cerebral peduncles and Corpora quadsigemina or optic lobes.
• crura cerebri: also called as Cerebral peduncles are present in anterior region and Consists of a pair of bundles of nerve fibers. It Connects cerebral hemispheres with pons and cerebellum . It relays sensory and motor impulses between fore brain and hind brain.
• Corpora quadrigemina: also Called as optic lobes. It consists of 2 Pairs of Colliculi ( small elevated round areas), a pair of superior Colliculi and a pair of inferior Colliculi.
superior Colliculi are for visual reflex i.e. movement of head with response to vision.
Inferior Colliculi are for audio reflex i.e. movement of head with response to audio.
• Hind brain: is posterior part of brain and consists of Pons varolli , cerebellum and medulla Oblongata.
• pons varolli: lies between midbrain and medulla oblongata.
It Consists of bundle of nerve fibers and they interconnect different parts of brain. Its outer surface has white matter while inner surface has grey matter. It Connects two lobes of cerebellum and also Connects midbrain with medulla oblongata. It has pneumotaxic and apneustic Centres to regulate respiration.
• Cerebellum:- It is second largest part of brain. It consists of two Cerebellar hemispheres connected with each other by a worm like structure Called vermis.
• Mid Brain:
It is middle part of brain and remains Covered by Cerebrum in front. It Consists of crura Cerebri or Cerebral peduncles and Corpora quadsigemina or optic lobes.
• crura cerebri: also called as Cerebral peduncles are present in anterior region and Consists of a pair of bundles of nerve fibers. It Connects cerebral hemispheres with pons and cerebellum . It relays sensory and motor impulses between fore brain and hind brain.
• Corpora quadrigemina: also Called as optic lobes. It consists of 2 Pairs of Colliculi ( small elevated round areas), a pair of superior Colliculi and a pair of inferior Colliculi.
superior Colliculi are for visual reflex i.e. movement of head with response to vision.
Inferior Colliculi are for audio reflex i.e. movement of head with response to audio.
• Hind brain: is posterior part of brain and consists of Pons varolli , cerebellum and medulla Oblongata.
• pons varolli: lies between midbrain and medulla oblongata.
It Consists of bundle of nerve fibers and they interconnect different parts of brain. Its outer surface has white matter while inner surface has grey matter. It Connects two lobes of cerebellum and also Connects midbrain with medulla oblongata. It has pneumotaxic and apneustic Centres to regulate respiration.
• Cerebellum:- It is second largest part of brain. It consists of two Cerebellar hemispheres connected with each other by a worm like structure Called vermis.
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The grey matter is present towards outer side with gyri and Sulci. It is Called Cerebellar Cortex. The white matter is present towards inner side and is Called Cerebellar medulla. The branching pattern of white matter forms a tree like structure called Arbor vitae also called as tree of life.
The largest type of nerve Cells Called purkinje's Cells are present in cerebellum.
It remains connected with other parts of brain by paired bundles of nerves Called Cerebellar Peduncles. superior cerebellar peduncles , middle cerebellar peduncles and inferior cerebellar peduncles connect Cerebellum with midbrain, pons and medulla respectively.
It is responsible for maintanance of posture and equilibrium, for muscle tone, rapid voluntary movements like talking, typing, dancing etc.
• Medulla oblongata: It is posterior most pyramid Shaped structure of brain which continues into spinal cord. Its outer surface has white matter while inner side has grey matter.
It Contains Cardiac Centre, respiratory Centre, vasoconstrictor Centre, hiccup, sneezing, vomitting, peristalsis etc are regulated by it.
In medulla, the ascending tract and descending tract cross each other. Thus, right part of brain Controls left part and
vice-verca.
Its cavity is Called metacoel or fourth ventricle. on its roof, posterior Choroid plexus is present which produces CSF. It remains Connected with third ventricle by Cerebral aqueduct or Aqueduct of sylvius or Iter.
• Brain Stem: Mid brain, Pons and medulla oblongata are Collectively Called brain stem. It Connects fore brain with Spinal Cord.
• Reticular activating system ( RAS): A diffuse network of nerve cell bodies and nerve tracts extends through the brainstem called RAS. It screens sensory information so that only Certain impulses Can reach upto Cerebrum. they Control Consciousness , sleep-wake cycle and arousal.
• ventricles of brain: There are 4 Cavities inside brain Called as ventricles of brain or Cerebral ventricles. they are filled with CSF.
A lateral ventricle lies inside each hemisphere of Cerebrum. The third ventricle also Called as diocoel lies in diencephalon. the fourth ventricle also called metacoel lies in hind brain in between Cerebellum and pons in medulla oblongata.
Each lateral ventricle is connected to third ventricle by an interventricular foramen ( Foramen of Monro).
The third ventricle is connected to fourth ventricle by the Cerebral aqueduct or aqueduct of sylvius or Iter present in the midbrain Portion of brain stem.
the fourth ventricle continues with the central Canal of spinal Cord.
vice-verca.
Its cavity is Called metacoel or fourth ventricle. on its roof, posterior Choroid plexus is present which produces CSF. It remains Connected with third ventricle by Cerebral aqueduct or Aqueduct of sylvius or Iter.
• Brain Stem: Mid brain, Pons and medulla oblongata are Collectively Called brain stem. It Connects fore brain with Spinal Cord.
• Reticular activating system ( RAS): A diffuse network of nerve cell bodies and nerve tracts extends through the brainstem called RAS. It screens sensory information so that only Certain impulses Can reach upto Cerebrum. they Control Consciousness , sleep-wake cycle and arousal.
• ventricles of brain: There are 4 Cavities inside brain Called as ventricles of brain or Cerebral ventricles. they are filled with CSF.
A lateral ventricle lies inside each hemisphere of Cerebrum. The third ventricle also Called as diocoel lies in diencephalon. the fourth ventricle also called metacoel lies in hind brain in between Cerebellum and pons in medulla oblongata.
Each lateral ventricle is connected to third ventricle by an interventricular foramen ( Foramen of Monro).
The third ventricle is connected to fourth ventricle by the Cerebral aqueduct or aqueduct of sylvius or Iter present in the midbrain Portion of brain stem.
the fourth ventricle continues with the central Canal of spinal Cord.
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Fig: ventricles of Brain
CSF is produced by Choroid plexus in ventricles. From lateral ventricles CSF Passes into third ventricle through foramen of monro and then into fourth ventricle through iter.
In fourth ventricle, three openings are present on roof; a pair of lateral openings Called foramen of Luaschka and Single median opening Called foramen of magendie. From these openings CSF passes into subarachnoid space and surrounds brain and spinal cord. From subarachnoid space CSF Passes into arachnoid villi (Small projections of arachnoid membrane which extends into dural venous Sinus) and reabsorbed into circulation.
CSF is produced by Choroid plexus in ventricles. From lateral ventricles CSF Passes into third ventricle through foramen of monro and then into fourth ventricle through iter.
In fourth ventricle, three openings are present on roof; a pair of lateral openings Called foramen of Luaschka and Single median opening Called foramen of magendie. From these openings CSF passes into subarachnoid space and surrounds brain and spinal cord. From subarachnoid space CSF Passes into arachnoid villi (Small projections of arachnoid membrane which extends into dural venous Sinus) and reabsorbed into circulation.