Download pdf - Brain & Limbic System

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    Presented To:

    Madam Mrs. Avinash Rana Presented By:Mukta (M.Sc.1st yr)

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    INTRODUCTIONSolving an equation, feeling hungry,laughing - the neural processesneeded for each of these activitiesoccurs in different regions of thebrain, that portion of the centralnervous system contained within the

    cranium. About 100 billion neurons & 10-50trillion neuroglia make up the brain.

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    Contd Brain has a mass of about 1300 g(almost 3 lb) in adults.Each neuron forms 1000 synapseswith other neurons.Total number of synapses are about1000 trillion, which is larger than thenumber of stars in the galaxy.

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    Contd.. Brain is the center for registeringsensations, correlating them with oneanother and with stored information,making decisions, and taking actions.It is also the center for the intellect,emotions, behavior, and memory.

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    Brain and spinal cord develop fromectoderm arranged in a tubular structure called neural tube .

    Anterior part of neural tube expandsand constricts to form 3 regions :-Prosencephalon (forebrain)Mesencephalon (midbrain)Rhombencephalon (hindbrain)

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    Contd Mesencephalon gives rise to themidbrain and aqueduct of themidbrain.prosencephalon andrhombencephalon develop intothalamus, hypothalamus, pons,cerebellum & upper part of 4 th ventricle.

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    FORE BRAINForebrain takes up a large portion of thebrain; it includes cerebrum, corpuscallosum, thalamus, hypothalamus, and thelimbic system.The overall functions of forebrain includecontrol of cognitive, sensory, and motor functions; regulation of temperature,eating, sleeping, emotions, andreproductive functioning.

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    MID BRAINMidbrain is located between the forebrainand the hindbrain. In itself it makes up apart of the brainstem, and connects it to the

    forebrain.The brainstem in itself makes the

    connection between spinal cord andforebrain. Primary function of midbrain is tocontrol sensory processes.

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    HIND BRAINHindbrain is makes up the bottom bitof the brainstem. It is composed of Pons, medulla, reticular formation,and cerebellum.Functions include co-ordination of motor activity, posture, andregulations of blood pressure andbreathing.

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    PARTS OF BRAINThe adult brain consists of 4 major

    parts :-Brain stem : consists of medullaoblongata, Pons & midbrain.Cerebellum

    Diencephalon : consists of thalamus,hypothalamus & Epithalamus.Cerebrum : largest part of brain.

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    The cranium & the cranial meningessurround and protect the brain.Cranial meninges are continuous withspinal meninges, have same basicstructure & bear the same names.Duramator (outermost)

    Arachnoidmater (middle)Piamator (innermost)

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    Contd.. Duramater has 3 extensions whichseparate various parts of brain :

    i. The falx cerebri (falx=sickle-shaped) it

    separates two hemispheres of cerebrum.ii. The falx cerebelli : - it separates two

    hemespheres of cerebellum.

    iii. The tentorium cerebelli (tent) : -itseparates cerebrum from cerebellum .

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    CSF is a clear, colorless liquid thatprotects the brain and spinal cordfrom chemical and physical injuries.It carries oxygen, glucose & other needed chemicals from blood toneurons and neuroglia.It circulates around brain & spinalcord in subarachnoid space.

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    Contd.. Total volume of CSF is 80 to 150 ml(3 5oz) in adults.CSF contains glucose, proteins, lacticacid, urea, cations (Na+, K+, Ca2+,Mg2+), and anions (Cl- and HCO3-).It also contains some WBCs.

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    Lateral ventricles lateral ventricles choroid plexus through interventricular foramina

    CSFThird ventricle 3rd ventricles choroid plexus

    through cerebral aqueduct CSFFourth ventricle 4 th ventricles choroid plexus through lateral and median apertures

    Subarachnoid space arterial blood

    Arachnoid villi of dural venous sinuses Heart and lungs

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    Contd.. It is the part of the brain b/w spinalcord & Diencephalon.It consists of following :

    Medulla oblongata Pons


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    MEDULLA OBLONGATAMedulla is a relay station for nerve signalsbetween the brain and the spinal cord. Itcontrols autonomic functions, thuscontrolling excitement and relaxation.It is continuous with superior part of spinalcord & forms the inferior part of the brainstem.

    The medulla begins at the foramenmagnum and extends to the inferior border of the pons, a distance of about 3 cm (1.2inches).

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    Contd.. Medulla contains all sensory (ascending)and motor (descending) tracts that extendb/w spinal cord & other parts of the brain.

    Decussation of pyramids occurs justsuperior to junction of medulla with spinalcord.It contains nuclei associated with 5 pairs of cranial nerves : 8 th,9 th,10 th,11 th & 12 th.

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    FUNCTIONS :Cardiac center : controls rate & forceof cardiac contraction.Respiratory center : controls rate &depth of respiration.Vasomotor center : controls thediameter of blood vessels.Reflex center : of vomiting, cough,sneezing & swallowing.

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    PONSPons (=bridge) lies directly superior tomedulla and anterior to cerebellum &is about 2.5 cm (1 inch) long.

    It consists of both nuclei & tracts .Pons is a bridge that connects part of brain with one another.

    It contains nuclei associated with 4pairs of cranial nerves : 5 th, 6 th, 7 th &8 th.

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    MIDBRAINThe midbrain is located between theforebrain and the hindbrain.This is the area that contains manynerve - fibre systems that ascend anddescend to connect the higher andlower portions of the brain.It extends from pons to diencephalonand is 2.5 cm (1 inch) long.

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    Contd.. Like medulla and pons, the midbraincontains both nuclei .The anterior part of the midbrain contains a

    pair of tracts called cerebral peduncles.These tracts neurons which conduct nerveimpulses from the cerebrum to spinal cord,pons, and medulla.It also contains right & left substantianigra which are large & pigmented.

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    It is the broad region where white matter &grey matter exhibit a net like arrangement.It extends from the upper part of the spinal

    cord, throughout the brain stem, and intothe lower part of the Diencephalon.Neurons with reticular system have bothascending (sensory) & descending (motor)functions. Example :- regulate muscle tone.

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    Contd.. reticular formation is involved instereotypical actions, such as walking,sleeping, lying down, etc.

    essential for basic functions of life and isconsidered to be the phylogenetically theoldest part of the brain (500 million years).Reticular formation also plays an importantrole in alertness, fatigue, and motivation.

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    2. CEREBELLUM Accounts for 1/10 th of brain mass. It isposterior to medulla & Pons andinferior to posterior portion of thecerebrum.

    A deep groove known as thetransverse fissure , along with thetentorium cerebelli , which supportsthe posterior part of cerebrum.

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    Contd.. The shape of the cerebellumresembles a butterfly.The central constricted area is thevermis (=worm), and the lateralwings or lobes are the cerebellarhemisphere.

    Each hemisphere consists of lobesseparated by deep and distinctfissures.

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    Contd.. The anterior & posterior lobes governsub conscious aspects of skeletalmuscle movements.

    The flocculonodular lobe ( wool-liketuft) on the inferior surface contributesto equilibrium.

    Superficial layer of cerebellum iscalled the cerebellar cortex havinggrey matter.

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    FUNCTIONS :Co-ordination of voluntary muscular movements, posture & balance.Maintenance of the balance & equilibrium

    of the body.Influence the contraction of skeletal muscleso that balance & posture are maintained.

    Damage to cerebellum through trauma or disease disrupts muscle co-ordinationcalled ataxia.

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    3.DIENCEPHALONIt extends from the brain stem to thecerebrum and surrounds the 3 rd ventricle; it includes the :-

    1. Thalamus2. Hypothalamus3. Epithalamus

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    THALAMUSIt is 3 cm(1.2 in) in length & makes up80% of the Diencephalon.It consists of paired oval masses of

    grey matter organized into nuclei withinters-persed tracts of white matter.The thalamus is the major relaystation for most sensory impulses thatreach the primary sensory areas.

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    FUNCTIONS :-Perception of sensation : painful, thermal,& pressure.Motor functions: transmitting informationfrom the cerebellum and basal ganglia &different areas of the cerebrum.Regulation of autonomic activities.Maintenance of consciousness.

    Controls emotions, regulation of alertness,learning, memory, awareness & cognition(thinking and knowledge).

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    HYPOTHALAMUSIt is a small part of the Diencephalonlocated inferior to the thalamus.It is composed of 4 major regions:-

    1. The mammillary region2. The tuberal region

    3. The supraoptic region4. The preoptic region

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    FUNCTIONS :-1. Control of ANS :- regulates the

    contraction of smooth and cardiacmuscles & secretion of many glands.

    2. Production of hormones3. Regulation of emotional and behavioral

    patterns.4. Regulation of eating & drinking.

    5. Control of body temperature6. Regulation of circulation rhythms and

    states of consciousness.

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    EPITHALAMUSIts a small region superior & posterior to the thalamus.Consists of pineal gland & nuclei. IsPineal gland is about the size of asmall pea & protrudes from 3 rd ventricle.Pineal gland secretes hormone


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    Cerebrum :-The cerebrum is the called as seatof intelligence. Provides ability to read, write, speak,

    to make calculations, to composemusic, & to remember past.The brain is divided in two

    hemispheres - left and right. Each of these is coated on the outside withgrey matter, or cerebral cortex.

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    Contd.. Two hemispheres are linked by thecorpus callosum, anterior commissure, posterior commissure,and hippocampal commissure totransfer information b/w the twohemispheres.Cerebral cortex:-

    the most important part of the brainwhere thoughts, concept integration,and abstract thinking take place.

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    Lobes of the cerebrum:-Frontal lobe.Parietal lobe.

    Temporal lobe.Occipital lobe.

    Functions :- these are involved in

    producing perceptions, resulting fromsensory organs, in the movements,planning, as well as abstract thought.

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    Functions of lobes:-1. Frontal lobe

    1. responsible for judgment, language,memory, motor functions, impulse control,problem solving, sexual behavior, andsocialization.

    2. It is involved in planning, coordinating,controlling and executing behavior.

    3. Human personality is incorporated in thefrontal lobe. Any damage results inserious personality disorders.

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    Parietal lobe is involved in visuo-spacial processing.It integrates sensory information from

    various parts of the body.Much less is known about this lobecompared with the other three.

    2. Parietal lobe:-

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    3. Temporal lobe :-It is involved in processing high-levelauditory information, or hearing,comprehension, naming, verbal memoryand other language functions.Broca's area (named after Paul Broca) is

    located in the frontal lobe.Wernicke's area (named after KarlWernicke) is located between temporal andparietal lobes.

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    4. Occipital lobe:-

    Main function is perception .In case of damage severe vision loss

    may occur.Occipital lesions can cause visualhallucinations.

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    SYSTEMIt is a ring of structures on theinner border of the cerebrumand floor of Diencephalonencircling the upper part of the

    brain stem & corpus callosum.


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    COMPONENTS OF LIMBICSYSTEM : --The main components include :- hypothalamus Hippocampus

    Amygdala Cingulate gyrus & parahippocampal gyrus Dentate gyrus & Olfactory bulbs

    Septal nuclei Mammillary body & Fornix

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    Contd.. FUNCTIONS :-

    Limbic system is also called as theemotional brain, as it plays importantrole in a range of emotions like pain,pleasure, affection & anger.Limbic system is also involved in olfaction

    (smell) and memory.So the limbic system is brain's emotionalside & lies in both hemispheres.

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    Contd.. Hypothalamus:-

    1. responsible for regulation of hunger, thirst,pain, pleasure, sexual satisfaction, anger.

    2. It also regulates parasympathetic(relaxing) and sympathetic (stimulating)nervous systems, which are both a part of the autonomic nervous system.

    3. Two ways in which hypothalamuscommunicates with the body is by :-

    (1) sending signals to the autonomousnervous system, thus controlling bloodpressure, heart rate, breathing, digestion.(2) by stimulating the pituitary gland.

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    Contd.. Hippocampus

    Hippocampus (seahorse) is a portion thatextends into the floor of the lateral

    ventricle. used in converting short-term memoryinformation into long-term.

    Damage to this area results in loss of the

    ability to create new long-term memories.

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    Contd.. Amygdala

    It is composed of several groups of neurons located close to the tail of caudate

    nucleus.Electrical stimulation of this area causerage and anger.removal of the area causes indifferencetowards stimuli as fear, anger and sexualpleasure.

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    Cingulate gyrus It lies above the corpus callosum in

    cerebral cortex. (Cingul means :-belt).

    Components contd

    parahippocampal gyrusIt lies in the temporal lobe below.

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    Components contd Dentate gyrus

    It lies between the hippocampus andparahippocampal gyrus.

    Olfactory bulbsThese are flattened bodies of the olfactorypathways that rests on the cribriform plate.

    Septal nuclie

    These are located within the Septal areaunder corpus callosum and Para terminalgyrus.

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    People with damage to certain limbicsystem structures forget recentevents & cannot commit anything tomemory.Damage to Amygdala results in failurein recognizing fearful expressions in

    others or to express fear inappropriate situation.


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    REFERENCES : -Gerard j. tortora ; Bryan derrickson,principles of anatomy and physiology,11 th edition, john Wiley & sons, incpublication, page no. Merry C. Townsend, psychiatrymental health nursing, 5 th edition,

    jaypee publications, page no. 50-55.
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