THE BRAINThe adult human brain weighs an average of 1.4kg, or about 2 percent of the total body weight.Despite this relatively small mass, the braincontains approximately 100 billion neurons.Functioning as a unit, these neurons make up themost complex and highly organized structure onEarth.
THE BRAINThe brain is responsible for many of the qualitiesthat make each individual unique-thoughts,feelings, emotions, talents, memories, and theability to process information.Much of the brain is dedicated to running thebody, the brain is responsible for maintainingHomeostasis by controlling and integrating thevarious systems that make up the body.
1. The brain is the main switching unit of the central nervous system; It is the place to which impulses flow and from which impulses originate.2. The spinal cord provides the link between the brain and the rest of the body.3. The brain has three main parts: 1. The cerebrum 2. The cerebellum 3. The brain stem
The Brain is a highly organized ORGAN thatcontains approximately 100 billion neurons andhas a MASS of 1.4 Kilograms.The Brain is Protected by a BONY Coveringcalled the SKULL.The Brain is also WRAPPED inTHREE LAYERS ofCONNECTIVE TISSUEknown as the MENINGES.
Connective Tissue connects one tissue to another.The INNER most layer, which covers and is boundto the surface of the brain, is called PIA MATER.It is a FIBEROUS LAYER made up of manyBlood Vessels which carry FOOD and OXYGENto the Brain.The OUTER Layer, called the DURA MATER, iscomposed of Thick Connective Tissue.
The ARACHNOID is the THIN, elastic, weblikelayer between the PIA MATER and the DURAMATER. Between the Pia Mater and theArachnoid is a space filled withCEREBROSPINAL FLUID.
Cerebrospinal Fluid separates the middle and innerMeninges and fills four interconnectedVENTRICLES, or Cavities in the Brain. Withinthe Ventricles, Cerebrospinal Fluid acts as aTransport Medium for substances that areimportant to Brain Function.
The Cerebrospinal Fluid is a clear liquid thatPROTECTS the Brain from mechanical injury byacting as a Shock Absorber.In order for the Brain to perform its functions, itmust have a constant supply of Food and Oxygen.If the Oxygen supply to the brain is cut off evenfor a few minutes, the brain will usually sufferenormous damage. Such damage may result inDEATH.
PARTS OF THE BRAINTHE CEREBRUM
THE CEREBRUM IS THE CONTROL CENTEROF THE BRAIN.The LARGEST and most PROMINENT part ofthe Human Brain is the CEREBRUM. 85% OFTHE WEIGHT OF A HUMAN BRAIN.The Cerebrum is responsible for all theVOLUNTARY (CONSCIOUS) ACTIVITIESOF THE BODY. It is the site of INTELLIGENCE,LEARNING AND JUDGMENT.
IT FUNCTIONS IN LANGUAGE, CONSCIOUSTHOUGHT, MEMORY, PERSONALITYDEVELOPMENT, VISION, AND OTHERSENSATIONS.The Cerebrum takes up most of the space in thecavity that houses the Brain. (SKULL)The CEREBRUM IS DIVIDED INTO TWOHEMISPHERES, THE LEFT AND RIGHTCEREBRAL HEMISPHERES.
There is a DEEP GROVE thatseparates the Two Hemispheres.The Hemispheres are Connectedin a region known as theCORPUS CALLOSUM.The right and left cerebralhemispheres are linked by a bundle of neuronscalled A TRACT tells each half of the brain whatthe other half is doing.
The MOST Obvious FEATURE on the surface ofeach hemisphere are NUMEROUS FOLDS.These FOLDS and the GROOVES INCREASEthe Surface Area of the Cerebrum. The Ridges arecalled GYRI, and the grooves are calledSULCUS.The Cerebrum, which looks like a wrinkledmushroom, is positioned over the rest of the brain.
It contains thick layers of Unmyelinated Neurons, which look GRAY. ("GRAY MATTER")The increasedsurface areapermits the largenumber of neuronsto fit easily withinthe confines of theSkull.
Each Hemisphere of the Cerebrum is divided intoFour regions called LOBES.These LOBES are named for the SKULL BONESthat cover them, FRONTAL, PARIETAL,TEMPORAL, AND OCCIPITAL LOBES.
The RIGHT hemisphere is associated withcreativity and artistic ability. The LEFThemisphere is associated with analytical andmathematical ability.
Sometimes blood vessels in the brain are blockedby blood clots, causing a disorder called ASTROKE. During a Stroke, circulation to an areain the brain is blocked and the brain tissue dies. Asevere Stroke in one side of the brain may causePARALYSIS of the other side of the body.
The Cerebrum consists of TWO SURFACESThe FOLDED OUTER SURFACE is called theCEREBRAL CORTEX and consists of GRAYMATTER (UNMYELINATED NEURONS).The INNER SURFACE is called the CEREBRALMEDULLA, which is made up of bundles ofMYELINATED AXONS. THE WHITE MATTER.The Myelin gives the White Matter its White Color.
THE CEREBELLUM The CEREBELLUM is the SECOND LARGEST part of the Brain, and is located at the back of the Skull. It coordinates muscle movements.
The Cerebellum coordinates and balances theactions of Muscles so that the body can movegracefully and efficiently.The Cerebellum CONTROLS BALANCE,POSTURE, and COORDINATION.The Cerebellum receives sensory impulses frommuscles, tendons, joints, eyes, and ears, as well asinput from other brain centers.
It processes information about position andcontrols posture by keeping skeletal muscles in aconstant state of partial contraction.The Cerebellum Coordinates rapid and ongoingmovements.This is a small CAULIFLOWER SHAPEDStructure.
A Major part of learning how to perform physicalactivities seems to be related to training theCerebellum to coordinate the proper muscles.Because the function of the Cerebellum isINVOLUNTARY (not under conscious control),learning a completely new physical activity can bevery difficult.
THE BRAIN STEMThe BRAIN STEM CONNECTS the BRAIN tothe SPINAL CORD.
The brain stem, which maintains life supportsystems, consist of the diencephalon, medullaoblongata, pons, and the midbrain.The Brain Stem Controls Vital Body Processes.The Brain stem not only coordinates and integratesall INCOMING INFORMATION; it also serves asthe place of entry or exit for ten of the TwelveCranial Nerves.
The Upper Brain Stem, the Diencephalon, containsimportant relay centers for information enteringand exiting the brain.The Lower Brain Stem consists of theMEDULLA OBLONGATA, PONS, ANDMIDBRAIN.The Lowest Part of the Brain Stem is the MedullaOblongata (Sometimes just called the Medulla).
The Medulla contains WHITE MATER thatconducts impulses between the Spinal Cord andBrain.The MEDULLA controls involuntary functionsthat include, breathing, blood pressure, heart rate,digestion, swallowing, and coughing.Another important part of the Medulla is aGROUP of CELLS known as THE RETICULARACTIVATING SYSTEM or RETICULARFORMATION (RAS).
The Reticular Activation System (RAS) actuallyhelps to alert, or awaken, the upper parts of theBrain, including the Cerebral Cortex. Such actionskeep the Brain alert and conscious.The RAS also helps to control respiration andcirculation and serves as a filtering system forincoming sensory signals. For example, weawaken to the sound of an alarm clock, to a brightlight flash, or to a painful pinch because activity inthe RAS that arouses the Cerebral Cortex.
Just above the Medulla, the brainstem enlarges toform the PONS. PONS mean BRIDGE, and thisarea of the brain stem contains mostly whitematter that provides a link between the cerebralcortex and the cerebellum. Above the PONS andcontinuous with it is the MIDBRAIN, the smallestdivision of the lower brain stem.
Midbrain• Contains: – Corpora quadrigemina: • Superior colliculi: – Involved in visual reflexes. • Inferior colliculi: – Relay centers for auditory information. – Cerebral peduncles: • Composed of ascending and descending fiber tracts. – Substantia nigra: • Required for motor coordination. – Red nucleus: • Maintains connections with cerebrum and cerebellum. – Involved in motor coordination.
– Pons: Hindbrain • Surface fibers connect to cerebellum, and deeper fibers are part of motor and sensory tracts. • Contains several nuclei associated with cranial nerves V, VI, VII. • Contains the apneustic and pneumotaxic respiratory centerss.– Cerebellum: • Receives input from proprioceptors. • Participates in coordination of movement. • Necessary for motor learning, coordinating different joints during movement, and limb movements.
Hindbrain• Medulla oblongata – All descending and ascending fiber tracts between spinal cord and brain must pass through the medulla. • Nuclei contained within the medulla include VIII, IX, X, XI, XII. • Pyramids: – Fiber tracts cross to contralateral side. – Vasomotor center: • Controls autonomic innervation of blood vessels. – Cardiac control center: • Regulates autonomic nerve control of heart. – Regulates respiration with the pons.
DIENCEPHALONTHE THALAMUS AND HYPOTHALAMUSThe Thalamus and Hypothalamus are found inthe part of the brain between the Brain Stem andCerebrum.The Thalamus, which is composed of GrayMatter, serves as a SWITCHING STATIONFOR SENSORY INPUT. With the Exception ofSMELL, each Sense Channels its Sensory Nervesthrough the Thalamus.
Thalamus and Epithalamus• Thalamus: – Composes 4/5 of the diencephalon. – Forms most of the walls of the 3rd ventricle. – Acts as relay center through which all sensory information (except olfactory) passes to the cerebrum. • Lateral geniculate nuclei: – Relay visual information. • Medial geniculate nuclei: – Relay auditory information. • Intralaminar nuclei: – Activated by many sensory modalities. – Projects to many areas. » Promotes alertness and arousal from sleep.• Epithalamus contains: – Choroid plexus where CSF is formed. – Pineal gland which secretes melatonin.
The Thalamus passes information to the properregion of the Cerebrum for further processing.Immediately Below the Thalamus is theHypothalamus, which is the CONTROLCENTER for hunger, thirst, fatigue, anger, andbody temperature.Parts of the Diencephalon and the Cerebrum areincluded in an important group of connected BrainCenters called the LIMBIC SYSTEM.
Hypothalamus• Contributes to the regulation of sleep, wakefulness, emotions, sexual arousal, anger, fear, pain, and pleasure.• Stimulates hormonal release from anterior pituitary.• Produces ADH and oxytocin.• Coordinates sympathetic and parasympathetic reflexes.
The Limbic System includes the Thalamus, theHypothalamus, some deeper parts of the CerebralCortex, and centers in the Temporal Lobes.The Limbic system plays an important role inemotions, memory, and motivation, among otherthings.
Pituitary Gland• Posterior pituitary: – Stores and releases ADH (vasopressin) and oxytocin.• Hypothalamus produces releasing and inhibiting hormones that are transported to anterior pituitary. – Regulate secretions of anterior hormones.• Anterior pituitary: – Regulates secretion of hormones of other endocrine glands.
Basal Nuclei (basal ganglia)• Masses of gray matter composed of neuronal cell bodies located deep within white matter.• Contain: – Corpus striatum: • Caudate nucleus. • Lentiform nucleus: – Putman and globus pallidus.• Functions in the control of voluntary movements.
Electroencephalogram (EEG)• Measures synaptic potentials produced at cell bodies and dendrites. – Create electrical currents.• Used clinically do diagnose epilepsy and brain death.
EEG Patterns• Alpha: – Recorded from parietal and occipital regions. • Person is awake, relaxed, with eyes closed. – 10-12 cycles/sec.• Beta: – Strongest from frontal lobes near precentral gyrus. • Produced by visual stimuli and mental activity. • Evoked activity. – 13-25 cycles/sec.• Theta: – Emitted from temporal and occipital lobes. • Common in newborn. • Adult indicates severe emotional stress. – 5-8 cycles/sec.• Delta: – Emitted in a general pattern. • Common during sleep and awake infant. • In awake adult indicate brain damage. – 1-5 cycles/sec.