1 Structural Organization of the Brain A Central Nervous System composed of the brain and spinal cord I Receives input from sensory neurons and directs activity of motor neurons that innervate muscles and glands II Association neurons integrate sensory info and help direct appropriate response to maintain homeostasis and respond to the environment a All vertebrates and most invertebrates are capable of at least rudimentary forms of learning and memory This capability permits behavior to be modified by experience B Embryonic Development I Early embryo contains ectoderm on its surface it eventually form the epidermis of the skin as development progresses a groove appears this becomes the neural tube eventually becoming the CNS at full development a B t the neural tube and developing epidermis neural crest forms eventually becomes II By week four after conception three swellings seen on neural tube PNS ganglia 1 Prosencephalon forebrain 2 Mesencephalon midbrain 3 Rhobencephalon hindbrain b By 5th week regions differentiate into 5 regions 1 Forebrain divides into telencephalon diencephalon 2 Mesencephalon remains mid brain 3 Rhobencephalon metencephalon and myelencephalon c 5th week terms are used to describe the adult brain III Basic structural plan of CNS can now be seen a Telencephalon forms two cerebral hemispheres of the cerebrum and two lateral ventricles 1 CNS begins as hollow tube and stays hollow as brain regions are formed 2 Cavities of the brain are known as ventricles and are filled with cerebral spinal fluid b Diencephalon forms thalamus hypothalamus and 3rd ventricle c Mesencephalon forms midbrain cerebral aqueduct d Metencephalon forms pons cerebellum upper 4th ventricle e Myelencephalon forms medulla oblongata lower 4th ventricle f Posterior neural tube spinal cord C Choroids Plexuses thin structures protruding into the ventricles which make Cerebrospinal Fluid I Consists of simple cuboidal to columnar epithelium in close association with blood capillaries a Capillaries are fenestrated meaning they have gaps that allow molecules through II Project into the roofs of the ventricles III Secrete CSF into ventricles and central canal of the cord IV CSF is made from blood and is returned to blood a Consistent hypertonic solution with a different concentration of ions compared to blood plasma b Constant fluid secretion and absorption of CSF into venous blood maintain healthy intracranial pressure of 5 15mm Hg V Brain statistics a Gray matter forms the cortex surrounding face layer and deep nuclei b White matter consists of axon tracts myelin sheaths produce white color that underlie the cortex and surround the nuclei c Adult brain 100 billion neurons weighs 3 5 lbs 1 5 kg d Receives 15 of the total blood flow to the body minute 1 High rate of blood flow is consequence of high metabolic requirements it needs e Scientists demonstrated neurogenesis formation of new neurons from neural stem cells in adult brains in 1 Subventricular zone of lateral ventricles a thin layer of cells adjacent to the ependymal cells that line the lateral ventricles i Newborn neurons migrate from here to olfactory bulbs of the brain where they become functional interneurons 2 Subglandular zone of hippocampus 2 The Cerebrum A Consists of five paired lobes within two convoluted hemispheres most higher functions are performed by the cerebrum I II Consists of right and left hemisphere connected internally by corpus callosum Largest portion of the brain 80 of the mass a Corpus callosum is a major tract of axons B Consists of an outer cerebral cortex 2 to 4 mm of gray matter with underlying white matter I Characterized by raised folds gyri separated by depressed grooves sulci together known as convolutions II Each cerebral hemisphere is divided by deep sulci or fissures into 5 lobes a Frontal Precentral sulcus in frontal lobe 1 motor control by upper motor neurons b Parietal Post central gyrus in parietal lobe c somatosensory cortex Responsible for perception of sensations from skin muscles tendons joint receptors d Temporal auditory centers e Occipital vision coordination of eye movements f Insula not visible from the surface encoding of memory and integration of sensory information w visceral responses 1 Olfactory auditory gustatory and pain info III Mirror Neurons studies show these are neurons fired when monkeys performed goal directed actions and when they observed others perform the same actions a Found in frontal parietal lobes to integrate sensory and motor neural activity b Connected through the insula cingulate gyrus to emotion centers of brain c May be involved in ability to learn social skills have been implicated in autism IV Visualizing the Brain a Electrocepalogram synaptic potentials produced at cell bodies and dnedrites of cerebral cortex create electrical currents that are measured by electrodes 1 Alpha waves from parietal and occipital lobe while a person is awake 2 Beta waves strongest from frontal lobe produced by visual stimuli and mental activity 3 Theta waves temporal and occipital lobes common in newborns and sleeping adults If seen if awake adults indicator of severe emotional stresss 4 Delta waves cerebral cortex sleeping adult and awake infant Presence of delta waves in awake adult indicates brain damage 3 Sleep A May be genetically controlled although is affected by environmental factors B Neurotransmitters involved I Histamine wakefulness II Adenosine GABA sleep III Serotonin induces REM sleep and stimulates non REM sleep C Two categories of sleep I REM rapid eye movement when dreams occur Theta waves are seen II Non REM aka resting sleep divided into 4 stages determined by EEG waves a Stages 3 and 4 called slow wave sleep delta waves D Sleep Pattern I When first fall asleep nonREM stage entered and progress through 4 stages then a person ascends back up the four stages of nonREM and enters REM sleep II Typically five REM to non REM cycles a night 90 minutes each III If allowed to awaken naturally typically during REM sleep IV REM sleep has higher total brain metabolism and higher blood flow to selected regions when compared to wakeing state a Limbic system active in REM involved in emotions b Consolidation of nondeclarative memories c Breathing and heart rate can be irregular V Non REM sleep a Breathing and heartrate are regular b Allows repair of metabolic damage done to cells by free radicals c Consolidation of spatial and declarative memories those that can be verbalized
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