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THE BRAIN Chapter 14 Brain Basics: 100 billion neurons in the adult brain 1000 billion neuroglia adult brain weighs almost 3 lbs 4 basic parts of the brain: – Brain stem – Cerebellum – Diencephalon – Cerebrum 4 Parts of the Brain -brain stem *continuous with the spinal cord *medulla oblongata *pons *midbrain -cerebellum -diencephalon *thalamus *hypothalamus -cerebrum *largest part *2 hemispheres COVERINGS OF THE BRAIN: Meninges: dura mater = outer layer arachnoid = middle layer pia mater =inner layer Fig. 14-3a, top, p. 456 Fig. 14-3, p. 456 BRAIN BLOOD FLOW AND THE BLOOD BRAIN BARRIER Basics: Blood supply to the brain is mainly from the cerebral arterial circle –or the circle of Willis at the base of the brain. Brain is 2% of body weight but consumes 20% of oxygen and glucose used at rest. Brain metabolizes glucose using oxidative respiration to generate ATP And….. There is a corresponding increase in blood supply when there is a localized increase in brain activity An interruption of blood flow can cause unconsciousness, 1-2 minutes can impair neuronal function, 4 minutes can result in permanent injury No glucose is stored in the brain so it must be continually supplied Ventricles of the Brain and CSF Ventricles: There are 4 ventricles filled with CSF -2 lateral, one in each cerebral hemisphere *separated by the septum pellucidum -Third ventricle *narrow cavity superior to the hypothalamus -Fourth ventricle *between the brain stem and the cerebellum Fig. 14-2a, p. 454 CSF –Cerebral Spinal Fluid Clear, colorless liquid Carries oxygen, glucose proteins, lactic acid, urea, cations (Na+, K+ , Ca2+, Mg2+) and anions (Cl- and HCO3-) and some white blood cells Circulates continually through the superarachnoid space and around the brain and spinal cord Total volume: 80-150 mL Contributes to homeostasis in 3 ways mechanical protection –shock absorber, the brain “floats” chemical protection –optimal chemical environment for accurate neuronal signaling Circulation –medium for exchange of nutrients and wastes between blood and nervous tissue Fig. 14-2b, p. 454 THE BRAIN STEM Basics: Between spinal cord and diencephalon Reticula formation -netlike gray and white matter -extends through the brain stem -RAS Reticular activating system *awakening from sleep *maintaining level of consciousness *arouses cerebral cortex in response to stimuli *maintains muscle tone Fig. 14-1, part 2, p. 453 3 parts of the brain stem: 1. Medulla Oblongata – continuation of the upper part of the spinal cord – begins at the foramen magnum and extends to the pons -3 cm – pyramids –anterior aspect -formed by largest motor tracts from spinal cord -conspicuous external bulges -cross over each other –decussation of pyramids inferior olivary nucleus (oval shaped swelling (olive) -relay stations to the thalamus -nucleus gracilis -nucleus cuneatus Autonomic Nuclei -regulation of vital functions -reflex centers receive inputs from cranial nerves, brain stem, and cerebral cortex -adjust activities of peripheral systems cardiovascular centers -cardiac -vasomotor respiratory rhythmicity centers -activity regulated by the pons Fig. 14-5b, p. 460 Fig. 14-5a, p. 460 2. Pons (bridge) -nuclei -control breathing with medulla pneumatoaxic area apneustic area 1. nuclei for cranial nerves Trigeminal (V) -mixed -largest cranial nerve -somatosensory info for head and neck -motor for chewing -Trigeminal neuralgia (Tic Douloureux) affects CV Abducens (VI) -motor -eye movements More…… – Facial (VII) -mixed -taste, secretion of saliva, tears, muscles for facial expression -Bell’s palsy- inflammation of CVII – Vestibulocochlear (VIII) -special sensory -balance and equilibrium Cranial Nerves To help you remember the cranial nerves: On occasion, our trusty truck acts funny— very good vehicle any how. 1. Olfactory, 2. optic, 3. oculomotor, 4. trochlear, 5. trigeminal, 6. abducens, 7. facial, 8. vestibulocochlear, 9. glossopharangeal, 10. vagus, 11. accessory, 12. hypoglossal 3. Midbrain (or mesencephalon) reflex centers – superior colliculi -movement of eyes, head, and neck in response to visual and other stimuli – Inferior colliculi -movement of head and trunk in response to auditory stimuli 2. Specialized nuclei a. Substantia nigra -subconscious muscle activities -fluidity of movement -secretes dopamine -Parkinson’s diseasedecrease in dopamine secreting cells b. red nuclei -control of skeletal muscle tone Fig. 14-1, part 1, p. 453 CEREBELLUM Basics: Second largest part of the brain Shape is like a butterfly Vermis =central constriction Cerebellar hemispheres -anterior and posterior lobe *govern subconscious movements of skeletal muscles -Flocculonodular lobe *inferior surface *sense of equilibrium Fig. 14-7a, left, p. 463 Main functions: -compares intended movements with what is actually happening -coordinates complex, skilled movements -regulates posture and balance Affected by drugs and trauma -alcohol affects cerebellum causing ataxia DIENCEPHALON 1. Thalamus –2 halves – – – – – 80% of diencephalon –3 cm long principal relay station for sensory impulses “the secretary” sends sensory input to cerebral cortex assorted nuclei and their roles: -medial geniculate nucleus –auditory -lateral geniculate nucleus -visual -ventral posterior nucleus -taste, touch, pressure, vibration, temperature, pain -anterior nucleus -emotions and memory functions in cognition and awareness Fig. 14-8b, p. 465 2. Hypothalamus Small, inferior to thalamus (in position) 4 major regions: 1. mammillary region -mammillary bodies -relay stations for reflexes related to sense of smell 2. tuberal region -widest part 3. infindibulum connects hypothalamus with the pituitary gland -supraoptic region -superior to optic chiasm (where optic nerves cross) -contains suprachiasmatic nucleus 4. preoptic region -contains medial and lateral preoptic nuclei -regulates certain autonomic activities Fig. 14-10b, p. 467 Functions: major regulator of homeostasis a. Control of ANS -axons from hypothalamus to parasympathetic and sympathetic -regulates visceral activities -regulates heart rate Controls Pituitary gland (master gland) -hypothalamic regulating hormones *stimulate or inhibit secretion of hormones from the anterior pituitary -axons from paraventricular and supraoptic nuclei *nerve cell bodies make oxytocin and ADH which are transported and stored in the posterior pituitary Regulation of emotional and behavioral patterns -works with the limbic system *rage *aggression *pain *pleasure *behavior patterns related to sexual arrousal And…… *Feeding center –hunger *Satiety center –fullness *Thirst center –cells stimulated by rising osmotic pressure -sensation of thirst Control of Body Temperature *monitors blood temperature *promotes cooling or warming up – Regulation of circadian rhythms and states of consciousness *sleep patterns of circadian rhythm 3. Epithalamus –superior and posterior to thalamus pineal gland -pea size -secretes melatonin -may promote sleepiness -may set biological clock habenular nuclei -olfaction -emotional responses to odors CEREBRUM - bulk of the brain Geographic basics of the Cerebrum: Cerebral cortex is the 2-4 mm layer of gray matter on the surface of the cerebrum –billions of neurons Cerebral white matter is underneath Folds or convolutions of the cerebrum are due to the rapid growth of gray matter during development which is faster than white matter Fissures are the deepest grooves Fig. 14-12c, p. 471 Sulci the shallower grooves Longitudinal fissure separates the right and left cerebral hemispheres Corpus callosum connects the two hemispheres –nerve net Cerebrum divided into lobes named for the bones that lie over them. Lobes of the Cerebrum -Frontal -central sulcus -parietal -pre-central gyrus –in front of the central sulcus- motor area -post-central gyrus –primary somatosensory area -Lateral cerebral sulcus -Temporal lobe -parieto-occipital sulcus -occipital lobe -insula (deep within the lateral cerebral fissure) Fig. 14-9a, p. 466 Fig. 14-12b, p. 471 BASAL GANGLIA Function: -receive input from and provide output to: -cerebral cortex -thalamus -hypothalamus Structures included: (paired nuclei) -corpus striatum -largest nuclei -includes: 1. -caudate nucleus *autonomic movement of skeletal muscles 2. -lentiform nucleus (2 parts) *putamen (lateral part) - autonomic movement of skeletal muscles -swinging of arms while walking, laughing *globus pallidus (medial) -muscle tone for specific body movements Huntington’s Disease Genetic Disease –dominant gene Affects the basal ganglia Progresses slowly over a period of 20 years Affects the coordination (chorea) controlled by the basal ganglia and the cortex involved in memory and thought Unsteady gait, lack of coordination, impaired reasoning and memory. Abnormal protein -Huntingtin Killed Woodie Guthrie Parkinson’s Disease Etiology: idiopathic (most do not know), head trauma, MDMA Cells of sustantia nigra no longer make dopamine Symptoms – – – – – Tremor –(pill rolling) Slowed movement (bradykinesia) Muscle rigidity Loss of facial expression mumbling treatment Levadopa Dopamine agonists (magnify the effects of dopamine. MAO B inhibitors -inhibit MAO type B in the breakdown of dopamine COMT –break down the enzyme that breaks down levadopa Anticholinergics -for tremors Limbic System Functional grouping The emotional brain Hippocampus Parahippocampus Amygdola hypothalamus Important in learning Amygdola acts as an interface between the cerebrum, sensory systems, and limbic system Encircles upper part of the brain stem and the corpus callosum Hippocampus along with portions of the cerebrum functions in memory Primative brain –life altering memories – Emotional context of memories. Fig. 14-11a, p. 469 Fig. 14-11b, p. 469 CEREBRAL CORTEX AND ASSOCITATION AREAS Sensory Areas Primary somatosensory (PSSA) Posterior to the central sulcus In postcentral gyrus of each parietal lobe Receives input from sensory receptors for touch, pain, proprioception, temperature Function of PSSA is to localize the part of the body receiving the impulse (Thalamus generalizes) Body parts are not represented in proportion to their size Fig. 14-13, p. 472 Primary visual (PVA) medial surface of the occipital lobe Optic nerve (C II) terminates at the geniculate nucleus of the thalamus Thalamus relays information to the PVA Primary Auditory (PAA) superior part of the temporal lobe near the lateral cerebral sulcus interprets basic characteristics of sound like pitch and rhythm Primary Gustatory (PGA) base of the postcentral gyrus, superior to the lateral cerebral sulcus in parietal cortex Taste Primary Olfactory (POA) in temporal lobe on the medial aspect (no visible) smell Motor Areas: Primary Motor precentral gyrus of the frontal lobe voluntary contractions of specific muscle groups controls muscles on opposite side of the body body parts are not represented in proportion to their size Broca’s Area –Speech in 97% of people on left frontal lobe superior to the lateral cerebral sulcus production of speech ASSOCIATION AREAS: Basics: – interpret incoming data – may incorporate a motor response – analyze, recognize, and act on sensory inputs – multiple inputs and outputs – independent of the primary sensory and motor areas – functions are complex Prefrontal cortex: anterior portions of the frontal lobes most complicated cortical region of all involved with intellect complex learning abilities (cognition) production of abstract ideas, judgment reasoning, planning, concern for others and conscience matures slowly (anywhere from late teens to early 20’s depending on the source) dependent on positive an negative feedback from the social environment linked to the limbic system lesions in this area (tumors) cause mental and personality disorders prefrontal lobotomy- severs the connections to the prefrontal cortex used in the 1930s-1950s to treat severe mental illness patients became less anxious cure worse than the disease patients developed personality disorders, lack of judgment or loss of initiative, even epilepsy Somatosensory Association Area just posterior to and receives input from the primary somatosensory area, thalamus functions to integrate and interpret sensations perceive relationship of one body part to another, shapes and textures without seeing, orientation of objects stores memories of sensory experiences Fig. 15-5a, p. 504 Visual Association Area occipital lobe relates present and past visual experiences essential for recognizing and evaluating visual images Common Integrative Area (General Interpretive Area) Sometimes called the Gnostic area bordered by somatosensory, visual, and auditory integrates sensory interpretations from association areas and impulse from other areas transmits signals to other parts of the brain based on the input usually only found in the left hemisphere Also….. appears to be storage site for complex memories associated with sensation integrates all incoming signals into a single thought or understanding of the situation assessment set to prefrontal cortex which adds emotional overtones and makes the appropriate response And…… example –drop a bottle of acid –overall message of danger supersedes visual crash of bottle, sound of shattering glass, smell of acid, burning on skin Research indicates that the gnostic area and prefrontal cortex work together to assemble new experiences into logical constructs or “stories” based on past experiences Not objective –based on past experience Storytelling may be a part of the hardware of mental processing! injury to this area can result in the ability to interpret any information -“imbecility” Premotor Area immediately anterior to the primary motor area learned motor activities of a complex and sequential nature generates nerve impulses that cause specific groups of muscles to contract in specific sequences memory bank for sequential movement Fig. 15-9, p. 510 Visceral Association area: the cortex of the insula may be involved in conscious perception of visceral sensations (upset stomach, full bladder) Frontal Eye Field frontal cortex scanning movements of eyes, like reading voluntary not always categorized as an association area Auditory Association Area inferior and posterior to the primary auditory area in temporal cortex determines if sound is speech, music, or noise Fig. 14-15a, p. 475 Language Areas Cortical regions involved in language occur in both hemispheres neurons from Broca’s area pass to premotor cortex impulses from premotor area coordinate the movements of the mouth, tongue etc. to form speech impulses also control breathing muscles to coordinate the mechanics of speech through the vocal cords Fig. 14-16, p. 477 Wernicke’s Area interprets the meaning of speech translates words into thoughts the dictionary PET scans indicate it also may be involved in sounding out words right hemisphere adds emotional context to the word “wet” and the speech region comparable to Broca’s area adds inflection and tone to the speech language comprehension occurs in the prefrontal cortex Clinical Correlation: Aphasia: inability to use or comprehend words Broca’s area damage: nonfluent aphasia, know what they want to say but are not able to articulate or form words Integrative area or auditory association areas –fluent aphasia- faulty understanding of spoken or written words –strings of words that have no meaning HEMISPHERIC LATERALIZATION Functional asymmetry of the 2 cerebral hemispheres Anatomical differences – Wernicke’s area is 50% larger on the left side in 66% of individuals – appears at 30 weeks of gestation in the fetus – Broca’s area is on the left in 97% of individuals Functional differences 1. Right side controls left side of the body and left side controls the right side of the body 2. In most individuals the left hemisphere is considered dominant or the categorical hemisphere: -responsible for language based skills *reading *writing *speech *use and understanding of sign language -analytical tasks *mathematical calculations *logical decision making Right Hemisphere important analyzing sensory information and relates the body to the sensory environment: *identify familiar objects by touch, smell, sight, taste, or feel *face recognition *understanding of 3 dimensional relationships *analysis of the emotional context of a conversation -Difference is less pronounced in females, perhaps due to larger white matter tracts communicating between both hemispheres Interesting addendum: 96% of right handed people are left brain dominant 9% of the human population is left handed, 70% of the left handed population are left brain dominant, 15% are right brain dominant, and the other 15% show no specialization. BRAIN WAVES: Electroencephalogram –EEG –detects brain waves 4 types of normal brain waves: Alpha waves: -rhythmic waves -8-13 cycles / sec (hertz) -awake or resting with eyes closed Beta waves: -generally appear when nervous system is active such as sensory input and mental activity -14-30 hertz And……. Theta waves: -children and adults experiencing emotional stress -4-7 hertz -may occur in brain disorders Delta waves: -1-5 hertz -occur in deep sleep in adults -normal in awake infants -appearance in an awake adult indicates brain damage Fig. 14-17abcd, p. 479 Sleep State of altered consciousness Exact trigger for sleep is unknown A chemical involved is adenosine – Produced during high ATP usage – Binds to A1 receptors and inhibits RAS pathway – Caffeine and theophylline work by binding these receptors instead. – Different levels of sleep and REM and non REM Dreams: most during REM sleep Sleep paralysis: can occur if you wake during REM sleep Sleepwalking occurs during stage 4 of nREM sleep Fig. 16-14, p. 540 Sleep Disorders Insomnia: can’t sleep Narcolepsy: REM sleep is not inhibited during waking hours and individual has involuntary periods (about 15 min.) of sleep during the day Sleep Apnea: Individuals have periods of not breathing during sleep (10 + seconds). Learning and Memory Learning= acquiring new knowledge Memory = knowledge is retained over time. Plasticity = change associated with learning. Parts of the brain associated with memory are: association areas of all the lobes fo the brain, limbic system (especially the hippocampus and the amygdala), diencephalon. Types of Memory Short term memory: information held for a brief amount of time Long term memory: more permanent memory –can be retrieved after months or years. Memory consolidation: repeated retrieval of information (rehearsal) that results in reinforcement of memory Long Term Potentiation Long lasting increase in strength of synapse response following stimulation. Especially in the hippocampus Neurotransmitter is Glutamate Involves NMDA-Glutamate receptors Nitric oxide is released from the post synaptic neuron and results in long term potentiation. Fig. 16-13, p. 538 Clinical correlations: anencephaly –absence of skull and cerebral hemispheres -neural folds fail to fuse rostrally -child is totally vegetative: unable to see, hear or process sensory input -no voluntary movement spina bifida – -incomplete formation of the vertebral arches -typically involves lumbo-sacral region -variable: *involves one or two vertebrae with no neural problems *severe (inferior spinal cord is rendered functionless) Folic acid supplementation during pregnancy is helpful in preventing both these conditions Cerebral Palsy: temporary lack of oxygen during birth and other conditions such as smoking, drug exposure, rubella neuromuscular disability –voluntary muscles poorly controlled or paralyzed due to brain damage spastic, speech difficulties, motor difficulties 50% have seizures 50% mentally retarded 33% some degree of deafness does not get worse over time, but not reversible largest single cause of crippling in children Traumatic Brain Injuries: Concussion -slight brain injury following blow to the head or sudden stopping of a moving head -most common brain injury -symptoms are relatively mild -dizzy, see stars, lose consciousness -headache, drowsiness, lack of concentration -confusion, or post-traumatic amnesia -no permanent neurological damage Contusion -bruising of the brain due to trauma -leakage of blood from microscopic vessels -pia mater may be torn -blood may leak into subarachnoid space -frontal lobe most commonly affected -loss of consciousness (brief) -loss of reflexes, transient cessation of repieraton and decreased BP –stabilize within a few seconds Laceration -tear of the brain -usually from skull fractur or gunshot wound -rupture of large blood vessels -bleeding into brain and subarachnoid space -cerebral hematoma, swells against brain tissue -increase in intracranial pressure HOMEOSTATIC IMBALANCES: Stroke (CVA cerebrovascular accident): Persistent neurological symptoms resulting from the destruction of brain tissue Causes: intracerebral hemorrhage, emboli, atherosclerosis of the cerebral arteries Plasminogen activator- drug used to open blocked blood vessels in brain Should be administered within 3 hours of the onset of the CVA Only works if the CVA is due to a blood clot Can decrease disability by 50% Coma Damage to the RAS State of deep unconsciousness Person cannot be aroused Different stages Light stage –brain stem and spinal reflexes active Deepest stage –cardiac and respiratory reflexes lost = death Transient Ischemic Attack (TIA) Temporary cerebral dysfunction caused by impaired blood flow to the brain Symptoms include dizziness, weakness, numbness, paralysis, headache, slurred speech, drooping of one side of the face, etc. Sudden onset, persists no more than 24 hours, leaves no persistent neurological deficits 33% of patients who experience a TIA will have a CVA within 5 years Treatment involves aspirin, and anticoagulants as well as cerebral artery bypass grafting and others. Other CLINICAL CORRELATIONS: 1. Alzheimer disease (AD) Affects 5 % of the population between 65 and 74 years -not part of normal aging. ½ the people over 85 years. Loss of reason and ability to care for oneself Loss of interest in surroundings Loss of long term memories Mental emptiness Loss of bodily functions Distinct structural abnormalities -decreased brain weight -cortical atrophy -subcortical atrophy (hippocampus, amygdala, basal nuclei) -senile plaques –hallmark of AD *contain amyloid deposits *kill neurons where they are deposited -neurobrillary tangles Treatment: Ach precursors AchE inhibitors other Dementia generalized term for senility Forgetfulness Untidiness Confusion Restlessness Lethargy Errors in judgment Impaired new memory storage Long-term memory mostly unaffected . Epilepsy Primary Etiology –idiopathic Secondary-trauma -neoplasm -infection -cerebrovascular disease -brain lesion More common in children 1% of population can result in brain cell loss many types of seizures -partial -generalized *Grand mal –generalized Tonic –clonic *Petit Mal –absence seizures Treatments -anticonvulsant mechanisms *increase GABA -valium -barbiturates -Depakote Pain Analgesics: drugs that relieve pain Pain Sensation: – Nociceptors –receptors for pain – Stimulated by prostaglandins, kinins Aspirin and other NSAIDs interrupt synthesis of protaglandins – Substance P =neurotransmitter for pain 2 types of pain fast pain -acute or shape slow pain -c fibers, develops over tim Endorphins enkephlins neuromodulate substance P Substance Abuse Abuse: self-administered use of any drug in a manner that deviates from the approved medical or social patterns within a given culture Some evidence for genetic predisposition Substance dependence -tolerance –need more for the same effect -withdrawal- characteristic syndrome for withdrawal from the substance *physical dependence-abnormal behavior and autonomic symptoms that occur upon the withdrawal of the drug *psychological dependence- dysphoria and intense craving upon withdrawal from the drug Categories of Drugs Hallucinogens – Marijuana – LSD – PCP Stimulants – Amphetamines – Cocaine – Caffeine – Nicotine And….. Depressants – – – – Alcohol Barbiturates Methaqualone Diazepam, Librium Narcotics – – – – Morphine Heroin Methadone Codeine Drug Mechanisms -Psychostimulants *(cocaine, amphetamines) *euphoric effects due to activation of mesolimbic DA system -Hallucinogens *activation of one type of 5HT receptors -Cannabinoids *activation of cannabinoid receptors -Nicotine *activation of nicotine receptors -Caffeine *activation of adenosine receptors -Opioid *complex! *euphoria through modulation of the mesolimbic DA transmission Just to clarify… Mesolimbic: nucleus accumbens, olefactory tubercle, and projections to the cortex Types of circuts Divergent Convergent Serial Parallel Reverberation Neuronal Circuits Nerves are organized into networks. Networks distribute the impulse in different manners to suit different needs. 1. simple series 2. diverging –one fiber stimulates many – -can be motor impulse – -can be a sensory impulse being distributed to many parts of the brain And…. 3. Converging -many neurons stimulate one neuron. -Effective in stimulating or inhibiting since you have multiple inputs. Complex motor skills. 4. Reverberating circuit circuit branches back to re-stimulate the pathway. Short term memory, waking up. 5. Parallel circuit -one neuron branches into parallel branches that all reach a final neuron. -mathematical calculations. Fig. 13-13, p. 438