Functional Brain System Networks of neurons working together and spanning wide areas of the brain...
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Transcript of Functional Brain System Networks of neurons working together and spanning wide areas of the brain...
Functional Brain SystemFunctional Brain System
Networks of neurons working together and Networks of neurons working together and spanning wide areas of the brainspanning wide areas of the brain
The two systems are:The two systems are: Limbic systemLimbic system Reticular formationReticular formation
Limbic SystemLimbic System
Structures located on the medial aspects of Structures located on the medial aspects of cerebral hemispheres and diencephaloncerebral hemispheres and diencephalon
Includes the rhinencephalon, amygdala, Includes the rhinencephalon, amygdala, hypothalamus, and anterior nucleus of the hypothalamus, and anterior nucleus of the thalamusthalamus
Limbic SystemLimbic System
Parts especially important in emotions:Parts especially important in emotions: Amygdala – deals with anger, danger, and fear Amygdala – deals with anger, danger, and fear
responsesresponses Cingulate gyrus – plays a role in expressing Cingulate gyrus – plays a role in expressing
emotions via gestures, and resolves mental conflictemotions via gestures, and resolves mental conflict Puts emotional responses to odors – e.g., Puts emotional responses to odors – e.g.,
skunks smell badskunks smell bad
Limbic SystemLimbic System
Figure 12.18
Limbic System: Emotion and Limbic System: Emotion and CognitionCognition
The limbic system interacts with the prefrontal The limbic system interacts with the prefrontal lobes, therefore:lobes, therefore: One can react emotionally to conscious One can react emotionally to conscious
understandingsunderstandings One is consciously aware of emotion in one’s lifeOne is consciously aware of emotion in one’s life
Hippocampal structures – convert new Hippocampal structures – convert new information into long-term memoriesinformation into long-term memories
Reticular FormationReticular Formation
Composed of three broad columns along the Composed of three broad columns along the length of the brain stemlength of the brain stem Raphe nucleiRaphe nuclei Medial (large cell) groupMedial (large cell) group Lateral (small cell) groupLateral (small cell) group
Has far-flung axonal connections with Has far-flung axonal connections with hypothalamus, thalamus, cerebellum, and hypothalamus, thalamus, cerebellum, and spinal cordspinal cord
Reticular FormationReticular Formation
Figure 12.19
Reticular Formation: RAS and Reticular Formation: RAS and Motor FunctionMotor Function
RAS – RAS – RReticular eticular AActivating ctivating SSystem ystem Sends impulses to the cerebral cortex to keep it Sends impulses to the cerebral cortex to keep it
conscious and alertconscious and alert Filters out repetitive and weak stimuliFilters out repetitive and weak stimuli
Motor functionMotor function Helps control coarse motor movementsHelps control coarse motor movements Autonomic centers regulate visceral motor Autonomic centers regulate visceral motor
functions – e.g., vasomotor, cardiac, and functions – e.g., vasomotor, cardiac, and respiratory centersrespiratory centers
Brain WavesBrain Waves Normal brain function involves continuous Normal brain function involves continuous
electrical activityelectrical activity An electroencephalogram (EEG) records this An electroencephalogram (EEG) records this
activityactivity Patterns of neuronal electrical activity recorded Patterns of neuronal electrical activity recorded
are called brain wavesare called brain waves Each person’s brain waves are uniqueEach person’s brain waves are unique Continuous train of peaks and troughsContinuous train of peaks and troughs Wave frequency is expressed in Hertz (Hz)Wave frequency is expressed in Hertz (Hz)
Types of Brain WavesTypes of Brain Waves Alpha waves – regular and rhythmic, low-Alpha waves – regular and rhythmic, low-
amplitude, slow, synchronous waves indicating amplitude, slow, synchronous waves indicating an “idling” brainan “idling” brain
Beta waves – rhythmic, more irregular waves Beta waves – rhythmic, more irregular waves occurring during the awake and mentally alert occurring during the awake and mentally alert statestate
Theta waves – more irregular than alpha Theta waves – more irregular than alpha waves; common in children but abnormal in waves; common in children but abnormal in adultsadults
Delta waves – high-amplitude waves seen in Delta waves – high-amplitude waves seen in deep sleep and when reticular activating deep sleep and when reticular activating system is dampedsystem is damped
Types of Brain WavesTypes of Brain Waves
Figure 12.20b
Brain Waves: State of the BrainBrain Waves: State of the Brain
Change with age, sensory stimuli, brain Change with age, sensory stimuli, brain disease, and the chemical state of the bodydisease, and the chemical state of the body
EEGs used to diagnose and localize brain EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, lesions, tumors, infarcts, infections, abscesses, and epileptic lesionsand epileptic lesions
A flat EEG (no electrical activity) is clinical A flat EEG (no electrical activity) is clinical evidence of deathevidence of death
EpilepsyEpilepsy
A victim of epilepsy may lose consciousness, A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking, fall stiffly, and have uncontrollable jerking, characteristic of epileptic seizurecharacteristic of epileptic seizure
Epilepsy is not associated with, nor does it Epilepsy is not associated with, nor does it cause, intellectual impairmentscause, intellectual impairments
Epilepsy occurs in 1% of the populationEpilepsy occurs in 1% of the population
Epileptic SeizuresEpileptic Seizures
Absence seizures, or petit mal – mild seizures Absence seizures, or petit mal – mild seizures seen in young children where the expression seen in young children where the expression goes blankgoes blank
Grand mal seizures – victim loses Grand mal seizures – victim loses consciousness, bones are often broken due to consciousness, bones are often broken due to intense convulsions, loss of bowel and bladder intense convulsions, loss of bowel and bladder control, and severe biting of the tonguecontrol, and severe biting of the tongue
Control of EpilepsyControl of Epilepsy
Epilepsy can usually be controlled with Epilepsy can usually be controlled with anticonvulsive drugsanticonvulsive drugs
Valproic acid, a nonsedating drug, enhances Valproic acid, a nonsedating drug, enhances GABA and is a drug of choiceGABA and is a drug of choice
Vagus nerve stimulators can be implanted Vagus nerve stimulators can be implanted under the skin of the chest and can keep under the skin of the chest and can keep electrical activity of the brain from becoming electrical activity of the brain from becoming chaoticchaotic
ConsciousnessConsciousness
Encompasses perception of sensation, Encompasses perception of sensation, voluntary initiation and control of movement, voluntary initiation and control of movement, and capabilities associated with higher mental and capabilities associated with higher mental processingprocessing
Involves simultaneous activity of large areas Involves simultaneous activity of large areas of the cerebral cortexof the cerebral cortex
Is superimposed on other types of neural Is superimposed on other types of neural activityactivity
ConsciousnessConsciousness
Is holistic and totally interconnectedIs holistic and totally interconnected Clinical consciousness is defined on a Clinical consciousness is defined on a
continuum that grades levels of behavior – continuum that grades levels of behavior – alertness, drowsiness, stupor, comaalertness, drowsiness, stupor, coma
Types of SleepTypes of Sleep
There are two major types of sleep:There are two major types of sleep: Non-rapid eye movement (NREM)Non-rapid eye movement (NREM) Rapid eye movement (REM)Rapid eye movement (REM)
One passes through four stages of NREM One passes through four stages of NREM during the first 30-45 minutes of sleepduring the first 30-45 minutes of sleep
REM sleep occurs after the fourth NREM REM sleep occurs after the fourth NREM stage has been achievedstage has been achieved
Types and Stages of Sleep: Types and Stages of Sleep: NREMNREM
NREM stages include:NREM stages include: Stage 1 – eyes are closed and relaxation begins; the Stage 1 – eyes are closed and relaxation begins; the
EEG shows alpha waves; one can be easily arousedEEG shows alpha waves; one can be easily aroused Stage 2 – EEG pattern is irregular with sleep spindles Stage 2 – EEG pattern is irregular with sleep spindles
(high-voltage wave bursts); arousal is more difficult(high-voltage wave bursts); arousal is more difficult Stage 3 – sleep deepens; theta and delta waves appear; Stage 3 – sleep deepens; theta and delta waves appear;
vital signs decline; dreaming is commonvital signs decline; dreaming is common Stage 4 – EEG pattern is dominated by delta waves; Stage 4 – EEG pattern is dominated by delta waves;
skeletal muscles are relaxed; arousal is difficultskeletal muscles are relaxed; arousal is difficult
Types and Stages of Sleep: REMTypes and Stages of Sleep: REM
Characteristics of REM sleep Characteristics of REM sleep EEG pattern reverts through the NREM stages to EEG pattern reverts through the NREM stages to
the stage 1 patternthe stage 1 pattern Vital signs increaseVital signs increase Skeletal muscles (except ocular muscles) are Skeletal muscles (except ocular muscles) are
inhibitedinhibited Most dreaming takes placeMost dreaming takes place
SleepSleep
Figure 12.21a.1
SleepSleep
Figure 12.21a.2
Sleep PatternsSleep Patterns
Alternating cycles of sleep and wakefulness Alternating cycles of sleep and wakefulness reflect a natural circadian rhythmreflect a natural circadian rhythm
Although RAS activity declines in sleep, sleep Although RAS activity declines in sleep, sleep is more than turning off RASis more than turning off RAS
The brain is actively guided into sleepThe brain is actively guided into sleep The suprachiasmatic and preoptic nuclei of the The suprachiasmatic and preoptic nuclei of the
hypothalamus regulate the sleep cyclehypothalamus regulate the sleep cycle A typical sleep pattern alternates between A typical sleep pattern alternates between
REM and NREM sleepREM and NREM sleep
Importance of SleepImportance of Sleep
Slow-wave sleep is presumed to be the Slow-wave sleep is presumed to be the restorative stagerestorative stage
Those deprived of REM sleep become moody Those deprived of REM sleep become moody and depressedand depressed
REM sleep may be a reverse learning process REM sleep may be a reverse learning process where superfluous information is purged from where superfluous information is purged from the brainthe brain
Daily sleep requirements decline with ageDaily sleep requirements decline with age
Sleep DisordersSleep Disorders
Narcolepsy – lapsing abruptly into sleep from Narcolepsy – lapsing abruptly into sleep from the awake statethe awake state
Insomnia – chronic inability to obtain the Insomnia – chronic inability to obtain the amount or quality of sleep neededamount or quality of sleep needed
Sleep apnea – temporary cessation of Sleep apnea – temporary cessation of breathing during sleepbreathing during sleep
MemoryMemory
Memory is the storage and retrieval of Memory is the storage and retrieval of informationinformation
The three principles of memory are:The three principles of memory are: Storage – occurs in stages and is continually Storage – occurs in stages and is continually
changingchanging Processing – accomplished by the hippocampus Processing – accomplished by the hippocampus
and surrounding structures and surrounding structures Memory traces – chemical or structural changes Memory traces – chemical or structural changes
that encode memorythat encode memory
Memory ProcessingMemory Processing
Figure 12.22
Stages of MemoryStages of Memory
The two stages of memory are short-term The two stages of memory are short-term memory and long-term memorymemory and long-term memory
Short-term memory (STM, or working memory) Short-term memory (STM, or working memory) – a fleeting memory of the events that – a fleeting memory of the events that continually happencontinually happen
STM lasts seconds to hours and is limited to 7 STM lasts seconds to hours and is limited to 7 or 8 pieces of informationor 8 pieces of information
Long-term memory (LTM) has limitless Long-term memory (LTM) has limitless capacitycapacity
Transfer from STM to LTMTransfer from STM to LTM Factors that effect transfer of memory from Factors that effect transfer of memory from
STM to LTM include:STM to LTM include: Emotional state – we learn best when we are alert, Emotional state – we learn best when we are alert,
motivated, and arousedmotivated, and aroused Rehearsal – repeating or rehearsing material Rehearsal – repeating or rehearsing material
enhances memoryenhances memory Association – associating new information with old Association – associating new information with old
memories in LTM enhances memorymemories in LTM enhances memory Automatic memory – subconscious information Automatic memory – subconscious information
stored in LTMstored in LTM
Categories of MemoryCategories of Memory
The two categories of memory are fact The two categories of memory are fact memory and skill memorymemory and skill memory
Fact (declarative) memory: Fact (declarative) memory: Entails learning explicit informationEntails learning explicit information Is related to our conscious thoughts and our Is related to our conscious thoughts and our
language abilitylanguage ability Is stored with the context in which it was learnedIs stored with the context in which it was learned
Skill MemorySkill Memory
Skill memory is less conscious than fact Skill memory is less conscious than fact memory and involves motor activitymemory and involves motor activity
It is acquired through practiceIt is acquired through practice Skill memories do not retain the context in Skill memories do not retain the context in
which they were learnedwhich they were learned
Structures Involved in Fact Structures Involved in Fact MemoryMemory
Fact memory involves the following brain Fact memory involves the following brain areas:areas: Hippocampus and the amygdala, both limbic Hippocampus and the amygdala, both limbic
system structuressystem structures Specific areas of the thalamus and hypothalamus Specific areas of the thalamus and hypothalamus
of the diencephalonof the diencephalon Ventromedial prefrontal cortex and the basal Ventromedial prefrontal cortex and the basal
forebrainforebrain
Structures Involved in Skill Structures Involved in Skill MemoryMemory
Skill memory involves:Skill memory involves: Corpus striatum – mediates the automatic Corpus striatum – mediates the automatic
connections between a stimulus and a motor connections between a stimulus and a motor responseresponse
Portion of the brain receiving the stimulus Portion of the brain receiving the stimulus Premotor and motor cortexPremotor and motor cortex
Mechanisms of MemoryMechanisms of Memory Neuronal RNA content is alteredNeuronal RNA content is altered Dendritic spines change shapeDendritic spines change shape Extracellular proteins are deposited at synapses Extracellular proteins are deposited at synapses
involved in LTMinvolved in LTM Number and size of presynaptic terminals may Number and size of presynaptic terminals may
increaseincrease More neurotransmitter is released by More neurotransmitter is released by
presynaptic neuronspresynaptic neurons New hippocampal neurons appearNew hippocampal neurons appear
Mechanisms of MemoryMechanisms of Memory
Long-term potentiation (LTP) is involved and Long-term potentiation (LTP) is involved and is mediated by NMDA receptorsis mediated by NMDA receptors
Synaptic events involve the binding of brain-Synaptic events involve the binding of brain-derived neurotropic factor (BDNF)derived neurotropic factor (BDNF)
BDNF is involved with NaBDNF is involved with Na++, Ca, Ca2+2+, and Mg, and Mg2+2+ influence at synapsesinfluence at synapses
Proposed Memory CircuitsProposed Memory Circuits
Figure 12.23
Protection of the BrainProtection of the Brain
The brain is protected by bone, meninges, and The brain is protected by bone, meninges, and cerebrospinal fluidcerebrospinal fluid
Harmful substances are shielded from the Harmful substances are shielded from the brain by the blood-brain barrierbrain by the blood-brain barrier
MeningesMeninges
Three connective tissue membranes lie Three connective tissue membranes lie external to the CNS – dura mater, arachnoid external to the CNS – dura mater, arachnoid mater, and pia matermater, and pia mater
Functions of the meningesFunctions of the meninges Cover and protect the CNSCover and protect the CNS Protect blood vessels and enclose venous sinusesProtect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF)Contain cerebrospinal fluid (CSF) Form partitions within the skullForm partitions within the skull
MeningesMeninges
Figure 12.24a
Dura MaterDura Mater
Leathery, strong meninx composed of two Leathery, strong meninx composed of two fibrous connective tissue layers fibrous connective tissue layers
The two layers separate in certain areas and The two layers separate in certain areas and form dural sinusesform dural sinuses
Dura MaterDura Mater
Three dural septa extend inward and limit Three dural septa extend inward and limit excessive movement of the brainexcessive movement of the brain Falx cerebri – fold that dips into the longitudinal Falx cerebri – fold that dips into the longitudinal
fissurefissure Falx cerebelli – runs along the vermis of the Falx cerebelli – runs along the vermis of the
cerebellumcerebellum Tentorium cerebelli – horizontal dural fold extends Tentorium cerebelli – horizontal dural fold extends
into the transverse fissureinto the transverse fissure
Dura MaterDura Mater
Figure 12.25
Arachnoid MaterArachnoid Mater
The middle meninx, which forms a loose brain The middle meninx, which forms a loose brain coveringcovering
It is separated from the dura mater by the It is separated from the dura mater by the subdural spacesubdural space
Beneath the arachnoid is a wide subarachnoid Beneath the arachnoid is a wide subarachnoid space filled with CSF and large blood vesselsspace filled with CSF and large blood vessels
Arachnoid villi protrude superiorly and permit Arachnoid villi protrude superiorly and permit CSF to be absorbed into venous bloodCSF to be absorbed into venous blood
Arachnoid MaterArachnoid Mater
Figure 12.24a
Pia MaterPia Mater
Deep meninx composed of delicate connective Deep meninx composed of delicate connective tissue that clings tightly to the braintissue that clings tightly to the brain
Cerebrospinal Fluid (CSF)Cerebrospinal Fluid (CSF)
Watery solution similar in composition to Watery solution similar in composition to blood plasmablood plasma
Contains less protein and different ion Contains less protein and different ion concentrations than plasmaconcentrations than plasma
Forms a liquid cushion that gives buoyancy to Forms a liquid cushion that gives buoyancy to the CNS organsthe CNS organs
Cerebrospinal Fluid (CSF)Cerebrospinal Fluid (CSF)
Prevents the brain from crushing under its own Prevents the brain from crushing under its own weightweight
Protects the CNS from blows and other traumaProtects the CNS from blows and other trauma Nourishes the brain and carries chemical Nourishes the brain and carries chemical
signals throughout itsignals throughout it
Circulation of CSFCirculation of CSF
Figure 12.26b
Choroid PlexusesChoroid Plexuses
Clusters of capillaries that form tissue fluid Clusters of capillaries that form tissue fluid filters, which hang from the roof of each filters, which hang from the roof of each ventricleventricle
Have ion pumps that allow them to alter ion Have ion pumps that allow them to alter ion concentrations of the CSFconcentrations of the CSF
Help cleanse CSF by removing wastesHelp cleanse CSF by removing wastes
Choroid PlexusesChoroid Plexuses
Figure 12.26a
Blood-Brain BarrierBlood-Brain Barrier
Protective mechanism that helps maintain a Protective mechanism that helps maintain a stable environment for the brainstable environment for the brain
Bloodborne substances are separated from Bloodborne substances are separated from neurons by:neurons by: Continuous endothelium of capillary wallsContinuous endothelium of capillary walls Relatively thick basal laminaRelatively thick basal lamina Bulbous feet of astrocytesBulbous feet of astrocytes
Blood-Brain Barrier: FunctionsBlood-Brain Barrier: Functions
Selective barrier that allows nutrients to pass Selective barrier that allows nutrients to pass freelyfreely
Is ineffective against substances that can diffuse Is ineffective against substances that can diffuse through plasma membranesthrough plasma membranes
Absent in some areas (vomiting center and the Absent in some areas (vomiting center and the hypothalamus), allowing these areas to monitor hypothalamus), allowing these areas to monitor the chemical composition of the bloodthe chemical composition of the blood
Stress increases the ability of chemicals to pass Stress increases the ability of chemicals to pass through the blood-brain barrierthrough the blood-brain barrier
Cerebrovascular Accidents (Strokes)Cerebrovascular Accidents (Strokes)
Caused when blood circulation to the brain is Caused when blood circulation to the brain is blocked and brain tissue diesblocked and brain tissue dies
Most commonly caused by blockage of a Most commonly caused by blockage of a cerebral arterycerebral artery
Other causes include compression of the brain Other causes include compression of the brain by hemorrhage or edema, and atherosclerosisby hemorrhage or edema, and atherosclerosis
Transient ischemic attacks (TIAs) – temporary Transient ischemic attacks (TIAs) – temporary episodes of reversible cerebral ischemiaepisodes of reversible cerebral ischemia
Tissue plasminogen activator (TPA) is the only Tissue plasminogen activator (TPA) is the only approved treatment for strokeapproved treatment for stroke
Degenerative Brain DisordersDegenerative Brain Disorders
Alzheimer’s disease – a progressive degenerative Alzheimer’s disease – a progressive degenerative disease of the brain that results in dementiadisease of the brain that results in dementia
Parkinson’s disease – degeneration of the Parkinson’s disease – degeneration of the dopamine-releasing neurons of the substantia dopamine-releasing neurons of the substantia nigranigra
Huntington’s disease – a fatal hereditary disorder Huntington’s disease – a fatal hereditary disorder caused by accumulation of the protein huntingtin caused by accumulation of the protein huntingtin that leads to degeneration of the basal nucleithat leads to degeneration of the basal nuclei
Embryonic Development of the Embryonic Development of the Spinal CordSpinal Cord
Develops from caudal portion of neural tubeDevelops from caudal portion of neural tube By week 6, there are two clusters of By week 6, there are two clusters of
neuroblasts:neuroblasts: Alar plate – will become interneuronsAlar plate – will become interneurons Basal plate – will become motor neuronsBasal plate – will become motor neurons
Neural crest cells form the dorsal root gangliaNeural crest cells form the dorsal root ganglia
Embryonic Development of the Embryonic Development of the Spinal CordSpinal Cord
Figure 12.28