The Brain Muse Spring2430 Lecture #10 7/16/12. An Introduction to the Brain and Cranial Nerves The...
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Transcript of The Brain Muse Spring2430 Lecture #10 7/16/12. An Introduction to the Brain and Cranial Nerves The...
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The Brain
Muse Spring2430Lecture #107/16/12
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An Introduction to the Brain and Cranial Nerves
• The Adult Human Brain
– Ranges from 750 cc to 2100 cc
– Contains almost 97% of the body’s neural tissue
– Average weight about 1.4 kg (3 lb)
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The Brain• Six Regions of the Brain– Cerebrum
– Cerebellum
– Diencephalon
– Mesencephalon
– Pons
– Medulla oblongata
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The Brain
Figure 14–1 An Introduction to Brain Structures and Functions.
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Figure 12.6c
Parietallobe
Frontal lobe
Right cerebralhemisphere
Occipitallobe
Left cerebralhemisphere
Cerebral veinsand arteriescovered byarachnoidmater
Longitudinalfissure
Posterior(c)
Anterior
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The Brain
Figure 14–2 Ventricles of the Brain.
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Brain Protection and Support• Cerebrospinal Fluid (CSF)
– Surrounds all exposed surfaces of CNS
– Interchanges with interstitial fluid of brain
– Functions of CSF
• Cushions delicate neural structures
• Supports brain
• Transports nutrients, chemical messengers, and waste
products
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Brain Protection and Support
Figure 14–4 The Formation and Circulation of Cerebrospinal Fluid.
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Figure 12.26b
Ependymalcells
Capillary
Connectivetissue ofpia mater
Wastes andunnecessarysolutes absorbed
Sectionof choroidplexus
(b) CSF formation by choroid plexuses
Cavity ofventricle
CSF forms as a filtratecontaining glucose, oxygen, vitamins, and ions(Na+, Cl–, Mg2+, etc.)
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Brain Protection and Support
• Blood Supply to the Brain
– Supplies nutrients and oxygen to brain
– Delivered by internal carotid arteries and
vertebral arteries
– Removed from dural sinuses by internal jugular
veins
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Brain Protection and Support
Figure 21–23 Arteries of the Brain.
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Brain Protection and Support• Blood–Brain Barrier
– Isolates CNS neural tissue from general circulation
– Formed by network of tight junctions
– Between endothelial cells of CNS capillaries
– Lipid-soluble compounds (O2, CO2), steroids, and
prostaglandins diffuse into interstitial fluid of brain and
spinal cord
– Astrocytes control blood–brain barrier by releasing
chemicals that control permeability of endothelium
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Figure 11.3a
(a) Astrocytes are the most abundantCNS neuroglia.
Capillary
Neuron
Astrocyte
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Brain Protection and Support• Four Breaks in the BBB– Portions of hypothalamus• Secrete hypothalamic hormones
– Posterior lobe of pituitary gland• Secretes hormones ADH and oxytocin
– Pineal glands• Pineal secretions
– Choroid plexus• Where special ependymal cells maintain blood–CSF
barrier
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The Medulla Oblongata• The Medulla Oblongata
– Allows brain and spinal cord to communicate
– Coordinates complex autonomic reflexes
– Controls visceral functions
– Nuclei in the Medulla
• Autonomic nuclei: control visceral activities
• Sensory and motor nuclei: of cranial nerves
• Relay stations: along sensory and motor pathways
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The Medulla Oblongata
Figure 14–5a The Diencephalon and Brain Stem.
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Figure 12.16c
Choroidplexus
Fourth ventricle
PyramidMedial lemniscus
Inferior olivarynucleus
Nucleusambiguus
Inferior cerebellarpeduncle
Cochlearnuclei (VIII)
Vestibular nuclearcomplex (VIII)
Solitarynucleus
Dorsal motor nucleusof vagus (X)
Hypoglossal nucleus (XII)
(c) Medulla oblongata
LateralnucleargroupMedialnucleargroupRaphenucleusRet
icu
lar
form
atio
n
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The Cerebellum
• Functions of the Cerebellum
– Adjusts postural muscles
– Fine-tunes conscious and subconscious
movements
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The Cerebellum• Structures of the Cerebellum
– Purkinje cells
• Large, branched cells
• Found in cerebellar cortex
• Receive input from up to 200,000 synapses
– Arbor vitae
• Highly branched, internal white matter of cerebellum
• Cerebellar nuclei: embedded in arbor vitae:
– relay information to Purkinje cells
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The Cerebellum
Figure 14–7b The Cerebellum.
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Figure 12.17d
(d)
Anteriorlobe
Posteriorlobe
Vermis(d)
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The Cerebellum
• Disorders of the Cerebellum
– Ataxia
• Damage from trauma or stroke
• Intoxication (temporary impairment)
• Disturbs muscle coordination
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The Diencephalon
• Integrates sensory information and motor commands
• Thalamus, epithalamus, and hypothalamus
– The pineal gland
• Found in posterior epithalamus
• Secretes hormone melatonin
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The Diencephalon• The Hypothalamus– Mamillary bodies
• Process olfactory and other sensory information
• Control reflex eating movements
– Infundibulum• A narrow stalk
• Connects hypothalamus to pituitary gland
– Tuberal area• Located between the infundibulum and mamillary bodies
• Helps control pituitary gland function
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The Diencephalon
Figure 14–10a The Hypothalamus in Sagittal Section.
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The Diencephalon
• Eight Functions of the Hypothalamus
– Provides subconscious control of skeletal muscle
– Controls autonomic function
– Coordinates activities of nervous and endocrine systems
– Secretes hormones
• Antidiuretic hormone (ADH) by supraoptic nucleus
• Oxytocin (OT; OXT) by paraventricular nucleus
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The Diencephalon• Eight Functions of the Hypothalamus
– Produces emotions and behavioral drives
• The feeding center (hunger)
• The thirst center (thirst)
– Coordinates voluntary and autonomic functions
– Regulates body temperature
• Preoptic area of hypothalamus
– Controls circadian rhythms (day–night cycles)
• Suprachiasmatic nucleus
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The Limbic System
• The Limbic System
– Is a functional grouping that
• Establishes emotional states
• Links conscious functions of cerebral cortex with autonomic
functions of brain stem
• Facilitates memory storage and retrieval
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The Limbic System
Figure 14–11a The Limbic System.
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The Limbic System• Components of the Limbic System– Amygdaloid body• Acts as interface between the limbic system, the
cerebrum, and various sensory systems
– Limbic lobe of cerebral hemisphere• Cingulate gyrus
• Dentate gyrus
• Parahippocampal gyrus
• Hippocampus
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The Limbic System• Components of the Limbic System– Fornix• Tract of white matter• Connects hippocampus with hypothalamus
– Anterior nucleus of the thalamus• Relays information from mamillary body to cingulate
gyrus
– Reticular formation• Stimulation or inhibition affects emotions (rage, fear,
pain, sexual arousal, pleasure)
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The Limbic System
Figure 14–11b The Limbic System.
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Figure 12.18
Corpus callosum
Septum pellucidum
Olfactory bulb
Diencephalic structuresof the limbic system
•Anterior thalamic nuclei (flanking 3rd ventricle)•Hypothalamus•Mammillary body
Fiber tractsconnecting limbic system structures
•Fornix•Anterior commissure
Cerebral struc-tures of the limbic system
•Cingulate gyrus•Septal nuclei•Amygdala•Hippocampus•Dentate gyrus•Parahippocampal gyrus
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Limbic System
• Emotional or affective brain– Amygdala—recognizes angry or fearful facial
expressions, assesses danger, and elicits the fear response
– Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict
• Puts emotional responses to odors– Example: skunks smell bad
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Limbic System: Emotion and Cognition
• The limbic system interacts with the prefrontal lobes, therefore:– We can react emotionally to things we consciously
understand to be happening– We are consciously aware of emotional richness in
our lives
• Hippocampus and amygdala—play a role in memory
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The limbic system
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The Cerebrum
• The Cerebrum
– Is the largest part of the brain
– Controls all conscious thoughts and intellectual
functions
– Processes somatic sensory and motor information
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The Cerebrum
• Gray matter
– In cerebral cortex and basal nuclei
• White matter
– Deep to basal cortex
– Around basal nuclei
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The Cerebrum
Figure 14–12c The Brain in Lateral View.
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The Cerebrum• Special Sensory Cortexes– Visual cortex • Information from sight receptors
– Auditory cortex • Information from sound receptors
– Olfactory cortex • Information from odor receptors
– Gustatory cortex • Information from taste receptors
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The Cerebrum
Figure 14–15a Motor and Sensory Regions of the Cerebral Cortex.
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The Cerebrum
Figure 14–16 Hemispheric Lateralization.
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The Cerebrum
• Monitoring Brain Activity
– Brain activity is assessed by an
electroencephalogram (EEG)
• Electrodes are placed on the skull
• Patterns of electrical activity (brain waves) are printed
out
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The Cerebrum• Four Categories of Brain Waves– Alpha waves
• Found in healthy, awake adults at rest with eyes closed– Beta waves 12-30 Hz
• Higher frequency• Found in adults concentrating or mentally stressed
– Theta waves• Found in children• Found in intensely frustrated adults• May indicate brain disorder in adults
– Delta waves 1-4 Hz• During sleep• Found in awake adults with brain damage
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The Cerebrum
Figure 14–17a-d Brain Waves.
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Cerebral Cortex
• Thin (2–4 mm) superficial layer of gray matter• 40% of the mass of the brain• Site of conscious mind: awareness, sensory perception,
voluntary motor initiation, communication, memory storage, understanding
• Each hemisphere connects to contralateral side of the body
• There is lateralization of cortical function in the hemispheres
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Functional Areas of the Cerebral Cortex
• The three types of functional areas are:– Motor areas—control voluntary movement– Sensory areas—conscious awareness of sensation– Association areas—integrate diverse information
• Conscious behavior involves the entire cortex
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Motor Areas
• Primary (somatic) motor cortex• Premotor cortex• Broca’s area• Frontal eye field
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Primary Motor Cortex
• Large pyramidal cells of the precentral gyri• Long axons pyramidal (corticospinal) tracts • Allows conscious control of precise, skilled,
voluntary movements• Motor homunculi: upside-down caricatures
representing the motor innervation of body regions
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Figure 12.9
Toes
Swallowing
Tongue
Jaw
Primary motorcortex(precentral gyrus)
MotorMotor map inprecentral gyrus
Posterior
Anterior
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Premotor Cortex
• Anterior to the precentral gyrus• Controls learned, repetitious, or patterned
motor skills• Coordinates simultaneous or sequential
actions • Involved in the planning of movements that
depend on sensory feedback
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Broca’s Area
• Anterior to the inferior region of the premotor area
• Present in one hemisphere (usually the left)• A motor speech area that directs muscles of
the tongue• Is active as one prepares to speak
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Frontal Eye Field
• Anterior to the premotor cortex and superior to Broca’s area
• Controls voluntary eye movements
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Sensory Areas
• Primary somatosensory cortex
• Somatosensory association cortex
• Visual areas• Auditory areas
• Olfactory cortex• Gustatory cortex• Visceral sensory area• Vestibular cortex
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Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
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Primary Somatosensory Cortex
• In the postcentral gyri• Receives sensory information from the skin,
skeletal muscles, and joints• Capable of spatial discrimination:
identification of body region being stimulated
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Figure 12.9
Genitals
Intra-abdominal
Primary somato-sensory cortex(postcentral gyrus)
SensorySensory map inpostcentral gyrus
Posterior
Anterior
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Lateralization of Cortical Function
• Lateralization – Division of labor between hemispheres
• Cerebral dominance– Designates the hemisphere dominant for language
(left hemisphere in 90% of people)
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Lateralization of Cortical Function
• Left hemisphere – Controls language, math, and logic
• Right hemisphere– Insight, visual-spatial skills, intuition, and artistic
skills
• Left and right hemispheres communicate via fiber tracts in the cerebral white matter
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Cerebral White Matter
• Myelinated fibers and their tracts• Responsible for communication – Commissures (in corpus callosum)—connect gray
matter of the two hemispheres – Association fibers—connect different parts of the
same hemisphere– Projection fibers—(corona radiata) connect the
hemispheres with lower brain or spinal cord
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Figure 12.10a
Corona radiata
Projectionfibers
Longitudinal fissure
Gray matter
White matter
Associationfibers
Lateralventricle
Fornix
Thirdventricle
Thalamus
Pons
Medulla oblongataDecussationof pyramids
Commissuralfibers (corpus callosum)
Internalcapsule
Superior
Basal nuclei• Caudate• Putamen• Globuspallidus
(a)
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Figure 12.11b (2 of 2)
Corpus callosumAnterior hornof lateral ventricleCaudate nucleus
Lentiform nucleus
(b)
Thalamus
Third ventricle
Cerebral cortexCerebral white matter
Inferior hornof lateral ventricle
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Consciousness
• Clinically defined on a continuum that grades behavior in response to stimuli– Alertness– Drowsiness (lethargy)– Stupor– Coma
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Consciousness
• Clinically defined on a continuum that grades behavior in response to stimuli– Alertness– Drowsiness (lethargy)– Stupor– Coma
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Figure 12.21b
(b) Typical progression of an adult through onenight’s sleep stages
Awake
REM
Stage 1
Stage 2NonREM Stage 3
Stage 4
Time (hrs)
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Importance of Sleep
• Slow-wave sleep (NREM stages 3 and 4) is presumed to be the restorative stage
• People deprived of REM sleep become moody and depressed
• REM sleep may be a reverse learning process where superfluous information is purged from the brain
• Daily sleep requirements decline with age• Stage 4 sleep declines steadily and may disappear after
age 60
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Sleep Disorders
• Narcolepsy – Lapsing abruptly into sleep from the awake state
• Insomnia – Chronic inability to obtain the amount or quality
of sleep needed
• Sleep apnea – Temporary cessation of breathing during sleep
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Memory
• Storage and retrieval of information• Two stages of storage– Short-term memory (STM, or working memory)—
temporary holding of information; limited to seven or eight pieces of information
– Long-term memory (LTM) has limitless capacity
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Figure 12.22
Outside stimuli
General and special sensory receptors
Data transferinfluenced by:
ExcitementRehearsalAssociation ofold and new data
Long-termmemory(LTM)
Data permanentlylost
Afferent inputs
Retrieval
Forget
Forget
Data selectedfor transfer
Automaticmemory
Data unretrievable
Temporary storage(buffer) in cerebral cortex
Short-termmemory (STM)
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Transfer from STM to LTM
• Factors that affect transfer from STM to LTM– Emotional state—best if alert, motivated,
surprised, and aroused– Rehearsal—repetition and practice – Association—tying new information with old
memories – Automatic memory—subconscious information
stored in LTM
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Categories of Memory
• Declarative memory (factual knowledge) – Explicit information– Related to our conscious thoughts and our
language ability– Stored in LTM with context in which it was
learned
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Categories of Memory
• Nondeclarative memory – Less conscious or unconscious– Acquired through experience and repetition– Best remembered by doing; hard to unlearn– Includes procedural (skills) memory, motor
memory, and emotional memory
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Brain Structures Involved in Declarative Memory
• Hippocampus and surrounding temporal lobes function in consolidation and access to memory
• ACh from basal forebrain is necessary for memory formation and retrieval
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Figure 12.23a
Smell
Basal forebrain
Prefrontal cortex
Taste
Thalamus
Touch
Hearing
Vision
Hippocampus
Thalamus
Prefrontalcortex
Basalforebrain
Associationcortex
Sensoryinput
ACh ACh
Medial temporal lobe(hippocampus, etc.)
(a) Declarativememory circuits
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memory
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Higher-Order Functions
• Amygdaloid body and hippocampus
– Are essential to memory consolidation
– Damage may cause
• Inability to convert short-term memories to new long-
term memories
• Existing long-term memories remain intact and
accessible
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memory
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Brain Structures Involved in Nondeclarative Memory
• Procedural memory– Basal nuclei relay sensory and motor inputs to the
thalamus and premotor cortex– Dopamine from substantia nigra is necessary
• Motor memory—cerebellum• Emotional memory—amygdala
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Figure 12.23b
Dopamine
Thalamus Premotorcortex
Substantianigra
Associationcortex
Basalnuclei
Sensory andmotor inputs
Premotorcortex
ThalamusSubstantia nigra
Basal nuclei
(b) Procedural (skills) memory circuits
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Molecular Basis of Memory
• During learning:– Altered mRNA is synthesized and moved to axons and
dendrites– Dendritic spines change shape– Extracellular proteins are deposited at synapses involved
in LTM– Number and size of presynaptic terminals may increase– More neurotransmitter is released by presynaptic neurons
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Molecular Basis of Memory
• Increase in synaptic strength (long-term potentiation, or LTP) is crucial
• Neurotransmitter (glutamate) binds to NMDA receptors, opening calcium channels in postsynaptic terminal
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Molecular Basis of Memory
• Calcium influx triggers enzymes that modify proteins of the postsynaptic terminal and presynaptic terminal (via release of retrograde messengers)
• Enzymes trigger postsynaptic gene activation for synthesis of synaptic proteins, in presence of CREB (cAMP response-element binding protein) and BDNF (brain-derived neurotrophic factor).
• Combination of potentiation and new synapse formation
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Increase the learning of this chapter!
– Emotional state—best if alert (beta wave), motivated, surprised, and aroused. Chocolate while studying!
– Rehearsal—repetition and practice – Association—tying new information with old
memories. Connect lecture to lab. Draw!!!– Automatic memory—subconscious information
stored in LTM. Test yourself– Get some sleep. Repeat often
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Review Guide for The Final will be posted on Blackboard and on the Website.
Pick up any old exams including you last exam in your lab sections or open labs
Open labs this week 11-1 today 11-1 Thursday