Part c - Hillsborough Community College

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Transcript Part c - Hillsborough Community College

PowerPoint® Lecture Slides
prepared by Vince Austin,
Bluegrass Technical
and Community College
CHAPTER
12
The Central
Nervous
System:
Part C
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Functional Brain Systems
• Networks of neurons that work together and
span wide areas of the brain
• Limbic system
• Reticular formation
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Limbic System
• Structures on the medial aspects of cerebral
hemispheres and diencephalon
• Includes parts of the diencephalon and some
cerebral structures that encircle the brain
stem
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Septum pellucidum
Diencephalic structures
of the limbic system
•Anterior thalamic
nuclei (flanking
3rd ventricle)
•Hypothalamus
•Mammillary
body
Olfactory bulb
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Corpus callosum
Fiber tracts
connecting limbic
system structures
•Fornix
•Anterior commissure
Cerebral structures of the
limbic system
•Cingulate gyrus
•Septal nuclei
•Amygdala
•Hippocampus
•Dentate gyrus
•Parahippocampal
gyrus
Figure 12.18
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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Reticular Formation
• Three broad columns along the length of the
brain stem
• Raphe nuclei
• Medial (large cell) group of nuclei
• Lateral (small cell) group of nuclei
• Has far-flung axonal connections with
hypothalamus, thalamus, cerebral cortex,
cerebellum, and spinal cord
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Reticular Formation: RAS and Motor Function
• RAS (reticular activating system)
• Sends impulses to the cerebral cortex to keep
it conscious and alert
• Filters out repetitive and weak stimuli (~99% of
all stimuli!)
• Severe injury results in permanent
unconsciousness (coma)
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Reticular Formation: RAS and Motor Function
• Motor function
• Helps control coarse limb movements
• Reticular autonomic centers regulate visceral
motor functions
• Vasomotor
• Cardiac
• Respiratory centers
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Radiations
to cerebral
cortex
Visual
impulses
Auditory
impulses
Reticular formation
Ascending general
sensory tracts
(touch, pain, temperature)
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Descending
motor projections
to spinal cord
Figure 12.19
Electroencephalogram (EEG)
• Records electrical activity that accompanies
brain function
• Measures electrical potential differences
between various cortical areas
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(a) Scalp electrodes are used to record brain wave
activity (EEG).
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Figure 12.20a
Brain Waves
• Patterns of neuronal electrical activity
• Generated by synaptic activity in the cortex
• Each person’s brain waves are unique
• Can be grouped into four classes based on
frequency measured as Hertz (Hz)
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Types of Brain Waves
• Alpha waves (8–13 Hz)—regular and rhythmic, lowamplitude, synchronous waves indicating an “idling”
brain
• Beta waves (14–30 Hz)—rhythmic, less regular
waves occurring when mentally alert
• Theta waves (4–7 Hz)—more irregular; common in
children and uncommon in adults
• Delta waves (4 Hz or less)—high-amplitude waves
seen in deep sleep and when reticular activating
system is damped, or during anesthesia; may
indicate brain damage
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1-second interval
Alpha waves—awake but relaxed
Beta waves—awake, alert
Theta waves—common in children
Delta waves—deep sleep
(b) Brain waves shown in EEGs fall into
four general classes.
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Figure 12.20b
Brain Waves: State of the Brain
• Change with age, sensory stimuli, brain
disease, and the chemical state of the body
• EEGs used to diagnose and localize brain
lesions, tumors, infarcts, infections,
abscesses, and epileptic lesions
• A flat EEG (no electrical activity) is clinical
evidence of death
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Epilepsy
• A victim of epilepsy may lose consciousness,
fall stiffly, and have uncontrollable jerking
• Epilepsy is not associated with intellectual
impairments
• Epilepsy occurs in 1% of the population
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Epileptic Seizures
• Absence seizures, or petit mal
• Mild seizures seen in young children where the
expression goes blank
• Tonic-clonic (grand mal) seizures
• Victim loses consciousness, bones are often
broken due to intense contractions, may
experience loss of bowel and bladder control,
and severe biting of the tongue
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Control of Epilepsy
• Anticonvulsive drugs
• Vagus nerve stimulators implanted under the
skin of the chest can keep electrical activity of
the brain from becoming chaotic
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Consciousness
• Conscious perception of sensation
• Voluntary initiation and control of movement
• Capabilities associated with higher mental
processing (memory, logic, judgment, etc.)
• Loss of consciousness (e.g., fainting or
syncopy) is a signal that brain function is
impaired
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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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Sleep
• State of partial unconsciousness from which a
person can be aroused by stimulation
• Two major types of sleep (defined by EEG
patterns)
• Nonrapid eye movement (NREM)
• Rapid eye movement (REM)
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Sleep
• First two stages of NREM occur during the
first 30–45 minutes of sleep
• Fourth stage is achieved in about 90 minutes,
and then REM sleep begins abruptly
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Awake
REM: Skeletal
muscles (except
ocular muscles
and diaphragm)
are actively
inhibited; most
dreaming occurs.
NREM stage 1:
Relaxation begins;
EEG shows alpha
waves, arousal is easy.
NREM stage 2: Irregular
EEG with sleep spindles
(short high- amplitude
bursts); arousal is more
difficult.
NREM stage 3: Sleep
deepens; theta and
delta waves appear;
vital signs decline.
(a) Typical EEG patterns
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NREM stage 4: EEG is
dominated by delta
waves; arousal is difficult;
bed-wetting, night terrors,
and sleepwalking may
occur.
Figure 12.21a
Sleep Patterns
• Alternating cycles of sleep and wakefulness
reflect a natural circadian (24-hour) rhythm
• RAS activity is inhibited during, but RAS also
mediates, dreaming sleep
• The suprachiasmatic and preoptic nuclei of
the hypothalamus time the sleep cycle
• A typical sleep pattern alternates between
REM and NREM sleep
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Awake
REM
Stage 1
Stage 2
Non
REM Stage 3
Stage 4
Time (hrs)
(b) Typical progression of an adult through one
night’s sleep stages
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Figure 12.21b
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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Language
• Language implementation system
• Basal nuclei
• Broca’s area and Wernicke’s area (in the
association cortex on the left side)
• Analyzes incoming word sounds
• Produces outgoing word sounds and grammatical
structures
• Corresponding areas on the right side are
involved with nonverbal language components
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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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Outside stimuli
General and special sensory receptors
Afferent inputs
Temporary storage
(buffer) in
cerebral cortex
Automatic
memory
Data permanently
lost
Data selected
for transfer
Short-term
memory (STM)
Forget
Forget
Data transfer
influenced by:
Retrieval
Excitement
Rehearsal
Association of
old and new data
Long-term
memory
(LTM)
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Data unretrievable
Figure 12.22
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
1. 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
2. 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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Thalamus
Basal forebrain
Touch
Prefrontal cortex
Hearing
Vision
Taste
Smell
Hippocampus
Sensory
input
(a) Declarative
memory circuits
Association
cortex
Thalamus
Medial temporal lobe
(hippocampus, etc.)
Prefrontal
cortex
ACh
ACh
Basal
forebrain
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Figure 12.23a
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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Sensory and
motor inputs
Association
cortex
Basal
nuclei
Thalamus
Dopamine
Premotor
cortex
Premotor
cortex
Substantia
nigra
Thalamus
Basal nuclei
Substantia nigra
(b) Procedural (skills) memory circuits
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Figure 12.23b
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)
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Protection of the Brain
• Bone (skull)
• Membranes (meninges)
• Watery cushion (cerebrospinal fluid)
• Blood-brain barrier
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Meninges
• Cover and protect the CNS
• Protect blood vessels and enclose venous
sinuses
• Contain cerebrospinal fluid (CSF)
• Form partitions in the skull
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Meninges
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater
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Superior
sagittal sinus
Subdural
space
Subarachnoid
space
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Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
Dura Mater
• Strongest meninx
• Two layers of fibrous connective tissue
(around the brain) separate to form dural
sinuses
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Dura Mater
• Dural septa limit excessive movement of the
brain
• Falx cerebri—in the longitudinal fissure;
attached to crista galli
• Falx cerebelli—along the vermis of the
cerebellum
• Tentorium cerebelli—horizontal dural fold over
cerebellum and in the transverse fissure
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Superior
sagittal sinus
Straight
sinus
Crista galli
of the
ethmoid
bone
Pituitary
gland
Falx cerebri
Tentorium
cerebelli
Falx
cerebelli
(a) Dural septa
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Figure 12.25a
Arachnoid Mater
• Middle layer with weblike extensions
• Separated from the dura mater by the
subdural space
• Subarachnoid space contains CSF and blood
vessels
• Arachnoid villi protrude into the superior
sagittal sinus and permit CSF reabsorption
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Superior
sagittal sinus
Subdural
space
Subarachnoid
space
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Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
Pia Mater
• Layer of delicate vascularized connective
tissue that clings tightly to the brain
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Cerebrospinal Fluid (CSF)
• Composition
• Watery solution
• Less protein and different ion concentrations
than plasma
• Constant volume
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Cerebrospinal Fluid (CSF)
• Functions
• Gives buoyancy to the CNS organs
• Protects the CNS from blows and other trauma
• Nourishes the brain and carries chemical
signals
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Superior
sagittal sinus
4
Choroid
plexus
Arachnoid villus
Interventricular
foramen
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
1
Right lateral ventricle
(deep to cut)
Choroid plexus
of fourth ventricle
3
Third ventricle
1 CSF is produced by the
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
(a) CSF circulation
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2
choroid plexus of each
ventricle.
2 CSF flows through the
ventricles and into the
subarachnoid space via the
median and lateral apertures.
Some CSF flows through the
central canal of the spinal cord.
3 CSF flows through the
subarachnoid space.
4 CSF is absorbed into the dural venous
sinuses via the arachnoid villi.
Figure 12.26a
Choroid Plexuses
• Produce CSF at a constant rate
• Hang from the roof of each ventricle
• Clusters of capillaries enclosed by pia mater
and a layer of ependymal cells
• Ependymal cells use ion pumps to control the
composition of the CSF and help cleanse CSF
by removing wastes
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Ependymal
cells
Capillary
Section
of choroid
plexus
Connective
tissue of
pia mater
Wastes and
unnecessary
solutes absorbed
CSF forms as a filtrate
containing glucose, oxygen,
vitamins, and ions
(Na+, Cl–, Mg2+, etc.)
(b) CSF formation by choroid plexuses
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Cavity of
ventricle
Figure 12.26b
Blood-Brain Barrier
• Helps maintain a stable environment for the
brain
• Separates neurons from some bloodborne
substances
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Blood-Brain Barrier
• Composition
• Continuous endothelium of capillary walls
• Basal lamina
• Feet of astrocytes
• Provide signal to endothelium for the
formation of tight junctions
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Capillary
Neuron
Astrocyte
(a) Astrocytes are the most abundant
CNS neuroglia.
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Figure 11.3a
Blood-Brain Barrier: Functions
• Selective barrier
• Allows nutrients to move by facilitated diffusion
• Allows any fat-soluble substances to pass,
including alcohol, nicotine, and anesthetics
• Absent in some areas, e.g., vomiting center
and the hypothalamus, where it is necessary
to monitor the chemical composition of the
blood
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Homeostatic Imbalances of the Brain
• Traumatic brain injuries
• Concussion—temporary alteration in function
• Contusion—permanent damage
• Subdural or subarachnoid hemorrhage—may
force brain stem through the foramen
magnum, resulting in death
• Cerebral edema—swelling of the brain
associated with traumatic head injury
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Homeostatic Imbalances of the Brain
• Cerebrovascular accidents (CVAs)(strokes)
• Blood circulation is blocked and brain tissue dies, e.g.,
blockage of a cerebral artery by a blood clot
• Typically leads to hemiplegia, or sensory and speed
deficits
• Transient ischemic attacks (TIAs)—temporary
episodes of reversible cerebral ischemia
• Tissue plasminogen activator (TPA) is the only
approved treatment for stroke
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Homeostatic Imbalances of the Brain
• Degenerative brain disorders
• Alzheimer’s disease (AD): a progressive degenerative
disease of the brain that results in dementia
• Parkinson’s disease: degeneration of the dopaminereleasing neurons of the substantia nigra
• Huntington’s disease: a fatal hereditary disorder
caused by accumulation of the protein huntingtin that
leads to degeneration of the basal nuclei and cerebral
cortex
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