1. 12
The Central Nervous System:
Part C
Functional Brain Systems
• Networks of neurons that work together and span wide areas of
the brain
• Limbic system
• Reticular formation
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
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
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
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

2. • Has far-flung axonal connections with hypothalamus, thalamus,
cerebral cortex, cerebellum, and spinal cord
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)
Reticular Formation: RAS and Motor Function
• Motor function
• Helps control coarse limb movements
• Reticular autonomic centers regulate visceral motor functions
• Vasomotor
• Cardiac
• Respiratory centers
Electroencephalogram (EEG)
• Records electrical activity that accompanies brain function
• Measures electrical potential differences between various
cortical areas
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)
Types of Brain Waves
• Alpha waves (8–13 Hz)—regular and rhythmic, low-amplitude,
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

3. 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
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
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
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
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
Consciousness
• Clinically defined on a continuum that grades behavior in
response to stimuli
• Alertness

4. • Drowsiness (lethargy)
• Stupor
• Coma
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)
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
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
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
Sleep Disorders
• Narcolepsy
• Lapsing abruptly into sleep from the awake state
• Insomnia

5. • Chronic inability to obtain the amount or quality of sleep needed
• Sleep apnea
• Temporary cessation of breathing during sleep
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
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
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
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
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

6. emotional memory
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
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
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
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
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)
Protection of the Brain

7. • Bone (skull)
• Membranes (meninges)
• Watery cushion (cerebrospinal fluid)
• Blood-brain barrier
Meninges
• Cover and protect the CNS
• Protect blood vessels and enclose venous sinuses
• Contain cerebrospinal fluid (CSF)
• Form partitions in the skull
Meninges
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater
Dura Mater
• Strongest meninx
• Two layers of fibrous connective tissue (around the brain)
separate to form dural sinuses
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
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
Pia Mater
• Layer of delicate vascularized connective tissue that clings
tightly to the brain

8. Cerebrospinal Fluid (CSF)
• Composition
• Watery solution
• Less protein and different ion concentrations than plasma
• Constant volume
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
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
Blood-Brain Barrier
• Helps maintain a stable environment for the brain
• Separates neurons from some bloodborne substances
Blood-Brain Barrier
• Composition
• Continuous endothelium of capillary walls
• Basal lamina
• Feet of astrocytes
• Provide signal to endothelium for the formation of tight
junctions
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

9. 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
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
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 dopamine-releasing 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