Download THE BRAIN

THE BRAIN
Chapter 14
Brain Basics:
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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
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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
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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
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*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
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-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
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-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
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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
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-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
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-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:
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(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
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Parkinson’s Disease
 Etiology: idiopathic (most do not know), head
trauma, MDMA
 Cells of sustantia nigra no longer make dopamine
 Symptoms
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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
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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
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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:
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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
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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……
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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
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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
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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 –
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-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
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-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
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-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
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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
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*contain amyloid deposits
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*kill neurons where they are deposited
 -neurobrillary tangles
Treatment:
Ach precursors
AchE inhibitors
other
Dementia
generalized term for senility
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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