Transcript The Central Nervous System

The Central Nervous
System
The Brain
The Brain looks pinkish grey, is wrinkly
like a walnut, and has the consistency of
oatmeal.
 It weighs on average 3.5 lbs for men and
3.2 pounds for women.
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Embryonic Development
At three weeks old, the outer layer of the
“brain” thickens and forms a line that runs
down the center called a neural plate.
 That plate invaginates to form a neural
fold. (That big line that runs down the
center of the brain).
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As the Neural groove deepens…
The superior edges of
the neural grooves
fuse and drop forming
a neural tube.
 This neural tube
deepens and extends
forming the caudal
(tail) end of the brain
forming what will
later be defined as
the spinal cord.
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In week five of
development, the
Primary vesicles of
the brain give rise to
secondary vesicles,
which will later form
the major regions of
the brain.
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Secondary structure
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Forms:
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Telencephalon 
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Diencephalon 
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Two cerebral
hemispheres of brain
Hypothalamus, thalamus,
epithalamus, and retina
of the eye
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Mesencephalon, 
metencephalon,
Myencephalon.
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Midbrain, pons and
cerebellum, and medulla
oblongata
Cerebral Hemispheres
Cerebral Hemispheres
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The most superior part of the brain,
makes up 83% of the brains body weight.
The elevated ridges of the cerebral
hemispheres are called gyri. They are
separated by grooves called sulci.
 The deeper grooves are called fissures.
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Regions of the brain
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Lobes:
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Frontal
Parietal
Occipital
Temporal
Cerebellum
Pons
 Medulla oblongata
 Brain stem
 Olfactoral stem
 Olfactoral tract
 Hypocampus
 hypothallumus
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Gyri and sulci
Precentral gyrus
 Postcentral gyrus
 Central sulcus
 Parieto-occipital sulcus
 Gyri of insula (medial to temporal lobe)
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Fissures
Longitudinal fissure
 Transverse cerebral fissure
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Thing to keep in “mind” about the
cerebral cortex.
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No one area of the cerebral cortex acts
alone, and all conscious behavior involves
every area of the cerebral cortex in some
way.
The cerebral cortex
Contains three function areas, motor
areas, sensory areas, and association
areas.
 Each hemisphere of the cerebral cortex is
contralaterally concerned with the senses
of the opposite side of the body.
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The cerebral cortex: motor areas
Primary motor cortex: contains a type of nerve
cell called pyramidal cells that allow us to
consciously control precise voluntary movement.
 These pyramidal cells serve for function of only
one area.
 For example, there are pyramidal cells that are
specifically for foot movement, while there are
other pyramidal cells that are designed for hand
movement.
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Stroke
Stroke is a very serious problem that
develops when there is an interruption in
the flow of blood to the brain. Also known
as cerebrovascular accidents or "brain
attacks."
 There are two main types of strokes.
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 If
a blood vessel is blocked by clots or other
particles, it is called an ischemic stroke.
 If a blood vessel breaks and bleeds, it is
called a hemorrhagic stroke.
Signs of a stroke
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Symptoms of stroke:
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Sudden weakness or numbness in your face, body,
arms or legs, especially if only one side is affected
Sudden loss of vision or problems seeing in one or
both eyes
Sudden confusion, inability to speak or understand
what others are saying
Sudden dizziness, instability or inability to stand, walk
or coordinate movement
Sudden severe, unexplained headache
Commonality of stroke
Stroke is the third leading cause of death,
after coronary heart disease and cancer.
 Each year there are about 600,000 strokes
in the US, and strokes kill over 150,000
Americans each year.
 Over 15% of people who have had a
stroke die within 30 days, and 15-30% of
people who survive a stroke are
permanently disabled.
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Who’s at risk
Anyone can have a stroke but most people
who have strokes are over the age of 55.
Strokes affect both men and women.
 African Americans tend to be at highest
risk, but people of all races and ethnicities
suffer from strokes.
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How to prevent stroke
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There are many things you can do to reduce
your risk of stroke:
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don't smoke
keep your blood pressure under control
stay physically active
if you have diabetes, treat it
eat a healthy diet that focuses on fruits, vegetables,
and whole grains
maintain a healthy weight
keep your blood cholesterol under control
avoid illegal drug use
Who should be screened?
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People of all ages should be periodically
screened for risk factors of stroke:
 diabetes
 high
blood pressure
 poor blood cholesterol levels
 overweight/obesity
motor areas continued
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Premotor cortex- In the frontal lobe of the
brain, just anterior of the precentral gyrus.
Responsible for learned motor skills and
repetitious and patterned nature.
motor areas continued
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Broca’s area- inferior to the anterior
region of the premotor area. Present only
on left side of the brain, directs muscles
involved in speech production.
motor areas continued
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Frontal eye field- superior to Broca’s area.
Controls voluntary movements of the eyes.
Sensory areas
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Sensory areas allow
for the conscious
awareness of
sensation. Mostly in
the parietal temporal
and occipital lobes.
Sensory areas continued
Primary somatosensory cortex- posterior
to the postcentral gyrus. Receives
information from skin, muscles and
tendons when stimulus is applied.
 It is not the size of the body part, but the
number of sensors in that region that
determines sensitivity. The face and
fingertips are the most sensitive areas.
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Sensory areas continued
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Somatosensory association cortexposterior to primary somatosensory
cortex. Integrates sensory inputs like
temperature, pressure, etc. from past
experience to judge a stimulus without the
use of another sense like sight.
Sensory areas continued
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Visual area- extreme posterior of occipital
lobe. It creates a contralateral map of
visual space.
Auditory areas
Primary auditory cortex: located in
superior portion of the temporal lobe.
Involved in interpreting pitch, loudness,
and sound.
 Auditory association area: Posterior to the
primary motor cortex. It interprets and
perceives a sound stimulus.
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Olfactory cortex:
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Medial area of temporal lobe. Used to
interpret impulses from smell receptors in
the nasal cavity.
Gustatory cortex
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Gustatory (taste) cortex: Located deep in
the temporal lobe. It’s involved in the
perception of tastes.
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EWW That tastes disgusting!
Visceral Sensory areas
Just posterior to the gustatory complex,
the visceral sensory area is responsible for
the perception of visceral sensation.
 (i.e. full bladder, upset stomach, feeling
like your lungs will explode if you hold
your breath too long.)
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Vestibular cortex
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Responsible for the conscious awareness
of balance.
Multimodal association areas
Multimodal association areas
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Multimodal association areas are
responsible for collecting a large amount
of information and processing it on
multiple levels.
Multimodal association areas:
prefrontal cortex
Encompasses most of the cerebrum.
 Is involved in the process of memory
formation, intellect, complex learning
abilities, recall, and personality.
 The ability of the prefrontal cortex varies
greatly from the use of positive and
negative feedback.
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Multimodal association areas:
Posterior association areas
Encompasses the parietal, temporal and
occipital lobes.
 Allows one to pay attention to the space
around them, also plays a role in written
and spoken language.
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Multimodal association areas:
Limbic association areas
Cingulate gyrus, parahippocampal gyrus,
and the hippocampus.
 Provides the emotional impact of a scene,
which allows for the proper response to a
stimulus.
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Cerebral White Matter
Responsible for communication between
hemispheres of the brain.
 Commissures (made of commissural
fibers) connect the grey areas of the
hemispheres. The largest fissure is called
the corpus callosum.
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Cerebral White Matter continued
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Association fibers- connects different parts
of the same hemisphere.
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Projection fibers- motor output from the
cerebral cortex to the rest of the body.
Projection fibers run vertically in the brain,
while association fibers and commissure
fibers run horizontally.
Basal Nuclei
Receives input from the entire cerebral
cortex as well as from other subcortical
nuclei and each other.
 The true function of the Basal nuclei is
unclear due to many parts of the cerebral
cortex having overlapping functions.
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Diencephalon
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Contains the:
 Thalamus
 Hypothalamus
 epithalamus.
Diencephalon: Thalamus
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The thalamus contains a pair of egg
shaped nuclei. The thalamus acts as the
relay station for all information that enters
the cerebral cortex.
Diencephalon: hypothalamus
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Hypothalamus (below the thalamus) is the main
visceral control center of the brain and is in
charge of homeostasis in the body.
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It is responsible for:
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autonomic control
emotional response
body temperature regulation
Regulation of food intake
regulation of water balance and thirst
regulation of sleep/wake cycle
control of endocrine system functions
Diencephalon: epithalamus
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Contains the pineal gland, which secretes
melatonin. This is a major part of the
sleep/wake cycle.
Brain stem
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Contains the:
 pons
 midbrain
 medulla
oblongata
Brain stem: midbrain
b/w the diencephalon and the pons.
Contains the:
 corpora quadragemina: forms four bumps
on the mid brain which themselves hold:
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 superior
colliculi-visual reflex center
 inferior colliculi-Allows for the reflex response
to sound.
Brain stem: Pons
Wedged between the midbrain and the
medulla oblongata. Composed mostly of
conduction tracts.
 The pons relays signals from the forebrain
to the cerebellum, along with nuclei that
deal primarily with sleep, respiration,
swallowing, bladder control, hearing,
equilibrium, taste, eye movement, facial
expressions, facial sensation, and posture.
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Brain stem: medulla oblongata
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Most inferior part of the brain stem.
The medulla oblongata controls autonomic functions,
and relays nerve signals between the brain and spinal
cord. It is also responsible for controlling several major
points and autonomic functions of the body:
 respiration– chemoreceptors
 cardiac center – sympathetic, parasympathetic
system
 vasomotor center – baroreceptors
 reflex centers of vomiting, coughing, sneezing, and
swallowing
The Cerebellum
The cerebellum
Located posteriorly, and is inferior to the
occipital lobe of the cerebrum. Has two
cerebellar hemispheres .
 Special purkinji cells are located in the
cerebellum, which send signals through
the white matter to synapse the central
nuclei of the cerebellum.
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Cerebellar processing
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The cerebellum processes information in
the following way:
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motor areas of the cerebral cortex notify
the cerebellum that it will trigger a voluntary
muscle movement.
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At the same time, the cerebellum receives
information from the body (muscle tension,
tendons, etc…). This allows the cerebellum to
evaluate body position and momentum.
 3. Cerebellar cortex calculates the best way to
handle force, direction, and extent of muscle
contraction to prevent overshoot, maintain
posture, and ensure smooth coordinated
movements.
 4. Then the cerebellum dispatches it’s
information for coordinated movement.
The cerebellum’s role in
cognition
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The cerebellum is responsible for
recognizes and predicts sequences of
events so that it can adjust for the
multiple movements exerted on a limb
involving several joints.
Functional Brain Systems
A function brain system is a system that
spans far distances in the brain but still
works closely together.
 Examples:
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 Limbic
system
 Reticular formation
The Limbic system
A group of structures located in the medial
aspect of the cerebral hemisphere and
diencephalon.
 This system is the main emotional, or
affective area of the brain.
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The Limbic System
The reticular formation
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Extends through the central core of the
medulla oblongata, pons, and midbrain.
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maintains tone, balance, and posture-especially during body movements.
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Acts as a filter for the massive amounts of
information from sensory input.
Higher Mental Functions
Higher mental functions
Brain wave patterns and EEG: The EEG is
a tool that records aspects of brain
activity.
 These activities are electrically recorded as
brain waves.
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Wave Types
Alpha Waves: regular, rhythmic and low
amplitude. Indicator of calm and awake brain.
 Beta waves: rhythmic but not as regular as
alpha waves. Occurs when focusing on a
problem or stimulus.
 Theta waves: less common than beta waves.
Uncommon in awake adults, but may appear
when concentrating.
 Delta waves: seen during sleep. In an awake
adult, this indicates brain damage.
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Brain Waves
What does it mean to be
clinically conscious?
These criteria are the suppositions about being
conscious:
 Consciousness involves stimulus of large areas
of the brain.
 It is superimposed on other types of neural
activity (like cognition and motor control).
 It is holistic and totally interconnected.
Information about thought can be collected by
different areas of the brain simultaneously.
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Sleep and Sleep-wake cycles
NREM sleep- The first two stages of sleep,
where we do not dream. (Takes 30-45
minutes)
 In the 3rd and 4th stages we enter slow
wave sleep where brain wave frequency
slows and wave amplitude increases.
 After stages four of NREM sleep
is achieved, EEG are changed
abruptly. (90 minutes)
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Sleep and Sleep-wake cycles
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REM sleep-After stage four of NREM, the EEG will
change back and forth to all various types of
wavelengths.
Increases, heart rate and breathing rate and other
sympathetic responses. Oxygen rates skyrocket
higher than when awake. A temporary paralysis
occurs in the skeletal muscles.
NOTE that most nightmare occur in NREM sleep
stages three and four.
Also, REM is associated with sexual arousal, thus
“morning wood.”
Language
Broca’s area: the region of the brain
responsible for language and language
interpretation.
 Wernicke’s area: the area responsible for
speech production. Damaging Wernicke’s
area will cause people to speak incoherent
gibberish.
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Memory
Involves the storage and retrieval of
information.
 Short term memory involves the
immediate retrieval of information and
application of that information. Short
term memory lasts for only up to 15
seconds.
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memory
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Long term memory involves the storage of
information for any time after 15 seconds.
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As sensory information bombards the
cerebral cortex, information we do not
even think of consciously is stored in our
minds.
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Emotional state: When norepinephrine is
present in the brain, emotional
information we receive is almost
instantaneous.
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Rehearsal: repeating a process or speech
over and over again. This is why studying
your notes repeatedly helps you do well
on a test.
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Association: Association of new memories
is easier to remember if it can be
associated with old memories.
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Automatic memory: Automatic memory
occurs when you are receiving input and
store other information while receiving
said input.
Categories of memory
Declarative memory: Learning explicit
information like names and faces.
 Procedural memory: (Skill) Learning a
process like playing the piano.
 Motor memory: doing a motor function
like riding a bike.
 Emotional memory: remembering
something that changing your emotional
state.
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Protecting the Brain
The meninges is the covering that protects
the brain. It reduces the damage from
impact and prevents the brain from
rubbing against the skull.
 The meninges formed by three layers:
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 Dura
mater
 Arachnoid mater
 Pia mater
The meninges formed by three
layers
 Dura
mater- Strongest layer; the dura
veinous sinuses are located here, which
drain blood back to the neck.
 Arachnoid mater- separated from the
dura mater by a space called subdural
space. Never enters the sulci of the
brain.
 Pia mater- Clings tightly to the brain like
a cellophane hat.
Cerebrospinal Fluid
Cushion that surrounds the brain and
spinal cord. Looks kind of like blood
plasma.
 About 500 ml of CSF is produced daily.
About 150 ml of CSF is covering the brain
and spine at any one time.
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Blood-Brain Barrier
The blood-brain barrier is the end-all-beall of maintaining homeostasis of the
brain.
 The blood-brain barrier prevents
fluxuations in the brain’s balance of
nutrients and minerals from causing the
neurons of the brain to fire uncontrollably.
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The Spinal Cord
The Spinal Cord
The spinal cord provides a two way
conduction path for information to enter
and leave the brain.
 The spinal cord is the major reflex center
in your body.
 The spinal dura mater is a meningx that
protects the spine from trauma with the
CSF.
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Drawing CSF for testing
The procedure known as a Lumbar
puncture is the process of drawing CSF to
screen for pathogens and drugs.
 Typically done below the L3 vertebrae,
due to there being a low chance of
damaging the spinal cord.
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For the majority of the spinal cord
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It is about the width of your thumb for the
majority of your body with the exception
of the cervical enlargement and the
lumbar enlargement, which are larger
bulbs in the spinal cord that act as nexus’
for spinal nerves.
Ascending pathways to the brain
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First order neurons: cell bodies that lie in a
ganglion (bundle of related sensory neurons)
which conduct impulses from cutaneous layers
of the skin.
 Second order neurons: Reside in dorsal portion
of the spinal cord. They transmit impulses to
the thalamus or to the cerebellum where they
synapse.
 Third order neurons: They relay impulses to the
somatosensory cortex of the cerebrum.
Developmental aspects of the
CNS
During prenatal development, there are
certain areas of the brain that develop
specific to each gender.
 Exposure to drugs and alcohol during
pregnancy can cause mental defects in the
fetus, if not death.
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