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The Brain and Cranial Nerves
The Brain
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(1)
Made up of a trillion cells (neurons)
Weighs about 3 pounds
Has four principle parts
Brain stem – medulla oblongata, pons, and
midbrain
(2) Diencephalon – thalamus and hypothalamus
(3) Cerebrum – largest part of the brain
(4) Cerebellum
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Meninges
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Protective coverings of the central
nervous system. There are three layers:
(1) Dura mater – tough and fibrous
(2) Arachnoid – looks like a spider’s web
(3) Pia mater – gentle inner layer that
adheres directly to the brain and spinal
cord
Cerebrospinal Fluid (CSF)
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Production and distribution (see next slide)
(1) Secreted by the choroid plexus of the Lateral
Ventricles
(2) Passes through the interventricular foramen into the
third ventricle
(3) The choroid plexus of the third ventricle adds more
CSF
(4) The CSF then passes through the cerebral aqueduct
into the fourth ventricle
(5) The choroid plexus of the fourth ventricle adds more
CSF
(6) The CSF passes through lateral and medial apertures
into the subarachnoid space and central canal of the
spinal cord
(7) The CSF is reabsorbed into veins through the
arachnoid villi
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Composition of CSF
• Totals about 3 to 5 fluid ounces
• Clear and colorless – contains, proteins,
glucose, urea, salts, and lymph fluid
• Consistency of water
• Serves as a shock absorber
• Delivers nutritive substances
• Removes wastes and toxic substances
Blood Supply to the Brain
• Brain needs a lot of oxygen and nutrients
• Brain is only 2% of the body weight but uses
20% of the oxygen
• Blood flow to the brain is effected by
concentrations of carbon dioxide and oxygen in
the blood
• An increase in CO2 = increase in H+
• An increase in H+ causes the arteries to the
brain to vasodilate and increase the blood flow
to ensure an adequate supply of oxygen and
nutrients
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Brain Stem
• Is composed of three parts
(1) Medulla oblongata
(2) Pons
(3) Midbrain
Medulla Oblongata
• Continuation of the upper portion of the spinal
cord
• Contains ascending and descending tracts
running between brain and spinal cord and the
decussation of pyramids
• Contains two vital reflex centers:
(1) Cardiovascular center – regulates heart
rate and force of contraction
(2) Respiratory center – regulates the basic
rhythm of breathing
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The Pons
• Means bridge – connects the medulla and
spinal cord with the cerebrum
• Connects with the cerebellum
• Contains two vital centers:
(1) Pneumotaxic center
(2) Apneustic area
Together these area define the limit of
respiration
The Midbrain
• The cerebral aqueduct runs through the
middle
• Contains the Corpora Quadrigemina
which in turn is composed of:
Superior colliculi vision reflex center
Inferior colliculi auditory reflex center
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The Reticular Formation
• Runs through medulla, pons and midbrain
• Functions include:
(1) Aids in regulating muscle tone
(2) Tells the cerebral cortex that sensory
information is coming in from the spinal
cord
(3) The reticular activating system
maintains consciousness, arousal from
sleep
The Diencephalon
• Has two principle parts:
(1) Thalamus
(2) Hypothalamus
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The Thalamus
• Forms the lateral walls of the third
ventricle
• Is the interpretive center for sensory
impulses like
- pain
- temperature
- light touch
- pressure
The Hypothalamus
• Is a collection of nuclei, each with a specific
function
• Forms the floor of the third ventricle
• Receives information from peripheral nerve
related to sound, taste, smell, somatic receptors
• Receives information from visceral receptors
related to blood pressure, and other
physiological factors important to body function
• Monitors the body’s water concentration,
hormone concentration, body temperature, and
release of hormones from the pituitary gland.
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Functions of the Hypothalamus
• Controls and regulates the Autonomic Nervous System
• Reception and integration of sensory input from the
viscera (internal organs)
• Intermediate between endocrine and nervous system
• Center for mind over body phenomenon
• Rage and aggression
• Controls normal body temperature
• Hunger and satiety center
• Thirst center
• Waking and sleeping states
• Controls biological rhythms
The Cerebrum
• The surface of the cerebrum is composed
of gray matter and is known as the
cerebral cortex
• The center of the cerebrum contains white
matter
• The cortex is highly folded with:
- gyri the folds or bumps
- Sulci the shallow grooves between the
gyri
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Fissures
• Are deep sulci and include:
Longitudinal fissure separates the
cerebral hemispheres
Lateral fissure separates frontal lobe
from temporal lobe
Transverse fissure separates the
cerebrum from the cerebellum
Central sulcus separates the frontal
lobe from the parietal lobe
White Matter of the Brain
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White matter is composed of myelinated
fibers running in three directions
(1) Association fibers run between gyri of the
same hemisphere
(2) Commissural fibers run between gyri of
one hemisphere to the same gyri on the
opposite hemisphere
(3) Projection fibers run between the
cerebrum and the spinal cord
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The Limbic System
• Is a collection of areas of gray matter
inside the white matter of the inner brain
• Functions:
- emotional aspects of behavior related to
survival
- memory
- pleasure and pain
- rage
Limbic System Illustration
Functional Areas of the Brain
• The cerebral cortex is divided into:
- sensory areas
- motor areas
- association areas
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Sensory Areas
Primary Somesthetic Area (general sensory)
Receives input from cutaneous,
muscular and visceral receptors from the
entire body via the thalamus
Sensory Areas
Somesthetic Association Area
Receives input from the thalamus and
Primary Somesthetic Areas
Integrates and interprets sensations
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Sensory Areas
Visual Association Area
Receives input from the input from the
retina of the eye
Interprets shape, color, and movement
Sensory Areas
Visual Association Area
Receives input from the Primary Visual
Area
Relates past to present visual
experiences
Sensory Areas
Primary Auditory Area
Receives input from cochlea of ear
Interprets basic character of sound
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Sensory Areas
Auditory Association Area
Receives input from Primary Auditory
Area
Determines if sound is music, speech,
or noise
Relates sounds to previous experience
Sensory Areas
Gnostic Area
Receive information from Auditory
Association Area
Interprets speech
Sensory Areas
Primary Gustatory Area
Receives input from taste buds
Interprets sensations related to taste
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Sensory Areas
Primary Olfactory Area
Receives input from taste buds
Interprets sensations related to smell
Motor Areas
Primary Motor Area
Controls specific muscles or groups of
muscles
Motor Areas
Frontal Eyefield Area
Voluntary scanning movement of the
eyes
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Motor Areas
Language Area
Translate thought into speech
Also called Broca’s Area or Motor
speech area
The Postcentral Gyrus
• The gyrus directly behind the Central
Sulcus is the Primary Somesthetic Area
• Sensory information from the entire body
comes into this gyrus
• The fraction of this gyrus that functions for
any particular area of the body is an
indication of how important that region is
to sensory input
The Somatosensory Cortex
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The Precentral Gyrus
• The gyrus directly in front of the Central
Sulcus is the Primary Motor Area
• Motor information for the entire body
comes from this area
• The fraction of the gyrus that functions for
any particular area of the body is an
indication of how important that region is
for movement
The Motor Cortex
Electroencephalogram (EEG)
• Millions of action potentials are occurring
in the brain at any moment
• The electrical activity they generate
produce wave forms that we can interpret
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Types of Brain Waves
(1) Alpha waves are present in normal individuals
when their eyes are closed, but are not present
when asleep
(2) Beta waves are present in individuals
experiencing sensory input and an active mind
(3) Theta waves are present in children and
adults in emotional stress
(4) Delta waves are present during deep sleep
Brain Wave Illustration
Brain Lateralization (Split-brain
concept)
• Cerebral Hemispheres are not exactly
alike structurally or functionally
• Some people are more right-brained and
some people are more left-brained
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Left Hemisphere
• People who primarily use the left
hemisphere of their brains tend to:
- right-hand control
- spoken and written language
- numerical and scientific skills
- ability to use and understand sign
language
- reasoning
Right Hemisphere
• People who primarily use the right
hemisphere of their brains tend to:
- Left hand control
- musical and artistic awareness
- space and pattern perception
- insight and imagination
- generating mental images of sight,
sound, touch, taste, and smell in order to
compare relationships
Cerebellum
• Motor area of the brain
• Controls coordinating subconscious movements
of skeletal muscle
• Receives input from:
- muscles, tendons and joints
- Equilibrium receptors in the ear
- visual receptors in the eye
Predicts the future position of a body part
Plays a role in emotional development
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Illustration of the Cerebellum
Cranial Nerves
• There are twelve pairs of cranial nerves
• They originate on the brain and exit
through holes (foramina) in the skull
• Some carry only sensory information
• Some carry both sensory and motor
information
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