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Brain and Cranial Nerves
Brain
Consists of the brain
stem, diencephalon,
cerebrum and
cerebellum.
Brain Stem
Located just superior to
the spinal cord, at the
foramen magnum.
Consists of…
Medulla oblongata
Pons
Midbrain
Brain
Diencephalon
Sup and lat to the brain stem.
Consists of …
Thalamus
Most sup and lateral to the midline
Hypothalamus
Inf and medial to the thalamus
Cerebrum
The largest part of the brain; cognitive functions and
memory reside here.
Cerebellum
Post and inf to the cerebrum; fine motor control and
coordination
Coverings
Cranial meninges
Similar to the spinal meningies
Dura mater
The cranial version has two layers
Outer- periosteal layer
…adheres to the cranium
Inner- meningeal layer
…sits next to the subdural space
and the arachnoid.
Between the two layers is a dural
sinus which contains venous blood.
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Coverings
Arachnoid
Pia mater
These layers are similar to their
spinal version
Cerebrospinal fluid
CSF; fills spaces in the brain called
ventricles. Makes about 500 ml/day.
~150 ml in ventricles and subarachnoid
Ventricles
Lateral (2)
…are located within each cerebral
hemisphere
Third
Med and inf to the lat ventricles
Fourth
Between the brain stem and cerebellum.
Interventricular foramen
An opening which connects the lateral
ventricles to the third ventricle.
Cerebrospinal fluid
Cerebral aqueduct
Connects the third with the fourth
Spinal central canal
Passes down the middle of the cord
Subarachnoid
This spaces surrounds the cord and
the brain
Choroid plexuses
Found within the ventricles, these tufts
of capillaries produce CSF, which is
very similar to blood plasma without
proteins.
Cerebrospinal fluid
Arachnoid villi
Are extensions of the subarachnoid
space which project into the …
Superior saggital sinus
This space is found between the
two layers of the dura.
It is filled with venous blood.
CSF passes through the arachnoid
villi and it mixes with the venous
blood of sinus and is returned to
circulation.
The sinus eventually drains into
jugular veins and then to the heart.
Cerebrospinal fluid
Function
Shock absorber
The CSF surrounds the brain and the cord; it creates a watery
cushion to absorb the normal shocks of everyday life.
Nutrients delivery
Glucose, oxygen, some amino acids are carried in CSF and
delivered to neural tissues.
Removal of wastes
Carbon dioxide and waste products of normal metabolism
and cell breakdown are removed by CSF.
Hydrocephalus
Or “water on the brain”
If there is an over production of
CSF or if the CSF is not drained
properly, then fluid pressure within
the ventricles of the brain can
increase substantially.
The increased pressure will compress neural tissue and this will lead to brain
damage and, in some cases, death.
Causes of hydrocephalus may include blockage of the the cerebral aqueduct, in
which case the CSF accumulates in the lateral and fourth ventricles.
A hydrocephalic shunt may have to be implanted to relieve the pressure.
Blood supply of the brain
The brain requires a constant and steady supply of blood (with oxygen and
glucose.) It receives about 15% of the total cardiac output.
Interruption
Even a short interruption can cause a loss of brain function; a drop in BP
can lead to dizziness and blackouts.
Unconsciousness
If the supply is blocked for longer than 5-10 seconds, unconsciousness
will follow
Permanent injury
Can occur if there is a loss of blood for longer than about 5 mins. This
may result in brain injury and perhaps death.
Blood supply of the brain
Blood brain barrier
The BBB is a selective
barrier which prevents
certain materials from
passing into the sensitive
cerebral tissues.
Selective barrier
Slightly permeable to Na+, K+,
Cl-.
Very permeable to oxygen, carbon
dioxide, water, alcohol, and most
anesthetics.
Not permeable to blood proteins
and non-lipid organic molecules
Brain stem
Medulla oblongata ( or medulla)
The most inferior part of the the
brain stem; just sup to the cord.
Pyramids
Descending through the medulla
are the pyramids, motor tracts
from the cortex of the cerebrum.
Decussation
As the tracts of both sides pass the
junction between the medulla and the
cord, they cross over (the decussation)
the midline and form the…
Lateral corticospinal tract
These tracts continue down the cord to pass motor signals to skeletal
muscles in the periphery.
Brain stem
Medulla oblongata ( or medulla)
Nucleus gracilis and cuneatus
A nucleus is a collection of somas
within a nerve tract within the CNS.
These nuclei relay body sensory
information to the thalamus.
Reticular formation and
reticular activating system
(RAS)
This group of nuclei extend into the
pons.
They send signals in to the cerebrum to
maintain a state of consciousness.
If signals are interrupted for any reason,
such as a blow to the chin to direct
trauma to the medulla, the person will
fall into unconsciousness or a coma.
Brain stem
Medulla oblongata ( or medulla)
Cardiac center
Regulates the activity of the heart; such
as the heart rate and contraction strength.
Medullary rhythmicity center
Regulates the rate of respiration
Vasomotor center
Regulates peripheral vasoconstriction
and blood pressure.
Origins of cranial nerves VIII-XII
Later.
Vestibular complex
Receives information from the
vestibule of the inner ear, which
helps maintain balance.
Brain stem
Pons
Origins of cranial nerves V-VIII part of VIII
Later.
Reticular formation
Continues from the medulla.
Pneumotaxis and apneustic areas
Involved in regulating respiratory
activities.
The former detects the amount of
stretch in the lungs and regulates
how much the lungs inflate.
Brain stem
Midbrain (mesencephalon)
The most superior part of
the brain stem.
Corpora quadrigemina
On the posterior side of the
midbrain; “four bodies”
Superior colliculi
These “bodies” regulate visual
reflexes, such as pupil size and
focusing.
Inferior colliculi
Regulate auditory reflexes.
If you are exposed to loud sounds, the inferior colliculi sends signals to the
middle ear to reduce the level of sound energy transmitted into the inner ear.
Brain stem
Midbrain (mesencephalon)
Substantia nigra
Carries signals from the
motor cortex which are
used to coordinate
muscle activity (along
with the cerebellum.)
Damage to the
substantia can lead to
involuntary movement
and rigidity.
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Diencephalon
Thalamus
The lobes of the
thalamus are located
sup and lat to the brain
stem, deep within each
hemisphere.
Intermediate relay center
It receives all of the sensory fibers (except smell) and sends signals to the
sensory part of the cerebral cortex.
It may be that the thalamus is the crucial structure for the perception of
some sensations, rather than the cortex, which may give fine detail to
sensations.
Origins of voluntary motor pathways
Diencephalon
Thalamus
Brain (cortical cycles)
May have their origins here.
Emotional expressions
Considered the seat of emotions. Receives sensory input and passes in
on to the cerebral cortex. Integrates sensations and emotions.
Pineal gland/body
Located on the posterior surface of the mid-body of the thalamus.
Melatonin
A hormone produced by the pineal gland that appears to regulate the
circadian rhythm; wake-sleep cycles of the brain.
Exposure to bright light (such as sunlight at dawn) suppresses the release of
melatonin and resets the wake cycle.
Melatonin at night may stimulate sleep cycles.
Diencephalon
Hypothalamus
Hormone production
Makes two hormones (antidiuretic
hormone and oxytocin) which are
transported to and released by the
pituitary gland.
Controls hormones
Makes control factors that regulate
the release of hormones from the
pituitary.
Functions
Information processing about
external/internal environment
Next page.
Hypothalamus
Control of ANS
Controls both divisions of the ANS; sympathetic and parasympathetic.
Process visceral sensory information
Part of the visceral reflex arc. Processes visceral sensory signals and, in
turn, activate motor neurons which control visceral effectors.
Interface between the nervous and endocrine
This is the place where the two control systems overlap and exert mutual
control
Mind over body
The NS can control the release of hormones to control the body. Through
various techniques, such as meditation and bio-feed back, it is possible to
“think” your heart slower, for example.
Rage/aggression
Is closely linked to both the thalamus (associated with emotions) and the
hypothalamus (release of hormones, such as adrenaline.)
Hypothalamus
Body temp
Hypothalamus monitors blood as it passes the preoptic area.
If varies from normal range (37°C); negative feedback to bring the temp
back in range.
Food intake regulation
Feeding behavior is regulated.
Associated with emotions and memory.
Appestat
Detects blood glucose levels: if glucose drops, feeding
behaviors are turned on.
Satiety center
Eaten enough?
Increases in blood glucose and stomach stretch
Turns off feeding
Hypothalamus
Thirst center
Water content of blood is monitored
Adjusts drinking behaviors
Stimulates the release of ADH- anti-diuretic hormone
Reduces urine output
Helps retain water in the body