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Brain
Integrative center of Nervous System
Different regions/different fcn
100 billion neurons and neuroglia
3 main sections: Forebrain, midbrain, hindbrain(brainstem)
Protected by: cranial bones, CSF, and meninges
CSF and meninges are continuous with
The Spinal cord
Cerebral Spinal Fluid(CSF):
80-150ml (3-5oz)
Filtered blood plasma(glucose, oxygen, H20)
Cushions, supports, nourishes, waste removal
Located in cavities within brain: ventricles
Lateral, third, and fourth ventricles
Dry weight of brain = 1400g(3.1 lb)
Weight of brain in CSF= 50g (1.7 oz)
Path of CSF:
1.Produced at choroid plexus(network of capillaries)
in walls of lateral ventricles(middle of cerebrum)
2. Foramen of Monro to 3rd Ventricle(center of
diencephalon)
3. Cerebral Aqueduct to
4. Fourth ventricle(between cerebellum and brainstem)
5 to central canal and subarachnoid space of SC
6. To cranial subarachnoid space passing out of
arachnoid villi and into the Superior Sagittal Sinus(a large
vein on top of brain) – ARACHNOID GRANULATIONS
= clusters of arachnoid villi
CSF under constant pressure/ continual flow
Brain uses 20% of the bodies Oxygen supply!!
(lysosomes in brain cells are sensitive to low O2
levels. If low O2 levels persist, cells die, leads to severe
retardation or death)
CEREBRUM(“higher brain”)
Supported on brainstem
Surface = gray matter(6 layers of nerve cell bodies)
= cerebral cortex
Cerebral white matter beneath cortex
Folds of gray matter = Gyri
Deep folds = fissures
Shallow folds = sulci
Longitudinal fissure separates cerebrum into
2 Hemispheres
Corpus Collosum: white matter connects 2 hemispheres
4 Lobes per hemisphere
Frontal, parietal, temporal, and occipital
Each lobe has specific functions
White matter = myelinated axons running in 3 directions
Association fibers = transmit impulses in same
hemisphere
Commisural fibers= transmit impulses between 2
hemispheres
Projection fibers = form ascending and descending
tracts. Transmit impulses from cerebrum to other parts of
brain and spinal cord
LIMBIC SYSTEM
The “emotional brain”
Located in diencephalon(below corpus collosum)
Emotional aspects of behavior related to survival and
memory
Amygdaloid(amydgda = almond shape)
Controls behavior: pleasure, pain, fear,
sorrow rage, sexual feelings, docility, affection
Diencephalon: thalamus and hypothalamus
Thalamus: surrounds 3rd ventricle
Relay station for sensory impulses and
involuntary motor impulses
Early conscious recognition of pain pressure
temp and touch(basic survival instincts)
Pineal gland posterior margin(releases melatonin
which inhibits release of GnRH)
Hypothalamus: EMOTION
Regulates food and water intake, waking and
sleep patterns
Control center for autonomic nervous system
Digestion, respiration, heart rate
Controls body temp
Controls mind over body phenomenon
Pituitary gland (stella turcica)= the master
Endocrine gland of body
MIDBRAIN: tiniest portion of brain – contains various
nuclei and ascending and descending fibers
Relays motor impulses from cerebral cortex to Pons
and spinal cord
Relays sensory impulses from SC to thalamus( via
sensory nuclei = colliculi(little hill)
Superior colliculi coordinate eye, head, neck
movement in response to BRIGHT VISUAL stimuli
Inferrior colliculi coordinate eye, head, neck
movement in response to LOUD noise
Motor nuclei for two cranial nerves – eye movement
Connects Pons and diencephalon
Cerebral Peduncles: anterior to midbrain
Myelinated DESCENDING fibers, motor
pathways cerebrum
To cerebellum
Corpora Quadrigemina: Posterior to midbrain
Reflex centers, rapid eye, head and trunk
movement
Reticular Formation: integrates involuntary functions
Interconnected nuclei extending length of brain stem
Contains Reticular Activating System (RAS) –
directly controls activity of cerebral cortex – RAS inactive
– we are inactive/ RAS active – we are attentive and
wakeful
PARKINSON’S DISEASE: midbrain nuclei (BASAL
NUCLEI) maintain muscle tone and posture –
Substantia nigra inhibits activity of basal nuclei by
releasing DOPAMINE
Basal nuclei become more active with less Dopamine –
increased muscle tone – Parkinson’s Disease have
difficulty starting voluntary movements B/C opposing
muscle groups DO NOT RELAX ( not enough Dopamine
is excreted by substantia nigra
BRAINSTEM(Hindbrain)
Pons and Medulla Oblongata
Pons: relays impulses within brain and between parts
of brain and spinal cord
Medulla oblongata:
Connects brain to spinal cord
Ascending and descending tracts
Sensory or motor nuclei that act as relay stations for
tracts
VITAL AUTONOMIC FUNCTIONS:
Cardiac center – regulates heart rate
Vasomotor center – controls peripheral blood
flow
Respiratory center – set pace for breathing
Coordinates swallowing, vomiting, coughing,
sneezing, and hiccuping
CEREBELLUM – automatic processing center
FCN: adjust our posture to maintain balance
Fine tune movements controlled at conscious
and subconscious levels
Ex: while walking our arms swing in unison with leg
movement
Posterior portion of hindbrain
Vermis: wormlike midline between 2
hemispheres
Arbor vitae – white matter pattern
Transverse fissure: separates cerebellum from
cerebrum
Cerebellar peduncles: 3 paired bundles of myelinated
Fibers
Carry sensory info from muscles,
Joints, and inner ear to mainTain equilibrium & balance
Regulates performance of skeletal
Muscles for coordination and
Posture maintenance(acts like
An automatic pilot)
Damage by trauma or alcohol – ATAXIA = lack of order –
inability to remain physically balanced
MOTOR AREAS of BRAIN
Frontal Lobe= Primary Motor area(anterior to central
sulcus)
Controls specific muscles: jaw,
tongue, lips, face, hand, knee, ankle toes
Stimulation of a specific point
result in muscular contraction on opposite side of body
Premotor Area: anterior to primary motor area
Skilled movements(writing)
Frontal Eye Field: frontal cortex
Controls voluntary scanning movements of
the eye
Language area: motor speech area = BROCA’s area
In Frontal Lobe
Coordinates contractions of speech and
breathing muscles to translate thought into speech
HOMUNCULUS(see pg 303
Sensory and motor functional map
Proportional to # of sensory or motor receptors in the
designated area