Chapter 15-1
The Brain and Cranial Nerves
The Brain
• The average male adult brain weighs about 3.5
lbs (1590 gms).
• Composed of 3 divisions:
– Cerebrum = Cerebral cortex and Basal nuclei
– Cerebellum – posterior and inferior to cerebrum
– Brainstem: Diencephalon (Thalamus,
Hypothalamus and Epithalamus), Midbrain
(superior and inferior colliculi), Pons and Medulla
oblongata
Midsagittal section
Midsagittal section
Brain Meninges
Brain Meninges
Arachnoid villi
Absorbs CSF back into venous sinuses and blood
Brain Ventricles
• Cavities within the cerebrum and brain stem where cerebrospinal fluid (CSF)
is manufactured and circulated.
• Two lateral ventricles over thalamus and roll out into temporal lobes, medial
third and fourth ventricles joined by cerebral aqueduct.
• Lateral ventricles look like a “Rocky Mountain” sheep Rams horns and
communicate to third ventricle via interventricular foreamen.
• CSF is formed by the ependymal cells of choroid plexus in all four ventricles;
is an ultrafiltrate of blood- no cells present; high in Na and K.
• CSF circulates through ventricular system as well as central canal of spinal
cord and subarachnoid space around brain and spinal cord.
Brain Ventricles
• CSF formation and
circulation into and
from blood vascular
system.
• CSF provides
protection and
nourishment to the
brain and spinal cord.
• Has higher levels of Na
and K than blood.
• CSF reduces weight of
brain (1400 gm to 50
gm).
Choroid plexus and Arachnoid
granulations
Dural sinuses
Dural sinuses
Cerebrum
• Cerebrum composes the vast majority of the
brain mass (80%). It is divided into 2 halves or
hemispheres, a right and a left hemisphere.
• Longitudinal fissure- midsagittal groove dividing
the two hemispheres into a right and left side.
• Consists of an outer layer of gray matter over
white matter (like crust on white bread).
• Sulci and gyri = valleys and ridges on surface of
cerebral hemispheres.
• Five lobes: Frontal, parietal, occipital, temporal
and insula.
Brain blood flow and barrier
• Blood flow to the brain is provided by the internal
carotid arteries and the vertebral arteries.
• The blood brain barrier (BBB) is thought to be due to
specialized endothelial cells that are influenced by the
glial astrocytes.
• In the choroid plexus there is also a CSF-BBB formed
by the ependymal cells.
• The BBB is absent in some places of the 3rd and 4th
ventricles at patches called circumventricular organs
where some substances may pass into the brain
tissue.
Cerebral hemispheres
Superior view
Cerebral Cortex
• The cortex is the outer layer of the cerebrum is
composed of gray matter and is where our
“consciousness” is located.
• It allows us to be who we are, perceive
sensations, comprehend and understand, as
well as learn and, communicate with the ability
to act and react at a conscious level.
Sulcus or Sulci
– sulcus/sulci – the valleys or grooves found
between the gyri. Some of these also have
specific names.
• central sulcus – separates the frontal and
parietal lobes..
• lateral sulcus – separates the temporal
lobe from the parietal/ frontal lobes.
• parieto-occipital sulcus – separates the
parietal and occipital lobes.
Gyrus or Gyri
– gyrus/gyri – the elevated ridges of tissue in the
cortex
1. precentral gyrus- motor cortex area 4
2. post central gyrus- sensory cortex areas 1-3
•
- homunculus (little man)- portrays primary
motor and sensory areas of body overlaying
precentral and postcentral gyri of the cortex
Sulci and Gyri
Humunculus “little man”
Broadmann areas
Functional areas of the Cortex
Three important areas of cortex:
• Motor areas control voluntary movement.
• Sensory areas provide consciousness and
awareness of sensations.
• Association areas act mainly to integrate
diverse information into decisive and
meaningful actions. This is done via
interneurons or association neurons.
Cortical motor, sensory and association
areas
Motor Areas of Cerebral Cortex
–
1° (primary) Motor Cortex – located in the precentral
gyrus.Also known as Broadmann’s area # 4.
-Contains large Pyramidal neurons that allow us to perform
precise and skilled movements with our skeletal muscles.
-Motor innervation is contralateral i.e. the left side of the
brain controls the right side of the body and vice versa.
• Broca’s Area – located superior to lateral sulcus and
anterior to precentral gyrus. Associated with motor
speech and is usually located in the left hemisphere
• Premotor cortex anterior to precentral gyrus
(Broadmann 6) thought to be site of memory bank for
fine motor skils.
Sensory Areas of Cerebral
Cortex
•
•
•
•
1° (primary) Somatosensory Cortex – located in
the postcentral gyrus of the parietal lobe. Areas 1-3
Visual Sensory Area – Located on the extreme
posterior tip of the occipital lobe. Receives input
from retina; is largest cortical sensory area.
Auditory Area – medial aspects of the temporal
lobes.
Gustatory Area –parietal lobe deep to the temporal
lobe at the tip of the tongue of humunculus.
Cerebral anatomy to know
• Longitudinal and transverse fissures
• Lateral, Central and Parieto-occipital sulci
• Precentral (motor #4) and Postcentral (sensory
#1-3) gyri
• Lobes: Frontal, Parietal, Temporal, Occipital
and Insula
• Basal nuclei: Caudate nucleus, Putamen,
Globus pallidus
• Corpus callosum, septum pellucidum, fornix,
and internal capsule
Cerebral anatomy to know
• White matter is myelinated neuronal tissue in
brain and spinal cord and contains neuronal
tracts.
• Gray matter is unmyelinated and contains
mostly neuronal nuclear groups or nuclei and
unmyelinated tracts.
Coronal section
Cerebral White Matter
•
is composed of myelinated processes. Within the
white matter are “roads” of ordered groups of neuron
processes called tracts. There are three major
types of tracts in the cerebral cortex:
1. Commissural fibers – connect the gray matter
between the two hemispheres. e.g. corpus callosum
2. Association fibers – connect adjacent gyri in same
hemisphere. e.g. visual and auditory association
areas.
3. Projection fibers – these connect to regions outside
of the cerebrum e.g. internal capsule; corona radiata
Gray and White Matter in CNS
Communication fibers
Association fibers
Commissural fibers
Projection fibers
Basal Nuclei “Corpus striatum”
• Masses of cerebral gray matter buried deep in
each hemisphere in the white matter and lateral
to the thalamus.
• Caudate nucleus, globus pallidus and putamen
– Communicate with cortex in controlling movement
– Complete function is ??, but may regulate start,
stop and intensity of voluntary body movements
from cortical levels.
Basal Nuclei “Corpus striatum”
The Limbic System
• Concerned with sense of smell in association
with long term memory and emotional
responses (anger, fear, rage, sex and hunger).
• Includes cingulate gyrus, amygdala,
hippocampus, septum, fornix, thalamus,
hypothalamus and olfactory bulbs.
The Limbic System