Download The Brain

The Brain
Overview of the Brain
• Contains over 100 billion neurons
• 3 major regions based on embryologic
development: forebrain (cerebrum and
diencephalon), midbrain, and hindbrain
(pons, medulla oblongata, and cerebellum)
• Midbrain and hindbrain can also be
referred to as the brain stem
Protective Coverings
• Protected by the cranium, CSF, and the
meninges
• Meninges are formed from 3 distinct layers
• From superficial to deep: the dura mater,
arachnoid, and pia mater
• Between arachnoid and pia mater is the
subarachnoid space which is filled with
CSF
CSF and Ventricles of Brain
• CSF is clear and colorless
• Functions as a liquid cushion for CNS and
helps to nourish the brain and removes
waste materials
• Much is contained within four ventricles
which are continuous with the central
canal of the spinal cord
• Has a lateral ventricle in each hemisphere
• The third ventricle is located in the center
of the diencephalon
• The fourth ventricle is located between the
cerebellum and the medulla oblongata
• Each lateral ventricle is connected to the
third ventricle by a channel called the
foramen of Monro
• The third is connected to the fourth by a
channel called the cerebral aqueduct
• CSF is formed within ventricles by filtration
of blood plasma through dense networks
of capillaries in jelly-like structures; each is
called a choroid plexus and is part of the
blood-brain barrier
• This structure is selectively permeable and
allows in substances such as water,
glucose, and oxygen while blocking cells,
bacteria, and many proteins.
• Pressure formed by this production causes
CSF to circulate
• Returns to bloodstream by arachnoid villi
The Cerebrum
• Largest structure in the brain; varied and
complex
• Functions in conscious thought, memory,
and learning
• Also receives and interprets sensation and
initiates many motor responses
• Divided into right and left portions called
hemispheres
• Has many prominent wrinkles of foldings,
called convolutions, which increase ratio of
surface area to volume (gyri project up,
sulci form grooves)
• Deep grooves are called fissures;
longitudinal fissure separates right from
left while transverse fissure separates
cerebrum from cerebellum
• Four lobes in each hemisphere named for
the cranial bones above them: frontal lobe,
parietal lobe, occipital lobe and temporal
lobe
• External surface of cerebrum is gray in
color because it is made up of
unmyelinated fibers, called the cerebral
cortex which is only 2mm thick
• The cortex contains billions of cell bodies
and associated synapses; source of
integrative function of brain
• Most of the brain is made of white matter
(myelinated) and forms connections with
other parts of CNS
• White matter extends from one
hemisphere to the other through a
structure called the corpus callosum
• Embedded within the white matter are
several masses of gray matter called basal
ganglia
• These serve as relay stations for motor
impulses originating in the cerebral cortex
en route to the spinal cord and control
large, unconscious movements of skeletal
muscles such as swinging arms while
walking
Diencephalon
• Located inferior to the corpus callosum
• Composed of the larger thalamus
(principal relay station for sensory
impulses and sensations related to
survival: pain, temperature, touch,
pressure) and the smaller hypothalamus
(controls involuntary activities that have
direct effect on homeostasis: digestion,
respiration, heart rate)
Hypothalamus
• Small in size, but a giant in function
• Intermediary between nervous and
endocrine system by stimulating that
system’s master organ, the pituitary gland
• Regulates food and water intake, waking
and sleeping patterns
• Associated w/ emotions (rage, aggression,
sex drives, and symptoms of emotional
stress such as crying)
Midbrain
• Located between the diencephalon and
pons
• Anterior portion contains bundles of nerve
fibers called cerebral peduncles which
provide a major connection for nerve
pathways between the cerebrum and
cerebellum
• Posterior contains corpora quadrigemina
which serve as reflex centers for rapid
eye, head, and trunk movements
Pons
• Rounded bulge inferior to the midbrain
made of white matter and embedded w/
scattered masses of gray matter
• Major function is to serve as a bridge
between spinal cord and brain and parts of
the brain with each other
• Some nuclei also help to regulate
breathing rhythm
Medulla Oblongata
• Lies below the pons, extends to the spinal cord
• Composed of white matter on the outside w/
gray matter on the inside
• White matter contains ascending and
descending nerve tracts
• On the posterior side, an enlargement known as
the pyramids is where descending nerve tracts
cross so that the left side of the brain controls
the right side of the body and vice versa
• The gray matter of the medulla contains
reflex centers that play a role in visceral
reflexes, consciousness, and arousal
• Some of its more important reflex centers
include the cardiac center which regulates
heart rate, the vasomotor center which
regulates blood pressure by controlling
diameter of blood vessels, and the
respiratory center which regulates
breathing depth and rhythm
Cerebellum
• Posterior portion of the hindbrain; divided
into two hemispheres connected by a
structure called the vermis
• Has a cortex, like the cerebrum
• White matter forms a distinctive tree-like
pattern called the arbor vitae
• Contains 3 paired bundles of myelinated
fibers called cerebellar peduncles
• Cerebellar peduncles carry information
from sensory organs in muscles, joints,
and inner ear to enable the brain to keep
track of the location of body parts (spatial
awareness) and maintain balance
• Also works to coordinate nerve impulses
so that movement is smooth and helps to
maintain posture