Download the brain

THE BRAIN
• It consumes about 20% of the energy used
by the body. In infants, it consumes about
60%. This generates a lot of heat, which
must be removed to prevent damage.
• It has a million billion synaptic connections,
making it one of the most densely
connected network systems among natural
and fabricated systems found on earth.
ANATOMY
• Myth: Humans use only 10% or 1% of their brain.
Though the brain still holds mysteries that are
being studied, every part of the brain is known to
have a function.
• A possible origin of this myth is the fact that only
about 10% of the neurons in the brain are firing at
any given time.
• However, if all of your neurons began firing at
once, you would not become smarter, but instead
suffer an epileptic seizure.
MENINGES
• The brain is the best protected organ in the body.
• The first layer of protection is the skull, which
acts as armor shielding the brain from blows.
• Next come the meninges, three membranes that
surround the brain to keep it from being damaged
by contact with the inside of the skull.
• It is these membranes that become infected when
someone gets meningitis, and it is because the
meninges are in direct contact with the brain that
meningitis is so dangerous.
• For even more protection, the brain (and the spinal
cord) are bathed in cerebro-spinal fluid.
• This fluid circulates through a series of
communicating cavities called ventricles.
• Cerebro-spinal fluid also circulates between the
pia mater and the arachnoid mater of the
meninges.
• In addition to cushioning blows, this fluid reduces
the pressure at the base of the brain by causing the
nerve tissue to “float”.
• As the Cerebro-spinal fluid flows downward, it
carries away toxic wastes and moves hormones
between widely separated regions of the brain.
The cerebrum
• Located in the anterior portion of the
forebrain.
• Divided into two hemispheres that are
connected by the corpus callosum.
• Cerebral cortex: surface of the cerebrum
Very convoluted. Spread out: 2500 sq
cm
10 billion neurons and 50 trillion
synapses
• The convolutions have "ridges" which are
called gyri (singular: gyrus), and "valleys"
which are called sulci (singular: sulcus).
• Some of the sulci are quite pronounced and
long, and serve as convenient boundaries
between four areas of the cerebrum called
lobes.
• How we know what we
are doing within our
environment
(Consciousness).
• How we initiate activity in
response to our
environment
• Judgments we make
about what occurs in our
daily activities.
• Controls our emotional
response.
• Controls our expressive
language. Assigns
meaning to the words we
choose. Involves word
associations.
• Memory for habits and
motor activities.
Broca’s Area
• In most people the
Broca's area is in
the lower part of the
left frontal lobe.
• It is one of the main
language areas in
the cerebral cortex
because it controls
the motor aspects of
speech.
• Broca Aphasia :
• Persons with a Broca
aphasia can usually
understand what words
mean, but have trouble
performing the motor or
output aspects of speech.
• Other names for this disorder
are 'expressive' and 'motor'
aphasia.
Wernicke's area
• Wernicke's area
is associated with
the processing of
words that we hear
being spoken
• Broca's area and
Wernicke's area are
connected by a
large bundle of
nerve fibres called
the arcuate
fasciculus.
Language model
• When you hear a word spoken, the
auditory signal is processed first in your
brain’s primary auditory cortex, which then
sends it on to the neighbouring Wernicke’s
area.
• Wernicke’s area associates the structure of
this signal with the representation of a word
stored in your memory, thus enabling you to
retrieve the meaning of the particular word.
• In contrast, when you read a word out loud, the
information is perceived first by your visual
cortex, which then transfers it to the angular gyrus,
from which it is sent on to Wernicke’s area.
• The mental lexicon in Wernicke’s area recognizes
this word and correctly interprets it according to
the context.
• For you then to pronounce this word yourself, this
information must be transmitted via the arcuate
fasciculus to a destination in Broca’s area, which
plans the pronunciation process.
• Lastly, this information is routed to the motor
cortex, which controls the muscles that you use to
pronounce the word.
Wernicke’s aphasia
• Lesions that cause Wernicke’s aphasia (also
known as sensory aphasia or receptive aphasia)
reduce understanding of spoken and written
language
• Responses to simple instructions, such as “Place
object A on top of object B” show that patients do
not understand what is being asked of them. They
can read an instruction correctly, but cannot
perform the action indicated by the meaning of the
words.
• When Wernicke’s aphasics speak, their
language is littered with jargon, made-up
terms, and other incomprehensible words.
Their grammar is often intact, but they
misuse so many words that conversation
with them is very difficult.
• Patients with Wernicke’s aphasia may be
unaware that their speech is disorganized or
that they are having any trouble in
understanding other people when they
speak.
Motor Cortex
• At the back portion of the frontal lobe, along the
sulcus that separates it from the parietal lobe, is an
area called the motor cortex.
• stimulating areas of the motor cortex with tiny
electrical probes caused movements. The lowest
portions of the motor cortex, closest to the
temples, control the muscles of the mouth and
face. The portions of the motor cortex near the top
of the head control the legs and feet.
The corpus callosum
• The corpus callosum is composed of a
band of nearly 800 million nerve fibers
adjoining the left and right cerebral
hemispheres.
• This information superhighway transmits
neural information from one hemisphere to
the other producing all integrated thought
patterns.
• In the central nervous system, the “grey matter” is
composed of the neurons’ cell bodies and their
dense network of dendrites.
• The grey matter includes the centre of the spinal
cord and the thin outer layer of the cerebral
hemispheres, commonly known as the cortex.
• The white matter consists of the myelin sheathing
that covers the axons of the neurons to enable
them to conduct nerve impulses more rapidly.
• These myelinated axons are grouped into bundles
(the equivalent of nerves) that make connections
with other groups of neurons.
Right and Left Hemispheres
• Left Brain
• Logical, sequential
Rational
Analytical
synthesizing
Objective
Looks at parts
Right Brain
Random
Intuitive
Holistic,
Subjective
Looks at wholes
• Location for visual
attention.
• Location for touch
perception.
• Goal directed
voluntary
movements.
Manipulation of
objects.
• Integration of
different senses that
allows for
understanding a
single concept.
• Vision and
visual
processing
• Hearing ability
• Memory
aquisition
• Some visual
perceptions
• Categorization
of objects.
• Breathing and Heart Rate
• Swallowing Reflexes to seeing
and hearing (Startle
Response).
• Controls sweating, blood
pressure, digestion,
temperature (Autonomic
Nervous System).
• Affects level of alertness.
Ability to sleep.
• Sense of balance
• Consists of the midbrain,
medulla oblongata, and the
pons
• Coordination of
voluntary
movement
• Balance and
equilibrium
• Some memory for
reflex motor acts.
THE EVOLUTIONARY LAYERS
OF THE HUMAN BRAIN
• Triune Brain theory ( 1970’s)
• 1. The reptilian brain, the oldest of the three,
controls the body's vital functions such as heart
rate, breathing, body temperature and balance.
• Our reptilian brain includes the main structures
found in a reptile's brain: the brainstem and the
cerebellum.
• The reptilian brain is reliable but tends to be
somewhat rigid and compulsive.
• The neocortex first assumed importance in
primates and culminated in the human brain
with its two large cerebral hemispheres that
play such a dominant role.
• These hemispheres have been responsible
for the development of human language,
abstract thought, imagination, and
consciousness.
• The neocortex is flexible and has almost
infinite learning abilities.
• 2. The limbic brain emerged in the first mammals.
It can record memories of behaviours that
produced agreeable and disagreeable experiences,
so it is responsible for what are called emotions in
human beings.
• The main structures of the limbic brain are the
hippocampus, the amygdala, and the
hypothalamus.
• The limbic brain is the seat of the value
judgments that we make, often unconsciously, that
exert such a strong influence on our behaviour.
Hippocampus
• The hippocampus is the brain's main entry point for
memory. It is here that the initial encoding of memory
elements gets processed for later recall.
• Has genetically-controlled specifications for exactly
where in the brain each important element of a
memory will be stored.
• Is involved in the recognition of novelty and in
processing spatial relations, such as the route to
school and home, or to one's office
• Damage to the hippocampus can render an individual
incapable of forming and storing any new memories
or retrieving previously learned information. The
consequence is various forms of amnesia.
Amygdala
• The amygdala is considered the brain’s
primary emotional center (it is more like an
emotional thermostat)
• It communicates with all other sensory input
systems and the cerebral cortex
• Recall, retention, and long-term memory are
all enhanced by the almost "hair-trigger" firing
of the amygdala, which performs a key role in
processing nearly all emotional events.
• Emotions assist in deciding what to pay
attention to, which impacts what will ultimately
be remembered.
• If the amygdala is removed surgically or
sustains damage, an individual would process
events devoid of any emotional input.
• Connections between the amygdala and the
cortex allow emotions to influence or
sometimes to prevent nearly all learning as
well as long-term memories.
• The brain comprises several different kinds of
memory. The hippocampus and the cortex make
explicit, conscious memories possible. For its
part, the amygdala enables one of the forms of
implicit memory: emotional memories associated
with fear.
• Various aspects of an especially emotional
situation such as a car accident will be processed
both by the hippocampus and by the amygdala,
working in parallel. Thanks to the hippocampus,
you will remember whom you were with, what
you did, and the fact that it was a particularly
painful situation. However, it is because of the
amygdala that when you remember the event, your
palms will sweat, your heart will race, and your
muscles will tense
The cingulate gyrus
• The cingulate gyrus influences impulsivity,
attention, and the control of emotional behaviors.
• An immature anterior cingulate gyrus is now
highly suspect in incidences of ADD and ADHD.
• During puberty, the cingulate gyrus and the corpus
callosum mature. At that time, the connections
from the frontal lobe back to the amygdala come
into better balance with the number of connections
going the opposite direction.
The Reticular Activating system
• The reticular activating system (RAS)
is involved in most central nervous
system activity, including control of
wakefulness, sleep and part of our
ability to direct attention toward
specific areas of our conscious
minds.
• The RAS is a network of interlacing
nerve cells and fibers that receives
input from multiple sensory pathways.
It extends from the spinal cord to the
lower brain stem, upward through the
mesencephalon and thalamus, and
then is distributed throughout the
cerebral cortex.
• RAS fibers affect the
autonomic and motor
systems. They integrate
the regulation of
cardiovascular,
respiratory and motor
response to external
stimuli.
• The RAS diffusely
distributes incoming
sensory stimulation
throughout the CNS,
upregulating and
readying the system to
respond more
specifically to input.