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Topic A.2 – The human brain
The anterior part of the neural tube expands to form the brain.
The neural tube goes on to form all the parts of the brain.
However, the anterior region expands much more rapidly,
resulting in the cerebral hemispheres and brain
structures.
Parts of the adult brain that are important are:
Medulla oblongata
Cerebral Cortex
Sulci/Gyri
Left Hemisphere
Right Hemisphere
Visual Cortex
Broca’s Area
Nucleus accumbens
Cerebellum
Hypothalamus
Pituitary gland
The autonomic nervous system controls involuntary processes in the body using centers located
in the medulla oblongata.
The medulla oblongata
contains neurons that
coordinate many of the
muscles of the mouth, throat
and larynx, and as such,
regulates the swallowing reflex
and the peristalsis that moves
food down the esophagus, and
not the windpipe.
The medulla also
controls the heart
beat by constantly
sending out cardioinhibitory signals.
During exercise, the
medulla stops sending
these signals, thereby
allowing the heart
rate to increase.
The medulla plays a large role in the
monitoring of blood carbon dioxide,
which controls the respiration rate.
High CO2 levels increase the rate, and
low CO2 levels lower the rate.
Application: Visual cortex, Broca’s area, nucleus accumbens as areas of the
brain with specific functions.
Visual Cortex
Area of the brain that receives visual
information and passes on to the
visual association area, which
processes the information.
Visual Cortex
Nucleus accumbens
Broca’s Area
Responsible for speech and
language. People with tumors
or damage in this area of the
brain have a severely limited
capacity to communicate
The center of the reward circuit of the
brain, dealing primarily with dopamine
and serotonin, which operate oppositely
with respect to desire.
Dopamine = Desire
Serotonin = Desire
The cerebral cortex forms a larger proportion of the brain and is more highly developed in
humans than other animals.
Correlated with our additional
development time as an embryo, our
cerebral cortex is much larger than our
animal counterparts.
This has to do with neural migration
Not to be outdone, humans created a
second index, in which incorporates the
average brain size for animals of that type
and we call this the Encephalization
Quotient (EQ).
This simple table
demonstrates the
increase in brain size
(E) with respect to
body size (S).
How can ants and
birds have a higher
ratio than us?
Notice…..humans are way at the top.
The human cerebral cortex has become enlarged principally by an increase in
total area with extensive folding to accommodate it within the cranium.
Wow….grammar
These folds in the brain allow for a much higher surface area
for neuronal connections. This allows for increased
interactions between lobes of the brain, and leads to the
complexity of our senses.
Brain metabolism requires large energy input.
At rest, the brain uses approximately
20% of the body’s energy , while
accounting for only 2% of your body
mass.
If your diet is 2000 kcal/day, then that is over 400
kcal! You are basically eating a whole meal each
day, just to fuel your brain.
This, when converted into electrical power, is
about 19.4 watts/day, which is pretty efficient
when you consider the supercomputers that
compete with the human brain often run on
~750 servers, each with over 1000 watts
powering them.
The left cerebral hemisphere receives sensory input from sensory receptors in the right side of
the body, and the right side of the visual field in both eyes, and vice versa for the right
hemisphere.
This allows us to partition the amount of sensory
information coming to any on part of the brain at any
time.
fMRI is used as a way to identify the areas
of the brain that are active, with respect
to certain actions.
Here you can see the two eyes connected to
the brain by the optic nerves. The left visual
field is giving information to the right side of
the primary visual cortex and vice versa.
Areas of high activity allow us to
determine the function of different parts
of the brain.
The left cerebral hemisphere receives sensory input from sensory receptors in the right side of
the body, and the right side of the visual field in both eyes, and vice versa for the right
hemisphere.
We used to treat the some
types of epilepsy through
the severing of the corpus
callosum in order to stop
seizures.
Roger Sperry carried out many different experiments that
confirmed what we believed to be the functions of each of the
hemispheres.
This lead to a series of revelations on how instrumental the
corpus callosum is in our daily function.
The role of experimentation in determining the role of the areas of the brain.
Outline the ability of each of the following methods of analysis on determining the role of
different brain areas:
-Lesions
-Pupil Reflex
-Animal
Experiments
-Autopsy
Give an example
experiment of the
method you are
investigating and
describe how the
results lead to
greater
understanding of
certain areas of the
brain.
Application: Use of animal experiments, autopsy, lesions and fMRI to identify the role of
different brain parts.
Self-administration experiments are one of
the most common types of animal
experimentation, in which mice can choose
what type of food to eat.
This is useful to determine whether a
substance is addictive, and whether it would
have withdrawal symptoms as well.
Results from such an
experiment shown to the right.
(A) Adolescent rats self-administered
nicotine combined with
acetaldehyde with increasing
frequency, but did not with any
variable alone.
(B) Adult rats did not have any
preference.
(C) Total intake was greatest in the
youngest group of animals.
Application: Use of the pupil reflex to evaluate brain damage.
The pupil reflex is the reflex within the eyes that causes the
pupil to widen or narrow in response to changes in light.
This is often used as a marker for brain activity in individuals
that are non-responsive, as a method of determining
whether brain death has occurred.
If there is no movement in the pupil, along with no response
to a variety of other tests, then it can be determined that the
individual is “brain dead”
The pathway of the pupil reflex is:
1. Optic nerve receives messages from
retina
2. Optic nerve connects with pretectal
nucleus of the brainstem
3. Message is sent to the EdingerWestphal nucleus, back to the eye
4. At the synapse with the ciliary
ganglion stimulates the muscle of the
iris to contract
Challenge Questions
After this
subunit, can
you do each
of these?
Describe how an fMRI is used
to identify the role of different
brain parts.
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Explain why the brain metabolism
requires a large input of energy.
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Draw and annotate a diagram of the
human brain.
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State the specific function of
each of the following: Broca’s
area, nucleus accumbens,
visual cortex.
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Explain how folding
has allowed the
cerebral cortex to
become more highly
developed in humans
than in other
animals.
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