1
HC1: Evolution & Function of the nervous system
We receive information through our senses. Predictions: what is going to happen next? These are important,
because only then you know what to do next. The brain works in combination with the nervous systems to do so.
Evolution & historical perspectives on mind and brain
Why is the brain so important? The brain’s primary function is to produce behavior. To do so, it must:
- Receive information about the world
- Integrate information to create a sensory reality
- Make a constant stream of predictions about what to expect
- Produce commands to control the movement of muscles
The make up of the nervous system altogether allows the brain to do so.
What is behavior? There are different types of behavior:
- Relatively fixed behaviors
o Dependent on the genes (zuigreflex bv), you can automatically do them. The behavior is innate.
- Relatively flexible behavior
o Dependent on learning, you must learn how to do them. The behavior is learned.
In different species it’s different how complex the behavior is. How more complex the nervous system is, how more
complex the behavior is.
Quick overview of the history about behavior.
- Mentalism: an explanation of behavior as a function of the nonmaterial mind. Nonmaterial = there is
something that is not in our body that influences our mind. Like our soul. It was once proposed to be the
source of our behavior, but it wasn’t observable. It would still be there if we would die. That was the idea of
Aristoteles.
- Dualism: Decartes said this wasn’t true and he proposed dualism. There was a nonmaterial mind, but also a
material body and together they contribute to our behavior. This made it even more complex. Some simple
behaviors were controlled by the body. There was no nonmaterial mind needed.
o Mind-body problem: how can something nonmaterial command something that’s material? That’s
not possible.
- Materialism: So the main philosophy now is Darwin. Behavior can be explained as a function of the nervous
system without considering the mind as a separate substance. Natural selection: differential success in the
reproduction (i.e. passing on your genes) of
different characteristics/behavior (phenotypes)
results from the interaction of organisms with
their environment. Traits/behavior that increase
reproductive success and chances of survival will
be passed on to offspring. Competition is a key
concept. If you’re better able to cope with the
environment the changes of passing on your
genes is more likely.
This picture shows how the concept of passing on genes
explained by Darwin works. The sea anemone is quite
basic, and the frog is more complex. As humans it’s also
likely that we started as a very basic species.
It turns out that the modern human brain has the largest size
relatively to our bodyweight. The more brain weight in comparison
to bodyweight means more complex behaviors.
Neuroplasticity: the brain is plastic: the brain is developing and
changing. Your brain changes your behavior, but your behavior
also changes your brain. Children who are raised in a more
stimulating environment have different brains then children raised
in a poor environment. This proves the environment is an
influence on the brain structure.
, 2
Neural tissue has the capacity to adapt to the world by changing how its functions are organized. Because the brain
can adapt to the world, different species could develop. Neuroplasticity is seen both in the developing brain and in
adaptions of brain structure following injury.
Epigenetics is the study of differences in gene expression related to environment and experiences. How the brain
adapts to the environment depends on epigenetics: which genes have an impact and which genes don’t depend on
the environment. That’s how the environment influences the brain structure: it can turn on or turn off certain genes.
This is how species could change and how evolution works. Epigenetics factors do not change your genes, but they
do influence how your genes operate. Epigenetic changes can persist throughout a lifetime and the cumulative
effects can make dramatic differences in how your genes work and how likely a species is to pass on its genes →
evolution.
Example: two mice with exact the same DNA. They received different kinds of food. The
type of food was affected certain genes in the mouse. Therefore, they look different.
The brain – and especially the cortex – is highly flexible. That means humans can live very
different life styles in very different environments, with equal skill and success. That also
means that individual differences in brain organization are huge. The average brain does not exist.
Anatomical & functional divisions of the nervous system: brain
The nervous system is about a lot of things. There are different
kinds of nervous systems
Somatic = information coming from your senses to your muscles.
Autonomic = heart rate, digestion, etc. Enteric = what you eat can
affect your mood. We are now going to research the brain part of
the nervous system.
This is the main makeup of the brain
- Forebrain: the major structure of the brain, consisting of two almost identical
hemispheres (left and right). Prominent in mammals and birds, responsible for most
higher order conscious behaviors.
- Cerebellum: “little brain”. Involved in coordination of motor and cognitive processes
- Brainstem: central structures of the brain, including the hindbrain, midbrain, thalamus
& hypothalamus. Source of behavior in simpler animals, responsible for most of our
unconscious behaviors.
- Spinal cord: consists of nerves that carry incoming and outcoming messages between the brain and the rest
of the body including reflexes.
Here we see the hierarchy of the brain. The cortex
explains the most complex behavior (like executive
decision making), the hindbrain explains more basic
behavior like pumping blood through your heart.
Forebrain: cerebral/neo-cortex.
The cortex is a thin layer which is folded a bunch of
times to fit in your head. There are 6 layers of nerve
cells. It’s used for high order functions: mental
activities. The
bumps are called
gyri and the
grooves are called
sulci.
, 3
The allocortex cortex is a different cortex and is already
found in less complex animals. It’s also called the
cingulate cortex. It consists of 3 or 4 layers of nerve cells
present in structures of the limbic system (cingulate
cortex, hippocampus, amygdala), as well as structures
related to the olfactory system. Controlling motivation,
self-monitoring, attention, etc.
Orientation
“Brain-body orientation” illustrates
brain-structure location form the
frame of reference of the face. These
things says something about where it
is in the brain. But there are different
terms for the same directions. So
rostral means the same as anterior.
And caudal = posterior.
“Anatomic orientation” illustrates the
direction of a cut, or section, through
the brain (part A) from the perspective of a viewer
(part B). axial = horizontal.
Checklist of terms that you’ll have to learn:
- Anterior
- Caudal
- Coronal
- Dorsal
- Frontal
- Horizontal
- Interior
- Leteral
- Medial
- Posterior
- Rostral
- Sagittal
- Superior
- Ventral
Cell structure
Important structural categories.
, 4
The outer layer (the cortex) is the darker sheet (darker than the white
part). It’s called gray matter. There are different things in those parts of the
brain. In the gray matter are cell bodies and in the white matter are axons.
The cell body sends information through it’s axion to the corpus callosum.
- Gray matter: the actual cell bodies (about 80 billion neurons) and
ther dendrites
- White matter: fat-sheated neuronal axons, plus glial cells (about
100 billion) for structural support
Corpus callosum: fiber system consisting of white matter tracts connection
the two cerebral hemispheres. The corpus callosum is the largest white
matter structure in the brian, consistion of 200-250 million contralateral
aconal projections.
A different word for cell body is soma. Several nerves together are calles
fibers.
Forebrain: lobes of the cerebral cortex
Each hemisphere is divided into four lobes:
- Frontal
o Speech, initiates muscle movement, planning, decision
making and executive functioning
o Blue
- Parietal
o Cognitive and sensory integration for touch and body position, attention
o Red
- Temporal
o Auditory, taste, memory, sensory integration
o Yellow
- Occipital
o Visual
o Purple
Forebrain: basal ganglia
Deeper into the fore brain there is the basal ganglia. The function of the
basal ganglia is a bit simpler than the function of the cortex; it is also found
in more simple species. The basal ganglia are a collection of structures:
caudate nucleus, putamen and globus pallidus.
The basal ganglia controls voluntary movement: control and coordination
of movement patterns rather than deciding to move or activating the
muscles to move. Deciding to move is more in the cortex, it’s more complex. The basal ganglia are more about the
control and coordination of the movement. Parkinson is a problem of the basal ganglia for example, and Tourette’s
syndrome. The basal ganglia works together with the thalamus, substantia nigra and subthalamic nucleus.
Forebrain: limbic system
The limbic system is a group of structures between the cortex and brain stem.
Principle structures are the amygdala, hippocampus and cingulate cortex. The limbic
system regulates emotions and memory in the principle structures.
- Hippocampus → memory
o Representation of episodic memories
o Some of these memories become semantic memories, not associated
with any particular event
- Amygdala → emotional associations
o Emotional associations (emotional memories) are formed here
o They color or stamp all perceptual information with emotional
significance
