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Unit 2
Neuroscience Fundamentals
Last Updated: 6/3/2024
Est. Read Time: 13 min
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Welcome to the second unit of BCI Bin. This unit will cover the basics of neuroscience - the study of the nervous system.
The nervous system is a complex network of nerves, veins, and cells that carry messages to and from the brain through the spinal cord to various body parts.
It's responsible for controlling and coordinating all bodily functions such as sensations, actions, and thoughts.
The field of neuroscience contains an abundance of information that wouldn't be possible to cover in one place. Therefore, this unit will provide a brief overview of the most essential concepts while providing resources for topics that are tangential to the fundamental concepts.
These core concepts include:
The major anatomical sections of the brain
How neurons work on a molecular level
Neural networks & the structure of the nervous system
As a disclaimer, while it's possible to skip past this unit and move straight to the more technical aspects of BCIs, it's not recommended.
By choosing to go without understanding the fundamentals of neuroscience, you'll miss out on most of the context and background that makes BCIs so fascinating.
Additionally, understanding the basics will aid in your comprehension of the more advanced topics that will be covered in later units of BCI Bin.
Anatomy of the Brain
The brain is divided into three main sections: the
brainstem/cerebellum
, the
limbic system
, and the
cerebral cortex
.
Brainstem & Cerebellum
The
brainstem
and
cerebellum
are the most primitive parts of the brain, responsible for most of the basic functions necessary for survival.
CrashCourse | Anatomy & Physiology
In his very beginner-friendly course on anatomy, Hank Green explores the brainstem, cerebellum, and other parts of the nervous system and human body.
The
brainstem
consists of the
medulla oblongata
,
pons
, and
midbrain
, while the
cerebellum
is isolated towards the back of the brain.
Wikipedia | Brainstem Diagram
Wait But Why | Brain-Machine Interfaces
In his article on Brain-Machine Interfaces, Tim Urban breaks down most of the brain's components with helpful illustrations and analogies. He describes the
medulla oblongata
as "really not wanting to die," so it
regulates autonomous functions
like breathing, heart rate, and blood pressure.
The
pons
is responsible for
maintaining your sleep-wake cycle
and, acts as an
information highway
between major brain areas such as the cerebellum and cerebrum.
The smallest part of the brainstem, the
midbrain
, controls eye movement, auditory and visual processing, and alertness. However, it's
mostly redundant
in humans because other brain areas in the cerebral cortex simultaneously perform most of these functions.
UCB | Overview of the Brainstem
For a more in-depth look at the brainstem and its processes, with a real example of a human brain dissection, see this video from the University of California, Berkeley.
And lastly, the
cerebellum
is responsible for
coordinating
voluntary and reflexive
movements
,
balance
, and
posture
. At the same time, it's also involved in
motor learning
and
cognitive functions
such as attention and language.
Limbic System
The limbic system consists of inner brain structures crucial to, once again, your primitive survival instincts, and your emotions and short-term memory.
Britannica | Limbic System
The
limbic system
includes the
hippocampus
,
amygdala
,
thalamus
, and
hypothalamus
in addition to a few other other smaller glands not shown in the graphic above.
The
hippocampus
is responsible for
forming new, short-term memories
as well as connecting emotions and sensations to memories.
MIT | Neural Circuits of Intelligence
Units 1.6 and 1.7 of this course on brains and machines from MIT provides excellent examples of how the hippocampus is involved in
memory formation and recall
.
The
amygdala
, split into two parts, is responsible for
processing emotions
and emotional memories.
Right amygdala
is associated with
negative emotions
such as fear, anxiety, and sadness, while
left amygdala
is associated with these
same negative emotions
, but with
positive emotions
such as joy and pleasure thrown into the mix.
The
thalamus
sits at the brain's center, from where it
relays signals
from your sensory organs to the cerebral cortex. It also
regulates sleep
,
alertness
, and
consciousness
.
The
hypothalamus
, a small but powerful gland located below the thalamus,
maintains homeostasis
in the human body. It regulates body temperature, hunger, thirst, and sleep and controls the body's fight or flight response.
Nerd Ninja | Limbic System
This video from Nerd Ninja provides an in-depth overview of the anatomy and functions of the limbic system. His channel also has many other great neuroscience videos worth exploring.
There are also a plethora of
other glands and structures
in the limbic system that have various functions, all of which
share overlap
with the structures already mentioned.
NCBI | Neuroanatomy, Limbic System
While there are too many of these glands and structures to list here, if you're interested in learning more about the rest of the limbic system, see this short paper from the National Center for Biotechnology Information.
Cerebral Cortex
The
cerebral cortex
, also referred to as the
cerebrum
or
neocortex
, is the largest part of the brain and is responsible for
higher brain functions
such as thought, perception, planning, movement, and much more.
It's divided into four lobes:
ISB | The Cerebral Cortex
The most sizeable lobe, the
frontal lobe
, is what makes you, you. It's responsible for your
personality
,
reasoning
, and
decision-making
. On top of that, it contains the
motor cortex
, which is in charge of voluntary movement.
CRASH | Essentials of Neuroanatomy
The
parietal lobe
's responsibility is
processing sensory information
, mainly through the primary somatosensory cortex. In this video on neuroanatomy, Dr. Bolin shows how
well mapped out
the somatosensory cortex is, with each part of the body having an individual subsection of the cortex.
The
occipital lobe
effectively has one job -
processing visual information
. Everything from depth perception to color recognition to visual memory formation is handled here.
McGraw-Hill | Principles of Neural Science
Finally, the
temporal lobe
has two responsibilities,
processing auditory information
and handling medium to long-term
storage for memories
. This textbook from Dr. Kandel provides a comprehensive overview of the temporal lobe as well as all of the other structures of the brain.
Meninges
The final piece of macro-brain anatomy covered in this unit is the
meninges
, which isn't a part of the brain but rather a series of
layers surrounding it
.
Between the brain and the skull, there are
three primary layers
of meninges: the
dura mater
,
arachnoid mater
, and
pia mater
. All of which can be broken down further into more distinct layers.
ThoughtCo | Functions and Layers of the Meninges
The
dura mater
and
arachnoid mater
are the outermost
protective layers
of the brain that exist to safeguard it.
The
dura mater
is a
durable layer
that defends the brain from
physical damage
, while the
arachnoid mater
is a thin,
web-like layer
that suspends the brain and
cushions it
from sudden movements.
The
pia mater
, the innermost layer, is a thin, delicate layer that clings to the brain's surface. It's responsible for
adhering blood vessels
to the brain and helps protect them from infection.
Neurons
Now that you have a high-level understanding of a macroscopic view of the brain, let's dive into the molecular side of things, where we'll explore the fundamental building blocks of the brain -
neurons
.
We'll explore the different types of neurons, their structure, and their methods of communication, both in isolation, and when combined with networks of other neurons.
Neuron Types
Neurons are not only the atomic unit not only of the brain but of the body's
entire nervous system
. They're constantly receiving, processing, and transmitting information throughout the body at every hour of the day.
MindProject | Neurons, Synapses, and Neurotransmission
While there are as many as
10,000
specific types of neurons (some of which can be seen above), generally speaking, there are three broad categories that these types fall into:
Sensory neurons - convey sensory information
Motor neurons - convey motor information
Interneurons - convey information between neurons
Nagwa | Nerve Cells
Sensory neurons
, typically encountered in the peripheral nervous system (
PNS
)
transmit sensory information
from sensory organs to the central nervous system (
CNS
). Of the total neurons in the PNS, sensory neurons comprise
90%
.
The CNS and PNS are
subsets
of the overall nervous systems that will be covered in more detail later in the nervous system section of this unit.
Different types of sensory neurons are responsible for different types of sensory information. For example, some neurons detect temperature, others detect pain, and some specialize in taste. The shape of these neurons largely varies depending on their function.
Motor neurons
, on the other hand, transmit motor information from the
CNS
to
muscles
,
organs
, and
glands
. They make up the motor division of the PNS, which is the remaining
10%
.
Lastly,
interneurons
, found
exclusively
in the
CNS
, transmit information between mostly other interneurons, and between sensory and motor neurons.
QBI | Types of Neurons
They're the
most abundant
type of neuron in the body by far, comprising around
99% of all neurons
. For more information on the different types of neurons, see this article from the Queensland Brain Institute.
Individual Neuron Breakdown
For a closer look at the structure of neurons, let's examine the most common type of neuron in the human body, the multipolar pyramidal neuron.
Socratic | Multipolar Neuron Example
HUJI | Synapses, Neurons and Brains
We'll briefly cover each component in the above diagram using definitions from the second unit of this free course from the Hebrew University of Jerusalem and additional resources mentioned at the end of this unit.
The overarching purpose of the neuron is to process and transmit information to other neurons, muscles, or glands. In the diagram neuron, this
flow of information
happens from
left to right
.
It begins with the
dendrites
, which
receive chemical signals
from other neurons at connection points called
synapses
.
The
soma
, often called the "control center" of the neuron,
continually listens
for these signals;
once it's received enough
of them, it will transmit a
new signal
via the
axon
.
The
axon
is an extended wire (anywhere from a few micrometers to over a meter) that
carries the signal
from the
soma
to the
axon terminals
, where the signal relays to
muscles
,
glands
, or
other neurons
through their synapses.
Depending on the neuron type, the axon might wrapped in a series of
myelin sheaths
, which
speed up
(300-fold) the
transmission
of the signal. Interneurons typically aren't myelinated, while sensory and motor neurons usually are due to the long distances the signals they send need to travel.
Concepts of Biology | How Neurons Communicate
The transmission of signals between neurons at the synaptic level is abstracted here due to its complexity. The actual process is very intricate and involves the
release and absorption
of chemicals called
neurotransmitters
. This procedure is explained in great depth in chapter 16.2 of this biology textbook, available for free on BCcampus.
Electrical Signals & Brain Waves
As previously mentioned, when the soma receives enough signals, it will transmit a new signal. At the risk of oversimplification, this
signal's transmission
, from dendrites to axon terminals, can be called an
action potential
.
HarvardX | Electrical Properties of the Neuron
This
action potential
can be considered a
wave of electrical activity
via depolarization and repolarization across a neuron's membrane. This is covered in more detail in this free online course offered by Harvard.
These
action potentials
are
binary
, meaning when the threshold has been met, the neuron either
fires at 100%
or,
doesn't fire at all
.
This means individual neurons
can't fire "stronger"
signals but rather can fire
more frequently
to convey
more information
to other neurons.
DB | Action Potential vs Synaptic Potential
This graph from DifferenceBetween demonstrates the binary nature of action potentials as well as failed initiations when the threshold isn't met.
In the first unit of BCI Bin, a few BCIs were introduced that listen to the brain's electrical signals, such as
EEGs
, and the majority of
invasive BCIs
.
For
invasive BCIs
, these
electrical signals
are
aggregates
of the
action potentials
of millions of
neurons firing in unison
.
EEGs
, on the other hand, listen to similar electric signals called
post-synaptic potentials
. The article tied to the diagram contains more information on these signals and how they're emitted.
The
brain waves
recorded by BCIs result from
synchronized firing
of groups of neurons. These waves can be categorized into different types based on
frequency
and
amplitude
.
The most common brain wave types are
alpha
,
beta
,
gamma
,
delta
, and
theta
waves. Each wave type is associated with different states of consciousness, such as relaxation, alertness, and deep sleep.
WSU | Generating Brain Waves
This paper Western Sydney University offers a closer look at the various brain waves and how they're generated.
The Nervous System
In isolation, a neuron is useless. However, when connected to muscles, sensory organs, and around 85 billion other neurons, it becomes a piece of the most information-dense and self-structuring matter known to mankind.
The
nervous system
is a broad term encompassing everything covered in this unit and more. As mentioned in the neuron types section, it's
divided
into the
CNS
and
PNS
.
The
CNS
(central nervous system) consists of the neurons in your
brain and spinal cord
, and the
PNS
(peripheral nervous system) consists of the neurons that
project outwards
from the
spinal cord
into the rest of the
body
.
Khan Academy | Nervous system physiology
This course from Khan Academy covers a few basic concepts of the nervous system and the sensory systems it's connected to.
Neural Networks
Within the
central nervous system
, billions of neurons form together to create
neural networks
that comprise
every anatomical structure
of the brain.
Similar to neural networks found in machine learning, these networks
dynamically adapt
based on the information they receive and the tasks they perform.
The
ability
of these networks
to change
is called
neuroplasticity
, and while it's at its highest in babies, it remains into the adult years of human lives, however, at a reduced rate. This is what allows us to learn, build habits, and more.
Brain Matter
When viewing a vertical slice of the brain, it can be observed that the brain is divided into two types of matter:
gray matter
and
white matter
.
SimplyPsychology | Brain Matter
The
outside layer
of the cerebrum is often called
gray matter
. This primarily consists of
interneurons
and the
cell bodies
of sensory and motor neurons.
The
inside layer
is called
white matter
. It consists of the
axons
and their
myelin sheath
wrappings. These myelin sheaths are made of fatty tissue that's the color white, which is where this matter gets its name.
The last element seen in the vertical slice diagram is a
ventricle
. These are
pockets
in the brain filled with
cerebrospinal fluid
and help cushion the brain and keep it buoyant.
Nervous System Support
Up to this point, the brain has been portrayed as exclusively neurons, however, there's also an entire underlying
support system
of
cells and structures
that help the brain function properly.
First, every cubic millimeter of the brain is packed with a meter's worth of
complex blood vessel networks
. These vessels
deliver oxygen and nutrients
to the brain and
remove waste products
.
Next, there are six different types of cells called
glia
, or
glial cells
, responsible for
maintaining homeostasis
in the CNS and PNS.
SimplyPsychology | Glial Cells
These cells do everything from
cleaning up chemicals
released into synapses to
wrapping axons
in myelin sheaths, to acting as the
brain's immune system
.
AnatomyZone | Neuro Basics - Glial Cells
The total glia-to-neuron ratio is around 1:1 in the human brain. For more information on each of the specific glial cells and their functions, check out this video from AnatomyZone.
Additional Content
The content in this unit is only a fraction of the information available on neuroscience. If you're interested in learning more, there are a few additional, highly recommended resources.
Duke | Medical Neuroscience
The first is this course from Duke University which covers more of the
medical aspects of neuroscience
. While it's designed for those already in the medical industry, it's likely still accessible for those with a basic understanding of biology and a determination to learn.
Academic Press | Fundamental Neuroscience
Next is a textbook from neuroscientist Dr. Squire on the
fundamentals of neuroscience
. This book extensively covers nearly every corner of the field from a cellular and molecular background.
Yale | Theoretical Neuroscience
Lastly is a book from neuroscientists Peter Dayan and L.F. Abbott on the
theoretical side of neuroscience
. Due to the abstract nature of the book, it's only recommended for those with a strong technical background looking to explore the mathematical/computational realm of neuroscience.
Feedback
Reach out via X
That's all for the second unit of BCI Bin. If you have any questions or feedback, please let me know by sending me a message on X.
Otherwise, feel free to continue exploring the resources provided in this unit to learn more about the fascinating world of neuroscience.
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