Hey guys, Welcome to this Mometrix video over the nervous system.
All systems, and parts of the body are important, but the nervous system is the system that
has it’s fingers in EVERYTHING your body does.
It is the system that literally controls every process within your body.
The nervous system includes anything within the body that would allow you to sense; so,
the brain, spine and spinal cord, all nerves, and any other sensory neurons.
The Nervous System has four main roles or functions.
First, to collect and receive information internally and externally; so, from within
the body and outside of the body.
Second, to process or derive meaning from the information collected and received.
Third, after the information has been processed, the nervous system forwards that information
to the appropriate party; so, to the muscles, organs, or glands.
This information sets them up to react how they need to.
And, fourth, the nervous system dispatches the information to the regions of the brain
that handle processing of the information.
Divisions of the nervous system: The nervous system, just like every other
structure and makeup of our bodies, is very ordered and systematic.
You can think of the nervous system as having two main divisions, and then several subdivisions
that fit within those two divisions.
The two divisions of the nervous system are the Central Nervous System and the Peripheral
Nervous System.
First, we will take a look at the Central Nervous System, and what exactly that includes.
Function of the CNS: The main function of the central nervous system
is to incorporate the information it is getting and systemize the information so that it can
queue a proper response.
Components of the Central Nervous System: The central nervous system is composed of
the brain and the spinal cord.
These two components encompass several other components.
So, we will take a closer look at the brain first.
The brain has six different regions: The cerebellum, cerebrum, medulla, brainstem, thalamus, and
hypothalamus.
Regions of the brain: The cerebellum sits right behind the upper
portion of the brain stem (which is where the brain and spinal cord connect), and consists
of two half spheres (or hemispheres).
The cerebellum is the region of the brain that coordinates movement, and where various
features of motor learning take place.
In other words, the cerebellum is the part of your brain that allows for balance, coordination,
speech, and posture; as well as things like muscle memory.
The cerebrum sits in the top portion of the cranial cavity.
The cerebrum is separated into a left and right hemisphere by a trench like line called
the longitudinal fissure.
Now, perhaps counterintuitively, the left half of the cerebrum manages the right side
of the body and the right half manages the left side of the body.
However, even though there is a groove that distinctly separates the two halves of the
cerebrum, there is a bundle of neural fibers, called the corpus callosum, that connects
the two halves, and allows them to work together.
The cerebrum is made up of four different lobes: the frontal lobe, the temporal lobe,
the parietal lobe, and the occipital lobe.
Frontal Lobe: The frontal lobe, like it’s name suggests,
is at the front most region of the brain, and, out of the four lobes, is the biggest.
The frontal lobe is split from the parietal and temporal lobe by fissures.
The fissure that separates it from the parietal lobe is called the central sulcus, and the
fissure that separates it from the temporal lobe, which is even deeper, is called the
lateral sulcus.
The frontal lobe contains the primary motor cortex.
The primary central cortex (M1) is one of the main components of the brain included
in the body’s motor function.
The primary motor cortex initiates electrical signals and impulses that initiate body movement.
The frontal lobe is also essential for problem solving, speech and articulation, and it’s
accountable for personality traits.
Temporal Lobe: You actually have two temporal lobes, one
for both hemispheres.
Your temporal lobes are located near your ears, and they mainly function in auditory
processing.The temporal lobe taps into other roles as well, such as visual memory, your
ability to learn language, and emotion association.
Parietal Lobe: The parietal lobe is set between the occipital
lobe and the frontal lobe.
The parietal lobe has a really big job of having to process the information that it
receives within milliseconds.
The somatosensory cortex is located inside of the parietal lobe, and is crucial for processing
the information from touch.
The somatosensory cortex allows us to pinpoint the exact locality of a touch perception,
and helps to distinguish pain levels and temperature.
The parietal lobe is important for our depth of perception, and communicates with other
parts of the brain in order to perform other tasks.
Occipital Lobe: The occipital lobe sits in the back part of
cortex.
The main function of the occipital lobe is to process visual information from the eyes
and relay that information.
The occipital lobe has to very quickly process that information, so that we are able to respond
accordingly.
Medulla
That is an overview of the cerebrum, now let’s look at the medulla, more officially known
as the medulla oblongata.
The Medulla is a section of your brainstem, and remember, your brainstem is where you
brain and spinal cord connect.The medulla is one of the three parts of the brainstem.
The medulla has immediate control over numerous autonomic nervous system responses, it aids
in the control of particular regions of the body, and it also plays a role in motor functions,
and outward motion.
The medulla is very important, just like every other part of our brain.
The medulla helps control breathing, and it controls our heart rate.
The medulla functions involuntarily.
The medulla responds to various heart functions by dilating the blood flow so that there is
a higher or lower amount of oxygen circulation, it can help by responding in fight or flight
situations by switching digestion off or on, causes us to cough or sneeze to get rid of
unwanted particles that get into your nasal cavity, and also controls vomiting or swallowing
in order to dispel anything that may bring harm to you.
The fourth region of the brain that we will look at is the brain stem.
The brains stem has three different parts: the medulla (which we just looked at), pons,
and midbrain.
The pons sort of functions as a message headquarters for many other parts of the brain.
It aids in communication between brain sections, like the cerebrum and cerebellum.The pons
is right above the medulla, and beneath the midbrain.
So, it sits right in the middle.
Many essential nerves stem from the pons.
The vestibulocochlear nerve permits sound to proceed from our ears into our brain.
The abducens nerve permits the eyes to move and look horizontally.
The trigeminal nerve allows for us to experience feeling in the face, and the facial nerve
allows for us to actually make facial expressions.
The pons helps in the duties of the medulla, and it is linked to managing our sleep cycles.
Now, the midbrain is called the midbrain, because it sits between the forebrain and
the hindbrain; but it’s important to note that out of the three parts of the brain stem
it is not located in the middle.
The midbrain functions, like the medulla, as this super message headquarters between
the forebrain (or cerebral cortex) and the hindbrain (or the cerebellum and brainstem).
The midbrain allows you to incorporate sensory data coming from your eyes and ears with data
coming from your body’s muscle movements; helping it to adjust your movements based
on important information.
All three parts of the brainstem function involuntarily.
The Thalamus is the fifth region of the brain.The Thalamus sits right above the brainstem sandwiched
between the midbrain and cerebral cortex.
The primary job of the thalamus is to inform the cerebral cortex of any sensory or motor
stimuli.
The thalamus also helps to control sleep, and aids in keeping us awake and alert.
The thalamus, along with the hypothalamus, epithalamus, and subthalamus, is a part of
the diencephalon, also sometimes called the interbrain.
The diencephalon is the area where the vertebrate neural tube is located, which helps bring
about the formation of the forebrain.
The sixth, and last, region of the brain is the hypothalamus.
The hypothalamus is positioned below the thalamus and is the bottom part of the diencephalon.
One of the main functions of the hypothalamus is that it connects the nervous system to
the endocrine system; which allows the hypothalamus to regulate our body’s temperature.
The hypothalamus also aids in certain metabolic processes, and helps to regulate the autonomic
nervous system.
That was a closer look at the brain itself.
The spinal cord is the other component that makes up the central nervous system.
The spinal cord administers motor data coming from our brain to the appropriate parts of
our body, and helps to perform slight reflexes.
It also administers sensory data directly from the peripheral nervous system to the
brain.
The spinal cord consists of 31 pairs of spinal nerves; because each of these nerves include
motor and sensory axons, they are referred to as mixed nerves.
So, that was the Central Nervous system.
The second, main division of the nervous system is the peripheral nervous system (PNS).
The peripheral nervous system is made up of nerves and what is called the ganglia.
Nerves are bundles of nerve fibers, also known as axons.
There are two types of nerves in the peripheral nervous system: Spinal nerves and cranial
nerves.
There are 31 pairs of spinal nerves, and 12 pairs of cranial nerves.
Ganglia refers to a cluster of neuron somas (or cell bodies).
The individual cell body attach to dendrites.
The dendrites send information to neurons.
The axons or nerve fibers then communicate that information to other neurons.
It’s all a connected web.
These nerves and ganglia are located around and outside of the brain and spinal cord.
The primary function of the peripheral nervous system is to link the central nervous system
to the body’s organs and appendages; thus acting as the primary messenger between the
brain, spinal cords, and everything else in the body.
You can kind of think of the peripheral nervous system as the system that helps our brains
and bodies to understand the world around us.
The peripheral nervous system has two subsystems, the somatic nervous system and the autonomic
nervous system.
The somatic nervous system is the part of the peripheral nervous system that is linked
to voluntary bodily movements.
It contains two parts, the sensory nervous system, as well as the somatosensory system,
which is a part of the sensory nervous system.
The sensory nervous system is responsible for processing, as you might guess, sensory
data.
The most familiar sensory systems are the ones that control touch, taste, smell, hearing,
and vision.
Now, the somatosensory system focuses on the conscious recognition of temperature, pain,
touch, pressure, movement, position, and any sort of vibration.
The somatosensory system communicates different sensations identified near the vicinity of
the body via the spinal cord, brainstem, and up to the sensory cortex located in the parietal
lobe.
The sensory nervous system contains sensory neurons (or afferent neurons) and motor neurons
(efferent neurons).
Afferent neurons transmit stimuli to the central nervous system, as opposed to transmitting
them from the CNS.
Efferent neurons, in response to the afferent neurons, transmit signals from the central
nervous system to the rest of the body.
This transmission of stimuli through afferent neurons to the CNS, and then from the CNS
to other parts of our body, allow for us to perform voluntary body movements as well as
moderate involuntary reflex arcs.
The Autonomic Nervous System is the other part of the peripheral nervous system that
manages involuntary movements and functions- involuntary meaning that these movements happen
without us be consciously in control of them happening.
The autonomic nervous system also communicates information to our internal organs.
There are two main divisions within the autonomic nervous system: the sympathetic nervous system,
and the parasympathetic nervous system.
The sympathetic nervous system is the system that gets our body ready for the reaction
that has been familiarized as the “fight or flight” response.
When our body is being threatened or at risk for potential injury, this is the system that
controls our response.
The sympathetic nervous system causes our bodies to become keenly alert, speeds our
heart rate, causes muscle contraction, and shuts off any function that is not essential
for survival.
The overall functioning of the sympathetic nervous system is largely due to the neurotransmitter
acetylcholine.
This neurotransmitter binds to nicotinic receptors to trigger the release of norepinephrine which
is produced by the adrenal gland to prepare our body and brain for action.
Nicotinic receptors are the main receptors in the muscles for motor neuron to muscle
correspondence, that manage the contraction of muscles.
The sympathetic nervous system originates in the thoracic and lumbar regions of the
spinal cord.
The parasympathetic nervous system, which is the other part of the autonomic nervous
system, manages the body’s function when at rest.
“Rest and Digest” is the phrase given to reference the response of the parasympathetic
nervous system .The parasympathetic nervous system works to conserve homeostasis within
the body.
It does the opposite of the sympathetic nervous system, and instead relaxes the body’s muscles,
and slows our heart rate.
Its job is to restore everything to a state of relaxation, and balance.
The parasympathetic nervous system increases bowel movements, and urinary output.
The neurotransmitter acetylcholine also plays a huge role in the parasympathetic nervous
system by binding to muscarinic receptors, allowing the contraction of smooth muscles.
This is what allows the parasympathetic to slow down the heart rate, regulate digestion,
and relax muscles.
The parasympathetic nervous system originates in the sacral portion of the spinal cord.
It’s important to note that both the central, and peripheral nervous system enlist the acetylcholine
receptors, both nicotinic and muscarinic.
We just covered a lot of information.
But, here is a very, very generalized diagram of the Nervous system to help you remember
the main parts.
You start with the nervous system itself.
Then, you have the two main divisions: the central nervous system (which includes the
brain and spinal cord), and the peripheral nervous system (which is made up of nerves
and ganglia).
The peripheral nervous system then has two subdivisions: the somatic nervous system (which
controls voluntary movement), and the autonomic nervous system (which control involuntary
movement).
Then, both the somatic and autonomic nervous systems contain two subdivision.
The somatic nervous system contains the sensory nervous system and the somatosensory system
(which is a part of the sensory nervous system).
And, lastly the autonomic nervous system contains the sympathetic nervous system (which controls
our “fight or flight” response), and the parasympathetic nervous system which controls
our “rest and digest” response).
If all of these systems seems pretty interconnected, the answer is yes.
I hope that this overview of the nervous system has been helpful to you.
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