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There are two big parts that I will have to start 

with. 

The Central Nervous System (CNS) is the part of 

the nervous system that includes the brain and 

the spinal cord.

The Peripheral Nervous System (PNS) is the 

part that includes all of the other nervous 

tissue in the body. Nervous tissue is 

everywhere! The nerves in the nervous tissue 

are what tell your brain what is going on when 

you touch, see, hear, smell, or taste something. 

Another important part is the spinal cord. A 

human spinal cord is a big stack of 31 

vertebrae that support your body. Many nerves 

go through your spinal cord to send messages 

to the brain. Each segment of your spinal cord 

has a pair of spinal nerves branching off to 

collect messages from the rest of your nerves 

(from the PNS). 

Meninges is a special word for the membranes 

that protect your spinal cord. They also carry 

blood for your body. 

The spinal cord is also divided into 31 segments, 

called vertebrae, that each have a pair of spinal nerves. 

White matter is made of mylinated axons and is closer

to the skin than gray matter. It is used to relay information

to the brain. Ascending tracts carry sensory information to 

the brain,   descending tracts carry motor commands to the 

spinal nerves. Basically, they tell the brain whats going on and

the nerves how to respond. 

Gray matter is made of unmylinated tissue and is used

to process the information about spinal reflexes. 

Dorsal roots are parts of the spinal cord. They are used to 

gather and send sensory information to the brain. Ventral roots 

are also parts of the spinal cord. They are used to receive motor 

commands from the brain and relay the information to the 

nerves. Spinal nerves have both functions. They both send 

sensory information and receive motor commands. 

Cervical Plexus: used for 

the neck

Brachial Plexus: for the 

arms and part of the neck

Lumbar Plexus and Sacral 

Plexuses: for the lower 

back, pelvis and legs

Spinal reflexes are fast and immediate responses 

that are triggered by different stimuli. These 

reflexes are controlled bu the gray matter in the 

spinal cord. The process it goes through has 4 

steps, sort of like a relay race...

1. A stimulus is activated in some part of the body 

which can be anything you feel.

2. This will activate a sensory neuron which will 

send the signals to the brain to be processed.

3. When the brain understands what is going on, it 

sends a response by activating a motor neuron.

4. This will pass a signal to an effector, which is a 

muscle or gland that will respond to the signal.

CSF stands for cerebrospinal fluid. It has a very 

important job because it has to not only protect 

the brain from physical harm, but it also has to 

help maintain the chemical levels in the brain. It 

helps control the intake of nutrients and releasing 

waste as well. 

The cerebrum is the biggest part of the brain. 

It controls all conscious thoughts and helps you 

learn and think. It also helps to sort and 

interpret the information that comes into the 

brain from the nerves. 

The cerebellum is what helps us 

move. It makes small adjustments so 

that our movements are just right. It 

helps with posture as well. 

The brain stem processes all the 

information between the spinal cord 

and the brain. We'll talk more about 

the parts of the brain stem later in the 

book. 

The cerebrum is split in half by a line called 

the logitudnal fissure. The two sides of the 

brain are called hemispheres. The brain has 

lots of folds and ridges on it which increases 

the surface area so that there is more room for 

gray matter. The outer layer of the brain is 

called the cerebral cortex.

The cerebrum is also split into four parts called 

lobes. They each have their own name and 

function. 

The corpus callosum connects the two 

hemispheres of the brain. The contra lateral 

refers to the fact that the two different 

hemispheres, or sides, send motor commands 

to the opposite side of the body. Which means 

that the left side of the brain controls the right 

side of the body. 

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