Three Parts of the Nervous System
1. Central Nervous System (CNS): brain and spinal cord.
2. Peripheral Nervous System (PNS): nerves of the body
3. Autonomic Nervous System (ANS): has parts of the CNS and PNS. Controls
automatic functions (blood pressure, digestion)
a. Sympathetic division
b. Parasympathetic division
Before we talk about these three parts, let’s talk about the nerve cells.
The brain has about a trillion nerve cells.
NEURON (main cell of the nervous system)
All neurons do three things:
1. Receive a signal.
2. Transmit a signal to another location.
3. Stimulate another cell
a. Another neuron ; transmit signal
b. Muscle ; contraction
c. Gland ; secretion
There are hundreds of different types of neurons, each one is specialized for a particular task (e.g. sense light, smell, tell muscles to contract, etc). They all share certain characteristics.
DENDRITES receive the signal
CELL BODY is where the nucleus, ribosomes, and most organelles are located AXON sends the signals. Some cells have many axons, some have one, some are short, and some are long.
SYNAPTIC KNOBS function to stimulate another cell.
MYELIN SHEATH is a coating of lipids around certain types of neurons. It is like the plastic coating around wires we use around the house. It functions to transmit the signals
faster. This is important because in a fetus, the only fat in the body is on the myelin sheaths of neurons. Therefore, excess vitamins A, D, E, and K will tend to lodge there and interfere with nerve transmission.
MULTIPLE SCLEROSIS is an autoimmune disease where the sheaths of the neurons are destroyed, interfering with the neuron functions in the CNS and brain. Starts to manifest in late teens and early 20’s. It progresses to paralysis and sometimes death. There are treatments, but no cure.
PRE-SYNAPTIC NEURON ; SYNAPTIC CLEFT ; POST SYNAPTIC CELL
How does the signal go through the space? By a chemical transmission.
The synaptic knob has vesicles filled with a neurotransmitter that carries the signal.
Now let’s talk about the three parts of the nervous system.
1. CENTRAL NERVOUS SYSTEM: The brain and spinal cord
THE BRAIN : ANATOMICAL REGIONS
The brain is divided into parts. The largest portion is the CEREBRUM, which makes up
80% of the brain. It’s responsible for consciousness and all the complex behaviors,
sensations, etc. The cerebrum is divided into 2 halves called CEREBRAL
HEMISPHERES. In general, the left side controls the right half of the body, and the right side of the brain controls the left half of the body. These two halves of the brain communicate with each other.
Since the brain is so important, it is protected by the skull, cerebrospinal fluid which cushions it, and meninges which are membranes that surround the brain and only let certain substances cross through to the brain.
The brain is one of the few organs that can only use glucose to get ATP as its energy source. Therefore, without some sugar in our bloodstream, the brain will die. That’s one reason why proper nutrition is so important.
By the way, geniuses have the same size brain as everyone else; they are just more efficient at forming synapses. We don’t use 10% of our brains, we use 100%.
These are tissues that cover the entire CNS. They have fluid between them (CSF) and serve to protect and cushion the brain.
CEREBRAL SPINAL FLUID
CSF is similar to plasma because it is derived from plasma.
1. Allows the brain to float. The brain has the consistency of Jell-O, and weighs
three pounds. Its weight would crush the inferior structures if it didn’t float.
2. It cushions. In sudden movement, like riding a bike into a tree, and hitting the
head on the tree, the brain hits inside the skull in the front, and then in recoil it
hits the back of the skull = closed head injury, not necessarily with a fracture.
This is when the meninges become infected. Can be caused from virus (not that bad) or bacteria (can be fatal). The main symptom is a headache, so when this occurs in an infant, they can’t say where they hurt.
So when an infant presents with a high fever of 104? with no other symptoms, they will
usually test for meningitis, because if they miss it, it’s fatal. The test is a SPINAL TAP,
where a needle is inserted in the low back below the level of the spinal cord. They draw the CSF to look at. It it’s cloudy or bloody, it’s usually meningitis.
HIGHER FUNCTIONS OF THE BRAIN (control behavior and emotion)
THE FRONTAL LOBE involved in planning and judgment. How much time do you
need to be ready for the test? Damage here causes people to become docile and do what they are told. 1930’s when people acted up, they did a pre-frontal lobotomy by going up
the eyelid and stirring up the brain. Stopped in 1960’s; we do it with drugs now. There was a 16 year old rebel who shot himself in the head, but the bullet went too far forward, and his personality improved! Riddlin suppresses CNS in children, stimulates it in adults. In a criminal psych ward, an inmate with a lobotomy got his hand caught in the electric
door, and while his hand was dangling half off, a nurse asked him if it hurt, and he just calmly said, “Yes, quite a lot.” No emotion.
Remember, when you kill a neuron, it does not regenerate; it’s gone forever.
You have different types of memories
MOTOR MEMORY is when you remember things by using your body movements.
Drummers and people who play other percussion instruments are good at this. When someone asks you to spell a word and you have to say, “Wait a minute” and you have to write it out, that’s because you learned the word with motor memory.
MEMORY OF EVENTS is when you remember people and events. This type of
memory is also used to convert short term memory into long term memory. When you have to look up a phone number, and then forget it 5 minutes later, that’s short
term memory. Memorizing new material is accomplished in two ways:
You can’t learn anything brand new; you have to add to what you already know, by putting it into context.
AMNESIA is not caused by a blow to the head; it has to be damage deeper, like from a stroke. Also, a second blow doesn’t cure the first one!
Strokes and Alzheimer’s are most likely to cause amnesia. Nemo’s fish friend, Dorothy,
has RETROGRADE AMNESIA, which is when a person cannot remember anything
new at all.
You can get around amnesia by using motor memory. Give an amnesiac a new puzzle; they’ll do it in 30 mins. The next day, they don’t recognize the puzzle, but they do it in 20 mins, the next day in 10. Therefore, they are learning by motor memory. They can learn their route from home to the market by repetition. But they can’t make a detour, and if anything bumps them off track, they’ll be lost.
No one can remember new things, so you need some context; you need to associate the new thing with something you are already familiar with. That’s why pneumonics are good. If the word “cerebrum” is a brand new word, it sounds like “Sir read broom”, which are words you already know and can visualize. Think of Harry Potter asking a wizard to read the strange words on his new broom: “Sir read broom”, and the wizard scratches his brain (cerebrum) as he tries to read the words. Now it’s easy to remember because you can relate it to something you already know and can picture.
Really, this is just a continuation of the brain. The primary functions of the spinal cord are for simple reflexes and to be a link between brain and body
The spinal cord can also use a SIMPLE REFLEX ARC. They process information
without the brain. So if you touch a hot stove, the sensory input comes into the spinal cord, a special neuron there immediately tells your muscles to contract, and you take your hand off the stove before your brain even knows it.
A doctor can inject Novocain into the spinal cord above the dura mater, so only the nerves are affected. What is that called? An EPIDURAL.
That’s it for the central nervous system. There is less information on the other two parts.
2. PERIPHERAL NERVOUS SYSTEM
These are the nerves of the body outside of the spinal cord and brain.
If a small nerve is cut, it will regenerate. Large nerves are harder to re-grow, but you can still stitch the ends together and you may get healing.
When a nerve gets pinched (e.g. herniated vertebral disc), it damages the nerve by interfering with its signal transmission, causing weakness, pain, or paralysis. Blood supply interfered with
When a body part “falls asleep”, the region is lacking blood flow, impairing the nerve signals as well. Unlike the CNS, when blood is restored, the nerves recover. Damage to the CNS tends to be permanent, but damage to the PNS tends to heal.
3. AUTONOMIC NERVOUS SYSTEM
These are the nerves supplying things we don’t have voluntary control over, such as
digestion, blood flow, urination, defecation, glandular secretion.
The autonomic nervous system has two divisions: sympathetic and parasympathetic.
a) SYMPATHETIC DIVISION
This is involved in ?heart rate and sweating, ?digestive system. E.g. when
running, ?heart rate = sympathetic. When hot ; sweat = sympathetic. The
term “Fight or Flight” refers to the reaction you get when you are scared and
need to run.
b) PARASYMPATHETIC DIVISION
The function of this division is the opposite of the sympathetic; it is “rest and
digest”. It ?heart rate, activates digestive system, and causes salivation,
urination, and defecation.
DAMAGE TO THE NERVOUS SYSTEM
If a person has a spinal cord injury in their cervical region, they could have quadriplegia (arms and legs paralyzed).
If a person has a spinal cord injury in their thoracic region, they could have paraplegia (just legs are paralyzed).