Download Nervous System Outline

Nervous System Outline
I. Nervous System
A. Overall function
1. Control network over all parts of the body
2. Communication between all parts of the body
B. Neuron - About half of all the cells in the nervous system are nerve cells or neurons. ("neur" means nerve)
1. There are three parts to a neuron:
a. Cell body - This is the part of the neuron where the organelles,
including the nucleus, are located.
b. Dendrite - The dendrite is the receiving end of the neuron. It acts as
a receptor of information. Some neurons have numerous dendrites all
branching out as receptors.
c. Axon - The axon is the conducting end of the neuron. It transmits a
message along its way. Some neurons can have very long axons, such
as an axon traveling from your foot to your spinal cord.
2. Nerve - When there are a group of neurons (specifically their axons) bundled
together in the peripheral (anywhere but brain and spinal cord) part of your body,
it is termed a nerve.
3. Nerve Impulse - A nerve impulse is the electrical message that is traveling
along a neuron.
4. Synapse - Sometimes, it takes more than one neuron to arrive at a destination.
The junction between neurons is a synapse. If one neuron is carrying a message,
the message must cross the synapse, in order to get to the next neuron.
5. Neurotransmitter (e.g. Dopamine, Serotonin, Norepinephrine) - A
neurotransmitter is a chemical of the nervous system that carries messages across
the synapses.
6. Myelin - Some neurons (specifically their axons) are coated with a white fatty
substance called myelin. Since it is white in color, these neurons are referred to as
white matter. The function of myelin is to transmit messages very, very fast. For
example, an axon without myelin may transmit a message at 2 mph. Compare this
with a myelinated axon that may transmit a message at 200 mph.
C. Classification
1. CNS - Central Nervous System
a. Brain
b. Spinal Cord
c. This is the part of the nervous system where thoughts are formed,
memory is stored, information is processed and the whole body is
controlled.
2. PNS - Peripheral Nervous System - This is the part of the nervous system
carrying messages towards and away from the CNS.
a. Sensory - As we sense information about our inside and outside
environment, the information is carried by sensory neurons towards the
CNS.
b. Motor - As information is carried to muscles and glands in order to
have a response, it must travel along motor neurons. They carry motor,
or movement, information away from the CNS.
1-Somatic - If that motor information is going to skeletal
muscles, such as a Biceps muscle, it travels in a somatic
motor neuron.
2-Autonomic - If the motor information is going to
cardiac muscle, smooth muscle or glands, it is carried
along with autonomic neurons. Your Fight or Flight
response travels along autonomic neurons. [If you have
not heard of Fight or Flight, these are all of the automatic
changes that occur in your body when you are so angry
that you want to fight, or so scared that you want to run.
Your heart beats faster, your eyes open wide, your airways
open and breathing is faster and your mouth is dry.]
D. Brain - ("enceph-" means brain. ) - Located within your skull is the complex brain. Only a
few of its parts will be studied.
1. Medulla oblongata - The very lowest portion of the brain is the medulla
oblongata. It is the connection between the brain and spinal cord. Motor and
sensory pathways cross to the other side of the body at this location. Therefore, a
stroke on the left side of the brain affects the right side of the body. Also located in
the medulla oblongata are some very important reflex centers that control
breathing, heart rate and blood pressure.
2. Cerebellum - Located at the lower back of the brain, the cerebellum is the
headquarters for balance and coordination.
3. Hypothalamus - The hypothalamus is a tiny area in the center of the skull that
controls many homeostasis mechanisms. Some of its functions include regulation
of: body temperature, hunger, thirst, the Autonomic neurons and
stimulating/inhibiting the pituitary gland (to be discussed soon).
4. Thalamus - Located just above the hypothalamus is your sensory relay center,
the thalamus. Sensory information must filter through the thalamus which decides
whether or not to send the sensory information (such as sight, sound, touch) on to
higher centers of the brain.
5. Cerebrum - The largest, highest center of the brain is the cerebrum. This is
where conscious awareness occurs, as well as thinking, memory, intelligence and
integration of sensory information by formulating a response.
6. EEG - Since all neuron activity is electrical, brain activity must be electrical.
Electrodes placed on the skin can detect the electrical "brain waves" and an
electroencephalogram can be performed and analyzed.
E. Spinal Cord ("Myel-" means spinal cord. What would be inflamed if you had
encephalomyelitis?)
1. Located within your vertebrae is the other part of your CNS, your spinal cord. It
has the job of sending messages up towards the brain (this would be sensory
information) and movement messages down away from the brain (this would be
motor information).
2. Reflex - A reflex is an unconscious, fast, repeatable response to a stimulus. For
example, without even thinking about it, you automatically remove your hand from
the hot stove as a reflex. After you have pulled away, thus protecting your hand,
you can send a message to your brain and process it and yell "ouch" - but this is
not part of the reflex. The reflex only involves touching the stove and reflexively
pulling away from it. The spinal cord is responsible for many reflexes in your body,
such as the example provided. The message must go from your hand to the spinal
cord (sensory neuron) and then back to your muscles to move your hand (motor
neuron).
3. Meninges - Meninges are tough membranes surrounding the brain and spinal
cord. They are protective. Within the meninges is a fluid cushion, which also
contains nutritive substances for the brain and spinal cord, called the CSF, or
Cerebrospinal Fluid. If your meninges are inflamed, you have meningitis. Its
seriousness results from the fact that the swelling can compress the brain and
spinal cord since they are all in enclosed chambers of bone.
F. Disorders of Nervous System
1. Brain damage - The brain can be damaged with limited ability to recover.
a. The brain needs oxygen. It must have aerobic metabolism for ATP
production. Lack of oxygen to the brain for more than 5 minutes can
kill brain cells.
b. The brain needs glucose in order to metabolize it into ATP. If the
brain is denied glucose for longer than 15 minutes, brain cells can die.
c. Neurons lack mitosis
2. Epilepsy - Although epilepsy manifests as rapid muscle tremors, it is actually a
brain disorder. The brain fires off abnormal signals that travel along neurons to
skeletal muscle causing it to contract. Larger seizures are accompanied by loss of
consciousness. [Interestingly, the term epilepsy means seizure, and derived its term
because in ancient times, it was thought that demon spirits "seized" the person and
that is how the convulsions occurred.] In about one-fourth of the cases of epilepsy,
an exact cause can be discovered, such as an injury or brain infection. In the
remainder of the cases, an exact cause cannot be found, although epilepsy tends to
run in families. Treatments include correcting the cause, if it is known, and drugs to
control and decrease the frequency of the seizures, such as Dilantin, Primidone and
Phenobarbital.
3. Multiple sclerosis - This disease literally means many hard scars. It is an
autoimmune disease in which the immune system erroneously attacks the myelin
sheaths of the white matter neurons. This results in numerous short circuits along
these nerve pathways. As a result, the person can have difficulty in vision, memory,
judgment and walking. It is a chronic disease that typically progresses slowly.
5. Cerebral palsy - If the motor centers of the cerebrum are damaged around the
time of birth, cerebral palsy occurs which can impair motor abilities. Causes
include German Measles virus, radiation exposure, and oxygen starvation to the
baby's brain at or around the time of delivery.