More On Neurotransmitters~Pt. 3

Ok, since I can't find my book Addiction: From Biology to Drug Policy I'll relate some information on neurotransmitters from my notes on the lectures from that class. (I got a burst of energy late one night and just had to rearrange my entire bookcase.) So, I'll apologize in advance if the information is a bit jumbled. If any of you have taken classes on the college level and have taken notes, you'll know that lecture notes tend to hop around some because the professors hop from topic to topic, especially Psych. professors. Also, it might be a bit refreshing to have lecture notes instead of me just referencing text from a book.

I know it's been nearly a month since I've posted the last actual information post, but I did drag out all of my Psych. books today in preparation for more consistent posts in this blog.

Lecture Notes-1/31/06
The communication between neurons, muscles and glands is chemical, not electrical.
Neuromuscular Junction
Skeletal Muscle- Chemical signals from the brain (neurons) tell muscles to move (acetylcholine is a neurotransmitter that functions at the neuromuscular junction).

Acetylcholine is the most prevalent neurotransmitter in the body. The entanglement (loss of structure of the axon) is implicated in Alzheimer's. The loss of structure of the axon prevents the neurotransmitter, acetylcholine, from going where it's supposed to go and is the beginning of Alzheimer's. Acetylcholine causes long-term memory to be generated. It is also very involved in cognition and memory. Dopamine is involved in movement and pleasure.

All neurons have four parts:
1.Cell body-contains the nucleus (DNA) and other structures. The neurotransmitter is made in the cell body and then sent down the axon to the axon terminal (end of the neuron)

2.Dendrites-The structures coming off of the cell body (means branchlike)~they are specialized to receive information. The sending neuron will send its message to the dendrite of the receiving neuron.

3.Axon-Carries information away from the cell body. When information is sent down the axon, it is electrical. There is only one axon/neuron per cell body. The axon can be very long or very short. In the cortex, there are cell bodies that have very little room between them. The axons between these cell bodies are only millimeters long.

4.Axon TerminalThe axon terminal is the pre-synaptic part of the synapse. A dendrite of the receiving neuron is the post-synaptic part of the synapse. (There are also pre and post synaptic membranes.)

The purpose of the axon terminal is to hold on to the chemicals until there is a message to be sent to another neuron (receiving dendrite). The sending and receiving neurons do not touch. There is a small space between the axon terminal and the dendrite, it is called the synaptic cleft, which is fluid-filled. The neurotransmitter will travel through this fluid-filled space to get to the receiving dendrite (chemical action). There are little structures on the receiving dendrite called receptors. When the neurotransmitter has been released from the pre-synaptic membrane, it will react with the receptor. The neurotransmitter fits the receptor like a lock & key. The neurotransmitter, when it binds with the receptor can either open or close it. Sometimes, it just sits in the receptor. This means that nothing else can bind with that receptor. For instance, cocaine prevents the reuptake of dopamine. It stays and builds in the synaptic cleft. Dopamine is associated with the pleaure centers of the brain. That's what causes the high.
Insecticides block the action of acetylcholine in insects and causes them to die. This can also work on humans (note to self: wear gloves)

After the neurotransmitters have bonded with the receptors they go back to the pre-synaptic membrane to wait for another message to be sent. Active process-transporter-takes the neurotransmitter out of the synaptic cleft and puts it back into the sending axon terminal. This process stops neurotransmission. This process of the transporter is called reuptake.
Exception: The neurotransmitter, acetylcholine does not reuptake. It is destroyed by an enzyme. The molecule is split in half (acetyl & choline), which stops neurotransmission (enzymatic destruction).

5.Axon Hillock-The cone-shaped region at the junction between the axon and the cell body where the electrical signal is generated. This is an electro-chemical process.

6.Axon-The long, arrow process that projects from the cell body.

7.Myelin-Fatty insulation around the axon. When myelin is destroyed, it causes inflammation and destruction of the axon (as in Multiple Sclerosis). One part of the axon causes the next part to become electrified (question for later: axon is segmented?) The gaps between sections of myelin are called Nodes of Ranvier. Because of the myelin, the electrical signal jumps from node to node speeding the process of conduction-the electrical signal going down the axon. This jumping conduction is called Saltatory Conduction (fast). Most of the neurons in the brain are myelinated and the electrical signals travel by Saltatory Condution.

A neurotransmitter can be either excitatory-needs to pass on information to the next neuron-or inhibitory-causes the message to be slowed.

Every neuron has a resting rate and will send a signal every so often even without having a message to send (Resting Rate of Firing). Inhibition is the dominant process in the brain. An inhibitory neurotransmitter will slow the neuron's Resting Rate of Firing.

8.Vesicles-The small balloon-like structures which contain the neurotransmitter. When an electrical signal is received, the vesicles will line up along the bottom of the pre-synaptic membrane (they line up before they release the neurotransmitters). There is very little space between the axon terminal and the dendrite (the measurement is called angstrom). The receptors are on the post-synaptic membrane.

9.Action Potential(=electrical signal)-It is called an action potential because the neuron is in a resting state and has potential for transmission of a neurotransmitter.

There are two major receptor sites within the brain:
a.Ionotropic Receptor-A Type of receptor that is "gated", meaning that the neurotransmitter is either going to cause the receptor to open or close. (The gate of the receptor determines whether the ion is excitatory or inhibitory. There are excitatory gates and inhibitory gates.) This receptor site goes from the outside to the inside. When a receptor site is opened, ions will be sucked into the membrane (note to self: wow. "sucked" is like a really scientific term [Just a little humor to keep me awake in class.]). If it is an excitatory ion, those will be the ions that get in. Inhibitory ions that come by the gate will inhibit the neuron from sending.
b.Metabotropic Receptor-This has an effect that can last anywhere from a few seconds to a week. It is where long-term memory occurs, which causes structural changes in the brain permanently.

Well, that's 6 pages of notes from one day of class. I hope it was informational to you at least. It was to me. Ha! I had forgotten most of this. I suppose this blog is not only to impart information, but also to remind me of the things I've learned, which is a good thing.



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