"Ask Me" about Introductory Biology

[Tron]

That's right. Tron, OOT Legend, has finally made an "Ask Me" post.

I certainly don't expect this post to achieve the popularity that the great Ask Me's of the past concerning Magic The Gathering and incarceration did, but I do hope that some of you will find it useful. To be completely honest, I am not making this post only out of my love for OOT, but also out of my love for good grades, because I have a final in (You guessed it!) introductory biology in a few days and I could use all the studying I can get. I figured this would be a neat way to ehance my knowledge and share it with the forum that has given me so much. [img]/images/graemlins/heart.gif[/img]

Anyway, I'm in Biological Sciences 220 at USC, which is the introductory class that most Pre-Med students take. I am not Pre-Med, but rather a Neuroscience major with plans of going to law school. Here are the topics we've covered this year:

The Cell
Cell Membranes
Energy & Cell Metabolism
Cell Communication
The Cell Cycle
Mitosis
Meiosis
Nutrition and Digestion
Circulation
Gas Exchange
Immunity
Excretion
Chemical Signals*
Reproduction*
Neural Signals*
Synapses*
Muscles & Movement*

Those topics marked with an astersik are worth a disproportionate amount on the final (half of all points will come from these topics), so it would be super-awesome if you could ask me lots of questions about them.

With that in mind... Have at it!

[itsmesteve]

I'm off to a physiology final in a matter of hours, so good luck, and here's one to start things off:

What are the two reproductive duct systems present in early fetal development? What do they become?

good luck

steve

[JaBlue]

how does the brain work? talk about synapses, neurotransmitters, everything

[Tron]

steve,

I don't believe that topic was covered in lectures of in our textbook, but I will go ahead and give it a try.

The two reproductive ducts present in early fetal development are the Wolffian or mesoneprhic ducts and the Müllerian or paramesonephric ducts.

The Wolffian ducts, upon exposure to testosterone during embryogenesis eventually develop into a system of connected organs between the testes and the prostate (including the vas deferens, seminal vesicle, etc.). In females, the Wolffian ducts wither away due to the lack of testosterone (though remnants may be present in the form of an epoophoron).

The Mullerian ducts, in females, develop into the upper vagina, cervix, uterus, and oviducts. In males, they wither away except for the vestigal organs of vagina masculina and appendix testis. Whether the Mullerian ducts develop or not is controlled by anti-Mullerian females, which is absent in females and present in males via production by the testes.

[keikiwai]

What are Okazaki fragments, and why are they important?

[Tron]

Ja,

Hell of a question.

The basic functional unit of the nervous system and, in turn, the brain is the neuron. A neuron consists of a cell body and two specific types of extensions that emerge from the cell body. The cell body of a neuron contains most of the neuron's organelles, including the nucleus, mitochondria, endoplasmic reticulum, etc. The two types of extensions that emerge from the cell body are dendrites and axons. A typical neuron has numerous dendrites and a single axon. Dendrites are highly branched extensions that receive signals from other neurons. An axon is usually a much longer extension that transmits signals to other cells.

The axon joins the cell body at a region called the axon hillock. This is the site of generation of the action potential (which will be discussed later). Many axons are enclosed by a myelin sheath, which speeds up the movement of signals along the axon by providing a layer of insulation. An axon typically divides into several branches toward its end, each of which terminate at a synaptic terminal.

The site of communication between a synaptic terminal and another cell is called a synapse. It is at this point where information is relayed from the transmitting or presynaptic cell to the receiving or postsynaptic cell, usually via neurotransmitters.

Action potentials (briefly mentioned earlier) are the signals that carry information along axons. They are generated by making the inside of the cell less electrically negative (a phenomenon known as depolarization, which I will be glad to elaborate upon if asked to do so). Action potentials move along the axon and typically, although not always, stop at the synaptic terminals. The action potential does not stop at electrical synapses, which contain gap junctions that allow for the direct transmission of electrical current. The vast majority of synapses, however, are not electrical, but are chemical. When an action potential reaches the synaptic terminals of a chemical synapse, it stimulates the release of a neurotransmitter. Neurotransmitters transmit information to postsynaptic cells through either direct synaptic transmission or indirect synaptic transmission. Simply put, direct synaptic transmission results in the generation of a postsnaptic potential by the binding of neurotransmitters to ion channels. Indirect synaptic transmission, on the other hand, involves the binding of neurotransmitters to receptors that are not part of an ion channel, which initiates a signal transduction pathway within the postsynaptic cell. Comparatively, the effects of indirect transmission have a slower onset than produced by direct transmission, but last longer.

The brain can be thought of as an extremely dense collection of axons. When you perceive something, information is collected by sensory neurons and trasmitted to the brain. When this information arrives at the brain (via the methods just discussed), it is processed through astonishingly complicated series of neurons. Once the information has been processed, responses are initiated by the transmission of instructions from neural cells to effector cells (such as muscle cells or glands).

Please feel free to ask me to elaborate on any of this.

Tron

[Tron]

keikiwai,

We never got down to the molecular basis of inheritance, so my answer will be a brief one.

Okazaki fragments are the relatively short segments of DNA created on the lagging strand during DNA replication. These are important because they allow for the efficent replication of DNA in the 5'-->3' direction.

Tron

[mslif]

Hi Tron:
Here is my question, please give me the classification of cell-surface receptors. Please include a brief description of each receptors.
Good luck on your final.

[mmbt0ne]

[ QUOTE ]
Anyway, I'm in Biological Sciences 220 at USC, which is the introductory class that most Pre-Med students take. I am not Pre-Med, but rather a Neuroscience major with plans of going to law school.

[/ QUOTE ]

What are the chances you have a 47th chromosome?

[AvivaSimplex]

I know the answers to these, but if I were your teacher I might ask something along these lines.

Why does heroin make you constipated?

Why does Prozac take a month before it starts working? (this might be too advanced)

If you place a heavy weight on a table, the table can support the weight nearly indefinitely. But if you hold a heavy weight above your head, your arms will get tired in a couple minutes, and will fail in a couple more. Why is that?