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Flashcards in Chapter 2 Deck (58):

Define "Neurons".

Sense changes in the environment, communicate these changes to other neurons, and command the body's responses to these sensations.


Define "Glia".

(Glial cells) Thought to contribute to brain function mainly by insulating, supporting, and nourishing neighboring neurons.


What is more important, neurons or glia?

Neurons are more important. However, there is still much we don't know about the function of the glia, and it may have a larger part to play in brain function.


Define "Histology".

The microscopic study of the structure of tissues.


The Nissl Stain (introduced by Franz Nissl), is...

...a class of basic dyes that stain the nuclei of all cells and also stain clumps of material (Nissl bodies) surrounding the nuclei of neurons.


What do Nissl stains "do"?

- Distinguish neurons and glia from one another.
- Enables histologists to study the arrangement (cytoarchitecture) of neurons in different parts of the brain.


What is the Golgi stain?

By soaking the brain tissue in silver chromate solution, a small percent of neurons become darkly colored in their entirety.


What has the Golgi stain showed us?

- That neurons have at least two distinguishable parts, a central region that contains the cell nucleus, and numerous thin tubes that radiate away from the central region.


Define "Soma".

The swollen region containing the cell nucleus (also called cell body, or perikaryon).


Define "neurites".

The thin tubes that radiate away from the soma. There are two types, axons and dendrites.


What are the differences between axons and dendrites?

- Axons are of uniform diameter, extremely long, and carry info out of the soma (output). The cell usually only makes one axon.
- Dendrites are short, their radius tapers, and they carry info to the soma (input). The cell usually has many dendrites.


Who is responsible for the neuron doctrine?

While Cajal's hypothesis was correct, both Golgi and Cajal are credited with its creation.


What is the neuron doctrine?

The neuron adheres to the cell theory. Neurites of different neurons are not continuous with one another and must communicate by contact, not continuity.


How big is the cell body of a typical neuron??

About 20 micrometers in diameter.


Define "Cytosol".

Salty potassium rich solution that is separated from the outside by the neuronal membrane. (Watery fluid inside the cell).


Define "Organelles".

Membrane enclosed structures within the soma.


What is the cytoplasm?

Everything contained within the confines of the cell membrane (excluding the nucleus).


Where does protein synthesis take place?

In the cytoplasm.


Can DNA leave the nucleus?

No, it must use an intermediary to get info out (mRNA).


Define "ribosomes".

Dense globular structures that dot the rough ER.


Does rough ER exist in neurons?

Yes, in massive quantities actually. Far more than in most glia or most other non-neuronal cells.


NOTE: In the past, what were ribosomes called?

Nissl bodies.


Rough ER is a major site of...

...protein synthesis in neurons.


How are proteins made in the rough ER?

RNA transcripts bind to the ribosomes, and the ribosomes translate the instructions contained in the mRNA to assemble a protein molecule.


Are ribosomes always attached to the rough ER?

No, some are freely floating (free ribosomes).


Define "polyribosomes".

Free ribosomes attached by thread (which is a single strand of mRNA).


What do polyribosomes do?

The associated ribosomes are working on it to make multiple copies of the same protein.


What is the difference between proteins made on the rough ER and those synthesized on the free ribosomes?

- Proteins made on the rough ER are destined to be inserted into the membrane of the cell or an organelle.
- Proteins made on free ribosomes are destined to reside within the cytosol of the neuron.


What is the smooth ER?

Stacks of membranous organelles that look like rough ER without the ribosomes. It is quite heterogenous and has multiple functions.
- Some is continuous with rough ER.


What does smooth ER do?

- The site where it is continuous with rough ER is believed to be where proteins that jut out from the membrane are carefully folded (giving them their 3D structure).
- Other types regulate the internal concentrations of substances such as calcium.


What is the golgi apparatus?

Stack of membrane enclosed disks in the soma that lie farthest from the nucelus.


What does the golgi apparatus do?

- Site of extensive post-translational chemical processing of proteins.
- Sorts certain proteins that are destined for delivery to different parts of the neuron, such as the axon and the dendrites.


What is the mitochondrion?

- The site of cellular respiration.
- Cotains multiple folds of an inner membrane called cristae.
- Between the cristae is an inner space called matrix.


When a mitochondrion "inhales"... pulls inside pyruvic acid and oxygen.


What happens after mitochondrion has pulled inside pyruvic acid and oxygen?

- Pyruvic acid enters the Krebs cycle.
- Biochemical products of the Krebs cycle provide energy that results in the addition of phosphate to adenosine diphosphate yielding ATP, the cell's energy source.


When the mitochondrion "exhales"...

...17 ATP molecules are released for every molecule of pyruvic acid that has been taken in.


What is the neuronal membrane?

- Serves as a barrier to enclose the cytoplasm inside the neuron and to exclude certain substances that float in the fluid that bathes the neuron.
- Studded with proteins.
- Some proteins pump substances from inside to outside.
- Others form pores that regulate which substances can gain access.


An important characteristic of neurons is that the protein composition of the neuronal membrane varies depending on...

...whether it is in the soma, the dendrites, or the axon.


What is the cytoskeleton?

It gives the neuron its characteristic shape.


What is the cytoskeleton made up of?

- MIcrotubules, microfilaments, and neurofilaments.
- NOTE: elements of the cytoskeleton are dynamically regulated and are very likely in continual motion.


Describe microtubules.

- Big and run longitudinally down neurites.
- Straight thick walled hollow pipe.
- Wall of pipe composed of smaller strands braided like a rope around the hollow core.


What are microtubules made out of?

- The protein tubulin, which is small and globular.
- Strands consists of tubulins stuck together.


Define "polymerization".

The process of joining small proteins to form a long strand (called a polymer).


Polymerization and depolymerization of microtubules and of neuronal shape can be regulated by...

...various signals within the neuron.


What are MAPs?

- Microtubule Associated Proteins, a class of proteins that participate in the regulation of microtubule assembly and function.
- They anchor the microtubules to one another and to other parts of the neuron.


What are the different ways to classify neurons?

- Number of neurites.
- Based on dendrites.
- Based on connections.
- Based on axon length.
- Based on neurotransmitter.


Describe classification of neurons by the number of neurites.

- Unipolar: A neuron that has a single neurite.
- Bipolar: Two neurites in a cell.
- Multipolar: Three or more neurites.
- Most neurons in the brain are multipolar.


Describe classification based on dendrites.

- Usually unique to a particular part of the brain.
- In the cerebral cortex, there are two broad classes:
- Stellate cells (star shaped)
- Pyramidal cells (duh)
- Another way to classify neurons is whether they are spiny, or aspinous (not spiny).


Describe classification based on connections.

- Primary Sensory neurons: Cells with neurites in the sensory surfaces of the body (how most info is delivered).
- Motor Neurons - Neurons that have axons that form synapses with the muscles and command movements.
- Interneurons - Neurons in the nervous system that form connnection only with other neurons (most neurons are like this).


Information is delivered to nervous systems by...

...neurons that have neurites in the sensory surfaces of the body (skin and retina).


Describe classification based on axon length.

- Golgi type I neurons - (Projection neurons) Neurons that have long axons that extend from one part of the brain to the other.
- Golgi type II neurons - (local circuit neurons) Neurons that have short axons that do not extend beyond the cell body.


What are astroycytes? What can they do?

- Most numerous glia in the brain (they fill the spaces between neurons).
- Appear to influence whether a neurite can grow or retract.
- Essential role is regulating chemical content of this extracellular space.
- Have special proteins in their membranes that actively remove many neurotransmitters from the synaptic cleft.
- Possess neurotransmitter receptors that can trigger electrical and biochemical events inside the glial cell (just like the receptors on neurons).
- Tightly control extracellular concentration of several substances that have potential to interfere with proper neuronal function.


What are myelinating glia?

- Oligodendroglial & Schwann Cells: These glia provide layers of membrane that insulate axons. This is their primary function.


What is myelin?

- The wrapping around axons that spirals around axons in the brain.
- Myelin sheath refers to the entire covering.
- Serves to speed the propagation of nerve impulses down the axon.


What is the node of ranvier?

- The short length where the axonal membrane is exposed (this happens when the sheath is interrupted periodically).


What is the difference between oligodendroglial and schwann cells?

- Oligodendroglia are found only in the CNS.
- Also, one oligodenroglial cell will contribute myelin to several axons.
- Schwann cells are found only in the PNS.
- Also, each schwann cell myelinates only a single axon.


What are ependymal cells?

Provide the lining of fluid filled ventricles within the brain, and they also play a role in direction cell migration during brain development.


What are microglia?

A class of cells that function as phagocytes to remove debris left by dead or degeneration neurons and glia.