Neurobiology 523: Unit 1

What is specialization?

Adaptation to serve a particular function.

What is the nervous system?

A network of cells that transmits signals throughout the body and organizes bodily functions.

What are neurons?

The characteristic signaling cells of the nervous system.

What are nerves?

Collections of axons that link parts of the nervous system.

What is a ganglion?

A cluster of neuron cell bodies.

Is a brain required for a nervous system to transmit signals and organize bodily functions?

No. Simpler organisms such as nematodes can accomplish these functions without a brain.

Which organism discussed in lecture has no neurons?

Sponges.

About how many neurons does a nematode have?

302.

About how many neurons does a jellyfish have?

5600.

About how many neurons does a fruit fly have?

100000.

About how many neurons does a zebrafish have?

10 million.

About how many neurons does a mouse have?

71 million.

About how many neurons does a human have?

86 billion.

What is neurophysiology?

The function of neurons especially in electrical terms.

Why are simpler organisms useful for studying neuroscience?

Basic neurophysiology is similar across species so simpler organisms can reveal how neurons function and interact.

In what animal were many basic neuronal functions discovered?

Squid.

What question did Golgi and Cajal disagree about?

Whether neurons formed one continuous structure or were separate cells that communicate.

What is the neuron doctrine?

Neurons are separate cells that communicate with one another.

Why is the neuron doctrine important?

It establishes neurons as independent cellular units of the nervous system.

What is a neuron considered computationally?

A computational unit that performs a task or decision such as whether to activate.

What allows neurons to accomplish complex functions?

Communication among many neurons.

What is a synapse?

A site of communication between cells in the nervous system.

Approximately how many synapses are present in the human nervous system?

On the order of a quadrillion or about 10^15.

Loosely what does having more neurons and connections allow?

More specialization; more varied activity; and more complex thought and action.

What makes the basic organization of a nervous system powerful and flexible?

It consists of elements that can make decisions and communicate with one another.

What are some feats produced by biological nervous systems?

Intelligence; creativity; learning; memory; emotion; communication; perception; attention; movement; dexterity; survival behaviors; breathing; arousal; sleep; and regulation of organ physiology.

What ultimately produces the feats of the nervous system?

Outputs of cells working together.

What is a neurite?

A projection extending from a neuron's cell body that is specialized for transmitting signals.

What are the two major types of neurites?

Dendrites and axons.

What is the soma?

The neuron cell body.

What does the soma contain?

The nucleus and genetic material plus most organelles.

Where does transcription occur in a neuron?

In the soma.

Can translation occur outside the soma?

Yes. Some translation occurs in neurites.

Can organelles enter neurites?

Yes.

What is Cajal's concept of dynamic polarization?

Different neuronal processes have different functions with information typically entering through dendrites and leaving through the axon.

What is the typical role of dendrites?

Receive incoming information especially from synapses.

What is the typical role of the axon?

Transmit the neuron's output downstream.

How many dendrites can a neuron have?

Many.

What is a primary dendrite?

A dendrite that connects directly to the soma.

What is a dendritic arbor?

The complete collection of a neuron's branching dendrites.

What does proximal mean on a neurite?

Closer to the soma.

What does distal mean on a neurite?

Farther from the soma.

How do proximal and distal dendrites generally differ in thickness?

Proximal dendrites tend to be thicker.

What is a dendritic spine?

A small protrusion from a dendrite where synapses can form.

Can synapses form somewhere other than dendritic spines?

Yes. They can also form directly on the dendritic shaft.

What advantage do dendritic spines provide?

Compartmentalization that allows local regulation of signaling.

Are dendritic spines permanent structures?

No. They can grow and be eliminated.

How many axons does a typical neuron have?

One.

How do axonal branches often differ visually from dendritic branches?

They may arise at right angles and look more sprawling and less tree-like.

What are axon collaterals?

Branches of an axon.

What can axons look like at high magnification?

Beads on a string.

What is white matter largely composed of?

Axons.

What is tractography?

Mapping the directions of white-matter connections.

Where are many neuron cell bodies located in the cerebral cortex relative to white matter?

Cell bodies are grossly toward the exterior cortex while axons travel through white matter.

What is the axon hillock?

The site where the axon connects to the soma.

What is the axon initial segment or AIS?

The proximal portion of the axon adjacent to the axon hillock.

What major event occurs at the AIS?

The neuron's electrical output signal is generated there.

Why is the AIS specialized for signal generation?

It is enriched in proteins involved in sending electrical signals down the axon.

What protein anchor was associated with the AIS in the slides?

Ankyrin G.

What is an axon terminal?

A swollen ending of an axon involved in synaptic communication.

What is a bouton?

A swollen axon ending. Bouton means button.

What happens at an axon terminal?

Neural activity is transformed into neurotransmitter release.

What is a neurotransmitter?

A chemical released by a neuron to convey neural activity.

What are boutons en passant?

Neurotransmitter-release sites located along an axon rather than only at its end.

What structures are apposed at a synapse?

A neurotransmitter-release site and neurotransmitter receptors on another cell.

Where is neurotransmitter stored before release?

Synaptic vesicles.

What is the synaptic cleft?

The gap between cells into which neurotransmitter is released.

What does the existence of a synaptic cleft support?

The neuron doctrine because it demonstrates that neurons are distinct cells.

What does presynaptic mean?

The side of the synapse that releases the signal or neurotransmitter.

What does postsynaptic mean?

The cell or membrane that receives the synaptic signal.

What is an axodendritic synapse?

A synapse from an axon onto a dendrite.

What is an axosomatic synapse?

A synapse from an axon onto a soma.

What is an axoaxonic synapse?

A synapse from an axon onto another axon.

What is a neuromuscular junction?

A specialized synapse between a motor neuron and muscle.

What is another name for a motor neuron?

Motoneuron.

Why is the neuromuscular junction highly reliable?

It has a high density of receptors.

What does histology study?

The microscopic structure of tissue.

What is immunohistochemistry or IHC?

A method using antibodies to visualize specific structures or molecules in tissue.

What is the key idea behind IHC?

Repurpose antibodies to bind targets in tissue rather than pathogens.

What is an antigen?

A substance that can elicit an immune response.

What is an epitope?

The part of an antigen specifically recognized and bound by an antibody.

What does a positive control demonstrate?

That an experiment was capable of working.

How can IHC be used to label synapses?

Use antibodies against proteins or epitopes unique to synapses.

What protein did the lecture show labeled green with an antibody?

MAP2 or microtubule-associated protein 2.

What protein did the lecture show labeled red?

MAPT or microtubule-associated protein tau.

What is the main take-home message of IHC?

Antibodies can act as labels for specific structures in tissue.

What principle connects neuronal morphology to neuronal function?

Structure reflects function.

What distinguishes a specialized neuron?

Its function; morphology; physiology; or a combination of all three.

What is characteristic of a pyramidal cell?

An apical dendrite and basilar dendrites. They are common in layered cortex and can sample input from above and below.

What is characteristic of retinal bipolar cells?

They connect outer and inner retina and help sort visual information into layers.

What is characteristic of chandelier cells?

They are inhibitory neurons that specifically target the AIS of many nearby neurons.

What effect can chandelier cells have?

They can shut off a patch of neurons.

What is the role of double bouquet cells described in lecture?

Influence a column of activity in cerebral cortex.

What is the role of starburst amacrine cells?

Support spatial processing in the retina.

What is characteristic of tufted cells?

They are found in the olfactory bulb and have dendrites associated with patches of odor-specific axons.

What overall property do neurons show across the nervous system?

Great diversity of morphology.

What is the rosehip neuron?

A neuron discovered in 2018 in human cerebral cortex.

What are the two broad cellular groups in the nervous system?

Neurons and glia.

What does neuroglia literally mean?

Nerve glue.

Are glia rare compared with neurons?

No. Glia are numerous and diverse.