Neuro Lecture 2

What does the cell theory state?

Individual cells are the foundational functional unit of all animal tissues.

What is histology?

The microscopic study of tissues.

What did the Nissl stain reveal, and what does it specifically stain?

Cell nuclei and Nissl bodies (rough ER) of neurons — It stains some parts of the cell.

What did the Golgi stain reveal?

Cell bodies and neurites of neurons (only a subset of neurons are stained, allowing individual cells to be visualized).

Who used the Golgi stain to develop drawings supporting the neuron doctrine, and what did his work help establish?

Santiago Ramon y Cajal — his drawings (e.g., of rodent hippocampus) helped establish that neurons are individual, discrete cells rather than a continuous network.

What are the two large structural features shared by all neurons?

The cell body (soma/perikaryon) and neurites (which radiate from the cell body).

What does the cell body (soma/perikaryon) contain?

The nucleus of the cell and organelles.

Neurites are further divided into which two structures?

Axons and dendrites.

What fills the cell body, and what does it contain?

Cytosol, which contains membrane-bound organelles (nucleus, rough/smooth ER, Golgi apparatus, mitochondria).

What defines an organelle?

A membrane-bound structure that serves a specific function within the cell.

What is the structure of the nucleus?

Spherical, contained within a double-membraned nuclear envelope; holds the chromosomes (DNA).

Why is mRNA necessary for protein synthesis?

DNA never leaves the nucleus, but protein synthesis occurs in the cytoplasm — mRNA carries the genetic message out.

What is transcription?

The process of assembling a piece of mRNA from a DNA template (occurs in the nucleus).

What is translation, and where does it occur?

The linking of amino acids to form a protein, based on the mRNA sequence; occurs in the cytoplasm via ribosomes.

What is the central dogma sequence shown in this lecture?

DNA to mRNA to Protein (via transcription, then translation).

What is a knockout animal, and what is it useful for studying?

An animal with a single gene deleted; useful for studying single-gene pathologies (e.g., Fragile X).

What is a transgenic animal?

An animal with additional genes or overexpression of a given gene, used to study that gene's function.

What is a knock-in animal?

An animal in which a native gene has been replaced with a modified gene.

What technology commonly enables these genetic manipulations?

CRISPR and other gene-editing technologies.

What is the function of rough ER, and why is it called 'rough'?

It is studded with ribosomes that synthesize proteins — giving it a rough appearance.

What organelle corresponds to the Nissl bodies seen with Nissl stain?

Rough ER.

What are polyribosomes?

Free ribosomes (not attached to rough ER) that also synthesize proteins.

Where are membrane-bound proteins synthesized vs. proteins expressed in the cytosol?

Membrane-bound proteins: rough ER. Cytosolic proteins: free ribosomes/polyribosomes.

Why do neurons have an unusually large amount of rough ER?

Because they have a large number of membrane-associated proteins.

What are the main functions of smooth ER?

Folding of membrane-bound proteins

regulation of internal cell ion/molecule concentrations (functions unrelated to translation).

What is the function of the Golgi apparatus?

Sorting proteins to be distributed to specific parts of the cell.

What two things happen in mitochondria?

The Krebs cycle and production of ATP.

What can the relative abundance of mitochondria in a region of a cell indicate?

The energy demand of that cell or region — especially informative in neurons, where many processes are energy-dependent.

What is the cytoskeleton, and how is the neuronal membrane related to it?

An internal scaffold; the neuronal membrane is "draped" over the cytoskeleton.

What are microtubules, and where are they found?

Relatively large hollow tubes made of tubulin, running longitudinally down neurites.

What are microfilaments (actin), and where are they found?

Much smaller filaments present throughout the neuron (mostly in neurites), closely associated with the cell membrane.

What are neurofilaments, and what is their role?

Intermediate-sized filaments, abundant in the axon; very strong and provide structural support.

What is polymerization/depolymerization, and why does it matter for neuron shape?

The joining (polymerization) or breaking apart (depolymerization) of protein chains (tubulin/actin) that lengthen or shorten microtubules/microfilaments, allowing neurons to dynamically remodel their shape.

What microtubule-associated protein is central to Alzheimer's pathology, and what does it normally do?

Tau

helps anchor microtubules to the cell and to each other.

How does abnormal tau contribute to Alzheimer's disease?

Tau builds up abnormally in cell bodies (related to the sticky protein amyloid-beta), disrupting the cytoskeleton and causing loss of synaptic connections.

What three regions make up the axon?

Axon hillock (beginning), axon proper (middle), and axon terminal (end).

How does axon diameter typically change along its length?

It generally stays the same diameter throughout.

What are axon collaterals?

Branches that leave the main axon at ~90 degree angles and connect to neurites of neurons elsewhere in the nervous system.

What are recurrent collaterals?

Axon collaterals that connect back to neurites of neighboring neurons or even the same neuron.

What two features distinguish the axon from the cell body?

(1) No rough ER (and very few free ribosomes) extends into the axon; (2) the protein composition of the axon membrane differs fundamentally from the cell body membrane.

What does the lack of rough ER/ribosomes in the axon imply about protein synthesis there?

Proteins are not synthesized locally in the axon — they must be synthesized in the cell body and transported.

Why is axonal transport necessary?

Because proteins and materials aren't synthesized in the axon, they must be moved from the cell body to the terminal (and back).

What happens to a neuron without adequate axonal transport?

It degenerates — a process called Wallerian degeneration.

What is slow axonal transport, and why isn't it sufficient alone?

A passive, slow movement of material; too slow to keep long axons functioning on its own.

What powers fast axonal transport?

Motor proteins that "walk" material along microtubules using ATP.

What is anterograde transport, and which motor protein drives it?

Movement from the cell body toward the axon terminal, driven by kinesins.

What is retrograde transport, and which motor protein drives it?

Movement from the axon terminal back toward the cell body, driven by dynein.

How can axonal transport mechanisms be used experimentally?

To trace neural connections in the brain (e.g., anterograde tracers injected into cortex reveal projection targets).

What is another name for the axon terminal?

The terminal arbor.

What happens when an axon terminal contacts another cell?

It innervates that cell, often forming a synapse.

Name the four features that distinguish the axon terminal from the rest of the axon.

(1) No microtubules; (2) contains synaptic vesicles; (3) synaptic membrane has many associated proteins; (4) contains many mitochondria.

What is the synaptic cleft?

The space between an axon terminal and the postsynaptic cell.

What is synaptic transmission?

The Electrical signal in the axon is converted to a chemical signal (via neurotransmitters) at the synapse, then converted back to an electrical signal in the postsynaptic cell.

Do all synapses form at the very end of the axon?

No — swollen sections along the axon can also contact other cells, forming "synapses in passing."

What is the dendritic tree?

The collection of many individual dendrites branching from a neuron.

What is the functional role of dendrites?

They act as an "antenna," receiving inputs (synaptic contacts) from other cells.

What are dendritic spines?

Specialized protrusions of the dendritic membrane that may support distinct types of synaptic activity; they are dynamically regulated by synaptic activity.

How do dendrites differ from axons in terms of protein synthesis machinery?

Unlike axons, dendrites contain polyribosomes.

Neurons can be classified by structure based on what two features covered in lecture?

Number of neurites (unipolar, bipolar, multipolar) and overall shape (e.g., pyramidal vs. stellate).

What is the difference between spiny and non-spiny neurons?

Spiny neurons have dendritic spines; non-spiny neurons lack them.

What are the three connection-based categories neurons can be classified into?

Primary sensory, motor, and interneurons.

What is the difference between projection neurons and circuit neurons in terms of axon length?

Projection neurons have long axons connecting distant brain regions; circuit neurons have short axons for local connections.

How can physiological properties be used to classify neurons?

Intrinsic structural differences (e.g., membrane characteristics) that produce different physiological behavior.

How can gene expression be used to classify neurons?

Transcriptomics identifies the RNA expressed in a cell, which can be leveraged to create transgenic animals with markers for specific cell types.