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Medical Neuroscience Block 1 > 2 - Neuron Structure > Flashcards

2 - Neuron Structure Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the function of neurons?

A

Receiving, conducting, and transmitting signals.

Sense internal and external environment.

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2
Q

What is used to stain neurons?

A

Golgi stain - stains 1/1000 neurons.

Stains cell bodies, processes, and some of the axon.

Empty spaces are occupied by the processes of axons.

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3
Q

What was Camillo Golgi’s theory about neurons? Was he correct?

A

They neurons form a reticular network and that that’s connected.

He was wrong - santiago cajal was correct: neurons do NOT form a syncytium but communicated via synapses.

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4
Q

What else did Cajal’s neuron doctrine say about the structure of neurons?

A

They are dynamically polarized, with a clear side for input and one for output (axon)

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5
Q

What are the four parts of a typical neuron?

A

Dendrite, call body, axon, axon terminal.

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6
Q

What are the characteristics of a cell body (soma)?

A
  1. Euchromatin: indicates neuron body is transcribing DNA into RNA
  2. Nissl substance: lots of RER b/c it’s busy making proteins from mRNA
  3. Neurofilaments
    4: Other organelles: golgi, mito, ER, lysosomes, cytoskeletal proteins
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7
Q

What part of the axon does not contain nissl substance? What does this indicate the need for?

A

The axon hillock.

This means there’s no proteins made their and it requires axotransport.

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8
Q

What is the structure and function of dendrites?

A

Major receptive sites for synapses; extensions of cell bodies that branch extensively.

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9
Q

What is the function of dendritic spines?

A

Protrusions that allow for increased SA for better reception.

Thought to facilitate learning and memory.

Also thought to sequester and release calcium.

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10
Q

What is the function of the axon? What is their structure? What is the initial portion important for?

A

Major effective site for synapses: conducts action potentials.

Long or short, can be myelinated or unmyelinated; initial portion is important because it’s where the action potential is initiated.

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11
Q

What is the axon hillock a part of? What is it’s membrane called?

A

Part of the cell body.

Membrane called axolemma.

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12
Q

What is found in presynaptic axon terminals?

A

Synaptic vesicles with neurotransmitters.

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13
Q

What is the structure of bipolar neurons? Where are these typically found?

A

Two processes - dendrite and axon.

Ear, retina, and olfactory system.

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14
Q

What is the structure of pseudounipolar neurons? Where are these typically found?

A

One process from the cell that bifurcate into 2 processes.

Terminal portions contact skin, muscles, and glands to bring info to cells bodies and transmit through the central process to bring it into the spinal cord.

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15
Q

What is the structure of multipolar neurons and where are they found?

A

Many dendrites from the cell body.

Found in the brain.

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16
Q

What are golgi type 1 and 2 neurons?

A

Golgi type 1: longer projections

Golgi type 2: interneurons with locally ramifying processes (most in the brain)

17
Q

What are the major differences between dendrites and axons? How many extensions does each have? What organelles do they contain? Are they myelinated? Do they consume energy?

A
  1. Dendrites can be single or multiple extensions of cell body (axons are just one)
  2. Both don’t contain golgi; Dendrites contain all other organelles (axons don’t have ER or ribosomes)
  3. Dendrites are almost never myelinated
  4. Dendrites are absent in unipolar cells.
  5. Dendrites are major energy consuming portion of neuron b/c of large SA. Axons have low energy consumption
18
Q

What are lipofuscin granules? What disease is associated with their accumulation.

A

Large end stage lysosomes associated with normal aging.

Accumulated in dementia.

19
Q

Name the three cytoskeletal components of neurons?

A
  1. Microtubules
  2. Neurofilaments (int. filaments)
  3. Microfilaments
20
Q

What are characteristics of microfilaments? What are they made of?

A

Most abundant protein in neurons; polar, ATPase.

~5-8 nm

Made of globular actin that polymerizes into F actin with a fast growing + end and shrinking - end.

21
Q

What is the function of microfilaments?

A

In cytoplasm of neuron and associated with plasma membrane.

Important in changing and/or maintaining cell shape.

22
Q

What depolymerizes F actin? What stabilized F actin? Are these good or bad?

A

Depolymerizes: Cytochalasins
Stabilizes: Phallodins

Both block turnover and threaten cell viability

23
Q

What is the structure of neurofilaments?

A

Nonpolar; ~10 nm

Monomers with two end domains coil around each other to form a dimer.

Tetramers are antiparallel (called protofilaments)

Forms protofibrils, 8 of which forms a neurofilament.

24
Q

Where are neurofilaments found in neurons? In what cases are neurofibrillary tangles seen?

A

In cytoplasm.

Hallmark of Alzheimers disease.

25
Q

What is the structure of microtubules? Where are they found in the neuron?

A

Polar, GTPase, 20-25 nm hollow tubes made of alpha and beta tubulin heterodimers.

Found in the cytoplasm.

26
Q

Hydrolyzation of GTP to GDP in microtubules favors ______?

A

Depolarization.

27
Q

Describe the treadmilling of microtubules? Where is the + end found in axons? What about in dendrites?

A

+ ends rapidly growing, - ends disassembling causing kinetic asymmetry

Axons: + ends away from soma
Dendrites: polarity mixed; + end point towards postsynaptic sites in distal dendrites (away from cell body).

28
Q

What are two antimitotic chemotherapeutic drugs? What is their effect on MTs?

A

Colchicine: depolymerizes MT

Taxol: stabilizes MT

29
Q

What are the three types of high molecular weight microtubule-associated proteins (MAPs)? What is the function of each?

A

MAP-2: present only in dendrites/synthesized in dendrites

Kinesin: for transport toward + end of mt

Cytoplasmic dynein (MAP-1C): for transport toward - end of mt

30
Q

What’s the name of the low molecular microtubule-associated protein (MAP)? In what cause are they associated with disease?

A

Tau proteins - hyperphosphorylated taue is found in neurofibrillary tangles of Alzheimer’s disease.

Normally serve to stabilize mt to prevent disassembly.

31
Q

Why aren’t proteins synthesized in the axon?

A

Because ribosomes are not located there?

32
Q

What is the slow component of slow axoplasmic transport? What does it transport?

A

0.2-2.5 mm/day

MT and NF components; soluble proteins

33
Q

What is the fast component of slow axoplasmic transport? What does it transport?

A

Up to 10 mm/day

Complex mixture or proteins, including actin.

Metabolic enzyme and calmodulin (CA2+ binding proteins).

34
Q

What is fast anterograde axonal transport? What does it transport?

A

~410 mm/day

ATP-dependent

Relies of mt and kinesin (motor)

Transports subcellular organelles: mito, synaptic vesicle precursors, smooth ER vesicles and contents.

35
Q

What is fast retrograde axonal transport? What does it transport?

A

~300 mm/day

ATP-dependent

Relies on mts and cytoplasmic dynein

Returns cell components for degradation, growth factors, viruses, toxins, and tracers.

36
Q

What is the function of kinesin? What are they made up of?

A

Moves cargo towards + end of mt.

High MW MAP ~360 kDa

2 heavy chains with globular heads are motor domains that bind mts and ATP

2 light chains bind to other cell components such as vesicles.

37
Q

What is the function of cytoplasmic dynein (MAP-1C)? What are they made up of?

A

Moves cargo towards - end or mt.

High MW MAP up to 2,000 kDa.

2 or 3 heavy chains form globular ATP-binding motor domains.

Variable # of light and int. chains: bind to other cell components.

38
Q

What are the characteristics or dendritic transport?

A

Rate and components similar to those of axoplasmic transport.

All newly synthesized membranous organelles are transported from the soma to dendrites.

All degradative products are transported from the dendrites back to the soma.

Medical Neuroscience Block 1 (10 decks)

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