ANAT242 - Test 2

How many neurons are in the brain?

86 billion

How many synapses are in the brain?

1 quadrillion

What is the ratio of glia to neurons?

outnumber them by around 50:1

What is special about neurons (shape and size)?

have different shapes and sizes depending on function

What are interneurons?

listen to many cells nearby, usually inhibitory

What is light microscopy (LM)?

illuminates tissue with a beam of light (lower magnification, photons from light sent through condenser lens, cells are mostly water, have to make them block light

What is the Nissl stain?

uses a basophilic dye which binds to negatively charged structures (nissl bodies)/attracted to basic substances, in the cell body of neurons and glia

What are the different types of azines?

thiazines and oxazines (chemicals in the dye), all have a particular colour (blue), extremely electronegative

What are nissl bodies?

rough endoplasmic reticulum in cell bodies, dye binds to structures with negative charge eg mRNA making proteins at ER (mRNA is negative)

What is darkly stained by nissl stains?

neurons but not glia

Why are neurons darkly stained by Nissl stains?

contain lots of endoplasmic reticulum with lots of mRNA as they are dynamic and constantly changing

Why do neurons require many proteins?

for signalling, growth and transport, doing lots of things (dynamic)

How many proteins does an average neuron contain?

50 billion

What are the pros of the Nissl stain?

stains majority of neurons, good for looking at gross structures

What are the cons of the Nissl stain?

weakly stains glia, can only see soma (cell bodies) clearly, can't see axons as cell making most of its proteins in soma (cell body)

What is the golgi stain?

dyes soem neurons black, uses chrome-silver reaction to stain neurons, mechanism still not completely understood, stains a few neurons seemingly at random/unsure why some neurons are stained and not others

What can you see on a golgi stain?

individual spines on dendrites, moving focal plane allows visualisation in 3D

What are the pros of the golgi stain?

can visualise entire neurons including dendritic arbor (tree), easy to determine type of neuron based on morphology (ie pyramidal vs star shaped cells)

What are the cons of the golgi stain?

only a subset of neurons take up the stain, glial cells don't take up the stain

What is transmission electron microscope (TEM)?

an electron microscope, gun fires electrons instead of photons (light), allows us to look at a very thin cross-section of an object eg a cell

What is the maximum magnification of TEM?

5,000,000x

What is TEM best for?

looking at the internal structure of objects, objects at very high resolution, relationships between structures at high resolution

What are the cons of TEM?

can't be used to look at living things (samples need to be prepared extensively before visualising - material has to be sliced extremely thing), expensive to run

What are the features of TEM?

extremely high resolution, allows us to look at extremely small structures at high resolution

What is a voxel?

volumetric pixel

vesicles (individual circles filled with neurotransmitter)

node of ranvier

myelin sheath under microscope

mitochondria under microscope

tightly folded structures

neurofilaments

intermediate filaments that aggregate to form bundles called neurofibrils

microtubules neurons

lines under the microscope, move neurotransmitter molecules through the cell (motor protein walks along them)

axon under microscope

synapses under microscope

postsynaptic density

area in the postsynaptic cell membrane that contains neurotransmitter receptors and structural proteins important for synapse function

why is the post-synaptic density dark?

because of a large number of proteins (receptors, G-proteins etc)

presynaptic density

collection of proteins for locating, exocytosis and recycling synaptic vesicles

what happens at the synaptic cleft?

lots of proteins, axons and dendrites connect to each other

What are the two hypotheses for Alzheimer's?

beta-amalyoid (plaques) and tau (tangles) hypothesis, breakdown of transport in neurons causes cell to die

What is tau?

microtubule associated protein

What is beta-amyloid?

a protein that accumulates in amyloid plaques in Alzheimer's disease

What are microtubules stabilised by?

tau protein, kinases phosphorylate tau protein

What is a neuron?

cell type specialised for communication, all cells have a soma (cell body)

What does the dendritic tree/dendrites do?

receive information

What is the initial segment?

axon hillock

What does the axon do?

send information

What are the features of action potentials?

all or nothing electrical signals (cell fires APs or not), most neurons fluctuate around -70mV RMP, depolarisation, repolarisation, overshoot (afterhyperpolarisation)

What happens during the action potential?

Na+ channels open (depolarisation), AP firing causes Na+ channels to close, K+ channels open, K+ channels close (repolarisation)

What is the function of synapses?

convert an electrical signal to a chemical signal

What happens at the synapse?

communication between neurons, AP at synapse causes vesicles to fuse and release neurotransmitter, neurotransmitter binds to receptors on post-synaptic cell, open to allow ions through, post-synaptic neuron depolarised generating AP

What is the shape of a neuron determined by?

connections

What is different between dendrites and axons?

proteins, present in dendrites

What are the three main components of the neuronal cytoskeleton?

microtubules, neurofilaments, microfilaments

microtubules

What is the largest component in the neuronal cytoskeleton?

neurofilaments

What is the middle component in the neuronal cytoskeleton?

microfilaments (mostly actin, also in muscles)

What is the smallest component in the neuronal cytoskeleton?

one actin molecule

What is globular actin?

filamentous actin

What is lots of actin?

largest, made of protein tubulin

What are microtubules?

originally thought to be made of three neurofilament proteins (but not true - lots)

What are neurofilaments?

composed of the protein actin, monomers of actin are globular (G-actin), for filamentous (F-actin) in a microfilament

What are microfilaments?

freeway for moving things around the neuron, microtubules - main roadway (move many things), actin filaments (microfilaments) - on/off ramps (things leave to go to destination), neurofilaments - joining parts (structure)

What is the cytoskeleton similar to? (analogy)

via microtubules (axonal transport), shown through ligation - vesicles accumulate on soma side, labelling a protein with fluorescence, ligation causes information to stop/blocks pathway down the axon

How is material transported down the axon?

20-28nm diameter

How big are microtubules?

hollow tube of protein tubulin, dimers (two molecules bound together), one molecule of alpha tubulin, one molecule of beta tubulin, has a positive and negative end, uses GTP as energy, microtubule network (labile - chnages/polymerises fast), tubulin dimers get added at positive end to elongate axon

What are microtubules made of?

have a positive and negative end

Why are microtubules said to be polarised molecules?

depolymerises or depolymerises as needed

Why are microtubules labile?

alpha/beta tubulin dimers bind GTP, polymerise/lose phosphate group and become GTP-bound, positive end where dimers polymerise and microtubule grows, associated with other proteins/accessory proteins that can stabilise or unstabilise proteins eg rescue factor (like glue - holds it together)

What do microtubules do?

connect microtubules to other cellular components, important in arranging microtubules into networks/holding microtubule together eg Tau in dendrite and axon, MAP-2 in soma and dendrite, many different proteins associated with microtubules that do a variety of jobs/have lots of functions

what are microtubule associated proteins (MAPs)?

microtubules anchored from the negative/stable end, gamma-tubulin binds with gamma-tubulin-complex proteins (GCPs), form a gamma-tubulin ring complex (gamma-TuRC) which binds the minus end of the microtubule and gets anchored to centrosome, microtubules take proteins and transport them down the synapse

what is the function of the negative end on microtubules?

play a stabilising role during assembly, making microtubule more likely to form and form faster, stabilise microtubules, many different MAPs that have diverse roles

What is the function of MAPs during microtubule assembly?

an anchoring protein complex

What is microtubule organising complex (MTOC)?

proteins etc move down microtubules via passive and axonal transport, energy intensive, used motor proteins (kinesin and dynein)

how do things move down microtubules?

bidirectional (250-400mm/day), uses motor proteins kinesin and dynein

What is fast axonal transport?

unidirectional (1mm per day), uses sliding/protein interactions (chemical reactions with micro-tubules), anterograde - mitochondria, vesicles, membrane lipids, retrograde - used materials

what is slow axonal transport?

towards synapse from soma (cell body)

what direction does kinesin move things in?

away from synapse back to soma

what direction does dynein move things in?

have a motor domain (contains ATPase - enzyme, conserved across species), have a tail domain, specifies function of motor molecule, binds to specific cargoes, diverse within/across species, docks with molecule being transported, specific tail domain for whatever is being transported

what are the features of motor proteins?

distinct protein docking adaptors, specific to cargo being transported

what do cargo carried by motor proteins have?

use ATP, convert chemical potential energy (phosphate) to mechanical energy, binding to microtubule causes conformational change in protein that swings the other domain forward, ATP-bound foot loses phosphate and is weakly bound, binds ATP and swings molecule forward, uses a molecule of ATP every time a foot swings (energy intensive)

how do motor proteins walk?

smaller than microtubules (around 10nm), predominant cytoskeleton component, huge mechanical strength, most stable part of cytoskeleton, important in structural framework, many more of them, linking parts that link them together

What are the features of neurofilaments?

light, medium and heavy neurofilament proteins, and many more

What are the main components of neurofilaments?

join together to make actin filaments, made up of actin (filamentous), actin is an ATPase enzyme, filaments made up of G-actin (bound to ATP and polymerises to F-actin, hydrolysing ATP to ADP, barbed and pointed ends

what are the features of microfilaments?

similar to tubulin, rapidly repolymerased and depolymerased, very dynamic, ATP-actin to ADP-actin, molecules of ATP-actin bump into each other and bind ("actin tread-milling")

What are the features of actin dynamics?

role is to aid in endocytosis and exocytosis

what is the function of actin in endocytosis and exocytosis?

size - large, tubulin molecule, 20nm diameter, function - trafficking of proteins, vesicles, mitochondria

What are the main features of microtubules?

intermediate filaments, 10nm diameter, strengthen axon (axonal integrity/strength and diameter)

What are the main features of neurofilaments?

small, actin molecules, 5nm diameter, function - endocytosis/exocytosis of cargo as well as spine growth, strength

What are the features of microfilaments?

tau protein stabilises microtubules, phosphorylated Tau dissociates from microtubule, microtubule depolymerises, phosphorylated Tau forms neurofibrillary tangles

What happens in Alzheimer's disease?

DNA transcribed to mRNA, three part code on mRNA transcribed to amino acid, assemble into chains to form proteins, have DNA (contains instructions for what cell is going to do), transcription, translation, folding, GTP to GDP

What is the central dogma of biology?

extremely dynamic, making new proteins all the time, more ER, more proteins, more darkly stained

Why does a neuron make so many proteins?

large stacks of rough endoplasmic reticulum

what are Nissl granules (nissl bodies)?

dynamic and varied, use a wide variety of different proteins for many different functions

how do neurons differ from other cells?

receptors located on presynaptic nerve cell membranes

what is an autoreceptor?

to make diverse proteins for the synapse

what is a major requirement of the soma?

calcium channels, docking proteins for vesicles, neurotransmitter auto receptors, reuptake channels, vesicle accessory proteins

what are some of the proteins at the presynaptic neuron?

voltage gated ion channels, G-protein receptors, enzymes (kinases, phosphatases)

what are some of the proteins at the postsynaptic neuron?

membrane proteins specialised for signalling

What are receptors?

directly change membrane potential, fast, eg GABA

what are ion channel receptors?

use G-protein to set off an intracellular signalling cascade eg kinases that phosphorylate things, slower due to more time for steps, eg serotonin (5HT), dopamine, more neuromodulatory, don't allow anything directly into cell

what are G-protein coupled receptors (GPCRs)?

inhibitory neurotransmitter, allows Cl- through, cell hyperpolarised, why GABA-agonists are nervous system depressants

what does GABA do?