Topic 2: Neurons and action potentials Flashcards
membranes
what gets through protein channels
outer sac water oxygen sodium chloride calcium potassium
mitochondria
how energy
function people with over and under active mitochondria or mutated?
powerhouse, metabolic provides energy for neuron functions
use enzymes to break down glucose into Adenosine Triposphate
over; burn fuel rapidly over heat
under; predisposed depression and pain
mutated; theory of autism
mitrochondria have some DNA (get from mum e.g mitochondrial eve)
ribosomes
where protein molecules are synthesized
endoplasmic reticulum
folded parallel layers
rough synthesise proteins
smooth synthesise fats
network of thin tubes that transport newly synthesized proteins from the ribosomes to other locations, some ribosomes are connected to endoplasmic reticulum
soma
cell body
dendrites
receive signals
not as long
can have dendridic spines
axon
transmit signals
can be much longer up to 1m (sciatic nerve), have constant radius, covered in myelin
myelin is made of 80% fat, protective and increases speed of AP. MS is inflammation scars and legions CNS myelin, causing cog decline (memory), motor problems, visual problems
not all axons are myelinated, some delayed pain signals.
myelin makes white matter white, somas etc is grey matter
At the end of an axon are terminal buttons/bootons (pre-synaptic terminal, axon terminal)
tiniest neruons don’t have them
Motor neuron v sensory neuron shape
motor; soma in spinal chord, has axon going out all the way to muscles (has also dendrites going out from the soma to receive info from nearby cells)
efferent neurons
sensory; has a long axon with the soma in the middle of it somewhere, at the end of the axon is specialized fibers for sensing (touch etc)
afferent neurons
nodes of ranvier
myelin interruptions for potentiating signal
afferent v efferent v intrinsic
towards (e.g. every sensory neuron is afferent to the rest of the nervous system)
away (e.g. every motor neuron is efferent from the nervous system)
instrinsic or interneuron is when a cells dendrites and axons are contained within a structure e.g. the neurons of the thalamus. they join sensory (afferent) and motor (efferent) messages. Often found in the spinal chord
variation within cell structure
purkinje
bipolar
purkinje; many widely branching dendrites, in the cerebellum, inputs from 200’000 cells
wheras bipolar neurons in retina, only 2 other cells input, small few branches
Glia
all the other parts of the nervous system
outnumber neurons in the cerebral cortex
while neurons outnumber glia in the cerebellum
overall numbers are roughly equal
astrocytes
star shaped glia
wrap around the axons of closely functionally related axons preventing influx of chemicals, taking up and releasing ions and transmitters to synchronize the axons of multiple cells for rhythmic activation patterns e.g. breathing
also can dilate blood vessels for increased nutrients to active areas
microglia
immune system
remove viruses and fungi from the brain
proliferate after brain damage removing damaged cells
remove weak unused synapses
use process called phagocytosis engulf and consume!
cause collateral damage, implicated in alsheimers
oli astrid and schwann are macroglia crew, mini wants in
oligodendrocytes and swann cells
oli in brain and spinal chord (CNS) and Shwann in PNS build myelin
provide nutrients
migration of neurons is by the…
radial glia (after embryonic development, differentiates into neurons astrocytes and oli’s)
blood brain barrier and viruses
regular cell virus response is to signal the immune system to destroy the cell which will be replaced. Nervous system cells don’t get replaced so the blood brain barrier prevents viral infections
exceptions; rabies and syphilis
and viruses that get contained but may come back eg chicken pox and herpes
built of endothelial cells which form the walls of blood vessels, are packed much tighter on the BBB
also keeps out fuel and amino acids necessary for building proteins, need ATP active transport to do it
area postrema at medulla of brain has weaker BBB, this is responsible for vomiting, sensitive to toxins making vomm quickly
blood brain barrier and nutrients 4 ways
small
lipid based
protein channels in endo wall
active transport
small uncharged particles can get through e.g. oxygen CO2
fat dissolved can get through vitamins A & D and psychotropic drugs
speed of effect of drugs dependent on how readily it dissolves in fat (heroin and nicotene readily disolve in fat) dopamine doesn’t dissolve in fat, L-dopa does and once inside can be catalysed by enzymes into dopamine for parkinsons sufferers
endothelial cell wall has protein channels to let through water
active transport - energy using protein mediated, glucose amino acids purines choline some vitamins iron
insulin and others also cross although we don’t yet know how
BBB and health
alsheimers, endothelial cells shrink (harmful chemicals in)
brain cancer problem - chemo cant cross
energy use in most cells vs in neurons cancer and testes cells
most use carbs and fats, neurons use glucose
metabolizing glucose requires oxygen
the brain is 2% of humans body weight but uses 20% of its oxygen and 25% of its glucose
its because glucose is the only nutrient that crosses the BBB in large quantities
you need B1 to use glucose, alcoholism leads to B1 deficiency which leads to brain cell death Korsakoff’s syndrome)
Bipolar axons
1 axon and 1 dendrite either side of the soma, most often found in visual and auditory systems
unipolar axons
1 axon, going either side of the soma which is somewhere in the middle of the axon. one side receives sensory information and the other side transmits it towards the CNS.
found in the somatosensory system
multipolar
most common CNS neuron
typical neuron diagram
many dendrites attached to the soma, with a long axon coming of the other side
micro-tubules
a structure within neuron, tracks to transmit stuff between the soma and terminal buttons
this is called axoplasmic transport needs ATP, its a kind of active transport.
2 types of axoplasmic transport
anterograde and retrograde
anterograde axoplasmic transport
john
carries proteins, vesicles of neuro transmistters and other vital things from the soma to the terminal buttons, carried by kinisin proteins
5m/day
retrograde axoplasmic transport
fred
carries thing like waste from the terminal buttons towards the soma, carried by dynein proteins
rabies, tetinis, polio, herpes, all transmitted into soma by the dynein doing retrograde axoplasmic transport
2.5m/day
the kinisn and dynein can compete in direction if not all conditions are right for transport in one direction or another
marker of alsheimers
is neurofibulary tangles.
caused by tau proteins (part of microtubles) have there structure changed by excessive phosphate ions.
this interupts axoplasmic transport, leading to cell death.
axoplasmic transport is a vital function of neurons
cytoskeleton & cytoplasm
The cytoskeleton is a network of filaments and tubules that extends throughout a cell, through the cytoplasm, which is all of the material within a cell except for the nucleus. It is found in all cells, though the proteins that it is made of vary between organisms.
cytoplasm is the fluid jelly, holds organelles
actin
laneways off the main track(microtubules) of the cytoskelitin
there is also interfilaments
neurofiliments
threads that form a matrix that maintain shape of neuron and support the membrane
golgi aparatus
smooth plate shaped membranous sac that packages up proteins etc into little sacs called vesicles
many in the cell body to transport neurotransmitters in vesicles down to the buttons
some are in the buttons, making vesicles out of scrap button wall bits!
also makes lisosomes that have enzymes to break down and recycle waste products
types of proteins
enzymes - chemical reactions, synthesise and break down stuff
peptide hormones - regulate body functions eg insulin
transporter proteins - haemoglobin
tubulin - struture of stuff
antibodies - immune proteins
all proteins are made of chains of amino acids, up to 50 with 20 essential aminos acids (from food)
cell membranes
details about active and passive transport
what determines what gets through a channel
made of phospho-lipid molecules while hydrophilic heads on the outer edge on the membrane, exposed to the water
and hydrophobic tails(inside of membrane)
In most cases, the movement of molecules in and out of the cell is controlled. Some very small molecules can cross freely (e.g. nitric oxide [NO], a soluble gas recently recognised as being important in learning). However, many ions cross the cell wall via channels found in the membrane’s protein molecules. These channels are called ion channels, and they are specific to that ion (e.g. potassium channels). Ion selectivity is determined by:
the size of the molecule the electrical charge of the molecule in the hydration of the channel.
Ion channels are a form of passive transport as the cell does not use its own energy supplies to transport molecules into or out of the cell. These channels can be permanently open (‘free passive transport’) or open only when certain conditions are present in the membrane (‘gated passive transport’).
Gated channels can be chemically gated, which means that they can only open when a specific molecule binds to the transport molecules. Alternatively, they can be voltage gated and open when certain electrical properties are present in that region of the cell wall.
There are also active transport mechanisms provided by membrane protein molecules. These require energy in the form of ATP to pump ions in and out of the cell. The most important active transport mechanism is the sodium-potassium pump.
Using these transport mechanisms, cells create electrical differences across the cell membrane (i.e. a membrane potential). Neurons, however, go one step further than other cells and exploit this electrical difference to transmit information.
proteins use in the cell
channels
transporters
signal takers
protein synthesis TTT
transcription; DNA is copied into mRNA
translation; the mRNA exits nucleus through pores and goes to ribosomes and tells them to make the proteins (which they make out of amino acids)
transport; newly synthesized proteins are carried by the axoplasmic transporter kyeine
resting membrane potential
no excititory (making the cell more positive, + charged neurotransmitters) or inhibitory (making the cell more negative, - charged neurotransmitters) messages being received.
the resting potential is the difference in electrical potential between the inside and outside.
inside is -70mV more negative than outside in resting potential state
this is POLARISED
membrane potential
electrical potential difference between inside and outside of the cell.
Polarized de-polerised and hyper-polerised
Polarized: inside of the cell is very negative (net compared to outside)
de-polerised: when the inside becomes more positive (it goes up to +40mV)
hyper-polerised: refracts down to lower than -70mV (-75mV)
ions that effect electrical charge
Na+ sodium
K+ potassium
Ca++ calcium
Cl- chlorine (this is what the lecturer wrote but it might be cloride Cl- which has an added negative ion making it Cl-, and wanting to form a compound)
whats the I-C and E-C composition in resting state
intracellular fluid has higher organic anions (-) and potassium (K+)
ion channels leak potassium out, keeping the overall charge negative
extracellular fluid has more chloride (Cl-) and sodium (Na+) overall positive charge (a lot of sodium)
(remember that the extracellular is saltwater NaCl in there)
ion channels types
free (can pass any time) or gated (only certain things) voltage opened (+40mV) e.g. for sodium it needs to be 40+ and then boom chemical opened (only specific ions can go through)
sodium potassium pump
requires ATP
passive transport in ions moving across cell membrane
Diffusion and electrostatic pressure
diffusion
kinetic energy - molecules bump around and distribute evenly
sodium will spread into the cell where there is a lower concentration. this changes the membrane potential towards less negative
electrostatic pressure
cations (+) and anions (-) electrolytes when dissolved split into these
sodium is a cation
cl is an anion
opposite charges attract, same charges repel
concentration gradient v membrane gradient v electrical gradient
concentration gradient is the high and low concentration within a fluid and diffusion happening
electrical gradient also known as polarization is the difference between the inside and outside of the cell
hypertonic
hypotonic
isotonic
high concentration
low concentration
equal concentration
axon hillock
dendrites pick up signal, it goes to the soma, the soma connects to the axon at the axon hillock. enough to reach the threshold of excitation means the action potential will be propagated.
rate law of action potentials
higher frequency rates of action potentials are for stronger stimulus. higher frequencies also increase likelihood of nearby neuron being triggered
threshold of excitation
-55mV at the axon hillock
saltatory conduction
nodes of ranvier allow quicker potentiating, ions jump from node to node (saltatory conduction) so not all channel opening is needed
also the sodium-potassium pump only need to be at the nodes, saving energy (cause they use ATP)
osmosis
Osmosis is the spontaneous net movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.
diffusion v osmosis
The main difference between the two is that diffusion can occur in any mixture, even when two solutions aren’t separated by a semipermeable membrane, whereas osmosis exclusively occurs across a semipermeable membrane.
in our case osmosis refers to the movement of water
