Neuronal Cell Biology Flashcards
give brief overview of the cerebral cortex
senses perception, voluntary movements, learning, memory, thinking, emotion and consciousness
what brain regions are are evolutionary conserved?
pituitary. spinal cord. medulla. hypothalamus.
what happens as you move up the brain?
get more complex
- cerebellum = highest neuron density
- cerebral cortex = higher thought
give a brief overview of the cerebellum.
muscle tone, balance, coordination of voluntary movement, motor learning
where would you find the brain areas that are evolutionary ancient?
the structures at the bottom
all animals have them
need for basic function
what is white matter?
higher lipid content
contents mainly axons with myelin
what is grey matter?
contains the cell bodies which have less lipid
how are grey and white matter connected?
tracts
what is an example of function due to a neural circuit?
reflex e.g. knee jerk
what is the knee jerk reflex?
- stimulation of peripheral sensors
- initiates receptors
- trigger action potentials
- travels on the afferent axons on sensory neurons
- stimulates motor neurons through synapses
- action potentials travel through efferent axons
- gives rise to muscle contraction and behavioral response
what did ramon y cajal do?
- used a stain to visualise neurons
- golgi stain
what does the silver chromate stain do?
- when labelled doesnt label all of the neurons
- can see whats happening in the tissue
how can you use genetic engineering to show pathways?
use a promoter to drive a reporter gene
how can we use a promoter to drive a reporter gene?
- cell type specific
- select a promoter to the neuron
- can track GFP
describe the process of genetic engineering using a reporter protein
- reporter protein that codes for a visible protein
- inserted into the genome
- under control of a cell type specifci promoter
- reporter expressed only in those cell types
- reveals the cell bodies/axons/dndrites of cells that express the gene
what are the 2 key points about neuron morphology?
- high degree of polarity
2. electrically excitable
describe dendrites
- provide the input
- more dendrites then axons
describe axons
- provides the ouput
- can be branched
what are spiny neurons?
dendritic spines, use neurotransmitter glutamate, excitatory
what are non-spiny neurons?
use NT gabba, inhibitory
what are glia?
- provide support to neurons
- not electrically excitable
what are the different types of glia?
astrocytes, oligodendrocytes, microglia
what are astrocytes?
most common, star like shape, involved in the blood brain barrier (BBB)
what are oligodendrocytes?
schwann cells in peripheral nervous system, ensheath the axons with myelin
what are microglia?
innate immune cells in the central nervous system (CNS), macrophages, activate when theres a problem, become highly motile
what is neuronal polarity underpinned by?
the neuronal cytokseleton: microtubules, neurofilaments, microfilament
what does a restriction at the cell body do?
only allows certain proteins in the axon. selective filter at the axon entrance.
what can be useful markers?
specific cytoskeletal isoforms
what is highly expressed in the axon?
tau
what is the problem with axonal transport?
synapse can be mm or m away from the cell body
what experiment did Weiss and Hiscoe do?
- exposed the nerve on cats
- tied a twine, restricted axons
- started to bulge, proteins etc get trapped
- suggests active transport
what do you need to transport materials?
motor proteins
how are mitochondria made?
mitochodnrial polypeptides are synthesised and imported in the cell body
how are synaptic vesicles made?
Synaptic vesicle polypeptides are synthesised and processed in the ER and Golgi
how are mitochondria and synaptic vesicles transported?
- Loaded onto kinesin molecules
- transported to synaptic terminus where they are used
- used bodies are transported back to the cell body
in what direction is there movement along the axon?
bidirectional
what is anterograde transport?
away from the cell body
what is retrograde transport?
too the cell body
what is the resting membrane potential?
- electrical potential recorded at rest
- expressed relative to the outside
- between -60 - 70 mV
how does the lipid bilayer play a role?
- impermeable to ions so they have to move through ion channels
- move through Na/K ATPase ump
describe ion movement in neurons
- membrane highly permeable to K+ ions
what is the Nernst potential?
membrane potential at which there is no net flow of that particular ion from one side to the other
- ion is in equilibrium
what is the Nernst potential equation?
Ek= RT/zF ln〖[K]out/[K]in〗
what is the concept of a current clamp
inject a known quantity of current into the cell which alters the neuronal membrane potential
what does the current clamp measure?
measure the Vm response
how does the current clamp work
- 2 microelectrodes
- one measures the membrane potential
- one injects current
what happens if you inject positive current in a current clamp?
- increases positivity, depolarize slightly
- above the threshold will trigger an action potential
what is the concept of a voltage clamp?
- measuring ion channel activity
- control the membrane voltage whilst measuring the current and injecting a metered amount to keep at a desired level
what do we measure in the voltage clamp?
measuring the current - equal and opposite to the current through the ion channels
describe the process of the voltage clamp
- internal electrodes measure the membrane potential - connected to a voltage clamp and a voltage clamp amplifier
- compares the Vm to command voltage
- if Vm is different an electrode injects current into the axon
where is the recording electrode in voltage clamp?
in the axon
where is the reference electrode in voltage clamp?
in the surrounding saline solution
what is the command voltage?
we set the membrane voltage
what is the patch clamp technique?
- smaller neurons
- pipette forms a high resistant seal on the membrane
- apply suction
- results in brief currents
- when the channels are open the trace goes down
what is the whole patch clamp technique?
- seal pipette to neuron
- apply more suction so the membrane ruptures
- pipette in phase with the cell
- voltage is that of the whole membrane
how can properties of one type of channel be studied with whole cell patch clamp technique?
can be studied by blocker other types with toxins/drugs/chemicals
describe the activation gate of Na+ channels?
fast kinetics, closed at resting potential, open in response to depolarisation
describe the inactivation gate of Na+ channels?
slow kinetics, open at resting potential, closes in response to depolarization
describe the activation gate of K+ channels?
slow kinetics, closed at resting potential, open in response to depolarization
describe the inactivation gate of K+ channels?
not present
what happens when there are changed concentrations of extracellular Na+?
- amplitude and rise of action potential decreased
- action potential –> changed shape
- no matter what happens to Na+ the resting potential stays around the same
describe the K+ ion channel?
- voltage gated
- tetrameric (4 subunits)
describe the Na+ ion channel
- monomeric
- one large protein that folds itself
what is meant by voltage gated?
- activation gate –> both open in response to depolarisation
- have a voltage sensor
what is the role of the transmembrane helix S4
- senses change
- twists via a conformational change and opens
- positively charged residues in S4 cause it to rotate
describe inactiavation
- closed resting - no Na+
- opens - Na+ flows in
- inactivated - second gate shuts, pore opens but no Na+ can get through
- closed inacitvated - membrane repolarise, activation gate closes and inactivation gate opens again
when is inactivation triggered?
when the channel is open
which is the more activated state?
inacitvation state is more energetically stable than the activated state
what is the inactivation gate?
- large intracellular loop on the channel protein
- contains amino acid motif (IFM) which blocks the pore
what is the Hodgkins and Huxleys model?
Rest –> activation gates closed
- depolarisation = Na+ channels open, influx, further depolarisation, K+ channels open, K+ flows out
- depolarisation slows down
reprolarisation - inactivation gate opens again and activation gate shuts
describe how TTX toxin modulates the Na+ channel?
- puffafish neurotoxin
- sticks into the pore of the channel blocking it
how would BTX and ScTX modulate the Na+ channel?
dont block - change how it operates - too much sodium as the channels are kept open
what can mutations in the channels caust?
epilepsy
