Wk1-3 FOUNDATIONS Flashcards
ICF ECF concs
ICF= inc K+ ECF= inc Ca2+ and Cl-
describe cytoskeleton of neurons
microtubules= run down neurites,mediate IC transport neurofilaments = structural support, regulate diameter microfilaments= actin molecules, link tubules and membrane
what is a neurite
projection out of the soma e.g: dendrites and axons
larger diameter=
lower resistance, easier transmittance
what is the axon proper
axon strand,
2 types of axon travel=
fast axoplasmic transport
slow axoplasmic transport
fast axoplasmic transport
proteins travelling down microtubule, active process, proteins synthesised in soma transported to synapse waste from synapse transported to soma, 1m/day use kinesin/dynein proteins
anterograde via kinesin protein
towards synapse
retrograde via dynein protein
towards soma
slow axoplasmic transport
unclear mechanisms (stops and go?) not simply passive diffusion as it requires energy, 0.1-10mm/day
structure of axon terminals
no microtubules
many internal vesicles containing neurotransmitters
protein dense membrane
lots of mitochondria
what is a synapse
special connection between 2 neurons
describe chemical synapse
electric signal travels down axon
vesicles released in pre-synaptic membrane
travels through synaptic cleft
binds to specialised proteins at post-synaptic membrane
converted to electrical signal
slower than electrical synapses
outline dendrites
come off soma
spines protrude off dendrites to receive axonal inputs
dendrite arbor (tree-like structure) affects function
classifications of neurons
number of neurites (uni bi multi polar) shape and dendrites connections axon length types of neurotransmitters used
what a glia
glia support neural function and may be involved in information transmission, some produce myelin (myelinating glia)
what does myelin sheath do
prevents ion movements in ICF and ECF
increases axonal conduction velocity
insulator
outline astrocytes
most glia in brain fill spaces between neurons and vessels
influence neurone growth and regulate ECF, neurotransmitters, metabolism, blood brain barrier
ensheath smaller molecules
outline microglia
remove debris of dead cells
flight response inflammation in brain
specialised immune system in brain
outline ependymal cells
epithelium-like cells
line fluid filled vesicles
produce cerebrospinal fluid (CSF) and controls release between brain tissue and ventricles
a higher ratio in nernst/GHK equation =
higher charge imbalance = higher ionic equilbrium potential
if a membrane is permeable to only 1 ion, mpot will
move towards that ions equilibrium potential
what is an ions equilibrium potentials
the voltage that counteracts the conc gradient of an ion.
if mpot = equilibrium pot then no movement of ion
GHK calculates
mpot
if you know conc and permeability of all ions involved
outline sodium potassium pump mechanism
2 conformations = open to ICF or ECF
ICF conf = bonds ATP and 3Na.
ATP hydrolysed changing conformation
ECF conf = releases Na bonds to 2K
causes dephosphorylation and a second conf change
outline potassium channels
membrane is 40x more permeable to K than Na due to K leaky channels
2 pore domain channels help set resting mpot
outline depolarisation
threshold potential is crossed causing voltage gated Na channels to open. mpot moves towards Na potential.
outline repolarisation
when the threshold potential is first reached K channels are told to open too but are slower than Na channels. Na channels close and then most of the K channels are open causing repolarisation
outline hyperpolarisation
these delayed-rectifier k channels take longer to close causing the mpot to become more negative. after all these are closed the mpot restores with leaky channels. this is also known as the relative refractory period limitng further AP generation
what is the absolute refractory period
where APs rarely occur
Nav channels remain inactive during hyperpolarisation
inactivation of Nav channels stops
back propagation
outline saltatory conduction
AP propagation from jumping to nodes of ranvier. This is where ion channels are concentrated. more frequent gaps & smaller amounts of myelin are more effective in preserving the signal.
outline electrical synapses
form gap junction of non selective channels
direct electrical coupling between cytosol of 2 neurons
physically close
small and instant
bidirectional
2nd synapse has smaller voltage
chemical synapse classification: axon location
axo dendritic : synapse attaches to dendrites of other neuron
axo somatic
axo axonic
chemical synapse classification: microscopic structure
grays type 1: asymmetrical, round vesicles, excitatory
grays type 2: symmetrical, inhibitory, less electron dense
chemical synapse classification: by size
number and size of 2 neuron synapses indicates strength and importance of signalling.
inc strength = inc mpot = inc active zones present
chemical synapse classification: by neurotransmitter
amino acids
amines
peptides
chemical synapse classification: by effector
special example: neurotransmuscular junction which specialises in connection from motor neurons to muscle fibres
outline neurotransmitter synthesis
made in neuron it belongs to
- amino acids available in neuron are packaged
- GABA and amines require enzymes
- peptides packed in granules in nucleus and transported
outline neurotransmitter release
Cav channels in active zones open when AP reaches.
Ca floods axon terminals triggering neurotransmitter release.
Na Ca exchanger pulls 1 Ca out of terminal for 3 Na
outline neurotransmitter binding
2 methods
ionotropic: ligand gated channel on post synaptic membrane specific to neurotransmitter
metabotropic: linked with ion channels. acts through a second messenger. broader, distributed effects
outline responses to neurotransmitter
post synaptic potential (PSP) change in mpot due to neurotransmitter mediated opening
Excitatory PSP (EPSP) = depolarisation (Na influx) Inhibitory PSP (IPSP) = hyperpolarisation (Cl channels open)
explain IPSP
Cl channels open but due to mpot being the same as Cl potential, no ion movement. however any Na influx that occurs will then be counteracted.
outline recycling neurotransmitters
diffusion away from synapse
reuptake in pre synaptic terminal
enzymatic destruction break down
outline receptor response to stimuli
stimulus has effect on target receptors
receptors convert into a type of energy (likely chemical)
signal received by sensory neurons (afferent nerve fibres)
passed to a relay neuron in brain
signal reaches motor neuron (efferent fibres) out to the effector which performs response
3 types of receptors
somatic: for physical, touch position etc
special : for sense, smell taste etc
visceral : internal organs
somatic nervous system
part of motor division of PNS
controls skeletal muscle contractions
autonomic nervous system
part of motor division of PNS
made up of sympathetic (fight/flight) and parasympathetic (rest/digest)
directions of body
top dorsal
bottom ventral
front rostral
back caudal
slicing through brain as a scanner
horizontal transverse
vertical scanning forward coronal
vertical scanning side sagittal
outline sensory/motor neurons in CNS
sensory neurons:
cell body = dorsal root ganglion
axons enter = dorsal root
synapses = dorsal horn
motor neurons:
cell body = ventral horn
axons exit = ventral root
synapses = muscle fibres
brain stem
made up of the medulla, pons and midbrain
cerebellum
role in motor control
diencephalon
thalamus: relay station, controls flow of signals to cerebrum
hypothalamus: regulates metabolic processes
pituitary gland: homeostasis, hormones
pineal gland: endocrine organ modulates sleep
cerebrum
cerebral cortex: outermost sheet of neural tissue, sensory perception, motor control
basal ganglia: 4 internal nuclei, form feedback circuits with cerebral cortex
limic system: disparate collection of nuclei. made of hippocampus and amygdala
meninges
3 protective membranes departing CNS and bone
dura mater: outermost closest to skull, tough bag surrounding brain and spinal cord
arachnoid mater: appearance of spiderwebbed web, impermeable to fluid, no space between dura
pia mater: thin membrane, close to brain surface, separated from arachnoid by CSF, many blood vessels
CSF
produced by choroid plexus
situated within ventricles (4 cavaties in core of brain)
BBB
restricts entry of macromolecules into brain
shield brain from abnormal variations in ionic composition and toxic molecules
tight junctions
astrocytes regulate blood flow
separation of blood flow incase of an increase in pressure
extracellular recordings
electrode positioned in EC space.
one or more neurons may be recorded
electrical changes due to EC ions detected
provide info about networks of neurons
intracellular recordings
electrode in single neuron
ion filled micropipette electrodes
patch clamp recording which can vary to look at different manipulation of mpot.
computed axial tomography (CT scan)
multiple x ray images of brain
stacked together to produce 3D brain model
only detects brain structure, not function
magnetic resonance imaging (MRI)
the energy emitted from the spin of hydrogen atoms subjected to strong magnetic field
fMRI looks at function changes
what is a BOLD repsonse
blood oxygen level dependent response.
detectors detect more in brain in places that have more blood flow. higher score of BOLD signal can help find relations of function in brain parts.
electroencephalography
recorded localised change in electrical activity in the brain through the placement of electrodes on the head.
transcranial stimulation (TMS)
localised excitation of brain tissue by a magnetic current.
helps find relations between parts of the brain and modulate peoples behaviour
optogenetics
modulates activity by introducing light sensitive channels and an electrode into subject brain
microstimulation
intracellular: injecting current into single cell will change mpot
extracellular: injecting current into ECF will depolarise 100s of neurons.
