PHYSIOLOGY - Neurones, nerve conduction and synaptic transmission Flashcards
what is the function of a dendrite
receives input from other neurones and conveys to soma
what are the 2 functions of the soma
- cell body - synthetic and metabolic centre - contains ribosomes, mitochondria and ER
- integrates incoming electrical signals and conducts them passively to the axon hillock
what is the site of initiation of all or none action potential
axon hillock and initial segment
what is the function of the axon
conducts output signals as APs to the presynaptic terminal
how are materials transported between the soma and the presynaptic terminal
axonal transport
what are the 2 types of axonal transport
anterograde - body to PST
retrograde - PST to body
which type of axonal transport do viruses exploit
retrograde
give 3 examples of viruses that exploit retrograde axonal transport to infect neurones
polio
rabies
herpes
what is a synapse
point of chemical communication between neurones / other cells
what are the 4 possible polarities of neurones and what do they entail
unipolar - one neurite
pseudounipolar - one neurite that bifurcates
bipolar - 2 neurites
multipolar - 3 or more neurites
give an examples of a unipolar neuron
peripheral autonomic nerve
give an examples of a pseudounipolar neuron
dorsal root ganglion neurone
give an examples of a bipolar neuron
retinal bipolar neurone
give an examples of a multipolar neurone
lower motor neuron
what is meant by golgi type I
long axon
golgi type II is short axon
what are the 4 functional regions of a neurone
input
integrative
conductile
output
K+ ions and organic anions are typically found at higher concentrations inside / outside the cell
inside
Na + and Cl- are typically found at higher concentrations inside / outside the cell
outside
at rest, the cell membrane is most permeable to which ion
K+
which ion has the biggest influence on the resting membrane potential
K+
what maintains the concentration gradients at rest
Na+/K+/ATPase via active transport
depolarisation causes what ion channels to open and in which direction do these ions move
voltage gated Na+ channels
causing Na+ influx
what is meant by all or nothing
AP will only occur if a threshold is met, and if this threshold is met there will be a maximal response
once the cell has been depolarised the ___ channels close and the __ channels open causes what ions to move where
Na+ channels close and K+ channels open
causing K+ ion efflux –> repolarisation
is Na/K/ATPase involved in repolarisation
no
what often occurs with repolarisation
undershoot of RMP making membrane potential more negative
what is meant by the absolute refractory period
once the sodium channels close after an AP they enter an inactive state when they can’t be reopened regardless of the membrane potential
what is meant by the relative refractory period
the Na ions slowly come out of inactivation during which time they may be excited with stimuli stronger than one normally needed
the refractory period ensures ….
unidirectional flow of AP
what is the overshoot
brief period when polarity is reversed to inside positive
what is the resting membrane potential of a neurone
- 70
why do passive signals not spread far from their site of origin
current loss across the membrane accompanied by a reduced change in potential - leaky membrane
what is ohm’s law
V= IR
for a given current, the potential change increases/decreases linearly with membrane resistance
increases
what is the equation for length constant (lambda)
( rm / ri )^0.5
the ____ the length constant, the further the local current spread and so the higher the AP conduction velocity
longer
the _____ the length constant, the higher the AP conduction velocity
longer
give 2 ways in which the passive current spread could be increased
decrease axial resistance
increase membrane resistance
how could axial resistance be reduced
increase diameter of axon
how could membrane resistance be increased
insulation - myelin sheath
what cells provide myelin in the CNS
oligodendrocytes
what cells provide myelin in the PNS
Schwann cells
schwann cells and oligodendrocytes are both types of ____ cells
macroglial cells
true/false
a single schwann cell can insulate up to 50 axons
false
an oligodendrocyte can, but a schwann cell can only insulate 1 axon
myelin increases/decreases membrane capacitance
decreases
what is saltatory conduction
AP jumps from one node of ranvier to the next
what clusters are the nodes of ranvier
voltage activated Na+ channels
give 2 disorders that would cause slowing or cessation of nerve conduction
MS (CNS)
Guillian Barre Syndrome (PNS)
what are the 8 steps in chemical neurotransmission at the synapse
uptake of precursor synthesis of transmitter storage of transmitter depolarisation by AP Ca influx through VGCC Ca induced release of transmitter (exocytosis) receptor activation enzyme mediated inactivation of transmitter or reuptake of transmitter
what holds the pre and post synaptic membranes together
matrix of fibrous extracellular protein within cleft
where are the active zones and what are they
pre-synaptic membranes
vesicles cluster around them and opposite to neurotransmitter receptors
what are the 3 types of synapse and what is the most common
axodendritic - most common
axosomatic
axoaxonic
what is the main excitatory transmitter in the CNS
glutamate
glutamate activates the post-synaptic, ____ selective (__), ___tropic glutamate receptors generating a local, graded, excitatory response
cation selective (Na+) ionotropic
excitatory stimulation causes ____
depolarisation
glutamate generates a ...
EPSP
excitatory post synaptic potential
what are the main inhibitory transmitters in the CNS
GABA or glycine
what is the actual name of GABA
gamma - aminobutyric acid
GABA/glycine activate a postsynaptic, ____ selective (__), ___tropic GABAa/glycine receptors generating a local, graded inhibitory response
anion selective (Cl-) ionotropic
inhibitory stimulation causes ____
hyperpolarisation
GABA/Glycine generate a ...
IPSP
inhibitory post synaptic potential
what are the 3 main amino acid neurotransmitters in the CNS
glutamate
glycine
GABA
what is spatial summation
how many of each type of stimulation (inhibitory/excitatory) a neuron is receiving - many inputs converge upon a neurone to determine its output
what is temporal summation
tempo
how often a neuron is receiving stimulation of each type - a single input may modulate output by variation in AP frequency of that input
name 4 amine neurotransmitters
dopamine
histamine
noradrenaline (NA)
serotonin (5-HT)
Ach, amino acids and amines are released from ___
synaptic vesicles
peptides are released from ____
secretory vesicles
what neurotransmitters can activate ionotropic ligand gated channels
glutamate gaba glycine Ach 5-HT
all except ___ can activate metabotropic G protein coupled receptors
glycine
ionotropic/metabotropic receptors mediate slow neurotransmission
metabotropic
ionotropic receptors mediate ___ neurotransmission
fast
what receptors use direct gating
ionotropic ligand gated ion channels
how do metabotropic receptors use indirect gating
neurotransmitter acts on a G-protein complex that is distinct from the ion channel it controls
how do ionotropic receptors use direct gating
receptor is an integral part of the channel it controls
cholinergic synaptic transmission in autonomic ganglia uses both direct and indirect transmitter action.
Fast EPSP is due to ionotropic ____ Ach receptors - channels conduct __ and __
nicotinic
Na+ and K+
cholinergic synaptic transmission in autonomic ganglia uses both direct and indirect transmitter action.
slow EPSP is due to metabotropic ____ Ach receptors - ACh closes a __ channel
muscarinic
K+ (m-type)
true/false
glutamate has inhibitory function aswell
true - via metabotropic glutamate receptors
how can ionotropic glutamate receptors be classified
response to non-endogenous agonists that mimic glutamate
which receptors bind the agonist that mimics glutamate
non-NMDA receptors
give 2 examples of exogenous agonists that mimic glutamate and bind to non-NMDA receptors
kainite or AMPA
non-NMDA channels are permeable to what 2 ions
Na+ and K+
NMDA channels are permeable to what 3 ions
Na+ Ca2+ and K+
how many channels are non-NMDA channels permeable to
2
how many channels are NMDA channels permeable to
3
non-NMDA channels mediate ___ excitatory synaptic transmission in the CNS
fast
NMDA channels contributes a ___ component to the excitatory synaptic potential
slow
what promotes neurotoxicity with regard to NMDA receptors
high permeability to Ca2+
give 2 drugs (anaesthetic agents) that are selective blockers of NMDA-operated channels
ketamine
psychomimetic agents - phencyclidine
what is the role of metabotropic glutamate receptors
modulation of neurotransmission
how do metabotropic glutamate receptors modulate neurotransmission
presynaptic inhibition - e.g. inhibition of Ca2+ channels
what does NMDA stand for
N-methyl-D-aspartate
what causes GBS
autoimmune damage to myelin sheath of PNS
how does GBS present
changes to sensation/pain/muscle weakness - begins distally in hands and feet and spreads proximally to the arms and upper body
where is ACh synthesised
axon
where are neuropeptides synthesised
cell body
give 5 symptoms of LMN disease
hypo/areflexia hypo/atonia flaccid muscle weakness or paralysis fasciculations muscle atrophy
