1: Physiology - Neurons, excitation and inhibition in the CNS Flashcards
What is the start of an axon called?
Hillock
How are materials like mitochondria, proteins etc. transported along a nerve axon?
Axonal transport
What are the names of axonal transport which move materials
a) towards the presynaptic terminal
b) towards the cell body?
a) Anterograde axonal transport
b) Retrograde axonal transport
How do viruses travel within nerves?
(Retrograde) axonal transport
What is a synapse?
Point of chemical/electrical communication between nerve cells
What is a neurite?
A structure which projects from a nerve cell body
so an axon or a dendrite
unipolar, multipolar neurons
What is meant when describing an axon by its Golgi type?
Golgi type I axons are long
Golgi type II axons are short
What is the membrane potential of
a) sodium
b) potassium?
a) +60 mV
b) -90mV
In general, what is the threshold potential of a neuron?
The membrane potential required for Na+ channels to open
Which channels open to cause the upstroke of an action potential in neurons?
Na+
What channels open to cause the downstroke of an action potential?
K+ channels
What overcompensations are caused by the opening of
a) sodium
b) potassium?
a) Overshoot
b) Undershoot
i.e the membrane hyperpolarises before returning to normal
What is the difference between the conduction of action potentials and passive signals through nerve axons?
Action potentials have a fixed amplitude all the way along so they can travel long distances
Passive signals decay in amplitude and can therefore only travel short distances
How far can action potentials travel in the body compared to passive signals?
Much further than passive signals
Revise ohm’s law (V=IR)
Resistance of axon is constant
Current leaks as you go along the axon
So the further along the axon you go, the greater the decrease in action potential
from what I can tell…
decreasing resistance INCREASES length constant because the action potential can travel further before decaying to 37% (specific number because it matches to exponential function)
look at ratio specifically
rm/ri
How does conduction velocity change with an increasing length constant?
The greater the length constant, the greater the distance the current can spread without decaying
So the greater the conduction velocity
How does insulating a nerve axon with myelin increase the conduction velocity?
Insulation INCREASES membrane resistance while internal resistance remains unchanged
So the ratio rm/ri INCREASES
So length constant INCREASES
So conduction velocity increases
Which glial cells insulate nerve axons in the
a) CNS
b) PNS?
a) Oligodendrocytes
b) Schwann cells
What is a Node of Ranvier?
Gap between Schwann cells (found only in the PNS)
What is saltatory conduction?
The jumping of an action potential between Nodes of Ranvier
Saltatory conduction occurs only in (myelinated / unmyelinated) neurons.
myelinated PNS neurons only
because they have Nodes of Ranvier
How does myelination change the conduction velocity?
Myelination increases conduction velocity
Which type of disease slows down or stops nerve conduction?
Demyelinating disorders
Which demyelinating disorders affect the
a) CNS
b) PNS?
a) MS
b) Guilain-Barre syndrome
What is the name of the space between pre-synaptic and post-synaptic neurons?
Synaptic cleft
In terms of a synapse, what is a vesicle?
Structure which contains neurotransmitter
What is a membrane differentiation?
Area between a vesicle and neurotransmitter receptor
small as possible to make neurotransmission quick
How do glial cells affect neurotransmission?
Hoover up neurotransmitters from the synaptic cleft
Describe
a) axodendritic
b) axosomatic
c) axoaxonic
synapses.
a) Synapse found between the AXON of one neuron and the DENDRITE of another
b) AXON “ BODY
c) AXON “ AXON
What are the three morphological types of synapse?
a) Axodendritic
b) Axosomatic
c) Axoaxonic
What are the two functional types of synapse?
Excitatory and inhibitory
Which neurotransmitters are usually found at
a) excitatory synapses
b) inhibitory synapses?
a) Glutamate
b) GABA, glycine
Which named action potentials are generated by
a) excitatory synapses
b) inhibitory synapses?
a) Excitatory post-synaptic potential
b) Inhibitory post-synaptic potential
In terms of changes in membrane potential, what happens at
a) excitatory synapses
b) inhibitory synapses?
a) Depolarisation (opening Na+ channels)
b) Hyperpolarisation (opening Cl- channels)
Many neurons receive more than one, i.e a sum of synapses.
How does this determine whether an output will be excitatory or inhibitory?
Summation
so if you get two excitatory post-synaptic potentials and one inhibitory, the net result will be excitation and vice versa
Action potentials can be summated to affect the overall output.
What other variable determines the output of a neuron?
Frequency
i,e if excitatory potentials are firing off quicker than inhibitory potentials, the output will be excitation and vice versa
What two types of summation change whether a neuron’s output is excitatory or inhibitory?
Spatial, i.e how many of each type a neuron is receiving
Temporal, i.e how often a neuron is receiving potentials of each kind
