Neuroscience Flashcards
Learn the structure of a neuron
cell body
nucleus
dendrite
axon hillock
Myelin sheath
axon
node on ranvier
axon terminals
How many neurons does the brain contain?
About 86 billion
What is the average number of connections a neuron makes?
1000
What does the property ‘excitability’ of neuronal cells refer to?
The ability to respond to stimuli
What does the property ‘conductivity’ of neuronal cells refer to?
Ability to generate and propagate electrical signals known as action potentials
What does the property ‘secretion’ of neuronal cells refer to?
When chemical neurotransmitters are used to bridge gaps at synapses between neurons
What is the resting charge across a membrane?
Approximately -70mV
(maintained as a result of balance between chemical and electrical gradient)
What is the permeability like of a resting neuron membrane?
Membrane itself is relatively impermeable to ions
What do Na+/K+ ATPase membrane protein pumps do to maintain resting potential?
Pumps out 3 Na+ for every 2 K+ it brings in
Works continuously in presence of ATP
What are ion channels?
Proteins found in membranes that selectively control the permeability to cations (Na+, K+) and some anions (Cl-)
Describe the charge inside and out a membrane during resting potential?
The inside of the membrane has a negative charge with respect to the outside
What is the equilibrium potential of an ion?
The point at which there would be no net movement of the ion across the membrane
What is the resting equilibrium potential for Potassium (Ek)?
approximately -80mV
What is the resting equilibrium potential for Sodium (ENa)?
approximately +60mV
What is the membrane more permeable to at rest?
K+ (this is what gives membrane resting potential of -70mV in neurons)
What is the membrane state during rest?
membrane potential of -70mV
Votage gated Na and K channels closed
Intracellular - high [K+]
Extracellular - high [Na+]
What is local potential?
Where membrane potential rises - Eg in respond to a ligand gated ion channel
What happens to local potential if it doesn’t reach threshold?
Potential will diminish without causing action potential
What happens when membrane reaches threshold?
Depolarisation
Voltage gated Na open
K channels remain closed
Sodium moves into cell - membrane potential rises rapidly
What happens when membrane potential peaks at approximately 35mV?
Repolarisation
Voltage gated Na channels inactivated (not closed)
Voltage gated K channels open
K+ ions move out of cell
Membrane potential falls back towards resting
What is absolute refractory period?
When it is impossible to fire another action potential
Lasts about 1ms
K channels closing, Na channels inactivated
Potential drops below resting
What is relative refractory period?
When it is possible to fire an action potential but a larger stimulus is required
Lasts several milliseconds
Potassium channels closing, sodium channels de-inactivated
Sodium/potassium pump restores ion balance
What ae action potential generated in and what by?
In the trigger zone
By graded potentials of sufficient size (when a certain voltage threshold is reached)
Are action potentials graded?
No!
All or none response
Are action potentials decremental?
No
They do not decrease in size with distance from initial stimulus (non-decremental)
How do action potentials carry sensory or motor information?
They propagate along axons to the appropriate location
What is myelinination?
Where the neuron axon is insulated
This allows for more rapid conduction of the action potential
Are all neurons myelinated?
No, different types of neurons may be myelinated or unmyelinated
What is the progress along an unmyelinated axon called?
Continuous propagation
What is the progress along a myelinated axon called?
Saltatory propagation
What are areas without myelin called?
Nodes of Ranvier
How do action potentials pass the nodes of Ranvier?
The action potential jumps along these nodes, allowing for much faster propagation
How does axon diameter affect the speed of action potentials across it?
The greater the diameter, the faster the action potential can travel (max up to 120m/s)
What myelinates the peripheral axons?
Schwann cells
What myelinates CNS axons?
Oligodendrocytes
What is axoplasm?
cytoplasm of axon
What is axolemma?
cell membrane of an axon
What is neurilemma?
Sheath surrounding nerve axon, including the myelin sheath
What is multiple sclerosis (MS)?
Autoimmune disorder when myelination of central nerves is targeted
What is Guillain-Barre syndrome?
An autoimmune disorder when myelination of peripheral nerves is targeted
Where do neurons communicate with one another?
At synapses
What are the 2 types of synaptic transmission?
Electrical and Chemical
Which type of synapse is rare in the adult brain?
Electrical synapse
What is the synaptic cleft?
A gap at a chemical synapse between the pre and post synaptic elements
What is the first step in synaptic transmission?
An action potential opens voltage-gated Ca2+ channels in presynaptic membrane
Entry of Ca2+ triggers release of ACh from vesicles
The ACh diffuses across synaptic cleft
What is step 2 in synaptic transmission after ACh diffuses across synaptic cleft?
ACh interacts with ACh receptors (Na+ channels) which trigger an influx of Na+ ions
What produces an excitatory postsynaptic potential?
Influx of Na+
When is an action potential triggered in the postsynaptic neuron?
When the excitatory postsynaptic potential reaches -55mV
What is reffered to as the language of the nervous system?
Neurotransmitters along with electrical signals (means of communication between neurons)
Name 3 additional neurotransmitters
- Acetylcholine (ACh)
- Adrenaline
- Noradrenaline
3 amino acid neurotransmitter examples
- glutamate
- GABA
- glycine
What ere monoamine neurotransmitters derived from? Example?
Derived from amino acids
Eg. Serotonin
3 catecholamine neurotransmitter exaples
- Dopamine
- Epinephrine
- Norepinephrine
(Also monoamines)
2 Peptide neurotransmitters examples
Substance P
Endorphins
Slide 32
Neurotransmitter examples
What are the 5 important processes in regulating different transmitter systems?
- Synthesis
- Storage
- Release
- Receptor binding
- Inactivation/Reuptake
Synthesis of acetylcholine
Choline acetyltransferase is not saturated. The substrate’s (choline’s) availability is the rate determining step
Supplementing/restricting choline can increase/decrease acetylcholine production
Synthesis of dopamine
L-Tyrosine—>L-Dopa (catalysed by tyrosine hydroxylase) - rate determining step as normally saturated by substrate.
L-Dopa—>Dopamine (catalysed by dopa decarboxylase DDC) - enzyme has high activity and is non-specific
Give an example of a treatment targeting synthesis
L-Dopa for Parkinson’s Disease
Provides additional substrate for substrate production
Storage: what is glutamate?
Glutamate is a neurotransmitter packaged in vesicles in the presynaptic terminal
How are transmitter systems relaeased?
- Action potential reaches the presynaptic terminal
- Voltage gated Ca2+ ion channels open
- Influx of calcium ions
- This causes vesicle to bind with presynaptic membrane
- Contents of vesicle is released into synaptic cleft by exocytosis
What is a receptor?
Protein target which initiates a cellular response when activated
What are the 2 main categories of receptors?
- Inotropic (eg. nicotinic Ach receptor and NMDA receptor)
- Metabotropic (eg.muscarinic Ach receptor and mGluR)
Where can receptors be located?
On both the presynaptic and postsynaptic membrane
What are excitatory postsynaptic potentials (EPSPs) caused by?
Excitatory neurotransmitter receptors to transmitters. These include:
-glutamate
-acetylcholine
-noradrenaline
What are inhibitatory post synaptic potentials (IPSPs) caused by?
Inhibitatory neurotransmitters such as:
-GABA
-Glycine
-Noradrenaline
See slide 43 onwards
