Axons and Transmissions Flashcards
What is the resting potential of a cell
-50 to -70 mV
At resting what is found at higher concentrations within the cell that outside
K+
At resting what is found at higher concentrations outside the cell than inside
Na+
Cl-
At depolarisation what channels are open
Voltage-gated sodium ion channels
Makes the inside cell more positive
What must be met for an action potential to be reached
Threshold potential
What is an action potential described as
All or nothing
Once the cell has depolarised what happens
Voltage gated sodium channels begin to close
Voltage gated potassium channels open
K+ moves out of the cell
When is the absolute refractory period
Overlaps depolarisation and around 2/3 of repolarisation phase
Absolute refraction
Can a new action potential be generated and why
No
Voltage-gated sodium channels already open
OR
Sodium channels inactive recover from inactive state
When is the refractory period
1/3 of repolarisation (last)
Can a new action potential be generated during reflective period
Possible
In depolarisation what ions are moving
Na+ IN
During repolarisation what ions are moving
K+ out
What re-establishes resting state
Refractory period
Define a synapse
Gap present between two neurones
Where is acetylcholine synthesised
In the axon
What are the basic components of the neuron
Dendrites
Cell body/soma
Axon
Presynaptic terminal
What can move across a neuronal cell membrane
Easily - K+ Cl-
Difficulty - Na+
Some not at all - large organic proteins -ve charge
What is role of myelination
Speeds up axonal conduction
What are between myelin
Nodes of Ranvier
What do most CNS neurones have
Myelin
What breaks down acetylcholine
Acetylcholinesterase
Describe synaptic transmission
Neurotransmitter released
Calcium ion channels open when action potential reaches pre-synaptic terminal
Ca2+ ions cause vesicles to move to the release sites - fuse with the cell membrane - and discharge their contents
Transmitter substance diffuses across synaptic cleft
Attach to receptor sites on post-synaptic membrane
What are the five processes of synaptic transmission
Manufacture - intracellular biochemical processes
Storage - vesicles
Release - by action potential
Interact with post-synaptic receptors - diffusion across the synapse
Inactivation - break down or re-uptake
Give examples of fast neurotransmitters
ACh
Glutamate (GLU)
Gamma-aminobutyric acid (GABA)
Give examples of slow neurotransmitters
Dopamine (DA)
Noradrenaline
Serotonin
Describe the initation and propagation of action potentials
Receptors - neurotransmitter activated ion channels (dendritic tree and cell body)
Summination at the axon hillock
Voltage activated ion channels (mainly Na+ and K+)
Positive outside to positive inside
What can neurotransmitters be divided into
Excitatory
Inhibitory
Define excitatory neurotransmitters
Increase likelihood of postsynaptic neurone depolarisation and generation of an action potential
Define inhibitory neurotransmitters
Reduce likelihood of postsynaptic neurone depolarisation and generation of an action potential
In the peripheral axons what is myelination produced by
Schwann cells
In the central axons what is myelination produced by
Oligodendrocytes
How do you remember which cell is responsible for myelination
COPS
Central - oligodendrocytes
Peripheral - Schwann
How many axons does a Schwann cell myelinate
1
How many Schwann cells will peripheral axons have
Multiple
One Schwann cell wraps a lipid-rich membrane around approx 1mm of an axons length
What are the gaps called between Schwann cells and myelin sheath
Nodes of Ranvier
How many axons does a single oligodendrocyte myelinate
Multiple
The cell body and nucleus of oligodendrocytes remain separate from the myelin sheath
In which cell that produces myelin is neurilemma found
Schwann cell
Cell body and nucleus enveloping an axon
What is the difference between Nodes of Ranvier between CNS and PNS
CNS have fewer
PNS - if an axon is damaged how much growth can there be
Can be growth
CNS - if an axon is damaged how much growth can there be
Little
Due to inhibitory influence on regrowth from the oligodendrocytes and lack of neurolemma
Describe chemical synapse
Involves neurotransmitter
Carry information from the pre-synaptic-sending-neuron to the post synaptic -receiving cell
Single axon can have multiple branches can synapse on various post synaptic cells
Synaptic vesicles - membrane bound spheres filled with neurotransmitter molecules
Describe electrical synapse
Direct physical connection between the presynaptic and postsynaptic neuron
Uses gap junctions - allow current-ions to flow from one cell to another
