Electrical and chemical signalling Flashcards
How are action potentials spread in unmylinated axons?
Action potentials are spread by passive voltage changes along axon membrane
How do positive charges formed during an action potential move?
Move towards areas which have a high concentration of negative charges
In very simple terms, what happens during an action potential?
Positive charges rush into cell
Why do action potentials only occur in 1 direction?
Because membrane behind an action potential is in absolute refractory period. This is the period immediately following the firing of an action potential when it cannot be stimulated no matter how great a stimulus is applied
What effect does myeline have on action potentials? What effect does the Nodes of Ranvier have?
Myelin provides high resistance to ion flow across the membrane
Resistance is lost at node of Ranvier
Where are Voltage-gated sodiumand potassium channels mainly located?
At the node of Ranvier
How does an action potential travel down a mylinated axon?
It jumps from one Node of Ranvier to another. Local current that flows to the next node is strong enough to initiate an action potential which jumps to the next node
What is Saltatory conduction?
The propagation of action potentials along myelinated axons from one node of Ranvier to the next node
Describe how action potentials jump from one node to another?
- as charge spreads down an axon, mylination prevents ions from leaking across the plasma membrane.
- Charge spreads unimpeded untill it reaches node of ranvier which has many Na+ channels
- Electrical signals jump down the axon, as it is faster than moving through the unmylinated section
3.
What is the conduction velocity in relation to action potential movement?
Current flowing along axon can leak across the cell membrane or travel through the cytoplasm depending on the path of least resistance
Effect of diameter on cytoplasmic resistance
Rc decreases with increased diameter
Larger axons conduct faster
Do large axons conduct faster? If so why?
cytoplasmic resistance decreases with increased diameter
Relationship between membrane resistance and insulation
Rm increased with insulation
Myelin insulates axons
Where in the axon is conduction fastest? Why is this?
Conduction is faster in myelinated axons
-Large diameter axons in mylinated axons offer less resistance to current flow.
-Myelin limits the amount of membrane in contact extracellular fluid so current leakage out of the axon is minimised
it also Creates a high resistance wall that prevents ion flow out of cytoplasm
Features of Aα = motor neurons in relation to function, receptors and conduction velocity
-proprioreceptors
-Muscle spindles
-Golgi tendon organs
CV- 80-120m/s
Features of Aβ = touch neurons in relation to function, receptors and conduction velocity
Function:Touch
Receptors: Mechanical touch / pressure
CV- 35-75
Features of Aδ and C neurons in relation to function, receptors and conduction velocity
Function- Aδ- fast pain and temp
C- slow pain and temp
Cv- Aδ =5-35
CV- C= 0.5-2.0
Difference between electrical and chemical synapse
Chemical synapses transmits signals indirectly using chemical transmitters
Electrical synapsestransmit excitation directly through gap junction
What happens when the action potential reaches the synapse?
How does this relate to the term summation?
The digital signal (action potential) is converted into an analogue signal (chemical neurotransmitter)
Different neurotransmitters are excitatory or inhibitory
The addition of all the excitatory and inhibitory signals is called summation
What happens after the action potential reaches the synaptic terminals in muscle cells?
Depolarisation opens voltage-activated Ca2+ channels in sarcoplasmic reticulum
[Ca2+]i very low 10-8M
[Ca2+]o 10,000 times higher 10-3M
Large inward gradient and electrical concentration
How are neurotransmitters released?
The vesicles dock and a SNARE complex anchors the vesicles to the cytoskeleton.
The vesicles fuse with the membrane to release there content. Calcium also enters
Name 3 amino acid Neurotransmitters and there functions
Glutamate- Memory, excitatory Neurotransmitter
γ-aminobutyric acid (GABA)- Calming (inhibitory)
Glycine
Name 3 Monoamine Neurotransmitters and there functions
Noradrenaline (adrenaline)- flight or fight/concentration
Serotonin (5-HT)-Mood, hunger, sleep arousal.
Dopamine- movement, attention emotion and pleasure
Name a Neuropeptides Neurotransmitters
Opiates
Name other Neurotransmitters
purinergic (adenosine; ATP, ADP, AMP)
Gasses (NO) (nitric oxide)
Function of the Neurotransmitter Acetylcholine?
Muscle action, learning and memory
What is the Excitatory Postsynaptic Potential(EPSP)
Postsynaptic membrane potential is more likely to result in carrying an action potential
Glutamate-gated channels cause a net influx of Na+ and depolarization of the postsynaptic neuron
What is Inhibitory Postsynaptic Potential(IPSP)
Decreases ability of the membrane to reach threshold and carry an action potential
GABA & Glycine-gated channels cause an net influx of Cl- hyperpolarizes the postsynaptic neuron
Describe the term temporal summation
Postsynaptic potentials at same synapse occurin rapid succession
Because 1st potential does not have time to dissipate the next potentials add to previous one and increase the change in potential
Describe Spatial summation
Multiple postsynaptic potentials from different synapses occur about the same time and add
EPSP’s (excitatory postsynaptic potential ) from different synapses are not strong enough to generate an action potential but by reinforcing one another may trigger an action potential
Where are small Neurotransmitters made? Give an example of small ones
synthesized in synapse and packaged into vesicles (ACh and NA)
Where are large Neurotransmitters made? Give an example of large ones
synthesized in cell body and transported inside vesicles down axon to the synapse
How are Neurotransmitters recycled? What are the different mechanisms?
Vesicles recycled by endocytosis.
Can be ultra fast <0.1s (cell takes in membrane bubbles and recycles them into vesicles)
kiss and run <2s (vesicles never fully fused)
Clathrin mediated 10-20s (conventional)
What is ACh made from?
Choline and acetyle CoA
Which enzyme breaks down ACh and where is it broken down?
Acetylcholinesterase breaks it down
Broken down in synaptic cleft
What happens to choline after ACh is broken down?
Transported back into the axon to make more ACh
What is the fate of small and protein Neurotransmitters after use?
Small Neurotransmitters are transported back into the neurons and usually recycled
Protein Neurotransmitters are degraded in the extracellular fluid by non-specific proteases
