Electrical and chemical signalling Flashcards
(37 cards)
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
