Electrical and chemical signalling

Question 1

How are action potentials spread in unmylinated axons?

Answer 1

Action potentials are spread by passive voltage changes along axon membrane

Question 2

How do positive charges formed during an action potential move?

Answer 2

Move towards areas which have a high concentration of negative charges

Question 3

In very simple terms, what happens during an action potential?

Answer 3

Positive charges rush into cell

Question 4

Why do action potentials only occur in 1 direction?

Answer 4

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

Question 5

What effect does myeline have on action potentials? What effect does the Nodes of Ranvier have?

Answer 5

Myelin provides high resistance to ion flow across the membrane
Resistance is lost at node of Ranvier

Question 6

Where are Voltage-gated sodiumand potassium channels mainly located?

Answer 6

At the node of Ranvier

Question 7

How does an action potential travel down a mylinated axon?

Answer 7

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

Question 8

What is Saltatory conduction?

Answer 8

The propagation of action potentials along myelinated axons from one node of Ranvier to the next node

Question 9

Describe how action potentials jump from one node to another?

Answer 9

1. as charge spreads down an axon, mylination prevents ions from leaking across the plasma membrane.
2. Charge spreads unimpeded untill it reaches node of ranvier which has many Na+ channels
3. Electrical signals jump down the axon, as it is faster than moving through the unmylinated section

3.

Question 10

What is the conduction velocity in relation to action potential movement?

Answer 10

Current flowing along axon can leak across the cell membrane or travel through the cytoplasm depending on the path of least resistance

Question 11

Effect of diameter on cytoplasmic resistance

Answer 11

Rc decreases with increased diameter

Larger axons conduct faster

Question 12

Do large axons conduct faster? If so why?

Answer 12

cytoplasmic resistance decreases with increased diameter

Question 13

Relationship between membrane resistance and insulation

Answer 13

Rm increased with insulation

Myelin insulates axons

Question 14

Where in the axon is conduction fastest? Why is this?

Answer 14

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

Question 15

Features of Aα = motor neurons in relation to function, receptors and conduction velocity

Answer 15

-proprioreceptors
-Muscle spindles
-Golgi tendon organs
CV- 80-120m/s

Question 16

Features of Aβ = touch neurons in relation to function, receptors and conduction velocity

Answer 16

Function:Touch
Receptors: Mechanical touch / pressure
CV- 35-75

Question 17

Features of Aδ and C neurons in relation to function, receptors and conduction velocity

Answer 17

Function- Aδ- fast pain and temp
C- slow pain and temp
Cv- Aδ =5-35
CV- C= 0.5-2.0

Question 18

Difference between electrical and chemical synapse

Answer 18

Chemical synapses transmits signals indirectly using chemical transmitters

Electrical synapsestransmit excitation directly through gap junction

Question 19

What happens when the action potential reaches the synapse?

How does this relate to the term summation?

Answer 19

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

Question 20

What happens after the action potential reaches the synaptic terminals in muscle cells?

Answer 20

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

Question 21

How are neurotransmitters released?

Answer 21

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

Question 22

Name 3 amino acid Neurotransmitters and there functions

Answer 22

Glutamate- Memory, excitatory Neurotransmitter
γ-aminobutyric acid (GABA)- Calming (inhibitory)
Glycine

Question 23

Name 3 Monoamine Neurotransmitters and there functions

Answer 23

Noradrenaline (adrenaline)- flight or fight/concentration
Serotonin (5-HT)-Mood, hunger, sleep arousal.
Dopamine- movement, attention emotion and pleasure

Question 24

Name a Neuropeptides Neurotransmitters

Answer 24

Opiates

Question 25

Name other Neurotransmitters

Answer 25

purinergic (adenosine; ATP, ADP, AMP)

Gasses (NO) (nitric oxide)

Question 26

Function of the Neurotransmitter Acetylcholine?

Answer 26

Muscle action, learning and memory

Question 27

What is the Excitatory Postsynaptic Potential(EPSP)

Answer 27

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

Question 28

What is Inhibitory Postsynaptic Potential(IPSP)

Answer 28

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

Question 29

Describe the term temporal summation

Answer 29

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

Question 30

Describe Spatial summation

Answer 30

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

Question 31

Where are small Neurotransmitters made? Give an example of small ones

Answer 31

synthesized in synapse and packaged into vesicles (ACh and NA)

Question 32

Where are large Neurotransmitters made? Give an example of large ones

Answer 32

synthesized in cell body and transported inside vesicles down axon to the synapse

Question 33

How are Neurotransmitters recycled? What are the different mechanisms?

Answer 33

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)

Question 34

What is ACh made from?

Answer 34

Choline and acetyle CoA

Question 35

Which enzyme breaks down ACh and where is it broken down?

Answer 35

Acetylcholinesterase breaks it down

Broken down in synaptic cleft

Question 36

What happens to choline after ACh is broken down?

Answer 36

Transported back into the axon to make more ACh

Question 37

What is the fate of small and protein Neurotransmitters after use?

Answer 37

Small Neurotransmitters are transported back into the neurons and usually recycled

Protein Neurotransmitters are degraded in the extracellular fluid by non-specific proteases