P: Synapses

Question 1

Define stimulus

Answer 1

Stimulus: an environmental event that excites sensory receptors to provide information about the event to the CNS.

Question 2

What happens if you block potassium channel or open a sodium channel

Answer 2

Blocking a K+ channel and opening a Na channel has same effect: builds up positive charge, so cell depolarises.

Question 3

Acetylcholine (ACh)

Answer 3

Used by spinal cord neurons to control muscles. Used by neurons in brain to control memory. Usually excitatory

Question 4

Dopamine (DA)

Answer 4

Produces feeling of pleasure. Usually inhibitory

Question 5

Gamma-aminobutyric acid (GABA)

Answer 5

Major inhibitory neurotransmitter in brain

Question 6

Glutamate

Answer 6

Major excitatory neurotransmitter in brain

Question 7

Glycine

Answer 7

Mainly used by spinal cord neurons. Usually inhibitory

Question 8

Norepinephrine/ Noradrenaline

Answer 8

Acts as neurotransmitter + hormone.
In PNS used for fight or flight.
In CNS regulates normal brain processes
Usually excitatory, but can be inhibitory in some brain areas.

Question 9

Serotonin

Answer 9

Involved in mood, appetite, sensory perception.
Inhibitory action in pain pathways of spinal cord.

Question 10

How can neurotransmitter be removed from synapse?

Answer 10

• Degradation by membrane bound enzymes
• Reuptake into presynaptic cell
• Diffusion out of synapse

Question 11

How do antidepressants work?

Answer 11

• Block enzymes that degrade neurotransmitters so that neurotransmitter concentration remains higher for longer
• Block neurotransmitter uptake into presynaptic membrane, so neurotransmitter concentration remains higher for long and more neurotransmission will occur.

Question 12

Excitatory postsynaptic potentials:

Answer 12

depolarisations bring membrane towards threshold

Question 13

Inhibitory postsynaptic potentials

Answer 13

hyperpolarisations that bring membrane further from threshold.

Question 14

EPSP characteristics:

Answer 14

• Summation
• No threshold
• No refractory period
• Occur in dendrites + cell bodies

Question 15

Spatial summation

Answer 15

Excitatory potentials from many neurons trigger threshold point

Question 16

Temporal summation

Answer 16

Many excitatory potentials from one neuron triggers threshold point.

Question 17

SNARE proteins

Answer 17

soluble N-ethylmaleimide sensitive factor attachment protein receptor.

Question 18

What are the types of SNARE proteins

Answer 18

• Synaptobrevin (v-SNARE)
• Synaptotagmin (v-SNARE)
• Syntaxin (t-SNARE)
• SNAP 25 (t-SNARE)

Question 19

Describe the mechanism of SNARE proteins

Answer 19

1. Action potential arrives at nerve terminal
2. Syntaxin and SNAP 25 (t-SNARE) form complex.
3. Synaptobrevin (v-SNARE) begins to join with Syntaxin and SNAP 25 complex and 3 SNARE proteins wind around each other to pull vesicle membrane and nerve terminal closer together
4. Entry of calcium into presynaptic neuron which binds to synaptotagmin, causing fusion of vesicle and release of Ach into synaptic cleft
5. ATP required to disassemble SNARE proteins

Question 20

How does ACh release lead to a muscle AP

Answer 20

Binding of ACh to nicotinic receptors allows simultaneous flow of Na+ in and K+ out through the ligand gated ion channels
The nicotinic receptor leads to fast synaptic transmission The movement of ions leads to generation of end plate potentials

Question 21

Tetrodotoxin

Answer 21

Blocks voltage gated Na+ channels
Novocaine, lidocaine –> block action potential rather than synapse.

Question 22

Calciseptine

Answer 22

Blocks Ca2+ channels

Question 23

Iberiotoxin

Answer 23

Blocks K+ channels

Question 24

Saxitoxin

Answer 24

Blocks voltage gated Na+ channels

Question 25

Compare absolute and relative refractory periods

Answer 25

• During absolute refractory period, another stimulus (AP) will not excite neuron
• During relative refractory period, another stronger stimulus can excite neuron

Question 26

Primary hyperkalemic paralysis

Answer 26

• Painful spontaneous muscle contractions followed by periods of paralysis of affected muscles
• Plasma + extracellular fluid have elevated K+
• Due to mutated Na+ channels causing reduction in rate of voltage inactivation and longer lasting action potentials –> increased K+ secretion
• Na+ channels become refractory so muscles cannot contract in response to further stimulatory action potentials.