Lecture #23 - The synapse (full pre much but go over last page of paper)

Question 1

What’s a synapse?

Answer 1

“The junction bw nerve cells, where a nerve impulse is transferred from one neuron to another.”

“Communication bw neurons occurs through a junction called a synapse”

Question 2

Electrical synapse (city of one cell connected to cyto of other)

1. Neurons linked by?
2. Explain gap junctions (three things)
3. DAP - stands for?
4. Very fast or slow synapse?

Answer 2

1. Neurons linked by?
   - gap junctions
2. Explain gap junctions (three things)
   - specific type of membrane channels
   - ‘tunnel’ connecting 2 diff neurons
   - physical link (direct connection)
3. DAP - stands for?
   - Direct propagate of Action Potential
4. Very fast or slow synapse?
   - Very fast synapse

Question 3

Chemical synapse (gap bw cells)

1. Neurons linked by?
2. What’s the messenger?
3. What does the messenger do?
4. IAP - stands for?
5. Slow or fast?

Answer 3

1. Neurons linked by?
   - Physical gap between neurons…linked by chemical compound
2. What’s the messenger?
   - neurotransmitter (released into synaptic cleft)
3. What does the messenger do?
   - bridges the gap (the synaptic cleft)
4. IAP - stands for?
   - Indirect propagation of Action Potential
5. Slow or fast?
   - Slower than electrical synapse

Most synapses in brain are chemical
Heart is connected all by gap junctions so AP just pass through that

Question 4

What kinda channels in input zone to allow AP to pass down neutron?

Answer 4

Stimulus-gated

Question 5

Depolarisation = trigger or inhibit?
Hyperpolarisation = trigger or inhibit?
(usually)

Answer 5

Depolarisation = trigger 
Hyperpolarisation = inhibit

Question 6

What’re the 8 key components of the chemical synapse?:

Answer 6

1. Presynaptic cell (output zone)
2. Synaptic knob
3. Synaptic cleft (the gap)
4. Postsynaptic cell (input zone)
   - the membrane of post has high density of ion channels
5. Voltage-gated Ca2+ channels
   - selective to Ca2+
   - in presynaptic cell
   - on the arrival of AP at knob, VGCaC open bc depolarisation of knob…allow extracellular Ca2+ to enter
   - Ca2+ triggers the rapid exocytosis of neurotransmitter molecules from vesicles in knob (trigger fusion of vesicles with pre membrane)
   - relases neurotrans into cleft
6. Vesicles
7. Cytoskeleton
   - protein fibres that keep certain structures
   - vesicles interact w/ these for transport
   - vesicles travel to membrane using cytoskeleton
8. Mitochondria
   - For e.g. Na/K ATPase

Question 7

Ca2+

1. What’s the conc in ECF?
2. Is it high or low inside cell?
3. Imp for?
4. Triggers what?

Answer 7

1. 2.2 to 2.6mmol/L
2. Very low inside (so if chann open, flows inside)
3. Important for bones and nervous system
4. Triggers release of vesicles

Question 8

What does G-protein coupled receptors do?

Answer 8

• Can activate “other K+” channels that aren’t voltage gated

- Don’t allow passage of ions but send messages in cell that can activate

Question 9

How is the signal transmitted?

Answer 9

1. Neurotrans DIFFUSES across the synaptic cleft to reach the post synaptic membrane
2. Neurotrans bind to specific receptors aka “stimulus gated channels”
3. If Na+ chain open - LOCAL depolarisation of the post cell (excitatory signal)
4. Net depolarisation - called the EPSP (excitatory post synaptic potential)

3’. If K+ [[OR]] Cl- channel open - hyper polarisation (inhibitory signal)

4’. Net hyperpolarisation - called the IPSP )inhibitory post synaptic potential)

Question 10

The opening of ion channels in the post synaptic membrane may produce a local potential called POSTSYNAPTIC POTENTIAL

Excitatory neurotransmitters cause…..

Inhibitory neurotrans cause……

Answer 10

Excitatory neurotransmitters cause both Na+ AND K+ to open. Bc Na+ rushes inward faster than K+ out, there’s temporary depolarisation called EPSP
-If EPSP reaches the -59mV threshold, AP is initiated

Inhibitory neurotrans cause K+ and/or Cl- to open. Cl- rushes in; K+ out. Either event makes the inside of membrane even more -ve than RMP - this temporary hyperpolarisation is called an IPSP
-the post mem less likely to reach the threshold potential; invitation of an act pot is thus inhibited

Question 11

How is a synapse switched off?

Answer 11

• Excess transmitter released into the cleft
• Excess transmitter must be removed
  a) Degradation - enzymic (makes compound inactive by break down)
  b) Reuptake - into the bouton (membrane transporter requires ATP so it can be recycled)
  c) Reuptake (diffusion) - into glia cells (reabsorbed)