Physiologic anatomy of the chemical synapses. Mechanism by which is caused a transmitter release from the presynaptic terminals.

Question 1

basic anatomical structures of chemical synapse

Answer 1

presynaptic terminal

synaptic cleft

postsynaptic terminal

Question 2

pre-synaptic terminal - 1

Answer 2

= part of neurone that releases neurotransmitter

voltaged gated calcium channels

• opens in response to AP
• influx of calcium ions enter to release neurotransmitter

Question 3

pre-synaptic terminal - 2

Answer 3

axon terminal
= end of axon that approaches post-synaptic terminal

Question 4

pre-synaptic terminal - 3

Answer 4

synaptic vesicles
= membrane-bound sacs with neurotransmitters inside
- chemicals that diffuse across synaptic cleft

Question 5

pre-synaptic terminal - 4

Answer 5

active zone

location where
- synaptic vesicles fuse
- neurotransmitter is released

Question 6

pre-synaptic terminal - 5

Answer 6

mitochondria
= energy for synaptic tranmission

Question 7

synaptic cleft

Answer 7

gap between pre-synaptic terminal + post-synaptic terminal

• 20-40 nanometres
• filled with extracellular fluid for easy neurotransmitter diffusion

Question 8

post-synaptic terminal - 1

Answer 8

= part of neurone receiving neurotransmitter

post-synaptic membrane = dendrite/ muscle cell/ gland cell that faces pre-synaptic terminal

Question 9

post-synaptic terminal - 2

Answer 9

post-synaptic density

= region beneath post-synaptic membrane
- contains receptors + signalling proteins for efficient signal transduction

Question 10

mechanism of transmitter release - step 1

Answer 10

ARRIVAL OF ACTION POTENTIAL

• action potential travels down the neurone along axon
• reaches the pre-synpatic terminal then the process begins

Question 11

mechanism of transmitter release - step 2

Answer 11

DEPOLARISATION

opening of voltage gated calcium gated ion channels
on the pre-synaptic membrane

calcium ions enter inside from ECF due to electrochemical gradient

Question 12

mechanism of transmitter release - step 3

Answer 12

CALCIUM SENSING PROTEINS

the influx of Ca2+ ions detected by these calcium sensing proteins e.g. synap-to-tagmin

they are part of vesicular membrane

synaptotagim fuses with calcium = conformational changes

Question 13

mechanism of transmitter release - step 4

Answer 13

SYNAPTIC VESICLE DOCKING

synaptic vesicles are docked on pre-synaptic membrane

via proteins involved in SNARE complex
- synapto-brevin
- syntaxin
- SNAP-25

Question 14

mechanism of transmitter release - step 5

Answer 14

NEUROTRANSMITTER RELEASE

fusion of pre-synaptic membrane + vesicular membrane = exit via pore neurotransmitter release by exocytosis

across synaptic cleft to receptors on post-synaptic membrane via diffusion to reach post-synaptic membrane receptors

Question 15

mechanism of transmitter release - step 6

Answer 15

RESPONSE

• opening of ion channels
• activation of secondary messenger pathways

Question 16

mechanism of transmitter release - step 7

Answer 16

TERMINATION

1 - reuptake of neurotransmitter into pre-synaptic terminal by transporter protein

2 - enzymatic degradation in synaptic cleft

3 - diffusion of neurotransmitter away synaptic cleft