Lecture 12 and 13 - Synapses

Question 1

Allow ions to move between cells. Thus, graded potentials & action potentials can be directly passed between cells.
Transmission is fast, essentially instantaneous.
Usually, but not always, bidirectional.
Common in many cell types excitable and non-excitable.
Closes when ↑ [Ca++] or ↑pH on either pre- or postsynaptic cells.

Answer 1

Gap junctions

Question 2

Presynaptic cell & postsynaptic cell are in close apposition.
Depolarization of synaptic terminal lead to fusion of synaptic vesicles to presynaptic membrane.
The content (transmitters) of the vesicle is dumped into the synaptic cleft (the extracellular space between the pre- & postsynaptic cells. (It’s the reverse of endocytosis in this respect.)
Transmitters bind to receptors in the postsynaptic membrane.
Binding to receptors results in either change in ion conductance or a second messenger cascade.

Answer 2

Chemical synapse

Question 3

Presynaptic side exocytosis steps

Answer 3

Action potential depolarizes the axon terminal.
Depolarization opens Ca2+ channels and Ca2+ enters cell.
This then allows exocytosis of vescicle contents

Question 4

modes of transmitter inactivation

Answer 4

1. Reuptake: some transmitters are taken back up by the presynaptic neuron or by glia (e.g. serotonin).
2. Enzymatic inactivation: for others, enzymes cleave transmitter to inactive form (e.g. acetylcholinesterase inactivates acetylcholine).
3. Diffusion. Simple diffusion away from the synaptic area also terminates transmission. This mode is to varying extent occurring with all transmitters.

Question 5

How does heroin work

Answer 5

• Binds to µ-opioid receptors (endogenous transmitter: enkephalin & endorphin).
• Is an agonist.
• Prolonged use results in tolerance and dependence associated with down-regulation of µ-opioid receptors

Question 6

_________ receptors – binding of transmitter to receptor initiates change in ion conductance. These are the ligand-gated ion channels

Answer 6

Ionotropic

Question 7

_________receptors – binding of transmitter to the receptor initiates a biochemical chain of events within the cell.

Answer 7

Metabolic

Question 8

Transmitter action via ionotropic receptors is _______; action via metabotropic receptors is ________.

Answer 8

Fast

Slower

Question 9

Entry of ______, ______ leads to EPSP

Answer 9

Na+, Ca2+

Question 10

Entry of ______ or exit of _______ leads to IPSP.

Answer 10

Cl-, K+

Question 11

Location of ionotropic or metatropic matters more?

Answer 11

Ionotropic

Question 12

Non vescicular release transmitters

Answer 12

lipids (e.g. eicosanoids)

gases (e.g. nitric oxide, NO)