Synaptic transmission 1

Question 1

describe electrical synapses

Answer 1

joined by gap junction
6 connexin form a connexon with central lumen
two connexons of adjacent cells join to form gap junction.
Allows passage of small molecules and ions (non selective)

Question 2

describe chemical synapses

Answer 2

normal neurotransmission.

Question 3

compare space between pre and postsynaptic cell membranes for electrical and chemical synapses

Answer 3

4nm; 20-50nm

Question 4

compare synaptic delay for electrical and chemical synapses

Answer 4

virtually non existent for electrical

atleast 0.3ms, 1-ms for chemical

Question 5

compare direction for electrical and chemical synapses

Answer 5

bidirectional for electrical

unidirectional for chemical.

Question 6

distinguish axo-dendritic, axo-somatic and axo-axonic chemical synapses

Answer 6

axo-dendritic: synapse between axon terminal and dendrite (most common)
axo-somatic: synapse between axon terminal and soma (usually inhibitory)
axo-axonic: synapse between axon terminal and axon (modulatory)

Question 7

describe Grays Type I chemical synapses

Answer 7

usually excitatory, hence contact dendritic spines
assymetrical
circular vesicles
more electron dense

Question 8

describe Grays Type II

Answer 8

usually inhibitory, hence contact dendritic shaft and soma
symmetrical
oval vesicles
less electron dense

Question 9

types of effectors after neurotransmitter release?

Answer 9

other neurons

neuromuscular junction

Question 10

define neurotransmitter

Answer 10

produced by presynaptic neuron
released from neuron and has defined action on postsynaptic neuron/effector
specific mechanism for removing nt from synaptic cleft
exogenous administration mimics actions of endogenous transmitter

Question 11

three types of nt

Answer 11

aas
peptides
amines

Question 12

describe process for release of NT

Answer 12

• cell prepares vesicles
• AP reaches axon terminal
• voltage gated Calcium channels activate, allowing calcium to enter cell
• calcium causes vesicles to bind to plasma membrane and release (exocytosis)
• nt binds to receptor
• membrane recovered via endocytosis

Question 13

describe how vesicles are pepared for amino acids, peptides and amiens

Answer 13

GABA (complex AA) and amines need enzyme; so precursor and enzyme are transported
Peptides are packaged into synaptic granules (100nm vs 50nm for vesicles), actively transported via kinesin to axon terminal

Question 14

are some synaptic vesicles already partially fused to the membrane to improve speed of release?

Answer 14

yes

Question 15

4 ways excess neurotransmitters can be recycled?

Answer 15

diffusion of nt’s away from synapse
reuptake
enzymatic degradation
Na+/Ca2+ exchanger: 1 calcium out, 3 Na+ in.

Question 16

two types of postsynaptic receptors?

Answer 16

ionotropic and metabotropic receptors

Question 17

describe ionotropic receptors

Answer 17

binding of nt to receptor causes conformational change of channel - it opens
-fast but brief

Question 18

describe metabotropic receptor

Answer 18

receptor indirectly linked with ion channel via signalling cascade –> G protein opens channel or actives enzyme
-slower, longer lasting

Question 19

describe potential responses to neurotransmitter

Answer 19

no response, or
postsynaptic potential: transient change in membrane potential
-excitatory (transient depolarisation) or inhibitory (transient repolarisation)

Question 20

describe spatial summation

Answer 20

APs from 3 neurons occurring simultaneously will add – more likely to reach threshold

Question 21

desecribe temporal summation

Answer 21

AP’s from one neuron happening shortly after each other can add – more likely to reach threshold

Question 22

is there more?

Answer 22

yes yeet