Synapsis

Question 1

Synapse

Answer 1

connection between two neurons or a neuron and an effector cell
Two types of synapse:
Electrical synapse
Chemical synapse

Question 2

Electrical Synapse

Answer 2

Function: Rapid transmission of signals. Faster than in chemical synapses!
Used to synchronize electrical activity in groups of cells: e.g. vertebrate heart, oscillations and brain rhythms.

Question 3

Chemical Synapse

Answer 3

At a chemical synapse, an electrical signal (membrane depolarization) is converted to a chemical signal (neurotransmitter).
Neurotransmitter binds to receptors in postsynaptic neuron.

Question 4

Chemical synapse: fast transmission

Answer 4

1. NT release close to receptors.
2. Receptors directly open ion channels (ionotropic).
3. Small vesicles

Question 5

Chemical synapse: slow transmission

Answer 5

1. NT release distant from receptors.
2. Receptors indirectly open ion channels (metabotropic).
3. Large vesicles

Question 6

Active zone

Answer 6

area of NT release

Question 7

In CNS neurons, vesicles are divided into:

Answer 7

1. Reserve pool (80-95%)
   
   2. Recycling pool (5-20%)
   3. Readily-releasable pool, RRP, (0.1-2%)

Question 8

Mild stimulation in synaptic vessels

Answer 8

triggers NT release from RRP.
A small fraction of vesicles (recycling pool) replenishes the RRP.

Question 9

Strong stimulation in synaptic vessels

Answer 9

causes reserve pool to mobilize and be released.

Question 10

Acetylcholine (ACh)

Answer 10

Primary neurotransmitter at vertebrate neuromuscular junction

Question 11

Neuromuscular junction

Answer 11

ACh receptor is a Na+/K+ channel
Inflow of Na+ causes depolarization

If depolarization exceeds threshold, then AP
If depolarization does not exceed threshold, then NO AP

Question 12

Neurotransmitter interaction with postsynaptic membrane:

Answer 12

1. Transmitter molecule combines with receptor molecule
   
   2. Occupied receptor sites cause activation of ion channels

Question 13

Graded potential

Answer 13

Change in membrane potential is a

Question 14

If ion current depolarizes the membrane

Answer 14

excitatory stimulates an AP in the postsynaptic cell

Question 15

If ion current hyperpolarizes the membrane

Answer 15

inhibitory prevents an AP in the postsynaptic cell

Question 16

Actions of Neurotransmitter

Answer 16

Graded Potential
When ligand-gated ion channels open, the membrane potential changes depending on which ion channel is open.
Opening Na+ or Ca2+ channels results in a graded depolarization called an excitatory postsynaptic potential (EPSP).
Opening K+ or Cl− channels results in a graded hyperpolarization called an inhibitory postsynaptic potential (IPSP).

Question 17

EPSPs

Answer 17

move membrane potential closer to threshold
EPSPs from several neurons may be needed to actually produce action potential

Question 18

IPSPs

Answer 18

move membrane potential farther from threshold
Can counter EPSPs from other neurons

Question 19

Summation of EPSPs and IPSPs

Answer 19

at initial segment of axon (next to axon hillock) determines whether action potential occurs.

Question 20

Presynaptic Inhibition

Answer 20

Inhibitory synapse on top of an excitatory synapse
Example: Renshaw cells, controlling overstimulation of muscle cells.

Question 21

Strychnine Poisoning

Answer 21

Renshaw cells in spinal cord normally release an inhibitory neurotransmitter (glycine) onto motor neurons preventing excessive muscle contraction.
Strychnine binds to and blocks glycine receptors in the spinal cord.
Massive contractions of all skeletal muscles are produced, convulsions.
When the diaphragm contracts & remains contracted, breathing can not occur!

Question 22

Free

Answer 22

Free