Synapses & Neurotransmitters

Question 1

What is a synapse

Answer 1

A structure that permits a neuron to communicate with other cells via passage of an electrical (ions) or chemical( neurotransmitters) signal

Question 2

Synaptic Locations

Answer 2

Synaptic contact can occur on the cell body, the dendrites, or the axon of the postsynaptic cell

Question 3

Axosomatic synapse

Answer 3

synaptic contact on the cell body

Question 4

Axodendritic synapse

Answer 4

Synaptic contact on the dendrites

Question 5

Axo-axonic synapse

Answer 5

Synaptic contact on the axon of the postsynaptic cell

Question 6

Neuronal Communication: Target cells

Answer 6

Target Cells for neurons may be:
- Neuron to Neuron ( local, projection interneurons)

• Neuron to Muscle ( skeletal, smooth, cardiac)
• Neuron to Glandular cells (adrenal, salivary, lacrimal, pancreas)

Question 7

Presynaptic neuron (terminal/membrane)

Answer 7

Neuron sending the signal

Question 8

Postsynaptic neuron ( terminal/membrane)

Answer 8

Target neuron ( or other) receiving the signal

Question 9

Modalities of Synaptic Transmission

Answer 9

Electrical Synapse
Chemical Synapse

Question 10

Electrical Synapse properties

Answer 10

Smaller distance between pre and postsynaptic cell membranes compared to chemical at 4nm.

Cytoplasmic continuity between pre-and postsynaptic cells

Ultrastructural components: Gap Junctions

Agent of transmission is ion current

Synaptic delay is virtually absent

The direction of transmission is usually bidirectional

Question 11

Chemical Synapse properties

Answer 11

Longer distance between pre and postsynaptic cell membranes compared to electrical at 20-40 nm

No cytoplasmic continuity between pre and postsynaptic cells

Ultrastructural components: Chemical transmitter

Agent of transmission is chemical transmitter

Significant synaptic delay, at least 0.3ms, usually 1-5 ms or longer

The direction of transmission is unidirectional

Question 12

Chemical synapses

Answer 12

Majority in CNS
One way conduction

Involves neurotransmitters and receptors

Question 13

Basic Structure of a Chemical Synapse

Question 14

Neurotransmitter definition

Answer 14

Neurotransmitters are endogenous chemicals that are released from neurons, act on receptor sites that are typically present on membranes of postsynaptic cells and produce a functional change in the properties of the target cell

Question 15

Criteria to define Neurotransmitters

Answer 15

1. A neurotransmitter must be synthesized by and released from neurons
2. Released with stimulation (depolarization)
3. Produces rapidly reversible responses on target cell
4. Existence on a specific receptor
5. There should be active mechanisms to terminate the action of the neurotransmitter

Question 16

Synthesis of Neurotransmitters

Answer 16

Synthesized in the soma and transported down the axon

Many are re-synthesized in the axon terminal
- our focus in the neurotransmitters class

Question 17

Synapse transmission

Answer 17

1. Action potential arrives at presynaptic terminal
2. Opens voltage-gated calcium channels, calcium influx into terminal triggers synaptic vesicle migration to active release zones
3. NEUROTRANSMITTER released**
   - amount of neurotransmitter released is dependent of the amount of calcium influx (intracellular calcium)**
4. Neurotransmitter binds to receptors on postsynaptic membrane
   —> Signal transduction

Removal of neurotransmitter from the synaptic region
1. Enzyme degradation (specific)
2. Reuptake into presynaptic terminal
3. or glial cells
4. Diffusion away from synapse