Synaptic Transmission

Question 1

Chemical synapse

Answer 1

Found at the ends of axons where they meet their target sell here in action potential is converted to a chemical signal.

1. An action potential reaches the end of an axon, the synaptic knob
2. Depolarization of the presynaptic membrane opens voltage gated calcium channels
3. Calcium influx into the presynaptic cell causes exocytosis of neurotransmitter stored in secretory vesicles
4. Neurotransmitter molecules diffuse across the narrow synaptic left
5. Neurotransmitters find two receptor proteins in the postsynaptic membrane. These receptors are ligand gated ion channels
6. The opening of these ion channels in the postsynaptic cell alters the membrane polarization
7. If the membrane depolarization of the postsynaptic cell reaches the threshold of voltage gated sodium channels, an action potential is initiated
8. Neurotransmitter in the synaptic cleft is degraded and or removed to terminate the signal

Question 2

Summation

Answer 2

The addition of stimuli that makes the decision if a postsynaptic neuron will fire an action potential. This is determined by adding the effect of all the synapses impinging on the neuron both excitatory and inhibitory

Question 3

Temporal summation

Answer 3

When a presynaptic neuron fires action potential so rapidly that the EPSPs or IPSPs pile up on top of each other. If they are EPSPs the additive effect might be enough to reach the threshold deplorization required to start a postsynaptic action potential. If they are IPSPs, the postsynaptic cell will hyperpolarized moving further and further away from threshold becoming inhibited.

Question 4

Spatial summation

Answer 4

When the EPSPs and the IPSPs from all of the synapses on the postsynaptic membrane are summed at a given moment in time. If the total of the EPSPs in the IPSPs causes the postsynaptic membrane to reach threshold voltage, an action potential will be fired

Question 5

Electrical synapse

Answer 5

Occur in the cytoplasm’s of two cells are joined by gap junctions. An action potential will spread directly from one cell to the other. The synapses are not common in the nervous system although they are quite important and propagating action potentials and smooth muscle and cardiac muscle.