Synapses, Neuromuscular Junction and Neurotransmitters

Question 1

What happens when the stimulus reaches the axon terminal?

Answer 1

A synape occurs

Question 2

What is the difference between a chemical synapse and an electrical synapse?
Which type of synapse is most abundant in the body?
Where in the body do electrical synapses occur?

Answer 2

CHEMICAL SYNAPSE
Neurotransmitters released from 1 neuron open/close LG ion channels on neighborhood neurons
The most abundant type of synapse.
ELECTRICAL SYNAPSE
Signals travel through gap junction
Occurs in brain and heart

Question 3

The above figure shows the neuromuscular junction. Describe all the major events that are taking place starting at: 1) Arrival of the action potential through the pre-synaptic neuron, to termination of the signal in the synaptic cleft.

Answer 3

an AP reaches the presynaptic terminal of a motor neuron, which activates voltage Ca+ channels to allow Ca+ to enter the neuron. Ca+ bind to synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft

Question 4

Describe what an IPSP or EPSP is.

Answer 4

EPSP (Excitatory Postsynaptic Potential)
A local hyperpolarization of postsynaptic membrane and brings the neuron closer to AP threshold. Neurontransmitter binding open LG ion channels, allowing the simultaneous passage of Na+ and K+
IPSP (Inhibitory Postsynaptic Potential)
A local hyperpolarization of postsynaptic membrane and drives the neuron away from AP threshold. Neurotransmitter binding opens K+ or Cl- channels.

Question 5

What are the main differences between an excitatory neurotransmitter and inhibitory neurotransmitter?

Answer 5

Excitatory Neurotransmitter
Increases likelihood of an AP occuring on Postsynaptic neuron
Leads to an EPSP
Most abundant is Acetylcholine (ACh)
Acetylcholine (ACh) works via opening Na+ ion channels.
Inhibitory Neurotransmitter
Decreases likelihood of an AP occuring on Postsynaptic neuron
Leads to an IPSP
Most abundant in brain is GABA
GABA works via the opening of Cl- ion Channels

Question 6

How does GABA work?

Answer 6

Binding of GABA to GABAA receptor opens up Chloride channels (Cl-)
Cl- ion rushes into cell and makes inside of cell more negative (an IPSP)

Question 7

What is the difference between temporal and spatial summation?

Answer 7

1, 2 or more EPSP’s occur in rapid succession at the same synapse
2, 2 or more EPSP’s occur at the same time at different synapses

Question 8

Briefly describe the functions of acetylcholine.

Answer 8

Both excitatory and inhibitory actions

Binds to muscarinic receptors

Question 9

Describe what drugs that target acetylcholine are used for?

Answer 9

Botox (Botulinum Toxin): inhibits fusion of the vesicles with membrane → inhibits release of ACh → ACh can’t reach the receptor of the muscle cell → The muscle can’t contract → muscle paralysis

Question 10

When it comes to neurotransmitters, describe the main functions of norepineherine?

Answer 10

Can be both excitatory or inhibitory
A major neurotransmitter of the sympathetic nervous system
Adrenergic recepotors
Low levels can lead to depression

Question 11

When it comes to neurotransmitters, describe the main functions of dopamine?

Answer 11

Excitatory or inhibitory neurotransmitter

A “feel good” neurotransmitter

Question 12

Describe what type of neurotransmitter serotonin is and what types of disorders is it implicated in?

Answer 12

Mainly inhibitory role
Implicated in sleep regulation, migraines, appetite, and mood regulation
Deficiencies related to depression

Question 13

Give an example of 2 drugs that can potentially affect serotonin?

Answer 13

Prozac:
Blocks its uptake from the synaptic cleft thus relieving anxiety and depression
Ecstasy:
Enhances activity of serotonin
Ecstasy prevents reuptake of seotonin by binding to transporters. But also promotes release of NE

Question 14

List the types of drugs that affect GABA or GABA receptors?

Answer 14

Agent that enhance activity of GABA synapses depress CNS activity
Drugs that promote GABA release or increase the available amount of GABA have anti-anxiety or relaxing effects.
Benzodiazepines (Valium) – increasing affinity for GABA at receptor
Alcohol
Positive receptor agonist (accentuates the effects of GABA)
receptor agonist is a compound that activates GABA receptors, in a manner similar to alcohol

Question 15

Local anesthetics

Answer 15

Many local anesthetics block neural transmission by inhibiting voltage gated sodium channels thus blocking the entry of Na+ into the neuron thus blocking depolarization.