The Nervous System 2

Question 1

What is the refractory period?

How is this related to the direction of action potentials?

Answer 1

An inactivation loop blocks voltage gated sodium channels in the neuron after they have been used. This results in a temporary inactivation of the Na+ channels and a second action potential cannot be initiated.

Action potentials travel toward the synaptic terminals. Inactivated sodium ion channels behind the zone of depolarization prevent the action potential from traveling backwards.

Question 2

How is an action potential conducted along the axon?

Answer 2

First, the action potential is (normally) generated at the axon hillock. Then, the action potential regenerates itself along the axon by depolarizing the neighboring regions of the axon membrane.

Question 3

How is the conduction speed of an action potential increased?

What is a node of ranvier? What is this process called?

Answer 3

In vertebrates, the myelin sheath insulates the axon. This causes the signal to travel from each Node of Ranvier and essentially skip most of the length of the axon. This is known as SALTATORY CONDUCTION

Node of Ranviers are gaps in the myelin sheath where Na+ channels are

Question 4

What is the difference between electrical synapses and chemical synapses?

Answer 4

At electrical synapses, the electrical current flows from one neuron to another.

At chemical synapses, a chemical neurotransmitter carries information across the gap junction.

Most synapses are chemical synapses.

Question 5

How are neurotransmitters emitted from a neuron at a chemical synapse?

Answer 5

1. At rest, a neuron is packaging its neurotransmitters into synaptic vesicles
2. Once an action potential arrives, the membrane is depolarized
3. The depolarization opens voltage gated calcium channels and calcium ions diffuse in
4. The calcium ions cause the synaptic vesicles to fuse with the synaptic membrane and release neurotransmitters by EXOCYTOSIS
5. The neurotransmitters then bind to ligand gated ion channels in the post synaptic membrane

Question 6

What is a postsynaptic potential?

Answer 6

A change in the membrane potential of the post synaptic cell.

Question 7

What is a postsynaptic potential?

Answer 7

A change in the membrane potential of the post synaptic cell.

Question 8

What is an EPSP & IPSP?

Answer 8

Excitatory postsynaptic potential: stimulates action potential
Inhibitory postsynaptic potential: blocks action potential

Question 9

Temporal summation of EPSPs

Answer 9

This is when multiple EPSPs are produces in rapid succession allowing the threshold to be reached for action potential.

A single EPSP is normally too weak to produce action potentials

Question 10

Spatial Summation of EPSPs

Answer 10

Spatial summation is when EPSPs are produced almost simultaneously and they are added together. This can also involve IPSPs.

A single EPSP is normally too weak to produce action potentials

Question 11

How are neurotransmitters terminated after they’re released at chemical synapses?

Answer 11

1. They can diffuse out of the synaptic cleft
2. They can be taken up by surrounding cells (back into presynaptic cell)
3. They can be degraded by enzymes

Question 12

What are the five major classes of neurotransmitters?

What are the types?

Answer 12

1. Acetylcholine
2. Biogenic Amines (Norepinephrine, Dopamine, Serotonin)
3. Amino Acids (Glutamate, GABA, Glycine)
4. Neuropeptides (Irrelevant)
5. Gases (Irrelevant)

Question 13

Acetylcholine: What is it used for? Where is it used? What are the two major classes of acetylcholine receptor?

What is sarin? Botulism?

Answer 13

Acetylcholine is a common neurotransmitter in vertebrates and invertebrates. It is involved in muscle stimulation, memory formation, and learning.

Acetylcholine receptors can either be ligand gated or metabotropic. Metabotropic just means that there are one or more metabolic steps, such as a GPCR involved with cAMP activation.

Sarin is a nerve gas (toxin) that disrupts acetylcholine neurotransmission. This can result in paralysis and death.

Botulism is a severe form of food poisoning and its toxin is produced by certain bacteria.

Question 14

Cholinergic Neurons

Where are their axons found?

Answer 14

A type of neurons that use acetylcholine as their neurotransmitter. Neurons only use one type of neurotransmitter that they use.

The axons extend all throughout the brain.

Question 15

Biogenic Amines: Where are they derived from? What are the three types? What are they used for?

What is LSD and mescaline and how does it work?
What is Parkinson’s disease and how does it work?
What is Prozac and how does it work?

Answer 15

Biogenic amines are a type of neurotransmitter that are derived from amino acids.
1. Serotonin (tryptophan)
2. Dopamine (tyrosine)
3. Epinephrine and Norepinephrine (also act as hormones)

Biogenic amines affect sleep, mood, attention, learning and memory.

1. LSD and mescaline are psychoactive drugs that produce hallucinatory effects by binding serotonin and dopamine receptors.
2. Parkinson’s disease is associated with lack of dopamine in the brain. Uncontrolled movements.
3. Prozac is a drug that attempts to treat depression by blocking reuptake of serotonin.

Question 16

What are dopaminergic neurons and where are they found in the brain? Where do their axons extend? What are these regions used for?

Answer 16

Dopaminergic neurons use dopamine as their neurotransmitter. They are only really found in the ventral tegmental area and the substantia nigra.
Their axons extend into the basal ganglia and the frontal lobe.
* The Basal Ganglia is involved in initiation, selection, and cessation of movement. People with parkinsons disease have damaged dopaminergic neurons which is why they have trouble with movement.
* The frontal lobe is the pleasure center of the brain.