Cell Membrane, Action Potential, Neurotransmitters

Question 1

Difference between chemical transmission and electrical transmission of an action potential?

Answer 1

Chemical transmission: slower, uses chemical messengers called neurotransmitters to bind to receptors on postsynaptic neuron. Ions stimulated by chemical messengers–neurotransmitters

Electrical transmission: faster, more direct, uses direct flow of ions to cross the synapse without neurotransmitters. Use GAP JUNCTIONS. Ions directly moving.

Question 2

Where are neurotransmitters synthesized and where are they stored?

Answer 2

Synthesized: in presynaptic neuron cell body or axon terminal
Stored: vesicles of presynaptic neuron (held by SNARE proteins)

Question 3

Steps of chemical transmission

Answer 3

1. Action potential comes down axon and causes PRESYNAPTIC membrane to DEPOLARIZE
2. VOLTAGE-gated CALCIUM channels open
3. Calcium flows into neuron
4. Calcium concentration increases leading to PHOSPHORYLATION of SNARE complex proteins. Conformational change that releases them from being bound to the cytoskeleton
5. Vesicles migrate to the presynaptic membrane
6. Vesicles fuse with the cell membrane and release their neurotransmitter molecules into the synaptic cleft
7. Neurotransmitters cross the synaptic cleft to BIND with POSTSYNAPTIC RECEPTORS
8. Receptor binding opens LIGAND ion channels leading to ion flux and generation of postsynaptic potential for the next neuron

Question 4

What are the usual methods for termination of neurotransmitters? Which neurotransmitter is the exception to this and what is its method of termination?

Answer 4

Usual method of termination is by reuptake of excess neurotransmitters by the presynaptic neuron OR glial reuptake (taken by other cells) OR simple diffusion

Acetylcholine is the exception in this case as it requires hydrolysis degradation by acetylcholinesterase to cleave it into acetate and choline and render it inactive.

Question 5

Steps of electrical transmission

Answer 5

1. Impulse arrives at presynaptic terminal and changes the charge/potential
2. Change in potential causes ions to flow across GAP JUNCTION to next neuron

Note: these gap junctions contain GATED CHANNELS to allow for one-way traffic

Question 6

Major monoamine neurotransmitters. What does “monoamine” mean?

Answer 6

Major monoamine neurotransmitters: dopamine, serotonin (5-HT), epinephrine, norepinephrine

Monoamines mean they are all derived from amino acids

Question 7

Two divisions of monoamines?

Answer 7

Based on amino acid precursors:

(Synthesis of catecholamines) Phenylalanine –> tyrosine: dopamine, norepinephrine, epinephrine

Tryptophan precursor: serotonin

Question 8

Order of transmitters synthesized in catecholamine synthesis

Answer 8

Phenylalanine –> tyrosine –> DOPA (offshoot: melanin) –> dopamine –> norepinephrine –> epinephrine

Note: with the exception of DOPA to melanin via tyrosinase, the enzymes describe the substrate making the product. Know what order the products are in and the enzyme names will be intuitive

Question 9

What products can be derived from tryptophan?

Answer 9

Serotonin, then serotonin can be converted into melatonin

Question 10

Acetylcholine responsible (in part) for which part of the nervous system. What is acetylcholine’s main function/role in the body?

Answer 10

Parasympathetic system. Responsible for skeletal muscle contraction.

Question 11

How is acetylcholine activity stopped?

Answer 11

Taken out of the synaptic cleft through hydrolysis degradation. The enzyme acetylcholinesterase (AChE) hydrolyzes acetylcholine to acetate and choline.

Question 12

What happens if there is a dysfunction of acetylcholine degradation?

Answer 12

Muscle remains in a state of constant contraction, cannot repolarize and relax

Question 13

What neurotransmitter is nicotinic and muscarinic receptors associated with? What is the difference between the receptors?

Answer 13

Associated with ACh. Nicotinic and muscarinic receptors are the two main classes of ACh receptors.

Nicotinic receptors are IONOTROPIC–meaning they bind ACh or nicotine and the pore opens. Binding is directly responding for the channel opening and the flow of ions. Rapid action

Muscarinic receptors are METABOTROPIC–meaning an indirect mechanism of signal transduction via G-proteins to move ions. Slower

Question 14

What happens when nicotinic receptor is impaired?

Answer 14

Acetylcholine cannot bind, acetylcholine responsible for muscle contraction, therefore muscle contraction cannot happen. Relaxation of skeletal muscle. Ion channel is closed

Question 15

Dopamine responsible for which part of the nervous system. What is dopamine’s main function/role in the body?

Answer 15

Excitatory neurotransmitter of the central nervous system. Controls limbic system (emotional response/pleasure) and voluntary movement

Question 16

What three pathways are associated with dopamine?

Answer 16

Mesocortical pathway: executive function/thinking
Mesolimbic pathway: behavior and mood
Nigrostriatal: normal movement

Question 17

4 ways to affect neurotransmitter concentration?

Answer 17

1. Rate of synthesis
2. Rate of release
3. Uptake to presynaptic cell
4. Degradation

Question 18

Tyrosine hydroxylase deficiency results in deficiency of what neurotransmitter? How can you get around this?

Answer 18

Dopamine. Supplement with DOPA. But remember excess dopamine is toxic to the body when in the bloodstream. To solve this, give an inhibitor that does not work in the brain. Transport to the brain and convert DOPA to dopamine. Keep DOPA in bloodstream

Question 19

Glutamate responsible for which part of the nervous system. What is glutamate’s main function/role in the body?

Answer 19

Glutamate the most important excitatory neurotransmitter in the central nervous system. Acts on both ionotropic and metabotropic receptors.

Question 20

Precursor for GABA?

Answer 20

Glutatmate

Question 21

How is glutamate implicated in excitotoxicity?

Answer 21

Nerve cells are damaged by excess glutamate because excess glutamate causes activation of NMDA receptor and excessive spike in calcium intake. Excessive calcium and overstimulation causes apoptosis. Also NMDA produces nitric oxide

Question 22

What part of the nervous system does GABA function and what is its primary role?

Answer 22

Central nervous system, main inhibitory transmitter.

Question 23

Associated neurotransmitter to GABAa and GABAb receptors and what makes them different? What makes them the same?

Answer 23

Associated neurotransmitter: GABA
GABAa: ionotropic, GABA binds to GABAa and ion channel opens. CHLORIDE enters the cell. – decreases transmembrane potential and inhibits the generation of action potentials

GABAb: metabotropic, mediated by G-protein. opens POTASSIUM channels. Potassium leaves cell and transmembrane potential decreases and inhibits AP generation.

Same: inhibitory effect, lowers transmembrane potential
Difference: ionotropic/metabotropic, Cl enter/K exit

Question 24

What part of the nervous system does norepinephrine play a role in? What is the main function of norepinephrine?

Answer 24

Major neurotransmitter of the sympathetic nervous system. Induces response known as the “fight-or-flight response”

Question 25

What receptors does norepinephrine bind to? Where are these receptors? Where else does norepinephrine go to?

Answer 25

Noradrenergic receptors of the post synaptic membrane. Also circulated as a hormone. Dopamine also circulated as a hormone just fyi

Question 26

Function of monoamine oxidase inhibitors?

Answer 26

MAO inhibitors prevent the catabolism of catecholamines (dopamine, norepinephrine, epinephrine) and serotonin. Leads to build up of these neurotransmitters in the vesicles and eventually when released increased concentration in the synapse.

Question 27

Serotonin nervous system involvement and main function of serotonin

Answer 27

Also known as 5-HT. CNS. Excitatory neurotransmitter. Involved in mood, appetite, and sleep.