General Concepts of the PNS and Neurotransmitters

Question 1

Synaptic transmission

Answer 1

When signaling factors (neurotransmitters) are released from one neuron and bind to the receptors of another neuron across a synaptic cleft.

Question 2

What determines how many transmitters should be released?

Answer 2

The amplitude of the action potential determines the amount of transmitters released.

Question 3

What role does Ca++ play in synaptic transmission?

Answer 3

When the presynaptic AP depolarizes the membrane, it opens the voltage-gated Ca++ channels. The influx of Ca++ causes vesicles in the axon terminal of the presynaptic neuron to empty quantum of transmitters into the synaptic cleft.

Question 4

What determines the action of a neurotransmitter?

Answer 4

Its receptors. One neurotransmitter can have different actions depending on the different receptors that bind it.

Question 5

What are the two types of cholinergic synapses?

Answer 5

Nicotinic - on neurons and skeletal muscle Muscarinic - on body tissues and CNS neurons

Question 6

What is an agonist substance? Give some examples.

Answer 6

A substance that mimics a naturally occurring signaling factor and binds to the same receptors to stimulate an action E.g. nicotine and muscarine can mimic acetyl choline

Question 7

Which neurotransmitters are released at adrenergic synapses? What are they classified as?

Answer 7

The catecholamines: norepinephrine, epinephrine, and dopamine.

Question 8

Which neurotransmitters stimulate adrenergic receptors?

Answer 8

Norepinephrine and epinephrine.

Question 9

Which catecholamine has its own receptor?

Answer 9

Dopamine.

Question 10

Describe the metabolism of ACh.

Answer 10

Choline acetyltransferase synthesizes ACh from acetyl CoA and choline in the presynaptic terminal. Acetylcholine esterase (AChE) breaks it down into choline and acetate in the synaptic cleft.

Question 11

What is the action (type of neurotransmission) of a nicotinic receptor?

Answer 11

Ionotropic transmission: it opens up a Na+/K+ channel

Question 12

What is the action (type of neurotransmission) of a muscarinic receptor?

Answer 12

Metabotropic transmission: uses G-proteins for its actions

Question 13

Compare the duration of the effects of muscarinic and nicotinic receptors.

Answer 13

Nicotinic receptors: short-term synaptic effects Muscarinic receptors: prolonged synaptic effects

Question 14

Where are nicotinic receptors located?

Answer 14

Autonomous ganglion neurons and skeletal muscles.

Question 15

Where are muscarinic receptors located?

Answer 15

Throughout the CNS and in tissues innervated by postganglionic parasympathetic and some sympathetic neurons.

Question 16

How do epinephrine and norepinephrine get removed from the synaptic cleft?

Answer 16

Reuptake or destruction by monoamine oxidase (MAO) or catechol-O-methyl transferase

Question 17

Describe the sequence of catecholamine synthesis from tyrosine.

Answer 17

Tyrosine –> L-DOPA –> Dopamine –> Norepinephrine –> Epinephrine

Question 18

What do adrenergic α1-receptors regulate?

Answer 18

Ca++ and K+ channels

Question 19

What do adrenergic β-receptors regulate?

Answer 19

Smooth muscle, the heart, and metabolism.

Question 20

What is the effect of propanolol on adrenergic receptors?

Answer 20

Blocks β-receptors to decrease heart rate.

Question 21

Rank these transmitters in terms of duration of effects (shortest to longest): neuropeptides, adrenergic, and cholinergic transmitters.

Answer 21

Cholinergic, adrenergic transmitters, and neuropeptides

Question 22

How do cocaine and amphetamine change the pathway for transmitters?

Answer 22

By blocking reuptake, which prolongs the action of the neurotransmitter.

Question 23

How can enzymes change the duration of the neuropeptide transmitter effect?

Answer 23

The slow breakdown of neuropeptides by enzymes extends the effect.

Question 24

Compare small molecule and neuropeptide transmitters in terms of synthesis and vesiculation.

Answer 24

Small molecule transmitters are synthesized and packaged in the axon terminal (with help from transported enzymes). Neuropeptide transmitters are transported as pre-peptides in vesicles from the cell body and are modified (by transported enzymes) in the axon terminal.

Question 25

What type of receptors (metabotropic or ionatropic) do neuropeptides bind to?

Answer 25

Metabotropic receptors (use second messengers)

Question 26

What makes the action and release of a neuropeptide unique compared to other neurotransmitters?

Answer 26

They are responsible for long-term changes in ion channel permeability, gene transcription, number of receptors, etc. They are typically co-released with another transmitter and at low thresholds, compared to small molecule transmitters.

Question 27

The peripheral nervous system can be further divided into which two systems?

Answer 27

Somatic motor system and the autonomic nervous system.

Question 28

Where are the cell bodies and axons of the _-motor neurons located?

Answer 28

Cell bodies are located in the ventral horn of the spinal cord. Axons are projected out to skeletal muscle.

Question 29

Where are the cell bodies and axons of the ANS located?

Answer 29

They comprise of two neurons in sequence: pre- and postganglionic neurons. The cell bodies of the preganglionic neurons are found in the intermediolateral column and projects axons to the postganglionic neurons within the autonomic ganglia. The cell bodies of the postganglionic neurons are found at the autonomic ganglia and project axons to smooth muscle, cardiac muscle, and glands.

Question 30

What system does the phrase fight, fright, or flight” typically refer to?”

Answer 30

Sympathetic nervous system (part of the ANS).

Question 31

What system does the phrase rest and digest” typically refer to?”

Answer 31

Parasympathetic nervous system (part of the ANS).

Question 32

Where are the cell bodies of preganglionic neurons in the sympathetic vs parasympathetic nervous systems?

Answer 32

Sympathetic: T1-L2 Parasympathetic: Cranial cells in brain stem, sacral cells of S2-4

Question 33

Compare the innervation of tissues by the somatic motor system and the ANS.

Answer 33

Motor neurons have axon branches that innervate single muscle fibers. Postganglionic neurons have axons with varicosities that synapse onto different tissue cells.

Question 34

What is the advantage to innervation by a somatic motor neuron as opposed to autonomic nervous system neuron?

Answer 34

More specificity.

Question 35

Which transmitter is used in all preganglionic neurons? Which receptor does it bind to at the ganglia synapse?

Answer 35

Acetyl choline (ACh), which binds to nicotinic receptors.

Question 36

Compare the postganglionic axons in the two parts of the ANS in terms of length, target tissue, and action.

Answer 36

Sympathetic: long axons project to organs and extremities (blood vessels, sweat glands, etc.); increases HR and BP Parasympathetic: short axons project to organs; lowers HR, promotes GI peristalsis

Question 37

Which parts of the brain directly control the ANS?

Answer 37

Hypothalamus through the brain stem directly controls the ANS.

Question 38

What role does the limbic system play in controlling the ANS?

Answer 38

It governs the hypothalamus and brain stem.

Question 39

Describe the sequence of events that lead to the release of transmitters into the synapse.

Answer 39

1) Presynaptic action potential depolarizes the membrane. 2) Presynaptic voltage-gated Ca++ channels open 3) Ca++ influx triggers vesicles to release transmitters into synaptic cleft

Question 40

If a medicine inhibits acetylcholine esterase, what impact would there be on the innervation of muscle and the activity of sympathetic and parasympathetic systems?

Answer 40

Increase ACh levels and produces extreme ANS responses: contraction of skeletal muscle, release of epinephrine from adrenal medulla, stimulation of both the sympathetic and parasympathetic systems.

Question 41

If a medicine specifically activated nicotinic receptors, what would be the impact on the motor and autonomic activities?

Answer 41

Similar to an increase in ACh, it would produce extreme ANS responses: contraction of skeletal muscle, release of epinephrine from adrenal medulla, stimulation of both the sympathetic and parasympathetic systems.

Question 42

If a medicine specifically blocked muscarinic receptors, what would be the impact on the motor and autonomic activities?

Answer 42

May have some upstream effects on somatic motor neurons, but no direct effect.

It would impair all parasympathetic and some sympathetic neuronal activity: inhibiting HR deceleration, sweating, digestion, blood vessel dilation, etc.