Chapter 6

Question 1

criteria to consider a molecule a neurotransmitter:

Answer 1

1. The molecule must be synthesized and stored in the presynaptic neuron
2. The molecule must be released by the presynaptic axon terminal upon stimulation
3. The molecule, when experimentally applied, must produce a response in the postsynaptic cell that mimics the response produced by the release of a neurotransmitter from the presynaptic neuron.

Question 2

Cholinergic neurons:

Answer 2

Acetylcholine (ACh) is the neurotransmitter at the neuromuscular junction and therefor is synthesized by all the motor neurons in the spinal cord and brain stem. Other cholinergic cells contribute to the functions of specific circuits in the PNS and CNS.

ACh synthesis requires a specific enzyme, choline acetyltransferase (ChAT). Like all presynaptic proteins, ChAT is manufactured in the soma and transported to the axon terminal. Only cholinergic neurons contain ChAT, so this enzyme is a good marker for cells that use ACh as a neurotransmitter. Immunocytochemistry with ChAT-specific antibodies, for example, can be used to identify cholinergic neurons. ChAT synthesizes ACh in the cytosol of the axon terminal, and the neurotransmitter is concentrated in synaptic vesicles by the actions of an ACh transporter.

ChAT transfers an acetyl group from acetyl CoA to choline. The source of choline is the extracellular fluid, where it exists in low micromolar concentrations. Choline is taken up by the cholinergic axon terminals via a specific transporter. Because the availability of choline limits how much ACh can be synthesized in the axon terminal, the transport of choline into the neuron is said to be the rate-limiting step in ACh synthesis. For certain diseases in which a deficit in cholinergic synaptic transmission has been noted, dietary supplements of choline are sometimes prescribed to boos ACh levels in the brain.

Cholinergic neurons also manufacture the ACh degradative enzyme acetylcholinesterase (AChE). AChE is secreted into the synaptic cleft and is associated with cholinergic axon terminal membranes. However, AChE is also manufactured by some noncholinergic neurons, so this enzyme is not as useful a marker for cholinergic synapses as ChAT

AChE degrades ACh into choline and acetic acid. This happens very quickly, because AChE has one of the fastest catalytic rates among all known enzymes. Much of the resulting choline is taken up by the cholinergic axon terminal and reused for ACh synthesis. Inhibition of AChE prevents the breakdown of ACh, disrupting transmission at cholinergic synapses on skeletal muscle and heart muscle. Acute effects include marked deceases in heart rate and blood pressure; however, death from teh irreversible inhibition of AChE is typically a result of respiratory paralysis

Question 3

Catecholamines:

Answer 3

Neurotransmitters that come from the amino acide tyrosine. Dopamine, norepinephrine, and epinephrine (also called adrenaline). dopamine–>norepinephrine–>epinephrine

Question 4

What s the first step in catecholamine synthesis?

Answer 4

The conversion of tyrosine to dopa