Test 37  (neurophysiology)

1. The following are true about acetylcholine:

a. it is synthesized from acetyl-coenzyme A and choline

b. its formation is catalysed by acetylcholinesterase

c. at the synaptic cleft, it is inactivated by hydrolysis

d. reuptake by the presynaptic neurones play an important in inactivating 
    acetylcholine

e. acetylcholine receptors are found in all autonomic ganglia

Answera.T   b.F   c.T   d.F   e.TThe synthesis of acetylcholine is catalysed by the enzyme choline acetyltransferase.Acetylcholine in the synaptic cleft is hydrolysed tocholine and acetate. Reuptake of acetylcholine does not play a part in theinactivation of acetylcholine.
 

2. The following are true about acetylcholine receptors:

a. receptors at all autonomic ganglia are nicotinic

b. receptors at the skeletal neuromuscular junction are muscarinic

c. acetylcholine receptors in the autonomic ganglia can be selectively blocked 
    by atropine

d. acetylcholine receptors in the neuromuscular junction can be selectively 
    blocked by  tubocurarine

e. pilocarpine is a muscarinic agonist

Answera.T   b.F   c.F   d.T   e.TThe acetylcholine receptors are of two types: muscarinic and nicotinic.Muscarinic receptors are found at the postganglionic parasympathetic synapses.Nicotinic receptors are found at all autonomic gangliaand the adrenal medulla which can be blocked selectivelyby hexamethonium. Whereas the nicotinic receptors foundat the neuromuscular junction can be blocked by tubocurarine but not by hexamethonium.

3. The following are true about the muscarinic receptors:

a. they are found at the postganglionic parasympathetic synapses

b. they can be selectively blocked by atropine

c. M1 muscarinic receptors are found in the brain

d. M4 muscarinic receptors are found in the pancreas

e. M2 muscarinic receptors mediate a positive chronotropic effect

Answera.T   b.T   c.T   d.T   e.FThey are five types of cholinergic muscarinic receptors which have been identified:M1 in the brainM2 in the heartM4 in the pancreasM3 and M5 are not well characterized.M2 mediates a negative chronotropic effect.
 

4. The following are true about the autonomic nervous system:

a. the preganglionic fibres are mainly myelinated, slow conducting B fibres

b. the postganglionic fibres are mainly unmyelinated C fibres

c. all preganglionic neurones are cholinergic neurons

d. all sympathetic postganglionic neurons are adrengic neurons

e. the postganglionic neurons of the sympathetic pathway is longer than that 
    of the parasympathetic pathway.

Answera.T   b.T   c.T   d.F   e.TAll preganglionic neurons and parasympathetic postganglionicneurons are cholinergic neurons.Postganglionic sympathetic neurones are adrengic neurons with exception of the sympathetic postganglionic neurons innervating seat gland and those that mediate vasodilatation in the skeletal muscles.

5. True statements about the following neurotransmitters include:

a. dopamine is formed from tyrosine

b. in the synapse, noradrenaline is inactivated by active reuptake into the 
    presynpatic terminals

c. noradrenaline is formed by hydroxylation of dopamine

d. noradrenaline is oxidized by monoamine oxidase found in the presynpatic 
    space

e. serotonin is formed from the amino acid tryptophan

Answera.T   b.T   c.T   d.F   e.TNoradrenaline is inactivated by the process of reuptakeinto the presynaptic neurons where it is oxidized by themonoamine oxidase found at the outer surface of themitochondria in the presynaptic terminals.