4

Question 1

Neurotransmitters

Answer 1

These are chemical substances that transmit the activity through the synapse from pre-synaptic to postsynaptic neurons

Question 2

Neurotransmitters They are classified into two groups according to

Answer 2

a-Their chemical structure b-Rapidity of action
1
• Small-Molecule, Rapidly
Acting Transmitters

2•Neuropeptide, Slowly Acting Transmitters

Question 3

Small-Molecule, Rapidly Acting Transmitters

Answer 3

Class I
Acetylcholine

Class III: Amino Acids

Gamma aminobutyric acid
(GABA) , Glycine, Aspartate, Glutamate
• Class II: The Amines
:Norepinephrine , Epinephrine , Dopamine , Serotonin ,Histamine
• Class IV
Nitric oxide (NO)

Question 4

The small molecular weight rapidly acting transmitter:
Properties

Answer 4

a-They are rapidly acting.
b-They usually act by activation of ion channels.
c- Responsible for transmission of sensory impulses to
the brain and motor signals to the muscles.
d-They are synthesized in the pre-synaptic terminals and
stored in transmitter vesicles.
e-They are released in large quantities .
f- They are removed by active reuptake or by enzymatic
destruction.

Question 5

2-Neuromodulators: (Large molecular weight neurotransmitters)
Properties

Answer 5

1-Usually slow and prolonged action .
2- Act by second messenger system.
3-Include several families of peptides that are present in other organs and systems ,beside the nervous system ,as endocrine and gastrointestinal system.
4-Synthesized by neurons in the C.N.S and so called neuropeptides .
5- Released in small quantities.
6-More potent.

Question 6

Neuropeptide, Slowly Acting Transmitters

Answer 6

Hypothalamic-releasing
• Pituitary peptides
Peptides that act on gut
• From other tissues
and brain

Question 7

Neuropeptides Synthesized by

Answer 7

ribosomes in the neuronal cell body
• Enter the Golgi apparatus Where it is . Splitt into small fragments
2. Packed into vesicles
• Transported all the way to the tips of the nerve fibers by axonal streaming . • These vesicles released as small-molecule
transmitters. • However, the vesicle is not reused

Question 8

Properties of Synaptic transmission

Answer 8

1- Unidirectional conduction.
2- Synaptic delay.
3- Synaptic fatigue. 4- Effect of changes in composition of ECF. 5- Effects of drugs

Question 9

Synaptic delay

Answer 9

time needed for conduction of an impulse
through a synapse. It is about 0.5 m.sec.
• This time is needed for:
a-release of the neurotransmitter.
b-Its diffusion through the synaptic cleft.
c-Its combination with the postsynaptic receptors.
d- Na influx to produce EPSP.
e-Summation of EPSP to the threshold value.
• The time of synaptic delay can be used to know the number of synapses.

Question 10

Fatigue

Answer 10

When the pre-synaptic neuron is stimulated
repetitively at a rapid rate, discharge from post-
synaptic neuron will gradually decrease .
This fatigue is due to decrease of neurotransmitter in pre-synaptic knobs because othe rate of release of neurotransmitter is greater than the rate of its reformation.
• Fatigue is a protective mechanism against excess
neural activity as it stops epileptic attack.

Question 11

Effect of drugs:

Answer 11

Inhibitory drugs: a-Anesthetics Sedatives hypnotics

Excitatory drugs: Strychnine : Inhibits
the action of Inhibits
transmitter as
glycine
a-Xanthines:By
decreased
stimulation threshold

Question 12

Effect of changes in ECF:

Answer 12

Inhibitory conditions: Id
a-Acidosis : leads to coma.

Hypoxia

Hypoglycemia

Hypocalcemia

Excitatory Conditions:
a- Alkalosis : Leads to Convulsions.
b- Hypercalcemia
c- Hyperthyroidism.