3

Question 1

area of contact between two neurons.

Answer 1

Synapses

Question 2

The pre-synaptic neuron as it reaches the area of
synapse it divides into many branches each of
them end in a swelling called

Answer 2

synaptic knob.

Question 3

Synapses classified according to sites:

Answer 3

1-Axo-dendritic junction which is least excitable
and the most common (80 95 % ).
2-Axo-axonic junction it is most excitable especially
the initial segment of the axon, it is least common.
3-Axo-somatic junction

Question 4

Types of synapses:

Answer 4

1-Electrical synapses

2-Chemical synapses

Question 5

Electrical synapses

Answer 5

The presynaptic and postsynaptic neuron
membranes come close together forming area
of fusion called gap junction

gap junction form low resistance bridges
that allow rapid conduction of electrical
potentials from one neuron to the next.

Question 6

Chemical synapses

Answer 6

impulse in the pre-synaptic axon causes
secretion of a chemical transmitter at the synapse. The chemical transmitter act on receptors in the
postsynaptic neuron to modify its activity either
exciting or inhibiting it.

Question 7

The process of synaptic transmission involves:

Answer 7

1- Release of the transmitter into the synaptic cleft. 2- The action of the transmitter on the postsynaptic
neuron. 3-Termination of synaptic transmission.

Question 8

Release of the transmitter

Answer 8

Depolarization of synaptic knob membrane causes transient opening of voltage gated Ca++ channel leading to Ca++ inflow that causes the release of its contents into the synaptic cleft .

The amount of neurotransmitter released to the
synaptic cleft is proportional to the amount of
Ca++ entered the synaptic knob.
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Question 9

Action of neurotransmitter on the post-synaptic neuron:

Answer 9

A) Ligand gated ionic channels.
B) Second messenger receptor system.

Question 10

Ligand gated ionic channels.

There are 2 types of channels:

Answer 10

Cation channel:
allows the passage of Na+ , K+ , and Ca++ Na+ influx is greater than K+ efflux leading to depolarization of postsynaptic membrane . The transmitter that produces this effect is called an excitatory transmitter (may beadrenaline or acetyle choline or any other transmitter). Excitatory postsynaptic potentials (EPSPs) inside of post-synaptic cell becomes less negative.

2-Anion channels.

Question 11

Second messenger receptor system:

Answer 11

type of receptors is provided by a specific membrane receptor protein called G-protein which consists of 3 components alpha ,beta and gamma components.

Binding of the chemical transmitter with this receptor leads to activation of G-protein and as separation of the -component from the reminder of G-protein.

Question 12

The movement of component freely within the postsynaptic cell leads to:

Answer 12

I- Opening of specific ion channels e.g. second messenger gated K+ channels K+ efflux & hyper-polarization of postsynaptic membrane
II- Activation of particular enzyme systems that mini
control the metabolic pathways in the neuron as cAMP , and cGMP.
III-Regulation of gene transcription & formation i
of new protein.

Question 13

Summation of EPS and IPSP Summation is of 2 types:

Answer 13

1-Spatial summation

Question 14

Pre-synaptic inhibition:

Presynaptic facilitation

Answer 14

Pre-synaptic inhibition: In pre-synaptic inhibition the inhibitory knobs lies directly on the termination of the excitatory pre-synaptic fiber.

Presynaptic facilitation. The neurotransmitter chemicals secreted at such terminals frequently cause facilitation lasting for seconds up to several minutes. mmmm