Synapses

Question 1

What are the parts of a neuron?

Answer 1

Dendrite, soma, nucleus, axon hillock, axon, myelin sheath, Node of ranvier, axon terminal, synapse

Question 2

What is the definition of a synapse?

Answer 2

A specialized area of contact between two cells where transmission of information takes place (synaptic transmission)

Question 3

What are the two types of synapses?

Answer 3

Electrical and chemical

Question 4

Describe the function of an electrical synapse

Answer 4

The element that the two cells communicate is the propagation of electric current

Question 5

Describe the function of chemical synapses

Answer 5

The element that the two cells communicate is a molecule (neurotransmittor)

Question 6

Describe the basic structure of synapsis

Answer 6

Presynaptic, postsynaptic and synaptic cleft

Question 7

What is the presynaptic membrane?

Answer 7

The membrane portion of the neuron that sends the information

Question 8

What is the postsynaptic membrane?

Answer 8

The membrane portion of the cell recieving the information

Question 9

What is the synaptic cleft?

Answer 9

The space between two membranes

Question 10

What are the junctions in electrical synapses?

Answer 10

Special junctions between neurons that acts as a “bridge” between their cytoplasm=gap-junctions

Question 11

What are the junctions between chemical synapses?

Answer 11

There is no continuity between the cytoplasm of the two cells. Cells are separated by a space= synaptic cleft

Question 12

How does the electrical synapse act?

Answer 12

A current injected into the presynaptic cell flows into the postsynaptic cell through gap-junctions (electrical connection)

Question 13

How does the chemical synapse act?

Answer 13

The injected current initiates the process in which molecules flow through the synaptic cleft to the postsynaptic cell

Question 14

Describe the characteristics of an electric synapse

Answer 14

Less abundant than chemical synapses
AP at the postsynaptic neuron is transmitted by direct current flow due to continuity between cytoplasm (gap-junctions)
Bidirectional
Distance between membranes ~3.5nm
Very fast responses

Question 15

Describe the characteristics of chemical synapses

Answer 15

More abundant
Unidirectional
Synaptic delay 0.5msec
Distance between membranes 20-40nm

Question 16

Describe the pathway of chemical synapse neurotransmittor

Answer 16

It is synthesized in neuron nucleus and are transported in synaptic vesicles along the axon. When reaching the synaptic terminal it releases its contents into the synaptic cleft. The material Will be reused by the cell

Question 17

Describe the stages of the chemical synapse

Answer 17

AP reaches the presynaptic terminal
Activation if voltage-dependent Ca++ channel
Increase of Ca++ in cytosol causes the fusion of vesicles to presynaptic membrane
Vesicles releases the NT via endocytosis into the synaptic cleft
NT spreads and bind to postsynaptic receptors
Opening of ion channels (Na+, K+ or Cl-) causes depolarization or hyperpolarization
Postsynaptic AP

Question 18

What are the two types of postsynaptic receptors?

Answer 18

Ionotropic and metabotropic

Question 19

How does the ionotropic receptor work?

Answer 19

Direct linkage to ionchannels (cationic or anionic)

Question 20

How does a metabotropic receptor work?

Answer 20

Indirect

Movement of ions through a channel depending on one or more metabolic steps-transduction signal

Question 21

Describe the characteristics of an ionotropic receptor

Answer 21

Two functional domains:
Extracellular that binds neurotransmitters
Membrane that forms ion channel
Rapid communication and in both excitatory and inhibitory responses
Neurotransmitter binding sites (also binds other molecules)

Question 22

What are the two types of ion channels in ionic receptors?

Answer 22

Cation channels- allows mostly Na+ to pass and are excitatory responses
Anion channels- allows mainly Cl- to pass, are inhibitory responses

Question 23

What is the meaning of signal transduction in metabotropic receptors?

Answer 23

Do not open ionchannels directly
Indirectly linked to ion channels in the membrane through signal transduction carried out by G proteins and intracellular messengers
The cellular response takes longer and gives higher effect= slow response

Question 24

What is excitatory postsynaptic potential (EPSP)?

Answer 24

Ion channel opens and allows entrance of cations- depolarization-increase privatbility of AP
Receptor channel= nicotinic/nAChR

Question 25

What is inhibitory postsynaptic potential (IPSP)?

Answer 25

Ionchannels open for anions
Produced hyperpolarization
Reduces the probability of AP
Inhibitory channel receptor=R GABA

Question 26

What is synaptic integration?

Answer 26

The interaction of EPSP and IPSP
Temporal summation- the integration of postsynaptic potentials that occur at the same place but at slightly dirrefrent times
Spatial summation- the integration occurs att different locations but at the same time
In the end if treshold potential is reached=AP

Question 27

How is NT removed from the receptor?

Answer 27

Diffusion away from postsynaptic membrane
Degradation (proteolytic enzymes)
Reuptake (active transport at the presynaptic nerve terminal)