Synapses Flashcards
What are the parts of a neuron?
Dendrite, soma, nucleus, axon hillock, axon, myelin sheath, Node of ranvier, axon terminal, synapse
What is the definition of a synapse?
A specialized area of contact between two cells where transmission of information takes place (synaptic transmission)
What are the two types of synapses?
Electrical and chemical
Describe the function of an electrical synapse
The element that the two cells communicate is the propagation of electric current
Describe the function of chemical synapses
The element that the two cells communicate is a molecule (neurotransmittor)
Describe the basic structure of synapsis
Presynaptic, postsynaptic and synaptic cleft
What is the presynaptic membrane?
The membrane portion of the neuron that sends the information
What is the postsynaptic membrane?
The membrane portion of the cell recieving the information
What is the synaptic cleft?
The space between two membranes
What are the junctions in electrical synapses?
Special junctions between neurons that acts as a “bridge” between their cytoplasm=gap-junctions
What are the junctions between chemical synapses?
There is no continuity between the cytoplasm of the two cells. Cells are separated by a space= synaptic cleft
How does the electrical synapse act?
A current injected into the presynaptic cell flows into the postsynaptic cell through gap-junctions (electrical connection)
How does the chemical synapse act?
The injected current initiates the process in which molecules flow through the synaptic cleft to the postsynaptic cell
Describe the characteristics of an electric synapse
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
Describe the characteristics of chemical synapses
More abundant
Unidirectional
Synaptic delay 0.5msec
Distance between membranes 20-40nm
Describe the pathway of chemical synapse neurotransmittor
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
Describe the stages of the chemical synapse
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
What are the two types of postsynaptic receptors?
Ionotropic and metabotropic
How does the ionotropic receptor work?
Direct linkage to ionchannels (cationic or anionic)
How does a metabotropic receptor work?
Indirect
Movement of ions through a channel depending on one or more metabolic steps-transduction signal
Describe the characteristics of an ionotropic receptor
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)
What are the two types of ion channels in ionic receptors?
Cation channels- allows mostly Na+ to pass and are excitatory responses
Anion channels- allows mainly Cl- to pass, are inhibitory responses
What is the meaning of signal transduction in metabotropic receptors?
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
What is excitatory postsynaptic potential (EPSP)?
Ion channel opens and allows entrance of cations- depolarization-increase privatbility of AP
Receptor channel= nicotinic/nAChR
What is inhibitory postsynaptic potential (IPSP)?
Ionchannels open for anions
Produced hyperpolarization
Reduces the probability of AP
Inhibitory channel receptor=R GABA
What is synaptic integration?
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
How is NT removed from the receptor?
Diffusion away from postsynaptic membrane
Degradation (proteolytic enzymes)
Reuptake (active transport at the presynaptic nerve terminal)
