8. Synapses + NTs Flashcards
What is the structure of an electrical synapse?
Gap junction connects cytosol of two cells together. 3 nm gap spanned by connexons with a 1-2 nm pore to allow the passage of ions and small organic molecules
What are the characteristics of electrical synapses?
Bidirectional Very fast (almost instantaneous)
Why are many connections needed to induce an AP for electrical synapses?
The electrical activity in the post synaptic cell is 1/100th of the size of the presynaptic cell. Need to sum many connections to induce AP
What fills the synaptic cleft of chemical synapses?
A matrix of fibrous extracellular protein to adhere cells
What structures are present in presynaptic axon terminals?
What structures are present in postsynaptic dendrites?
Active zones with many vesicles and lots of mitochondria
High density of receptors
What triggers NT release from the presynaptic axon?
The arrival of the AP causes voltage gated Ca2+ channels to open. Ca2+ floods in, triggers NT release
What are the two main inhibitory NTs?
The main excitatory?
GABA and Glycine - inhibitory
ACh and Glutamate - excitatory
What are the four criteria for an NT?
Must be:
- synthesised in presynaptic neuron
- released from presynaptic membrane
- have action on postsynaptic membrane, activate receptors
- inactivated
What did Leowi’s experiment show?
That chemicals were involved in the transmission of APs from one cell to another
What is responsible for creating EPSPs and IPSPs?
EPSPs occur when Na+ enters the cell through ligand-gated ion channels and depolarises the membrane
IPSPs occur when Cl- enters the cell and hyperpolarises the membrane (becomes more -ve)
What are the main differences between transmitter-gated ion channels and G-protein coupled receptors?
Transmitter-gated give fast synaptic transmission. G-protein is slower but longer lasting and has more diverse effects on postsynaptic cell
How does the G-protein coupled receptor work?
Activated G-protein can open ion channel or trigger a second messenger and enzyme cascade
Why are G-protein receptors known as metabotropic?
They trigger widespread metabolic effects.
How does the action of ACh differ in cardiac and skeletal muscle?
ACh depolarises skeletal muscle cells to induce contraction, via Na+. It hyperpolarises cardiac cells to slow heart rhythm, via K+.
What is the job of the postsynaptic neurone?
Integrate information to give rise to one output, the AP
