Answer: 
A presynaptic neuron knows when and how much of a certain neurotransmitter it has to release into the synapse by the frequency of the action potential.
Explanation:
Two nuerons connect to each other through synapse. When an action potential, or nerve impulse, arrives at the axon terminal, it activates voltage-gated calcium channels in the cell membrane, then the calcium which is present in hi highconcentration outside the neuron than inside, rushes into the cell. The Calcium then allows synaptic vesicles to fuse with the axon terminal membrane, releasing neurotransmitter into the synaptic cleft.
The nuerotransmitter than binds to the receptors at the post-synaptic cleft and causes the opening or closing of the channels, hence, depolarizing or hyperpolarizing the cells.This can produce a change in the membrane potential—voltage across the membrane of the receiving cell.
 
        
             
        
        
        
Answer:
They are called hydrogen bonds
 
        
             
        
        
        
Answer:
Explanation:
The myosin head rotates, causing overlap
with actin.
The myosin head attaches to a binding site
on the actin filament.
The myosin head detaches from one
binding site and reattaches to another.
 
        
                    
             
        
        
        
This is false. Absolute brightness is the term used to describe how bright a star would look if it were a standard distance from Earth. Apparent brightness is how bright it would look as far as it currently is from Earth. Hope this was helpful!
 
        
                    
             
        
        
        
The pressure from sound waves makes the eardrum vibrate.
The vibrations are transmitted further into the ear via three bones in the middle ear : the hammer (malleus), the anvil (incus) and the stirrup (stapes).