Parkinson's disease (characterized by tremors and rigidity in limbs) is caused by the degeneration of neurons in the brain that are associated with the secretion and use of which neurotransmitter?

Assertion : Transmission of nerve impulse across a synapse is accomplished by neurotransmitters.
Reason : Transmission across a synapse usually requires neurotransmitters because there is a small space,i.e.,synaptic cleft,that separates one neuron from another.

In the neural system,a chemical synapse shows a synaptic gap of about . . . . . . .

Synaptic vesicles contain chemicals called

Which of the following statements are correct regarding electrical synapses?
$i.$ At electrical synapses,the membranes of pre- and post-synaptic neurons are in very close proximity.
$ii.$ Electrical current can flow directly from one neuron into the other across these synapses.
$iii.$ Impulse transmission across an electrical synapse is very similar to impulse conduction along a single axon.
$iv.$ Electrical synapses transmit signals using neurotransmitters like acetylcholine.
$v.$ Electrical synapse transmission is very fast.
$vi.$ Electrical synapses are rare in our system.

The figure shows an axon terminal and synapse. Select the option giving correct identification of labels $A-D$.