In humans, transmission of nerve impulses across a synaptic cleft is carried out by *

In humans, transmission of nerve impulses across a synaptic cleft is carried out by neurotransmitter.

Explanation:

In humans, nerve impulses are carried out by neurotransmitter diffusion. Communication between the cells occur through the small gap called the synapses.

The transmission happens through the neurotransmitter  which helps by diffusing across the synaptic cleft and binding the receptor molecule to the synaptic membrane hence sharing information and transmitting them.

The chemical found inside the neuron is responsible and it is depolarized within the neuron and sent as an information by the synaptic receptors transmitted by the neurotransmitter .

answer; polycythemia is the correct answer;

more words for this could be abiotic and biotic

abiotic: living organisms within an ecosystem

biotic: non-living organisms within an ecosystem