Which of the following crosses the synaptic cleft from one axon to the dendrite of another cell? avesicles bdopamine ccerebrospinal fluid dglia

The substance that crosses the synaptic cleft from one axon to the dendrite of another cell is dopamine (b). Here's a step-by-step explanation:

1. When an electrical signal reaches the end of a neuron (the axon terminal), it triggers the release of neurotransmitters. These are chemical messengers stored in small sacs called vesicles.

2. These neurotransmitters, which include substances like dopamine, are released into the small gap between neurons. This gap is known as the synaptic cleft.

3. The neurotransmitters cross the synaptic cleft and bind to specific receptors on the next neuron (on its dendrite). This can either trigger or inhibit a new electrical signal in this second neuron.

So, while vesicles (a) are involved in the process, they don't actually cross the synaptic cleft. They stay in the neuron and release the neurotransmitters into the cleft. Cerebrospinal fluid (c) surrounds the brain and spinal cord, but it doesn't cross the synaptic cleft. Glia (d) are supportive cells in the nervous system, but they also don't cross the synaptic cleft. Therefore, the correct answer is dopamine (b).