Biological Systems MCAT Practice Exam 2025 – The Comprehensive All-in-One Guide for Exam Success!

Synaptic knobs, also known as synaptic terminals or boutons, play a crucial role in neuronal communication by facilitating the transmission of signals between neurons. The primary function of synaptic knobs is to release neurotransmitters into the synaptic cleft, which is the small gap between adjacent neurons. When an electrical impulse, or action potential, travels down an axon and reaches the synaptic knob, it triggers the opening of voltage-gated calcium channels. The influx of calcium ions prompts synaptic vesicles, which are small sacs containing neurotransmitters, to fuse with the presynaptic membrane and release their contents into the synaptic cleft.

Furthermore, synaptic knobs can also be involved in the initial reception of impulses when they are connected to receptors that sense incoming signals, although this is more the function of dendrites or the cell body of neurons. The term "receive impulses" typically refers to the action of dendrites, which are designed to detect synaptic signals from other neurons.

Thus, recognizing that synaptic knobs release neurotransmitters into the synaptic cleft is key, as this process is central to the communication between neurons. However, the complexity of synaptic function acknowledges that information transfer also requires the recognition of incoming signals, establishing