Figure A.4 Brain Synapse Comparison. Them refers to crustacean skeletal muscle. Each muscle fiber can receive multiterminal input (more than one synapse from a single neuron), polyneuronal input (synapses from more than one neuron), and inhibitory input (shown in red; inhibitory synapses may be directly on the muscle or may presynaptically modulate excitatory synapses). In the superficial flexor, synaptic stimulation causes only PSPs; the muscle fiber does not fire an AP. Brain refers to a dendrite of a vertebrate brain neuron. Like the crayfish superficial flexor, it receives multiterminal, polyneuronal, and inhibitory input. Dendrites do not fire APs, although axons may.