Final answer:
A reflex arc where the sensory neuron directly synapses with the motor neuron is known as a monosynaptic reflex arc, involving only a single synapse, so the answer is option 1.
Step-by-step explanation:
A reflex arc is the neural pathway that controls a reflex. It consists of five main components:
Receptor: The receptor is a specialized sensory neuron that detects a stimulus, such as touch, pressure, pain, or light.
Sensory neuron: The sensory neuron carries the signal from the receptor to the spinal cord.
Interneuron: Interneurons are relay neurons that connect the sensory neuron to the motor neuron.
Motor neuron: The motor neuron carries the signal from the interneuron to the effector.
Effector: The effector is the muscle or gland that produces the reflex response.
Most reflex arcs are polysynaptic, meaning that they have multiple interneurons between the sensory neuron and the motor neuron.
However, some reflex arcs are monosynaptic, meaning that they have only one interneuron. Monosynaptic reflex arcs are the simplest and fastest type of reflex arc.
In a monosynaptic reflex arc, the sensory neuron synapses directly on the motor neuron. This means that the signal can travel from the receptor to the effector in just two neurons, which makes the reflex response very fast.
Monosynaptic reflex arcs are responsible for some of our most important reflexes.
So the answer to the question is 1) Monosynaptic reflex arc.