Final answer:
A reflex where the sensory cell synapses directly onto the motor cell is known as a monosynaptic reflex, an example of which is the knee reflex.
Step-by-step explanation:
Types of Reflexes
A reflex where the sensory cell synapses directly onto the motor cell is anatomically defined as a monosynaptic reflex. These types of reflexes are fundamental for quick, automatic responses without the need for input from the brain. One commonly known monosynaptic reflex is the knee reflex, which is often tested during a routine physical examination. Monosynaptic reflexes involve only a single synapse between a sensory neuron and a motor neuron, making it possible for these reflexes to occur extremely quickly and involuntarily.
Another example of this kind of reflex is the stretch reflex. When a skeletal muscle is suddenly stretched, the stretch causes muscle spindle receptors to be activated, which then create a direct reflex arc that leads to the muscle contracting. This mechanism is important for maintaining muscle tone and for the rapid adjustment of posture to maintain balance.