neurons

• Neuron - nerve cells which process and transmit messages through electrical and chemical signals
• Sensory neuron - carry messages from the PNS to the CNS. They have long dendrites and short axons
• Relay neuron - connect the sensory neurons to motor neurons or other relay neurons. They have short dendrites and short axons
• Motor neurons - connect the CNS to effectors such as muscles or glands. They have short dendrites and long axons
• The knee-jerk reflex is an example of a reflex arc
• reflex arc is the pathway of a reflex action from the sensory receptor to the effector
• A reflex arc: a stimulus is detected by sense organs in the peripheral nervous system, which conveys a message along a sensory neuron. This message reaches the central nervous system, which then transfers the message with a relay neuron to a motor neuron. This then carries the message to an effector such as a muscle, causing a response