Reflex Arc

A reflex is not like a coordinated response and is quicker to prevent injury. 

Explain in detail the reflex arc and all the junctions.

A stimulus (for example a sharp pin *****) provokes a response and it is picked up by a receptor which starts an impulse, The sensory neuron picks up the impusle from the receptor and it crosses the synapse to get to the relay neuron. The neuron cannot jump across the synapse which is a junction but instead neurotransmitters which carry the impulse are secreted. These diffuse across the gap and then the impulse reaches the relay neuron which relays around the spinal cord (and the unconscious part of the brain) and it crosses the synapse to the motor neuron which is connected to an effector organ which can either be a muscle or a gland. If it is a muscle then the muscle contracts and if it is a gland then the gland secretes hormones.

Reflexes are quicker because they cross less synapses than coordinated responses and they are different because they don't get to the brain

We (as humans) react to our surroundings and sense what is going on around us. We send this information to the CNS and it travels along nerves as electrical impulses. The spinal cord connects the nerves to the brain which sorts out the information and decides what action is needed. The brain sends impulses along other nerves to get to the correct muscles and they carry out an appropriate response.