Explain the reflex arc using an example in humans

The reflex arc describes a sequence of events leading to an action that takes place rapidly in response to a stimulus without having to think about it i.e. without an impulse travelling to the brain for coordination. For example, the response to touching a sharp object is to remove your finger from it quickly. The pain/pressure receptors in your finger are stimulated by the stimulus of touching a sharp object - the receptor acts as a transducer to convert the energy of the stimulus into electrical energy that is transmitted along the sensory/afferent neurone. This is known as the action potential. This AP travels to the central nervous system (CNS) where the sensory neuorne synapses with a relay/inter neuorne within the spinal cord. The spinal cord processes the sensory information and coordinates a response to it. In this case, an AP will be sent along a motor/efferent neurone to the bicep muscle (the effector) of the affected arm and it will cause it to contract, moving your finger away from the sharp object. Fast action is achieved by bypassing the brain in the circuitry as, to think about the stimulus and produce a response through thought is longer and takes more time. In normal everyday activity, where one may consciously respond to a stimulus. Sensory information still travels to the CNS but as the sensory neurone arrives at the spinal cord, it travels up the neuronal tracts in the spinal cord where it will synapse with the relavent neurones in the brain that coordinate a complex response. This response then must travel back down the spinal cord to the appropriate motor neurone for an effective response to take place. The reflex arc for stimuli-responses that don't require thought, skips the process of having to travel up tracts to the brain, so in this way you don't need to consciously realise, your finger is being pierced, before you decide to do something about it. You'll sort it out subconsciously