<P> Pain receptors are known as nociceptors . Two main types of nociceptors exist, A-fiber nociceptors and C - fiber nociceptors . A-fiber receptors are myelinated and conduct currents rapidly . They are mainly used to conduct fast and sharp types of pain . Conversely, C - fiber receptors are unmyelinated and slowly transmit . These receptors conduct slow, burning, diffuse pain . </P> <P> The absolute threshold for touch is the minimum amount of sensation needed to elicit a response from touch receptors . This amount of sensation has a definable value and is often considered to be the force exerted by dropping the wing of a bee onto your cheek from a distance of one centimeter . This value will change based on the body part being touched . </P> <P> Vision provides opportunity for the brain to perceive and respond to changes occurring around the body . Information, or stimuli, in the form of light enters the retina, where it excites a special type of neuron called a photoreceptor cell . A local graded potential begins in the photoreceptor, where it excites the cell enough for the impulse to be passed along through a track of neurons to the central nervous system . As the signal travels from photoreceptors to larger neurons, action potentials must be created for the signal to have enough strength to reach the CNS . If the stimulus does not warrant a strong enough response, it is said to not reach absolute threshold, and the body does not react . However, if the stimulus is strong enough to create an action potential in neurons away from the photoreceptor, the body will integrate the information and react appropriately . Visual information is processed in the occipital lobe of the CNS, specifically in the primary visual cortex . </P> <P> The absolute threshold for vision is the minimum amount of sensation needed to elicit a response from photoreceptors in the eye . This amount of sensation has a definable value and is often considered to be the amount of light present from someone holding up a single candle 30 miles away, if one's eyes were adjusted to the dark . </P>

Which of the following refers to the change from a physical stimulus to a neural impulse