2. An action potential is an all-or-none event, meaning that the amplitude is al

Question

2. An action potential is an all-or-none event, meaning that the amplitude is always the same, regardless of the characteristics of the stimulus. If action potentials are the only information that the brain receives from sensory neurons, how then is the brain able to perceive each of the following? Hint: see Silverthorn Chapter 10 Coding and processing distinguish stimulus properties a) Changes in the intensity of a stimulus (I pt) b) Change in the duration of a stimulus (1 pt) o) The location or specifie modality (Cype) of stimulus (I p) 3. Temperature receptors are scattered throughout the body. Between 20°C and 40°C they adapt slowly, and eventually stop firing action potentials. They do not adapt at temperatures below 20°C and above 40°C. In other words at those extremes of temperature they continue to fire action potentials which reach the brain. How does this have survival value for an animal or a person? Nothing really to look up here - think about it! (1 pt) 4. Why are mint flavored foods containing menthol perceived as cold, and foods containing capsaicin (the active ingredient in hot peppers), perceived as hot? Hin: See nociceptor patheways in S pts)

Explanation / Answer

1-Change in intensity of stimulus is detected by-

I) Rate of action potential. Intense stimulus will fire Action potential at higher rate, i.e, rapidly. Less intense stimulus will fire Action potential at slower rate. For eg- 10 action potential in 1 second versus 100 action potential in 1 second.

Il) Number of receptors stimulated. Intense stimulus will activate more number of receptors as compared to less intense stimulus.

2- Change in Duration of stimulus is detected by Action potential duration. Action potential is fired as long as the receptors are activated.

3- The location of stimulus and type of stimulus-

I) Sensory stimulus is first encountered by Receptors. Receptors are situated at different location. For eg, auditory receptors in ear. Touch receptors on skin. Visual receptors in eye.Thus for touch sensation, the stimulus has to act on skin for it to be perceived, sound should reach ear for it to be perceived, for vision the person must see the object, if the object is behind and that makes a sound, the object can only be heard and not seen.

Each receptor is supplied by sensory nerves. Activation of receptor induces Action potential in these afferent neurons. They then carry the sensation to respective area in the brain. Each neuron carry only one type of stimulus for eg, auditory nerve will carry only sound sensation till the auditory cortex in brain and nowhere else. Thus the brain( Auditory cortex) gets to know that the signal is coming from ear via auditory neuron and hence it is sensation of Sound. Similarly other sensations are localise and its type is detected by brain

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