Chapter 7

1) A cells ability to respond to a stimuli is by eliciting an electrical response. A cell in the eye can detect even the faintest of lights, therefore light is its sensory modulation. Another different stimulus can elicit a response because of the electrical dependence. That is a different stimulus can induce a change in cell state with a larger input of energy. This can possibly occur due to the similarity in most proteins that act as receptors for the input stimulus. That is the incorrect input can take advantage of the similarity by being more intense and thus elicit a response.

2) I will use taste as an example. Alanine is detected by a receptor on the surface of the cell. Transduction occurs and the receptor activates a cascade of protein interactions. The signal is then amplified by second a messenger system. Channels then open and encode the signal as an electronic response. The signal then may become an AP (action potential) and go to the brain.

3) Action potentials are the currency of the brain because they are regenerative. Receptor potentials could never send a signal with enough strength to be effective without the help of an AP.

4) With differentiate between these because the different regions of the CNS are made to accept different inputs. They accept the different inputs because of the circuits. The brain just assumes that a signal from a certain area is due to stimulus of the ears or eyes. The type of stimuli is not for the sensor to determine only strength and time. What does this last sentence mean?

5) In taste again, the transduction is accomplished by the receptors binding the stimulus and then activating a G protein, which eventually opens channels. Thus, transduction is simply the process of changing one form of energy into another (chemical to electrical). Amplification is accomplished when the G protein is activating multiple second messenger molecules. This determines how much larger the electrical signal will be than the chemical input. This in turn will open channels for depolarization.

6) Frequency of stimulation is the only way to modulate this. What is"this"?The magnitude of the signal is related to the amount of amplification of the signal. If the signal is very intense, there will be little amplification, and the input and output will be almost equal. If the signal is quite weak, then more amplification will occur and the signal sent out will be larger than the stimulus. The intensity itself is encoded by the frequency of AP's. The sensory system will respond to large changes in intensities by adaptation. Additionally, sensory systems usually contain cells with a large range of sensitivities, so as one cell saturates, another will respond.

7) The receptor cell itself can act as a filter to only include transient responses and not sustained responses. Second, molecules in the pathway to cause an AP may be depleted or bleached as in the eye. Thirdly, enzymatic products may accumulate and lead to inhibition of the system. More are listed on pg.228.

8) In muscle, stretch receptors are under efferent control. This is done to keep the receptor at a given length. This, in turn, will set the sensitivity of this cell. For example if the muscle is stretched then the receptor is stretched as well (since the receptor is a modified muscle fiber and runs the length of any given muscle). But if the muscle contracts then the receptor is to long since it did not contract. Therefore we have efferent control on the sensor so it will always be the same length as the muscle.