what does it mean by "when a stimulus has a high intensity

Hi guys, what does it mean by "when a stimulus has a high intensity"?

For touch, how hard you’re pressed
For light, how strong the light intensity is
For sound, how loud the sound is

etc

The main point here is that the regardless of the intensity of the stimulus the action potential generated is always the same. So for example, if the stimulus is big like say bright light or loud noise the action potential is not bigger but rather more action potentials are generated. As long as the stimulus can reach the threshold an action potential will be generated regardless of how big or small the stimulus was.

Ohh so a bigger stimulus excites the membrane more, causing more na+ ion movement into neurone, and so a bigger change in potential difference across membrane which is the same thing as saying a bigger generator potential is produced. Then when generator potential reach threshold level (so when potential difference across membrane reached a certain level), action potential is generated in neurone.And a bigger stimulus, means action potential is generated more frequently

Thanks so much!
one more thing:
is light intensity in terms of the number of different wavelengths of light reaching your eyes or the frequency of light reaching your eyes?

so lots of diff wavelengths of light = high light intensity or short wavelength/high frequency wavelength of light = high light intensity? I am conflicted between the two.

In short: When the intensity of the stimulus is increased, the size of the action potential does not become larger. Rather, the frequency or the number of action potentials increases.

To answer your question about light as a stimulus the important thing is that the light stimulus hits a photoreceptor which initiates action potential production. You're complicating things by introducing different wave lengths of light so I would say leave that part out for now. Obviously shorter wavelengths have more energy but like I said that's a different kettle of fish. You're aware that there two main types of photoreceptors (light receptors) cones and rodes? Cones (three different types of cones receptors in humans) are sensitive to light of different wavelengths which is why you see in colour!

Ohh so a bigger stimulus excites the membrane more, causing more na+ ion movement into neurone, and so a bigger change in potential difference across membrane which is the same thing as saying a bigger generator potential is produced. Then when generator potential reach threshold level (so when potential difference across membrane reached a certain level), action potential is generated in neurone.And a bigger stimulus, means action potential is generated more frequently

Thanks so much!
one more thing:
is light intensity in terms of the number of different wavelengths of light reaching your eyes or the frequency of light reaching your eyes?

so lots of diff wavelengths of light = high light intensity or short wavelength/high frequency wavelength of light = high light intensity? I am conflicted between the two.

As Haviland-Tuf has said, you're complicating things by talking about different wavelengths of light and light intensity. Yes, shorter frequencies have higher energy however, this will not impact the frequency of action potentials. When talking about phototransduction, think about light as a photon. When a photon hits a photoreceptor in the retina, an action potential is fired. This does not depend on the wavelength of the light, shorter wavelengths will not lead to a greater frequency of action potentials. Different photoreceptors respond to different wavelengths of light.

Oh I see what you mean in my book, it says the higher the intensity of a stimulus, the higher the no. of action potentials generated. But if the stimulus is light, we can't really go about it in terms of intensity right? If the stimulus is pressure, then the intensity of the pressure applied on the pacinian corpuscle affects the no. of action potentials generated. But it doesn't work the same way for light because as you kindly advised, different photoreceptors respond to different wavelengths of light?

Exactly. It's really difficult to link light intensity to the number of action potentials. Especially when rods are more sensitive to light than cones, and therefore cones only operate in well-light conditions (photopic vision) whereas rods operate in low-light conditions (scotopic vision). There are also red, green and blue cones which respond to the wavelengths which correspond to red, green and blue light. But as you said, it's much simpler to talk about the relationship between stimulus strength and action potential frequency when it comes to mechanoreceptors. Using your example of Pacinian corpuscles, deep pressure or vibration causing deformation of the receptor, opening mechanosensitive sodium channels, leading to sodium influx which depolarises the membrane - known as a receptor potential. This receptor potential is a graded potential (i.e. the depolarisation is proportional to the stimulus strength). If the membrane potential reaches the threshold potential, an action potential will be fired. The greater the generator potential, the greater the frequency of action potentials.

Thanks very much! This makes total sense. However If something comes up about light, then I'll just stick to bright light,means more action potentials generated for my a level exams.

Is phototransduction on your syllabus at all?

No I don't think it is - I do OCR A Biology new spec

Hi, one little point to clarify what you are confused about - wavelength of light (almost reciprocal of frequency in simple terms) determines colour of the light NOT its intensity - intensity of light is its luminance or luminosity (these two terms are different but don't worry about that unless you later study optometry) - you might have seen on the packaging of modern lights/torches [pop down to your local Aldi, they are selling one right now ], where it says something like 500 candlepower (this candlepower is one unit of light intensity i.e. it is a way of measuring intensity of light, so a 1000 candlepower searchlight provides HIGHER INTENSITY of light than a 200 candlepower torch). Another unit of intensity of light is the lumen.

Wavelength of light (REMINDER: NOTHING TO DO WITH INTENSITY) is measured in nanometres (nm = 10E-9 metre)

Similar to a term you might have heard of for intensity [loudness] of sound (decibel).

M

Correct cos frequency and wavelength are very closely (reciprocally) related.

Frequency of any electromagnetic radiation (including visible light, UV light, X-rays, etc) multiplied by wavelength gives the speed of that radiation = 186,000 miles per second (mind-blowing) [you will know in km/s as Imperial units were used when I was a baby like you [sorry!] rather than metric units now)