Responses to internal stimuli

Cells which detect specific stimulus + convert energy into a generator potential

Initial action potential
Occurs at receptor

Pressure receptor

At rest, stretch mediated Na+ channels (SMNC) too narrow to allow Na+ in
Pressure applied
Pacinian corpuscle changes shape
Stretches open SMNC
Na+ diffuses into neurone and makes inside of membrane more positive
GP produced if threshold reached
Stimulates more Na+ channels to open and AP generated

More pressure = more SMNC open = more Na+ open = threshold more likely

More intense = more frequent AP

Rods
Cones

Sensitive to low light
Low visual acuity
Black and white
Evenly spread on retina

Multiple rod cells to 1 bipolar neurone
Retinal convergence means brain can't distinguish between AP

Multiple rod cells to 1 bipolar neurone
Spatial summation
Threshold for AP more likely to be reached

Rhodopsin

High visual acuity
Colour vision
Mainly in fovea

1 cone cell to 1 bipolar neurone
No retinal convergence
Brain can distinguish between AP

Red
Blue
Green

Phototopsin

Pigment in rod/cone cells broken down by light
Initiated GP
AP in bipolar neurone
Travels to optic nerve

Contracts and relaxes without receiving signal from brain
Cardiac muscle (cells beats on their own)

Medulla

Pressure receptors
In aorta and carotid artery
Stimulated by high and low BP

pH receptors in aorta, carotid artery and medulla
Affected by CO2 conc.

Bbaroreceptors detect high BP
Medulla
More electrical impulses along parasympathetic pathway
Reduced frequency of electrical impulses at SAN
Reduced contractions
Reduced HR

Chemo receptors detect high CO2
Medulla
More electrical impulses along sympathetic pathway
Increased frequency of electrical impulses at SAN
More contractions
Increased HR

Noradrenaline

Ach