Physiology Flashcards
What are the 3 main functions of CSF?
1) Mechanical protection: shock absorbing medium that protects brain tissue
2) Homeostatic function: pH of CSF affects pulmonary ventilation and cerebral blood flow, also transports hormones
3) Circulation: medium for minor exchange of nutrients and waste products between blood and brain tissue
CSF is produced by the secretory epithelium of _____
the choroid plexus
CSF is found in the _____
ventricles and subarachnoid space
Define depolarisation and hyperpolarisation
- Depolarization – the membrane potential becomes less negative (or even positive)
- Hyperpolarization – the membrane potential becomes more negative
The retina contains 2 types of photoreceptors which are?
Rods and cones
The axons of the ganglion cells attached to photoreceptors form the ______
optic nerve/ disc
Photoreceptors contain GCPRs called _____ bound to _____
opsins
Prosthetic group retinal
Explain the dark current and photoreceptors resting membrane potential
Photoreceptors have a more positive resting membrane potential compared to other neutrons. Technically already depolarises so hyper polarises in the light > hence the dark current as a sodium channel is open in the dark due to cGMP and closes in the light causing the hyperpolarisation (this is the dark channel)
Describe detection of light and how signal is generated?
1) When a photon of light is absorbed by retinal it changes shape which causes a conformational change in the rhodopsin
2) The change in rhodopsin leads to activation of G proteins which goes onto activate phosphodiesterase
3) This hydrolyses cGMP from ligand gated Na+ channels so channels close and inwards leakage of Na+ stops
4) If sufficient build up of Na+ membrane becomes hyper polarised and a nerve impulse is generated
NOTE AS CELLS ARE HYPERPOLARISED NO NEUROTRANSMITTER IS INITIALLY RELEASED IT’S JUST A GENERATOR POTENTIAL
Describe five differences between rods and cones?
RODS: Rhodopsin Low levels of light 100 rods to a ganglion so greater amplification Peripheries of the retina Greyscale
CONES: Photopsin Bright light 1 cone: 1 ganglion Centre of retina in macula Colour
Describe the basis of colour vision?
Different types of photopsins in different cone cells with maximal sensitivity to specific wavelengths
One to blue, one to green and one to red
Describe visual perception
Our visual system detects local differences in light intensity not the absolute amount of light
Therefore in different contexts you may think 2 identical colours are different due to the different contrasts they are in
