PSL300H1 Lecture 5: Lecture 5L Neurophysiology
PSL300
Lecture 5: Neurophysiology 5
Receptor Potential
• Receptor potential: change in the MP due to receipt of signal from exterior sensory cue
• The energy form the environment will react with membrane proteins and in general this will cause depolarization
• Depolarization of sensory receptors upon receipt of specific energy
o Exception: photoreceptors hyperpolarize
• Similar to PSP, the receptor proteins are embedded in sensory cell membrane
• The receptor proteins of the sensory cells will change shape when specific energy is received
• When the receptor protein changes shape, it can either:
o Directly open ion channels (e.g. cation channels → leads to depolarization of the membrane)
o Enzyme is activated via G-protein coupled receptors → leading to production of 2nd messengers
(cAMP,cGMP, InP3) → lots of 2nd messengers will be made → amplifying the signal
Post Synaptic Receptors
• Chemical stimulus binds to specific metabotropic receptor (GPCR’s) and
activates it
• Activation of adjacent enzyme (adenyl cyclase) produces more 2nd
messengers
• cAMP activates kinases which directly interact with ion channels or
phosphorylate other proteins
Stages of Amplification
• There are 2 stages of amplification
1. G-protein can activate a number of different enzyme molecules
2. Each of these enzyme molecules will produce lots of 2nd messenger
(cAMP)
• Thus, one stimulus molecule can produce lots of 2nd messengers (cAMP)
Olfactory Receptor
• Specific receptor proteins bind specific odorant
• Sensory proteins are embedded in the membrane
• Olfactory neurons involved with the sensation of smell
o Finger like projections inside the nasal passage
o Mucus also covers the finger like projections
• There are olfactory receptor cells
o This is where the chemical stimulus gets dissolved
in the mucus and is presented and binds to a
specific olfactory receptor
• There are different receptors for every single different
odorant
• Our system of smell is sensitive due to the process of amplification
o Receptor protein binds to a specific odorant
o Activate G-protein
o Activate adynyl cyclase
o Production of cAMP
o cAMP directly binds to ion channels
o Allows cations (Na+ and Ca+) to enter
o Depolarization of the membrane
• The depolarizing current has to travel down the membrane and
down to the trigger zone of the axon
o The wave can degrade over time
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Document Summary
Post synaptic receptors: chemical stimulus binds to specific metabotropic receptor (gpcr"s) and activates it, activation of adjacent enzyme (adenyl cyclase) produces more 2nd messengers camp activates kinases which directly interact with ion channels or phosphorylate other proteins. Influx of ca+ ions and trigger exocytosis vesicles: sensory cell is releasing vesicles and not producing an ap. Adaptation: the mp can decay over time leading to adaptation", the original voltage is not sustained and it"s dropped over time, even though the stimulus may be constant, we have 2 types of adaptation , slowly adapting, rapidly adapting. Slow adaptation: slowly-adapting: receptor potential sustained for duration of stimulus, a stimulus will last for a long time. Interested in overall magnitude of the stimulus: the receptor potential decays over time (slowly) even though the stimulus is always there in the background. Rapid adaptation: rapidly adaptation: receptor potential elicited by change in stimulus energy, decays to zero when stimulus is constant.
