Sense organ - A structure composed of nerve tissue and other tissues that enhance its response to a certain type of stimulus.
Main purpose of sensory receptors is transduction, conversion of one form of energy to another. The transducer is the device that converts the energy ie sense organ.
Receptor potential - the local electrical change from a stimulus on a neuron.
1.Define sensation and describe its process
•Conscious or subconscious awareness of changes in the external or internal environment
•Sensory impulses may only reach the level of the spinal cord (e.g. stretch reflex), the lower brain stem (e.g. reflexes like blood pressure) or the cerebral cortex and we become aware of them (e.g. touch, pain, hearing etc)
•The process of sensation begins in a sensory receptor which can be either a specialised cell or the dendrites of a sensory neuron
The following must take place for sensation to occur:
•A stimulus must occur within the receptive field of the receptor (receptive field is the pickup area of a particular neuron).
•The sensory receptor transduces energy in a stimulus (e.g. mechanical, thermal, chemical) into a graded/receptor potential (electrochemical energy). Note that each type of sensory receptor can only transduce one kind of stimulus; selectivity
•If graded potential reaches threshold, an action potential is triggered which propagates to CNS via 1st order neurons (the 1st order neuron is always associated with the receptor/stimulus)
•Integration of sensory input takes place in a particular region of the CNS via 2nd & 3rd order neurons with conscious sensation perceived in cerebral cortex only. Note that most sensory input is filtered out at brainstem level