Sensory receptors•All stimuli represent forms of energy.•Sensation involves converting energy into a change in the membrane potential of sensory receptors.•Sensations are action potentials that reach the brain via sensory neurons.•The brain interprets sensations, giving the perception of stimuli.
Sensory Pathways•Functions of sensory pathways: sensory reception, transduction, transmission, and interpretation.1.sensory reception, detection of stimuli by sensory receptors.2.Sensory transduction is the conversion of stimulus energy into graded action potentials3.transmission – conduction of action potentials to the CNS along an afferent pathway.4.Interpretation– the brain creates a sensory perception
Amplification and Adaptation•Amplification is the strengthening of stimulus energy by cells in sensory pathways.•Sensory adaptation is a decrease in responsiveness to continued stimulation.
Types of Sensory Receptors•Receptors fall into 3 categories:•Mechanoreceptors•Chemoreceptors•Electromagnetic receptors•Also can be either •Exteroceptors – receptors that sense stimuli that arise in the External environment •Interoceptors – sense stimuli from within the body
Sensory Transduction and Gated Ion Channels •Stimulus-gated ion channels •Ion channels that open or close depending on the sensory system involved •Usually cause a depolarization •Receptor potential: a depolarization that occurs in a sensory receptorupon stimulation. (the next step after the initial receptor) •The greater the sensory stimulus, the greater the depolarization of the receptor potential and the higher the frequency of action potentials.
•The relationship between stimulus intensity and action potential is (usually) logarithmic •This way the CNS has a simple method of interpreting the strength of the stimulus based on the frequency of incoming signals.
Chemoreceptors•General chemoreceptors respond to chemicals/ chemical changes.•When a stimulus molecule binds to a chemoreceptor, the chemoreceptor becomes more or less permeable to ions.
Mechanoreceptors•Mechanoreceptorssense physical deformation caused by stimuli such as pressure, pain, heat, cold, stretch, motion, and touch.•Cutaneous receptors •found in skin•Technically are classified as interoceptors
Cutaneous Receptors •Merkle cells – near the surface, sensitive to touch pressure and duration•Meissner Corpuscle – in hairless skin, sensitive to fine touch •Ruffini Corpuscle – near the skin surface that are sensitive to pressure and duration •Pacinian Corpuscle – located deep within the subcutaneous tissue and is sensitive to pressure
Phasic vs Tonic•Phasic – intermittently activated•So for instance the phasic sensors could send a signal when the stimulus is applied and when it stops.