Sensory Nervous System Objectives:  Describe the process of sensory transduction in general  List the stimuli to which we have receptors and, for each, identify the general type of receptor  Distinguish receptor potential from action potential  Distinguish tonic and phasic receptor function

Somatic senses fine touch, deep touch, pressure, temp, pain, joint and muscle position, muscle stretch Visceral senses pH, O 2, CO 2, OsM, glucose, blood pressure, lung inflation, stomach stretch Special senses olfaction, gustation, hearing, equilibrium, vision

ear (sense organ) with mechanoreceptors (transducers) CNS (decoder) -medulla to thalamus to auditory cortex Vestibulocochlear nerve non-neural receptors -receptor potentials (like graded potentials) graded potentials action potentials coding: which receptors are activated and AP frequency Receptors are transducers, neural or non-neural Types: chemo-, mechano-, photo-, thermo-, noci-

General principles of sensory function 1.Each sensory organ and receptor is specialized to convert one form of stimulus into sensory neuron action potentials. 2.Each modality has a discrete pathway to the brain. 3.The specific sensation and location of stimulus perceived is determined by area of brain activated. 4.‘Intensity’ is coded by frequency of action potentials and number of receptors activated.

Group the following senses according to whether they use chemical or mechanical receptors. taste (gustation) pain (nociception) smell (olfaction) touch vibration vision oxygen levels pressure (baroreception) Which one can be both and which one is neither? -chem -chem and mech -chem -mech -neither -chem -mech

A somatic sense: touch Free nerve endings Meissner’s corpuscle (light) Pacinian corpuscles (deep)

Example sensory pathway: touch (receptor cell)  sensory neuron  to spinal cord or brainstem  to thalamus  to somatosensory cortex

General principles of sensory function 1.Each sensory organ and receptor is specialized to convert one form of stimulus into sensory neuron action potentials. 2.Each modality has a discrete pathway to the brain. 3.The specific sensation and location of stimulus perceived is determined by area of brain activated. 4.‘Intensity’ is coded by frequency of action potentials and number of receptors activated.

The specific sensation and location of stimulus perceived is determined by area of brain activated.

FREQUENCY CODING LIGHT PRESSURE LOW FREQUENCY MORE PRESSURE HIGHER FREQUENCY ‘Intensity’ is coded by frequency of action potentials and number of receptors activated.

POPULATION CODING LIGHT PRESSURE MORE PRESSURE ‘Intensity’ is coded by frequency of action potentials and number of receptors activated.

Receptor Types Chemoreceptors : pH, O 2, CO 2, glucose, taste, odor, some pain Mechanoreceptors : muscle, cell, joint, lung, blood vessel and stomach stretch, sound, equilibrium Photoreceptors : light Thermoreceptors : hot or cold All receptors are transducers sensitive to a specific stimulus. Some are neurons, some are not.

General principles of sensory function Somatic senses -touch, pressure, temp, pain Objectives: For each sense identify… Any specialized structures or sense organs Receptor type Receptor signal transduction mechanism Coding of intensity and duration Pathway of conduction to the CNS Coding for perceived sensation