2. Sensory Physiology Sections 3.3-3.6

3. Regulatory Mechanism Sensor Controller Effector (Feedback)

4. Simple Nerve Pathway Sensor CNS (Interneurons) Effector Sensory Neuron Motor Neuron E.g. Reflex - simple, stereotyped response; very fast

5. Complex Nerve Pathway Sensor CNS Effector Sensory Neuron Motor Neuron More complex, modulated response; slower Other sensorsOther motor Other sensors Other motor

6. Simple Nerve Pathway: Spinal Reflexes Stretch spindle fiber in muscle → sensory neuron sensory neuron synapses directly with motor neuron in CNS Motor neuron → muscle

7. Inhibitory Stretch Reflex Golgi tendon organ sensory neuron synapses w/interneuron, which synapses w/motor neuron Inhibits MN, thus prevents contraction

8. Reciprocal Innervation Activation of both excitatory and inhibitory motor responses in antagonistic muscles Prevents both muscles from contracting simultaneously

9. Experiment: Spinal Reflexes Whack your partner! –Patellar reflex –Achilles reflex –Biceps reflex

10. Punctate Distribution of Cutaneous Sensors Different sensations perceived at different points on surface of the skin Different sensor types distributed throughout skin. Perception localized to specific points

11. Acuity –ability to discriminate size, shape of an object in the environment Determined by size of receptive field –area that, if stimulated, will cause a response from a single sensory neuron  receptor density,  receptive field size,  acuity

12. Touch Acuity Large Fields, Low DensitySmall Fields, High Density

13. Experiment: Two Point Touch Discrimination Subject should have eyes closed Start with tines ~2.5 cm apart Touch to subject’s skin w/ both tines simultaneously If they can feel two points, close slightly and repeat. Repeat until subject can feel only one pt. Distance btw tines at pt where subject loses ability to feel two pts = diameter of receptive field Test –Index finger –Palm –Lower Arm –Nape of Neck

14. Sensory Adaptation Response of sensors to constant stimulation Phasic receptors –exhibit sensory adaptation –firing rate of receptor (# AP’s) decreases with constant stimulus Tonic receptors –exhibit little adaptation –maintain constant firing rate as long as stimulus is applied

15. Experiment: Thermoreceptor Adaptation Place one hand in cold water, the other in hot water for 60 seconds Place both hands simultaneously in warm water. What do you feel in each hand?

16. Sensory Pathways and Perception sensors are transducers –convert environmental change into an electrical signal CNS interprets electrical signals –not the environmental changes directly –e.g. blow to head perceived as flash of light CNS interprets origin of stimuli based upon neurons that deliver sensory info. into CNS –Can deceive CNS with respect to origin

17. Sensory Pathways and Perception Referred pain –perception of pain originating from location other than actual site of tissue damage –E.g. phantom limb pain Irritation of severed nerve endings induces AP’s CNS perceives stimulus being applied to limb not present –E.g. angina pectoris Damage to heart perceived in left chest, shoulder & arm pain sensors of visceral organs often use shared pathways of interneurons leading to the brain

18. Sensory Pathways and Perception