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Sensory Physiology. Sections 3.3-3.6. Regulatory Mechanism. Controller. Effector. Sensor. (Feedback). Simple Nerve Pathway. CNS (Interneurons). Sensory Neuron. Motor Neuron. Effector. Sensor. E.g. Reflex - simple, stereotyped response; very fast. Complex Nerve Pathway. Other motor.
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Sensory Physiology Sections 3.3-3.6
Regulatory Mechanism Controller Effector Sensor (Feedback)
Simple Nerve Pathway CNS (Interneurons) Sensory Neuron Motor Neuron Effector Sensor E.g. Reflex - simple, stereotyped response; very fast
Complex Nerve Pathway Other motor Other sensors CNS Sensory Neuron Motor Neuron Effector Sensor Other sensors Other motor More complex, modulated response; slower
Simple Nerve Pathway:Spinal Reflexes • Stretch spindle fiber in muscle → sensory neuron • sensory neuron synapses directly with motor neuron in CNS • Motor neuron → muscle Manual Fig 3.11
Inhibitory Stretch Reflex • Golgi tendon organ • sensory neuron synapses w/interneuron, which synapses w/motor neuron • Inhibits MN, thus prevents contraction Textbook Fig 12.28
Reciprocal Innervation • Activation of both excitatory and inhibitory motor responses in antagonistic muscles • Prevents both muscles from contracting simultaneously Textbook Fig 12.29
Experiment: Spinal Reflexes • Whack your partner! • Patellar reflex • Achilles reflex • Biceps reflex
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
Acuity • 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
Touch Acuity Large Fields, Low Density Small Fields, High Density
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 Textbook Fig 10.5
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 Textbook Fig 10.1
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?
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
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
