sensory physiology sections 3.3-3.6 regulatory mechanism sensor controller effector (feedback)
TRANSCRIPT
Sensory Physiology
Sections 3.3-3.6
Regulatory Mechanism
Sensor
Controller
Effector
(Feedback)
Simple Nerve Pathway
Sensor
CNS (Interneurons)
Effector
Senso
ry Neu
ron Motor Neuron
E.g. Reflex - simple, stereotyped response; very fast
Complex Nerve Pathway
Sensor
CNS
Effector
Senso
ry Neu
ron Motor Neuron
More complex, modulated response; slower
Other sensors Other motor
Other sensors Other motor
Simple Nerve Pathway:Spinal Reflexes
• Stretch spindle fiber in muscle → sensory neuron
• sensory neuron synapses directly with motor neuron in CNS
• Motor neuron → muscle
Inhibitory Stretch Reflex
• Golgi tendon organ • sensory neuron synapses
w/interneuron, which synapses w/motor neuron
• Inhibits MN, thus prevents contraction
Reciprocal Innervation
• Activation of both excitatory and inhibitory motor responses in antagonistic muscles
• Prevents both muscles from contracting simultaneously
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
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
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
Sensory Pathways and Perception