Sensorimotor Control of Behavior:
SomatosensationLecture 8
Somatosensation
Sensory info from body Cutaneous senses
exteroceptors touch / pain
Kinesthesia interoceptors body position & movement ~
Somatosensory cortex
S1 - Postcentral Gyrus Somatotopic Organization
topographic representation of body Distorted Homunculus
disproportionate amount of cortex for body parts
high sensitivity: large cortical area ~
Somatosensory Cortex
Formation of a Body Image Does not simply respond to
sensory input Phantom Limbs
after amputation also pain ~
M1S1PPC
Kinesthesia
Kinesthesia
Body Position & Movement proprioception
Joint information Pacinian corpuscles & Ruffini endings
Muscle & tendon information changes in tension
Golgi tendon organmuscle spindle fibers ~
Cutaneous Receptors
Stretching of the skin Limited role in proprioception
Ruffini Endings slow adapting population of neurons responding
simultaneously ~
Cutaneous Receptors
Role depends on location Anesthetize skin assess ability to detect passive
movement Knee: no affect on proprioception Mouth, hands, & feet
proprioception significantly reduced ~
Muscle Receptors
Major role in proprioception Stretch receptors
detect changes in tension 2 types of receptors
Muscle spindles & Golgi tendon organs differences in threshold & location ~
Muscle length detectors Parallel with extrafusal fibers Low threshold
Monosynaptic stretch reflex Postural adjustments Muscle tonus
Sensory neuron ---> alpha motor neuronsmonosynaptic excitationdisynaptic inhibition ~
Muscle-Spindle Receptors
Dorsal
Ventral
++
MS
-
+
+
Golgi Tendon Organ
Gauges muscle tension high threshold
Stretch receptor safety mechanism controlled muscle contraction ~
Dorsal
Ventral
-+
GTO
+Inhibits alphamotor neuron
GTO: Function
Inhibits muscle contraction Control of motor acts
slow contraction as force increases e.g., holding an egg
breaks if too much force Autogenic inhibition
safety mechanism too much tension ---> damage ~
The Orienting Senses
Orientation: The Vestibular System
Position & motion of body in space critical for adaptive interaction largely unnoticed except unusual conditions
motion sickness: nausea, dizziness Maintenance of balance & posture
coordinating body position with other sensory information ~
Receptors for Orientation Inner ear Gravity detectors
plane of reference Mechanoreceptors Vestibular Organs
otocysts• saccule• utricle
semicircular canals ~
Otocysts
Liquid-filled “ear sacs” lined with hair cells contain otoliths
“ear stones : direction of acceleration
saccule: vertical movement utricle: horizontal movement ~
At rest tilted Acceleration to right
Direction of gravity
Acceleration to right
Semicircular Canals
Rotary acceleration direction & extent of circular movement
any direction 3 fluid-filled canals
right angles to each other 1 for each major plane
Movement causes fluid to circulate displaces cupula ~
Semicircular canals
UtricleAmpulla
Cristahair cells
Cupula
Vestibular Pathway
Vestibulocochlear nerve (VIII) Some axons directly to cerebellum Most axons to medulla
vestibular nuclei cerebellum, spinal cord, medulla & pons motor nuclei for eyes (III, IV, & VI)
compensates for movement of head temporal cortex (dizziness) ~
Input to Vestibular System Other sensory information
eyestrunk & necklimbscerebellum
Constant postural adjustments Maintains visual image fixed on retina maintains center of gravity during movement ~
Sensorimotor Integration
Sensorimotor Integration
Somatosensory cortex provides spatial coordinates
Motor Cortex executes movements
Results in meaningful behavior ~
Posterior Parietal Cortex - PPC
Constructs spatial coordinates for behavior
Apraxia inability to purposefully organize
movements Left parietal apraxia
bilateral inability to perform requested movements ~
Constructional apraxia - damage to PPC
Spatial Neglect Contralateral neglect
neglect of left side of body and world Damage to right PPC
map of body & space destroyed ~
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