Transcript Control of Movement

Sensorimotor Control
of Behavior:
Somatosensation
Lecture 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 ~

PPC
M1
S1
Kinesthesia
Kinesthesia
Body Position & Movement
 proprioception
 Joint information
 Pacinian corpuscles & Ruffini endings
 Muscle & tendon information
 changes in tension

Golgi tendon organ
muscle 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-Spindle Receptors
Muscle length detectors
 Parallel with extrafusal fibers
 Low threshold
 Monosynaptic stretch reflex
 Postural adjustments
 Muscle tonus
 Sensory neuron ---> alpha motor neurons
monosynaptic excitation
disynaptic inhibition ~

Dorsal
+
M
S
-
+
Ventral
+
+
Golgi Tendon Organ
Gauges muscle tension
 high threshold
 Stretch receptor
 safety mechanism
 controlled muscle contraction ~

Dorsal
GTO
Inhibits alpha
motor neuron
-
Ventral
+
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
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
Ampulla
Crista
hair cells
Utricle
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
eyes
trunk & neck
limbs
cerebellum

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 ~
