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POWERPOINT PRESENTATION
FOR BIOPSYCHOLOGY,
9TH EDITION
BY JOHN P.J. PINEL
P R E PA R E D B Y J E F F R E Y W. G R I M M
WESTERN WASHINGTON UNIVERSITY
COPYRIGHT © 2014 PEARSON EDUCATION, INC.
ALL RIGHTS RESERVED.
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Chapter 8
The Sensorimotor System
How You Move
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Learning Objectives
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LO1: List and discuss 3 principles of sensorimotor function.
LO2: Describe 2 major areas of sensorimotor association cortex and
evidence of their functions.
LO3: List the current areas of secondary motor cortex.
LO4: Discuss mirror neurons.
LO5: Describe the organization of primary motor cortex and the current view
of its function.
LO6: Discuss the functions of the cerebellum and basal ganglia.
LO7: List and explain the 4 descending motor pathways.
LO8: Summarize the classic study of Lawrence and Kuypers.
LO9: Describe the neural circuits that control muscles.
LO10: Explain the stretch reflex, withdrawal reflex, and walking reflex.
LO11: Discuss central sensorimotor programs and the principles of
sensorimotor learning.
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Three Principles of
Sensorimotor Function
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Hierarchical Organization
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Association cortex at the highest level,
muscles at the lowest
Parallel structure: signals flow between levels
over multiple paths
Motor output is guided by sensory input.
Learning changes the nature and locus of
sensorimotor control.
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E.g., conscious to automatic
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FIGURE 8.1 A general model of the sensorimotor system. Notice its
hierarchical structure, functional segregation, parallel descending
pathways, and feedback circuits.
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Sensorimotor Association
Cortex
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Posterior Parietal Association Cortex
Dorsolateral Prefrontal Association Cortex
Each is composed of several different
areas with different functions.
Some disagreement exists regarding how
to divide the areas up.
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Posterior Parietal Association
Cortex
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Integrates Information about:
 Body part location
 External objects
Receives Visual, Auditory, and Somatosensory
Information
Outputs to Motor Cortex
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Including dorsolateral prefrontal association cortex,
secondary motor cortex, and frontal eye field
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FIGURE 8.2 The major cortical input and output pathways of
the posterior parietal association cortex. Shown are the
lateral surface of the left hemisphere and the medial surface
of the right hemisphere.
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Damage to the Posterior
Parietal Cortex
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Apraxia: disorder of voluntary movement;
problem only evident when instructed to
perform an action; usually a consequence of
damage to the area on the left
Contralateral neglect: inability to respond to
stimuli contralateral to the side of the lesion;
usually seen with large lesions on the right
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Dorsolateral Prefrontal
Association Cortex
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Input from Posterior Parietal Cortex
Output to Secondary Motor Cortex, Primary
Motor Cortex, and Frontal Eye Field
The dorsolateral prefrontal association cortex
evaluates external stimuli and initiates
voluntary reactions; it is supported by
neuronal responses.
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FIGURE 8.3 The major cortical input and output pathways of the
dorsolateral prefrontal association cortex. Shown are the lateral
surface of the left hemisphere and the medial surface of
the right hemisphere.
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Secondary Motor Cortex
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Input Mainly from Association Cortex
Output Mainly to Primary Motor Cortex
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Identifying the Areas of
Secondary Motor Cortex
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There are at least eight different areas.
Three Supplementary Motor Areas
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Two Premotor Areas
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SMA and preSMA, and supplementary eye
field
Dorsal and ventral
Three Cingulate Motor Areas
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FIGURE 8.4 Four areas of secondary motor cortex—the supplementary motor
area, the premotor cortex, and two cingulate motor areas—and their output to the
primary motor cortex. Shown are the lateral surface of the left hemisphere and the
medial surface of the right hemisphere.
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Identifying the Areas of
Secondary Motor Cortex (Con’t)
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The secondary motor cortex may be
involved in programming movements in
response to input from the dorsolateral
prefrontal cortex.
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Active during imagining or planning of
movements
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Mirror Neurons
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Mirror neurons are active when performing an
action or watching another perform the same action.
In monkey studies, mirror neurons fired while:
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Grasping or watching another grasp a particular object but
not other objects
Grasping or watching another grasp an object for a
specific purpose but not for another purpose
Mirror neurons are a possible neural basis of social
cognition (knowledge of others’ mental processes—
e.g., intentions).
Likely to Be Found in Humans
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Indirect evidence from functional brain-imaging studies
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FIGURE 8.5 Responses of a
mirror neuron of a monkey.
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Primary Motor Cortex
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Precentral Gyrus of the Frontal Lobe
Major Point of Convergence of Cortical
Sensorimotor Signals
Major Point of Departure of Signals from
Cortex
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Conventional View of Primary
Motor Cortex Function
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Somatotopic: more cortex devoted to body
parts that make complex movements
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Motor homunculus
Until recently, each neuron was thought to
encode the direction of movement.
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FIGURE 8.6 The motor homunculus: the
somatotopic map of the human primary
motor cortex. Stimulation of sites in the
primary motor cortex elicits simple
movements in the indicated parts of the
body. (Based on Penfield & Rasmussen,
1950.)
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Current View of Primary Motor
Cortex Function
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Regions of primary motor cortex support
initiation of species-typical movements.
Neurons direct to target of movement, rather
than simply a pre-coded direction.
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Effects of Primary Motor
Cortex Lesions
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Small lesions often have minimal effects.
Large lesions may disrupt a patient’s ability
to move one body part independently of
others.
Large lesions may also produce
stereognosia.
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Deficit in stereognosis (ability to identify an
object by touch)
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Cerebellum and Basal Ganglia
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Interact with Different Levels of the
Sensorimotor Hierarchy
Coordinate and Modulate
May Permit Maintenance of Visually Guided
Responses Despite Cortical Damage
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Cerebellum
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10 Percent of Brain Mass, but More than
50 Percent of Its Neurons
Input from Primary and Secondary Motor
Cortexes
Input from Brainstem Motor Nuclei
Feedback from Motor Responses
Involved in Timing, Fine-Tuning, and
Motor Learning
May Also Do the Same for Cognitive
Responses
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Basal Ganglia
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A Heterogeneous Collection of
Interconnected Nuclei
Part of Neural Loops that Receive Cortical
Input and Send Output Back via the
Thalamus
Modulate Motor Output and Cognitive
Functions, Including Learning
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Descending Motor Pathways
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Two Dorsolateral
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Two Ventromedial
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Corticospinal
Corticorubrospinal
Corticospinal
Cortico-brainstem-spinal tract
Both corticospinal tracts are direct.
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Dorsolateral Tracts
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Most dorsolateral tracts synapse on
interneurons of spinal gray matter.
Corticospinal: descend through the
medullary pyramids, then decussate
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Betz cells: synapse on motor neurons projecting to leg
muscles
Control of wrist, hands, fingers, toes
Corticorubrospinal: synapse at red
nucleus and cross before the medulla
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Some control muscles of the face
Distal muscles of arms and legs
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FIGURE 8.7 The two divisions of the dorsolateral
motor pathway: the dorsolateral corticospinal tract
and the dorsolateral corticorubrospinal tract. The
projections from only one hemisphere are shown.
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Ventromedial Tracts
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Corticospinal
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Descends ipsilaterally
Axons branch and innervate interneuron circuits
bilaterally in multiple spinal segments.
Cortico-Brainstem-Spinal
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Interacts with various brainstem structures and
descends bilaterally, carrying information from both
hemispheres
Synapses on interneurons of multiple spinal segments
controlling proximal trunk and limb muscles
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FIGURE 8.8 The two divisions of the ventromedial motor
pathway: the ventromedial corticospinal tract and the
ventromedial cortico-brainstem-spinal tract. The projections
from only one hemisphere are shown.
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Comparison of the Two
Dorsolateral Motor Pathways
and the Two Ventromedial
Motor Pathways
Dorsolateral
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Ventromedial
One direct tract, one
that synapses in the
brain stem
Terminate in one
contralateral spinal
segment
Distal muscles
Limb movements
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One direct tract, one
that synapses in the
brain stem
More diffuse
Bilateral innervation
Proximal muscles
Posture and whole
body movement
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Sensorimotor Spinal Circuits
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Motor circuits of the spinal cord show
considerable complexity.
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Independent of signals from the brain
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Muscles
Motor units: a motor neuron plus
muscle fibers; all fibers contract
when the motor neuron fires.
 Number of fibers per unit varies; fine
control, fewer fibers/neuron
 Muscle: muscle fibers bound
together by a tendon
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Muscles (Con’t)
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Acetylcholine released by motor neurons at the
neuromuscular junction causes contraction.
Motor pool: all motor neurons innervating the
fibers of a single muscle
Fast muscle fibers fatigue quickly.
Slow muscle fibers are capable of sustained
contraction due to vascularization.
Muscles are a mix of slow and fast fibers.
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Muscles (Con’t)
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Flexors bend or flex a joint.
Extensors straighten or extend.
Synergistic muscles: any two muscles
whose contraction produces the same
movement
Antagonistic muscles: any two muscles
that act in opposition
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Receptor Organs of Tendons
and Muscles
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Golgi Tendon Organs
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Embedded in tendons
Tendons connect muscle to bone.
Detect muscle tension
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Receptor Organs of Tendons
and Muscles (Con’t)
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Muscle Spindles
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Embedded in muscle tissue
Detect changes in muscle length
Intrafusal muscle within each muscle spindle is
innervated by its own intrafusal motor neuron.
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Keeps tension on the middle, stretch-sensitive portion
of the muscle spindle to keep it responsive to changes
in the length of the extrafusal muscle
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FIGURE 8.11 The muscle-spindle feedback
circuit. There are many muscle spindles in
each muscle; for clarity, only one muchenlarged muscle spindle is Illustrated here.
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FIGURE 8.12 The function of the intrafusal
motor neurons.
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Reflexes
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Stretch reflex: monosynaptic; serves to maintain
limb stability
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E.g., The patellar tendon reflex is monosynaptic.
Withdrawal reflex is NOT monosynaptic.
Reciprocal innervation: antagonistic muscles
interact so that movements are smooth; flexors
are excited while extensors are inhibited, etc.
Recurrent collateral inhibition: feedback loop
through Renshaw cells that gives muscle fiber a
rest after every contraction
Walking: a complex reflex in some animals
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FIGURE 8.13 The elicitation of a stretch
reflex. All of the muscle spindles in a muscle
are activated during a stretch reflex, but only
a single muscle spindle is depicted here.
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FIGURE 8.16 The
excitatory and inhibitory
signals that directly
influence the activity of a
motor neuron.
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Central Sensorimotor
Programs
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Perhaps all but the highest levels of the
sensorimotor system have patterns of
activity programmed into them, and
complex movements are produced by
activating these programs.
Cerebellum and basal ganglia then serve
to coordinate the various programs.
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Central Sensorimotor
Programs Are Capable of
Motor Equivalence
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A given movement can be accomplished
various ways, using different muscles.
Central sensorimotor programs must be
stored at a level higher than the muscle (as
different muscles can do the same task).
Sensorimotor programs may be stored in
secondary motor cortex.
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Sensory Information that
Controls Central Sensorimotor
Programs Is Not
Necessarily Conscious
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There is evidence that patients can respond to
visual stimuli of which they have no conscious
awareness.
There is also evidence that patients can not
effectively interact with objects that they
consciously perceive.
Ebbinghaus illusion: conscious perception of
disk size differs from motor response.
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FIGURE 8.17 The
Ebbinghaus illusion. Notice
that the central disk on the
left appears larger than the
one on the right. Haffenden
and Goodale (1998) found
that when volunteers
reached out to pick up either
of the central disks, the
position of their fingers
as they approached the
disks indicated that their
responses were being
controlled by the actual sizes
of the disks, not their
consciously perceived sizes.
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The Development of Central
Sensorimotor Programs
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Central sensorimotor programs may be
hierarchically organized and capable of
using sensory feedback without direct
control at higher levels.
Programs for many species-specific
behaviors are established without practice.
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Fentress (1973): mice without forelimbs still
make coordinated grooming motions.
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The Development of Central
Sensorimotor Programs (Con’t)
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Practice can also generate and modify
programs.
 Response Chunking
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Practice combines the central programs controlling
individual response.
Shifting Control to Lower Levels
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Frees up higher levels to do more complex tasks
Permits greater speed
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Functional Brain Imaging of
Sensorimotor Learning
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Functional brain-imaging studies in
humans have generally supported the
findings from more invasive studies of
non-human primates.
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FIGURE 8.18 The activity recorded by PET scans
during the performance of newly learned and
well-practiced sequences of finger movements.
(Based on Jenkins et al., 1994.)
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