LECTURE 16: VOLUNTARY MOVEMENT

1
LECTURE 16 VOLUNTARY MOVEMENT
REQUIRED READING Kandel text, Chapters 33 38

• Voluntary movement differs from reflexes in
  several important ways
• Voluntary movement is governed by conscious
  planning
• It is organized around performance of a specific
  task
• Sensory stimuli do not dictate the resulting
  movement,
• although they guide the specified task
• Task performance becomes more efficient with
  experience
• Voluntary movement can be initiated internally
  without
• a sensory stimulus trigger
• VOLUNTARY MOVEMENT OFTEN REPRESENTS COMPLEX MOTOR
  TASKS THAT ARE
• ACCOMPLISHED IN SEEMINGLY EFFORTLESS FASHION,
  WITH NO THOUGHT
• GIVEN TO THE MUSCLE GROUPS AND JOINTS THAT
  PARTICIPATE

2
SENSORY INPUTS GUIDE VOLUNTARY MOVEMENT
THROUGH FEED-BACK AND FEED-FORWARD MECHANISMS
3
EXAMPLE OF FEEDBACK AND FEEDFORWARD MOVEMENT
CONTROL CATCHING A FALLING BALL

• Visual input provides feed-forward
• control of the task enabling us to
• 1) Position hand under where ball is
• anticipated to fall
• 2) Partially stiffen joints in anticipation
• of balls impact on hand
• Somatosensory and proprioceptive inputs
• provide feed-back control used
• to grasp ball.
• Some aspects of feedback control
• involve task-specified programming
• of spinal reflexes

4
PROCESSING OF A MOTOR TASK BEGINS WITH AN
INTERNAL REPRESENTATION OF THE DESIRED RESULT OF
MOVEMENT
EXAMPLE 1 HANDWRITING IS SIMILAR STYLE
REGARDLESS OF LIMB USED TO WRITE We write text to
conform to an internally preimaged style template
5
PROCESSING OF A MOTOR TASK BEGINS WITH AN
INTERNAL REPRESENTATION OF THE DESIRED RESULT OF
MOVEMENT
EXAMPLE 2 REACHING IS A STRAIGHT-LINE TASK,
REGARDLESS OF DIRECTION AND MUSCLES/JOINTS
REQUIRED We program the direction and endpoint of
task, and use sensory input during task for
guidance correction
6
PROCESSING OF A MOTOR TASK BEGINS WITH AN
INTERNAL REPRESENTATION OF THE DESIRED RESULT OF
MOVEMENT
EXAMPLE 3 SPEED OF REACHING IS PRE-SCALED TO
THE DISTANCE OF TARGET The endpoint is built into
the premotor program
7
EFFICIENCY OF EXECUTING MOTOR TASK IMPROVES WITH
PRACTICE (LEARNING)
Both explicit and implicit memory are components
of motor learning Improved efficiency in reaching
task is form of implicit learning
8
CENTRAL PATHWAYS FOR VOLUNTARY MOTOR CONTROL
Motor areas of cerebral cortex project directly
and indirectly to spinal cord motor neurons and
interneurons Motor areas also project to basal
ganglia and cerebellum, which project back to
cortex via thalamus Cerebellum critical for
integrating desired task and sensory inputs into
motor planning and execution Cerebellum is a
major site for learning within motor
circuits Basal ganglia control muscle tone
(readiness) and execution of rapid motor tasks
9
MOTOR CORTEX AND PREMOTOR CORTICES PROJECT TO
MOTOR UNITS AND CONSTITUTE SOMATOTOPIC MAPS OF
THE BODY
Motor cortex axons project to motor neurons both
monosynaptically and through brain stem
nuclei FOCAL STIMULATION IN MOTOR AREAS INDUCES
CONTRACTION OF SPECIFIC MUSCLE OR MUSCLE
SET FOCAL LESIONS IN MOTOR AREAS CAUSE LOSS OF
SPECIFIC MUSCLE SETS
10
SOMATOTOPIC MAP IN MOTOR CORTEX CHANGES FOLLOWING
FOCAL LESION
Remapping of motor cortex following lesion is
influenced by experience in the weeks after
injury Profound neurological implications for
role of physical therapy following brain injury
EXPERIMENT-INDUCED FOCAL STROKE AFFECTING MUCH
OF HAND/DIGIT REGION OF MOTOR CORTEX
PHYSICAL THERAPY FOR HAND
NO PHYSICAL THERAPY FOR HAND
1 MONTH
REMAINING HAND REPRESENTATION IN MOTOR CORTEX
LOST (converted to arm/shoulder
representation) LOSS OF GRASPING CAPACITY
REMAINING HAND REPRESENTATION SPARED AND MORE
CORTEX RECRUITED (converted from arm/shoulder
representation) GRASPING CAPACITY RESTORED
11
MOTOR CORTEX IS ESSENTIAL FOR FINE CONTROL OF THE
DIGITS
Severing corticospinal tract causes permanent
loss of fine digit control Coordinated use of
more proximal muscles improves over time, making
use of indirect projections from motor cortex
through brain stem
12
FIRING OF MOTOR CORTEX NEURONS DURING VOLUNTARY
MOVEMENT DIRECTLY ACTIVATES MOTOR NEURONS IN
SPINAL CORD
Technique of POST-SPIKE FACILITATION OF MUSCLE
ACTIVITY
13
EACH MOTOR CORTEX NEURON ACTIVATES MUTLIPLE
MUSCLES TO DIFFERENT DEGREES DIRECTION OF LIMB
MOVEMENT IS SUM OF CORTICAL NEURON VECTORS
14
PREMOTOR AREAS CONTRIBUTE TO MOTOR PLANNING
EEG recordings show that medial premotor area is
active to performance or mental rehearsal of
complex tasks
15
THE MOTOR CORTEX IS DRIVEN BY DIFFERENT PREMOTOR
AREAS IN RESPONSE TO VISUAL CUES VERSUS
PERFORMING REHEARSED TASKS