Ch. 5 Flashcards
Observable Motor Behavior Requires
Nervous System
Musculoskeletal system
Sensory System
Nervous System
Plan of action
Control of skeletal muscles
Musculoskeletal System
Execution of the movement
Ongoing control of the action plan (some relation to sensory system)
Sensory System
Provides information to the CNS
Feedback
Motor Control
Distributed through the CNS (NOT only the brain)
Neural task centers
Neural Task Centers
areas of the CNS that have specific functions during planning/execution of a task
Functional Neural Task Centers
Limbic system
Association cortex
Projection system
Spinal System
Limbic System
the decision to act
Association cortex
What to do (the general plan)
Projection system
How to do (adds the details)
Spinal system
Execution (final details, control, modification)
The Limbic System
Initiates the decision to act: decision triggers subsequent events in the planning process
Involved in emotion, motivation, and learning
Includes the thalamus, hypothalamus, amygdule, septal area, and hippocampus
System receives and analyzes information: analysis is dependent upon memory
The Association Cortex
Develops the general plan of action
Includes portions of the frontal, parietal and temporal lobes (wide distribution)
Receives partially processed sensory information from other areas of the CNS (processing continues)
Identifies, selects, and combines meaningful information for distribution to higher cortical levels
The Association Cortex Cont.
The quality of the general plan is influenced by previous experience and the initial evaluation of the situation
Neural pathways connect the limbic system and the association cortex: function cooperatively to guide goal-directed behavior
The Projection System
Adds details to the general plan
Provides detailed motor and sensory information to match the goal of the movement and the environmental demands
Includes the basal ganglia, the cerebellum, and the motor cortex
Basal Ganglia
Located in the midbrain
Relay station for motor impulses passing from cortex to the brain stem/spinal cord
Modifies pattern of these motor impulses (thereby control various activities)
Responsible for scaling of movement parameters
The Cerebellum
Located in occipital lobes; posterior to the brain stem
Communicates with other parts of CNS
Compares arriving sensory information with information being sent out from the cortex/projection system
Error detection and correction
Cerebellum Communcates with
other parts of the CNS through peduncles (nerve tracts)
superior
middle
inferior
The Cerebellum (Cont.)
Receives sensory info concerning the position of the body parts (inferior peduncles)
Receives signals from the cortex and intended position of the body (middle peduncles)
After integrating/analyzing this information, the cerebellum sends correcting info to the midbrain (superior peduncles)
-The corrections are incorporated into motor impulses traveling downward through the brainstem/spinal cord to move the body in the intended way
The Motor Cortex
Involved in the production of fine motor skills; not all skills
Helps regulated muscular force during movement
Primary Motor Cortex (M1)
Actual execution of movements and control of speed and force in contracting muscles
Supplementary Motor Cortex (SMA)
Preparation of internally generated movements
Premotor Cortex (PMA)
Advanced planning and coordination of complex bilateral movement sequences
Corticospinal Tract (CST)
CST fibers orientate at M1, with some originating in SMA, PMA, and sensory cortex
The uninterrupted pathway synapse in the spinal cord
CST has large-diamtere axons, most are myelinated. This guarantees that information reaches its destination fast
Functions: controls fine movements and modulates the flow of sensory information being conveyed by the somatosensory pathways
Medial Brainstem System (MBS)
Comprised of three pathways:
Vestibulospinal tract (lateral vestibular nucleus in the brainstem)
Reticulospinal tract (originates in the reticular formation)
Tectospinal tract (originates in the superior colliculus)
Functions: postural control including control of axial musculature, balance reflexes, and head and neck orienting reactions
Lateral Brainstem System (LBS)
The rubrospinal tract is the major pathway
It originates in the red nucleus
Functions: facilitates alpha motor neurons that innervate the extensor muscles
Works with eh CST in facilitating the same spinal reflexes and innervating the same distal flexor muscles groups
Controls the action of a few muscle groups. This pathway is not well developed in the human brain.
Spinal System
Executes the plan of action
Regulates the timing of muscles
-Alpha motor neurons > skeletal muscles
-Gamma motor neurons > muscle spindle
Adds the final details about execution and ongoing control and/or modification
Contrains feedback loops: sampling the movement for comparison with the goals and the environment
Post movement evaluation based on feedback
Moment to moment control of action
Once the plan of action has been developed within the CNS, the appropriate muscle response synergies must be recruited to execute the plan
Muscle Response Synergies
Groups of muscles constrained to act as a single functional unit
Reduces the number of degrees of freedom
Simplifies the decision-making process for the CNS:
type of action produced at the joint(s) crossed by the muscle response synergy
the totally number of synergies needed to generate enough force to produce the desired action
Spinal System Neurons: Alpha Motor Neurons
Final pathway from CNS to skeletal muscles
Organized into groups, or pools, within the spinal cord
Function as teams to innervate groups of muscles
Spinal System Neurons: Gamma Motor Neurons
Pathway from brain to muscle spindle
Increase precision of control
Spinal System Neurons: Interneurons
Synapse with alpha motor neurons
Exist in elaborate networks within the spinal cord
Create the opportunity for excitation or inhibition of the motor neuron pools with which they synapse
-Reciprocal inhibition
-Appears to occur without being directed to do so by other subsystems within the CNS
The motor unit
One alpha motor neuron and all the muscle fibers it innervates
Innervation Ratio
Smaller motor units increase precision
Larger motor units increase force
Types of Motor Units
Slow-Twitch / Fatigue Resistant (SFR)
Fast-Twitch / Fatigue Resistant (FTR)
Fast-Twitch / Fatiguable (FTF)
How do we recruit the right motor units for the desired action?
Size Principle:
Smaller motor units: recruited first; longer firing duration
-first on/last off
Larger motor units: recruited progressively; shorter firing duration
-last on/first off
Advantages (Motor Unit)
Graded force production
Smooth and efficient motion
recruitment can stop when the force is appropriate
decreased the degrees of freedom possible
Subconscious Control of Movement: Short Loop Reflexes
Involved a single segment of the spinal cord
Used for small adjustments
Subconscious Control of Movement: Stretch Reflex
The SR involves the sensory receptor, afferent and efferent motor neuron (triggered when the length of muscle is altered)
Impulses are sent to spinal cord where they synapse with alpha motor neurons that innervate the muscle just altered
Activation of the SR enables us to continually alter muscle tone and/or make subtle adjustments in muscle length during movement
Subtle corrections in limb position are achieved much more quickly via the SR (30-50 ms) than by visual correction (150-200 ms)
Subconscious Control of Movement: Long loop reflexes
Influence force levels in muscle groups that are far from the point of the original stimulation; a portion goes to the brain
Large modifications
Ex. withdraws reflex
Constraints on Action: Intrinsic Capabilities of the Performer
Perceptual-motor abilities: reaction time, multi limb coordination
Physical proficiency abilities: flexibility, strength, etc.
Constraints on Action: Task-Related Contraints
Accuracy and speed demands Fitts Law Lower accuracy = higher speed higher accuracy = lower speed Cognitive/Attentional Demands
