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Goal-Directed Behavior and Reflexive Behavior
Goal-Directed Reflex
Relatively Complex Relatively Simple
Consciousness? Intention Automatic
Plastic Relatively Inplastic
Requires Cortex Cortex not required
Learning /experiences are major influence
Genetics are major influence
Goal-Directed Behaviors Require:
• Goal selection and prioritization• Resistance to distracters
-Cross-modal Sensory integration– Perception of target– Awareness of location of movable body part– Ability to aim movement of body part– Ability to detect errors and re-adjust, (use
feedback)– Ability to use feedback to control movement of
body part
Sensory-Motor Integration in the frontal lobes
THE DLPFC: “The conductor”Integrates cross modal input- may initiate goal-directed behaviors
Lesions of the dorsolateral frontal areas results in a number of “executive” motor impairments. These include perseveration, incoordination, motor impersistence, apraxias and hypokinesia. http://www.youtube.com/watch?v=p_uhP1vDfoo
The premotor and supplementary motor ctx: “The sections”
Stimulation= complex sequences of behavior (aimless behavior)
Damage to the secondary Motor Cortex?
• Ideomotor Apraxia• This apraxia is associated with great difficulty in the sequencing and
execution of movements. A common test of apraxia is to request the patient to demonstrate the use of a tool or household implement (e.g., "Show me how to cut with scissors"). Difficulties are apparent when the patient moves the hand randomly in space or uses the hand as the object itself, such as using the forefinger and middle finger as blades of the scissors. They have additional trouble sequencing the correct series of movements and make errors in orienting their limbs in space consistent with the desired action. Imitation of the movements of others will usually improve performance but it is still usually defective.
• Memories for skilled acts are probably stored in the angular gyrus of the parietal lobe in the left hemisphere.
• http://www.youtube.com/watch?v=gewP1T7GYcc
The primary motor cortex; “the instrument”
Stimulation = relatively simple fragments of behavior
TWO MAJOR DESCENDING PATHWAYS FROM THE PRIMARY MOTOR CORTEX:
The Dorsolateral pathway
And the VM Path.
• The VM pathway does not discretely decussate, but does branch and innervate contra lateral segments in the spinal cord.
DL vs VM descending motor paths
• Dorsolateral
• Decussates at medullary pyramids
• Distal muscle groups• More direct• More volitional control• Higher resolution of
control
• Ventromedial
• Does not cross• Medial muscle groups• Gives off spinal
collaterals• Yoking• Lower resolution of
control
Other Motor Pathways
• In addition there are other motor paths that have relays in the brainstem
• These other paths innervate nuclei of the RAS, cranial nerve nuclei, etc…
Descending paths get additional inputs
Both pathways terminate in spinal cord segments
According to part of the body they control
On lower motor neurons (alpha motor neurons)
Amyotropic lateral sclerosis (ALS)disease of the alpha motor neurons
ALS
Alpha motor neurons project to form part of spinal nerve pairs
Terminate on muscle fibers
At each spinal segment
Muscle groups are complex; attach bone to bone via tendons and
ligaments
A muscle group has many fibers
The motor unit helps us understand “resolution”
The motor unit: If ratio is high=low resolution
The Neuromuscular junction (NMJ): The receptive portion of muscle-the
motor end-plate
The NMJ ( sometimes called the motor end-plate)
nACHr
End-plate potential
• Larger
• Longer
• Leads to Ca+ influx in sarcolema of muscle– Ca+ causes muscle contraction
muscle fibers encase myofibrils. The casing is called the sarcolema
Muscle group
Muscle fibermyofibril
End-plate potential causes ca+ influx into sarcolemma
Myofibrils in turn contain “Actin and Myosin” filaments
When the NMJ is activated Actin-myosin interact to shorten the length of
a muscle fiber
Sliding filament model of muscular contraction
Muscle shortens=work
Disease of the NMJ? MG
MG
MG
Cortical vs Spinal control of behavior
• Goal-directed
• Complex• Higher levels of
control• Plastic• Numerous reflexive
behaviors are involved
• Reflexive
• Simple• Automatic• inplastic
Spinal reflex ARCs
• Monosynaptic– stretch
• Polysynaptic– Withdrawal– Antagonist muscle groups– Synergistic muscle groups– Polysegmental relexes– Cross-spinal reflexes
A “monosynaptic” spinal reflex arc- the Stretch reflex
The stretch reflex involves neuromuscular “spindles”
Stretch reflex regulates muscle tension in every muscle group
The polysynaptic part of stretch reflexes: inhibition of Antagonist
muscles
Spinal inhibition of antagonist muscles require inhibitory interneurons
The “withdrawal reflex arc” a polysynaptic spinal reflex
Also involves interneurons
And may involve more than one spinal cord segment
And/or Cross spinal reflex arcs
The Goli tendon organ (GTO) reflex
Neural activity of spinal neurons related to whole muscle group
activity
Lower motor neurons “the final common pathway”
“the final common path: