Goal-Directed Behavior and Reflexive Behavior Goal-DirectedReflex Relatively ComplexRelatively Simple Consciousness? IntentionAutomatic PlasticRelatively Inplastic Requires CortexCortex 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.

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.

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 fiber myofibril

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

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: