How Does the Nervous System Respond to Stimulation and Produce Movement? (Pt 1)

Major components of the motor system

– Cerebrum (forebrain): conscious control of movement
– Brainstem: direct movements
– Spinal cord: direct movements

Other regions of the motor system

– Basal ganglia helps to produce appropriate amount of force for grasping.
– The cerebellum helps regulate timing and accuracy of movement.

Relating the Somatosensory and Motor
Systems (part 1)

• Afferent somatosensory information travels in via the somatic nervous system.
• Movement information travels out of the central nervous system via a parallel efferent motor system.

Homuncular Man

Illustrates the fact that extensive areas of the motor cortex to regulate hands, fingers, lips, and tongue.

Experimental Evidence for the Hierarchical and Parallel Movement Control

Frontal lobe regions in each hemisphere that plan, coordinate, and execute precise movements in a hierarchical manner.
• Prefrontal cortex formulates a plan of action.
• Prefrontal cortex instructs premotor cortex to organize sequence of behaviors.
• Primary motor cortex executes the movements.

Animals with damage to the premotor cortex cannot put motor sequences together.

Primary Motor Cortex

Produces focal skilled movements, of the arms, hands, and mouth.
• Damage to M1 impairs reaching and shaping their fingers to perform various hand grasps.

Motor cortex neurons increase a
movement’s force by increasing firing
rate and duration.

Plasticity In The Motor Cortex

Nudo and colleagues (1996)
• Damaged part of motor cortex that controlled the hand in monkeys
• Without rehabilitation:
• The hand area of the motor cortex became smaller, whereas the elbow and shoulder area became larger
• Monkeys lost most ability to move the hand
• With rehabilitation:
• The hand area of the motor cortex retained its size
• Monkeys retained some ability to move hand

Brainstem: Species-Typical Movement

Brainstem organizes many adaptive movements
– Maintaining posture, standing upright, coordinating movements of the limbs, swimming and walking,
grooming the fur, and making nests
• Cerebral palsy
– Caused by brainstem trauma

Brainstem

Maintains posture, standing upright, coordinating limb movements of the limbs, swimming and walking, grooming, and making nests

Cerebral Palsy

Voluntary movements difficult to make, whereas conscious behavior controlled by the cortex may remain intact
• Caused by brainstem trauma

Locked In Syndrome

Condition in which a patient is aware and awake but cannot move or communicate verbally because of
complete paralysis of nearly all muscles except the eyes
• Due to brainstem damage

Quadriplegia

Paralysis and loss of sensation in the legs and arms due to spinal cord injury (Reeve’s injury)

Paraplegia

Paralysis and loss of sensation confined to legs and lower body due to spinal cord injury

The Basal Ganglia

– Receive input from
• All areas of the neocortex and allocortex.
• The nigrostriatal dopaminergic system from the substantia nigra
– Project back to the motor cortex and substantia nigra
– Subserve a wide range of functions, including association or habit learning, motivation, emotion, and motor control
– caudate nucleus and putamen (dorsal striatum).
– subthalamic nucleus.
– globus pallidus.
• Cortical loops participate in selecting and producing skilled movements for learned actions and emotional expression.

Hyperkinetic Syndrome

Damage to the caudate putamen causes unwanted movements called dyskinesias; seen in Huntingon’s
and Tourette’s.

Hypokinetic Syndrome

Damage to the basal ganglia results in a loss of movement, leading to rigidity and difficulty initiating and producing movement; seen in Parkinson’s
Disease.

Volume Hypothesis

Recordings made from globus pallidus cells show excessive activity.
– Inhibits movement in people with Parkinson disease
• If the globus pallidus or the subthalamic nucleus is lesioned in Parkinson patients, muscular rigidity is reduced, and movement is improved.
• Deep brain stimulation (DBS) of the globus pallidus inactivates it, freeing movement.

How The Cerebellum Improves Movement Control

Cortex sends motor instructions to the spinal cord.
• Copy of same instructions is sent to the cerebellum.
• Sensory receptors code actual movement and report to the cerebellum.

Cerebellum has information about both versions of the movement—what you intended to do and what you actually did—and can calculate the error and tell the cortex how to correct the
movement.