Autonomic Nervous System (ANS) and Motor Control

Control of Visceral Motor Function (ANS)

• All movement ultimately results from excitation or relaxation of muscles.
• Voluntary movements are initiated consciously but are coordinated at a more subcortical level of the brain.

Hierarchical Organization of SMS

• Motor cortexes
• Basal nuclei
• Thalamus
• Cerebellum
• Brainstem
• Spinal cord
• Peripheral nerves

Voluntary Movement and Primary Motor Cortex

• Voluntary movement is directed by the primary motor cortex.
• Most voluntary movements are achieved when the cortex activates patterns of function stored in lower CNS areas.

Organization of Complex and Skilled Patterns

• Higher-order areas concern themselves with global tasks regarding action, such as deciding when to act, planning an appropriate sequence of actions, and coordinating the activity of many limbs.
• Lower-order areas perform low-level tasks, such as programming the exact force and velocity of individual muscles, or coordinating movements with changes in posture.

Reflexes and Central Pattern Generators (CPGs)

• Reflexes involve complex circuits in interneurons, such as the flexor and crossed extensor reflexes.
• CPGs produce oscillatory outputs used for controlling rhythmical motor activity, such as locomotion, scratching, chewing, and breathing.
• CPGs associated with locomotion and scratching are in the spinal cord intumescences.
• Control centers that initiate and terminate the rhythmical activity are in the brainstem.

Sensory Input and Integration

• Sensory input for the reflexes comes from muscle spindles, Golgi tendon organs, joints, and tactile receptors.
• Integration of that input in the spinal cord causes inhibition or excitation of LMNs, as appropriate.

Cerebellum and Posture

• The cerebellum coordinates agonistic/antagonistic muscle activity to permit posture and to create movement that occurs at the correct rate, range, and force.
• The cerebellum coordinates overall posture by coordinating contraction-relaxation of all muscles in the body used for maintaining posture, both at rest and during movement.

Tectospinal Tract and Rubrospinal Tract

• The tectospinal tract is involved in reflex orientation of the head toward environmental stimuli and controls rapid reflex movement of the eyes.
• The rubrospinal tract is a lateral brainstem UMN pathway that controls distal limb musculature associated with movement, and is important for gait generation in quadrupeds.

Movement and Muscle Activity

• Movement can be divided into two general forms: dominated by flexor muscles (largely learned, voluntary, conscious, and skilled) and dominated by extensor muscles (postural, antigravity muscle activity, generally subconscious and involuntary).
• The control of these two types of movements is made by different neurons and tracts in the nervous system.

Lateral and Medial Systems

• Skilled voluntary movement of distal musculature (flexors) is primarily controlled by a lateral system (lateral funiculus) of lower and upper motor neurons' spinal tracts.
• Postural and antigravity activity of the proximal and axial musculature (extensors) is controlled by a more medial system (ventral funiculus) of such neurons and tracts.

Spinal Cord and Movement Control

• The spinal cord is the most caudal and simplest level of movement control.
• It contains the UMN tracts, alfa lower motor neurons, interneurons, and complex neural circuits for motor control.
• The spinal cord executes the low-level commands that generate proper forces on individual muscles groups to enable adaptive movements.