Central Control of Movement Flashcards
Hierarchy of motor control
Cortex= Planning
Mid-brain = equilibrium
Brain stem = Posture
Spinal cord = movement execution
Movements
Voluntary
- skilled, learned, conscious
Involuntary
- postural, antigravity
Voluntary movement
- Dominated by flexor muscle activation
- Due to contraction of a few muscle groups, which are distal to the spinal column
- In the spinal cord gray matter, the α motor neurons that control the more distal muscles are located laterally
- Initiated by UMN whose tracts project through more lateral regions of spinal c. white matter and terminate in lateral regions of spinal c. gray matter
Involuntary Movement: postural, antigravity
- Dominated by extensor muscle contraction
- Maintenance of posture includes longer-term contraction of larger groups of muscles, which are closer to or proximal to the spinal column
- In the spinal cord, the neurons controlling proximal and axial muscles for posture are located medially
- UMN tracts project through and terminate in more medial regions of spinal c. white and gray mater, respectively
Motor neuron pool
The group of all motor neurons innervating a single muscle
Two major groups of descending pathways: originate from the brainstem
Lateral Pathway
Ventromedial Pathway
Lateral Pathways
Involved in voluntary movement of the distal musculature.
Passes through lateral region of the spinal cord and involved in voluntary skilled movement
*Rubrospinal (from Red nucleus)- receives significant input from motor cortex and cerebellum
Ventromedial Pathways
Involved in the control of posture and locomotion;
Pass through the medial region of the spinal cord; involved in involuntary ctrl of posture/antigravity:
1.vestibulospinal tract (originates from Vestibular nuclear complex)
2.reticulospinal tract ( (from cell bodies of reticular formation)
3. tectospinal tract (from rostral colliculus)
Corticospinal tract: Lateral Pathway
α motor neuron is signaled by descending upper motor neurons or from incoming sensory neurons (or interneurons) in a reflex arc
Extrafusal muscle fibers contract by commands from α lower motor neuron
Movement is by contraction of a number of extrafusal skeletal muscle fibers within varying numbers of motor units
Thus the α motor neuron is the “final common neural pathway” by which the nervous system can initiate the extrafusal muscle contractions that result in movement
Lesion of Corticospinal Tract
inability to manipulate the lips and tongue.
Deficit in fore legs-MUSCLE WEAKNESS
Conscious proprioceptive deficit
Spastic paralysis
Clinsig of lesion of corticospinal tract
In horses and cows, the loss of corticospinal (and corticobulbar) tracts results in inability to manipulate the lips and tongue. In small animals, this deficits is most seen in the fore legs, which are used to play with and paw their food and toys.
Rubrospinal Tract: Lateral Pathway
A lateral descending brainstem motor pathway; axons course thru and terminate in the more lateral regions of spinal white and grey matter, respectively
Axons originate in cells of the red nucleus
- Red nucleus receives input from the cerebral cortex and cerebellum
- Through this cortico-rubrospinal route, motor cortices indirectly influence spinal LMNs and distal musculature
Has unilateral control over a limited complement of flexors of distal limbs and is needed for skilled movements of extremities
More important in quadrupeds than primates
Lesion in Rubrospinal Tract
ATAXIA ( precise aiming at the target)
impairment of distal movement (impaired ability to grasp)
Lesion in Rubrospinal Tract: Clin sig
Normal cats after grasping food made a rotatory movement in the wrist, brought meat to the mouth and ate it out of the paw.
The motor performance in tests, in which flexion and adduction of digits were required, turned
out to be more impaired after red nucleus lesions.
Reticulospinal Tract: Ventromedial
Controls the magnitude of steady-state contraction level, or muscle tone, of antigravity muscles
The subconscious control of postural musculature is essential for skilled voluntary movement of distal musculature
Nuclei are in the reticular formation of the brainstem
The primate reticulospinal tract is usually considered to control proximal and axial muscles, and to be involved mainly in gross movements such as locomotion, reaching and posture.
Able to predict changes in posture, and generate an appropriate stabilizing response.
Some muscles fire in anticipation of a need for postural adjustment.
Some muscles fire in anticipation of a need for postural adjustment.
- gastrocnemius muscle needs to adjust for the anticipation of contracting the biceps that would naturally pull the body forward – stabilizing response
Reticular formation and Reticulospinal tract important for this.
- Lesion or pharmacologically block it in a cat and compensatory muscle changes do not occur.
Stimulate motor cortex in the right place can induce paw lifting, also induces other limbs’ muscles to fire. Inhibit reticulospinal tract, paw still moves but other legs do not.
Lesion in Reticulospinal tract
Lack of anticipatory adaptation
Increase in reflex activity
Impaired motor movement
Abnormal Posture
The reticulospinal tract can be divided into a lateral and a medial division. The effect of the lateral division is excitatory to extensors and inhibitory to flexors, whereas the medial division has mixed effects, most frequently inhibition of extensors and excitation of flexors.
Vestibulospinal tract
Lesion in Vestibulospinal Tract
Loss of antigravity muscle tone
Postural destabilization
Vestibular ataxia
The vestibulospinal tract is tonically active. It innervates extensor muscles and resists gravity.
Tectospinal Tract: Ventromedial
Organization of the descending brainstem motor pathways to the spinal cord
Brain stem: Motor and sensory nuclei
Motor and sensory functions for the face and head regions
Respiration, cardiovascular system, GIT (partially), equilibrium and eye movements
Central pattern generators (CPG)
specific repeatable (rhythmic) motor output without rhythmic sensory or central
walking, running, swimming, certain eye movements, shivering and scratching
breathing, swallowing, chewing and certain eye movements -BRAINSTEM
CPG for locomotion like walking, trotting and cantering and protective motions like scratching and paw shaking are within the spinal cord.
“Neural circuits that produce specific repeatable (rhythmic) motor output without rhythmic sensory or central input- a type of Pacemakers”
Somatotopic map of primary motor cortex
Cerebral Cortex
Primary motor cortex - discrete purposeful movements
Premotor area - patterns of movement
Supplemental motor area - bilateral movements, fixation movements
M1=primary motor cortex
premotor area (PMA) and
supplemental motor
area (SMA) = premotor
cortex
3 Primary functional areas of the cerebral cortex
Motor, sensory and association
- Located in precentral sulcus area of frontal lobe in humans
- Many non primate species lack central sulcus; the motor center is located near the cruciate sulcus
Inputs to Motor Cortex
Somatosensory, frontal, auditory, visual.
Cerebellum and Basal ganglia.
Supplementary and premotor cortex
Basal Ganglia
Basal Ganglia-Their Motor Functions
Role of the Basal Ganglia for Cognitive Control of sequences of Motor Patterns—Caudate Circuit.
Most afferents come from the cerebrum, most efferents go to the cerebrum
Connected to the motor area of the cortex and to the thalamus
No direct connection to alpha motor neurons
+
Motor Component of Basal Ganglia
Corpus Striatum ( Caudate Nucleus and Putamen)
Globus Pallidus
Afferents –from the striatum, subthalamus
Efferents – to substantia nigra, subthalamus, thalamus, RF
Motor relay, tonic background contractions
Neurotransmitters
Dopamine (-): substantia nigra to caudate nucleus
ACh (+): from cortex to putamen and caudate
GABA (-): from caudate and putamen to globus pallidus and substantia nigra
Basal Ganglia and Cerebellum
What do basal ganglia lesions produce
Contralateral Signs
Cerebellar lesions produce
Ipsilateral Signs
Basal Ganglia: Voluntary Movement
Initiation of Movement
Change from one pattern to another
Programing and correcting movement while it is happening
Postural Control
Basal Ganglia: Disorders
Bradykinesis
Rapid Alternating Movement
Tremor
Postural abnormality
Gait disorder
The cerebellum is the great comparator
- It compares cortical willful command with muscle tension, joint position, & tone (via ipsilateral spinocerebellar tracts)
- Advises the cortex on how much, how many, how fast
- The motor cortex sends the revised command down the corticospinal tract
The BASAL GANGLIA are the autopilot for procedural movements.
The CEREBELLUM is the refiner of finely controlled movements(particularly of fingers).
Clinsig: Yellow star thistle
Consumption for >30 days can lead to
Nigropallidal encephalomalacia in horses
