Chapter 14 Flashcards
Upper motor neurons are classified as…
Postural/gross movement tracts
Selective motor control tracts
Nonspecific tracts
Postural/gross movement tracts
Control contraction of antigravity muscles and groups of limb muscles
Selective motor control tracts
Isolates contraction of individual muscles of the limbs and face
Ex. Extending index finger while other fingers remain flexed
Nonspecific motor tracts
Facilitate all lower motor neurons
Contribute to background levels of excitation in the cord and facilitate local reflex arcs
Medial motor tracts
Synapse with lower motor neurons that innervate postural and limb muscles
Lateral corticospinal tract
Only tract that facilitates specific lower motor neurons innervating the distal muscles, wrist and finger extensors, ankle and toe dorsiflexors, and hand and foot intrinsic muscles
Most important pathway controlling voluntary movement
Reticulospinal, medial/lateral vestibulospinal, and medial corticospinal tracts
Deliver signals that control posture and gross limb movements to medial lower motor neuron pools in the spinal cord
Reticulospinal tract
Neurons activate LMNs that elicit simultaneous contraction of muscle groups across multiple joints
Provides anticipatory postural adjustments, prepare body for upcoming movement
Controls basic synergies: flexor or extensor synergies of the limbs
Essential for coordinating muscular activity of the trunk and the proximal muscles of all 4 limbs during walking
Elicits voluntary gross reaching and grasping movements
Muscle synergy
The activation of a group of muscles to achieve a specific task
Normal synergies simplify movements: ex. Neck reflexes, coordination during walking, reaching and grasping
Medial vestibulospinal tract
Receive information about head movement and position from the vestibular apparatus located in inner ear
Originals in vestibular nucleus ad projects bilaterally to the cervical and thoracic spinal cord
Lateral vestibulospinal tract
Respond to gravity information from vestibular apparatus
Facilitates ipsilateral LMNs to extensors while inhibiting ipsilateral LMNs to flexors
Medial corticospinal tract
Descends from the cortex through the internal capsule and the anterior brainstem
Synapse with LMNs that control neck, shoulder, and trunk muscles
Provide voluntary muscle control
Selective motor control
Ability to activate individual muscle independently of other muscles
Essential for normal movement of the hands
Rubrospinal tract
Arises in the red nucleus of the midbrain
Raphespinal tract
Releases serotonin, modulating the activity of spinal LMNs
Activated during intense emotions
May contribute to poorer motor performance when anxiety is high
Ceruleospinal tract
Releases norepinephrine, producing tonic facilitation of spinal LMNs
Activated during intense emotions
May contribute to poorer motor performance when anxiety is high
Corticobrainstem tracts
Provide voluntary control of muscles in the head and many muscles in the neck
Facilitates LMNs innervating the muscles of the face, tongue, pharynx, and larynx, and the trapezius and sternocleidomastoid muscles
2 regions anterior to the primary motor cortex are involved in preparing for movement
Premotor area on the lateral surface of the hemisphere
Supplementary motor area on the superior and medial surface
UMN syndrome
Arises from UMN lesions
Causes: stroke, SCI, TBI, abnormal development, neurodegenerative disorders, anoxic brain injury, tumors, infections, inflammatory disorders, and metabolic disorders
Stroke
Sudden onset of neurological deficits due to disruption of the blood supply in the brain
Affects middle cerebral artery damaging corticospinal, corticoreticular, and Corticobrainstem tracts
Complete spinal cord injury
Severs all ascending and descending axons
Total absence of sensory and voluntary motor function below injury
Incomplete spinal cord injury
Some axons are spared and the spinal cord below the lesion is able to convey some messages
Interferes with selective motor control doing overground walking
In spastic CP
All of the motor deficits arise from damage to corticospinal, corticoreticular, and corticobrainstem tracts during perinatal period
Has both spinal and cerebral lesions
ALS
Causes death of both upper and lower motor neurons
Signs of UMN syndrome
Variety of neuralgic signs and abnormal muscle tone that are categorized as loss of function and gain of function
Loss of function
Absence of a feature that is normally present
Ex. Paresis/paralysis, absent/decreased muscle tone, impaired selective motor control
Gain of function
Presence of a feature that is not normally present
Ex. Spasticity, rigidity, abnormal reflexes, compensatory cocontraction
Muscle tone
Resistance to stretch in resting muscle
Abnormal resistance from loss of function
Flaccid, hypotonia
Normal resistance to gain of function
Spasticity, dependent hypertonia
Hemiplegia
Weakness affecting one side of the body
Paraplegia
Affects the body below the arms
Tetraplegia
Affects all 4 limbs
Lateral corticospinal tract lesions
Prevent normal coordination throughout the limbs
Hyperreflexia
Excessive reflex response to muscle stretch
Caused by reduced descending inhibition of LMNs and the subsequent development of interneuron and LMN excessive excitability
Contributes to movement disorders post spinal cord injury and in spastic CP
