Motor Pathways (other) Flashcards
Medullary (Lateral) Reticulospinal Tract
START: medullary reticular nuclei receive bilateral (mostly ipsilateral) cortical input from corticoreticular fibers and somatosensory projections through the spinoreticular tract
END: Interneurons in spinal cord
ROUTE: From medullary reticular nucleus, ipsilateral and contralateral tracts ending in spinal interneurons.
(Flexor muscles)
Rubrospinal Tract
START: Red nucleus receives cortical projections via corticorubral tract
END: Alpha and gammamotor neurons in the anterior horn of the cervical spinal cord.
ROUTE: Red nuclear efferents decussate in midbrain. Descend through the lateral brainstem and spinal cord.
FUNCTION: Voluntary flexion of the muscles of the contralateral arm
(note: connections from the ipsilateral motor cortex and from contralateral cerebella)
Pontine (medial) Reticulospinal Tract
START: Bilateral (mostly ipsilateral) cortical input from corticoreticular fibers and somatosensory projections through the spinoreticular tract (ALS collaterals)
END: Ipsilateral anterior horn of the spinal cord. (mostly gamma motor neurons)
ROUTE: From the pontine reticular nuclei descend ipsilaterally throughthe medulla and ventral spinal cord.
FUNCTION: Limb extensor muscles.
Spinoreticular Tract
Sensory Pathway
START: Pain and Temp. Receptors
END: Reticular nuclei in Pons and Medulla
ROUTE: Collaterals from ALS
FUNCTION: relays sensory information (pain, temp,) from one side of the body to the opposite to reticular nuclei. Facilitates contraction of ipsilateral limb muscles.
Lateral Vestibulospinal Tract
START: Lateral vestibulospinal nucleus receives input from inner ear and cerebellum.
END: Anterior horn of the spinal cord (Alpha motor neurons)
ROUTE: Axons of lateral vestibular nuclear cells descend in the ipsilateral medulla and spinal cord.
FUNCTION: Axial and limb extensor (anti-gravity muscles). Regulates muscular responses necessary for balance.
Medial Vestibulospinal Tract
START: Medial vestibular nucleus. Receives input from vestibular organs inthe inner ear and the cerebellum.
END: alpha motor neurons at the cervical and upper thoracic levels.
ROUTE: Efferents descend ipsilaterally into the spinal cord and run as the caudal extension of MLF.
FUNCTION: Roles in muscular contraction of the neck, often in close coordination with movements of the eyes.
Decorticate Posturing vs. Decerebrate Posturing
Intact Red Nucleus (lesion in upper medulla) vs. Not (lesion in lower medulla)
Arm Flexion in Decorticate
Arm Extension in Decerebrate
- Corticospinal tract interrupted – mainly flexion impaired.
- Corticobulbar tract interrupted – paralysis of motor cranial nerves.
- Medullary reticulospinal tract intact – flexion of extremities
- Pontine reticulospinal tract intact – extension of extremities
- Vestibulospinal tracts intact – extension of extremities (particularly lateral vestibulospinal tract)
Gamma Loop
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General features of movement disorders
- Impaired postural reflexes that would normally contribute to balance (either during movement or while stationary).
- Diminished or slowed movements (hypokinesia/bradykinesia).
- Excessive involuntary movements (hyperkinesia).
- Uncoordinated or unsteady movements (ataxia).
Describe the clinical assessment of posture, station, and gait.
Posture is intimately linked to muscle tone, which can be adversely
affected by a broad array of lesions of either motor or sensory systems
Station is sensitive to damage to conscious and unconscious sensory systems and the motor systems.
Gait is sensitive to varied dysfunction of sensory and motor systems.
The patient attempts to walk in a straight path
Identify the clinical features and progression of Parkinson disease (a hypokinetic disorder).
Akinesia reflects absence of movement (or limited movement – as in hypokinesia).
Bradykinesia
Facial expression commonly diminishes early, resulting in a masked
appearance (“masked facies”).
muscular rigidity (stiffness) of differing forms
Difficulties initiating movement commonly accompany a loss of postural reflexes.
Muscular regidity
speech tends to be quiet, hoarse, and monotonous but
occasionally with accelerative bursts (festination of speech).
Intention (kinetic) tremor
Arises with voluntary movement. Cerebellar lesions commonly yield intention tremors
Chorea
Brief, purposeless, irregular jerky movements of bodyparts, often stemming from basal gangliar disease.
Athetosis
continuous slow writhing of body parts, often related to basal gangliar pathology.
Ballismus
“Flinging” and rotatory movements are characteristic. Causal lesions often involve the subthalamus, which contributes to basal gangliar function
Dystonia
muscle spasms or sustained abnormal postures.
Spasmodic torticollis
specific dystonia involving the neck. In this condition, neck muscles (e.g., sternocleidomastoid) contract involuntarily and may become hypertrophic.
Tourette syndrome
genetic disorder with an onset about seven years
of age, is a specific form of tic disorder.
o Multifocal tics are common and often accompany attention deficit
hyperactivity disorder.
o Key to the diagnosis of Tourette syndrome is a vocal tic (e.g.,
barking, grunting).
Tic Syndromes
irregularly occurring stereotyped movements that are usually
transient and coordinated. They range from simple (e.g. eye blinking, arm jerks) to more complex (head-shaking, spitting, floor-licking).
Tardive dyskinesia
occur in patients exposed to some antipsychotic drugs (dopamine receptor antagonists). The condition commonly features stereoptypic oral movements.
Dopa-induced dyskinesia
arises during treatment of Parkinson disease with the precursor to dopamine. Choreic movements predominate, but facial dystonias (e.g., grimacing or eye closure) are not uncommon.
