UMN System Flashcards
What is the pyramidal system primarily composed of?
Neurons whose cell bodies are located predominantly in the motor area of the cerebral cortex. Includes giant pyramidal cells/Betz cells located in lamina V of the cerebral cortex.
Where do the axons of the pyramidal system descend?
Through white matter of cerebral hemisphere and brainstem. They form a pyramid on the ventral surface of the medulla.
What percentage of axons cross at the pyramidal decussation?
At least 75%. These axons pass to the dorsal portion of the lateral funiculus.
What is the function of the lateral corticospinal tract?
Neurons with cell bodies in the motor cortex terminate on interneurons in the ventral gray horn that influence GSE-LMN.
What is the role of corticoneuclear axons?
Terminate in nuclei of cranial nerves with GSE-LMN.
What is the primary function of the extrapyramidal system?
Support of body against gravity and recruiting spinal reflexes for voluntary movement.
Where do neurons of the extrapyramidal system originate?
In the cerebral cortex and in all divisions of the brain.
What are the main components of the basal nuclei?
- Caudate nucleus
- Putamen
- Pallidum
- Claustrum
- Nucleus accumbens
What is the function of the red nucleus?
Receives input from ipsilateral neocortex and influences alpha and gamma LMNs. Axons decussate and course as rubrospinal tract
Which layer of the cerebral cortex is the molecular layer?
Lamina I
What is the primary role of neuromuscular spindles?
Located in the belly of skeletal muscle and maintain normal muscle tone.
What type of sensory neuron is associated with nuclear bag fibers?
1a sensory neurons.
What reflex is appreciated in the function of 1a sensory fibers?
Patellar reflex.
What does the Golgi tendon organ do?
Provides smooth skeletal muscle activity and protection from overstretching.
What are the phases of gait generation?
- Postural phase
- Protraction phase
What is the clinical sign of upper motor neuron disease characterized by increased muscle tone?
Spasticity.
What is decerebrate rigidity?
Uninhibited extensor tonus of antigravity muscles.
What is the effect of lesions in the pontine or medullary reticular formation nuclei?
Affect gait generation and result in paresis.
What is the result of unilateral lesions in the caudal midbrain?
Shift from affecting contralateral limbs to ipsilateral limbs.
What condition is associated with necrosis of substantia nigra and pallidum in horses?
Nigropalladial encephalomalacia. Yellow star thistle and Russian knapweed
What type of sensory neuron is associated with Golgi tendon organ?
1b sensory neurons
