Motor (descending) pathways Flashcards
(22 cards)
What are the main functions of somatic motor systems?
Support body (anti-gravity), stable posture, start, stop and control voluntary movement
What type of neurons are found in the ventral horn of the spinal cord?
Myelinated neurons, either y-neuron (fusimotor) or a-neuron (skeletomotor)
What is the main function of pyramidal tracts?
Voluntary, fine-skill motor control
Where do pyramidal tracts run through in the brain?
Through ‘pyramids’ of medulla oblongata
What types of activities do extrapyramidal tracts control?
Autonomic and subconscious muscular activity, e.g., locomotion, feeding, posture
What is the main difference between pyramidal and extrapyramidal tracts?
Pyramidal tracts are voluntary and fine motor control, while extrapyramidal tracts are more about automatic and subconscious functions
What is the structure of the pyramidal (cortospinal) tracts?
3-neurone relay (2 main +/- interneurone), long axon of UMN, decussation in medullary pyramids
What role does the cerebellum play in motor control?
Regulates actions via return pathways, informs cerebellum of intended action
What is the significance of decussation in motor pathways?
Lesions above decussation result in deficits on the opposite side, while lesions below result in deficits on the same side
What are the characteristics of upper motor neurons (UMNs)?
Receive input from motor planning areas, can stimulate or inhibit lower motor neurons (LMNs)
What are the characteristics of lower motor neurons (LMNs)?
Receive input from UMNs and sensory input, cause muscle contraction, release ACh to support tone
What are the four major functions of the extrapyramidal system?
Automatic muscular activity, semi-automatic somatic activity, rhythmic activity, and posture
What is a key principle of lesion localization?
Evaluate multiple pathways; localizing lesion is a major aim of the neurological examination
Fill in the blank: UMNs are the ‘______’ and LMNs are the ‘______’.
managers, workers
What is the typical relay structure of extrapyramidal tracts?
3-neurone relay (2 main +/- interneurone)
True or False: Most extrapyramidal tracts decussate in the spinal cord.
False, nearly all decussate in the pons or medulla
What is the role of the cerebellum in relation to muscle activity?
Has indirect control of muscle activity on the same side (ipsilateral) as the muscle
List the types of movements controlled by the extrapyramidal tracts.
- Posture
- Locomotion
- Feeding
- Defence
What are some signs that differentiate UMN from LMN lesions?
UMN lesions characterized by reflex atrophy tone; LMN lesions show distinct features
What does the term ‘decussation’ refer to in the context of motor pathways?
The crossing of nerve fibers from one side of the brain or spinal cord to the other
What is the function of the LMN cell body?
Located in the ventral horn of the spinal cord, projects into the PNS
What does the cerebellum inform about during motor control?
Intended action
