11. spinal cord, brainstem, cortex control of motor function II Flashcards
What are the components of the pyramidal system?
- corticospinal tract
- corticobulbar tract
- tracts pass through the medullary pyramidals
What are the characteristics of pyramidal systems within the upper motor neurons?
- originate in motor cortices
- 75-85% decussate in pyramids and form the lateral corticospinal tracts
- others decussate in the lower motor neurons
What are the different classifications of upper motor neurons of the pyramidal system?
- medial activation system: innervate postural and girdle muscles
- lateral activation system: associate with distally located muscles used for fine movements
- nonspecific activating system: facilitate local reflex arcs
What are the lateral cortical tract used for?
- made of corticospinal fibers that cross in medulla
2. supply all levels of spinal cord
What makes up the anterior corticospinal tract?
- uncrossed corticospinal fibers that cross near the level of synapse with the lower motor neurons
- supply to the neck and upper limbs
Where does the corticospinal tract originate?
primary motor cortex, premotor cortex, somatosensory area
Where are the giant pyramidal cells located?
- in corticospinal tract (motor cortex)
- send collaterals back to cortex quickly.
- large cells/fibers
Fibers of the corticospinal tract run from the cortex into what different regions of the brain?
- into caudate nucleus and putamen
- to red nucleus
- to reticular substance and vestibular nuclei
- to pontine nuclei
What are the functions of the corticospinal tract?
- add speed and agility to conscious movements
2. provide high level of motor control
What happens if a lesion arises in the corticospinal tract?
- loss of muscle tone
- clumsiness
- weakness
- paralysis will only occur if the pyramidal and extrapyramidal systems are damaged
Where do the majority of fibers terminate from the corticobulbar tract?
- reticular formation near cranial nerve nuclei
2. this tract innervates the head
What does red nucleus stimulus results in?
- stimulation of flexors
2. inhibition of extensors
What forms the red nucleus?
- formed by fibers from primary motor cortex and corticospinal tract that synapse in magnocellular portion
Where is a somatotopic representation of the muscles of teh body located?
- magnocellular region of the red nucleus
What forms the extrapyramidal system?
- rubrospinal tract
- vestibulospinal tract
- reticulospinal tract
What are characteristics of the rubrospinal tract?
- originate in red nucleus
- decussate in midbrain
- descends lateral funiculus
What happens if a lesion arises in the rubrospinal tract?
- impair distal arm and hand movement
2. intention tremors appear
Where does the vestibulospinal tract originate, descend, and synapse?
- originate: receives major input from vestibular nerve (CN 8)
- descends anterior funiculus
- synapse with lower motor neurons, involved with maintaining upright posture
What are the acharacteristics of the reticulospinal tract?
- originates in regions of reticular formation
- descends anterior portion of lateral funiculus
- mediates larger movements of trunk and limbs
The reticular nuclei contains the pontine reticular nuclei and has what function?
- fibers form the pontine reticulospinal tract
2. stimulatory effect on extensors, and minor effect on flexors
The reticular nuclei contains the medullary reticular nuclei and has what function?
- the fibers form the medullary reticulospinal tract
2. have major inhibitory effect on extensors, and minor inhibition on flexors
What are the components of the vestibular componentts?
- utricle: located on horizontal plane that determines the orientation of the head when upright
- saccule: located in vertical plane, that signals the head orientation while laying down
- semicircular canals
What is the function of the hair cell in the macula?
- bends the sterocilia towards kinocilium causes depolarization
- bending of sterocilia away from kinocilium causes hyperpolarization
How do the semicircular canals align when the head is bent forward 30 degrees?
- lateral ducts are horizontal
- anterior ducts are in vertical planes and project forward and outward 45 degrees
- posterior ducts are in vertical planes and project backwards and 45 degrees outward
What is an ampulla?
- enlargement at each of the semicircular canal ducts, filled with endolymph.
- contain the crista ampullaris (small crest in the ampulla)
- the cupula contained. (loose gelatinous tissue on the crista)
