Flashcards in Spinal Cord, Brainstem, Cortex Control Of Motor Function Deck (67)
What are some characteristics of the upper motor neurons?
-originate in motor cortices
-75-85% decussate in pyramids and form the lateral corticospinal tracts. remainder decussate near synapse with lower motor neurons to form anterior corticospinal tracts
-most synapse with association neurons in spinal cord central gray
How are the upper motor neurons of the pyramidal system classified?
-classified according to where they synapse in the ventral horn
What are the classes of upper motor neurons of the pyramidal system?
-medial activation system: innervate postural and girdle muscles
-lateral activation system: associated with distally located muscles used for fine movements
-nonspecific activating system: facilitate local reflex arcs
What is the difference between the layer and anterior corticospinal tract?
-made up of corticospinal fibers that have crosses in medulla
-supply all levels of spinal cord
-made up of uncrossed corticospinal fibers that cross near level of synapse with LMNs
-supply neck and upper limbs
What is the corticospinal tract? Where does it originate?
-aka pyramidal tract
-origin of tract:
1. Primary motor cortex
2. Premotor cortex
3. Somatosensory area
What is the pathway of the corticospinal tract?
-site of origin -> internal capsule -> medullary pyramids -> cross in lower medulla(most fibers) -> lateral columns of spinal cord (lateral corticospinal tract)
-some fibers do not cross but continue down ipsilateral lay in ventral corticospinal tract
What are giant pyramidal (Betz) cells?
-located in motor cortex
-transmit at 70/sec
-make up about 3% of fibers in the tract
-send collaterals back to cortex
What happens to the other fibers from the cortex?
-pass into caudate nucleus and putamen
-pass to red nucleus
-pass to reticular substance and vestibular nuclei
-large numbers of fibers pass to pontine nuclei
What are the functions of the corticospinal tract?
-adds speed and agility to conscious movement -> especially the hand
-provides a high degree of motor control -> ex. Movement of individual fingers
What are symptoms of corticospinal tract lesions?
-reduced muscle tone
-not complete paralysis (only complete if both pyramidal and extrapyramidal systems are involved)
What is the corticobulbar tract?
-innervates the head
Where does the corticobulbar tract terminate?
-most fibers terminate in reticular formation near cranial nerve nuclei
+leave reticular formation and synapse in cranial nerve nuclei
+synapse with lower motor neurons
Describe the red nucleus.
-fibers from primary motor cortex (corticorubral pathway) and branches from corticospinal tract synapse in magnocellular portion of red nucleus
-large neurons from magnocellular region of red nucleus give rise to rumors pineal tract which decussate said in lower brain stem
-magnocellular region has somatotropin representation of all the muscles of the body
What does stimulation of the the red nucleus result in?
-stimulation of flexors
-inhibition of extensors (antigravity muscles)
What is the extrapyramidal system? What does it include?
-pathways that contribute to motor control but that are not part of the corticospinal system
-includes descending motor tracts that do not pass through medullary pyramids or corticobulbar tracts
Describe the rubrospinal tract.
-originates in red nucleus
-decussates in midbrain
-descends in lateral funiculus
-function is closely related to cerebellar function
What do lesions of the rubrospinal tract result in?
-impairment of distal arm and hand movement
-intention tremors (similar to cerebellar lesions)
Describe the vestibulospinal tract.
-originates in vestibular nuclei -> receives major input from vestibular nerve
-descends in anterior funiculus
-synapses with LMNs to extensor muscles -> primarily involved in maintenance of upright posture
Describe the reticulospinal tract.
-originates in various regions of reticular formation
-descends in anterior portion of lateral funiculus
-through to mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs
Describe the pontine reticular nuclei.
-fibers that make up pontine reticulospinal tract (anterior column)
-stimulators effects on both extensors and flexors, especially flexors
Describe the medullary reticular nuclei.
-fibers make up the medullary reticulospinal tract (lateral column)
-inhibitory effect on both extensors and flexors, especially extensors
What is the vestibular apparatus?
-membranous labyrinth consisting of three semicircular canals and vestibule (includes cochlea)
What is the vestibule composed of?
-utricle and saccule
Describe the functions of the vestibular apparatus.
-detects angular (semicircular canals) and linear (utricle and saccule) acceleration of head
-involved in reflex adjustment of head, eyes, and postural muscles
-provides a stable visual image and steady posture
Describe the structure of the vestibular apparatus.
-filled with endolymph and surrounded by perilymph
-utricle and saccule each contain a macula, which contains hair cells
-each semicircular canal has an enlargement at one end called the ampulla -> contains hair cells
What structures have a macula?
-utricle and saccule
What role does the utricle play in orientation?
-located on horizontal plane
-plays role in determining orientation of head when head is upright
What does the saccule do?
-located in a vertical plane
-signals head orientation when person is lying down
What is a macula?
-covered in gelatinous layer
-contains lathe number of small CaCO3 crystals (statoconia)
-contains thousands of hair cells which project cilia into the gelatinous layer
-the weight of the statoconia bends cilia in the direction of gravitational pull