Spinal Cord, Brainstem, Cortex Control Of Motor Function Flashcards Preview

Physiology II Exam 2 > Spinal Cord, Brainstem, Cortex Control Of Motor Function > Flashcards

Flashcards in Spinal Cord, Brainstem, Cortex Control Of Motor Function Deck (67)
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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

-large cells

-large fibers

-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

-association neurons
+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

-rubrospinal tracts
-vestibulspinal tracts
-reticulospinal 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


What are the functions of the hair cells in the macula?

-bending of stereocilia toward kinocilium opens hundreds of cation channels causing receptor membrane depolarization

-bending of cilia in opposite direction closes channels and hyperpolarizes membrane

-hair cells are oriented such that bending the head in different directions causes different groups of hair cells to depolarize