Corticospinal Flashcards
___________ movements are carried out by means of the corticospinal tract for the body and corticobulbar (corticonuclear) tracts for the cranial nerve motor nuclei that innervate muscles of the______.
Volitional
face
The corticospinal tract and corticobulbar tracts (pathways) arise in the cerebral cortex; descend through the _____________ to end in ___________________ or the ventral horn of the spinal cord.
internal capsule
brainstem motor nuclei
Most of the fibers descending to the spinal cord cross in the ___________________ at the _____________ decussation. The remainder of the fibers descend ipsilaterally to individual segments and then cross.
lower medulla
pyramidal
This organization describes how volitional movement on the left side of the body is controlled by the ____________________; and the right side of the body to be controlled by the ______________________.
right side of the brain
left side of the brain
REMEMBER, the sensory information from the left side of the body crossed and ascended to end in the right side of the brain; and all of the information from the right side of the body crossed and ascended to end in the left side of the brain. Makes for a pretty efficiently organized system!!
REMEMBER, the sensory information from the left side of the body crossed and ascended to end in the right side of the brain; and all of the information from the right side of the body crossed and ascended to end in the left side of the brain. Makes for a pretty efficiently organized system!!
Corticospinal tract =
voluntary motor pathway for the body
Primary cells of origin are located in the _____________ (primary motor cortex; area 4). There are also neurons found in area 6 (________________________________________________), area 8 (____________) and also to a lesser extent in the ______________________ (areas 3,1, 2) whose axons travel in the corticospinal tract.
precentral gyrus
premotor region; lateral premotor and supplementary motor
frontal eye fields
primary somatosensory cortex
The fibers that make up the corticospinal tract exit the gray matter of the cortex and travel through the __________________ (the fiber bundles underlying the cortex).
medullary white matter
List some of the structures that the fibers travel through in the medullary white matter:
(in sequence):
- corona radiata
- posterior limb of the internal capsule
- cerebral peduncles
- corticospinal fibers in the ventral pons
- pyramids.
At the lower end of the medulla, ____of the fibers cross at the pyramidal decussation and continue their descent as the _____________________________ (located in the lateral funiculus).
85%
lateral corticospinal tract
The remaining fibers that do not cross descend as the ______________________________ (located in the anterior funiculus). These latter fibers then cross at the __________ level where they innervate the _______________________________
anterior corticospinal tract
segmental
lower motor neuronal pool.
The organization of the fibers as they descend is __________________ arranged.
topographically
The termination of the corticospinal tract fibers is primarily on ____________________ (97%).
interneurons
The majority of the corticospinal fibers terminate in the _________________ (55%) and lesser numbers in the _______________ (20%) and _____________ (25%) regions.
cervical region
thoracic region
lumbosacral
It is the ____________ that then excite or inhibit the lower motor neurons (neurons in the ventral horn that make up the ventral root) to influence the activity of a given motor unit.
interneurons
Lower motor neurons that are responsible for activation of extrafusal muscle fibers (volitional movements) are termed ___________ neurons and are the final _______________________ to the muscle or effecter organ.
alpha () motor
common pathway
___________________ neurons are also lower motor neurons. They innervate the _______________ muscle fibers of the muscle spindle. (Think about this distribution and what parts of the body have the most delicate and fine motor movements.)
Gamma () motor
intrafusal
Corticoreticulospinal pathway runs __________ to the corticospinal tract.
The cells giving rise to these fibers are located in the ______________________________________ areas.
parallel
supplementary motor and lateral premotor
The axons descend along with the corticospinal fibers to the level of the ___________________________________, where they synapse bilaterally. Reticulospinal fibers then descend into the spinal cord where they synapse in the __________________ on the lower motor neuron pool; primarily interneurons.
pontine and medullary reticular formation
ventral horn
Functionally, this system has a dual purpose. The premotor and secondary motor areas provide the information to primary motor cortex for ______________ movement.
voluntary
The information from primary motor cortex then descends for fine motor control distally on the extremities, i.e., the fingers. This precise individual movement is termed __________________ movement.
fractionated
At the same time, these premotor areas are activating the __________________ and subsequently the reticulospinal fibers. This information is transferred to the spinal cord for initiation of _____________________________of axial and proximal limb musculature – it sets the platform for movement in anticipation of the fractionated movement.
reticular formation
complementary activation
Pontine (medial) reticulospinal pathway =
primarily ipsilateral and facilitory to axial and limb musculature, especially the extensors and works with the medial vestibulospinal tract.
Medullary (lateral) reticulospinal pathway =
bilateral (greater ipsilateral) and is facilitory to flexor musculature and inhibitory to axial and limb extensor musculature.
Lateral vestibulospinal pathway =
ipsilateral and excitatory on extensors of lower extremity musculature (inhibits flexor musculature).
Medial vestibulospinal pathway =
projects bilaterally and descends only to cervical and upper thoracic levels. Control of neck and upper thoracic musculature.
Tectospinal pathway =
descends only to cervical levels and coordinates neck movement toward a stimulus.
Rubrospinal pathway =
contralateral and described as descending the entire length of cord.
However, in bipedal locomotion this tract (rubrospinal pathway) has diminished in importance and functions mostly at the _____________. Current thinking is that in humans this pathway is involved in ________________________ of the upper extremity, primarily distal musculature and plays a role in fractionated movements.
cervical level
flexor activation
Medial vs Lateral Activation Systems: This differentiation is defined primarily by the location of the axons of the upper motor neurons. Medial activation pathways are involved in more ______________ movements and activities. They are named for both their ___________ in the cord and their ___________. The lateral activation system is more involved with the _________________________, i.e., fractionated movement.
postural
POSITION in the cord and their FUNCTION
distal limb musculature
The _____________ activation system is located in the anterior funiculus and consists of the anterior corticospinal, medial reticulospinal, medial and lateral vestibulospinal, and tectospinal pathways.
medial
The _______ activation system is located in the lateral funiculus and consists of the lateral corticospinal, rubrospinal, and lateral reticulospinal pathways.
lateral
Primary somatosensory cortex sends axons caudally through the ________________ pathway. These axons terminate in the ________________ and are thought to function as a feedback mechanism that integrates cortical understanding of sensation with incoming sensory information.
lateral corticospinal
dorsal horn
_______________ and ____________ pathways (originate in reticular formation nuclei – ____________ and ______________) are also involved in modification of afferent sensory information at the dorsal horn level.
Raphespinal and
Cerulospinal
Raphe nuclei and
Locus Ceruleus
___________________ and _________________ pathways activate a number of reticular system components. These descending components play a role in the modulation of incoming _____ stimuli.
Spinomesencephalic and spinoreticular
pain
The entire motor component of cranial nerves (both sides) receives bilateral corticobulbar input. What does this mean with respect to strokes damaging the descending control?
???
EXCEPTION:
Cortical control of Facial Motor Nucleus (muscles of facial expression) and Hypoglossal Nucleus (muscles controlling tongue movement).
EXCEPTION:
Cortical control of Facial Motor Nucleus (muscles of facial expression) and Hypoglossal Nucleus (muscles controlling tongue movement).
EXCEPTION:
Cortical control of extraocular eye muscles (specific circuitry will be discussed with the oculomotor system).
EXCEPTION:
Cortical control of extraocular eye muscles (specific circuitry will be discussed with the oculomotor system).
Lower motor neurons are located in either the _________ horn of the spinal cord or in a _________________ nucleus.
ventral
cranial nerve motor
The ________ of this lower motor neuron cell body leaves the spinal cord or brainstem to innervate motor units of __________________. These axons along with the sensory axons make up the ________________________ we dissected in anatomy.
axon
skeletal muscle
peripheral nerves
Lesions of lower motor neurons (damage to axon or cell body) classically are described as resulting in the following symptoms:
- Flaccid paralysis (atonia or hypotonia)
- Areflexia or hyporeflexia
- Atrophy of muscle (muscle wasting)
- Fasciculations and fibrillations
Flaccid paralysis (atonia or hypotonia) =
flaccid paralysis = weakness or paralysis and reduced muscle tone w/o obvious cause.
Atonia or hypotonia = tone is not velocity dependent
Areflexia or hyporeflexia =
below normal or absent reflexes
Fasciculations and fibrillations =
fasci curation= brief, spontaneous contraction affecting a small number of muscle fibers, often causing a flicker of movement under the skin.
Upper motor neurons are the neurons whose cell bodies are located at __________________ levels of the CNS with axons that end in the ________________ or cranial nerve motor nucleus. These UMN synapse on interneurons or or motor neurons.
suprasegmental
ventral horn
Upper motor neuron lesions (damage to descending fiber tracts classified as UMN) classically are described as resulting in the following symptoms:
-Initial flaccid paralysis followed by:
-Abnormal cutaneous reflexes (Babinski sign)
-Abnormal reflexes: clonus, clasp knife)
-Spasticity – velocity dependent hypertonia
-Abnormal timing of muscle activation (slower onset, prolonged contraction)
Paresis or plegia (weakness)
Paralysis =
total loss of motor function
-plegia =
A loss of activation of voluntary motor activity sometimes incorrectly referred to as paralysis; i.e., hemiplegia is a loss of accurate activation of muscle activity over half of the body.
-paresis =
weakness; small strokes can result in a paresis or weakness, as opposed to the (plegia of a major stroke)
Brown-Sequard Syndrome:
This lesion is a hemisection of the spinal cord. It is not a common occurrence, but is useful in understanding the distribution of symptoms as they relate to the ascending and descending pathways. We have already discussed this with respect to ascending somatosensory systems.
Syringomyelia:
A lesion caused by cavitation of the central canal, the remnant of the lumen of the neural tube. This lesion encroaches upon the anterior white commissure. Further ventral and lateral enlargement of the cavity will then encroach upon the ventral horn, effecting LMNs of axial then appendicular musculature.
Poliomyelitis:
Disease that attacks LMNs in the ventral horn of the spinal cord or cranial nerve nuclei. This has been almost eradicated with vaccine treatment. Flu-like symptoms followed by weakness (flaccid) of muscles and fasciculations. Post-Polio syndrome is now a clinical concern due to overuse of intact motor units.
Amyotrophic Lateral Sclerosis (ALS; Lou Gehrig’s disease):
ALS is a chronic and progressive disease of unknown origin. It destroys LMNs in the ventral horn and brainstem nuclei. Slow in onset. This disease also destroys white matter pathways.
Multiple Sclerosis:
Multifocal disease (can have more than one site of lesion). Thought to be an autoimmune attack on myelin. Develops in the spinal cord, brainstem and optic nerve. Disease of upper motor neurons and central myelinated pathways, as well as sensory pathways.
