Corticospinal system:

Consists of all fibers that:

arise from cells in the cerebral cortex

pass through the internal capsule

descend into the brain stem or spinal cord

Corticospinal -Cell Bodies of Origin:

Neurons located primarily in _____ of the ______, ______, and ____.

lamina V

primary motor cortex (area 4)

premotor and supplementary motor areas (area 6)

postcentral gyrus (areas 3,1,2)

*some in other areas of the cerebrum

Corticospinal- Cell Bodies of Origin:

THe organization of neurons within the primary motor cortex is ______. It is maintained through the ____, but may be disrupted thereafter.

somatotopic organization (motor homunculus)

midbrain

problems in this area lead to major deficits in the UE(due to number and size of UE neurons in the homunculus)

Corticospinal System (Cell Bodies of Origin):

From the cortex, fibers converge in the ____ and travel in the ____. At the midbrain levels, the corticospinal fibers form the _____, while corticobulbar fibers are located just ____ to them at this point.

corona radiata

posterior limb (corticospinal) and genu (corticobulbar) of the internal capsule

middle 1/3 of the crus cerebri

medial

Corticospinal System:

In the pons, the fibers of the corticospinal system are:

Corticospinal System:

In the medulla, the fibers of this system:

coalesce again into the medullary pyramids

the pyramids decussate, then the fibers travel on to the spinal cord

Lateral Corticospinal Tract:

Around ___ of corticospinal fibers cross at caudal medullary levels (junction of the medulla and spinal cord) and enter the posterior part of the ___ of the spinal cord, forming the lateral corticospinal tract.

80-90%

lateral funiculus

Lateral Corticospinal Tract:

The tract descends the length of the spinal cord giving off fibers to synapse on ____ and ___ in the ____ and ___ of the spinal cord at all levels.

interneurons

motor neurons (a few)

intermediate gray

anterior horn

distal flexor musculature

terminate in the cervical (as opposed to lumbar) enlargement

*more UE control than LE

Anterior Corticospinal tract:

Decussation

***does not decussate in the medulla

decussates in the anterior white commisure

Anterior Corticospinal Tract:

Composed of the remaining ____ fibers from the corticospinal system. They descend ____ into the spinal cord and occupies an area located ____. Most fibers of this tract terminate on ___. It is present primarily in the ___ and controls ____ muscles.

uncrossed

uncrossed

adjacent to the anterior median fissure

interneurons in the cord

cervical spinal cord

axial

Corticobulbar fibers:

They provide cortical innervation for ______.

Corticobulbar fibers:

axons travel with the ____ and terminate on _______ motor nuclei of certain cranial nerves.

corticospinal system

ipsilateral, contralateral, and bilateral

Tectospinal Tract:

Cell Bodies of Origin:

Tectospinal tract:

axons from these neurons cross ______ and descend in the _____

in the midbrain tegmentum just anterior to the PAG

medial longitundinal fasciculus (MLF)

Tectospinal Tract:

in the spinal cord, the tract lies in the ____ near the ___

anterior funiculus

anterior median fissure

Tectospinal Tract:

fibers terminate on interneurons in the ____ and ____ - they influence _____

major function:

intermediate gray

anterior horn

motor neurons of the neck musculature

mediates reflex turing of the head in response to visual (possibly auditory) stimuli

Rubrospinal Tract:

Cell Bodies of Origin:

Rubrospinal Tract

Decussation:

Rubrospinal Tract:

In the spinal cord, the tract lies _____. The fibers descend primarily to ____ where most influence is  ____.

anterior to the lateral corticospinal tract in the lateral funiculus

cervical enlargement

facilitory to UE flexors

Reticulospinal Tracts:

These tracts arise from areas in the _____ known as the _____.

brain stem

reticular formation- groups of nuclei located throughout the brain stem

pontine (medial) reticulospinal tract

medullary (lateral) reticulospinal tract

Pontine (medial) reticulospinal tract:

CBO's are in _____.

Axons from these nuclei descend in the brain stem in association with the ______.

reticular formation of the pons

medial longitudinal fasiculus

Pontine (medial) reticulospinal tract:

in the spinal cord, the tract lies in the _____ and remains ____.

medial part of the anterior funiculus

ipsilateral

Medullary (lateral) reticulospinal tract:

CBO's are located _____.

Most fibers of this pathway remain ____ and descend in the _____.

reticular formation of the medulla

uncrossed

anterior part of the lateral funiculi

alternative pathways for control of spinal motor neurons

*regulate sensitivity of spinal reflexes

may initiate some movements (gait)

Lower motor neurons:

motor neurons of the ____ or _____

Lower Motor Neuron

(definition)

anterior horn cells and their axons, projecting via the ventral root to striated muscle

Lower Motor Neuron Syndrome:

Injury or disease of the anterior horn cells or projecting axons result in:

• paralysis of muscles innervated by these fibers
• loss of muscle tone (hypotonia)
• atrophy of denervated muscle
• hypoactive of absent myotatic (DTR) reflex in that segment or segments (hyporeflexia)

Upper Motor Neuron

(definition)

• paresis (difficulty moving) of muscles involved - can have paralysis, but less common
• initial loss followed by increased muscle tone (hypertonia)
• hyperactive myotatic reflexes (hyperreflexia)
• positive babinski sign - if corticospinal system is injured
• muscle atrophy is not seen initially because segmental innervation of striated muscle remains intact - long term disuse atrophy will occur

lesion to the brain stem in area of the midbrain *caudal* to the red nucleus

all descending motor pathways, except reticulospinal

modulateing influence from cortex on pontine reticulospinal tract

cortical modulation of the rubrospinal system

BUT leaves the rubrospinal system intact

still have increased activity of the reticulospinal system

Decerebrate rigidity:

Decorticate rigidity:

extensor posturing in all 4 extremities

extensor postureing of LE, but flexor posturing of the UE

the area of the lesion is spreading

- swelling or bleeding is occuring