Descending Motor Systems Flashcards
Select the true statement about the anterolateral pathway:
A) Decussates in medulla as internal arcuate fibers
B) Enters cerebellum via the inferior cerebellar peduncle
C) Spinomesencephalic fibers synapse in periaqueductal gray
D) Fibers enter cord in medial division of entry zone
E) Second order neurons located in posterior horn of cord
C
Select the true statement about the dorsal column-medial lemniscus pathway:
A) Carries pain and temperature information
B) DRG rootlets enter the lateral division
C) Crosses midline in anterior commissure
D) Cell bodies of crossing fibers are located in anterior horn of spinal cord
E) Injury results in loss of discriminative tactile sensation
E
Select the trust statement about the posterior spinocerebellar tract:
A) Enters the cerebellum using the superior cerebellar peduncle
B) Crosses the midline in the anterior commissure of the spinal cord
C) Carries proprioceptive information from the arm
D) Formed by axons from cell bodies in Clarke’s nucleus
D
Select the true statement about the somatosensory cortex:
A) It is in the precentral sulcus
B) It is located in the insula
C) It is located in the parietal lobe
D) It is somatotopically organized with foot and leg representation situated laterally
C
What is the definition of a lower motor neuron?
-It innervates striated (skeletal) muscle, directly signals the muscle to contract, only way movement can be initiated. It is the last neuron in a chain of neurons
What 2 things does a lower motor neon include?
- Alpha motor neuron: extrafusal muscle fibers
(tell muscle to contract) - Gamma motor neuron: intrfusal muscle fibers
(regulate spindle/sensitivity)
What are some symptoms of a lower motor neuron lesion?
- Atonia: loss of muscle tone
- Areflexia: loss of myotatic (knee jerk) reflex
- Flaccid paralysis
- Fasciculation: spontaneous muscle contractions
- Atrophy: loss of muscle tissue
What are some symptoms of an upper motor neuron lesion?
- Spastic paralysis (paresis)
- Hypertonia (increased resting tension)
- Arm flexors, leg extensors
- Hyperreflexia
- Pathologic reflexes:
- Babinski sign/neg. plantar reflex
- Big toe dorsoflexion with fanning of other toes when side of heal is stroked
During a routine exam you note that the patient has tongue fasciculations. This raises concern for: A) Corticospinal tract injury B) Primary myopathy C) Lower motor neuron injury D) Neuromuscular junction disorder E) Hypoglossal nuclear injury
C
Describe the systematic arrangement of motor neurons.
- Neurons controlling axial muscles are medial to those controlling distal muscles
- Neurons controlling flexors are located posterior to the extensor groups
What is a motor unit?
- 1 motor neuron plus all of the muscle fibers it innervates
* In areas we have more control over, like eyes, we have less myofibers (~10) per motor unit
Role of basal ganglia, cerebellum, and association cortex in motor control?
They are vital in design, choice, and monitoring of movement, but they do NOT have a direct effect on lower motor neurons. Instead, they effect motor and premotor cortex.
What do descending motor pathways mostly terminate or synapse on?
- Dorsal horn neurons
- Interneurons
Name a couple descending motor pathways
- Corticospinal tract
- Corticobulbar tract
- Corticopontine tract
- Rubrospinal tract
- Reticulospinal tract
- Vestibulospinal tract
What 4 areas are involved in the origin of the corticospinal tract?
- Premotor area (area 6)
- Primary motor area (area 4)
- Somatic sensory area (areas 1-3)
- Superior parietal lobule (areas 5&7)
Primary motor area:
- Brodmann area
- Function
- Projects to where
- Symptoms of lesion
- Area 4 on medial and lateral aspect
- Execution of contralateral voluntary movements (control fine digital movements)
- Projects to brainstem and spinal cord-some monosynaptic termination on spinal cord motor neurons (hand)
- Paralysis of contralateral musculature
Premotor Area:
- Brodmann area
- Function
- Projects to where
- Symptoms of lesion
- Area 6 on lateral aspect
- Plans movements in response to ext. cues (instructions), controls proximal and axial musculature (trunk/shoulder/hip), empathetic facial movements
- Projects to primary motor area and reticular formation (some fibers to all spinal cord levels)
- Moderate weakness of contralateral proximal muscles, lose ability to associate learned hand movements to verbal or visual cues
Supplementary Motor Area:
- Brodmann area
- Function
- Projects to where
- Area 6 on medial aspect
- Plans movements while thinking, assembles (learns) new sequence (playing new music), assembles previously learned sequence, “imagines” movements
- Projects to premotor & primary motor areas
Where does the somatic sensory area and superior parietal lobule project to?
- Primary motor area
- Direct motor patterns in response to sensory input
- Sensory areas of brainstem and spinal cord
- Modulate sensory signals
Describe the path of the Corticospinal tract.
-Originates in cerebral cortex, precentral gyrus, and nearby areas (Betz cells; layer V). Then descends thru cerebral peduncle, basis pontis, medullary pyramid, decussates at spinomedullary junction. About 15% of fibers do not decussate and remain ipsilateral.
What 2 arteries supply the internal capsule?
- Lateral striate aa.
- Anterior choroidal aa.
Select the true response about the corticospinal tract:
A) It has no somatotopic organization
B) It consists of small bundles in the midbrain
C) A left sided spinal cord lesion that involved the CST would cause ipsilateral weakness
D) Lesions are associated with flaccid paralysis
E) Decussates in the pons
C (it has already decussated in the spinomedullary junction)
What does the Rubrospinal tract control?
-Control of shoulder and proximal arm musculature
from red nucleus to spinal cord
What does the Reticulospinal tract control?
-Control of axial musculature-walking, rhythmic movements
reticular formation
