The Upper Motor Neurons Flashcards
The corticospinal tract originates from 3 different regions of the cortex. Name them and their percentages:
- 30% from precentral gyrus (area 4, Primary Motor Cortex)
- 40% from postcentral gyrus (areas 3,1,2, Primary somatosensory cortex)
- remaining 30% from supplemental motor area (area 6, SMA) and the premotor cortex (PMC)
Explain the somatotopism of the precentral gyrus (primary motor cortex, area 4)
- dorsal and medial aspects control lower limb
- more lateral aspects control upper limb
- far lateral aspect control face and tongue
The corticospinal tracts arise from what cell layer in the cortex? (Name and Roman numeral)
Internal pyramidal cell layer (V)
Corticospinal fibers are located in the ____ limb of the internal capsule
Posterior
Corticobulbar fibers are located within the _____ limb of the internal capsule
Genu
Explain the location of the corticospinal and corticobulbar fibers in the crus cerebri of the midbrain:
Located in middle 3/5 of crus cerebri.
Corticospinal are more lateral (lower limb most lateral, upper limb medial to them) and finally, corticobulbar (head region) are more medial
What % of corticospinal tract fibers NEVER cross the midline
2% (considered lateral corticospinal tract fibers)
Fibers from the cerebellum that project to the primary motor cortex (area 4) do so via a relay in the ____ nucleus of the thalamus
Ventrolateral (VL)
The fibers of the primary motor cortex project to the ____ horn at all levels of the spinal cord, but most predominantly the cervical and lumbar levels
Ventral
The key inputs to the primary somatosensory cortex are from the ____ nucleus of the thalamus
Ventral posterolateral (VPL)
Descending pyramidal tract fibers originating in the somatosensory cortex project to cells of the ____ horn of the spinal cord
Dorsal
The actions of area 6 neurons can only occur if they receive integrated somatosensory and visual signals from the ____
Posterior Parietal Cortex (PPC, areas 5 and 7)
Area 6 consists of what two secondary motor regions (of the cortex)?
Supplemental Motor Area (SMA) Premotor Cortex (PMC)
A small localized area of dead tissue resulting from failure of blood supply
Infarct
The corticobulbar tracts arise from the lateral most aspect of the _____
Primary motor cortex (M1)
The corticobulbar fibers innervate cranial nerve nuclei mostly bilaterally. The exceptions are CN’s ___ and ___, which are only innervated contralaterally
VII (Facial - lower face)
XII (Hypoglossal - genioglossus muscle)
Approximately what % of the pyramidal fibers cross the midline to become the LCST?
85-90%
The precentral gyrus (primary motor cortex) is in the ____ lobe, while the post central gyrus (primary somatosensory cortex) is in the ____ lobe
Frontal, parietal
The basal nuclei input to the various motor areas of the cortex travels through the _____ nucleus in the thalamus, mainly
Ventral Anterior (VA)
Lesions of the supplemental motor area (SMA) result in _____, the inability to initiate specific, purposeful movements
Apraxia
The inability to execute a movement upon request is called _____ apraxia. An example would be the inability to brush one’s hair or tie one’s shoe laces.
Ideomotor
____ apraxia is the inability to conceptualize the movements, and the patient is unable to identify the sequences of movements that are necessary for carrying out the response in question. Example: the patient would have a hard time when asked to do different things with both arms simultaneously.
Ideational
The posterior parietal cortex (PPC, areas 5 and 7) is mainly concerned with relaying _____ and _____ signals to area 6
Vestibular, visual
Lesions of the RIGHT PPC will result in ____-sided apraxia or “sensory neglect”
Left
These motor fibers project to the DWC and dorsal horn of the spinal cord, and function in “sensory filtering”: only the pieces of information that are necessary to the present movement are allowed, others are filtered out
Somatosensory cortex fibers (areas 3, 1, 2)
Fibers from the ____ tract supply mainly the neurons that innervate distal flexor musculature
Rubrospinal
The reticulospinal tract arising from the Pons is the ____ reticulospinal tract, while the one arising from the Medulla is the _____ reticulospinal tract
Medial, lateral
The primary motor function of the ____ tract is to facilitate voluntary or cortical induced movements and to increase muscle tone
Medial reticulospinal
The actions of this pathway inhibit voluntary movements and cortically induced movements, and reduce muscle tone
Lateral reticulospinal tract
This tract arises from the medial vestibular nucleus and projects as the descending component of the medial longitudinal fasciculus (MLF) to reach cervical levels of the cord bilaterally
Medial vestibulospinal tract
The vestibular nuclei (medial and lateral) are first found in the ____
Pons (middle)
This tract arises from the lateral vestibular nucleus and projects to all levels of the spinal cord. It’s major function is to stimulate the neurons that innervate extensor muscles, mainly of the lower limb.
Lateral vestibulospinal tract
The medial vestibulospinal tract fibers activate LMNs associated with CN __. This activation can cause rotation and lifting of the head as well as scapular rotation. This helps orient the individual in response to forces that can cause changes in posture and balance.
XI, Spinal Accessory
The ____ tract arises from the red nucleus (motor tract)
Rubrospinal tract
Do rubrospinal tract fibers cross?
Yes - via ventral tegmental decussation
The ____ tract arises from the superior colliculus in the superior midbrain and soon crosses over via the dorsal tegmental decussation
Tectospinal tract
Where does the tectospinal tract terminate?
Cervical levels of the cord
Little is known about this tract, but it is believed to produce postural changes in response to visual stimuli
Tectospinal tract
Motor fibers from this part of the cortex are involved in the planning of response. They provide muscle contraction of individual muscles
Primary motor cortex (area 4)
